TFT Channel Materials for Display Applications: From Amorphous Silicon to Transition Metal Dichalcogenides

Digital Mini-LED Lighting Using Organic Thin-Film Transistors Reaching over 100,000 Nits of Luminance

This paper demonstrates the use of organic thin-film transistors (OTFTs) to drive active digital mini light-emitting diode (mini-LED) backlights, aiming to achieve exceptional display performance. Our findings reveal that OTFTs can effectively power mini-LED backlights, reaching brightness levels exceeding 100,000 nits. This approach not only enhances image quality but also improves energy efficiency. OTFTs offer a flexible and lightweight alternative to conventional silicon-based transistors, enabling innovative and versatile display designs. The integration of mini-LED technology with OTFTs produces displays with superior contrast ratios, enhanced color brightness, and lower power consumption. This technological advancement is poised to revolutionize high-dynamic-range (HDR) displays, including those in televisions, smartphones, and wearable devices, where the demand for high brightness and energy efficiency is paramount.

Machine Learning Strategy for Optimizing Multiple Electrical Characteristics in Dual-Layer Oxide Thin Film Transistors

A machine learning (ML) strategy is suggested to optimize dual-layer oxide thin film transistor (TFTs) performance. In this study, Bayesian optimization (BO), an algorithm recognized for its efficiency in optimizing material design, is applied to guide the design of a channel layer composed of IZO and IGZO. The sputtering fabrication process, which has attracted attention as an oxide semiconductor channel layer deposition method, is fine-tuned using ML to enhance multiple electrical characteristics of transistors: field-effect mobility, threshold voltage, and subthreshold swing. Using BO, the sputtering conditions─plasma power, pressure, and gas ratio, which intricately influence device performance─were modified using 19 data sets of 84 scenarios. It reveals that the modulated process conditions improve field-effect mobility up to 46.7 cm2V-1s-1, achieving more than double the performance of conventional IGZO TFTs. Furthermore, it was observed that threshold voltage is optimized to zero voltage, and the subthreshold swing is considerably improved, contributing to reduced power consumption. This study demonstrates that leveraging ML to optimize TFTs design not only accelerates the design process but also improves device performance dramatically. Overall, this ML strategy manages complex correlations among process parameters, properties, and performance and sets a precedent for the expeditious optimization of semiconductor devices.

High-Mobility All-Transparent TFTs with Dual-Functional Amorphous IZTO for Channel and Transparent Conductive Electrodes

The increasing demand for advanced transparent and flexible display technologies has led to significant research in thin-film transistors (TFTs) with high mobility, transparency, and mechanical robustness. In this study, we fabricated all-transparent TFTs (AT-TFTs) utilizing amorphous indium-zinc-tin-oxide (a-IZTO) as a dual-functional material for both the channel layer and transparent conductive electrodes (TCEs). The a-IZTO was deposited using radio-frequency magnetron sputtering, with its composition adjusted for both channel and electrode functionality. XRD analysis confirmed the amorphous nature of the a-IZTO layers, ensuring structural stability post-thermal annealing. The a-IZTO TCEs demonstrated high optical transparency (89.57% in the visible range) and excellent flexibility, maintaining a low sheet resistance with minimal degradation even after 100,000 bending cycles. The fabricated AT-TFTs exhibit superior field-effect mobility (30.12 cm2/V·s), an on/off current ratio exceeding 108, and a subthreshold swing of 0.36 V/dec. The AT-TFT device demonstrated a minimum transmittance of 75.46% in the visible light range, confirming its suitability for next-generation flexible and transparent displays.

Deeply Implantable, Shape-Morphing, 3D MicroLEDs for Pancreatic Cancer Therapy

Controlled photooxidation-mediated disruption of collagens in the tumor microenvironment can reduce desmoplasia and enhance immune responsiveness. However, achieving effective light delivery to solid tumors, particularly those with dynamic volumetric changes like pancreatic ductal adenocarcinoma (PDAC), remains challenging and limits the repeated and sustained photoactivation of drugs. Here, 3D, shape-morphing, implantable photonic devices (IPDs) are introduced that enable tumor-specific and continuous light irradiation for effective metronomic photodynamic therapy (mPDT). This IPD adheres seamlessly to the surface of orthotopic PDAC tumors, mitigating issues related to mechanical mismatch, delamination, and internal lesions. In freely moving mouse models, mPDT using the IPD with close adhesion significantly reduces desmoplastic tumor volume without causing cytotoxic effects in healthy tissues. These promising in vivo results underscore the potential of an adaptable and unidirectional IPD design in precisely targeting cancerous organs, suggesting a meaningful advance in light-based therapeutic technologies.

Clinical Validation of Face-Fit Surface-Lighting Micro Light-Emitting Diode Mask for Skin Anti-Aging Treatment

Photobiomodulation therapy based on micro light-emitting diodes (µLEDs) holds remarkable potential for the beauty industry. Here, a cosmetically effective face-fit surface-lighting µLED mask for skin anti-aging is introduced. The face-conformable mask enables deep tissue treatment through proximal light irradiation, with a 3D origami structure capable of adapting to complex facial contours with closed adherence. A blister-assisted laser transfer achieves rapid and accurate µLEDs transfer at a high throughput of 50 chips per second, facilitating a mass-producible and large-area process. Finally, clinical trials demonstrate significant improvements in elasticity, sagging, and wrinkles across six facial areas, with a maximum enhancement of 340% in deep skin elasticity of the perioral area compared to the conventional LED mask group.

Light-Material Interactions Using Laser and Flash Sources for Energy Conversion and Storage Applications

This review provides a comprehensive overview of the progress in light-material interactions (LMIs), focusing on lasers and flash lights for energy conversion and storage applications. We discuss intricate LMI parameters such as light sources, interaction time, and fluence to elucidate their importance in material processing. In addition, this study covers various light-induced photothermal and photochemical processes ranging from melting, crystallization, and ablation to doping and synthesis, which are essential for developing energy materials and devices. Finally, we present extensive energy conversion and storage applications demonstrated by LMI technologies, including energy harvesters, sensors, capacitors, and batteries. Despite the several challenges associated with LMIs, such as complex mechanisms, and high-degrees of freedom, we believe that substantial contributions and potential for the commercialization of future energy systems can be achieved by advancing optical technologies through comprehensive academic research and multidisciplinary collaborations.

Dielectric Design of High Dielectric Constant Poly(Urea-Urethane) Elastomer for Low-Voltage High-Mobility Intrinsically Stretchable All-Solution-Processed Organic Transistors

Stretchable organic transistors for skin-like biomedical applications require low-voltage operation to accommodate limited power supply and safe concerns. However, most of the currently reported stretchable organic transistors operate at relatively high voltages. Decreasing their operational voltage while keeping the high mobility still remains a key challenge. Here, the study presents a new dielectric design to achieve high-dielectric constant poly(urea-urethane) (PUU) elastomer, by incorporating a flexible small-molecular diamine crosslinking agent 4-aminophenyl disulfide (APDS) into the main chain of (poly (propylene glycol), tolylene 2,4-diiso-cyanate terminated) (PPG-TDI). Compared with commercial elastomers, the PUU elastomer as dielectric of the stretchable organic transistors shows the outstanding advantages including lower surface roughness (0.33 nm), higher adhesion (45.18 nN), higher dielectric constant (13.5), as well as higher stretchability (896%). The PUU dielectric enables the intrinsically stretchable, all-solution-processed organic transistor to operate at a low operational voltage down to -10 V, while preserving a substantial mobility of 1.39 cm2 V-1 s-1. Impressively, the transistor also demonstrates excellent electrical stability under repeated switching of 10 000 cycles, and remarkable mechanical robustness when stretched up to 100%. The work opens up a new molecular engineering strategy to successfully realize low-voltage high-mobility stretchable all-solution-processed organic transistors.

Automotive Augmented Reality Head-Up Displays

As the next generation of in-vehicle intelligent platforms, the augmented reality heads-up display (AR-HUD) has a huge information interaction capacity, can provide drivers with auxiliary driving information, avoid the distractions caused by the lower head during the driving process, and greatly improve driving safety. However, AR-HUD systems still face great challenges in the realization of multi-plane full-color display, and they cannot truly achieve the integration of virtual information and real road conditions. To overcome these problems, many new devices and materials have been applied to AR-HUDs, and many novel systems have been developed. This study first reviews some key metrics of HUDs, investigates the structures of various picture generation units (PGUs), and finally focuses on the development status of AR-HUDs, analyzes the advantages and disadvantages of existing technologies, and points out the future research directions for AR-HUDs.

Solution Process-Based Thickness Engineering of InZnO Semiconductors for Oxide Thin-Film Transistors with High Performance and Stability

To fabricate oxide thin-film transistors (TFTs) with high performance and excellent stability, preparing high-quality semiconductor films in the channel bulk region and minimizing the defect states in the gate dielectric/channel interfaces and back-channel regions is necessary. However, even if an oxide transistor is composed of the same semiconductor film, gate dielectric/channel interface, and back channel, its electrical performance and operational stability are significantly affected by the thickness of the oxide semiconductor. In this study, solution process-based nanometer-scale thickness engineering of InZnO semiconductors was easily performed via repeated solution coating and annealing. The thickness-controlled InZnO films were then applied as channel regions, which were fabricated with almost identical film quality, gate dielectric/channel interface, and back-channel conditions. However, excellent operational stability and electrical performance suitable for oxide TFT backplane was only achieved using an 8 nm thick InZnO film. In contrast, the ultrathin and thicker films exhibited electrical performances that were either very resistive (high positive VTh and low on-current) or excessively conductive (high negative VTh and high off-current). This investigation confirmed that the quality of semiconductor materials, solution process design, and structural parameters, including the dimensions of the channel layer, must be carefully designed to realize high-performance and high-stability oxide TFTs.

Approaching Theoretical Limits in the Performance of Printed P-Type CuI Transistors via Room Temperature Vacancy Engineering

Development of a novel high performing inorganic p-type thin film transistor could pave the way for new transparent electronic devices. This complements the widely commercialized n-type counterparts, indium-gallium-zinc-oxide (IGZO). Of the few potential candidates, copper monoiodide (CuI) stands out. It boasts visible light transparency and high intrinsic hole mobility (>40 cm2 V-1 s-1 ), and is suitable for various low-temperature processes. However, the performance of reported CuI transistors is still below expected mobility, mainly due to the uncontrolled excess charge- and defect-scattering from thermodynamically favored formation of copper and iodine vacancies. Here, a solution-processed CuI transistor with a significantly improved mobility is reported. This enhancement is achieved through a room-temperature vacancy-engineering processing strategy on high-k dielectrics, sodium-embedded alumina. A thorough set of chemical, structural, optical, and electrical analyses elucidates the processing-dependent vacancy-modulation and its corresponding transport mechanism in CuI. This encompasses defect- and phonon-scattering, as well as the delocalization of charges in crystalline domains. As a result, the optimized CuI thin film transistors exhibit exceptionally high hole mobility of 21.6 ± 4.5 cm2 V-1 s-1 . Further, the successful operation of IGZO-CuI complementary logic gates confirms the applicability of the device.

Progress, Challenges, and Opportunities in Oxide Semiconductor Devices: A Key Building Block for Applications Ranging from Display Backplanes to 3D Integrated Semiconductor Chips

As Si has faced physical limits on further scaling down, novel semiconducting materials such as 2D transition metal dichalcogenides and oxide semiconductors (OSs) have gained tremendous attention to continue the ever-demanding downscaling represented by Moore's law. Among them, OS is considered to be the most promising alternative material because it has intriguing features such as modest mobility, extremely low off-current, great uniformity, and low-temperature processibility with conventional complementary-metal-oxide-semiconductor-compatible methods. In practice, OS has successfully replaced hydrogenated amorphous Si in high-end liquid crystal display devices and has now become a standard backplane electronic for organic light-emitting diode displays despite the short time since their invention in 2004. For OS to be implemented in next-generation electronics such as back-end-of-line transistor applications in monolithic 3D integration beyond the display applications, however, there is still much room for further study, such as high mobility, immune short-channel effects, low electrical contact properties, etc. This study reviews the brief history of OS and recent progress in device applications from a material science and device physics point of view. Simultaneously, remaining challenges and opportunities in OS for use in next-generation electronics are discussed.

Composition Engineering of Indium Zinc Oxide Semiconductors for Damage-Free Back-Channel Wet Etching Metallization of Oxide Thin-Film Transistors

In contrast to lift-off and shadow mask processes, the back-channel wet etching (BCWE) process is suitable for industrial-scale metallization processes for the large-area and mass production of oxide thin-film transistors (TFTs). However, chemical attacks caused by the corrosive metal etchants used in the BCWE process cause unintended performance degradation of oxide semiconductors, making it difficult to implement oxide TFT circuits through industrial-scale metallization processes. Herein, we propose composition engineering of oxide semiconductors to enhance the chemical durability and electrical stability of oxide semiconductors. The chemical durability of InZnO against Al etchants can be improved by increasing the content of indium oxide, which has a higher chemical resistance than zinc oxide. As a result, A damage-free BCWE-based metallization process was successfully demonstrated for oxide TFTs using In-rich InZnO semiconductors. Furthermore, In-rich InZnO TFTs with wet-etched Al electrodes exhibited electrical performance comparable to that of lift-off Al electrodes, without chemical attack issues.

Addressing the Conflict between Mobility and Stability in Oxide Thin-film Transistors

Amorphous oxide semiconductor thin-film transistors (AOS TFTs) are ever-increasingly utilized in displays. However, to bring high mobility and excellent stability together is a daunting challenge. Here, the carrier transport/relaxation bilayer stacked AOS TFTs are investigated to solve the mobility-stability conflict. The charge transport layer (CTL) is made of amorphous In-rich InSnZnO, which favors big average effective coordination number for all cations and more edge-shared structures for better charge transport. Praseodymium-doped InSnZnO is used as the charge relaxation layer (CRL), which substantially shortens the photoelectron lifetime as revealed by femtosecond transient absorption spectroscopy. The CTL and CRL with the thickness suitable for industrial production respectively afford minute potential barrier fluctuation for charge transport and fast relaxation for photo-generated carriers, resulting in transistors with an ultrahigh mobility (75.5 cm² V^-1 s^-1 ) and small negative-bias-illumination-stress/positive-bias-temperature-stress voltage shifts (-1.64/0.76 V). The design concept provides a promising route to address the mobility-stability conflict for high-end displays.

Integration Technology of Micro-LED for Next-Generation Display

Inorganic micro light-emitting diodes (micro-LEDs) based on III-V compound semiconductors have been widely studied for self-emissive displays. From chips to applications, integration technology plays an indispensable role in micro-LED displays. For example, large-scale display relies on the integration of discrete device dies to achieve extended micro-LED array, and full color display requires integration of red, green, and blue micro-LED units on the same substrate. Moreover, the integration with transistors or complementary metal-oxide-semiconductor circuits are necessary to control and drive the micro-LED display system. In this review article, we summarized the 3 main integration technologies for micro-LED displays, which are called transfer integration, bonding integration, and growth integration. An overview of the characteristics of these 3 integration technologies is presented, while various strategies and challenges of integrated micro-LED display system are discussed.

Ambipolar operation of progressively designed symmetric bidirectional transistors fabricated using single-channel vertical transistor and electrochemically prepared copper oxide

In this study, a symmetric bidirectional transistors (SBT) is proposed. The device simultaneously implements the "strong-inversion" and "accumulation" mechanisms of a metal-oxide semiconductor field-effect transistor and TFT, respectively, in different bias directions in a single-channel vertical transistor (V-Tr). This ideal SBT device is designed and fabricated by selecting appropriate materials exhibiting a narrow bandgap and intrinsic characteristics of Sb-doped p-type Cu2O, using a V-Tr to optimize the device structure for high-field-induced short-channel and ambipolar operation, and implementing facile electrochemical deposition for channel and plasma channel treatments. To adopt artificial conductivity control for producing the transporting path of minority electron carriers, the patterned-channel-layer sidewall is locally treated using oxygen plasma, thereby suppressing the minority-carrier self-compensation. The SBT device exhibits an excellent on-current (i.e., symmetric accumulation and strong inversion modes in the p- and n-type channel regions, respectively) and excellent midregion off-current, similar to those of ideal ambipolar transistors. Moreover, owing to multilevel signals and excellent inverter behaviors, the SBT device is suitable for application in complementary-metal-oxide-semiconductors and logic memories.

Evaporated nanometer chalcogenide films for scalable high-performance complementary electronics

The exploration of stable and high-mobility semiconductors that can be grown over a large area using cost-effective methods continues to attract the interest of the electronics community. However, many mainstream candidates are challenged by scarce and expensive components, manufacturing costs, low stability, and limitations of large-area growth. Herein, we report wafer-scale ultrathin (metal) chalcogenide semiconductors for high-performance complementary electronics using standard room temperature thermal evaporation. The n-type bismuth sulfide delivers an in-situ transition from a conductor to a high-mobility semiconductor after mild post-annealing with self-assembly phase conversion, achieving thin-film transistors with mobilities of over 10 cm² V^-1 s^-1, on/off current ratios exceeding 10⁸, and high stability. Complementary inverters are constructed in combination with p-channel tellurium device with hole mobilities of over 50 cm² V^-1 s^-1, delivering remarkable voltage transfer characteristics with a high gain of 200. This work has laid the foundation for depositing scalable electronics in a simple and cost-effective manner, which is compatible with monolithic integration with commercial products such as organic light-emitting diodes.

Scalable Growth of Organic Single-Crystal Films via an Orientation Filter Funnel for High-Performance Transistors with Excellent Uniformity

Organic single-crystal films (OSCFs) provide an unprecedented opportunity for the development of new-generation organic single-crystal electronics. However, crystallization of organic films is normally governed by stochastic nucleation and incoherent growth, posing a formidable challenge to grow large-sized OSCFs. Here, an "orientation filter funnel" concept is presented for the scalable growth of OSCFs with well-aligned, singly orientated crystals. By rationally designing solvent wetting/dewetting patterns on the substrate, this approach can produce seed crystals with the same crystallographic orientation and then maintain epitaxial growth of these crystals, enabling the formation of large-area OSCFs. As a result, this unique concept for crystal growth not only enhances the average mobility of organic film by 4.5-fold but also improves its uniformity of electrical properties, with a low mobility variable coefficient of 9.8%, the new lowest record among organic devices. The method offers a general and scalable route to produce OSCFs toward real-word electronic applications.

Improving Device Characteristics of Dual-Gate IGZO Thin-Film Transistors with Ar-O2 Mixed Plasma Treatment and Rapid Thermal Annealing

In this study, high-performance indium-gallium-zinc oxide thin-film transistors (IGZO TFTs) with a dual-gate (DG) structure were manufactured using plasma treatment and rapid thermal annealing (RTA). Atomic force microscopy measurements showed that the surface roughness decreased upon increasing the O2 ratio from 16% to 33% in the argon-oxygen plasma treatment mixture. Hall measurement results showed that both the thin-film resistivity and carrier Hall mobility of the Ar-O2 plasma-treated IGZO thin films increased with the reduction of the carrier concentration caused by the decrease in the oxygen vacancy density; this was also verified using X-ray photoelectron spectroscopy measurements. IGZO thin films treated with Ar-O2 plasma were used as channel layers for fabricating DG TFT devices. These DG IGZO TFT devices were subjected to RTA at 100 °C-300 °C for improving the device characteristics; the field-effect mobility, subthreshold swing, and ION/IOFF current ratio of the 33% O2 plasma-treated DG TFT devices improved to 58.8 cm2/V·s, 0.12 V/decade, and 5.46 × 108, respectively. Long-term device stability reliability tests of the DG IGZO TFTs revealed that the threshold voltage was highly stable.

Wide Bandgap Oxide Semiconductors: from Materials Physics to Optoelectronic Devices

Wide bandgap oxide semiconductors constitute a unique class of materials that combine properties of electrical conductivity and optical transparency. They are being widely used as key materials in optoelectronic device applications, including flat-panel displays, solar cells, OLED, and emerging flexible and transparent electronics. In this article, an up-to-date review on both the fundamental understanding of materials physics of oxide semiconductors, and recent research progress on design of new materials and high-performing thin film transistor (TFT) devices in the context of fundamental understanding is presented. In particular, an in depth overview is first provided on current understanding of the electronic structures, defect and doping chemistry, optical and transport properties of oxide semiconductors, which provide essential guiding principles for new material design and device optimization. With these principles, recent advances in design of p-type oxide semiconductors, new approaches for achieving cost-effective transparent (flexible) electrodes, and the creation of high mobility 2D electron gas (2DEG) at oxide surfaces and interfaces with a wealth of fascinating physical properties of great potential for novel device design are then reviewed. Finally, recent progress and perspective of oxide TFT based on new oxide semiconductors, 2DEG, and low-temperature solution processed oxide semiconductor for flexible electronics will be reviewed.

Film-Sponge-Coupled Triboelectric Nanogenerator with Enhanced Contact Area Based on Direct Ultraviolet Laser Ablation

Triboelectric nanogenerators (TENGs) recently have emerged as applicable and eco-friendly harvesting devices. Numerous studies have been actively conducted to fabricate a flexible and robust TENG with high-output performance. Herein, a film-sponge-coupled TENG (FS-TENG) is proposed using direct ultraviolet laser ablation, as a method for surface modification of a polyimide (PI) film. This state-of-the-art method has advantages of accuracy as well as time efficiency in creating the pattern on the surface; thus, the pre-designed patterns can be precisely constructed within only a minute. In the laser-ablated PI film, the structural design and chemical modification on the surface are investigated related to the triboelectric output performance. Thereafter, a sponge is fabricated based on non-woven polyamide and silicone rubber, which can fully contact with the micro-/nano-scaled structure on the surface of the PI film. After an optimization, the FS-TENG exhibits 48.19 V of open-circuit voltage and 1.243 μA of short-circuit current, which shows approximately 3 times enhanced electric performance compared to the FS-TENG using a pristine PI film. The FS-TENG device demonstrates its robustness through both mechanical stress and flexible stress by showing less than 5% degradation after 50,000 cycles. On the basis of the high flexibility and stability of the FS-TENG, a self-powered scoreboard is successfully developed for lighting a scoreboard in a soccer field. This feasible lighting system can be operated by harvesting the kinetic energy of a soccer player without an additional power source. The novel FS-TENG, thus, provides remarkable potential for a self-powered indoor harvesting system.

A Review of the Progress of Thin-Film Transistors and Their Technologies for Flexible Electronics

Flexible electronics enable various technologies to be integrated into daily life and fuel the quests to develop revolutionary applications, such as artificial skins, intelligent textiles, e-skin patches, and on-skin displays. Mechanical characteristics, including the total thickness and the bending radius, are of paramount importance for physically flexible electronics. However, the limitation regarding semiconductor fabrication challenges the mechanical flexibility of thin-film electronics. Thin-Film Transistors (TFTs) are a key component in thin-film electronics that restrict the flexibility of thin-film systems. Here, we provide a brief overview of the trends of the last three decades in the physical flexibility of various semiconducting technologies, including amorphous-silicon, polycrystalline silicon, oxides, carbon nanotubes, and organics. The study demonstrates the trends of the mechanical properties, including the total thickness and the bending radius, and provides a vision for the future of flexible TFTs.

An integrated actuating and sensing system for light-addressable potentiometric sensor (LAPS) and light-actuated AC electroosmosis (LACE) operation

To develop a lab on a chip (LOC) integrated with both sensor and actuator functions, a novel two-in-one system based on optical-driven manipulation and sensing in a microfluidics setup based on a hydrogenated amorphous silicon (a-Si:H) layer on an indium tin oxide/glass is first realized. A high-intensity discharge xenon lamp functioned as the light source, a chopper functioned as the modulated illumination for a certain frequency, and a self-designed optical path projected on the digital micromirror device controlled by the digital light processing module was established as the illumination input signal with the ability of dynamic movement of projected patterns. For light-addressable potentiometric sensor (LAPS) operation, alternating current (AC)-modulated illumination with a frequency of 800 Hz can be generated by the rotation speed of the chopper for photocurrent vs bias voltage characterization. The pH sensitivity, drift coefficient, and hysteresis width of the Si3N4 LAPS are 52.8 mV/pH, -3.2 mV/h, and 10.5 mV, respectively, which are comparable to the results from the conventional setup. With an identical two-in-one system, direct current illumination without chopper rotation and an AC bias voltage can be provided to an a-Si:H chip with a manipulation speed of 20 μm/s for magnetic beads with a diameter of 1 μm. The collection of magnetic beads by this light-actuated AC electroosmosis (LACE) operation at a frequency of 10 kHz can be easily realized. A fully customized design of an illumination path with less decay can be suggested to obtain a high efficiency of manipulation and a high signal-to-noise ratio of sensing. With this proposed setup, a potential LOC system based on LACE and LAPS is verified with the integration of a sensor and an actuator in a microfluidics setup for future point-of-care testing applications.

Graded Channel Junctionless InGaZnO Thin-Film Transistors with Both High Transporting Properties and Good Bias Stress Stability

InGaZnO (IGZO) is currently the most prominent oxide semiconductor complement to low-temperature polysilicon for thin-film transistor (TFT) applications in flat panel displays. However, the compromised transport performance and bias stress instability are critical issues inhibiting its application in ultrahigh-resolution optoelectronic displays. Here, we report the fabrication of graded channel junctionless IGZO:O|N TFTs with both high transporting properties and good bias stress stability by systematic manipulation of oxygen vacancy (V_O) defects through sequential O antidoping and O/N codoping of the continuous IGZO framework. The transporting properties and bias stress stability of the graded channel IGZO:O|N TFTs, which exhibited high field-effect mobilities close to 100 cm² V^-1 s^-1, negligible performance degradations, and trivial threshold voltage shifts against gate bias stress and photobias stress, are simultaneously improved compared to those of the controlled single-channel uniformly doped IGZO:O TFTs, IGZO:N TFTs, and double-channel barrier-confined IGZO:O/IGZO:N TFTs. The synergistic improvements are attributed to the sequential mobility and stability enhancement effects of O antidoping and O/N codoping where triple saturation currents are induced by O antidoping of the front-channel regime while the trapped electrons and photoexcited holes in the back-channel bulk and surface regions are suppressed by O/N codoping. More importantly, fast accumulation and barrier-free full depletion are rationally realized by eliminating the junction interface within the graded channel layer. Our observation identifies that graded channel doping could be a powerful way to synergistically boost up the transport performance and bias stress stability of oxide TFTs for new-generation ultrahigh-definition display applications.