TITLE:
Influence of Extended Bias Stress on the Electrical Parameters of Mixed Oxide Thin Film Transistors
AUTHORS:
Winnie P. Mathews, Rajitha N. P. Vemuri, Terry L. Alford
KEYWORDS:
Electrical Stress; a-IGZO; Thin Film Transistors; Degradation; Threshold Voltage; Drain to Source Resistance; Power Factor; Equivalent Circuit
JOURNAL NAME:
Circuits and Systems,
Vol.3 No.4,
October
30,
2012
ABSTRACT: This paper investigates the variation of electrical characteristic of indium gallium zinc oxide (IGZO) thin film transistors (TFTs) under gate bias stress. The devices are subjected to positive and negative gate bias stress for prolonged time periods. The effect of bias stress time and polarity on the transistor current equation is investigated and the underlying effects responsible for these variations are determined. Negative gate stress produces a positive shift in the threshold voltage. This can be noted as a variation from prior studies. Due to variation of power factor (n) from two, the integral method is implemented to extract threshold voltage (vt) and power factor (n). Effective, mobility (ueff), drain to source resistance (RDS) and constant k' is also extracted from the device characteristics. The unstressed value of n is deter-mined to be 2.5. The power factor increases with gate bias stress time. The distribution of states in the conduction band is revealed by the variation in power factor.