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 -