A New Electrically Reversible Depassivation/Passivation Mechanism in Polycrystalline Silicon

Abstract

An electrically reversible depassivation/passivation phenomenon, recently found for hydrogen passivated polysilicon [11 is further explored in this report. This reversible effect is seen in both ECR and RE h, •rogen passivated n-channel thin film transistors (TFTs) but is not seen in the corresponding hydrogen passivated pchannel TFrs, nor is it seen in either n-or p-channel TETs before hydrogenation. This phenomenon has been observed when room temperature bias stressing TFTs fabricated on solid phase or laser crystallized polysilicon films on quartz substrates [1]. A model involving hydrogen release or capture at defects, positively charged hydrogen motion in device electric fields, and subsequent hydrogen capture at other defects has been proposed. This phenomenon has significant implications for polycrystalline silicon TFT' design and operation. By extension, it also offers significant insight into the stability problems of hydrogenated amorphous silicon.

The effect of substrates on the performance and hot-carrier reliability of n-channel thin film transistors

“…Figure 3 shows similar patterns to those in figure 2 except that HCS had significantly degraded the parameters of TFTs on 1737 glass. This is attributed to trap depassivation (electrical reactivation) by HCS [6,9], which is expected to be more enhanced in poly-Si on glass due to its high trap content.…”