Amorphous Metal Oxide Semiconductors Research Articles

Improving the photoswitching performance of a transistor with amorphous metal oxide semiconductor thin film by a gradient annealing approach

Metal oxides are attracting attention as electronic mate rials in research and industry. Thin films of amorphous indium gallium zinc oxide (a-IGZO) exhibit low absorbance in the visible spectrum, making them ideal components in transparent electronics. To widen the scope of use for thin film transistor (TFT) devices based on a-IGZO in on-chip sensing applications, photoresponsive behavior has been achieved by proper engineering of the active layers by either introducing a photosensitive top layer or using a method to generate localized states inside the band gap. In this paper, we propose a bilayer structured with the use of thermal annealing of a-IGZO film at different temperatures. Thermal annealing has been shown to improve the electrical performance of the TFT devices because of the improved film quality but negatively affects the photoresponsivity by removing tarp sites that play an important role in both charge generation and photomultiplication via the photogating effect. Therefore, here we propose an a-IGZO film with a high temperature-annealed bottom layer and pristine top layer. The bottom layer plays a vital role in the charge transport behavior, resulting in a low threshold voltage and subthreshold swing similar to the device with a fully annealed film, while the photoresponse of the device is driven by the higher density of gap states in the pristine top layer. This proposed method is advantageous to previously published procedures due to the simplicity of using no additional materials and complex steps to introduce trap sites into the photoactive layer, but only differential annealing temperature.

Tailoring the Ni-O Microenvironment in Amorphous-Dominated Highly Active and Stable Zn/NiO for Hydrogen Sulfide Detection.

Amorphous metal oxide semiconductor (MOS) materials are endowed with great promise to modulate electronic structures for gas-sensing performance improvement. However, the elevated-temperature requirement of gas sensors severely impedes the application of amorphous materials due to their low thermal stability. Here, a cationic-assisted strategy to tailor the Ni-O microenvironment in an amorphous-dominated Zn/NiO heterogeneous structure with high thermal stability was developed. It was found that 6 mol % Zn incorporation into amorphous NiO can effectively preserve the amorphous-dominated NiO phase even at high temperature. After calcination, the amorphous oxide can only be converted to crystals partly thus leading to the formation of amorphous/crystalline compounds, and the content of the amorphous phase can be adjusted by changing the calcination temperature. This amorphous/crystalline configuration can induce more electron transfer from Ni to Zn species, leading to the formation of active Niδ+ (δ>2) centers. Ex situ XPS and in situ Raman spectroscopy studies proved that the generated Niδ+ species pronouncedly promote the electron transfer during the H2S adsorption process. The amorphous/crystalline-6 mol % Zn/NiO sensor exhibits exceptional hydrogen sulfide response (2 ppm, 3.23), outstanding repeatability (as long as 5 weeks), and low limit of detection (as low as 50 ppb), surpassing most reported nickel-based gas sensors such as the crystal nickel oxide prepared in this work. The response and detection limit of the latter is only (2 ppm, 1.89) and (0.05 ppm) respectively. Our work thus opens up more opportunities for fundamental understanding and modulating of highly active amorphous sensing materials.

Thin-film memristor using an amorphous metal–oxide semiconductor with a gradient composition of conducting components

A thin-film memristor using an amorphous metal–oxide semiconductor (AOS) with a gradient composition of conducting components has been developed, which is another way to achieve memristive properties. The advantages are that conductivity distribution is already obtained as fabricated without forming operation, and an analog characteristic is obtained by optimizing the component composition in AOS. As the binary characteristic, the set operation induces the transition from a low conductance state to a high conductance state, whereas the reset operation does vice-versa. The switching ratio (SR) is high, 448. As the analog characteristic, the SR becomes greater rapidly as the V set increases, namely, the dynamic range is outstanding.

Role of interface engineering in amorphous InGaZnO ETL for non-fullerene organic solar cells

Amorphous metal-oxide semiconductors have been developed as prospective substitutes for organic and silicon compounds, and their applications have been expanded due to their superior mobility in amorphous phase. As a result, this study demonstrated a facile approach to amend the interface quality by oxygen vacancy engineering. Here, we compared the performance of optimized oxygen-deficient (Od) and oxygen-rich (Or) amorphous indium–gallium–zinc oxide (a-IGZO) electron transport layers (ETL) for non-fullerene organic solar cells (OSCs). The ETL was fabricated using rf magnetron sputtering by changing oxygen contents. The power conversion efficiency (PCE) of Or device is 5.1 %, which was boosted to 6.6 % for Od device. The device with Od a-IGZO ETL outperforms the Or device, as the oxygen vacancies in Od device aid as electron donors, which deliver free electron carriers to IGZO film. These free electron carriers promote electron concentration, device mobility and deteriorate the resistivity, which facilitate charge transport and collection towards the electrode. Furthermore, devices improved their stability, as device with Od a-IGZO ETL retained almost 80 % of its initial PCE in ambient conditions. Consequently, interfacial engineering has played a crucial role in bringing OSC towards commercialization as it has substantial influence on charge collection and transport properties in devices.

Low-Voltage Operated High DC Gain Amplification Stage Based on Large-Area Manufacturable Amorphous Oxide Semiconductor Thin-Film Transistor

The industry-standard amorphous metal–oxide–semiconductor (AOS) thin-film transistor (TFT) technology is demonstrated for making low-voltage high intrinsic gain devices. It is revealed by the technology computer-aided design (TCAD) simulation that, without need of making Schottky barrier contacts, large output resistance and high intrinsic gain can be achieved in a subthreshold regime for AOS TFTs. It is further proved by the measurement results with the fabricated AOS TFT from a Gen-4.5 manufacturing line. A simple single-stage zero- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{V}_{\text{GS}}$</tex-math> </inline-formula> load amplifier is implemented as a proof of concept, achieving a voltage gain larger than 50 for weak signal detection at a supply voltage of 5 V.

Influence of metal capping thin film transistor with different Si concentration in ZnSnO

An amorphous metal-oxide semiconductor is emerging as a representative next-generation semiconductor material due to its high electric field mobility, excellent uniformity, and high transmittance in the visible region. The a-SZTO material shows high performance despite its In-free composition. In addition, Si acts as an excellent oxygen vacancy inhibitor to control its electrical properties and stability. Since Si has high binding energy with oxygen, the concentration of oxygen vacancies decreases as the composition of Si increases. As the Si composition increased due to the reduced oxygen vacancies, the mobility, which is an electrical characteristic, decreased from 27.90 cm2/Vs to 17.37 cm2/Vs, and the on current decreased from 7.0 × 10-4 A to 3.9 × 10-4 A, respectively. Amorphous metal-oxide limits improving its electrical properties due to oxygen vacancies by doping. According to the Si concentrations, a metal capping structure was applied to the a-SZTO thin-film transistor. In the metal capping structure, an additional metal rod is inserted between the source and drain electrodes which helps to improve the device characteristics with simple processing techniques. A systematic change was observed in the device by varying the length of the metal capping. The mobility from conventional to MC structures (40 μm) is improved from 27.90 to 86.25 cm2/Vs and 17.36 to 52.91 cm2/Vs for 0 and 1 wt% of Si concentrations, respectively. As for the stability characteristics for NBTS (Negative Bias Thermal Stress), it was confirmed that as the Si concentrations increased, the threshold voltage (Vth) shift decreased from 0.85 V to 0.71 V, and the stability characteristics improved. It has been confirmed that the stability characteristics of these unique channel characteristics (with different Si concentrations) are maintained even when MC TFT is applied. When an inverter logic circuit was manufactured, an excellent voltage gain of 7.47 was obtained using MC.

Ultrasensitive Near-Infrared InAs Colloidal Quantum Dot-ZnON Hybrid Phototransistor Based on a Gradated Band Structure.

Amorphous metal oxide semiconductor phototransistors (MOTPs) integrated with colloidal quantum dots (QDs) (QD-MOTPs) are promising infrared photodetectors owing to their high photoconductive gain, low off-current level, and high compatibility with pixel circuits. However, to date, the poor mobility of conventional MOTPs, such as indium gallium zinc oxide (IGZO), and the toxicity of lead (Pb)-based QDs, such as lead sulfide and lead selenide, has limited the commercial applications of QD-MOTPs. Herein, an ultrasensitive QD-MOTP fabricated by integrating a high-mobility zinc oxynitride (ZnON)-based MOTP and lead-free indium arsenide (InAs) QDs is demonstrated. A new gradated bandgap structure is introduced in the InAs QD layer that absorbs infrared light, which prevents carriers from moving backward and effectively reduces electron-hole recombination. Chemical, optical, and structural analyses confirm the movement of the photoexcited carriers in the graded band structure. The novel QD-MOTP exhibits an outstanding performance with a responsivity of 1.15 × 105 A W-1 and detectivity of 5.32 × 1016 Jones at a light power density of 2 µW cm-2 under illumination at 905nm.

High-speed hybrid complementary ring oscillators based on solution-processed organic and amorphous metal oxide semiconductors

Solution-processed single-crystal organic semiconductors (OSCs) and amorphous metal oxide semiconductors (MOSs) are promising for high-mobility p- and n-channel thin-film transistors (TFTs), respectively. Organic−inorganic hybrid complementary circuits hence have great potential to satisfy practical requirements. However, some chemical incompatibilities between OSCs and MOSs, such as heat and chemical resistance, make it difficult to rationally integrate TFTs based on solution-processed OSC and MOS onto the same substrates. Here, we report a rational integration method based on the solution-processed semiconductors by carefully managing the device configuration and the deposition and patterning techniques from a materials point of view. The balanced high performances as well as the uniform fabrication of the TFTs led to densely integrated five-stage ring oscillators with a short propagation delay of 1.3 µs per stage.

Wirelessly powered large-area electronics for the Internet of Things

Powering the increasing number of sensor nodes used in the Internet of Things creates a technological challenge. The economic and sustainability issues of battery-powered devices mean that wirelessly powered operation—combined with environmentally friendly circuit technologies—will be needed. Large-area electronics—which can be based on organic semiconductors, amorphous metal oxide semiconductors, semiconducting carbon nanotubes and two-dimensional semiconductors—could provide a solution. Here we examine the potential of large-area electronics technology in the development of sustainable, wirelessly powered Internet of Things sensor nodes. We provide a system-level analysis of wirelessly powered sensor nodes, identifying the constraints faced by such devices and highlighting promising architectures and design approaches. We then explore the use of large-area electronics technology in wirelessly powered Internet of Things sensor nodes, with a focus on low-power transistor circuits for digital processing and signal amplification, as well as high-speed diodes and printed antennas for data communication and radiofrequency energy harvesting.

(Edward G. Acheson Award) Exploration of Amorphous Thin Film Electronics

Thin films are critical elements in modern semiconductor devices. They are often prepared in the amorphous phase due to practical reasons, such as the reliability and manufacturability concerns. For example, the amorphous high-k gate dielectric is less prone to current leakage than the polycrystalline dielectric in the MOS device (1). The utilization of amorphous silicon (a-Si:H) or metal oxide semiconductor layer enables the commercial production of thin film transistor (TFT) arrays for flat panel displays (2). Requirements for amorphous thin films are related to the products. For advanced MOSFETs, the nanometer EOT gate dielectric is necessary (3). For LCD or OLED TVs or monitors, the fabrication process has to be low temperature, large area capability, and high throughput (4). In addition, the fabricated device has to be highly reliable, i.e., resistant to damages from subsequent process steps and environmental exposure.In this talk, examples on amorphous thin films conducted in my group will be given and discussed. The doped metal oxide high-k thin film, which has a crystallization temperature higher than that of the undoped film (5), will be examined with respect to fundamental material and electrical properties. Novel devices made from this kind of film, e.g., nanocrystals embedded nonvolatile memories (6) and nano-resistor solid state incandescent LEDs (SSI-LEDs) (7), will be shown and the principles will be deliberated. Separately, PECVD process condition affects the a-Si:H TFT performance as well as the uniformity of the large-area material properties (8), which can be explained with the generalized deposition-etching mechanism (9). Applications of a-Si:H TFTs in nonvolatile memories, e.g., using the floating-gate structure (10), and protein/DNA analysis, e.g., attached with the microchannel device (11), will also be examined.In order to achieve the best device performance with high reliability, both the bulk film and the interface properties of the amorphous thin film have to be tightly controlled, which requires the multidisciplinary approach. This is the early stage of the field. Many new and unique applications of the amorphous thin films can be expected in the near future. Y. Kuo, ECS Trans., 54(1), 273-281 (2013).Y. Kuo, Amorphous Silicon Thin Film Transistors, Kluwer, Norwell, MA, 2004.J. Yan, Y. Kuo, and J. Lu, Electrochem. Solid-State Lett., 10(7), H199-H202 (2007).Y. Kuo, ECS Interface, 22(1), 55-60 (2013).J.-Y. Tewg, Y. Kuo, and J. Lu, Electrochem. Solid-State Lett., 8(1), G27-G29 (2005).Y. Kuo, ECS Trans., 3(3), 253-263 (2006).Y. Kuo and C.-C. Lin, Appl. Phys. Letts., 102(3), 031117 (2013).Y. Kuo, J. Electrochem. Soc., 142, 186-190 (1995).Y. Kuo, Appl. Phys. Lett., 63(2), 144-146 (1993).Y. Kuo and H. Nominanda, Appl. Phys. Letts., 89, 173503 (2006).H. Lee and Y. Kuo, Electrochem. Solid-State Letts., 9, J21-J23 (2006).

Control of Hydrogen Concentration in Ingazno Thin Film Using Cryopumping System

Recently, amorphous metal-oxide semiconductors (AOSs) such as indium gallium zinc oxide (IGZO) have attracted great attention with their lower power consumption and higher mobility than amorphous silicon in the display field. However, the threshold voltage (Vth) shift of IGZO thin film transistor (TFT) caused by their poor reliability leads to the drop panel luminance. Therefore, improvement of IGZO TFT reliability is necessary, which is largely influenced by oxygen vacancy and hydrogen. In particular, hydrogen has shown different roles inside the IGZO active layer by hydrogen concentration. At lower concentration, the hydrogen passivation of oxygen deficiency region induces the improvement of initial electrical characteristics and reliability [2]. Meanwhile, Vth shift and degradation reliability are generated at higher concentration owing to the hydrogen related defect states [3]. Therefore, controlling excess hydrogen is necessary for reliability enhancement.In this work, IGZO thin film was fabricated by cryopumping system instead of a turbo molecular pump (TMP) for radio frequency sputtering to reduce hydrogen concentration. Cryopump is an adsorption type that enables excellent evacuation ability of hydrogen and moisture taking up most of the partial pressure in high vacuum. As a result, deposition of IGZO thin film with lower hydrogen impurity is available. The hydrogen concentration in the IGZO thin film using both cryopump and TMP was quantitatively analyzed by elastic recoil detection (ERD) analysis. Then, electrical characteristics of the self-aligned top-gate structure TFTs fabricated by both pumps were measured with bias stress conditions.To sum up, we showed the improved reliability of IGZO TFT by controlling excess hydrogen using cryopumping system. Fig.1. (a) Schematic of RF magnetron sputtering process with cryopump. (b) TOF-SIMS depth profiles of hydrogen concentration in IGZO film using TMP and cryopump Acknowledgment This work was supported by the Korea Evaluation Institute of Industrial Technology(KEIT) grant funded by the Korea government (MOTIE) (No. 2021-11-1283) References Chung, Ui-Jin, et al. "15‐1: Invited Paper: Manufacturing Technology of LTPO TFT." SID Symposium Digest of Technical Papers. Vol. 51. No. 1. 2020.Hanyu, Yuichiro, et al. "Hydrogen passivation of electron trap in amorphous In-Ga-Zn-O thin-film transistors." Applied Physics Letters 103.20 (2013): 202114.Mativenga, Mallory, et al. "Origin of light instability in amorphous IGZO thin-film transistors and its suppression." Scientific reports 11.1 (2021): 1-12 Figure 1

Probing the Efficacy of Large-Scale Nonporous IGZO for Visible-to-NIR Detection Capability: An Approach toward High-Performance Image Sensor Circuitry.

The technological ability to detect a wide spectrum range of illuminated visible-to-NIR is substantially improved for an amorphous metal oxide semiconductor, indium gallium zinc oxide (IGZO), without employing an additional photoabsorber. The fundamentally tuned morphology via structural engineering results in the creation of nanopores throughout the entire thickness of ∼30 nm. See-through nanopores have edge functionalization with vacancies, which leads to a large density of substates near the conduction band minima and valence band maxima. The presence of nanoring edges with a high concentration of vacancies is investigated using chemical composition analysis. The process of creating a nonporous morphology is sophisticated and is demonstrated using a wafer-scale phototransistor array. The performance of the phototransistors is assessed in terms of photosensitivity (S) and photoresponsivity (R); both are of high magnitudes (S = 8.6 × 104 at λex = 638 nm and Pinc = 512 mW cm2-; R = 120 A W1- at Pinc = 2 mW cm2- for the same λex). Additionally, the 7 × 5 array of 35 phototransistors is effective in sensing and reproducing the input image by responding to selectively illuminated pixels.

Reactively-sputtered AlOx passivation layer for self-aligned top-gate amorphous InGaZnO thin-film transistors

The direct-current reactive sputtering of aluminum oxide (AlOx) films with Al target was investigated to provide a preferable passivation layer (PL) for self-aligned top-gate (SATG) amorphous metal oxide semiconductor (AOS) like amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs). The grown AlOx films exhibited excellent electrical characteristics, with major parameters including a relative dielectric constant around 9, breakdown electric field of 3.7 MV/cm, and leakage current of 6.29 × 10−8 A/cm2 at 2 MV/cm. It is shown that the AlOx PL, together with a PECVD SiO2 interlayer could provide SATG a-IGZO TFTs with trustworthy environmental and electrical stability.

Neuromorphic chip integrated with a large-scale integration circuit and amorphous-metal-oxide semiconductor thin-film synapse devices

Artificial intelligences are promising in future societies, and neural networks are typical technologies with the advantages such as self-organization, self-learning, parallel distributed computing, and fault tolerance, but their size and power consumption are large. Neuromorphic systems are biomimetic systems from the hardware level, with the same advantages as living brains, especially compact size, low power, and robust operation, but some well-known ones are non-optimized systems, so the above benefits are only partially gained, for example, machine learning is processed elsewhere to download fixed parameters. To solve these problems, we are researching neuromorphic systems from various viewpoints. In this study, a neuromorphic chip integrated with a large-scale integration circuit (LSI) and amorphous-metal-oxide semiconductor (AOS) thin-film synapse devices has been developed. The neuron elements are digital circuit, which are made in an LSI, and the synapse devices are analog devices, which are made of the AOS thin film and directly integrated on the LSI. This is the world's first hybrid chip where neuron elements and synapse devices of different functional semiconductors are integrated, and local autonomous learning is utilized, which becomes possible because the AOS thin film can be deposited without heat treatment and there is no damage to the underneath layer, and has all advantages of neuromorphic systems.

Combustion Synthesis and Polymer Doping of Metal Oxides for High-Performance Electronic Circuitry.

ConspectusTransparent conducting oxides (TCOs) are inorganic electrical conductors with optical band gaps greater than 3.3 eV. TCOs have been extensively explored in functional windows, touch screen applications, transparent displays, solar cells, and even electronic circuits. Amorphous metal oxide (a-MO) semiconductors are a TCO class that has made impressive progress since the first 2004 demonstration of their utility as the semiconducting layer in thin-film transistors (TFTs). Their excellent counterintuitive electron mobilities in the amorphous state fill the performance gap between amorphous silicon and polysilicon, widening TFT applicability to high-value products such as high-resolution flat panel displays and emerging flexible/wearable electronics. The possibility of solution processing MO "inks" from air-stable precursors, via roll-to-roll and high-throughput printing, further expands their appeal. However, most MO TFTs fabricated using solution-processing require postdeposition film annealing at elevated temperatures (>400 °C) to ensure high-quality films and stable charge transport. Thus, MO fabrication on and TFT integration with inexpensive and typically temperature-sensitive flexible polymer substrates remains challenging, as does reducing MO processing times to those acceptable for high-throughput semiconductor circuit manufacture. Consequently, new MO film processing methodologies are being developed to meet these requirements. Among them, science-based combustion synthesis (CS) and polymer doping are promising complementary approaches to optimize materials quality and manufacturing efficiency; they are the topic of this Account.This Account summarizes the progress in CS and MO polymer doping research, made largely at Northwestern University over the past decade, to create high-performance MO TFTs. Regarding CS, we begin with an overview of combustion precursor chemistry that strongly affects the resulting film quality and device performance. Then, single fuel and dual fuel combustion syntheses for diverse MO systems are discussed. Representative examples highlight recent advances, with a focus on the relationship between (co)fuel-oxidizer types/amounts, thermal behavior, film microstructure, and TFT performance. Next, the discussion focuses on polymer doping of several MO matrices as a new approach to achieve semiconducting MO compositions with excellent performance and mechanical flexibility. Thus, the effect of the polymer architecture and content in the MO precursor formulations on the MO film composition, microstructure, electronic structure, and charge transport are discussed. The concluding remarks highlight challenges and emerging opportunities.

Multilayer Crossbar Array of Amorphous Metal-Oxide Semiconductor Thin Films for Neuromorphic Systems

A multilayer crossbar array has been developed using amorphous metal-oxide semiconductor (AOS) thin films and implemented into a neuromorphic system. The multilayer structure can be realized, because the AOS thin films can be deposited by a simple sputtering method without heat treatment, which does not damage the underlying structures. First, Au thin films are deposited by vapor evaporation as electrodes, an amorphous In-Ga-Zn-O (α-IGZO) thin film is deposited by a sputtering method as a conductance change layer, these processes are repeated, and a multilayer crossbar array is completed, where each of the three conductance change layers is sandwiched between the electrodes. Next, the multilayer crossbar array is implemented into a neuromorphic system with modified Hebbian learning, which enables autonomous learning without control circuitry, and an associative memory function is confirmed, which guarantees the possibility of further advanced functions. These results lead to astronomical large-scale integration (LSI) of synaptic elements in neuromorphic systems in the future.

Continuous Tuning of the Fermi Level in Disorder-Engineered Amorphous Films of Li-Doped ZnO for Thermoelectric Applications.

Amorphous metal-oxide semiconductors can be readily prepared by a solution process at low temperatures, and their energy band structures and carrier concentrations can be controlled based on the oxide composition or the addition of dopants in the design of thermoelectric (TE) materials. However, research on the correlation between the charge transport and TE performance of amorphous metal-oxide semiconductors is still in its infancy. Herein, we present the energy-dependent TE performance characteristics of Li-doped ZnO thin films with different doping levels and charge carrier concentrations. Thin films were prepared by the solution process, and the Li doping level was controlled by the Li precursor concentration added to a Zn precursor solution. Subsequently, a field-effect-modulated Seebeck coefficient measurement device was built to study the energy-dependent TE performance. Notably, the higher ratio of interstitial Li (Liinter) and oxygen vacancies (Ova) in the Li-ZnO device indicates an improved n-type TE performance. To investigate more thoroughly the charge transport phenomena, the localized density of states (DOS) was derived from the temperature-dependent transfer curve; the higher ratio of interstitial Li (Liinter) and oxygen vacancy (Ova) induces a reduction in the localized DOS and lowers the degree of disorder in their DOS. The determined energy-dependent TE characteristics can be used as guidance for the design of efficient TE devices with amorphous metal-oxide semiconductors.

Reduction of leakage current in amorphous Oxide-Semiconductor Top-gated thin film transistors by interface engineering with dipolar Self-Assembled monolayers

Top gate (TG) thin film transistors (TFTs) featuring amorphous metal oxide semiconductors (a-MOS), such as indium-gallium-zinc-oxide (IGZO), bear a great potential for large-area flexible and transparent electronics. The fabrication costs of these devices can be noticeably reduced by introduction of solution processes instead of standard fabrication routes involving vacuum deposition and complicate photolithography. However, solution-processed TG a-MOS TFT often causes considerable gate leakage in comparison with vacuum-processed device. In this context, we present a simple and straightforward approach to reduce the gate leakage of IGZO-based TG TFTs, which predominantly involves solution-based procedures. We engineer the IGZO/insulator interface by dipolar, silane-anchored self-assembled monolayers (SAMs) providing a favorable built-in electric field to reduce the leakage current in TFTs. The parameter correlates well with the direction and value of the molecular dipole moment defined by either electron accepting or electron donating character of the terminal tail group. These SAMs, prepared by spin-coating procedure, were characterized in detail by a combination of several complementary experimental techniques, providing also a useful background information for the device experiments.

High-Entropy Oxides: Advanced Research on Electrical Properties

The concept of “high entropy” was first proposed while exploring the unknown center of the metal alloy phase diagram, and then expanded to oxides. The colossal dielectric constant found on the bulk high-entropy oxides (HEOs) reveals the potential application of the high-entropy oxides in the dielectric aspects. Despite the fact that known HEO thin films have not been reported in the field of dielectric properties so far, with the high-entropy effects and theoretical guidance of high entropy, it is predictable that they will be discovered. Currently, researchers are verifying that appropriately increasing the oxygen content in the oxide, raising the temperature and raising the pressure during preparation have an obvious influence on thin films’ resistivity, which may be the guidance on obtaining an HEO film large dielectric constant. Finally, it could composite a metal–insulator–metal capacitor, and contribute to sensors and energy storage devices’ development; alternatively, it could be put into application in emerging thin-film transistor technologies, such as those based on amorphous metal oxide semiconductors, semiconducting carbon nanotubes, and organic semiconductors.

Amorphous-Metal-Oxide-Semiconductor Thin-Film Planar-Type Spike-Timing- Dependent-Plasticity Synapse Device

An amorphous-metal-oxide-semiconductor (AOS) thin-film planar-type spike-timing-dependent-plasticity (STDP) synapse device has been developed. The AOS is a non-rare material and can be easily deposited, and therefore it is inexpensive. On the other hand, the STDP is promising as a learning principle for neuromorphic systems. In this study, first, an AOS thin-film planar-type STDP synapse device is actually fabricated. Next, spiking pulses are applied to the synapse device as pre-signals and post-signals. Finally, STDP characteristics, namely, long-term-depression (LTD) and long-term-potentiation (LTP), are observed, which seem to be due to charge injection into the underlayer insulator film.