@misc{PrueferWengerBieretal.,
author = {Pr{\"u}fer, Mareike and Wenger, Christian and Bier, Frank F. and Laux, Eva-Maria and H{\"o}lzel, Ralph},
title = {Activity of AC electrokinetically immobilized horseradish peroxidase},
series = {Electrophoresis},
volume = {43},
journal = {Electrophoresis},
number = {18-19},
issn = {1522-2683},
doi = {10.1002/elps.202200073},
pages = {1920 -- 1933},
abstract = {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.},
language = {en}
}
@misc{FranckDabrowskiSchubertetal.,
author = {Franck, Max and Dabrowski, Jaroslaw and Schubert, Markus Andreas and Wenger, Christian and Lukosius, Mindaugas},
title = {Towards the Growth of Hexagonal Boron Nitride on Ge(001)/Si Substrates by Chemical Vapor Deposition},
series = {Nanomaterials},
volume = {12},
journal = {Nanomaterials},
number = {19},
issn = {2079-4991},
doi = {10.3390/nano12193260},
abstract = {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},
language = {en}
}
@misc{GlukhovLepriMiloetal.,
author = {Glukhov, Artem and Lepri, Nicola and Milo, Valerio and Baroni, Andrea and Zambelli, Cristian and Olivo, Piero and P{\´e}rez, Eduardo and Wenger, Christian and Ielmini, Daniele},
title = {End-to-end modeling of variability-aware neural networks based on resistive-switching memory arrays},
series = {Proc. 30th IFIP/IEEE International Conference on Very Large Scale Integration (VLSI-SoC 2022)},
journal = {Proc. 30th IFIP/IEEE International Conference on Very Large Scale Integration (VLSI-SoC 2022)},
doi = {10.1109/VLSI-SoC54400.2022.9939653},
pages = {1 -- 5},
abstract = {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.},
language = {en}
}
@misc{WenBaroniPerezetal.,
author = {Wen, Jianan and Baroni, Andrea and P{\´e}rez, Eduardo and Ulbricht, Markus and Wenger, Christian and Krstic, Milos},
title = {Evaluating Read Disturb Effect on RRAM based AI Accelerator with Multilevel States and Input Voltages},
series = {2022 IEEE International Symposium on Defect and Fault Tolerance in VLSI and Nanotechnology Systems (DFT)},
journal = {2022 IEEE International Symposium on Defect and Fault Tolerance in VLSI and Nanotechnology Systems (DFT)},
isbn = {978-1-6654-5938-9},
issn = {2765-933X},
doi = {10.1109/DFT56152.2022.9962345},
pages = {1 -- 6},
abstract = {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.},
language = {en}
}
@misc{PerezMaldonadoPerezBoschQuesadaetal.,
author = {P{\´e}rez, Eduardo and Maldonado, David and Perez-Bosch Quesada, Emilio and Mahadevaiah, Mamathamba Kalishettyhalli and Jimenez-Molinos, Francisco and Wenger, Christian},
title = {Parameter Extraction Methods for Assessing Device-to-Device and Cycle-to-Cycle Variability of Memristive Devices at Wafer Scale},
series = {IEEE Transactions on Electron Devices},
volume = {70},
journal = {IEEE Transactions on Electron Devices},
number = {1},
issn = {0018-9383},
doi = {10.1109/TED.2022.3224886},
pages = {360 -- 365},
abstract = {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.},
language = {en}
}
@misc{NitschRatzkePozarowskaetal.,
author = {Nitsch, Paul-G. and Ratzke, Markus and Pozarowska, Emilia and Flege, Jan Ingo and Alvarado Chavarin, Carlos and Wenger, Christian and Fischer, Inga Anita},
title = {Deposition of reduced ceria thin films by reactive magnetron sputtering for the development of a resistive gas sensor},
series = {Verhandlungen der DPG, Berlin 2024},
journal = {Verhandlungen der DPG, Berlin 2024},
publisher = {Deutsche Physikalische Gesellschaft},
address = {Bad Honnef},
issn = {0420-0195},
abstract = {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.},
language = {en}
}
@misc{StrobelAlvaradoChavarinKnautetal.,
author = {Strobel, Carsten and Alvarado Chavarin, Carlos and Knaut, Martin and V{\"o}lkel, Sandra and Albert, Matthias and Hiess, Andre and Max, Benjamin and Wenger, Christian and Kirchner, Robert and Mikolajick, Thomas},
title = {High Gain Graphene Based Hot Electron Transistor with Record High Saturated Output Current Density},
series = {Advanced Electronic Materials},
volume = {10},
journal = {Advanced Electronic Materials},
number = {2},
issn = {2199-160X},
doi = {10.1002/aelm.202300624},
abstract = {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.},
language = {en}
}
@misc{PechmannPerezWengeretal.,
author = {Pechmann, Stefan and P{\´e}rez, Eduardo and Wenger, Christian and Hagelauer, Amelie},
title = {A current mirror Based read circuit design with multi-level capability for resistive switching deviceb},
series = {2024 International Conference on Electronics, Information, and Communication (ICEIC)},
journal = {2024 International Conference on Electronics, Information, and Communication (ICEIC)},
publisher = {Institute of Electrical and Electronics Engineers (IEEE)},
isbn = {979-8-3503-7188-8},
issn = {2767-7699},
doi = {10.1109/ICEIC61013.2024.10457188},
pages = {4},
abstract = {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.},
language = {en}
}
@misc{NikiruyPerezBaronietal.,
author = {Nikiruy, Kristina and P{\´e}rez, Eduardo and Baroni, Andrea and Dorai Swamy Reddy, Keerthi and Pechmann, Stefan and Wenger, Christian and Ziegler, Martin},
title = {Blooming and pruning: learning from mistakes with memristive synapses},
series = {Scientific Reports},
volume = {14},
journal = {Scientific Reports},
number = {1},
issn = {2045-2322},
doi = {10.1038/s41598-024-57660-4},
abstract = {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.},
language = {en}
}
@inproceedings{WenVargasZhuetal.,
author = {Wen, Jianan and Vargas, Fabian Luis and Zhu, Fukun and Reiser, Daniel and Baroni, Andrea and Fritscher, Markus and P{\´e}rez, Eduardo and Reichenbach, Marc and Wenger, Christian and Krstic, Milos},
title = {Cycle-Accurate FPGA Emulation of RRAM Crossbar Array: Efficient Device and Variability Modeling with Energy Consumption Assessment},
series = {2024 IEEE 25th Latin American Test Symposium (LATS)},
booktitle = {2024 IEEE 25th Latin American Test Symposium (LATS)},
publisher = {IEEE},
doi = {10.1109/LATS62223.2024.10534601},
pages = {6},
abstract = {Emerging device technologies such as resistive RAM (RRAM) are increasingly recognized in enhancing system performance, particularly in applications demanding extensive vector-matrix multiplications (VMMs) with high parallelism. However, a significant limitation in current electronics design automation (EDA) tools is their lack of support for rapid prototyping, design space exploration, and the integration of inherent process-dependent device variability into system-level simulations, which is essential for assessing system reliability. To address this gap, we introduce a field-programmable gate array (FPGA) based emulation approach for RRAM crossbars featuring cycle-accurate emulations in real time without relying on complex device models. Our approach is based on pre-generated look-up tables (LUTs) to accurately represent the RRAM device behavior. To efficiently model the device variability at the system level, we propose using the multivariate kernel density estimation (KDE) method to augment the measured RRAM data. The proposed emulator allows precise latency determination for matrix mapping and computation operations. Meanwhile, by coupling with the NeuroSim framework, the corresponding energy consumption can be estimated. In addition to facilitating a range of in-depth system assessments, experimental results suggest a remarkable reduction of emulation time compared to the classic behavioral simulation.},
language = {en}
}
@misc{DoraiSwamyReddyPerezBaronietal.,
author = {Dorai Swamy Reddy, Keerthi and P{\´e}rez, Eduardo and Baroni, Andrea and Mahadevaiah, Mamathamba Kalishettyhalli and Marschmeyer, Steffen and Fraschke, Mirko and Lisker, Marco and Wenger, Christian and Mai, Andreas},
title = {Optimization of technology processes for enhanced CMOS-integrated 1T-1R RRAM device performance},
series = {The European Physical Journal B},
volume = {97},
journal = {The European Physical Journal B},
publisher = {Springer Science and Business Media LLC},
issn = {1434-6028},
doi = {10.1140/epjb/s10051-024-00821-1},
pages = {9},
abstract = {Implementing artificial synapses that emulate the synaptic behavior observed in the brain is one of the most critical requirements for neuromorphic computing. Resistive random-access memories (RRAM) have been proposed as a candidate for artificial synaptic devices. For this applicability, RRAM device performance depends on the technology used to fabricate the metal-insulator-metal (MIM) stack and the technology chosen for the selector device. To analyze these dependencies, the integrated RRAM devices in a 4k-bit array are studied on a 200 mm wafer scale in this work. The RRAM devices are integrated into two different CMOS transistor technologies of IHP, namely 250 nm and 130 nm and the devices are compared in terms of their pristine state current. The devices in 130 nm technology have shown lower number of high pristine state current devices per die in comparison to the 250 nm technology. For the 130 nm technology, the forming voltage is reduced due to the decrease of HfO2 dielectric thickness from 8 nm to 5 nm. Additionally, 5\% Al-doped 4 nm HfO2 dielectric displayed a similar reduction in forming voltage and a lower variation in the values. Finally, the multi-level switching between the dielectric layers in 250 nm and 130 nm technologies are compared, where 130 nm showed a more significant number of conductance levels of seven compared to only four levels observed in 250 nm technology.},
language = {en}
}
@misc{JiaPechmannMarkusetal.,
author = {Jia, Ruolan and Pechmann, Stefan and Markus, Fritscher and Wenger, Christian and Zhang, Lei and Hagelauer, Amelie},
title = {Soft-Error Analysis of RRAM 1T1R Compute-In-Memory Core for Artificial Neural Networks},
series = {2024 39th Conference on Design of Circuits and Integrated Systems (DCIS)},
journal = {2024 39th Conference on Design of Circuits and Integrated Systems (DCIS)},
publisher = {IEEE},
doi = {10.1109/DCIS62603.2024.10769203},
pages = {1 -- 5},
abstract = {This work analyses SEU-induced soft-errors in analog compute-in-memory cores using resistive random-access memory (RRAM) for artificial neural networks, where their bitcells utilize one-transistor-one-RRAM (1T1R) structure. This is modeled by combining the Stanford-PKU RRAM Model and the model of the radiation-induced photocurrent in access transistors. As results, this work derives the maximal RRAM crossbar size without occurring any logic flip and indicates the requirements for RRAM technology to achieve a SEU-resilient 1T1R compute-in memory cores.},
language = {en}
}
@misc{PerezBoschQuesadaMistroniJiaetal.,
author = {Perez-Bosch Quesada, Emilio and Mistroni, Alberto and Jia, Ruolan and Dorai Swamy Reddy, Keerthi and Reichmann, Felix and Castan, Helena and Due{\~n}as, Salvador and Wenger, Christian and Perez, Eduardo},
title = {Forming and resistive switching of HfO₂-based RRAM devices at cryogenic temperature},
series = {IEEE Electron Device Letters},
volume = {45},
journal = {IEEE Electron Device Letters},
number = {12},
publisher = {Institute of Electrical and Electronics Engineers (IEEE)},
issn = {0741-3106},
doi = {10.1109/LED.2024.3485873},
pages = {2391 -- 2394},
abstract = {Reliable data storage technologies able to operate at cryogenic temperatures are critical to implement scalable quantum computers and develop deep-space exploration systems, among other applications. Their scarce availability is pushing towards the development of emerging memories that can perform such storage in a non-volatile fashion. Resistive Random-Access Memories (RRAM) have demonstrated their switching capabilities down to 4K. However, their operability at lower temperatures still remain as a challenge. In this work, we demonstrate for the first time the forming and resistive switching capabilities of CMOS-compatible RRAM devices at 1.4K. The HfO2-based devices are deployed following an array of 1-transistor-1-resistor (1T1R) cells. Their switching performance at 1.4K was also tested in the multilevel-cell (MLC) approach, storing up to 4 resistance levels per cell.},
language = {en}
}
@misc{WeisshauptSuergersBloosetal.,
author = {Weißhaupt, David and S{\"u}rgers, Christoph and Bloos, Dominik and Funk, Hannes Simon and Oehme, Michael and Fischer, Gerda and Schubert, Markus Andreas and Wenger, Christian and van Slageren, Joris and Fischer, Inga Anita and Schulze, J{\"o}rg},
title = {Lateral Mn5Ge3 spin-valve in contact with a high-mobility Ge two-dimensional hole gas},
series = {Semiconductor Science and Technology},
volume = {39},
journal = {Semiconductor Science and Technology},
number = {12},
publisher = {IOP Publishing},
issn = {0268-1242},
doi = {10.1088/1361-6641/ad8d06},
pages = {1 -- 10},
abstract = {Abstract Ge two-dimensional hole gases (2DHG) in strained modulation-doped quantum-wells represent a promising material platform for future spintronic applications due to their excellent spin transport properties and the theoretical possibility of efficient spin manipulation. Due to the continuous development of epitaxial growth recipes extreme high hole mobilities and low effective masses can be achieved, promising an efficient spin transport. Furthermore, the Ge 2DHG can be integrated in the well-established industrial complementary metal-oxide-semiconductor (CMOS) devices technology. However, efficient electrical spin injection into a Ge 2DHG—an essential prerequisite for the realization of spintronic devices—has not yet been demonstrated. In this work, we report the fabrication and low-temperature magnetoresistance (MR) measurements of a laterally structured Mn5Ge3/Ge 2DHG/ Mn5Ge3 device. The ferromagnetic Mn5Ge3 contacts are grown directly into the Ge quantum well by means of an interdiffusion process with a spacing of approximately 130 nm, forming a direct electrical contact between the ferromagnetic metal and the Ge 2DHG. Here, we report for the first time a clear MR signal for temperatures below 13 K possibly arising from successful spin injection into the high mobility Ge 2DHG. The results represent a step forward toward the realization of CMOS compatible spintronic devices based on a 2DHG.},
language = {en}
}
@misc{CapistaLukoseMajnoonetal.,
author = {Capista, Daniele and Lukose, Rasuole and Majnoon, Farnaz and Lisker, Marco and Wenger, Christian and Lukosius, Mindaugas},
title = {Optimization of the metal deposition process for the accurate estimation of Low Metal-Graphene Contact-Resistance},
series = {47th MIPRO ICT and Electronics Convention (MIPRO), 20-24 May 2024, Opatija, Croatia},
journal = {47th MIPRO ICT and Electronics Convention (MIPRO), 20-24 May 2024, Opatija, Croatia},
isbn = {979-8-3503-8250-1},
issn = {2623-8764},
doi = {10.1109/MIPRO60963.2024.10569895},
pages = {5},
language = {en}
}