Defense Event

Amorphous In-Ga-Zn-O Thin-Film Transistors for Next Generation Ultra-High Definition Active-Matrix Liquid Crystal Displays

Eric Kai-Hsiang Yu

PhD Candidate
Friday, April 03, 2015
09:00am - 11:00am
2000A Phoenix Memorial Laboratory

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About the Event

Next generation ultra-high definition (UHD) active-matrix flat-panel displays have resolutions of 3840×2160 (4K) or 7680×4320 (8K) pixels shown at 120 Hz. The UHD display is expected to bring about viewing experiences with immersive sensation and perceived realness. The amorphous In-Ga-Zn-O (a-IGZO) thin-film transistor (TFT) is a prime candidate to be the backplane technology for UHD active-matrix liquid crystal displays (AM-LCDs) because it simultaneously fulfills two critical requirements: (i) sufficiently high field-effect mobility (μFE = 10 cm2/V·s) and (ii) uniform deposition in the amorphous phase over a large area. We have developed a robust a-IGZO density of states (DOS) model based on a combination of experimental results and information available in the literature. The impact of oxygen partial pressure during a-IGZO deposition on TFT electrical properties/instability is studied. Photoluminescence (PL) spectra are measured for a-IGZO thin films of different processing conditions to identify the most likely electron-hole recombination. For the first time, we report the PL spectra measured within the a-IGZO TFT channel region, and differences before/after bias-temperature stress (BTS) are compared. To evaluate the reliability of a-IGZO TFTs for UHD AM-LCD backplane, we have studied its ac BTS instability using a comprehensive set of conditions including unipolar/bipolar pulses, frequency, duty cycle, and drain biases. The TFT dynamic response, including charging characteristics and feedthrough voltage (ΔVP), are studied within the context of 4K and 8K UHD AM-LCD and comparisons are made to hydrogenated amorphous silicon technology. We show that the a-IGZO TFT is fully capable of supporting 8K UHD at 480 Hz. In addition, it is feasible to reduce a-IGZO TFT ΔVP by controlling for non-abrupt TFT switch-off.

Additional Information

Sponsor(s): ECE

Faculty Sponsor: Jerzy Kanicki

Open to: Public