Effect of Series Resistance on Field-Effect Mobility at Varying Channel Lengths and Investigation into the Enhancement of Source/Drain Metallized Thin-Film Transistor Characteristics

Abstract

The degradation in device performance due to parasitic resistance along the source and drain electrodes is a serious problem in thin-film transistor fabrication. The effect of this series resistance on the field-effect mobility has been discussed and solutions for the reduction of this unexpected resistance were studied in this work. From the derivation of the drain current, it was shown that the additional resistance had a greater influence on short-channel devices. The ratio of the series resistance to the channel resistance determined the amount of degradation to the field-effect mobility. A thin-film transistor using an aluminum-metallized source/drain was suggested; it showed an improvement in comparison with the conventional doped source/drain device, with a maximum mobility of 105 cm2 V-1 s-1. However, significant degradation of the mobility in the short-channel cases exposed the limitations of the structure. By employing doping for the source/drain metallized structure the maximum mobility reached a value of 150 cm2 V-1 s-1. The decrease in the mobility caused by the channel length decrease was also improved. This study clearly explained the problem of additional resistance on the field-effect mobility of thin-film transistors and the achievements of a device using a self-aligned fabrication process with metallized electrodes.