Instability and temperature-dependence assessment of IGZO TFTs Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/1n79h788g

Descriptions

Attribute NameValues
Creator
Abstract or Summary
  • Amorphous oxide semiconductors (AOSs) are of great current interest for thin-film transistor (TFT) channel layer applications. In particular, indium gallium zinc oxide (IGZO) is under intense development for commercial applications because of its demonstrated high performance at low processing temperatures. The objective of the research presented in this thesis is to provide detailed assessments of device stability, temperature dependence, and related phenomena for IGZO-based TFTs processed at temperatures between 200 °C and 300 °C. TFTs tested exhibit an almost rigid shift in log₁₀(I[subscript D]) – V[subscript GS] transfer curves in which the turn-on voltage, V[subscript ON], moves to a more positive gate voltage with increasing stress time during constant-voltage bias-stress testing of IGZO TFTs. TFT stability is improved as the post-deposition annealing temperature increases over the temperature range of 200 – 300 ºC. The turn-on voltage shift induced by constant-voltage bias-stressing is at least partially reversible; V[subscript ON] tends to recover towards its initial value of V[subscript ON] if the TFT is left unbiased in the dark for a prolonged period of time and better recovery is observed for a longer recovery period. V[subscript ON] for a TFT can be set equal to zero after bias-stress testing if the TFT electrodes are grounded and the TFT is maintained in the dark for a prolonged period of time. Attempts to accelerate the recovery process by application of a negative gate bias at elevated temperature (i.e., 100 ºC) were unsuccessful, resulting in severely degraded subthreshold swing. An almost rigid log₁₀(I[subscript D]) – V[subscript GS] transfer curve shift to a lower (more negative) V[subscript ON] with increasing temperature is observed in the range of –50 °C to +50 °C, except for a TFT with an initial V[subscript ON] equal to zero, in which case the log₁₀(ID) – V[subscript GS] transfer curve is temperature-independent. A more detailed temperature-dependence assessment, however, indicates that the log₁₀(I[subscript D]) – V[subscript GS] transfer curve shift is not exactly rigid since the mobility is found to increase slightly with increasing temperature. A noticeable anomaly is observed in certain log₁₀(I[subscript D]) – VGS transfer curves, especially when obtained at elevated temperature (e.g., 30 and 50 ºC), in which I[subscript D] decreases precipitously near zero volts in the positive gate voltage sweep. This anomaly is attributed to a gate-voltage-step-involved detrapping and subsequent retrapping of electrons in the accumulation channel and/or channel/gate insulator interface. In fact, all IGZO TFT stability and temperature-dependence trends are attributed to channel interface and/or channel bulk trapping/detrapping.
Resource Type
Date Available
Date Copyright
Date Issued
Degree Level
Degree Name
Degree Field
Degree Grantor
Commencement Year
Advisor
Committee Member
Academic Affiliation
Non-Academic Affiliation
Keyword
Subject
Rights Statement
Language
Replaces
Additional Information
  • description.provenance : Approved for entry into archive by Julie Kurtz(julie.kurtz@oregonstate.edu) on 2008-11-06T18:38:12Z (GMT) No. of bitstreams: 1 MS Thesis.pdf: 10734090 bytes, checksum: 28cdab2803b2f09f3cddd46963352630 (MD5)
  • description.provenance : Approved for entry into archive by Laura Wilson(laura.wilson@oregonstate.edu) on 2008-11-12T22:26:21Z (GMT) No. of bitstreams: 1 MS Thesis.pdf: 10734090 bytes, checksum: 28cdab2803b2f09f3cddd46963352630 (MD5)
  • description.provenance : Submitted by Ken Hoshino (hoshinok@onid.orst.edu) on 2008-11-02T19:23:04Z No. of bitstreams: 1 MS Thesis.pdf: 10734090 bytes, checksum: 28cdab2803b2f09f3cddd46963352630 (MD5)
  • description.provenance : Made available in DSpace on 2008-11-12T22:26:22Z (GMT). No. of bitstreams: 1 MS Thesis.pdf: 10734090 bytes, checksum: 28cdab2803b2f09f3cddd46963352630 (MD5)

Relationships

Parents:

This work has no parents.

Last modified

Downloadable Content

Download PDF

Items