Semiconductors and Devices

A numerical analysis of the electrical characteristics of small-grains poly-Si TFTs

N. H. Touidjen^a1 and F. Mansour^a1

LEMEA MED Laboratory, Department of Electronics, Faculty of the Engineer's Sciences, University of Mentouri Constantine, Algeria

Abstract

Voltage characteristics of polysilicon thin films transistors (Poly-Si TFTs) are related to basic material and device parameters. Understanding and modeling the electrical behavior of poly-Si TFT require knowledge of equivalent properties of polysilicon which are strongly affected by defects present in this material. A numerical analysis, which studies the electrical characteristics of small-grains poly-Si TFTs, has been investigated. The density of states (DOS) in the band gap is modeled by assuming an exponential distribution of deep and tail states. The proposed model evaluates the influence of both deep and tail states on the electrical conduction process and the dominant contribution of tail states on the threshold voltage values while the deep states in the middle of polysilicon gap controls the lower threshold regime. The surface potential and ON/OFF current ratio are also calculated. The comparison of the generated current-voltage characteristics obtained from numerical simulation TCAD-ATLAS with those reported in the literature show a good agreement.

(Received August 18 2008)

(Revised April 22 2009)

(Accepted April 27 2009)

(Online publication July 21 2009)

PACS:

• 71 – Electronic structure of bulk materials;
• 71.55.-i – Impurity and defect levels;
• 71.55.Jv – Disordered structures; amorphous and glassy solids;
• 71.23.An – Theories and models; localized states

houdatouidjen@yahoo.fr