Four-terminal polycrystalline-silicon vertical thin-film transistors on glass substrates

Abstract

This study aimed to fabricate n-channel four-terminal (4 T) polycrystalline silicon (poly-Si) vertical thin-film transistors (VTFTs) with submicron gate lengths on a glass substrate. The 4 T VTFTs have a poly-Si active layer crystallized via metal-induced crystallization using nickel (Ni-MIC), a top gate (TG), and a bottom gate (BG). Here, the TG covers all the channel regions, and the BG affects only a part of the channel region. A double-gate drive (simultaneous operation of both gates) displayed a high I on/I off ratio and small s.s. compared with those of a single-gate drive. In addition, the threshold voltage (V th) of the TG drive varied depending on the BG voltages (V BG), with a γ-value (=ΔV th/ΔV BG) of 0.17. This value is smaller than the theoretically expected value because of the localized effects of the BG on the channel region and the inferior crystalline quality of the Ni-MIC poly-Si film.