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.

Scaling Down Effect on Low Frequency Noise in Polycrystalline Silicon Thin-Film Transistors

“…As switching devices and peripheral circuits, lowtemperature polycrystalline silicon (poly-Si) thin film transistors (TFTs) have been widely used in high-performance active-matrix flat panel displays [1], [2]. To obtain a low-temperature manufacture process and high-performance TFTs, excimer laser annealing (ELA) is proposed for achieving high-quality poly-Si layer [3]. However, this lowtemperature process may induce to nonuniform and high source/drain parasitic contact resistances, which are caused by low dopant activation efficiency [3].…”

Dimension Scaling Effects on Conduction and Low Frequency Noise Characteristics of ITO-Stabilized ZnO Thin Film Transistors

“…The degradation of field effect mobility in short channel devices may dominate by the contact resistance [12], [17]. Unlike conventional MOSFETs, ITO-stabilized ZnO TFTs do not have a stable doped source/drain regions.…”

“…A weak ohmic contact may exist caused by the mismatch between the work functions of the active region and the electrode. Thus, the contacts may play a dominant role in short devices, which caused mobility decreases with the decrement of channel lengths [12], [17].…”

“…To integrate more functions on the same substrate, the channel length of devices should be reduced from typical values of L=10 μm to L=1-2 μm, or less [12], [16]. Thence, contact resistance and short channel effects may affect device performance and there should be controlled for proper operation of these devices [17]- [20]. Up to now, the effects of channel length on conduction performance have been examined [16], [17], [20].…”

“…Thence, contact resistance and short channel effects may affect device performance and there should be controlled for proper operation of these devices [17]- [20]. Up to now, the effects of channel length on conduction performance have been examined [16], [17], [20]. However, the dimension scaling effects on LFN of Sn-doped IZO TFTs has less been reported.…”