High-Performance Poly-Si TFTs Using Ultrathin $\hbox {HfSiO}_{x}$ Gate Dielectric for Monolithic Three-Dimensional Integrated Circuits and System on Glass Applications

High-performance poly-Si thin-film transistors (TFTs) using an ultrathin high- κ metal gate stack with a subthreshold swing (SS) of 193 mV/dec when operating at room temperature and maximum thermal budget of 700°C are readily compatible with monolithic 3-D integrated circuits (3D-ICs) and silicon-on-glass (SOG) applications. The SS is reduced to 31 mV/dec, and the on/off current ratio is increased to 10⁸ at 77 K; the result is a significant reduction of leakage current and lower power consumption. Long-channel TFTs have a higher drain current noise spectral density S_ID and a smaller exponential frequency factor (γ) due to the influence of numerous grain boundaries on carrier transport, as confirmed by gap state density extraction. These devices may pave the way for high-performance circuit designs and applications, such as monolithic 3D-ICs, SOG, and active-matrix organic LED.