Device-Algorithm Co-Optimization for an On-Chip Trainable Capacitor-Based Synaptic Device with IGZO TFT and Retention-Centric Tiki-Taka Algorithm.

Abstracta-IGZO TFT is a promising candidate device for an alternative to poly-Si TFTs or a-Si TFTs, because they provide better uniformity in terms of their important device parameters, including the threshold voltage and mobility due to their amorphous phase, and a high mobility (>10 cm2/Vs) is attainable with these devices even in the amorphous phase. Recently, a-IGZO TFTs have been extensively studied by various groups. However, there is little report on interface and bulk effect on device performances and reliability as separately. For investigating the interface and bulk effect, we fabricated two a-IGZO thin film transistors with different channel deposition conditions, RF and DC magnetron sputtering. Specific conditions of RF and DC sputtering are described as follows; magnetron power density of 1.4 W/cm2/2.0 W/cm2 in Ar/O2 gas ratio of (65/35)/(72/28), and the entire gas pressure was 5.0 mTorr and 3.4 mTorr, respectively.In order to characterize the channel quality, C-V curve was measured with various frequencies of (10KHz˜1MHz). RF sputtered channel has higher frequency dependency compared to DC sputtered channel. It means that RF sputtered channel has higher bulk traps in channel compared to DC sputtered channel.Device performance was characterized through the ID-VG measurement. Electrical parameters of RF and DC sputtered devices are VT=3.5/2.7V, on-off ratio=105/08, SS=2/0.4 V/decade, and uFE= 5/11 cm2/V-s, respectively. It is thus clear that the device performance of DC sputtered device is more superior to RF sputtered device. Therefore, it can be said that the poor device performance of RF device is ascribed to insufficient channel quality, as mentioned in C-V curve.For reliability study, we measured PBTI and ID-VG hysteresis with normalized gate stress bias and high temperature hot chuck system. Through the unchanged field effect mobility during the stress and relaxation time, and nearly recovered VT and subthreshold slope (SS) after long relaxation time, we were able to know that pre-existed trap was main factor of reliability degradation. Moreover, SS degradation during stress time is more severe in RF device than DC device. It is also proving that RF channel characteristic is worse than DC channel. In high temperature, leakage current increments of RF device were more severe than DC device. This also indicates that bulk traps of RF device in channel region are larger than that of DC device. VT shift of DC sputtered device for PBT stress and hysteresis was higher than that of RF sputtered device. As well known, PBTI is closely related to insulator bulk traps, which shows that channel deposition conditions affect insulator trap characteristics. In summary, device performance of a-IGZO deposited by DC sputtering is better than RF sputtering, which is because DC sputtering improves channel quality of a-IGZO. However, VT shift of DC sputtered device are worse than RF sputtering, which may be related with high magnetron power density.

Synaptic elements based on memory devices play an important role in boosting neuromorphic system performance. Here, we show two types of fab-friendly HfO2 material-based resistive memories categorized by configuration and an operating principle for a suitable analog synaptic device aimed at inference and training of neural networks. Since the inference task is mainly related to the number of states from a recognition accuracy perspective, we first demonstrate multilevel cell (MLC) properties of compact two-terminal resistive random-access memory (RRAM). The resistance state can be finely subdivided into an MLC by precisely controlling the evolution of conductive filament constructed by the local movement of oxygen vacancies. Specifically, we investigate how the thickness of the HfO2-switching layer is related to an MLC, which is understood by performing physics-based modeling in MATLAB from a microscopic view. Meanwhile, synaptic devices driven by an interfacial switching mechanism instead of local filamentary dynamics are preferred for training accelerated neuromorphic systems, where the analogous transition of each state ensures high accuracy. Thus, we introduce three-terminal electrochemical random-access memory that facilitates mobile ions across the entire HfO2 switching area uniformly, resulting in highly controllable and gradually tuned current proportional to the amount of migrated ions.

An efficient method of preparing a α‐IGZO TFT with better negative‐bias‐temperature‐stress (NBTS) stability is presented. When the α ‐IGZO TFT is used as the switch of a pixel, it suffers a long time NBTS. The NBTS of α ‐IGZO TFT would cause the Vth shift toward negative value, and thus increase the leakage current which leads to the pixel voltage drop when pixel is holding. In this work, some post‐IGZO plasma treatments methods are studied for the optimized NBTS stability process. with N2O plasma treatment being employed, the α ‐IGZO TFT shows excellent NBTS stability.

Complementary logic and memory circuits based on n-type indium gallium zinc oxide (IGZO) and p-type tin monoxide (SnO) thin-film transistors (TFTs) were demonstrated with low-voltage, hysteresis-free operation. Optimization of IGZO channel thickness precisely tuned the inverter switching point to near VDD/2, achieving a high voltage gain of 146.6 V/V at VDD = 3 V and ultra-low static power consumption in the nanowatt range. SU-8 passivation effectively suppressed bias-stress-induced degradation in both IGZO and SnO TFTs, enhancing long-term stability and reducing device variation. Using these optimized devices, a 3-stage ring oscillator exhibited stable oscillations, and 6T-SRAM cells achieved tunable static noise margins by adjusting transistor strength ratios. This work represents one of the first implementations of IGZO/SnO-based 6T-SRAM and demonstrates the potential of oxide semiconductor complementary circuits for low-power and reliable system integration, with promising future applicability to non-volatile memory and on-device artificial intelligence hardware.Graphical abstract

Tin oxide has been demonstrated as an ideal material for fabricating p-type and n-type thin film transistors (TFTs) for transparent CMOS type device fabrication. Both p and n-type conduction was observed in the thin films, prepared from metallic tin target by simply varying the oxygen flow rate during RF magnetron sputter deposition. Films deposited at room temperature were amorphous in nature, which after annealing at 200°C in air, crystallized to SnO and/or SnO2 phases. The TFTs fabricated on thermally oxidized silicon substrates showed high field effect mobility of 4.13 and 16 cm2/Vs with drain current on-off ratio 6 × 102 and 107 respectively for SnO p-type and SnO2 n-type TFTs. These are the highest values for p-type and n-type oxide TFTs fabricated from same source material.

Low voltage high mobility n-type thin film transistors (TFTs) based on sol-gel processed zinc oxide (ZnO) were fabricated using a high capacitance ion gel gate dielectric. The ion gel gated solution-processed ZnO TFTs were found to exhibit excellent electrical properties. TFT carrier mobilities were 13 cm2/V s, ON/OFF current ratios were 105, regardless of the sintering temperature used for the preparation of the ZnO thin films. Ion gel gated ZnO TFTs are successfully demonstrated on plastic substrates for the large area flexible electronics.

An investigation of drain pulse induced hot carrier degradation in n-type low temperature polycrystalline silicon thin film transistors

High-performance amorphous indium-gallium–zinc oxide thin-film transistors (IGZO TFTs) were demonstrated at ${\hbox{360}} ^{\circ}{\hbox{C}}$ with the IGZO channel and aluminium oxide (AlOx) gate dielectric stack that was deposited by ozone $({\hbox{O}}_{3})$ -assisted atmospheric pressure chemical vapor deposition (AP-CVD) using an ultrasonic atomized solution mist. The AlOx gate dielectric with a breakdown electric field of over 8 MV/cm and dielectric constant of 7.0 was obtained. In addition, the introduction of ${\hbox{O}}_{3}$ oxidant during the IGZO deposition decreases the carbon and hydrogen contamination in the film. Field effect mobility and the sub-threshold swing of the IGZO TFT with AP-deposited IGZO/AlOx stack were significantly improved to ${\hbox{7.5}}~{\hbox{cm}}^{2} / {\hbox{V}}{\hbox{s}}$ and 0.38 V/dec, respectively, by the ${\hbox{O}}_{3}$ oxidant introduced in the IGZO and AlOx depositions. The ${\hbox{O}}_{3}$ oxidant is very effective in improving the electrical properties of solution-processed oxide TFTs.

Photo-patterned oxide films produced using polymeric metal acrylate for low-voltage thin-film transistors

This paper presents, to the best of the authors' knowledge, the first complete integration of a Spiking Neural Network combining analog neurons and SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> -based resistive memory (RRAM) synapses. The implemented topology is a perceptron, and the circuit is aimed at performing MNIST digits classification. An existing framework was adapted for off-line learning and weight quantization, and the network was later converted into its spiking equivalent. The test chip, fabricated in 130 nm CMOS, shows a classification accuracy of 82%, with a 180 pJ energy dissipation per spike.

In this letter, we report on the resistive switching originating from the rupture/rejuvenation of single-crystalline Cu filaments in a nitrogen-doped porous carbon-based memristive device Cu/CN0.15/Pt. Cu filaments are confined in conical nanopores in CN0.15 thin films. Dislocations exist in the Cu filaments, resulting in obvious crystal lattice distortions. The Cu/CN0.15/Pt device shows outstanding high temperature retention performance for both ON and OFF states, indicating that it is promising for resistance memory applications. Furthermore, continuous RESET (ON-to-OFF switching) and SET (OFF-to-ON switching) processes could be realized indicating the adaptive learning ability of Cu/CN0.15/Pt, which has potential applications in synaptic devices.

The discovery of oxide electronics is of increasing importance today as one of the most promising new technologies and manufacturing processes for a variety of electronic and optoelectronic applications such as next-generation displays, batteries, solar cells, memory devices, and photodetectors[1]. The high potential use seen in oxide electronics is due primarily to their high carrier mobilities and their ability to be fabricated at low temperatures[2]. However, since the majority of oxide semiconductors are n-type oxides, current applications are limited to unipolar devices, eventually developing oxide-based bipolar devices such as p-n diodes and complementary metal-oxide semiconductors.We have contributed to a wide range of oxide semiconductors and their electronics and optoelectronic device applications. Particularly, we have demonstrated n-type oxide-based thin film transistors (TFT), integrating In2O3-based n-type oxide semiconductors from binary cation materials to ternary cation species including InZnO, InGaZnO (IGZO), and InAlZnO. We have suggested channel/metallization contact strategies to achieve stable and high TFT performance[3, 4], identified vacancy-based native defect doping mechanisms[5], suggested interfacial buffer layers to promote charge injection capability[6], and established the role of third cation species on the carrier generation and carrier transport[7]. More recently, we have reported facile manufacturing of p-type SnOx through reactive magnetron sputtering from a Sn metal target[8]. The fabricated p-SnOx was found to be devoid of metallic phase of Sn from x-ray photoelectron spectroscopy and demonstrated stable performance in a fully oxide-based p-n heterojunction together with n-InGaZnO. The oxide-based p-n junctions exhibited a high rectification ratio greater than 103 at ±3 V, a low saturation current of ~2x10-10, and a small turn-on voltage of -0.5 V.In this presentation, we review recent achievements and still remaining issues in transition metal oxide semiconductors and their device applications, in particular, bipolar applications including p-n heterostructures and complementary metal-oxide-semiconductor devices as well as single polarity devices such as TFTs and memristors. In addition, the fundamental mechanisms of carrier transport behaviors and doping mechanisms that govern the performance of these oxide-based devices will also be discussed.ACKNOWLEDGMENTThis work was supported by the U.S. National Science Foundation (NSF) Award No. ECCS-1931088. S.L. and H.W.S. acknowledge the support from the Improvement of Measurement Standards and Technology for Mechanical Metrology (Grant No. 20011028) by KRISS. K.N. was supported by Basic Science Research Program (NRF-2021R11A1A01051246) through the NRF Korea funded by the Ministry of Education.REFERENCES[1] K. Nomura et al., Nature, vol. 432, no. 7016, pp. 488-492, Nov 25 2004.[2] D. C. Paine et al., Thin Solid Films, vol. 516, no. 17, pp. 5894-5898, Jul 1 2008.[3] S. Lee et al., Journal of Applied Physics, vol. 109, no. 6, p. 063702, Mar 15 2011, Art. no. 063702.[4] S. Lee et al., Applied Physics Letters, vol. 104, no. 25, p. 252103, 2014.[5] S. Lee et al., Applied Physics Letters, vol. 102, no. 5, p. 052101, Feb 4 2013, Art. no. 052101.[6] M. Liu et al., ACS Applied Electronic Materials, vol. 3, no. 6, pp. 2703-2711, 2021/06/22 2021.[7] A. Reed et al., Journal of Materials Chemistry C, 10.1039/D0TC02655G vol. 8, no. 39, pp. 13798-13810, 2020.[8] D. H. Lee et al., ACS Applied Materials & Interfaces, vol. 13, no. 46, pp. 55676-55686, 2021/11/24 2021.

Improvement of a reactive metal layer (AlCu, Ti, or Ta) for the bipolar resistance switching (BRS) performance of HfOx based resistive memory (RM) with TiN as electrodes are studied in this work. After appropriate post metal annealing (PMA), the reactive metal layer with high oxygen content serves as an embedded resistor and modifies the insulator properties of theses stacked layers, which show stable repetitive switching through by the migration of oxygen ions in HfOx layer during operation. The Gibbs free energy for the oxidation of the reactive metal with respect to that of HfO2 dominates the optimal PMA temperature for the devices with stable BRS. Except for the reduction of forming voltage and leakage current, the AlCu layer with high resistance after PMA of 500 °C is beneficial for the devices with successive BRS and on/off ratio of 4. The forming voltage of the Ti devices seems insensitive on the PMA. Compared with the Ta device, the Ti/HfOx RM device after the PMA of 450 °C for 5 min exhibits a different current–voltage behavior during the first RESET voltage sweep and a higher resistance ratio (>40). These results are attributed to the higher affinity of oxygen in the Ti capping layer. The combination of HfOx with a reactive metal and an enough PMA shows great potential for future nonvolatile memory application.

The memristor (memory resistor) is the fourth passive element of electrical circuits having dynamic resistance with the ability to keep the last level of resistance even after the power supply is interrupted. This article presents a simplified mathematical function with the capability to define the threshold conditions for memristor operation and a new pattern to describe and modeling of the unwanted current leakage in the subthreshold situation for HP TIO2 memristor. These special features provide a more realistic scheme of TIO2 memristor behavior. Our proposed mathematical function is adaptive with the majority of previous prominent works around the ionic drift modeling of HP memristor and is easy to use in SPICE simulators so can be utilized in a wide range of designs and applications. To our best known this is the first research paper in which the issue of subthreshold current leakage modeling of the memristor is addressed.

A highly efficient and stable electron injection layer (EIL) for inverted organic light-emitting diodes (OLEDs) is developed. A 1 nm-thick Al is deposited between indium tin oxide cathode and commonly used Cs2CO3 EIL, which can significantly improve the stability. The Al may react with evaporated Cs2CO3 and form a much stabler Al-O-Cs complex, avoiding Cs oxidization by air according to X-ray photoemission spectroscopy measurement. When the Al is evaporated after Cs2CO3 layer, although such a Al-O-Cs complex also forms, the inferior electron injection at Al/4,7-diphenyl-1,10-phenanthroline interface leads to a joule heat-induced resistance that adversely affects the air stability of the device. It is expected that the developed Al/Cs2CO3 EIL promotes high efficiency and stable active-matrix OLEDs based on n-type thin film transistor.