Channel Defect Profiling and Passivation for ZnO Thin-Film Transistors.

Soo Cheol Kang,Sang Kyung Lee,Byoung Hun Lee,Billal Allouche,Hyeon Jun Hwang,Kiyung Kim,So Young Kim

doi:10.3390/nano10061186

Abstract

The electrical characteristics of Zinc oxide (ZnO) thin-film transistors are analyzed to apprehend the effects of oxygen vacancies after vacuum treatment. The energy level of the oxygen vacancies was found to be located near the conduction band of ZnO, which contributed to the increase in drain current (ID) via trap-assisted tunneling when the gate voltage (VG) is lower than the specific voltage associated with the trap level. The oxygen vacancies were successfully passivated after the annealing of ZnO in oxygen ambient. We determined that the trap-induced Schottky barrier lowering reduced a drain barrier when the drain was subjected to negative bias stress. Consequentially, the field effect mobility increased from 8.5 m2 V−1·s−1 to 8.9 m2 V−1·s−1 and on-current increased by ~13%.

Highlights

Zinc oxide (ZnO) is an amorphous oxide semiconductor that can be economically patterned via simple wet chemical etching at low temperatures
thin-film transistors (TFTs) stored in vacuum were subjected to a negative drain bias stress, to investigate the degradation of the Schottky barrier (VD.stress = −2.5 V, VG.stress = 0 V); (iii) The effect of stress on the channel/drain junction was investigated by measuring the in drain current (ID) –VG transfer curve and the capacitance between the source and the drain
When the ZnO TFTs were annealed at 150 ◦ C for 10 min in oxygen ambient, the hump at the subthreshold region almost disappeared, indicating that the hump at the subthreshold region is due to the oxygen vacancies, which can be reversibly controlled by oxygen treatment

Summary

Introduction

Zinc oxide (ZnO) is an amorphous oxide semiconductor that can be economically patterned via simple wet chemical etching at low temperatures. The electrical characteristics of TFTs, having an amorphous oxide semiconductor channel including ZnO, show a strong ambient dependence during the fabrication process [10] and electrical operation [11,12], which were attributed to the various oxygen vacancies such as VO , VO + and VO 2+. These oxygen vacancies can exist at different energy levels: VO at. Schottky barrier lowering after drain was subjected negative bias stress [20]

Methods

Results and Discussions

Conclusions