Relationship between crystallinity and device characteristics of In‐Sn‐Zn oxide

We have reported that the transistors having the c-axis-aligned crystalline (CAAC) In-Ga-Zn oxide (IGZO) show good performance. Recently, In-Sn-Zn Oxide (ITZO) has attracted much attention because of its high electron mobility, as well as IGZO. However, it has been reported that ITZO field effect transistors (FET) tend to have positive Vth (normally-on characteristics) and poor reliability compared with IGZO-FETs. We have reported that high-performance and high-reliability OS-FETs can be fabricated by using CAAC-IGZO, which has high crystallinity and has no clear grain boundaries, as an active layer. Therefore, we have fabricated CAAC-ITZO thin films to improve performance of ITZO-FETs by using CAAC-ITZO as an active layer. In addition, FETs employing CAAC-ITZO have better characteristics and reliability than FETs using nano-crystal ITZO. Furthermore, constant photocurrent method (CPM) measurement was carried out in order to estimate density of deep-level defect states caused by oxygen vacancies in oxide semiconductors. The results show that CAAC-ITZO has lower density of deep-level defect states than nano-crystal ITZO. We attribute the improvement in reliability of ITZO-FETs to a decrease in deep-level defect states of an ITZO active layer, as is the case with IGZO.