High-Frequency Modeling of Poly-Si Thin-Film Transistors for Low-Cost RF Applications

In this paper, we present high-frequency characteristics of transistors and inductors in low-temperature polycrystalline-silicon thin-film transistor (LTPS TFT) technology for low-cost radio frequency applications. From 2-D device simulations, we show that the linearity of LTPS TFTs is independent of the channel length due to the presence of grain boundaries. Furthermore, since LTPS TFTs can be fabricated on insulating substrates, on-chip spiral inductors on such substrates have negligible substrate loss, leading to high quality ( $Q$ ) factor. From electromagnetic simulations, we observe that spiral inductors in LTPS TFT technology show lower parasitics, higher $Q$ factor, and higher self-resonance frequency $(f_{\rm RES})$ compared to typical bulk CMOS inductors having similar inductance. Such high $Q$ of inductors allows compensating for low $g_{m}$ of LTPS TFTs.