Graduate Thesis Or Dissertation
 

DC/AC Stability of In-Ga-Zn-O Thin-Film Transistors

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  • The electrical stability of amorphous indium-gallium-zinc oxide (a-IGZO) thinfilmtransistors (TFTs) is investigated for flat-panel display applications. Althoughproducts incorporating a-IGZO TFT backplanes are already commercially available,e.g., iMac with 5K retina display, technical challenges need to be addressed for nextgenerationapplications, e.g., active-matrix organic light-emitting diode displays.Device stability is one crucial issue. The objective of the research presented herein isto provide an in-depth assessment of the effect of DC and AC bias temperature stresson 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 operationtemperature, using a bipolar AC waveform rather than a unipolar waveform, oremploying an optimized passivation layer that suppresses moisture incorporation intothe a-IGZO channel layer. A two-parameter stretched-exponential expression is usedto describe the time-dependent instability trend. The long-term reliability of an a-IGZOTFT as a function of gate voltage, temperature, or duty ratio is successfully modeledusing the two-parameter stretched-exponential expression. The stretched-exponentialactivation energy is correlated with the Meyer-Neldel rule activation entropy.Technology computer-aided design (TCAD) simulation provides insight into thenatural 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.
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  • Existing Confidentiality Agreement
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  • 2017-11-08 to 2019-10-21

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