Radio Frequency Sputtered Zinc Oxide Thin Film Transistors
Date Issued
2012
Date
2012
Author(s)
Lin, Yu-De
Abstract
The RF-sputtered ZnO films are optimized by deposition parameters and annealing processes. The deposition temperature, RF-power and Ar/O2 ratio are changed, and the best deposition parameters are the sample H-50 in Table 3.5. The best annealing conditions for a high Hall mobility ZnO film are annealing in air at 300°C for 0.5 hour.
Two methods are used to improve the performance of ZnO-TFT by reducing the surface roughness of the ZnO layer, decreasing the ZnO active layer thickness and changing gate insulator. The result of decreasing the thickness of ZnO layer in TFT indicates the threshold voltage is improved from 12.9 V to 10.5 V. In the other method, the single SiNx gate insulator of ZnO-TFT is change to the SiO2/SiNx bi-layer gate insulator. The average threshold voltage is improved from 12.9 V to 8.5 V and the average mobility of bi-layer ZnO-TFT is 3.2 times better than that of single SiNx ZnO-TFT.
In order to protect the ZnO layer from moisture degradation, the RF-sputtered TiOx is used to passivate the device. It has been demonstrated that the TFTs annealed in air at 200°C for 30 minutes are the best post-passivation conditions for a TiOx passivated device. After the SiO2/SiNx bi-layer insulator ZnO-TFTs is passivated with 40 nm thick TiOx, the result indicate that the on/off ratio before and after passivation increases from 105.6 to 106.1, the threshold voltage increases from 10.3 V to 19.2 V, and the mobility are almost the same, i.e., 1.19 cm2/V-s and 1.14 cm2/V-s. Finally, the electrical properties of passivated ZnO-TFTs are stable as the devices are exposed to atmosphere for 22 days.
Subjects
ZnO
Transister
thin film
sputter
passivation,anneal
Type
thesis
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