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Compact Spice Modeling and Design Optimization of Low Leakage a-Si:H TFTs for Large-Area Imaging Systems

Published online by Cambridge University Press:  10 February 2011

R.V.R. Murthy ,
D. Pereira ,
B. Park ,
A. Nathan  and
S.G. Chamberlain
R.V.R. Murthy
Affiliation:
ECE Department, University of Waterloo, Waterloo, Ontario, Canada, N2L 3G I, murthy@venus.uwaterloo.ca
D. Pereira
Affiliation:
ECE Department, University of Waterloo, Waterloo, Ontario, Canada, N2L 3G I
B. Park
Affiliation:
ECE Department, University of Waterloo, Waterloo, Ontario, Canada, N2L 3G I
A. Nathan
Affiliation:
ECE Department, University of Waterloo, Waterloo, Ontario, Canada, N2L 3G I
S.G. Chamberlain
Affiliation:
DALSA Inc., 605 McMurray Rd., Waterloo, Ontario N2V 2E9, Canada
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Abstract

We present a SPICE model that takes into account the different mechanisms contributing to leakage current in hydrogenated amorphous silicon (a-Si:H) thin film transistors (TFTs). The main sources of leakage current in these devices have been identified to be the parasitic reverse-biased p-i-n diode at the vicinity of the drain as well as diffusion of phosphorous atoms from micro-crystalline (n+ μc-Si:H) contact layer into the intrinsic a-Si:H region. The latter gives rise to ohmic conduction which dominates at very low drain voltages (< I V) and very low gate voltages (< 5 V). At higher gate voltages (5V ≤ VG ≤ 20 V), the reverse current of the parasitic p-i-n diode can be attributed to thermal generation of electrons from the valence to conduction bands through the mid-gap states in the a-Si:H. At even higher gate voltages (> 20 V), the reverse current is due to trap-assisted tunneling, whereby the electrons tunnel to the conduction band via the mid-gap states. A systematic characterization of TFTs with different a-Si:H layer thicknesses shows that the optimal thickness for low leakage current is around 50 nm. The bias dependent leakage current behavior has been modeled and implemented in SPICE using simple circuit elements based on voltage controlled current sources (VCCS). Simulated and measured reverse leakage current characteristics are in reasonable agreement.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 507: Symposium A – Amorphous & Microcrystalline Silicon Technology 1998 , 1998 , 415
Copyright
Copyright © Materials Research Society 1998

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References

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