Double-Gate Two-Step Source/Drain Poly-Si Thin-Film Transistor

Feng-Tso Chien,Ching-Hwa Cheng,Hsien-Chin Chiu,Chih-Ping Hung,Yao-Tsung Tsai,Tsung-Kuei Kang

doi:10.3390/coatings9040233

Feng-Tso Chien, Ching-Hwa Cheng + Show 4 more

Open Access

https://doi.org/10.3390/coatings9040233

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Abstract

A current improved and electric field reduced double-gate (DG) polycrystalline silicon thin-film transistor with two-step source/drain (DGTSD-TFT) design is proposed and demonstrated in this study. The two-step source/drain (TSD) design, which consists of a raised source/drain (RSD) area together with a partial gate overlapped lightly doped drain (P-GOLDD) structure, can lower the device drain electric field (DEF) to reveal a better device performance. Comparisons have been made with respect to a traditional single top gate (STG) device. The operation current of the proposed DGTSD-TFT is almost twice as large as that of the STG structure. The OFF-state leakage current and kink effect, as well as the ON/OFF current ratio for this double-gate and two-step source/drain structure, are also improved simultaneously because of a reduced DEF. A hot carrier stress test reveals that that two-step source/drain structure can achieve more stable device characteristics than the traditional device.

Highlights

The low temperature polycrystalline silicon thin film transistor fabricated on glass substrates has been widely studied and used for active-matrix organic liquid crystal display (AMOLCD)and active matrix organic light emitting (AMOLED) display applications, peripheral driver and pixel switches circuits [1], because it has a high electron mobility and On-state current when compared to the amorphous silicon (a-Si) TFT [2]
Active matrix organic light emitting (AMOLED) display applications, peripheral driver and pixel switches circuits [1], because it has a high electron mobility and On-state current when compared to the amorphous silicon (a-Si) TFT [2]
The most critical issue for the conventional poly-Si TFT is its high drain electric field (DEF) that causes a great deal of impact ionization, which leads to an intense kink effect and degrades the device performance [3,4]

Summary

Introduction

Active matrix organic light emitting (AMOLED) display applications, peripheral driver and pixel switches circuits [1], because it has a high electron mobility and On-state current when compared to the amorphous silicon (a-Si) TFT [2]. The most critical issue for the conventional poly-Si TFT is its high drain electric field (DEF) that causes a great deal of impact ionization, which leads to an intense kink effect and degrades the device performance [3,4]. This drawback limits this device’s use in digital and analog circuits on glass for high resolution displays. The offset-gate device was shown to lower the DEF effectively, but its On-current was significantly decreased because of an additional series resistance [6]

Methods

Discussion

Conclusion