Effect of Channel-Width Widening on a Poly-Si Thin-Film Transistor Structure in the Linear Region

Abstract

This is the first paper to discuss the ON-state drain-current of a special thin-film transistor structure with a wide channel width and a narrow source/drain width in the linear region. The experimental results indicate that when the channel width is wider than the source/drain width, the side-channel current effect is generated. This effect increases the ON-state drain-current due to the additional current-flow paths existing in the side-channel regions and low channel resistance. As the side-channel width increases, the ON-state drain-current initially increases and then gradually becomes independent of the side-channel width when the side-channel width is larger than the effective side-channel width, which depends on the channel width and is largely independent of the source/drain width. This paper also demonstrates that the ON-state drain-current gain is directly proportional to the channel length and the ratio of the channel length to the source/drain width and dependent on the side-channel width.Index Terms-Drain-current, poly-Si thin-film transistor (TFT), source/drain width, wide channel width. I. INTRODUCTIONL OW-TEMPERATURE polycrystalline-silicon thin-film transistors (TFTs) are one of the most promising technologies for the ultimate goal of building large-area electronic systems on glass substrates [1]. In flat-panel liquid-crystal, electroluminescence, and plasma displays, as well as other applications such as high-speed printers and page-width optical scanners, poly-Si TFTs can be utilized to integrate peripheral driver circuits on glass for system integration [2]. To integrate peripheral driving circuits on the same glass substrate, a large current drive and a high drain breakdown voltage are necessary for poly-Si TFT devices. Previous studies reported that use of a thin active-channel film is beneficial in obtaining a high current drive [3], [4]. However, the use of a thin activechannel layer typically results in poor source/drain contact and large parasitic series resistance. A thick source/drain region not only reduces the lateral electric field, thus maintaining the Manuscript