Four-terminal Cu-MIC Poly-Ge1−xSnx TFT with a High-k Bottom-gate Dielectric

We previously reported four-terminal polycrystalline germanium-tin (poly-Ge1−xSnx) thin-film transistors (TFTs) on glass substrates and succeeded in an independent operation of top (TG) and bottom (BG) gates. However, the gate dielectric used in the previous experiment was silicon-dioxide (SiO2) for both TG and BG. Thus, the subthreshold swing and controllability of the threshold voltage were insufficient. In the experiment conducted in this study, we applied a high-k gate dielectric (HfO2) for BG and compared the performance between the TG and BG drives. Moreover, we compared the performance of the TFTs in this study with our previous poly-Ge1−xSnx TFTs using a SiO2 gate stack. As a result, an improved TFT performance was confirmed using the high-k dielectric.