Wan-Fang Chung

Bias-induced oxygen adsorption in zinc tin oxide thin film transistors under dynamic stress

This study investigates the effects of bias-induced oxygen adsorption on the electrical characteristic instability of zinc tin oxide thin film transistors in different ambient oxygen partial pressures. When oxygen pressure is largest, the threshold voltages showed the quickest increase but the slowest recovery during the stress phase and recovery phase, respectively. This finding corresponds to the charge trapping time constant and recovery time constant, which are extracted by fitting the stretched-exponential equation and which exhibit a relationship with oxygen pressure. We suggest that the gate bias reduces the activation energy of oxygen adsorption during gate bias stress.

Environment-dependent thermal instability of sol-gel derived amorphous indium- gallium-zinc-oxide thin film transistors

The environment-dependent electrical performances as a function of temperature for sol-gel derived amorphous indium-gallium-zinc-oxide (a-IGZO) thin film transistors are investigated in this letter. In the ambients without oxygen, thermal activation dominates and enhances device performance. In oxygen-containing environments, mobility and drain current degrades and the threshold slightly increase as temperature increases. We develop a porous model for a-IGZO film relating to the drain current and mobility lowering due to film porosity and oxygen adsorption/penetration. It also relates to the threshold voltage recovery at high temperature owing to the varying form of adsorbed oxygen and the combination of oxygen and vacancies.

High-stability oxygen sensor based on amorphous zinc tin oxide thin film transistor

This research presents a sol-gel derived zinc tin oxide thin film transistor (TFT) as a high-stability oxygen sensor. Due to its high sensitivity, oxygen has been traditionally regarded as having a negative influence on the electrical characteristics of zinc-based TFTs; however, TFTs can also act as an oxygen sensor. After illumination with visible light in oxygen-rich ambient, a significant increase in drain current of nearly 104 times occurs with fixed gate and drain voltages. It is expected that an optimized method of illumination can help to reset the electrical characteristics or distinguish the on/off state of this reliable oxygen sensor.

The Impact of Active Layer Pre-Treatment on Bias Stress Stability of Sol-gel Derived Amorphous Indium-Gallium-Zinc-Oxide Thin Film Transistor

We have investigated the gate bias stress-induced instability on the electrical properties with different pre-treatments for sol-gel derived amorphous indium gallium zinc oxide thin film transistors (a-IGZO TFTs). The device with illuminating and heating pretreatments under the positive/negative gate bias stress in vacuum had the smallest threshold voltage shift as the stress duration increased, while the device with oxygen gas pre-treatment exhibited an obvious variation. These electrical instabilities were ascribed to the charge trapping in the gate insulator and the oxygen/water adsorption on the active layer. It indicates that the specific pre-treatment for the a-IGZO film can improve the device stability. It also provides the important information for the subsequent passivation process concerning the pre-treatment of the active layer.

Effects of Post-Deposition Annealing Atmosphere and Duration on Sol-Gel Derived Amorphous Indium-Zinc-Oxide Thin Film Transistors

This work shows the effects of post-deposition annealing atmosphere and duration on the properties of sol-gel derived amorphous indium zinc oxide thin film transistors (a-IZO TFTs). Two different post-deposition annealing atmospheres, nitrogen and oxygen, were used in this study. Experimental results showed that the O2-annealed devices showed better electrical characteristics than the N2-annealed samples. Under O2-annealing, field effect mobility was enhanced to 1.47 cm 2 /V s, the threshold voltage increased to -4.61 V and the subthreshold swing improved to 0.86 V/dec. Also, the transfer characteristics of a-IZO TFTs improve with annealing time. X-ray photoelectron spectroscopy (XPS) analysis indicated that the chemical composition of the IZO film was modified by the oxygen annealing.