Bias temperature instability comparison of CMOS LTPS-TFTs with HfO2 gate dielectric

•BTI of CMOS LTPS-TFTs with HfO2 gate dielectric are studied and compared.•Gm degradation of PBTI for n-type device shows saturation behavior.•NBTI shows the hole trapping and the hydrogen reaction and diffusion effect.•Gm degradation is the dominant factor of driving current degradation.

In this paper, the positive and negative bias temperature instability (P/NBTI) of complementary metal–oxide–semiconductor (CMOS) low-temperature poly-Si thin-film transistors (LTPS-TFTs) with HfO2 gate dielectric are studied simultaneously. Significant threshold voltage shift ΔVTH, degradation of the subthreshold swing S.S. and transconductance Gm are observed for both n-type LTPS-TFTs after PBTI stress and p-type LTPS-TFTs after NBTI stress. Moreover, the Gm degradation rate with the stress time of p-type devices during NBTI shows significantly different behavior from the PBTI of n-type devices. The PBTI of n-type device shows a saturation behavior of the Gm degradation with various stress bias and temperature. Conversely, the NBTI of p-type device shows an enhanced Gm degradation rate with the increase of stress time and stress temperature. In addition, the threshold voltage shift |ΔVTH| of PBTI does not obey the traditional empirical power law model, but the NBTI obeys it with higher time exponent. Consequently, the NBTI of the p-type device shows worse driving current Idrv degradation than the PBTI of the n-type device mainly due to the different Gm degradation behavior.