Thin-film Transistors Research Articles

Quasi‐Single‐Crystal Tin Halide Perovskite Films with High Structural Integrity for Near‐Infrared Imaging Array Enabling Hidden Object Recognition

AbstractNear‐infrared (NIR) image sensors based on solution‐processed thin film are gaining prominence in various applications, including security detection, remote sensing, medical imaging, and environmental monitoring, owing to superior penetration capabilities of NIR light. However, the reported perovskite image sensors suffer from limited resolution and performance due to poor structural integrity, bioincompatibility, and constrained response wavelength range from lead‐based perovskite materials employed. In this study, we present non‐toxic quasi‐single‐crystal (QSC) CH(NH2)2SnI3 (FASnI3) perovskite films, prepared via a simple spin‐coating technique, that demonstrate high structural integrity and effective NIR response. Through a series of in situ characterizations, we reveal that the orderly growth mode of QSC‐FASnI3 perovskite films enables a more oriented crystal growth with reduced trap and grain boundaries. Consequently, self‐powered NIR photodetector based on QSC‐FASnI3 films exhibited large detectivity over 1013 Jones in the NIR range (780–890 nm). Ultimately, due to the high structural integrity, the high‐resolution 64×64 (4096) pixels NIR imaging array, exhibiting reduced photo and dark response non‐uniformity value, was fabricated on the thin‐film transistors (TFT) backplanes, enabling ultraweak NIR light (63 nW cm−2) real‐time imaging, fingerprint imaging, and hidden object recognition. This work pioneers the application of lead‐free perovskite for high‐resolution NIR imaging arrays.

Quasi-Single-Crystal Tin Halide Perovskite Films with High Structural Integrity for Near-Infrared Imaging Array Enabling Hidden Object Recognition.

Near-infrared (NIR) image sensors based on solution-processed thin film are gaining prominence in various applications, including security detection, remote sensing, medical imaging, and environmental monitoring, owing to superior penetration capabilities of NIR light. However, the reported perovskite image sensors suffer from limited resolution and performance due to poor structural integrity, bioincompatibility, and constrained response wavelength range from lead-based perovskite materials employed. In this study, we present non-toxic quasi-single-crystal (QSC) CH(NH2)2SnI3 (FASnI3) perovskite films, prepared via a simple spin-coating technique, that demonstrate high structural integrity and effective NIR response. Through a series of in situ characterizations, we reveal that the orderly growth mode of QSC-FASnI3 perovskite films enables a more oriented crystal growth with reduced trap and grain boundaries. Consequently, self-powered NIR photodetector based on QSC-FASnI3 films exhibited large detectivity over 1013 Jones in the NIR range (780-890 nm). Ultimately, due to the high structural integrity, the high-resolution 64×64 (4096) pixels NIR imaging array, exhibiting reduced photo and dark response non-uniformity value, was fabricated on the thin-film transistors (TFT) backplanes, enabling ultraweak NIR light (63 nW cm-2) real-time imaging, fingerprint imaging, and hidden object recognition. This work pioneers the application of lead-free perovskite for high-resolution NIR imaging arrays.

Retina-Inspired X-Ray Optoelectronic Synapse Using Amorphous Ga2O3 Thin Film.

Machine vision techniques are widely applied for object identification in daily life and industrial production, where images are captured and processed by sensors, memories, and processing units sequentially. Neuromorphic optoelectronic synapses, as a preferable option to promote the efficiency of image recognition, are hotly pursued in non-ionizing radiation range, but rarely in ionizing radiation including X-rays. Here, the study proposes an X-ray optoelectronic synapse using amorphous Ga2O3 (a-Ga2O3) thin film. Boosted by the interfacial VO 2+ defects and its slow neutralization rate, the enhanced electron tunneling process at metal/a-Ga2O3 interface produces remarkable X-ray-induced post-synaptic current, contributing to a sensitivity of 20.5, 64.3, 164.1 µC mGy-1 cm-2 for the 1st, 5th, and 10th excitation periods, respectively. Further, a 64×64 imaging sensor is constructed on a commercial amorphous Si (a-Si) thin film transistor (TFT) array. The image contrast can be apparently improved under a series of X-ray pulses due to an outstanding long-term plasticity of the single pixel, which is beneficial to the subsequent image recognition and classification based on artificial neural network. The merits of large-scale production ability and good compatibility with modern microelectronic techniques belonging to amorphous oxide semiconductors may promote the development of neuro-inspired X-ray imagers and corresponding machine vision systems.

Amorphous Doped Indium Tin Oxide Thin‐Films by Atomic Layer Deposition.Insights into Their Structural, Electronic and Device Reliability

AbstractThin semiconducting films of magnesium doped indium‐ and tin oxide are prepared by thermal atomic layer deposition (ALD). The metal oxide films are deposited at 200 °C from the precursors trimethylindium, tetrakis(dimethylamido)tin, bis(ethylcyclopentadienyl)magnesium and water as oxidant. These thin‐films are observed to be amorphous by electron microscopy and X‐ray diffraction. However, they exhibited a near‐range atomic order with correlation lengths of up to 10 Å, as demonstrated by high energy total scattering at grazing incidence employing synchrotron radiation. Even minor alterations in composition reveal a significant impact on the thin‐film transistor (TFT) device parameters, due to magnesium's high oxygen binding capability and its ability to inhibit the formation of oxygen vacancies, resulting in a decrease of free charge carriers in the material. Stability tests indicate a device degradation after storage in ambient conditions due to water adsorption on the surface, which could be reversed by an additional annealing step which qualify the films as robust. This studie demonstrate the possibility of employing minor amounts of high band gap oxides such as MgO to manipulate and control the electric behavior of the active channel layer performance in inorganic TFT devices.

Nanometer-thick TiO2 channel thin film transistors as radical monitors for plasma enhanced atomic layer deposition

Nanometer-thick-TiO2-channel thin-film transistors (TFTs) are examined as oxidizing-agent monitors for room-temperature atomic layer deposition (RTALD). RTALD is a plasma-based process using plasma-excited humidified argon where OH radicals oxidize the precursor-gas adsorbed surface. In the TFT, the anatase TiO2 channel, with a thickness of 16 nm, is attached to a 300 nm thick gate capacitor of SiO2, while the channel surface is exposed to the ALD ambient. A heavily doped n-type Si substrate attached to the gate SiO2 is used as the gate electrode. The gate width and length are 1000 and 60 μm, respectively. When the TFT is installed in the RTALD chamber, the drain-current waveform is recorded in the course of the metal organic gas adsorption, evacuation of the residual gas, oxidization, and evacuation. In the present study, three kinds of metal organic (MO) precursors, tetrakis(dimethyl)amino titanium, tris(dimethyl)amino silane, and trimethyl aluminum are examined. The drain current exhibits strong responses upon the exposure of the plasma excited humidified argon. This suggests that OH radicals in the plasma might oxidize the adsorbed MO precursors to produce the OH moieties, where the surface polarization of OH moieties might enhance channel conductivity. The experimental results suggest the applicability of the present TFT as a plasma monitor in RTALD.

Double-gate metal–oxide TFT pixel circuit for improved luminance uniformity of mobile OLED display

The small subthreshold swing (SS) of metal–oxide (MOx) thin-film transistors (TFTs) reduces the data voltage (VDAT) range of the organic light-emitting diode (OLED) display pixel circuit. This leads to a large OLED current error when a small change occurs in the gate-to-source voltage (VGS) of the driving TFT in the pixel. Therefore, we propose a new pixel circuit adopting a double-gate TFT structure for the driving TFT, which is mainly driven by the bottom gate with a thicker gate insulator to provide a wide VDAT range. The proposed pixel circuit further expands the VDAT range by employing threshold voltage (VTH) modulation effect depending on the gray level. It also allows for flexible adjustment of the VTH extraction time to reduce OLED current error at low gray levels. SPICE simulation and measured results verify that the proposed pixel circuit reduces the OLED current error rate to less than 10% even with a VTH variation of ±0.5 V or SS variation of ±5% for the current level from 0.1 nA to 30 nA.

Chitosan-Based Electronics: The Importance of Acid Strength and Plasticizing Additives on Device Performance.

A rise in demand for disposable consumer electronics such as smart packaging, wearable electronics, and single-use point-of-source sensors requires the development of eco-friendly and compostable electronic materials. Chitosan is derived from crustacean waste and offers high dielectric constant values without requiring rigorous purification, making it sustainable for large-scale electronic device manufacturing. When processed in acidic media, the protonated backbone of chitosan pairs with counterions from the acid dissociation to form chitosan thin films with electrical double layers (EDLs) and tunable capacitive properties. We report the importance of the choice of acid when processing chitosan by surveying a series of halogenated and biosourced acids with varying pKa values and solutions with different pH values. Oxalic acid outperforms other acids, with a maximum areal capacitance of 161 nF·mm-2. Tartaric acid and citric acid, despite lower capacitance values, showed promising results with a stable EDL capacitance and high reproducibility, making them optimal for large-area manufacturing. The incorporation of sorbitol as a plasticizer boosts the EDL formation onset of all chitosan-acid combinations to 1 × 103-105 Hz and improves reproducibility. High-performing single-walled carbon nanotube thin film transistors were made using chitosan-based dielectrics treated with different acids with and without sorbitol, leading to transconductance as high as ≈5.2 μS and Ion/Ioff of 105. The capacitors and transistors remain functional after one year of storage in ambient conditions. Overall, this study demonstrates durable high-performance electronics based on chitosan and stresses the importance of processing acid and the use of plasticizing additives, such as sorbitol.

Addressing Mobility Overestimation in Short-Channel IGZO TFTs Using the Gated Van der Pauw Method.

The determination of field-effect mobility in indium gallium zinc oxide (IGZO) thin-film transistors (TFTs) is pivotal for advancing high-performance electronic devices. However, accurately evaluating the field-effect mobility in IGZO-TFTs with short channel lengths of less than a few micrometers poses a formidable challenge. This difficulty arises due to the increasing significance of contact resistance in the total resistance as the channel length decreases. Consequently, increasing contact resistance can lead to inaccurate sheet resistance values, resulting in overestimating critical parameters, such as mobility and contact resistance, during device evaluations. Therefore, a precise method for extracting sheet resistance, an intrinsic channel characteristic, is imperative for short-channel IGZO TFTs. Herein, a gated van der Pauw (gVDP) method was employed to extract sheet resistance precisely and independently of contact resistance. This contact-resistance-independent approach mitigates the risk of overestimating charge behaviors in IGZO TFTs. Furthermore, it facilitates precise evaluations of intrinsic channel mobility, enabling accurate predictions of the maximum performance of devices with short channels.

Applications of bio-composites in electronics

Abstract Functional biomaterials are being used in many promising industries to improve human quality of life and advance environmental objectives. Consideration has been given to many applications in the domains of medical, electronics, food, and pharmaceuticals. The use of bio-inspired materials enables the creation of more sustainable alternatives that strive to advance environmental preservation while simultaneously ensuring customer satisfaction. It was discovered that biopolymers are used in a number of different industries for the production of a wide range of functional bio-products. These bio-products include organic thin film transistors, organic phototransistors, emitting diodes, photodiodes, photovoltaic solar cells, hybrid dental resins, sustainable medicines, and consumer food packaging. A growth of this magnitude makes it possible to conduct substantial research in order to more inspection of the limitless requests and uses of bio-based composites. In order to fulfill the needs of certain applications, it is necessary to adjust and reassess attributes and parameters– such as hardness, durability, crack toughness, binding, solubility, polarization, plasticity, hydrogen bonding, thermal characteristics, and dielectric behavior. By virtue of their electronic and electrical properties, bio-composites and biopolymers have been put to use in a variety of applications; some includes organic thin-film transistors, electrical applications, electromagnetic insulation, energy harvesting, and thermoelectric processes. Substantial proportions of electronic waste, also referred to as E-waste, are regularly released into the environment due to the continuous growth in the production of electronic devices. Consequently, this leads to substantial environmental and ecological problems caused by the release of non-degradable polymers, hazardous compounds, and toxic heavy metals into the environment. The advancement of biodegradable polymers has significant potential for effectively reducing the environmental burden, since they may be decomposed or absorbed into the surrounding environment without generating any toxic effects. Hence, the purpose of this study is to illustrate the creation of biocompatible composites and their prospective uses in electrical applications.

Advances in Organic Materials for Next-Generation Optoelectronics: Potential and Challenges

This review provides a comprehensive overview of recent advancements in the synthesis, properties, and applications of organic materials in the optoelectronics sector. The study emphasizes the critical role of organic materials in the development of state-of-the-art optoelectronic devices such as organic solar cells, organic thin-film transistors, and OLEDs. The review further examines the structure, operational principles, and performance metrics of organic optoelectronic devices. Organic materials have emerged as promising candidates due to their low-cost production and potential for large-area or flexible substrate applications. Additionally, this review highlights the physical mechanisms governing the optoelectronic properties of high-performance organic materials, particularly photoinduced processes relevant to charge carrier photogeneration. It discusses the unique benefits of organic materials over traditional inorganic materials, including their light weight, simple processing, and flexibility. The report delves into the challenges related to stability, scalability, and performance, while highlighting the wide range of electronic properties exhibited by organic materials, which are critical for their performances in optoelectronic devices. Furthermore, it addresses the need for further research and development in this field to achieve consistent performance across different types of devices.

High Memory Window, Dual‐Gate Amorphous InGaZnO Thin‐Film Transistor with Ferroelectric Gate Insulator

Ferroelectric (FE) hafnium zirconium oxide (HZO) thin‐film transistors (TFTs) are of increasing interest for next‐generation memory and computing applications. However, these devices face challenges in achieving a substantial memory window (MW). This report presents amorphous InGaZnO (a‐IGZO) ferroelectric–dielectric (FD), dual‐gate thin‐film transistors (DG‐TFTs) with FE‐HZO as a bottom gate insulator (GI) and SiO2 as a top GI. The ferroelectricity in HZO is confirmed through the grazing incidence X‐ray diffraction (GI‐XRD), capacitance, and polarization measurements. The FD‐DG TFT can increase the MW by tuning the threshold voltage (VTH) due to electrostatic coupling between the top gate (TG) and bottom gate (BG). The increase of MW at the TG driving is related to the coupling factor which is equal to the ratio of the equivalent capacitance of top to bottom gated transistors. During the bottom sweep, the FD‐DG‐TFT demonstrates an anticlockwise hysteresis with a MW of 4.98 V, a high ION/IOFF ratio of ≈106, and a steep subthreshold swing (SS) of 90 mV dec−1. On the contrary, MW of 12 V and SS of 140 mV dec−1 are observed for the top sweep operation. A thinner ferroelectric GI at BG TFT induces sufficient electrostatic coupling to cause a large VTH shift at TG driving, resulting in a boosted MW.

Channel length dependency in Sn: ZnO/ZrO2 thin film transistors: a performance analysis

Channel length dependency in Sn: ZnO/ZrO2 thin film transistors: a performance analysis

A Mura model‐based optical compensation for organic light‐emitting diode display luminance nonuniformity utilizing two image capturing

AbstractIn this paper, we proposed a new optical Mura compensation method that requires only a few Mura detections for all gray levels. We analyzed the characteristics of Mura resulting from process variations in the thin film transistor (TFT) of each pixel and developed a new model using a logarithmic function. The proposed compensation algorithm has been verified with simulation and experimental results. We found that the uniformity of the proposed compensation algorithm at 7G, 24G, 75G, 100G, 150G, and 255G, which required only two image captures, was comparable to those that required five captures. The model improved uniformity from 41.32% to 68.60% at 0.18 nit brightness, demonstrating its effectiveness. Additionally, the method significantly reduces the number of image captures needed from five to two and decreases the image capturing process time from 2183 to 150 ms, saving over 14 times in process efficiency. The proposed methodology demonstrates significant advancements in achieving luminance uniformity in OLED displays, addressing mass production constraints.

Enhanced Mobility in MoS2 Thin Film Transistors Through Kr Ion Beam-Generated Surface Defects

Enhanced Mobility in MoS2 Thin Film Transistors Through Kr Ion Beam-Generated Surface Defects

Image quality enhancement in variable refresh rate LTPO-based AMOLED displays using a gate in panel voltage compensation scheme

This study investigated novel driving scheme for low-temperature polycrystalline silicon and oxide (LTPO) active-matrix organic light-emitting diode (AMOLED) displays under variable refresh rate (VRR) driving conditions with aim of reducing the brightness instability (i.e., flicker and luminance variation) for seamless performance. The mechanisms underlying brightness fluctuations in displays were examined, focusing on frequency-dependent differences in gate-inpanel (GIP) operations. Notably, our study revealed additional factors within the GIP operation that cause LTPO flicker and VRR performance, in addition to previously identified factors of thin-film transistor hysteresis and OLED charging. Consequently, variable GIP voltage driving method that reduced these issues and enhanced display performance was proposed. The proposed method could minimize brightness fluctuations to levels imperceptible to users and facilitate performance improvement through driving options in peripheral circuits without modifying panel design and is applicable across various applications utilizing LTPO OLED technology. Its driving scheme was validated through simulation and measurement of luminance variation during frequency transition using 6.0-inch LTPO-applied AMOLED displays. The experimental results indicated a decrease in luminance difference from 14.2% to 1.5%, particularly at extremely low brightness level of 0.2 nit. The luminance distortion decreased from 7 to less than 1, which is a just noticeable color difference (JNCD).

Perovskite Thin-Film Transistors for Ultra-Low-Voltage Neuromorphic Visions.

Perovskite thin-film transistors (TFTs) simultaneously possessing exceptional carrier transport capabilities, nonvolatile memory effects, and photosensitivity have recently attracted attention in fields of both complementary circuits and neuromorphic computing. Despite continuous performance improvements through additive and composition engineering of the channel materials, the equally crucial dielectric/channel interfaces of perovskite TFTs have remained underexplored. Here, it is demonstrated that engineering the dielectric/channel interface in 2D tin perovskite TFTs not only enhances the performance and operational stability for their utilization in complementary circuits but also enables efficient synaptic behaviors (optical information sensing and storage) under an extremely low operating voltage of -1mV at the same time. The interface-engineered TFT arrays operating at -1mV are then demonstrated as the preprocessing hardware for neuromorphic visions with pattern recognition accuracy of 92.2% and long-term memory capability. Such a low operating voltage provides operational feasibility to the design of large-scale-integrated and wearable/implantable neuromorphic hardware.

Long‐Channel Effects in Randomly Oriented Carbon Nanotube Thin Film Transistors

AbstractCarbon nanotube (CNT) thin film transistors (TFTs) have demonstrated great potential for application in highly sensitive biosensors and large‐area electronics. However, research on the electrical behavior of long‐channel CNT TFTs is lacking; thus, the purposeful improvement in the performance of biosensors or circuits is difficult. In this study, the electrical transport characteristics of ionic‐liquid‐gate CNT TFTs with channel lengths (Lch) ranging from 10 to 400 µm are investigated. The CNT TFTs present classical drift‐diffusion transport at on‐state with a carrier mobility of around 27 cm2 V−1 s−1. In the subthreshold region of the CNT TFTs, an abnormal Lch‐dependent subthreshold swing (SS) relationship, named as the long‐channel effect (LCE)is observed, where SS worsens with increasing Lch. The existence of the junctions between the CNTs results in an unconventional density of states for carriers and a large series resistance for sharing the gate voltage; this dominates the abnormal scaling behavior in the subthreshold region by degrading the electrostatic integrity. The discovery of the abnormal LCE can aid in the construction of device models and purposefully improve the performance of CNT TFTs for biosensors and other large‐scale electronic applications.

Adaptive frequency driving scan driver based on a‐InGaZnO TFTs for extremely low‐power displays

AbstractIn this paper, we propose a novel scan driver combined with a logic circuit using amorphous indium‐gallium‐zinc‐oxide (a‐InGaZnO) thin‐film transistors (TFTs) in order to enhance the electrical stability and reduce power consumption in display panels. The latest mobile displays with high resolution and refresh rates consume more battery power, which inevitably limits portability and usability. The proposed scan driver can mask the signal by combining the output stage with a logic circuit, thereby blocking the output pulse for static images. This allows the display panel to operate in a partial driving mode depending on the display content. Due to the masking of the scan driver's output pulses, the connected pixel circuits are consistently maintained in the same state as the previous frame, leading to a lower refresh rate and reduced power consumption. Furthermore, by constructing additional control signals, the proposed scan driver can operate stably in depletion mode under a ∆VTH = −3 V.

Highly Productive Laser Annealing Manufacturing Method Using Continuous Blue WBC (Wavelength Beam Combining) Technique

Blue laser annealing can be used to obtain a high-mobility thin-film transistor (TFT) through a laser annealing (i.e., LTPS: low-temperature Poly-Si) process. However, the laser annealing process’s low productivity (as well as high cost) is an issue because the high output power of blue lasers still needs to be addressed. Therefore, productivity can be improved if blue laser energy is efficiently supplied during the laser annealing process using a continuous wave laser instead of a conventional pulsed excimer laser. We developed a blue laser light source (440 ± 10 nm) using the wavelength beam combining (WBC) method, which can achieve a laser power density of 73.7 kW/cm2. In this semiconductor laser, when the power was increased s by 2.9 times, the laser scanning speed was increased by 5.0 times, achieving twice the productivity of conventional lasers. After laser annealing, the size of the crystal grains varied between 2 and 15 μm, resulting in a crystallization rate of 100% by Raman scattering rsult and low resistivity of 0.04 Ωcm. This increase in production capacity is not an arithmetic increase with increased power but a geometric production progression.

Combustion-assisted low-temperature ZrO2/SnO2 films for high-performance flexible thin film transistors

We developed high-performance flexible oxide thin-film transistors (TFTs) using SnO2 semiconductor and high-k ZrO2 dielectric, both formed through combustion-assisted sol-gel processes. This method involves the exothermic reaction of fuels and oxidizers to produce high-quality oxide films without extensive external heating. The combustion ZrO2 films were revealed to have an amorphous structure with a higher proportion of oxygen corresponding to the oxide network, which contributes to the low leakage current and frequency-independent dielectric properties. The ZrO2/SnO2 TFTs fabricated on flexible substrates using combustion synthesis exhibited excellent electrical characteristics, including a field-effect mobility of 26.16 cm2/Vs, a subthreshold swing of 0.125 V/dec, and an on/off current ratio of 1.13 × 106 at a low operating voltage of 3 V. Furthermore, we demonstrated flexible ZrO2/SnO2 TFTs with robust mechanical stability, capable of withstanding 5000 cycles of bending tests at a bending radius of 2.5 mm, achieved by scaling down the device dimensions.