Positive-Bias Temperature Instability Improvement of Poly-Si Thin-Film Transistor With HfO2 Gate Dielectric by Ammonia Plasma Treatment

In this paper, positive-bias temperature instability (PBTI) stress with different stress voltage at T = 125 degrees C is executed on the high-performance polycrystalline silicon (poly-Si) thin-film transistors (TFTs) with HfO2 gate dielectric and ammonia (NH3) plasma surface treatment. The NH3 plasma surface treatment on the poly-Si TFT with HfO2 gate dielectric can significantly decrease the threshold voltage (V-TH) approximately -1.86 V, reduce the subthreshold slope (S.S.) approximately -88 mV/decade, enhance the transconductance (G(m)) approximately 2.4x, and driving current (I-drv) approximately 2.34. In addition, the device degradation after PBTI stress with stress voltage V-G - V-TH = 7 V for 1000 s at T = 125 degrees C can also be improved after the NH3 plasma surface treatment, such as the suppressing of V-TH shift from 2.063 to 0.617 V, S.S. degradation quantity from 0.284 V/decade to 0.172 V/decade, and I-drv reduction from -77% to -44%. The improvement of the PBTI of poly-Si TFTs with NH3 plasma surface treatment is attributed to the suppression of oxide charge trapping effect and the degradation of interface state density (N-it) and grain boundary trap state density (N-GB).