Metal Oxide Thin-film Transistors Research Articles

Enhancing the Carrier Mobility and Bias Stability in Metal-Oxide Thin Film Transistors with Bilayer InSnO/a-InGaZnO Heterojunction Structure.

In this study, the electrical performance and bias stability of InSnO/a-InGaZnO (ITO/a-IGZO) heterojunction thin-film transistors (TFTs) are investigated. Compared to a-IGZO TFTs, the mobility (µFE) and bias stability of ITO/a-IGZO heterojunction TFTs are enhanced. The band alignment of the ITO/a-IGZO heterojunction is analyzed by using X-ray photoelectron spectroscopy (XPS). A conduction band offset (∆EC) of 0.5 eV is observed in the ITO/a-IGZO heterojunction, resulting in electron accumulation in the formed potential well. Meanwhile, the ∆EC of the ITO/a-IGZO heterojunction can be modulated by nitrogen doping ITO (ITON), which can affect the carrier confinement and transport properties at the ITO/a-IGZO heterojunction interface. Moreover, the carrier concentration distribution at the ITO/a-IGZO heterointerface is extracted by means of TCAD silvaco 2018 simulation, which is beneficial for enhancing the electrical performance of ITO/a-IGZO heterojunction TFTs.

Cation doping strategy for improved carrier mobility and stability in metal-oxide Heterojunction thin-film transistors

The heterojunction channel architecture has emerged as a viable solution to enhance the performance of metal-oxide thin-film transistors (TFTs), addressing the performance limitations of single-channel counterparts. However, carrier mobility enhancement through a channel thickness design often encounters significant challenges such as the negative threshold voltage (Vth) shift. In this study, we present a cation doping strategy, designed to regulate Vth shift while simultaneously boosting carrier mobility in zinc-tin-oxide (ZTO)-based heterojunction TFTs. A comprehensive investigation of ZTO-based semiconductors was conducted to explore the impact of cation doping on the energy band structure and to find an optimal heterojunction channel structure for high carrier mobility and stability. The resulting ZTO/Ti-doped ZTO (Ti:ZTO) heterojunction TFTs demonstrated a field-effect mobility of 39.7 cm2/Vs, surpassing the performance of ZTO TFTs (16.1 cm2/Vs), with a minimal change in the Vth. Furthermore, the ZTO/Ti:ZTO TFTs exhibited enhanced bias-stress stability compared to the ZTO TFTs. We attribute the improved mobility and stability to the electron accumulation near the oxide channel heterointerface facilitated by band bending and defect passivation effect arising from the Ti:ZTO back-channel layer, respectively.

Solution-Processed Metal Oxide Thin-Film Transistor at Low Temperature via A Combination Strategy of H2 O2 -Inducement Technique and Infrared Irradiation Annealing.

Solution processing has emerged as a promising technique for the fabrication of oxide thin-film transistors (TFTs), offering advantages such as low cost, high throughput, and exceptional compositional control. However, achieving reasonable electrical properties typically demands high annealing temperatures in the fabrication process. In addressing this challenge, a novel combination strategy is proposed that involves integrating the H2 O2 inducement technique with infrared (IR) irradiation annealing. The study investigates the effects of precursors and IR irradiation annealing temperatures on the electrical properties of In2 O3 TFTs. It is found that H2 O2 can help accelerate the decomposition of organic residues, while IR irradiation annealing could enhance the film densification. By employing the proposed strategy, metal oxide TFTs consisting of a Zr-Al-O dielectric fabricated at 230°C and an In2 O3 channel layer fabricated at 185°C demonstrated high performance with field-effect mobility = 31.7 cm2 V-1 ·s-1 , threshold voltage = 1.3 V, subthreshold swing = 0.13 V per decade, and on-to-off current ratio = 1.1 × 105 . This work demonstrates the proposed combinational strategy is a general method to fabricate not only metal oxide semiconductorsbut also dielectrics.

An analog PWM pixel circuit with shaping function for low grayscale display of Micro-LEDs

This paper presents a new analog pulse width modulation (PWM) micro light-emitting diode (LED) pixel circuit with a shaping function. The rising/falling time of PWM signal generated by the proposed pixel circuit can be greatly reduced to improve the low grayscale display quality of micro-LED. Metal oxide thin film transistors with the top-gate (TG) coplanar structure are used to realize the proposed pixel circuit on the glass substrate. It is shown that the pulse width of micro-LED current can be linearly modulated by the data voltage. Furthermore, the measured rising time and falling time of the PWM signal are 15.6 μs and 25.5 μs, respectively, which are much smaller than that of the PWM signal in the conventional analog PWM pixel circuits.

Research on correlation between metal oxide semiconductor target and magnetron sputtered film based on TFT application

The research on the intrinsic relationship between target quality and TFT (thin film transistor) performance is not perfect for magnetron sputtering processes. The systematic analysis of target-film-device still needs to be improved. This paper studied the internal relationship between metal oxide semiconductor targets, thin films, and TFT devices for the deterioration problem of device performance caused by the failure of the aging target. The experimental results showed that the target surface with a long cumulative sputtering time had apparent macroscopic concave, related to the electromagnetic field distribution. The concave region was the primary source of thin film composition, so the research object of this work was mainly the concave region. A multi-oxide target was used in this work, and its selective sputtering phenomenon was serious, mainly reflected in the sputtering rate of In2O3 grains with higher electrical conductivity than other components. There were many failure sites on the surface of the target, including nodules, holes, coating layers, and cracks. The failure sites would hinder the normal sputtering process and eventually form a vicious circle, failing the target. Due to the decline of target quality, sputtering particles would be in a state of insufficient kinetic energy, resulting in particle agglomeration, element segregation, weak M-O (metal-oxide) bonds, loose accumulation, and surface or block defects. Ultimately, the TFT performance with the aging target showed lower mobility, larger subthreshold swing, increased off-state current, and poorer stability. Clarifying the relationship between target quality and device performance is beneficial for the development of electronic devices.

Effects of Heat-Treatment on the Population of Intrinsic Defects in and the Stability of an Amorphous Metal-Oxide Thin-Film Transistor

Effects of Heat-Treatment on the Population of Intrinsic Defects in and the Stability of an Amorphous Metal-Oxide Thin-Film Transistor

Low-frequency noise in InSnZnO thin film transistors with high-quality SiO2 gate oxide stacks

Low-frequency noise (LFN) in InSnZnO (ITZO) thin-film-transistors (TFT) with high-quality SiO2 gate oxide (GO) stacks is studied. This stack is fabricated by the plasma enhanced chemical vapor deposition (PECVD) and comprises two single layers. One layer is deposited by a SiH4 source (SiH4–SiO2), and the other uses a tetraethyl-orthosilicate precursor (TEOS-SiO2). The drain current noise power spectral densities follow the typical 1/f rule, and the main origin of LFN changes with the variation of drain current intensities. At low drain current intensities, LFN is affected by grain boundaries in the channel. As the drain current intensities increase, LFN originates from the carrier number fluctuations in devices with single TEOS-SiO2 GOs and from the carrier number with correlated mobility fluctuations in devices with SiO2 stacks GOs. At extremely high drain current intensities, the contact noise acts as a significant source of LFN in devices with SiO2 GO stacks. According to the carrier number with correlated mobility fluctuation (ΔN−Δμ) model, the devices with optimal stacks GOs exhibit a relatively low trap density near the ITZO/SiO2 interface. Additionally, these devices have a lower border trap density in GOs compared to those with single compositions. It demonstrates that high-quality SiO2 stacks reduce traps near the SiO2/ITZO interface, leading to enhanced devices performance. This work provides a precise and efficient method to evaluate the quality of GOs in metal oxide TFTs.

Inkjet printing high mobility indium-zinc-tin oxide thin film transistor

Metal oxide thin film transistor has been widely used in flat panel display industry because of its low leakage current, high mobility and large area uniformity. Besides with the development of printed display technology, inkjet printing process can fabricate the customizable patterns on diverse substrates without the need for vacuum or lithography, can significantly reduce cost and has received more and more attention. In this paper, we fabricate a bottom gate bottom contact structure thin film transistor (TFT) with indium-zinc-tin-oxide (IZTO) semiconductor using inkjet printing process. The surface morphology of the printed IZTO film is modified by adjusting the solvent composition and solute concentration of the printing precursor ink. The experimental result show that the use of binary solvents can effectively overcome the coffee ring shape caused by the accumulation of solute edge during the volatilization process of a single solvent, and finally show a uniform and flat contour surface. Further increase in solute concentration is in favor of formation of convex surface topology. The reason for the formation of the flat surface of the oxide film is the balance between the inward Marangoni reflux of the solute and the outward capillary flow during volatilization. In addition, using binary solvents printed IZTO thin film transistor exhibit excellent electrical properties. The ratio of width/length=50/30 exhibit a high on-off ratio of 1.21×10<sup>9</sup>,a high saturation field-effect mobility of 16.6 cm<sup>2</sup>·V<sup>-1</sup>·s<sup>-1</sup>,a low threshold voltage of 0.84 V and subthreshold swing of 0.24 V/dec. The uniform and flat active layer thin film pattern can form good contact with the source leakage electrode, and the contact resistance of TFT devices with different width-to-length ratios is less than 1000 Ω, which can achieve the basic conditions of high mobility thin film transistors prepared by inkjet printing. Therefore, using mixture solvents provides a universal and facile way to print oxide films with desired surface topology and provide a visible path for inkjet printing of high-mobility thin film transistors.

Physical modeling for photo-capacitance characteristics of metal oxide TFTs

We propose an amorphous metal oxide thin film transistor photo-capacitance model in the depletion region that takes Fermi level splitting and band-bending rearrangement into consideration. The split Fermi level is used to characterize the variation in trapped electrons under illumination. Those trapped electrons are excited by optical energy transport under the electric field induced by gate voltage, changing the charge density in the space charge and inducing the rearrangement of band bending. By comparing the data calculated from the model with the test data under three different illumination conditions, that is, 808, 635, and 520 nm, we verify the correctness of this model. Furthermore, the fitting results were in accordance with the general law: the higher the photon energy, the higher the energy level splitting.

Low voltage-driven, high-performance TiO2 thin film transistors with MHz switching speed.

High-speed circuits based on thin film transistors (TFTs) show promising potential applications in biomedical imaging and human-machine interactions. One of the critical requirements for high-speed electronic devices lies in high-frequency switching or amplification at low voltages, typically driven by batteries (∼3.0 V). To date, however, most electrical performances of metal oxide TFTs are measured under direct current (DC) conditions, and their dynamic switching behaviour is scarcely explored and studied systematically. Here in this work, we present low voltage-driven, high-performance TiO2 thin film transistors, which can be operated at a switching speed of MHz. Our proposed TiO2 TFTs demonstrated a high on-off ratio of 107, together with a subthreshold swing (SS) of ∼150 mV Dec-1 averaged over four orders of magnitude, which can be further reduced below 100 mV Dec-1 when the temperature cools to 77 K. Additionally, the TiO2 TFTs exhibit excellent gate-pulse switching at various frequencies ranging from 1.0 Hz to 1.0 MHz. We also explored the potential application of the TiO2 TFTs as logic gates by constructing a resistive-loaded inverter, which shows stable operation at 10 kHz frequency and various temperatures. Thus, our results show the great potential of TiO2 TFTs as a new platform for high-speed electronic applications.

Multiplexed Surface Electrode Arrays Based on Metal Oxide Thin-Film Electronics for High-Resolution Cortical Mapping.

Electrode grids are used in neuroscience research and clinical practice to record electrical activity from the surface of the brain. However, existing passive electrocorticography (ECoG) technologies are unable to offer both high spatial resolution and wide cortical coverage, while ensuring a compact acquisition system. The electrode count and density are restricted by the fact that each electrode must be individually wired. This work presents an active micro-electrocorticography (µECoG) implant that tackles this limitation by incorporating metal oxide thin-film transistors (TFTs) into a flexible electrode array, allowing to address multiple electrodes through a single shared readout line. By combining the array with an incremental-ΔΣ readout integrated circuit (ROIC), the system is capable of recording from up to 256 electrodes virtually simultaneously, thanks to the implemented 16:1 time-division multiplexing scheme, offering lower noise levels than existing active µECoG arrays. Invivo validation is demonstrated acutely in mice by recording spontaneous activity and somatosensory evoked potentials over a cortical surface of ≈8×8mm2 . The proposed neural interface overcomes the wiring bottleneck limiting ECoG arrays, holding promise as a powerful tool for improved mapping of the cerebral cortex and as an enabling technology for future brain-machine interfaces.

A review of RFID Tag based on TFT

Radiofrequency identification is a non-contact wireless identification technology that uses wireless radio frequency signals for specific target identification or data transmission and has broad application prospects in the period of the Internet of Things. A thin film transistor is a kind of field-effect transistor which is widely applied in the field of flat panel display, but it can also be applied to RFID technology. This paper first introduces the development history of RFID technology and explains the working principle, then briefly describes the structure and characteristics of TFT. After that, the article summarizes the research progress of RFID tags based on different kinds of TFTs at home and abroad by literature review. It is found that RFID tags based on metal oxide thin film transistors have the most advantages, such as better electrical properties, lower cost, good flexibility, high transparency, etc., which meet the need of people in certain application scenarios. Finally, the application prospects of this tag are presented.

Sub-volt metal-oxide thin-film transistors enabled by solution-processed high-k Gd-doped HfO2 dielectric films

Sub-volt metal-oxide thin-film transistors enabled by solution-processed high-k Gd-doped HfO2 dielectric films

Signal and noise analysis of a metal oxide transistor-based flat-panel detector

Recently, metal-oxide thin-film transistor (TFT)-based flat-panelx-ray detectors have attracted attention owing to their fast readouttimes and low noise characteristics. We empirically analyzed the signaland noise characteristics of an indium gallium zinc oxide (IGZO) TFT-baseddetector in comparison with those of a conventional hydrogenated amorphoussilicon (a-Si:H) TFT-based detector. We compared the large-areasignal transfer functions of the detectors as a function of air kermaat their entrance surfaces. Signal and noise performances were evaluatedby measuring the modulation-transfer function, noise-power spectrum,and detective quantum efficiency (DQE). The low-dose imaging capabilityof the detectors was assessed by investigating the large-area or zero-frequencyDQE as a function of air kerma. Herein, we evaluated the value ofthe IGZO detector in terms of dose efficiency in comparison to theconventional a-Si:H detector.

A 6-bit Analog-to-Digital Converter for Electromyography Implemented Using N-Type Metal-Oxide Thin-Film Transistors

Consisting of more than 2000 n-type metal-oxide thin-film transistors (TFTs), a 6-bit analog-to-digital converter (ADC) adopting the subranging architecture is designed, fabricated, characterized and applied to digitize an electromyogram (EMG). Consisting of amplifiers each with a feedback stage for gain-boosting, the comparators at the heart of the ADC incorporate a scheme for compensating the offset error arising from the inevitable non-uniformity of the TFT parameters. Compared to the specifications of reported ADCs based on TFTs, a higher sampling rate of 1000 S/s, a smaller differential non-linearity of 0.76 least-significant bit (LSB) and a smaller integral non-linearity of 0.88 LSB are achieved. Since the same low-temperature TFT technology for fabricating the EMG acquisition system on a flexible substrate is used to construct the ADC, the two could be readily monolithically integrated.

Significant Degradation Reduction in Metal Oxide Thin-Film Transistors via the Interaction of Ionized Oxygen Vacancy Redistribution, Self-Heating Effect, and Hot Carrier Effect

In this work, device degradation of metal oxide (MO) thin-film transistors (TFTs) under positive bias stress, linear stress, and saturation stress is systematically investigated. A significant degradation reduction in InGaZnO TFTs is observed for the first time under saturation stress. Incorporated with electric field simulations and temperature simulations, a degradation model, considering the interaction of ionized oxygen vacancy redistribution, self-heating effect, and hot carrier effect, is tentatively proposed to understand the degradation behaviors under various stress combinations. Moreover, a similar degradation reduction phenomenon is also reproduced in InSnZnO TFTs, demonstrating the applicability of the proposed degradation model in MO TFTs.

A chaos-metastability TRNG for natively flexible IGZO circuits

Modern technologies of truly flexible integrated circuits are usually based on large single-type transistors. If considered as a platform for Internet-of-Things (IoT) devices, they would require dedicated cryptographic solutions that could fit their limitations. In this article, we present an implementation of an efficient and fast-start true random number generator (TRNG) developed with a metal-oxide thin-film transistor (TFT) technology on a flexible substrate. This is our first full-custom TRNG implementation following the programmable logic ones. The architecture of the TRNG utilizes a chaotic circuit boosting an RS flip-flop leading to random oscillatory metastable behavior. The implementation is based on indium-gallium-zinc oxide (IGZO or InGaZnO) n-type TFT transistors with 0.8 × 5 μm channels. The solution delivers constant 66.7 kbit/s stream produced by 0.3 square millimeters of a flexible thin-film circuit using 200 μW of power. The randomness of the TRNG binary stream was verified by Diehard and NIST Suit tests.

Metal oxide thin film transistor and its active layer materials

Metal oxide thin-film transistors (MOTFTs) have the characteristics of high electron mobility, large-area production, and relatively low fabrication temperature and have received extensive attention as a research hotspot in recent years. Based on a large number of literatures, this paper introduces the typical single-component representative of MOTFT, multi-component compound oxide semiconductor active layer materials such as IZO, IGO, IGZO, etc. At the same time, due to the unique advantages of nanomaterials, material modification is carried out in different dimensions, and six physical and chemical preparation methods of its active layer are described, including a relatively unique Low-temperature preparation method based on improved gel precursor components and UV photocatalysis. Multi-component oxides and composite structures based on nanomaterials are currently the most studied fields, and on this basis, more excellent performance can be studied and prepared. It mainly summarizes its application in large-scale display and flexible electronics and looks at its development direction.

In Situ Radiation Hardness Study of Amorphous Zn-In-Sn-O Thin-Film Transistors with Structural Plasticity and Defect Tolerance.

Solution-processed metal-oxide thin-film transistors (TFTs) with different metal compositions are investigated for ex situ and in situ radiation hardness experiments against ionizing radiation exposure. The synergetic combination of structural plasticity of Zn, defect tolerance of Sn, and high electron mobility of In identifies amorphous zinc-indium-tin oxide (Zn-In-Sn-O or ZITO) as an optimal radiation-resistant channel layer of TFTs. The ZITO with an elemental blending ratio of 4:1:1 for Zn/In/Sn exhibits superior ex situ radiation resistance compared to In-Ga-Zn-O, Ga-Sn-O, Ga-In-Sn-O, and Ga-Sn-Zn-O. Based on the in situ irradiation results, where a negative threshold voltage shifts and a mobility increase as well as both off current and leakage current increase are observed, three factors are proposed for the degradation mechanisms: (i) increase of channel conductivity, (ii) interface-trapped and dielectric-trapped charge buildup, and (iii) trap-assisted tunneling in the dielectric. Finally, in situ radiation-hard oxide-based TFTs are demonstrated by employing a radiation-resistant ZITO channel, a thin dielectric (50 nm SiO2), and a passivation layer (PCBM for ambient exposure), which exhibit excellent stability with an electron mobility of ∼10 cm2/V s and aΔVth of <3 V under real-time (15 kGy/h) gamma-ray irradiation in an ambient atmosphere.

Fabrication of non-volatile memory transistor by charge compensation of interfacial ionic polarization of a ferroelectric gate dielectric

Lithium niobate (LiNbO3) is a popular lead free perovskite ferroelectric materials, but its implementation as a gate dielectric for developing a ferroelectric thin film transistor (FeTFT) has not been investigated much due to its low band gap. Low band gap introduces high gate leakage current that results in very low retention time of the device. In this report a solution processed Li5AlO4/LiNbO3/Li5AlO4 stacked layer has been used as a gate dielectric of a metal oxide thin film transistor which reduces gate leakage current by four orders of magnitude with respect to the single layer LiNbO3 gate dielectric device. Besides, due to the ionic polarization of Li5AlO4 thin film that originated from the mobile Li+, charge compensation of the depolarization field has been nearly removed. By reducing these factors, it becomes possible to fabricate metal oxide based FeTFT that has retention time of 7 h which is ∼200 times higher with respect to the LiNbO3 only FeTFT. The ratio of On and Off state of FeTFT is ∼103 which retains ∼ 95% after 7 h of operation. The carrier mobility, ON/OFF ratio and subthreshold swing (SS) of this FeTFT are 2.9 cm2 V − 1 s − 1,7.2 × 104 and 328 mV.decade−1 respectively.