TY - GEN A1 - Mahadevaiah, Mamathamba Kalishettyhalli A1 - Perez, Eduardo A1 - Lisker, Marco A1 - Schubert, Markus Andreas A1 - Perez-Bosch Quesada, Emilio A1 - Wenger, Christian A1 - Mai, Andreas T1 - Modulating the Filamentary-Based Resistive Switching Properties of HfO2 Memristive Devices by Adding Al2O3 Layers T2 - Electronics : open access journal N2 - The resistive switching properties of HfO2 based 1T-1R memristive devices are electrically modified by adding ultra-thin layers of Al2O3 into the memristive device. Three different types of memristive stacks are fabricated in the 130 nm CMOS technology of IHP. The switching properties of the memristive devices are discussed with respect to forming voltages, low resistance state and high resistance state characteristics and their variabilities. The experimental I–V characteristics of set and reset operations are evaluated by using the quantum point contact model. The properties of the conduction filament in the on and off states of the memristive devices are discussed with respect to the model parameters obtained from the QPC fit. KW - RRAM KW - HfO2 KW - filamentary switching Y1 - 2022 U6 - https://doi.org/10.3390/electronics11101540 SN - 2079-9292 VL - 11 IS - 10 ER - TY - GEN A1 - Wen, Jianan A1 - Baroni, Andrea A1 - Perez, Eduardo A1 - Ulbricht, Markus A1 - Wenger, Christian A1 - Krstic, Milos T1 - Evaluating Read Disturb Effect on RRAM based AI Accelerator with Multilevel States and Input Voltages T2 - 2022 IEEE International Symposium on Defect and Fault Tolerance in VLSI and Nanotechnology Systems (DFT) N2 - RRAM technology is a promising candidate for implementing efficient AI accelerators with extensive multiply-accumulate operations. By scaling RRAM devices to the synaptic crossbar array, the computations can be realized in situ, avoiding frequent weights transfer between the processing units and memory. Besides, as the computations are conducted in the analog domain with high flexibility, applying multilevel input voltages to the RRAM devices with multilevel conductance states enhances the computational efficiency further. However, several non-idealities existing in emerging RRAM technology may degrade the reliability of the system. In this paper, we measured and investigated the impact of read disturb on RRAM devices with different input voltages, which incurs conductance drifts and introduces errors. The measured data are deployed to simulate the RRAM based AI inference engines with multilevel states. KW - RRAM KW - Multilevel switching KW - AI accelarator Y1 - 2022 SN - 978-1-6654-5938-9 SN - 978-1-6654-5937-2 U6 - https://doi.org/10.1109/DFT56152.2022.9962345 SN - 2765-933X SP - 1 EP - 6 ER - TY - GEN A1 - Akhtar, Fatima A1 - Dabrowski, Jaroslaw A1 - Lukose, Rasuole A1 - Wenger, Christian A1 - Lukosius, Mindaugas T1 - Chemical Vapor Deposition Growth of Graphene on 200 mm Ge (110)/Si Wafers and Ab Initio Analysis of Differences in Growth Mechanisms on Ge (110) and Ge (001) T2 - ACS Applied Materials & Interfaces N2 - For the fabrication of modern graphene devices, uniform growth of high-quality monolayer graphene on wafer scale is important. This work reports on the growth of large-scale graphene on semiconducting 8 inch Ge(110)/Si wafers by chemical vapor deposition and a DFT analysis of the growth process. Good graphene quality is indicated by the small FWHM (32 cm–1) of the Raman 2D band, low intensity ratio of the Raman D and G bands (0.06), and homogeneous SEM images and is confirmed by Hall measurements: high mobility (2700 cm2/Vs) and low sheet resistance (800 Ω/sq). In contrast to Ge(001), Ge(110) does not undergo faceting during the growth. We argue that Ge(001) roughens as a result of vacancy accumulation at pinned steps, easy motion of bonded graphene edges across (107) facets, and low energy cost to expand Ge area by surface vicinals, but on Ge(110), these mechanisms do not work due to different surface geometries and complex reconstruction. KW - Graphene KW - Chemical Vapor Deposition Y1 - 2023 U6 - https://doi.org/10.1021/acsami.3c05860 SN - 1944-8244 VL - 15 IS - 30 SP - 36966 EP - 36974 ER - TY - GEN A1 - Rizzi, Tommaso A1 - Baroni, Andrea A1 - Glukhov, Artem A1 - Bertozzi, Davide A1 - Wenger, Christian A1 - Ielmini, Daniele A1 - Zambelli, Cristian T1 - Process-Voltage-Temperature Variations Assessment in Energy-Aware Resistive RAM-Based FPGAs T2 - IEEE Transactions on Device and Materials Reliability N2 - Resistive Random Access Memory (RRAM) technology holds promises to improve the Field Programmable Gate Array (FPGA) performance, reduce the area footprint, and dramatically lower run-time energy requirements compared to the state-of-the-art CMOS-based products. However, the integration of RRAM in FPGAs is hindered by the high programming power consumption and by non-ideal behaviors of the device due to its stochastic nature that may overshadow the benefits in normal operation mode. To cope with these challenges, optimized programming strategies have to be investigated. In this work, we explore the impact that different procedures to set the device have on the run-time performance. Process, voltage, and temperature (PVT) variations as well as time-dependent drift effect of the RRAM device are considered in the assessment of 4T1R MUX designs characteristics. The comparison with tradition CMOS implementations reveals how the choice of the target resistive state and the programming algorithm are key design aspects to reduce the run-time delay and energy metrics, while at the same time improving the robustness against the different sources of variations. KW - RRAM KW - FPGA Y1 - 2023 U6 - https://doi.org/10.1109/TDMR.2023.3259015 SN - 1530-4388 VL - 23 IS - 3 SP - 328 EP - 336 ER - TY - GEN A1 - Perez, Eduardo A1 - Maldonado, David A1 - Mahadevaiah, Mamathamba Kalishettyhalli A1 - Perez-Bosch Quesada, Emilio A1 - Cantudo, Antonio A1 - Jimenez-Molinos, Francisco A1 - Wenger, Christian A1 - Roldan, Juan Bautista T1 - A comparison of resistive switching parameters for memristive devices with HfO2 monolayers and Al2O3/HfO2 bilayers at the wafer scale T2 - 14th Spanish Conference on Electron Devices (CDE 2023), Valencia, Spain, 06-08 June 2023 N2 - Memristive devices integrated in 200 mm wafers manufactured in 130 nm CMOS technology with two different dielectrics, namely, a HfO2 monolayer and an Al2O3/HfO2 bilayer, have been measured. The cycle-to-cycle (C2C) and device-todevice (D2D) variability have been analyzed at the wafer scale using different numerical methods to extract the set (Vset) and reset (Vreset) voltages. Some interesting differences between both technologies were found in terms of switching characteristics KW - RRAM Y1 - 2023 SN - 979-8-3503-0240-0 U6 - https://doi.org/10.1109/CDE58627.2023.10339417 PB - Institute of Electrical and Electronics Engineers (IEEE) ER - TY - GEN A1 - Morales, Carlos A1 - Mahmoodinezhad, Ali A1 - Tschammer, Rudi A1 - Kosto, Yuliia A1 - Alvarado Chavarin, Carlos A1 - Schubert, Markus Andreas A1 - Wenger, Christian A1 - Henkel, Karsten A1 - Flege, Jan Ingo T1 - Combination of Multiple Operando and In-Situ Characterization Techniques in a Single Cluster System for Atomic Layer Deposition: Unraveling the Early Stages of Growth of Ultrathin Al2O3 Films on Metallic Ti Substrates T2 - Inorganics N2 - This work presents a new ultra-high vacuum cluster tool to perform systematic studies of the early growth stages of atomic layer deposited (ALD) ultrathin films following a surface science approach. By combining operando (spectroscopic ellipsometry and quadrupole mass spectrometry) and in situ (X-ray photoelectron spectroscopy) characterization techniques, the cluster allows us to follow the evolution of substrate, film, and reaction intermediates as a function of the total number of ALD cycles, as well as perform a constant diagnosis and evaluation of the ALD process, detecting possible malfunctions that could affect the growth, reproducibility, and conclusions derived from data analysis. The homemade ALD reactor allows the use of multiple precursors and oxidants and its operation under pump and flow-type modes. To illustrate our experimental approach, we revisit the well-known thermal ALD growth of Al2O3 using trimethylaluminum and water. We deeply discuss the role of the metallic Ti thin film substrate at room temperature and 200 °C, highlighting the differences between the heterodeposition (<10 cycles) and the homodeposition (>10 cycles) growth regimes at both conditions. This surface science approach will benefit our understanding of the ALD process, paving the way toward more efficient and controllable manufacturing processes. KW - Atomic layer deposition (ALD) KW - in-situ KW - operando KW - X-ray photoelectron spectroscopy KW - ellipsometry KW - quadrupol mass spectrometry (QMS) Y1 - 2023 U6 - https://doi.org/10.3390/inorganics11120477 SN - 2304-6740 VL - 11 IS - 12 ER - TY - GEN A1 - Capista, Daniele A1 - Lukose, Rasuole A1 - Majnoon, Farnaz A1 - Lisker, Marco A1 - Wenger, Christian A1 - Lukosius, Mindaugas T1 - Study on the metal -graphene contact resistance achieved with one -dimensional contact architecture T2 - IEEE Nanotechnology Materials and Devices Conference (NMDC 2023), Paestum, Italy, 22-25 October 2023 N2 - Graphene has always been considered as one of the materials with the greatest potential for the realization of improved microelectronic and photonic devices. But to actually reach its full potential in Si CMOS technology, graphene -based devices need to overcome different challenges. They do not only need to have better performances than standard devices, but they also need to be compatible with the production of standard Si based devices. To address the first challenge the main route requires the optimization of the contact resistance, that highly reduces the devices performance, while the second challenges requires the integration of graphene inside the standard production lines used for microelectronic. In this work we used an 8” wafer pilot -line to realize our devices and we studied the behavior of the contact resistance between metal and graphene obtained by one -dimensional contact architecture between the two materials. The contact resistance has been measured by means of Transmission Line Method (TLM) with several contact patterning. KW - Graphene Y1 - 2023 SN - 979-8-3503-3546-0 U6 - https://doi.org/10.1109/NMDC57951.2023.10343775 SP - 118 EP - 119 PB - Institute of Electrical and Electronics Engineers (IEEE) ER - TY - GEN A1 - Lukosius, Mindaugas A1 - Lukose, Rasuolė A1 - Lisker, Marco A1 - Dubey, P. K. A1 - Raju, A. I. A1 - Capista, Daniele A1 - Majnoon, Farnaz A1 - Mai, A. A1 - Wenger, Christian T1 - Developments of Graphene devices in 200 mm CMOS pilot line T2 - Proc. Nanotechnology Materials and Devices Conference (NMDC 2023),Paestum, Italy, 22-25 October 2023 N2 - Due to the unique electronic band structure, graphene has opened great potential to extend the functionality of a large variety of devices. Despite the significant progress in the fabrication of various graphene based microelectronic devices, the integration of graphene devices still lack the stability and compatibility with Si-technology processes. Therefore, the investigation and preparation of graphene devices in conditions resembling as close as possible the Si technology environment is of highest importance. This study aims to explore various aspects of graphene research on a 200mm pilot line, with a focus on simulations and fabrication of graphene modulator. To be more precise, it includes design and fabrication of the layouts, necessary mask sets, creation of the flows, fabrication, and measurements of the Gr modulators on 200 mm wafers. KW - Graphene Y1 - 2023 SN - 979-8-3503-3546-0 U6 - https://doi.org/10.1109/NMDC57951.2023.10343569 SP - 505 EP - 506 PB - Institute of Electrical and Electronics Engineers (IEEE) ER - TY - GEN A1 - Maldonado, David A1 - Cantudo, Antonio A1 - Perez, Eduardo A1 - Romero-Zaliz, Rocio A1 - Perez-Bosch Quesada, Emilio A1 - Mahadevaiah, Mamathamba Kalishettyhalli A1 - Jimenez-Molinos, Francisco A1 - Wenger, Christian A1 - Roldan, Juan Bautista T1 - TiN/Ti/HfO2/TiN Memristive Devices for Neuromorphic Computing: From Synaptic Plasticity to Stochastic Resonance T2 - Frontiers in Neuroscience N2 - We characterize TiN/Ti/HfO2/TiN memristive devices for neuromorphic computing. We analyze different features that allow the devices to mimic biological synapses and present the models to reproduce analytically some of the data measured. In particular, we have measured the spike timing dependent plasticity behavior in our devices and later on we have modeled it. The spike timing dependent plasticity model was implemented as the learning rule of a spiking neural network that was trained to recognize the MNIST dataset. Variability is implemented and its influence on the network recognition accuracy is considered accounting for the number of neurons in the network and the number of training epochs. Finally, stochastic resonance is studied as another synaptic feature.It is shown that this effect is important and greatly depends on the noise statistical characteristics. KW - RRAM KW - Neural network Y1 - 2023 U6 - https://doi.org/10.3389/fnins.2023.1271956 SN - 1662-4548 VL - 17 ER - TY - JOUR A1 - Sohal, Rakesh A1 - Lupina, Grzegorz A1 - Lippert, Gunther A1 - Wenger, Christian A1 - Seifarth, Olaf A1 - Schröder, Thomas A1 - Tallarida, Massimo A1 - Schmeißer, Dieter T1 - Interface chemistry of high-k PrxAl2-xO3 (x=2-0) dielectrics on TiN for dynamic random access memory applications KW - high-k KW - dielectric KW - random Y1 - 2008 ER - TY - GEN A1 - Lupina, Grzegorz A1 - Dabrowski, Jarek Marek A1 - Formanek, Peter A1 - Schmeißer, Dieter A1 - Sorge, Roland A1 - Wenger, Christian A1 - Zaumseil, Peter A1 - Müssig, Hans-Joachim T1 - Solid-state reaction between Pr and SiO2 studied by photoelectron spectroscopy and ab initio calculations T2 - Materials Science in Semiconductor Processing N2 - We report on the structural and electrical properties of Pr-based high-k dielectric films fabricated by solid-state reaction between metallic Pr and SiO2 underlayers. A non-destructive depth profiling using synchrotron radiation excited photoelectron spectroscopy (SR-PES), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) were employed to examine the chemical composition and microstructure. Ab initio calculations were done to gain insight into the physical processes involved. SR-PES results indicate that Pr deposition at room temperature (RT) leads to the formation of a Pr silicide and a Pr oxide, what is in good agreement with the scenario expected from ab initio calculations. As revealed by TEM and electrical measurements, oxidation of the reacted structures, followed by annealing, results in a stacked dielectric composed of a SiO2-based buffer with an enhanced permittivity and a Pr silicate film with a high dielectric constant. The leakage current density of 10-4 A/cm2 was measured for stacks with capacitance equivalent thickness (CET) of 1.5 nm prepared by evaporation of the Pr layer on a 1.8 nm SiO2 film, followed by oxidation in air ambient and annealing in N2 atmosphere. The capacitance-voltage (C-V) curves exhibit a large flatband voltage (VFB) shift indicating the presence of a positive charge in the stack. Switching away from the Al contacts to Au gate electrodes introduces a significant reduction of the VFB by 1.3 eV, what is much more than the change expected from the work function difference between Al and Au (not, vert, similar0.9 eV). This in turn implies that VFB is strongly affected by the gate interface electrode. KW - High-k dielectrics KW - Photoelectron spectroscopy KW - Interface reaction Y1 - 2004 SN - 1369-8001 VL - 7 IS - 4-6 SP - 215 EP - 220 ER - TY - GEN A1 - Müssig, Hans-Joachim A1 - Dabrowski, Jarek Marek A1 - Wenger, Christian A1 - Lupina, Grzegorz A1 - Sorge, Roland A1 - Formanek, Peter A1 - Zaumseil, Peter A1 - Schmeißer, Dieter T1 - Ultrathin Dielectric Films Grown by Solid Phase Reaction of Pr with SiO2 T2 - MRS Proceedings Y1 - 2004 SN - 1946-4274 VL - 811 ER - TY - GEN A1 - Perez, Eduardo A1 - Mahadevaiah, Mamathamba Kalishettyhalli A1 - Perez-Bosch Quesada, Emilio A1 - Wenger, Christian T1 - In-depth characterization of switching dynamics in amorphous HfO2 memristive arrays for the implementation of synaptic updating rules T2 - Japanese Journal of Applied Physics N2 - Accomplishing truly analog conductance modulation in memristive arrays is crucial in order to implement the synaptic plasticity in hardware-based neuromorphic systems. In this paper, such a feature was addressed by exploiting the inherent stochasticity of switching dynamics in amorphous HfO2 technology. A thorough statistical analysis of experimental characteristics measured in 4 kbit arrays by using trains of identical depression/potentiation pulses with different voltage amplitudes and pulse widths provided the key to develop two different updating rules and to define their optimal programming parameters. The first rule is based on applying a specific number of identical pulses until the conductance value achieves the desired level. The second one utilized only one single pulse with a particular amplitude to achieve the targeted conductance level. In addition, all the results provided by the statistical analysis performed may play an important role in understanding better the switching behavior of this particular technology. KW - RRAM KW - memristive device KW - HfO2 KW - memristive switching Y1 - 2022 U6 - https://doi.org/10.35848/1347-4065/ac6a3b SN - 0021-4922 VL - 61 SP - 1 EP - 7 ER - TY - GEN A1 - Strobel, Carsten A1 - Alvarado Chavarin, Carlos A1 - Knaut, Martin A1 - Völkel, Sandra A1 - Albert, Matthias A1 - Hiess, Andre A1 - Max, Benjamin A1 - Wenger, Christian A1 - Kirchner, Robert A1 - Mikolajick, Thomas T1 - High Gain Graphene Based Hot Electron Transistor with Record High Saturated Output Current Density T2 - Advanced Electronic Materials N2 - Hot electron transistors (HETs) represent an exciting frontier in semiconductor technology, holding the promise of high-speed and high-frequency electronics. With the exploration of two-dimensional materials such as graphene and new device architectures, HETs are poised to revolutionize the landscape of modern electronics. This study highlights a novel HET structure with a record output current density of 800 A/cm² and a high current gain α, fabricated using a scalable fabrication approach. The HET structure comprises two-dimensional hexagonal boron nitride (hBN) and graphene layers wet transferred to a germanium substrate. The combination of these materials results in exceptional performance, particularly in terms of the highly saturated output current density. The scalable fabrication scheme used to produce the HET opens up opportunities for large-scale manufacturing. This breakthrough in HET technology holds promise for advanced electronic applications, offering high current capabilities in a practical and manufacturable device. KW - Graphene KW - Transistor Y1 - 2024 U6 - https://doi.org/10.1002/aelm.202300624 SN - 2199-160X VL - 10 IS - 2 ER - TY - GEN A1 - Pechmann, Stefan A1 - Perez, Eduardo A1 - Wenger, Christian A1 - Hagelauer, Amelie T1 - A current mirror Based read circuit design with multi-level capability for resistive switching deviceb T2 - 2024 International Conference on Electronics, Information, and Communication (ICEIC) N2 - This paper presents a read circuit design for resistive memory cells based on current mirrors. The circuit utilizes high-precision current mirrors and reference cells to determine the state of resistive memory using comparators. It offers a high degree in adaptability in terms of both resistance range and number of levels. Special emphasis was put on device protection to prevent accidental programming of the memory during read operations. The realized circuit can resolve eight states with a resolution of up to 1 k Ω, realizing a digitization of the analog memory information. Furthermore, the integration in a complete memory macro is shown. The circuit was realized in a 130 nm-process but can easily be adapted to other processes and resistive memory technologies. KW - RRAM KW - memristive device Y1 - 2024 SN - 979-8-3503-7188-8 U6 - https://doi.org/10.1109/ICEIC61013.2024.10457188 SN - 2767-7699 PB - Institute of Electrical and Electronics Engineers (IEEE) ER - TY - GEN A1 - Nitsch, Paul-G. A1 - Ratzke, Markus A1 - Pozarowska, Emilia A1 - Flege, Jan Ingo A1 - Alvarado Chavarin, Carlos A1 - Wenger, Christian A1 - Fischer, Inga Anita T1 - Deposition of reduced ceria thin films by reactive magnetron sputtering for the development of a resistive gas sensor T2 - Verhandlungen der DPG, Berlin 2024 N2 - The use of cerium oxide for hydrogen sensing is limited by the low electrical conductivity of layers deposited from a ceria target. To increase the electrical conductivity, partially reduced cerium oxide layers were obtained from a metallic cerium target by reactive magnetron sputtering. The proportions of the oxidation states Ce3+, present in reduced species, and Ce4+, present in fully oxidized species, were determined by ex-situ XPS. For electrical characterization, films were deposited on planarized tungsten finger electrodes. IV curves were measured over several days to investigate possible influences of oxygen and humidity on electrical conductivity. The morphological stability of the layers under ambient conditions was investigated by microscopical methods. The XPS results show a significant amount of Ce3+ in the layers. The electrical conductivity of as-grown samples is several orders of magnitude higher than that of samples grown from a ceria target. However, the conductivity decreases over time, indicating an oxidation of the layers. The surface morphology of the samples was found to be changing drastically within days, leading to partial delamination. KW - ceria KW - metalic cerium target KW - electrical conductivity KW - X-ray photoelectron spectroscopy (XPS) KW - oxidation states KW - morphology Y1 - 2024 UR - https://www.dpg-verhandlungen.de/year/2024/conference/berlin/part/ds/session/11/contribution/18 SN - 0420-0195 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - GEN A1 - Nikiruy, Kristina A1 - Perez, Eduardo A1 - Baroni, Andrea A1 - Reddy, Keerthi Dorai Swamy A1 - Pechmann, Stefan A1 - Wenger, Christian A1 - Ziegler, Martin T1 - Blooming and pruning: learning from mistakes with memristive synapses T2 - Scientific Reports N2 - AbstractBlooming and pruning is one of the most important developmental mechanisms of the biological brain in the first years of life, enabling it to adapt its network structure to the demands of the environment. The mechanism is thought to be fundamental for the development of cognitive skills. Inspired by this, Chialvo and Bak proposed in 1999 a learning scheme that learns from mistakes by eliminating from the initial surplus of synaptic connections those that lead to an undesirable outcome. Here, this idea is implemented in a neuromorphic circuit scheme using CMOS integrated HfO2-based memristive devices. The implemented two-layer neural network learns in a self-organized manner without positive reinforcement and exploits the inherent variability of the memristive devices. This approach provides hardware, local, and energy-efficient learning. A combined experimental and simulation-based parameter study is presented to find the relevant system and device parameters leading to a compact and robust memristive neuromorphic circuit that can handle association tasks. KW - RRAM KW - Neural network Y1 - 2024 U6 - https://doi.org/10.1038/s41598-024-57660-4 SN - 2045-2322 VL - 14 IS - 1 ER - TY - GEN A1 - Strobel, Carsten A1 - Alvarado Chavarin, Carlos A1 - Leszczynski, Sebastian A1 - Richter, Karola A1 - Knaut, Martin A1 - Reif, Johanna A1 - Völkel, Sandra A1 - Albert, Matthias A1 - Wenger, Christian A1 - Bartha, Johann Wolfgang A1 - Mikolajick, Thomas T1 - Improved Graphene-base Heterojunction Transistor with Different Collector Semi-conductors for High-frequency Applications T2 - Advanced Materials Letters N2 - A new kind of transistor device with a graphene monolayer embedded between two n-type silicon layers is fabricated and characterized. The device is called graphene-base heterojunction transistor (GBHT). The base-voltage controls the current of the device flowing from the emitter via graphene to the collector. The transit time for electrons passing by the ultrathin graphene layer is extremely short which makes the device very promising for high frequency RF-electronics. The output current of the device is saturated and clearly modulated by the base voltage. Further, the silicon collector of the GBHT is replaced by germanium to improve the device performance. This enabled the collector current to be increased by almost three orders of magnitude. Also, the common-emitter current gain (Ic/Ib) increased from 10-3 to approximately 0.3 for the newly designed device. However, the ON-OFF ratio of the improved germanium based GBHT has so far been rather low. Further optimizations are necessary in order to fully exploit the potential of the graphene-base heterojunction transistor. KW - Graphene KW - transistor Y1 - 2022 U6 - https://doi.org/10.5185/amlett.2022.011688 SN - 0976-3961 VL - 13 IS - 1 ER - TY - GEN A1 - Kloes, Alexander A1 - Bischoff, Carl A1 - Leise, Jakob A1 - Perez-Bosch Quesada, Emilio A1 - Wenger, Christian A1 - Perez, Eduardo T1 - Stochastic switching of memristors and consideration in circuit simulation T2 - Solid State Electronics N2 - We explore the stochastic switching of oxide-based memristive devices by using the Stanford model for circuit simulation. From measurements, the device-to-device (D2D) and cycle-to-cycle (C2C) statistical variation is extracted. In the low-resistive state (LRS) dispersion by D2D variability is dominant. In the high-resistive state (HRS) C2C dispersion becomes the main source of fluctuation. A statistical procedure for the extraction of parameters of the compact model is presented. Thereby, in a circuit simulation the typical D2D and C2C fluctuations of the current–voltage (I-V) characteristics can be emulated by extracting statistical parameters of key model parameters. The statistical distributions of the parameters are used in a Monte Carlo simulation to reproduce the I-V D2D and C2C dispersions which show a good agreement to the measured curves. The results allow the simulation of the on/off current variation for the design of memory cells or can be used to emulate the synaptic behavior of these devices in artificial neural networks realized by a crossbar array of memristors. KW - RRAM KW - memristive device KW - variability Y1 - 2023 U6 - https://doi.org/10.1016/j.sse.2023.108606 SN - 0038-1101 VL - 201 ER - TY - GEN A1 - Prüfer, Mareike A1 - Wenger, Christian A1 - Bier, Frank F. A1 - Laux, Eva-Maria A1 - Hölzel, Ralph T1 - Activity of AC electrokinetically immobilized horseradish peroxidase T2 - Electrophoresis N2 - Dielectrophoresis(DEP) is an AC electrokinetic effect mainly used to manipulate cells.Smaller particles,like virions,antibodies,enzymes,andevendyemolecules can be immobilized by DEP as well. In principle, it was shown that enzymesare active after immobilization by DEP, but no quantification of the retainedactivity was reported so far. In this study, the activity of the enzyme horseradishperoxidase (HRP) is quantified after immobilization by DEP. For this, HRP is immobilized on regular arrays of titanium nitride ring electrodes of 500 nm diameter and 20 nm widths. The activity of HRP on the electrode chip is measured with a limit of detection of 60 fg HRP by observing the enzymatic turnover of Amplex Red and H2O2 to fluorescent resoruf in by fluorescence microscopy. The initial activity of the permanently immobilized HRP equals up to 45% of the activity that can be expected for an ideal monolayer of HRP molecules on all electrodes of the array. Localization of the immobilizate on the electrodesis accomplished by staining with the fluorescent product of the enzyme reac-tion.The high residual activity of enzymes after AC field induced immobilization shows the method’s suitability for biosensing and research applications. KW - dielectrophoresis KW - immobilization KW - nanoelectrodes Y1 - 2022 U6 - https://doi.org/10.1002/elps.202200073 SN - 1522-2683 VL - 43 IS - 18-19 SP - 1920 EP - 1933 ER - TY - GEN A1 - Ossorio, Óscar G. A1 - Vinuesa, Guillermo A1 - Garcia, Hector A1 - Sahelices, Benjamin A1 - Duenas, Salvador A1 - Castan, Helena A1 - Perez, Eduardo A1 - Mahadevaiah, Mamathamba Kalishettyhalli A1 - Wenger, Christian T1 - Performance Assessment of Amorphous HfO2-based RRAM Devices for Neuromorphic Applications T2 - ECS Transactions N2 - The use of thin layers of amorphous hafnium oxide has been shown to be suitable for the manufacture of Resistive Random-Access memories (RRAM). These memories are of great interest because of their simple structure and non-volatile character. They are particularly appealing as they are good candidates for substituting flash memories. In this work, the performance of the MIM structure that takes part of a 4 kbit memory array based on 1-transistor-1-resistance (1T1R) cells was studied in terms of control of intermediate states and cycle durability. DC and small signal experiments were carried out in order to fully characterize the devices, which presented excellent multilevel capabilities and resistive-switching behavior. KW - RRAM KW - resistive switching KW - HfO2 Y1 - 2021 U6 - https://doi.org/10.1149/10202.0029ecst SN - 1938-6737 SN - 1938-5862 VL - 102 IS - 2 SP - 29 EP - 35 ER - TY - GEN A1 - Baroni, Andrea A1 - Glukhov, Artem A1 - Perez, Eduardo A1 - Wenger, Christian A1 - Calore, Enrico A1 - Schifano, Sebastiano Fabio A1 - Olivo, Piero A1 - Ielmini, Daniele A1 - Zambelli, Cristian T1 - An energy-efficient in-memory computing architecture for survival data analysis based on resistive switching memories T2 - Frontiers in Neuroscience N2 - One of the objectives fostered in medical science is the so-called precision medicine, which requires the analysis of a large amount of survival data from patients to deeply understand treatment options. Tools like Machine Learning and Deep Neural Networks are becoming a de-facto standard. Nowadays, computing facilities based on the Von Neumann architecture are devoted to these tasks, yet rapidly hitting a bottleneck in performance and energy efficiency. The In-Memory Computing (IMC) architecture emerged as a revolutionary approach to overcome that issue. In this work, we propose an IMC architecture based on Resistive switching memory (RRAM) crossbar arrays to provide a convenient primitive for matrix–vector multiplication in a single computational step. This opens massive performance improvement in the acceleration of a neural network that is frequently used in survival analysis of biomedical records, namely the DeepSurv. We explored how the synaptic weights mapping strategy and the programming algorithms developed to counter RRAM non-idealities expose a performance/energy trade-off. Finally, we assessed the benefits of the proposed architectures with respect to a GPU-based realization of the same task, evidencing a tenfold improvement in terms of performance and three orders of magnitude with respect to energy efficiency. KW - RRAM KW - In-Memory Computing KW - Multilevel switching Y1 - 2022 U6 - https://doi.org/10.3389/fnins.2022.932270 SN - 1662-4548 VL - Vol. 16 SP - 1 EP - 16 ER - TY - GEN A1 - Pérez-Bosch Quesada, Emilio A1 - Romero-Zaliz, Rocío A1 - Perez, Eduardo A1 - Mahadevaiah, Mamathamba Kalishettyhalli A1 - Reuben, John A1 - Schubert, Markus Andreas A1 - Jiménez-Molinos, Francisco A1 - Roldán, Juan Bautista A1 - Wenger, Christian T1 - Toward Reliable Compact Modeling of Multilevel 1T-1R RRAM Devices for Neuromorphic Systems T2 - Electronics (MDPI) N2 - In this work, three different RRAM compact models implemented in Verilog-A are analyzed and evaluated in order to reproduce the multilevel approach based on the switching capability of experimental devices. These models are integrated in 1T-1R cells to control their analog behavior by means of the compliance current imposed by the NMOS select transistor. Four different resistance levels are simulated and assessed with experimental verification to account for their multilevel capability. Further, an Artificial Neural Network study is carried out to evaluate in a real scenario the viability of the multilevel approach under study. KW - RRAM KW - multilevel switching KW - compact modeling KW - Verilog-A Y1 - 2021 U6 - https://doi.org/10.3390/electronics10060645 SN - 2079-9292 VL - 10 IS - 6 ER - TY - GEN A1 - Petryk, Dmytro A1 - Dyka, Zoya A1 - Perez, Eduardo A1 - Mahadevaiah, Mamathamba Kalishettyhalli A1 - Kabin, Ievgen A1 - Wenger, Christian A1 - Langendörfer, Peter T1 - Evaluation of the Sensitivity of RRAM Cells to Optical Fault Injection Attacks T2 - EUROMICRO Conference on Digital System Design (DSD 2020), Special Session: Architecture and Hardware for Security Applications (AHSA) Y1 - 2021 SN - 978-1-7281-9535-3 U6 - https://doi.org/10.1109/DSD51259.2020.00047 SN - 978-1-7281-9536-0 ER - TY - GEN A1 - Glukhov, Artem A1 - Lepri, Nicola A1 - Milo, Valerio A1 - Baroni, Andrea A1 - Zambelli, Cristian A1 - Olivo, Piero A1 - Perez, Eduardo A1 - Wenger, Christian A1 - Ielmini, Daniele T1 - End-to-end modeling of variability-aware neural networks based on resistive-switching memory arrays T2 - Proc. 30th IFIP/IEEE International Conference on Very Large Scale Integration (VLSI-SoC 2022) N2 - Resistive-switching random access memory (RRAM) is a promising technology that enables advanced applications in the field of in-memory computing (IMC). By operating the memory array in the analogue domain, RRAM-based IMC architectures can dramatically improve the energy efficiency of deep neural networks (DNNs). However, achieving a high inference accuracy is challenged by significant variation of RRAM conductance levels, which can be compensated by (i) advanced programming techniques and (ii) variability-aware training (VAT) algorithms. In both cases, however, detailed knowledge and accurate physics-based statistical models of RRAM are needed to develop programming and VAT methodologies. This work presents an end-to-end approach to the development of highly-accurate IMC circuits with RRAM, encompassing the device modeling, the precise programming algorithm, and the VAT simulations to maximize the DNN classification accuracy in presence of conductance variations. KW - RRAM KW - HfO2 KW - neural network KW - memristive switching Y1 - 2022 U6 - https://doi.org/10.1109/VLSI-SoC54400.2022.9939653 SP - 1 EP - 5 ER - TY - GEN A1 - Perez, Eduardo A1 - Ossorio, Óscar G. A1 - Duenas, Salvador A1 - Castan, Helena A1 - García, Hector A1 - Wenger, Christian T1 - Programming Pulse Width Assessment for Reliable and Low-Energy Endurance Performance in Al:HfO2-Based RRAM Arrays T2 - Electronics (MDPI) N2 - A crucial step in order to achieve fast and low-energy switching operations in resistive random access memory (RRAM) memories is the reduction of the programming pulse width. In this study, the incremental step pulse with verify algorithm (ISPVA) was implemented by using different pulse widths between 10 μ s and 50 ns and assessed on Al-doped HfO 2 4 kbit RRAM memory arrays. The switching stability was assessed by means of an endurance test of 1k cycles. Both conductive levels and voltages needed for switching showed a remarkable good behavior along 1k reset/set cycles regardless the programming pulse width implemented. Nevertheless, the distributions of voltages as well as the amount of energy required to carry out the switching operations were definitely affected by the value of the pulse width. In addition, the data retention was evaluated after the endurance analysis by annealing the RRAM devices at 150 °C along 100 h. Just an almost negligible increase on the rate of degradation of about 1 μ A at the end of the 100 h of annealing was reported between those samples programmed by employing a pulse width of 10 μ s and those employing 50 ns. Finally, an endurance performance of 200k cycles without any degradation was achieved on 128 RRAM devices by using programming pulses of 100 ns width KW - RRAM KW - Reliability Y1 - 2020 U6 - https://doi.org/10.3390/electronics9050864 SN - 2079-9292 VL - 9 IS - 5 ER - TY - GEN A1 - Petzold, Stefan A1 - Piros, Eszter A1 - Eilhardt, Robert A1 - Zintler, Alexander A1 - Vogel, Tobias A1 - Kaiser, Nico A1 - Radetinac, Aldin A1 - Komissinskiy, Philipp A1 - Jalaguier, Eric A1 - Nolot, Emmanuel A1 - Charpin-Nicolle, Christelle A1 - Wenger, Christian A1 - Molina-Luna, Leopoldo A1 - Miranda, Enrique A1 - Alff, Lambert T1 - Tailoring the Switching Dynamics in Yttrium Oxide-Based RRAM Devices by Oxygen Engineering: From Digital to Multi-Level Quantization toward Analog Switching T2 - Advanced Electronic Materials N2 - This work investigates the transition from digital to gradual or analog resistive switching in yttrium oxide‐based resistive random‐access memory devices. It is shown that this transition is determined by the amount of oxygen in the functional layer. A homogeneous reduction of the oxygen content not only reduces the electroforming voltage, allowing for forming‐free devices, but also decreases the voltage operation window of switching, thereby reducing intra‐device variability. The most important effect as the dielectric becomes substoichiometric by oxygen engineering is that more intermediate (quantized) conduction states are accessible. A key factor for this reproducibly controllable behavior is the reduced local heat dissipation in the filament region due to the increased thermal conductivity of the oxygen depleted layer. The improved accessibility of quantized resistance states results in a semi‐gradual switching both for the set and reset processes, as strongly desired for multi‐bit storage and for an accurate definition of the synaptic weights in neuromorphic systems. A theoretical model based on the physics of mesoscopic structures describing current transport through a nano‐constriction including asymmetric potential drops at the electrodes and non‐linear conductance quantization is provided. The results contribute to a deeper understanding on how to tailor materials properties for novel memristive functionalities. KW - RRAM KW - Multilevel switching Y1 - 2020 U6 - https://doi.org/10.1002/aelm.202000439 SN - 2199-160X VL - 6 IS - 11 ER - TY - GEN A1 - Glukhov, Artem A1 - Milo, Valerio A1 - Baroni, Andrea A1 - Lepri, Nicola A1 - Zambelli, Cristian A1 - Olivo, Piero A1 - Perez, Eduardo A1 - Wenger, Christian A1 - Ielmini, Daniele T1 - Statistical model of program/verify algorithms in resistive-switching memories for in-memory neural network accelerators T2 - 2022 IEEE International Reliability Physics Symposium (IRPS) N2 - Resistive-switching random access memory (RRAM) is a promising technology for in-memory computing (IMC) to accelerate training and inference of deep neural networks (DNNs). This work presents the first physics-based statistical model describing (i) multilevel RRAM device program/verify (PV) algorithms by controlled set transition, (ii) the stochastic cycle-to-cycle (C2C) and device-to-device (D2D) variations within the array, and (iii) the impact of such imprecisions on the accuracy of DNN accelerators. The model can handle the full chain from RRAM materials/device parameters to the DNN performance, thus providing a valuable tool for device/circuit codesign of hardware DNN accelerators. KW - RRAM KW - Multilevel switching KW - neural network Y1 - 2022 SN - 978-1-6654-7950-9 SN - 978-1-6654-7951-6 U6 - https://doi.org/10.1109/IRPS48227.2022.9764497 SN - 2473-2001 SP - 3C.3-1 EP - 3C.3-7 PB - Institute of Electrical and Electronics Engineers (IEEE) ER - TY - GEN A1 - Perez-Bosch Quesada, Emilio A1 - Mahadevaiah, Mamathamba Kalishettyhalli A1 - Rizzi, Tommaso A1 - Wen, Jianan A1 - Ulbricht, Markus A1 - Krstic, Milos A1 - Wenger, Christian A1 - Perez, Eduardo T1 - Experimental Assessment of Multilevel RRAM-based Vector-Matrix Multiplication Operations for In-Memory Computing T2 - IEEE Transactions on Electron Devices N2 - Resistive random access memory (RRAM)-based hardware accelerators are playing an important role in the implementation of in-memory computing (IMC) systems for artificial intelligence applications. The latter heavily rely on vector-matrix multiplication (VMM) operations that can be efficiently boosted by RRAM devices. However, the stochastic nature of the RRAM technology is still challenging real hardware implementations. To study the accuracy degradation of consecutive VMM operations, in this work we programed two RRAM subarrays composed of 8x8 one-transistor-one-resistor (1T1R) cells following two different distributions of conductive levels. We analyze their robustness against 1000 identical consecutive VMM operations and monitor the inherent devices’ nonidealities along the test. We finally quantize the accuracy loss of the operations in the digital domain and consider the trade-offs between linearly distributing the resistive states of the RRAM cells and their robustness against nonidealities for future implementation of IMC hardware systems. KW - RRAM KW - Vector Matrix Multiplication KW - variability Y1 - 2023 U6 - https://doi.org/10.1109/TED.2023.3244509 SN - 0018-9383 VL - 70 IS - 4 SP - 2009 EP - 2014 ER - TY - GEN A1 - Perez, Eduardo A1 - Maldonado, David A1 - Perez-Bosch Quesada, Emilio A1 - Mahadevaiah, Mamathamba Kalishettyhalli A1 - Jimenez-Molinos, Francisco A1 - Wenger, Christian T1 - Parameter Extraction Methods for Assessing Device-to-Device and Cycle-to-Cycle Variability of Memristive Devices at Wafer Scale T2 - IEEE Transactions on Electron Devices N2 - The stochastic nature of the resistive switching (RS) process in memristive devices makes device-to-device (DTD) and cycle-to-cycle (CTC) variabilities relevant magnitudes to be quantified and modeled. To accomplish this aim, robust and reliable parameter extraction methods must be employed. In this work, four different extraction methods were used at the production level (over all the 108 devices integrated on 200-mm wafers manufactured in the IHP 130-nm CMOS technology) in order to obtain the corresponding collection of forming, reset, and set switching voltages. The statistical analysis of the experimental data (mean and standard deviation (SD) values) was plotted by using heat maps, which provide a good summary of the whole data at a glance and, in addition, an easy manner to detect inhomogeneities in the fabrication process. KW - RRAM KW - memristive device KW - cycle-to-cycle variability KW - device-to-device variability Y1 - 2023 U6 - https://doi.org/10.1109/TED.2022.3224886 SN - 0018-9383 VL - 70 IS - 1 SP - 360 EP - 365 ER - TY - GEN A1 - Baroni, Andrea A1 - Glukhov, Artem A1 - Perez, Eduardo A1 - Wenger, Christian A1 - Ielmini, Daniele A1 - Olivo, Piero A1 - Zambelli, Cristian T1 - Low Conductance State Drift Characterization and Mitigation in Resistive Switching Memories (RRAM) for Artificial Neural Networks T2 - IEEE Transactions on Device and Materials Reliability N2 - The crossbar structure of Resistive-switching random access memory (RRAM) arrays enabled the In-Memory Computing circuits paradigm, since they imply the native acceleration of a crucial operations in this scenario, namely the Matrix-Vector-Multiplication (MVM). However, RRAM arrays are affected by several issues materializing in conductance variations that might cause severe performance degradation. A critical one is related to the drift of the low conductance states appearing immediately at the end of program and verify algorithms that are mandatory for an accurate multi-level conductance operation. In this work, we analyze the benefits of a new programming algorithm that embodies Set and Reset switching operations to achieve better conductance control and lower variability. Data retention analysis performed with different temperatures for 168 hours evidence its superior performance with respect to standard programming approach. Finally, we explored the benefits of using our methodology at a higher abstraction level, through the simulation of an Artificial Neural Network for image recognition task (MNIST dataset). The accuracy achieved shows higher performance stability over temperature and time. KW - RRAM KW - neural network KW - Multilevel switching Y1 - 2022 U6 - https://doi.org/10.1109/TDMR.2022.3182133 SN - 1530-4388 VL - 22 IS - 3 SP - 340 EP - 347 ER - TY - GEN A1 - Franck, Max A1 - Dabrowski, Jaroslaw A1 - Schubert, Markus Andreas A1 - Wenger, Christian A1 - Lukosius, Mindaugas T1 - Towards the Growth of Hexagonal Boron Nitride on Ge(001)/Si Substrates by Chemical Vapor Deposition T2 - Nanomaterials N2 - The growth of hexagonal boron nitride (hBN) on epitaxial Ge(001)/Si substrates via high-vacuum chemical vapor deposition from borazine is investigated for the first time in a systematic manner. The influences of the process pressure and growth temperature in the range of 10−7–10−3 mbar and 900–980 °C, respectively, are evaluated with respect to morphology, growth rate, and crystalline quality of the hBN films. At 900 °C, nanocrystalline hBN films with a lateral crystallite size of ~2–3 nm are obtained and confirmed by high-resolution transmission electron microscopy images. X-ray photoelectron spectroscopy confirms an atomic N:B ratio of 1 ± 0.1. A three-dimensional growth mode is observed by atomic force microscopy. Increasing the process pressure in the reactor mainly affects the growth rate, with only slight effects on crystalline quality and none on the principle growth mode. Growth of hBN at 980 °C increases the average crystallite size and leads to the formation of 3–10 well-oriented, vertically stacked layers of hBN on the Ge surface. Exploratory ab initio density functional theory simulations indicate that hBN edges are saturated by hydrogen, and it is proposed that partial de-saturation by H radicals produced on hot parts of the set-up is responsible for the growth KW - Boron nitride KW - 2d materials KW - Chemical vapour deposition Y1 - 2022 U6 - https://doi.org/10.3390/nano12193260 SN - 2079-4991 VL - 12 IS - 19 ER - TY - GEN A1 - Strobel, Carsten A1 - Alvarado Chavarin, Carlos A1 - Wenger, Christian A1 - Albert, Matthias A1 - Mikolajick, Thomas T1 - Vertical Graphene-Based Transistors for Power Electronics, Optoelectronics and Radio-Frequency Applications T2 - IEEE Nanotechnology Materials and Devices Conference (NMDC), Paestum, Italy, 22-25 October 2023 N2 - The combination of two-dimensional materials, such as graphene, with established thin films offers great opportunities for enabling next-generation vertical transistors for various applications. This paper gives a brief overview about different vertical transistor concepts using twodimensional materials proposed so far, e.g. the hot electron transistor and the Barristor. With the arrival of twodimensional materials, the hot electron transistor also experienced a revival with predicted cut-off frequencies in the THz range. The Barristor overcomes the weak current saturation of lateral graphene field-effect transistors and high on-off ratios up to 107 were demonstrated, which are suitable parameters for logic applications. By combining a semiconductor-graphene-semiconductor design of the simplest hot electron transistor with the Barristor operating principle a new device, called graphene adjustable-barriers transistor, can be realized. This new device concept provides the potential for RF, power electronics, and optoelectronic applications. KW - Graphene Y1 - 2023 SN - 979-8-3503-3546-0 SN - 979-8-3503-3547-7 U6 - https://doi.org/10.1109/NMDC57951.2023.10344102 SN - 2473-0718 SP - 196 EP - 201 PB - Institute of Electrical and Electronics Engineers (IEEE) ER - TY - GEN A1 - Stanke, Sandra A1 - Wenger, Christian A1 - Bier, Frank F. A1 - Hölzel, Ralph T1 - AC electrokinetic immobilization of influenza virus T2 - Electrophoresis N2 - The use of alternating current (AC) electrokinetic forces, like dielectrophoresis and AC electroosmosis, as a simple and fast method to immobilize sub-micrometer objects onto nanoelectrode arrays is presented. Due to its medical relevance, the influenza virus is chosen as a model organism. One of the outstanding features is that the immobilization of viral material to the electrodes can be achieved permanently, allowing subsequent handling independently from the electrical setup. Thus, by using merely electric fields, we demonstrate that the need of prior chemical surface modification could become obsolete. The accumulation of viral material over time is observed by fluorescence microscopy. The influences of side effects like electrothermal fluid flow, causing a fluid motion above the electrodes and causing an intensity gradient within the electrode array, are discussed. Due to the improved resolution by combining fluorescence microscopy with deconvolution, it is shown that the viral material is mainly drawn to the electrode edge and to a lesser extent to the electrode surface. Finally, areas of application for this functionalization technique are presented. KW - dielectrophoresis KW - immobilization KW - virus Y1 - 2022 U6 - https://doi.org/10.1002/elps.202100324 SN - 1522-2683 VL - 43 IS - 12 SP - 1309 EP - 1321 ER - TY - GEN A1 - Perez-Bosch Quesada, Emilio A1 - Rizzi, Tommaso A1 - Gupta, Aditya A1 - Mahadevaiah, Mamathamba Kalishettyhalli A1 - Schubert, Andreas A1 - Pechmann, Stefan A1 - Jia, Ruolan A1 - Uhlmann, Max A1 - Hagelauer, Amelie A1 - Wenger, Christian A1 - Perez, Eduardo T1 - Multi-Level Programming on Radiation-Hard 1T1R Memristive Devices for In-Memory Computing T2 - 14th Spanish Conference on Electron Devices (CDE 2023), Valencia, Spain, 06-08 June 2023 N2 - This work presents a quasi-static electrical characterization of 1-transistor-1-resistor memristive structures designed following hardness-by-design techniques integrated in the CMOS fabrication process to assure multi-level capabilities in harsh radiation environments. Modulating the gate voltage of the enclosed layout transistor connected in series with the memristive device, it was possible to achieve excellent switching capabilities from a single high resistance state to a total of eight different low resistance states (more than 3 bits). Thus, the fabricated devices are suitable for their integration in larger in-memory computing systems and in multi-level memory applications. Index Terms—radiation-hard, hardness-by-design, memristive devices, Enclosed Layout Transistor, in-memory computing KW - RRAM Y1 - 2023 SN - 979-8-3503-0240-0 U6 - https://doi.org/10.1109/CDE58627.2023.10339525 PB - Institute of Electrical and Electronics Engineers (IEEE) ER - TY - GEN A1 - Zahari, Finn A1 - Perez, Eduardo A1 - Mahadevaiah, Mamathamba Kalishettyhalli A1 - Kohlstedt, Hermann A1 - Wenger, Christian A1 - Ziegler, Martin T1 - Analogue pattern recognition with stochastic switching binary CMOS‑integrated memristive devices T2 - Scientific Reports N2 - Biological neural networks outperform todays computer technology in terms of power consumption and computing speed when associative tasks, like pattern recognition, are to be solved. The analogue and massive parallel in-memory computing in biology differs strongly with conventional transistor electronics using the von Neumann architecture. Therefore, novel bio-inspired computing architectures are recently highly investigated in the area of neuromorphic computing. Here, memristive devices, which serve as non-volatile resistive memory, are used to emulate the plastic behaviour of biological synapses. In particular, CMOS integrated resistive random access memory (RRAM) devices are promising candidates to extend conventional CMOS technology in neuromorphic systems. However, dealing with the inherent stochasticity of the resistive switching effect can be challenging for network performance. In this work, the probabilistic switching is exploited to emulate stochastic plasticity with fully CMOS integrated binary RRAM devices. Two different RRAM technologies with different device variabilities are investigated in detail and their use in a stochastic artificial neural network (StochANN) to solve the MINST pattern recognition task is examined. A mixed-signal implementation with hardware synapses and software neurons as well as numerical simulations show the proposed concept of stochastic computing is able to handle analogue data with binary memory cells. KW - RRAM KW - memristive device KW - neural network KW - HfO2 Y1 - 2020 U6 - https://doi.org/10.1038/s41598-020-71334-x SN - 2045-2322 VL - 10 ER - TY - GEN A1 - Zanotti, Tommaso A1 - Puglisi, Francesco Maria A1 - Milo, Valerio A1 - Perez, Eduardo A1 - Mahadevaiah, Mamathamba Kalishettyhalli A1 - Ossorio, Óscar G. A1 - Wenger, Christian A1 - Pavan, Paolo A1 - Olivo, Piero A1 - Ielmini, Daniele T1 - Reliability of Logic-in-Memory Circuits in Resistive Memory Arrays T2 - IEEE Transactions on Electron Devices N2 - Logic-in-memory (LiM) circuits based on resistive random access memory (RRAM) devices and the material implication logic are promising candidates for the development of low-power computing devices that could fulfill the growing demand of distributed computing systems. However, these circuits are affected by many reliability challenges that arise from device nonidealities (e.g., variability) and the characteristics of the employed circuit architecture. Thus, an accurate investigation of the variability at the array level is needed to evaluate the reliability and performance of such circuit architectures. In this work, we explore the reliability and performance of smart IMPLY (SIMPLY) (i.e., a recently proposed LiM architecture with improved reliability and performance) on two 4-kb RRAM arrays based on different resistive switching oxides integrated in the back end of line (BEOL) of the 0.25- μm BiCMOS process. We analyze the tradeoff between reliability and energy consumption of SIMPLY architecture by exploiting the results of an extensive array-level variability characterization of the two technologies. Finally, we study the worst case performance of a full adder implemented with the SIMPLY architecture and benchmark it on the analogous CMOS implementation. KW - RRAM KW - in-memory computing KW - HfO2 Y1 - 2020 U6 - https://doi.org/10.1109/TED.2020.3025271 SN - 0018-9383 SN - 1557-9646 VL - 67 IS - 11 SP - 4611 EP - 4615 ER - TY - GEN A1 - Romero-Zaliz, Rocío A1 - Perez, Eduardo A1 - Jimenez-Molinos, Francisco A1 - Wenger, Christian A1 - Roldan, Juan Bautista T1 - Study of Quantized Hardware Deep Neural Networks Based on Resistive Switching Devices, Conventional versus Convolutional Approaches T2 - Electronics (MDPI) N2 - A comprehensive analysis of two types of artificial neural networks (ANN) is performed to assess the influence of quantization on the synaptic weights. Conventional multilayer-perceptron (MLP) and convolutional neural networks (CNN) have been considered by changing their features in the training and inference contexts, such as number of levels in the quantization process, the number of hidden layers on the network topology, the number of neurons per hidden layer, the image databases, the number of convolutional layers, etc. A reference technology based on 1T1R structures with bipolar memristors including HfO2 dielectrics was employed, accounting for different multilevel schemes and the corresponding conductance quantization algorithms. The accuracy of the image recognition processes was studied in depth. This type of studies are essential prior to hardware implementation of neural networks. The obtained results support the use of CNNs for image domains. This is linked to the role played by convolutional layers at extracting image features and reducing the data complexity. In this case, the number of synaptic weights can be reduced in comparison to conventional MLPs. KW - RRAM KW - resistive switching KW - neural network Y1 - 2021 U6 - https://doi.org/10.3390/electronics10030346 SN - 2079-9292 VL - 10 IS - 3 ER - TY - GEN A1 - Soltani Zarrin, Pouya A1 - Rockendorf, Niels A1 - Wenger, Christian T1 - In-Vitro Classification of Saliva Samples of COPD Patients and Healthy Controls Using Machine Learning Tools T2 - IEEE Access N2 - Chronic Obstructive Pulmonary Disease (COPD) is a life-threatening lung disease and a major cause of morbidity and mortality worldwide. Although a curative therapy has yet to be found, permanent monitoring of biomarkers that reflect the disease progression plays a pivotal role for the effective management of COPD. The accurate examination of respiratory tract fluids like saliva is a promising approach for staging the disease and predicting its upcoming exacerbations in a Point-of-Care (PoC) environment. Nonetheless, this approach is only feasible by concurrent consideration of patients' demographic and medical parameters. Therefore, Machine Learning (ML) tools are necessary for the comprehensive recognition of COPD in a PoC setting. As a result, the objective of this work was to implement ML tools on the data acquired from characterizing saliva samples of COPD patients and healthy controls for classification purposes. First, a permittivity biosensor was used to characterize dielectric properties of saliva samples and, subsequently, ML tools were applied on the acquired data for classification. The XGBoost gradient boosting algorithm provided a high classification accuracy of 91.25%, making it a promising model for COPD recognition. Integration of this model on a neuromorphic chip, in the future, will enable the real-time detection of COPD in PoC, with low energy consumption and high patient privacy. KW - COPD KW - Machine learning KW - Point of care Y1 - 2020 U6 - https://doi.org/10.1109/ACCESS.2020.3023971 SN - 2169-3536 VL - Vol. 8 SP - 168053 EP - 168060 ER - TY - GEN A1 - Bogun, Nicolas A1 - Perez-Bosch Quesada, Emilio A1 - Perez, Eduardo A1 - Wenger, Christian A1 - Kloes, Alexander A1 - Schwarz, Mike T1 - Analytical Calculation of Inference in Memristor-based Stochastic Artificial Neural Networks T2 - 29th International Conference on Mixed Design of Integrated Circuits and System (MIXDES), 23-24 June 2022 , Wrocław, Poland N2 - The impact of artificial intelligence on human life has increased significantly in recent years. However, as the complexity of problems rose aswell, increasing system features for such amount of data computation became troublesome due to the von Neumann’s computer architecture. Neuromorphic computing aims to solve this problem by mimicking the parallel computation of a human brain. For this approach, memristive devices are used to emulate the synapses of a human brain. Yet, common simulations of hardware based networks require time consuming Monte-Carlo simulations to take into account the stochastic switching of memristive devices. This work presents an alternative concept making use of the convolution of the probability distribution functions (PDF) of memristor currents by its equivalent multiplication in Fourier domain. An artificial neural network is accordingly implemented to perform the inference stage with handwritten digits. KW - RRAM KW - neural network Y1 - 2022 SN - 978-83-63578-22-0 SN - 978-83-63578-21-3 SN - 978-1-6654-6176-4 U6 - https://doi.org/10.23919/MIXDES55591.2022.9838321 SP - 83 EP - 88 ER - TY - GEN A1 - Soltani Zarrin, Pouya A1 - Zahari, Finn A1 - Mahadevaiah, Mamathamba Kalishettyhalli A1 - Perez, Eduardo A1 - Kohlstedt, Hermann A1 - Wenger, Christian T1 - Neuromorphic on‑chip recognition of saliva samples of COPD and healthy controls using memristive devices T2 - Scientific Reports N2 - Chronic Obstructive Pulmonary Disease (COPD) is a life-threatening lung disease, affecting millions of people worldwide. Implementation of Machine Learning (ML) techniques is crucial for the effective management of COPD in home-care environments. However, shortcomings of cloud-based ML tools in terms of data safety and energy efficiency limit their integration with low-power medical devices. To address this, energy efficient neuromorphic platforms can be used for the hardware-based implementation of ML methods. Therefore, a memristive neuromorphic platform is presented in this paper for the on-chip recognition of saliva samples of COPD patients and healthy controls. The results of its performance evaluations showed that the digital neuromorphic chip is capable of recognizing unseen COPD samples with accuracy and sensitivity values of 89% and 86%, respectively. Integration of this technology into personalized healthcare devices will enable the better management of chronic diseases such as COPD. KW - RRAM KW - memristive device KW - neural network Y1 - 2020 U6 - https://doi.org/10.1038/s41598-020-76823-7 SN - 2045-2322 VL - 10 ER - TY - GEN A1 - Lukosius, Mindaugas A1 - Lukose, Rasuolė A1 - Lisker, Marco A1 - Luongo, G. A1 - Elviretti, M. A1 - Mai, Andreas A1 - Wenger, Christian T1 - Graphene Research in 200 mm CMOS Pilot Line T2 - 45th Jubilee International Convention on Information, Communication and Electronic Technology (MIPRO), 2022 N2 - Due to the unique electronic structures, graphene and other 2D Materials are considered as materials which can enable and extend the functionalities and performance in a large variety of applications, among them in microelectronics. At this point, the investigation and preparation of graphene devices in conditions resembling as close as possible the Si technology environment is of highest importance.Towards these goals, this paper focuses on the full spectra of graphene research aspects in 200mm pilot line. We investigated different process module developments such as CMOS compatible growth of high quality graphene on germanium and its growth mechanisms, transfer related challenges on target substrates, patterning, passivation and various concepts of contacting of graphene on a full 200 mm wafers. Finally, we fabricated proof-of-concept test structures e.g. TLM, Hall bars and capacitor structures to prove the feasibility of graphene processing in the pilot line of IHP. KW - Graphene KW - CMOS Y1 - 2022 SN - 978-953-233-103-5 SN - 978-953-233-102-8 SN - 978-1-6654-8434-3 U6 - https://doi.org/10.23919/MIPRO55190.2022.9803362 SN - 2623-8764 SN - 1847-3938 SP - 113 EP - 117 ER - TY - GEN A1 - Baroni, Andrea A1 - Zambelli, Cristian A1 - Olivo, Piero A1 - Perez, Eduardo A1 - Wenger, Christian A1 - Ielmini, Daniele T1 - Tackling the Low Conductance State Drift through Incremental Reset and Verify in RRAM Arrays T2 - 2021 IEEE International Integrated Reliability Workshop (IIRW), South Lake Tahoe, CA, USA, 10 December 2021 N2 - Resistive switching memory (RRAM) is a promising technology for highly efficient computing scenarios. RRAM arrays enabled the acceleration of neural networks for artificial intelligence and the creation of In-Memory Computing circuits. However, the arrays are affected by several issues materializing in conductance variations that might cause severe performance degradation in those applications. Among those, one is related to the drift of the low conductance states appearing immediately at the end of program and verify algorithms that are fundamental for an accurate Multi-level conductance operation. In this work, we tackle the issue by developing an Incremental Reset and Verify technique showing enhanced variability and reliability features compared with a traditional refresh-based approach. KW - RRAM KW - resistive switching KW - neural network Y1 - 2021 SN - 978-1-6654-1794-5 SN - 978-1-6654-1795-2 U6 - https://doi.org/10.1109/IIRW53245.2021.9635613 SN - 2374-8036 PB - Institute of Electrical and Electronics Engineers (IEEE) ER - TY - GEN A1 - Milo, Valerio A1 - Anzalone, Francesco A1 - Zambelli, Cristian A1 - Perez, Eduardo A1 - Mahadevaiah, Mamathamba Kalishettyhalli A1 - Ossorio, Óscar G. A1 - Olivo, Piero A1 - Wenger, Christian A1 - Ielmini, Daniele T1 - Optimized programming algorithms for multilevel RRAM in hardware neural networks T2 - IEEE International Reliability Physics Symposium (IRPS), 2021 N2 - A key requirement for RRAM in neural network accelerators with a large number of synaptic parameters is the multilevel programming. This is hindered by resistance imprecision due to cycle-to-cycle and device-to-device variations. Here, we compare two multilevel programming algorithms to minimize resistance variations in a 4-kbit array of HfO 2 RRAM. We show that gate-based algorithms have the highest reliability. The optimized scheme is used to implement a neural network with 9-level weights, achieving 91.5% (vs. software 93.27%) in MNIST recognition. KW - RRAM KW - Multilevel switching KW - neural network KW - memristive switching Y1 - 2021 SN - 978-1-7281-6894-4 U6 - https://doi.org/10.1109/IRPS46558.2021.9405119 SN - 1938-1891 ER - TY - GEN A1 - Dirkmann, Sven A1 - Kaiser, Jan A1 - Wenger, Christian A1 - Mussenbrock, Thomas T1 - Filament Growth and Resistive Switching in Hafnium Oxide Memristive Devices T2 - Plasma Sources Science and Technology Y1 - 2018 U6 - https://doi.org/10.1021/acsami.7b19836 SN - 1361-6595 SN - 0963-0252 VL - 10 IS - 17 SP - 14857 EP - 14868 ER - TY - GEN A1 - Strobel, Carsten A1 - Alvarado Chavarin, Carlos A1 - Völkel, Sandra A1 - Jahn, Andreas A1 - Hiess, Andre A1 - Knaut, Martin A1 - Albert, Matthias A1 - Wenger, Christian A1 - Steinke, Olaff A1 - Stephan, Ulf A1 - Röhlecke, Sören A1 - Mikolajick, Thomas T1 - Enhanced Electrical Properties of Optimized Vertical Graphene-Base Hot Electron Transistors T2 - ACS Applied Electronic Materials N2 - The arrival of high-mobility two-dimensional materials like graphene leads to the renaissance of former vertical semiconductor–metal–semiconductor (SMS) hot electron transistors. Because of the monolayer thickness of graphene, improved SMS transistors with a semimetallic graphene-base electrode are now feasible for high-frequency applications. In this study we report about a device that consists of amorphous silicon, graphene, and crystalline silicon. For the first time, this device is fabricated by a four-mask lithography process which leads to significant improvements in the device performance. A strongly increased common-emitter current gain of 2% could be achieved while the on–off ratio improved to 1.6 × 105, which is already higher than predicted theoretically. This could be mainly attributed to better interface characteristics and decreased lateral dimensions of the devices. A cutoff frequency of approximately 26 MHz could be forecasted based on the DC measurements of the device. KW - Graphene KW - Transistor Y1 - 2023 U6 - https://doi.org/10.1021/acsaelm.2c01725 SN - 2637-6113 VL - 5 IS - 3 SP - 1670 EP - 1675 ER - TY - GEN A1 - Strobel, Carsten A1 - Alvarado Chavarin, Carlos A1 - Richter, Karola A1 - Knaut, Martin A1 - Reif, Johanna A1 - Völkel, Sandra A1 - Jahn, Andreas A1 - Albert, Matthias A1 - Wenger, Christian A1 - Kirchner, Robert A1 - Bartha, Johann Wolfgang A1 - Mikolajick, Thomas T1 - Novel Graphene Adjustable-Barrier Transistor with Ultra-High Current Gain T2 - ACS Applied Materials & Interfaces N2 - A graphene-based three terminal barristor device was proposed to overcome the low on/off ratios and insufficient current saturation of conventional graphene field effect transistors. In this study, we fabricated and analyzed a novel graphene-based transistor, which resembles the structure of the barristor but uses a different operating condition. This new device, termed graphene adjustable-barriers transistor (GABT), utilizes a semiconductor-based gate rather than a metal−insulator gate structure to modulate the device currents. The key feature of the device is the two graphene-semiconductor Schottky barriers with different heights that are controlled simultaneously by the gate voltage. Due to the asymmetry of the barriers, the drain current exceeds the gate current by several orders of magnitude. Thus, the GABT can be considered an amplifier with an alterable current gain. In this work, a silicon−graphene−germanium GABT with an ultra-high current gain (ID/IG up to 8 × 106) was fabricated, and the device functionality was demonstrated. Additionally, a capacitance model is applied to predict the theoretical device performance resulting in an on−off ratio above 106, a swing of 87 mV/dec, and a drivecurrent of about 1 × 106 A/cm2. KW - Graphene KW - Transistor Y1 - 2022 U6 - https://doi.org/10.1021/acsami.2c10634 SN - 1944-8244 SN - 1944-8252 VL - 14 IS - 34 SP - 39249 EP - 39254 ER - TY - GEN A1 - Mahmoodinezhad, Ali A1 - Morales, Carlos A1 - Naumann, Franziska A1 - Plate, Paul A1 - Meyer, Robert A1 - Janowitz, Christoph A1 - Henkel, Karsten A1 - Kot, Małgorzata A1 - Zöllner, Marvin Hartwig A1 - Wenger, Christian A1 - Flege, Jan Ingo T1 - Low-temperature atomic layer deposition of indium oxide thin films using trimethylindium and oxygen plasma T2 - Journal of Vacuum Science and Technology A N2 - Indium oxide (InxOy) thin films were deposited by plasma-enhanced atomic layer deposition (PEALD) using trimethylindium and oxygen plasma in a low-temperature range of 80–200 °C. The optical properties, chemical composition, crystallographic structure, and electrical characteristics of these layers were investigated by spectroscopic ellipsometry (SE), x-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD), as well as current-voltage and capacitance-voltage measurements. The SE results yielded a nearly constant growth rate of 0.56 Å per cycle and a thickness inhomogeneity of ≤1.2% across 4-in. substrates in the temperature range of 100–150 °C. The refractive index (at 632.8 nm) was found to be 2.07 for the films deposited at 150 °C. The PEALD-InxOy layers exhibit a direct (3.3 ± 0.2 eV) and an indirect (2.8 ± 0.1 eV) bandgap with an uptrend for both with increasing substrate temperature. Based on XPS characterization, all InxOy samples are free of carbon impurities and show a temperature-dependent off-stoichiometry indicating oxygen vacancies. XRD diffraction patterns demonstrate an onset of crystallization at 150 °C. Consistent with the optical, XPS, and XRD data, the films deposited at ≥150 °C possess higher electrical conductivity. Our findings prove that a low-temperature PEALD process of InxOy is feasible and promising for a high-quality thin-film deposition without chemical impurities on thermally fragile substrates. KW - Indium oxide KW - Plasma-enhanced atomic layer deposition KW - X-ray photoelectron spectroscopy KW - Ellipsometry KW - X-ray diffraction KW - Electrical properties Y1 - 2021 U6 - https://doi.org/10.1116/6.0001375 SN - 0734-2101 SN - 1520-8559 VL - 39 IS - 6 ER - TY - GEN A1 - Janowitz, Christoph A1 - Mahmoodinezhad, Ali A1 - Kot, Małgorzata A1 - Morales, Carlos A1 - Naumann, Franziska A1 - Plate, Paul A1 - Zöllner, Marvin Hartwig A1 - Bärwolf, Florian A1 - Stolarek, David A1 - Wenger, Christian A1 - Henkel, Karsten A1 - Flege, Jan Ingo T1 - Toward controlling the Al2O3/ZnO interface properties by in situ ALD preparation T2 - Dalton Transactions N2 - An Al2O3/ZnO heterojunction was grown on a Si single crystal substrate by subsequent thermal and plasma-assisted atomic layer deposition (ALD) in situ. The band offsets of the heterointerface were then studied by consecutive removal of the layers by argon sputtering, followed by in situ X-ray photoelectron spectroscopy. The valence band maximum and conduction band minimum of Al2O3 are found to be 1.1 eV below and 2.3 eV above those of ZnO, resulting in a type-I staggered heterojunction. An apparent reduction of ZnO to elemental Zn in the interface region was detected in the Zn 2p core level and Zn L3MM Auger spectra. This suggests an interface formation different from previous models. The reduction of ZnO to Zn in the interface region accompanied by the creation of oxygen vacancies in ZnO results in an upward band bending at the interface. Therefore, this study suggests that interfacial properties such as the band bending as well as the valence and conduction band offsets should be in situ controllable to a certain extent by careful selection of the process parameters. KW - ALD heterojunction KW - band alignement KW - ZnO KW - Al2O3 KW - interface properties Y1 - 2022 U6 - https://doi.org/10.1039/D1DT04008A SN - 1477-9234 SN - 1477-9226 VL - 51 SP - 9291 EP - 9301 ER - TY - GEN A1 - Fritscher, Markus A1 - Knödtel, Johannes A1 - Mallah, Maen A1 - Pechmann, Stefan A1 - Perez-Bosch Quesada, Emilio A1 - Rizzi, Tommaso A1 - Wenger, Christian A1 - Reichenbach, Marc T1 - Mitigating the Effects of RRAM Process Variation on the Accuracy of Artifical Neural Networks T2 - Embedded Computer Systems: Architectures, Modeling, and Simulation. SAMOS 2021. Lecture Notes in Computer Science N2 - Weight storage is a key challenge in the efficient implementation of artificial neural networks. Novel memory technologies such as RRAM are able to greatly improve density and introduce non-volatility and multibit capabilities to this component of ANN accelerators. The usage of RRAM in this domain comes with downsides, mainly caused by cycle-to-cycle and device-to-device variability leading to erroneous readouts, greatly affecting digital systems. ANNs have the ability to compensate for this by their inherent redundancy and usually exhibit a gradual deterioration in the accuracy of the task at hand. This means, that slight error rates can be acceptable for weight storage in an ANN accelerator. In this work we link device-to-device variability to the accuracy of an ANN for such an accelerator. From this study, we can estimate how strongly a certain net is affected by a certain device parameter variability. This methodology is then used to present three mitigation strategies and to evaluate how they affect the reaction of the network to variability: a) Dropout Layers b) Fault-Aware Training c) Redundancy. These mitigations are then evaluated by their ability to improve accuracy and to lower hardware overhead by providing data for a real-word example. We improved this network’s resilience in such a way that it could tolerate double the variation in one of the device parameters (standard deviation of the oxide thickness can be 0.4 nm instead of 0.2 nm while maintaining sufficient accuracy.) KW - RRAM KW - memristive device KW - neural network Y1 - 2022 SN - 978-3-031-04579-0 SN - 978-3-031-04580-6 U6 - https://doi.org/10.1007/978-3-031-04580-6_27 SN - 0302-9743 SN - 1611-3349 SP - 401 EP - 417 PB - Springer ER -