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PhD Final Examination – Fan Zhou


Thursday, September 14, 2017 10:00 AM - 12:00 PM

DC/AC Stability of In-Ga-Zn-O Thin-Film Transistors
The electrical stability of amorphous indium-gallium-zinc oxide (a-IGZO) thin-film transistors (TFTs) is investigated for flat-panel display applications. Although products incorporating a-IGZO TFT backplanes are already commercially available, e.g., iMac with 5K retina display from Apple, Inc., technical challenges need to be addressed for next-generation applications, e.g., active-matrix organic light-emitting diode displays. Device stability is one crucial issue. The objective of the research presented herein is to provide an in-depth assessment of the effect of DC and AC bias temperature stress on the stability of a-IGZO TFTs. It is found that TFT threshold voltage instability, ΔVTH, is reduced by decreasing the unipolar AC duty ratio, decreasing the operation temperature, using a bipolar AC waveform rather than a unipolar waveform, or employing an optimized passivation layer that suppresses moisture incorporation into the a-IGZO channel layer. A two-parameter stretched-exponential expression is used to describe the time-dependent instability trend. The long-term reliability of an a-IGZO TFT as a function of gate voltage, temperature, or duty ratio is successfully modeled using the two-parameter stretched-exponential expression. The stretched-exponential activation energy is correlated with the Meyer-Neldel rule activation entropy. Technology computer-aided design (TCAD) simulation provides insight into the natural of a-IGZO TFT instability from the perspective of the subgap density of states (DOS). It is found that less DOS change results in a more stable TFT.

Major Advisor: John Wager
Committee: Larry Cheng
Committee: John Conley
Committee: Alan Wang
GCR: Oksana Ostroverkhova


Kelley Engineering Center (campus map)
1007
Calvin Hughes
1 541 737 3168
Calvin.Hughes at oregonstate.edu
Sch Elect Engr/Comp Sci
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