The influence of ZnO layer thickness on the performance and electrical bias stress instability in ZnO thin film transistors

Abstract

Thin Film Transistors (TFTs) are the active elements for future large area electronic applications, in which low cost, low temperature processes and optical transparency are required. Zinc oxide (ZnO) thin film transistors (TFTs) on SiO 2 /n+-Si substrate are fabricated with the channel thicknesses ranging from 20 nm to 60 nm. It is found that both the performance and gate bias stress related instabilities of the ZnO TFTs fabricated were influenced by the thickness of ZnO active channel layer. The effective mobility was found to improve with increasing ZnO thickness by up to an order in magnitude within the thickness range investigated (20-60 nm). However, thinner films were found to exhibit greater stability in threshold voltage and turn-on voltage shifts with respect to both positive and negative gate bias stress. It was also observed that both the turn on voltage (V on ) and the threshold voltage (V T ) decrease with increasing channel thickness. Moreover, the variations in subthreshold slope (S) with ZnO thickness as well as variations in V T and V on suggest a possible dependence of trap states in the ZnO on the ZnO thickness. This is further correlated by the dependence of V T and V on instabilities with gate bias stress.

Effect of SiO2 Thickness Variation on Threshold Voltage and Trans-Conductance of TFT

“…Threshold voltage of the thin film transistor decrease with increasing channel thickness [2].The effect of SiO2 thickness on the electrical properties of proposed device was observed for constant channel length L=5 and 30nm thickness of IGZO semiconductor materials and drain voltage is Vd=2V.…”

“…Oxide-based thin film transistors have been investigated for a number of applications, including switching components in flat panel display backplanes, gas sensor applications, and UV detecting devices. Thin film transistors are made by depositing a thin layer containing a dielectric material on a variety of substrates, such as plastic, fibre, paper, and silicon [1][2][3], and then removing it. The contact between the semiconductor layer and the source, drain, and gate is established by the source, drain, and gate.…”