Abstract
Amorphous and nanocrystalline Zinc Oxynitride (nc-ZnON) has been found to be one kind of potential materials for thin film transistors in the application of advanced display because of their high carrier mobility and low persistent photocurrent. We report a systematic study of ZnON properties and their correlation to the deposition conditions in a reactive sputtering process using a metallic Zn target in a gas mixture of Ar, N2 and O2. The most sensitive parameter to the material properties is O2 and N2 flow rates. At given N2 and Ar flow rates, the ZnON materials show polycrystalline ZnO properties when a relatively high O2 flow rate is used; become a mixture of ZnO and Zn3N2 with a nanocrystalline structure when a medium O2 flow rate is used; and finally show polycrystalline Zn3N2 properties when a small or no O2 flow rate is used. The RF power also shows a strong influence on the material properties. At a given gas mixture, a low RF power produces polycrystalline ZnO-like materials and a high power produces polycrystalline Zn3N2-like materials. At an optimized medium RF power, the material shows nc-ZnON properties. Finally, under the optimized condition, the nc-ZnON films are made with an optical bandgap of 1.3-1.5 eV, electron mobility above 80 cm2/V.s and electron density of 1x1018 cm-3, which are suitable for high quality TFTs in advanced display application.
Highlights
Hydrogenated amorphous silicon (a-Si:H) thin film transistors (TFT) has been widely used in conventional liquid crystal display (LCD) as the driver switches,[1,2] which are benefited from the large area uniform deposition using plasma enhanced chemical vapor deposition (PECVD) at low substrate temperature
In order to resolve these issues, new channel materials have been widely explored, including hydrogenated microcrystalline silicon,[5] polycrystalline silicon[6] and amorphous metal oxide semiconductors (AMO).[7] μc-Si:H TFTs have higher carrier mobility than a-Si:H TFTs, such as the electron field effect mobility μFE can reach to 10-50 cm2/V.s,5 but the growth of μc-Si:H starts from an a-Si:H incubation layer, which is not suitable for bottom gate TFTs, and the material properties are not easy to be uniform in a large area substrate
The results show that 1) a high RF power leads to a high deposition rate; 2) the deposition rate increases with the O2 flow rate in general; and 3) it levels off for the set of RF=200 W at O2 flow rate higher than 1 sccm
Summary
A-IGZO TFT shows a large persistent photocurrent,[11] which means it takes a long time to return to its off-state after an illumination This problem could be resolved by masking the device, but it adds extra cost as well for the product. Another interesting AMO material is amorphous zinc oxynidride (a-ZnON) that has a single cation of Zn and double anions of O and N This material was first systematically studied by Ye et al in Applied Materials,[12] and followed by detailed studies in Samsung Electronics,[13,14,15] The advantage of a-ZnON TFTs over other multi-cation AMO TFTs are 1) higher carrier mobility, 2) simpler one-target sputtering with well controlled process, and 3) much lower persistent photocurrent. We show the optimized deposition conditions and the properties of the optimized ncZnON materials, where high carrier mobility of 80-90 cm2/V.s is achieved without thermal annealing
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call