Oxide semiconductor-based thin-film transistors (TFTs) have emerged as a critical technology for modern electronics, particularly in display applications. Among the most studied materials are indium-gallium-zinc oxide (IGZO) and zinc oxide (ZnO), which offer a unique combination of high mobility, transparency, and low-temperature processing compatibility. These materials have enabled advancements in high-resolution, low-power displays, including active-matrix organic light-emitting diode (AMOLED) and liquid crystal displays (LCDs). This article explores the key aspects of oxide semiconductor TFTs, focusing on channel engineering, contact resistance reduction, and mobility enhancement techniques, while also discussing their display applications.

The performance of oxide TFTs heavily depends on the properties of the semiconductor channel. IGZO, for instance, is favored due to its amorphous nature, which ensures uniformity over large areas and reduces grain boundary scattering. The composition of IGZO can be tuned to optimize performance, with indium contributing to high mobility, gallium improving stability, and zinc aiding in film formation. ZnO, on the other hand, is often used in polycrystalline form, which can achieve higher mobility but may suffer from variability due to grain boundaries. Channel engineering involves optimizing the stoichiometry, doping, and deposition conditions to achieve the desired electrical characteristics. For example, increasing the indium content in IGZO can enhance electron mobility but may also lead to higher off-currents, requiring careful balancing.

Contact resistance is a significant challenge in oxide TFTs, as it can limit the overall device performance. The interface between the oxide semiconductor and the source/drain electrodes often forms a Schottky barrier, leading to high contact resistance. To mitigate this, several strategies are employed. One approach is the use of low-work-function metals, such as titanium or molybdenum, which reduce the barrier height for electron injection. Another method involves doping the contact regions heavily to create ohmic contacts. For instance, hydrogen plasma treatment or argon ion bombardment can increase the carrier concentration near the contacts, lowering resistance. Additionally, inserting a thin interlayer, such as aluminum-doped ZnO, between the semiconductor and the metal electrodes can improve charge injection.

Mobility enhancement is another critical area of research for oxide TFTs. While IGZO typically exhibits mobilities in the range of 10–30 cm²/Vs, higher values are desirable for faster switching and better display performance. One way to achieve this is through post-deposition annealing, which can reduce defects and improve crystallinity in ZnO-based TFTs. For amorphous IGZO, mobility is primarily determined by the overlap of metal s-orbitals, so optimizing the composition and deposition conditions is key. Another technique involves dual-gate or back-channel passivation designs, which can suppress interface traps and enhance carrier transport. High-k dielectrics, such as hafnium oxide or aluminum oxide, are also used to increase gate capacitance, thereby improving the on-current without requiring higher mobility.

The applications of oxide TFTs in displays are vast and transformative. Their high mobility and uniformity make them ideal for driving pixels in high-resolution AMOLED displays, where consistent performance across the panel is crucial. Unlike traditional silicon-based TFTs, oxide semiconductors can be deposited at low temperatures, enabling their use on flexible substrates for foldable and rollable displays. Additionally, their low off-currents contribute to reduced power consumption, a critical factor for battery-powered devices. Oxide TFTs are also being explored for ultra-high-definition LCDs, where their fast response times and excellent switching characteristics enhance image quality.

Stability is a key consideration for oxide TFTs in display applications. Bias stress, both under positive and negative gate voltages, can cause threshold voltage shifts over time, leading to image retention or brightness variations. This instability is often attributed to charge trapping at the semiconductor-dielectric interface or oxygen vacancy migration. Strategies to improve stability include careful selection of dielectric materials, such as silicon nitride or aluminum oxide, which can reduce trap densities. Passivation layers, such as silicon oxide or organic polymers, are also used to protect the channel from environmental factors like moisture and oxygen, which can degrade performance.

The transparency of oxide semiconductors is another advantage for displays. Unlike opaque silicon, materials like IGZO and ZnO are transparent in the visible spectrum, allowing for brighter and more energy-efficient displays. This property is particularly beneficial for transparent displays or augmented reality applications, where the TFT backplane must not obstruct light transmission. The combination of transparency and high performance makes oxide TFTs a leading candidate for next-generation display technologies.

Scalability is another strength of oxide semiconductor TFTs. The deposition techniques, such as sputtering or solution processing, are compatible with large-area manufacturing, making them cost-effective for mass production. This scalability has driven their adoption in consumer electronics, where large displays are produced in high volumes. Furthermore, the ability to integrate oxide TFTs with other emerging technologies, such as quantum dot LEDs or micro-LEDs, opens new possibilities for future display innovations.

In summary, oxide semiconductor-based TFTs, particularly those using IGZO and ZnO, have revolutionized display technology through their unique combination of high mobility, transparency, and scalability. Channel engineering, contact resistance reduction, and mobility enhancement techniques are critical to optimizing their performance. Their applications in AMOLED and LCD displays highlight their importance in modern electronics, offering advantages in power efficiency, resolution, and flexibility. As research continues to address challenges like stability and contact resistance, oxide TFTs are poised to remain at the forefront of display innovation.