Poly-Si Thin Film Transistors: Opportunities for low-cost RF applications

The demand for low-power and low-cost RF applications such as wireless sensor nodes and radio frequency identification (RFID) have driven the development of new technologies in lieu of bulk CMOS. Low Temperature Polycrystalline Silicon Thin Film Transistors (LTPS TFTs) on glass substrates is one of the promising candidates for its low manufacturing cost. However, due to inherent grain boundaries (GBs) in the channel, poly-Si TFTs suffer from lower carrier mobility compared to bulk CMOS transistors. This has been the critical limiting factor for its use in low-voltage and high-speed operations. In this paper, our device modeling present the potential of optimized LTPS TFTs for high frequency operations - cut off frequency f_T ~40 GHz of nFETs. We show that high resistivity channel due to the presence of GBs leads to high linearity and independence from channel length. In addition, glass substrate also presents a major advantage by providing negligible substrate-loss, leading to high quality-factor inductors. With the proposed LTPS TFTs and inductors, we designed an inductive coupling wireless link having 2.7 mW of power consumption. This wireless link demonstrates an upper limit of 408 Mbps data rate with inductive coupling distance of 5 cm between two coupling inductors. The designed wireless link presents new opportunities for low-cost RF applications.