Hsiao-Wen Zan

Oxygen-Dependent Instability and Annealing/Passivation Effects in Amorphous In–Ga–Zn–O Thin-Film Transistors

This letter discusses the reason for the instability of amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistors (TFTs) under both positive and negative bias stresses. This instability is significantly influenced by the oxygen content in the bulk IGZO and the surrounding environment. The as-fabricated low-temperature devices can only endure a single polarized bias stress. An a-IGZO TFT that is stable toward both positive and negative bias stresses with large relaxation times of 95 × 104 and 371 × 104 s, respectively, is achieved by annealing and passivation.

Achieving High Field-Effect Mobility in Amorphous Indium-Gallium-Zinc Oxide by Capping a Strong Reduction Layer

An effective approach to reduce defects and increase electron mobility in a-IGZO thin-film transistors (a-IGZO TFTs) is introduced. A strong reduction layer, calcium, is capped onto the back interface of a-IGZO TFT. After calcium capping, the effective electron mobility of a-IGZO TFT increases from 12 cm(2) V(-1) s(-1) to 160 cm(2) V(-1) s(-1). This high mobility is a new record, which implies that the proposed defect reduction effect is key to improve electron transport in oxide semiconductor materials.

Dual gate indium-gallium-zinc-oxide thin film transistor with an unisolated floating metal gate for threshold voltage modulation and mobility enhancement

In this study, we propose a floating dual gate (FDG) indium-gallium-zinc-oxide (IGZO) thin film transistor (TFT) with a floating metal back gate that is directly contact with IGZO without a dielectric layer. The floating back gate effect is investigated by changing the work function (ϕ) of the back gate. The FDG IGZO TFT exhibits an improved field-effect mobility (μ), unchanged subthreshold swing (SS), high on/off current ratio, and a tunable threshold voltage ranged (Vth) from −5.0 to +7.9 V without an additional back gate power supply.

Room-temperature-operated sensitive hybrid gas sensor based on amorphous indium gallium zinc oxide thin-film transistors

An organic sensing layer is capped onto an amorphous indium gallium zinc oxide (a-IGZO) thin-film transistor (TFT) to form a hybrid sensor. The organic layer, served as a second gate, forms a p-n junction with the a-IGZO film. Oxidizing or reducing vapor molecules act like electron acceptors or electron donors to change the potential of the organic layer and the current of a-IGZO TFT. A sensitive and reversible response to 100 ppb ammonia and 100 ppb acetone is obtained at room temperature. This letter opens a route to develop low-cost large-area bio/chemical sensor arrays based on the emerging a-IGZO TFT technology.

Continuous blade coating for multi-layer large-area organic light-emitting diode and solar cell

A continuous roll-to-roll compatible blade-coating method for multi-layers of general organic semiconductors is developed. Dissolution of the underlying film during coating is prevented by simultaneously applying heating from the bottom and gentle hot wind from the top. The solvent is immediately expelled and reflow inhibited. This method succeeds for polymers and small molecules. Uniformity is within 10% for 5 cm by 5 cm area with a mean value of tens of nanometers for both organic light-emitting diode (OLED) and solar cell structure with little material waste. For phosphorescent OLED 25 cd/A is achieved for green, 15 cd/A for orange, and 8 cd/A for blue. For fluorescent OLED 4.3 cd/A is achieved for blue, 9 cd/A for orange, and 6.9 cd/A for white. For OLED with 2 cm by 3 cm active area, the luminance variation is within 10%. Power conversion efficiency of 4.1% is achieved for polymer solar cell, similar to spin coating using the same materials. Very-low-cost and high-throughput fabrication of efficient ...

Investigation of efficiency droop for InGaN-based UV light-emitting diodes with InAlGaN barrier

The efficiency droop in InGaN-based UV light emitting device (LED) with AlGaN and InAlGaN barrier is investigated. Electroluminescence results indicate that the light performance of quaternary LEDs can be enhanced by 25% and 55% at 350 mA and 1000 mA, respectively. Furthermore, simulations show that quaternary LEDs exhibit 62% higher radiative recombination rate and low efficiency degradation of 13% at a high injection current. We attribute this improvement to increasing of carrier concentration and uniform redistribution of carriers.

Pentacene-Based Organic Thin Film Transistors for Ammonia Sensing

Non-invasive ammonia sensors are attractive alternatives for the diagnoses of a variety of chronic diseases such as liver cirrhosis and renal failure. A low cost pentacene-based organic thin film transistor (OTFT) fabricated by a novel and simple process was demonstrated to be highly sensitive and specific for ammonia gas. Various measurement parameters that reflected OTFT device characteristics for ammonia detection were investigated. Significant variations of the turn-on current, intrinsic mobility, and threshold voltage (Vth) were observed while subthreshold swing (S.S.) was almost unchanged to the alteration of ammonia concentration. The OTFT device detected 0.5 ~ 5 ppm concentration ammonia gas at room temperature, which is in the critical range that can distinguish between healthy person and paticents with liver cirrhosis and renal failure. The sensitivity of the device was further enhanced following a simple UV irradiation treatment to modify the functional groups on poly(methyl methacrylate) (PMMA) dielectric layer. Possible interference for ammonia detection such as humidity effect and selectivity among nitrogen, alcohol, carbon dioxide, acetone, methane and ammonia were also examined. We concluded that the proposed pentacene-based OTFT is a promising device for the future application in non-invasive medical diagnoses.

Amorphous indium-gallium-zinc-oxide visible-light phototransistor with a polymeric light absorption layer

This work demonstrates a real-time visible-light phototransistor comprised of a wide-band-gap amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistor (TFT) and a narrow-band-gap polymeric capping layer. The capping layer and the IGZO layer form a p-n junction diode. The p-n junction absorbs visible light and consequently injects electrons into the IGZO layer, which in turn affects the body voltage as well as the threshold voltage of a-IGZO TFT. The hysteresis behavior due to the charges at IGZO back interface is also discussed.

Effective Mobility Enhancement by Using Nanometer Dot Doping in Amorphous IGZO Thin‐Film Transistors

IO N With a high mobility ( > 10 cm 2 V − 1 s − 1 ) and a low threshold voltage ( < 5 V) in low-temperature processes, transparent oxide semiconductor thin-fi lm transistors (TOS TFTs) have drawn considerable attention due to their applications on fl exible displays, level shifters, drivers, and pixel-driving circuits for activematrix organic light-emitting-diode (AMOLED) displays. [ 1 − 3 ] In addition to display applications, amorphous indium gallium zinc oxide (a-IGZO) TFTs are also promising for the development of radio-frequency identifi cation (RFID) tags, smart cards, and other types of fl exible electronics. When TOS TFTs are developed for a low-power high-frequency circuit, high electron mobility and a low parasitic capacitance are required. Most TFTs fabricated with ZnO, SnO 2 , In 2 O 3 , IGZO, or other semiconducting oxide thin fi lms exhibit electron mobilities smaller than 35 cm 2 V − 1 s − 1 . [ 4–6 ] Recent reports on transparent oxide nanowire transistors (NWTs) have demonstrated high electron mobilities approximately 70 to 4000 cm 2 V − 1 s − 1 . [ 7–9 ] The quasi1D structure of NWTs may reduce low-angle carrier scattering to produce high electron mobility. [ 9 ] However, the fabrication process of NWTs has poor reproducibility and is still not practical for real-world applications. Because TOS transistors are transparent, developing TOS circuits on windows is appealing. Particularly, for modern buildings or trains with series of windows, TOS RFID circuits on windows can deliver various types of signals through a low-power transmission system. In this type of application, the dimension of the transparent transistor can be large because an integrated circuit on a small chip is not necessary. A low-cost production method for delivering a highperformance TOS transistor is a critical challenge. Here, a nanostructure to improve the effective mobility in a-IGZO TFTs is proposed. A large channel dimension of 1000 μ m, defi ned by a shadow mask, is utilized. The nanostructure is developed using a low-cost, lithography-free process to produce abundant nanometer-scale dot-like doping in a-IGZO channel. The new method, called nanodot doping (NDD) increases the effective electron mobility to a level 19 times higher than that of the control and the intrinsic electron mobility is also 10 times higher than that of the control. This study demo nstrates a process utilizing self-organized polystyrene spheres with a diameter of 200 nm to fabricate a porous gate structure. Ar plasma treatment through the porous gate performs dot-like doping on a-IGZO channel region. A top-gate

High efficiency light emitting diode with anisotropically etched GaN-sapphire interface

We report the fabrication and study of high efficiency ultraviolet light emitting diodes with inverted micropyramid structures at GaN-sapphire interface. The micropyramid structures were created by anisotropic chemical wet etching. The pyramid structures have significantly enhanced the light output efficiency and at the same time also improved the crystal quality by partially relieving the strain and reducing the dislocation defects in GaN. The electroluminescent output power at normal direction was enhanced by 120% at 20 mA injection current and the output power integrated over all directions was enhanced by 85% compared to a reference sample.