NBTI Degradation in LTPS TFTs Under Mechanical Tensile Strain

Abstract

This letter investigates the negative-bias temperature instability (NBTI) degradation of p-channel low-temperature polycrystalline-silicon thin-film transistors (LTPS TFTs) under mechanical tensile stress. Experimental results reveal that the interface state density N it and grain boundary trap density N trap of tensile-strained LTPS TFTs are more pronounced than those of unstrained LTPS TFTs. Extracted density of states and conduction activation energy E a both show increases due to the strained Si-Si bonds, which implies that strained Si-Si bonds are able to react with dissociated H during NBTI stress. Therefore, NBTI degradation is more significant after tensile strain than in an unstrained condition.

Alleviation of abnormal NBTI phenomenon in LTPS TFTs on polyimide substrate for flexible AMOLED

“…Grain boundary trap‐state generation and V th negative shift during NBTI on glass substrate is explained well with the established NBTI degradation phenomenon 14,15 . Also, grain boundary trap‐state reduction and V th positive shift during NBTI can be explained with the established phenomenon such as NBTI recovery and hydrogen diffusion from PI substrate 18,19 .…”

“…The H‐dissociated, Si dangling bonds become interface and grain boundary trap states existed in the channel. Those generations in interface and grain boundary trap states are fitted well with a straight line in V th negative shift during NBTI 14, 15 . However, most studies have focused on the NBTI of LTPS TFTs on glass substrate and the NBTI degradation of LTPS TFTs on plastic substrate has not been studied well.…”

“…The NBTI degradation in MOSFETs, which is mainly attributed to the generation of interface trap states and fixed oxide charges, activated thermally and electrically 12, 13 . And the NBTI mechanism in poly‐Si TFTs is explained that the inversion hole at the poly‐Si/SiO 2 interface and grain boundaries reacts with Si─H, resulting in H dissociation and diffusion into the gate oxide to form many OH groups bonded to Si atoms and fixed oxide charges 14, 15 . The H‐dissociated, Si dangling bonds become interface and grain boundary trap states existed in the channel.…”

P‐137: Vt Behaviors of LTPS‐TFT Fabricated on PI substrate for Flexible Applications

“…Latest researches of TFTs on PI substrate were mainly focused on the improvement of the device initial characteristics up to those of TFTs on the glass substrate [1][2]. On the other hand, the reliability assessment of TFTs on PI substrate under various electrical stresses is required but was rarely reported [3]. In this paper, the difference of reliability characteristics are compared between the two devices and lifetime of LTPS TFT on PI substrate is increased by optimization of the PI substrate process.…”

9.1‐inch stretchable AMOLED display based on LTPS technology

“…Various studies have been carried out on the bending properties of flexible p-channel LTPS TFTs, which reveal the change in the interface state density and grain boundary trap density after bending strain. [7][8][9] In general, the leakage current in LTPS TFTs is attributed to thermionic field emission via grain-boundary traps in the surface depletion region at the drain terminal, and the threshold voltage shift of the TFT is caused by charge trapping or defect creation in the gate oxide. Thus, if the p-channel LTPS TFT is bent, the leakage current is increased and the threshold voltage can fluctuate and more the long-term reliability characteristics will be compromised.…”