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

Abstract

In this work we present the electrical characterization of ZnO-based thin-film transistors fabricated at room temperature. The ZnO films were deposited by radiofrequency magnetron sputtering at variable argon pressure (3 mTorr to 10 mTorr) at room temperature. The sputtered ZnO films were polycrystalline with hexagonal structure and electrical resistivity ranging from 10 1 X cm to 10 8 X cm for films deposited from 3 mTorr to 10 mTorr. The trend in the electrical behavior of the devices was found to be due to the variation of the electron concentration of the ZnO films. The devices with better performance showed a field-effect mobility of 2.9 cm 2 /Vs, threshold voltage of 20 V, I on / I off % 10 6 , and electrical resistivity of $10 8 X cm. In addition, linear behavior of I on /I off with deposition pressure was observed. The lowest I on /I off ratio ($2) was calculated for devices with ZnO layers deposited at 3 mTorr, and the highest ratio ($10 6 ) for devices processed at 10 mTorr. Hall-effect measurements were performed on ZnO films showing the lowest resistivity. The layer grown at 3 mTorr showed a Hall mobility of l H = 8.9 cm 2 /Vs and carrier concentration of n = 4.2 9 10 16 cm À3 with resistivity of q = 31.8 X cm. For films deposited at 5 mTorr, the Hall mobility, carrier concentration, and resistivity were l H = 7.9 cm 2 /Vs, n = 3.4 9 10 16 cm À3 , and q = 38.4 X cm, respectively. Films deposited at 8 mTorr and 10 mTorr could not be measured due to their high resistance.

The Effects of Zn Ratio on the Microstructure Electrical Properties of InGaZnO Films

“…This appearance does not change much until the Zn ratio increases up to 0.32 for the sample deposited at a ZnO target power of 50 W. For the 80 W sample, a small peak emerges around 32 from the broad amorphous peak and the peak position is close to that of the (0002) reflection of the hexagonal ZnO phase. 11 For the films deposited at higher ZnO powers, the peak rises stronger and shifts close to the ZnO (0002) reflection (34.4 ), and an additional peak appears around 62 , a peak position closely matching that of the (10-13) reflection of ZnO. Finally, the sample with the highest Zn ratio (150 W sample) shows several additional small peaks pertaining to the ZnO phase, which indicates that the film fully transformed to the ZnO phase.…”

Annealing dependence on flexible p-CuGaO2/n-ZnO heterojunction diode deposited by RF sputtering method

“…Transparent conducting oxide (TCO) thin films have been extensively studied because it's have very interesting properties in various electrical and optical application such as gas sensor, light-emitting diodes, solar cells, thin-film transistors and varistor [1,2]. ZnO have become a promising TCO materials due to its nontoxic, inexpensive and abundant material compared to ITO that once was a commonly used materials [3][4][5][6].…”

Improving source/drain contact resistance of amorphous indium–gallium–zinc-oxide thin-film transistors using an n+-ZnO buffer layer

“…[28][29][30][31][32] In this study, to avoid high temperature thermal annealing and plasma damage and improve the electrical properties of α-IGZO TFTs, especially, for flexible electronics, a simple and efficient technique using a sputtering-deposited n + -ZnO BL between the S=D electrode and the α-IGZO channel is proposed and demonstrated. Since carrier concentration in sputtering deposited ZnO films are highly sensitive to chamber pressure, [33][34][35] impacts of the chamber pressure on the carrier concentration of the sputtering-deposited n + -ZnO buffer layer (BL) and its thickness on the degree of improvement in the performance of α-IGZO TFTs are analyzed and discussed.…”