Effect of Rapid Thermal Annealing on the Electrical Characteristics of ZnO Thin-Film Transistors

Abstract

Thin-film transistors (TFTs) with a bottom-gate configuration were fabricated with an RF magnetron sputtered undoped zinc oxide (ZnO) channel layer and plasma-enhanced chemical vapor deposition (PECVD) grown silicon nitride as a gate dielectric. Postfabrication rapid thermal annealing (RTA) and subsequent nitrous oxide (N 2 O) plasma treatment were employed to improve the performance of ZnO TFTs in terms of on-current and on/off current ratio. The RTA treatment increases the on-current of the TFT significantly, but it also increases its off-current. The off-current of 2 Â 10 À8 A and on/off current ratio of 3 Â 10 3 obtained after the RTA treatment were improved to 10 À10 A and 10 5 , respectively, by the subsequent N 2 O plasma treatment. The better device performance can be attributed to the reduction of oxygen vacancies at the top region of the channel due to oxygen incorporation from the N 2 O plasma. X-ray photoelectron spectroscopy (XPS) analysis of the TFT samples showed that the RTA-treated ZnO surface has more oxygen vacancies than as-deposited samples, which results in the increased drain current. The XPS study also showed that the subsequent N 2 O plasma treatment reduces oxygen vacancies only at the surface of ZnO so that the better off-current and on/off current ratio can be obtained.

Compositional influence on the electrical performance of zinc indium tin oxide transparent thin-film transistors

“…Oxygen vacancies can be reduced by thermal annealing in air atmosphere and would reduce the n-type character of the semiconductor [14]. According to reference [5], the oxygen vacancy density is much higher at the surface than in the bulk.…”

“…Each sample was heated during 1 h at 300 °C, with a temperature ramp-up of 30 min. The aim of the thermal treatment was to oxidize the film to decrease the carrier concentration by reducing the oxygen vacancy density [14] or by chemisorption of oxygen at the ZITOs surface and nano-grain boundaries. The morphology of the samples was previously characterized by X-Ray Diffraction Spectroscopy and High-Resolution Transmission Electron Microscopy [15].…”

Evolution of electrical performance of ZnO-based thin-film transistors by low temperature annealing

“…One effective routine to obtain TFTs with good performance is to deposit ZnO channel layer with higher resistivity and then to treat with post-annealing. Although many groups have reported that the post-annealing is an effective way to improve the performance of TFTs fabricated at room temperature, [10][11][12][13][14] few study has been studied on the performance evolution by post-annealing treatment. And the mechanism of how annealing treatment improves the performance of ZnO TFTs is rarely discussed as well.…”

Effect of Sputtered ZnO Layers on Behavior of Thin-Film Transistors Deposited at Room Temperature in a Nonreactive Atmosphere

“…3 When used as the active channel layer in TFTs, the deposition parameters of ZnO can be optimized to achieve high mobility, [4][5][6][7][8][9] low threshold voltage, 4 and high current ratios (I on / I off ). 6,10 The channel mobility is directly related with the crystalline quality of the semiconductor active layer, and it can be improved by employing epitaxial deposition techniques 8,9 and/or by postdeposition annealing treatment. 7 Zinc oxide thin films have been fabricated using several deposition techniques such as chemical vapor deposition (CVD), 11 pulsed laser deposition (PLD), 12 spin coating, 13 atomic layer deposition (ALD), 14 laser molecular-beam epitaxy (L-MBE), 8,9 and radiofrequency (RF) magnetron sputtering.…”