Low-Temperature-Processed Zinc Oxide Thin-Film Transistors Fabricated by Plasma-Assisted Atomic Layer Deposition

We investigated zinc oxide (ZnO) thin films prepared by plasma assisted atomic layer deposition (PA-ALD), and thin-film transistors (TFTs) with the ALD ZnO channel layer for application to next-generation displays. We deposited the ZnO channel layer by PA-ALD at 100 or 300 degrees C, and fabricated TFTs. The transfer characteristic of the 300 degrees C-deposited ZnO TFT exhibited high mobility (5.7 cm(2) V-1 s(-1)), although the threshold voltage largely shifted toward the negative (-16 V). Furthermore, we deposited Al2O3 thin film as a gate insulator by PA-ALD at 100 degrees C for the low-temperature TFT fabrication process. In the case of ZnO TFTs with the Al2O3 gate insulator, the shift of the threshold voltage improved (-0.1 V). This improvement of the negative shift seems to be due to the negative charges of the Al2O3 film deposited by PA-ALD. On the basis of the experimental results, we confirmed that the threshold voltage of ZnO TFTs is controlled by PA-ALD for the deposition of the gate insulator. (C) 2012 The Japan Society of Applied Physics