Role of SiOxNy surface passivation layer on stability improvement and kink effect reduction of ELA poly silicon thin film transistors

•NH3 plasma treatment is the effective surface passivation method by the formation of Si—H bonds which reduced the interface traps at the insulator/channel interface.•The thin SiOxNy layer growth by nitridation process improves TFTs instability, which caused by mobile charges, than the untreated device.•NH3 plasma treatment and SiOxNy thin layer combination shows an excellent electrical stability for TFT under high hot carrier injection. With SiOxNy layer on the surface, strong bonding Si—N and Si—O were formed which could not be broken at high energy bias and this kind of layer also protects the Si—H bonding formed under previous NH3 treatment.•After long time gate bias stress or a number of operating cycles, a negligible change in TFT characteristics was observed at this device.

The role of SiOxNy thin layer growth on excimer laser annealed (ELA) polysilicon, by N2O plasma treatment, on the stability improvement under prolonged operation and bias stress of TFT was investigated. After NH3 plasma treatment, field effect mobility in p-channel TFT devices increased from 50 to 76 cm2 V− 1 s− 1, ON/OFF current ratio improved to 4.6 × 107, threshold voltage shrank from − 9.8 V to − 7.7 V and kink effect in the ID-VD characteristics was diminished. Using NH3 plasma treatment combined with SiOxNy layer indicated a lesser effectiveness in decreasing interface states, but better in reducing of the influence of mobile charges on TFT performance, than the previous approaches. An improvement in field effect mobility of 60.5 cm2 V− 1 s− 1, excellent stability under bias stress of ± 1 MV·cm− 1 for 2 h with ΔVth ~ 0.1 V were achieved. We found that under NH3 plasma treatment combined with SiNxOy thin layer; the effect of hot carrier injection were reduced significantly due to creating the SiN, and SiO bonding at the interface of gate insulator and active layer. This result indicated that thin film transistor using NH3 plasma treatment with SiOxNy passivated layer promises to improve TFT performances with high field effect mobility, high ON/OFF current ratio, low leakage current and excellent stability.

Graphical abstractThis study has performed NH3 and NH3/N2O plasma treatments on the surface of ELA poly-Si TFTs and examined the effect of those plasma treatments on TFTs instability, especially under high hot carrier stress condition. The PT1 devices with NH3 plasma treatment have shown the most effective surface passivation by the formation of SiH bonds which reduced the interface traps at the insulator/channel interface. It was concluded that the PT1 device showed the largest μFE, and ON/OFF ratio, the lowest Vth and a small kink current. In addition, the existence of a thin SiOxNy layer growth by nitridation process (NH3/N2O plasma treatment) improves TFTs instability, which caused by mobile charges, than the untreated device. Although the combination of NH3 plasma treatment and SiOxNy thin layer shows a small degradation in electrical characteristics compared with NH3 treatment devices, it shows an excellent electrical stability for TFT under high hot carrier injection due to the effective impurity barrier of SiOxNy layer. With SiOxNy layer on the surface, strong bonding SiN and SiO were formed which could not be broken at high energy bias and this kind of layer also protects the SiH bonding formed under previous NH3 treatment. After long time gate bias stress or a number of operating cycles, a negligible change in TFT characteristics was observed at this device.Figure optionsDownload full-size imageDownload as PowerPoint slide