Thin-BOX Poly-Si Thin-Film Transistors for CMOS-Compatible Analog Operations

Abstract

This paper presents device models and optimization methodology for reducing short-channel effects in low-temperature polycrystalline-silicon thin-film transistors (LTPS TFTs), which are suitable for standard complementary metal-oxide-semiconductor (CMOS)-compatible analog operations. We analyze channel-length modulation to determine appropriate channel length having a single grain boundary in the channel fabricated using excimer laser-annealed crystallization under low-temperature constraint. Furthermore, buried-oxide-induced barrier lowering (BIBL) is investigated in poly-Si TFTs. BIBL makes the effective channel length shorter, resulting in difficulty to use LTPS TFTs for analog applications due to small output resistance rout. We show that, with scaling of the buried-oxide (BOX) thickness Tbox and an appropriate channel length, rout and the normalized transconductance gm/Id (with Tbox = 10 nm) can be improved by 103% and 8%, respectively, compared with thicker BOX (Tbox = 50 nm). In addition, due to the decrease in leakage currents, the Ion/Ioff ratio of the thin-BOX device can be three times larger than that of the thicker BOX device. Based on the process-constrained optimized device, we designed a 417-μW 65-dB folded-cascode operational amplifier with 2-V supply for CMOS-compatible operations.