Amorphous oxide semiconductor (AOS) TFTs (thin film transistors) have attracted keen attention mainly for their application to flat-panel devices. The first AOS TFT[1]  was demonstrated with a device structure of top-gate top-contact configuration using ITO (indium tin oxide) source and drain (SD) electrodes. Since then, various device structures have been reported with various insulator and SD materials, including types of top/bottom/double gate, top/bottom contact, back-channel etch (BCE), etch-stop, and homojunction coplanar[2]. While the device structure has to be selected in view of the application and fabrication processes, there has not been sufficient discussion in terms of TFT characteristics.

The most critical condition to the device structure arises from the selection of the SD electrodes which are limited to a few materials such as Ti, Mo, and transparent oxide conductors (TCO) for good ohmic contact and low contact resistance. There is no problem in patterning them for a bottom-contact configuration, but the deposition of the AOS layer can cause contact problems through the oxidation of the SD surfaces. For the top-contact configuration fabricated with BCE process, only Mo is available so far for patterning the SD electrodes by etching techniques. In any top-contact TFTs, it is not easy to lower the contact resistance when the AOS layer is deposited as being highly resistive. It will be shown in this paper that BCE TFTs fabricated with deposition of low-resistivity AOS and homojunction coplanar TFTs yield parasitic resistivity as low as 10-20 ohm cm along with high mobility of 12 cm²V^-1s^-1, small subthreshold swing of 0.15 Vdec^-1, and their operation is almost close to ideal MOSFETs. 

[1] K. Nomura, et al., Nature 432, 488 (2004).

[2] R. Hayashi, et al., Digest of Technical Papers, SID’08, p.621.

• Legal notice:
  

  Copyright (c) Pielaszek Research, all rights reserved.
  The above materials, including auxiliary resources, are subject to Publisher's copyright and the Author(s) intellectual rights. Without limiting Author(s) rights under respective Copyright Transfer Agreement, no part of the above documents may be reproduced without the express written permission of Pielaszek Research, the Publisher. Express permission from the Author(s) is required to use the above materials for academic purposes, such as lectures or scientific presentations.
  In every case, proper references including Author(s) name(s) and URL of this webpage: https://science24.com/paper/16349 must be provided.