A Comparative Study of E-Beam Deposited Gate Dielectrics on Channel Width-Dependent Performance and Reliability of a-IGZO Thin-Film Transistors.

Gwomei Wu,Dave Chen,J Chang,Anup Sahoo

doi:10.3390/ma11122502

Gwomei Wu, Dave Chen + Show 2 more

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https://doi.org/10.3390/ma11122502

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Abstract

A comparative study on the effects of e-beam deposited gate dielectrics for amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors (TFTs) has been carried out using SiO2, Si3N4, and Ta2O5 dielectric materials. The channel width dependent device electrical performances were investigated using three different sizes of 500 μm, 1000 μm, and 1500 μm. The reliability characteristics were revealed by the threshold voltage variation and drain current variation under positive bias stress. The e-beam deposited high-k dielectric Ta2O5 exhibited the highest stability at the stress voltage of 3 V for 1000 s due to its high capacitance density at 34.1 nF/cm2. The threshold voltage variation along the channel width decreased from SiO2, then Si3N4, to Ta2O5, because of the increased insulating property and density of capacitance. The SiO2-based a-IGZO TFT achieved a high field effect mobility of 27.9 cm2/V·s and on–off current ratio > 107 at the lower channel width of 500 μm. The gate leakage current also decreased with increasing the channel width/length ratio. In addition, the SiO2 gate dielectric-based a-IGZO TFT could be a faster device, whereas the Ta2O5 gate dielectric would be a good candidate for a higher reliability component with adequate surface treatment.

Highlights

Recent studies have been focused on several transparent conducting oxides (TCO), such as zinc oxide (ZnO), indium zinc oxide (IZO), amorphous zinc tin oxide (a-ZTO) and amorphous indium gallium zinc oxide (a-IGZO) [1,2,3]
The electrical performances could be significantly improved after employing plasma treatment on the gate dielectric [13].The atomic layer deposited (ALD) SiO2 gate dielectric was reported on a-IGZO thin-film transistors (TFTs) that could maintain a good stability under a negative gate bias stress, while exhibiting very high field-effect mobility without any post-annealing [14]
The results clearly indicated that the as-deposited e-beam high-k Si3 N4 and Ta2 O5 films could not improve the performances of a-IGZO TFTs because of the higher surface roughness

Summary

Introduction

Recent studies have been focused on several transparent conducting oxides (TCO), such as zinc oxide (ZnO), indium zinc oxide (IZO), amorphous zinc tin oxide (a-ZTO) and amorphous indium gallium zinc oxide (a-IGZO) [1,2,3]. These materials showed advantages, such as an easy film coating process, better surface morphology, and electrical stability during operation. A-IGZO has been proven to be a promising material because of its high mobility and transparency [4] It exhibited a smooth surface quality when deposited at room temperature [5].

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