Demonstration of CMOS inverter on poly-crystalline Ge on glass

Fabrication of germanium (Ge) thin-film transistors (TFTs) at low temperature on an insulator is essential for the realization of monolithic three-dimensional large-scale integration and flexible electronic devices. We investigated a complementary metal-oxide semiconductor (CMOS) inverter comprising an accumulation-mode p-channel (p-) TFT and inversion-mode n-channel (n-) TFT on poly-crystalline Ge formed on a glass substrate by solid-phase crystallization. We successfully fabricated accumulation-mode p-TFT and inversion-mode n-TFT on the same chip at low temperature (<500 °C). We also confirmed inverter operation with DC and pulse signals up to 10 kHz. Hydrogen (H) introduction was carried out to improve the CMOS characteristics. The on/off ratios of the p- and n-channel TFTs with forming gas (H 2 /Ar) annealing were up to five times those with nitrogen (N 2 ) annealing, and supply voltage ( V DD ) loss in the output signal ( V OUT ) was suppressed. We suggested that this improvement is due to a reduction in hole density through the influence of hydrogen annealing. These results pave the way for monolithic three-dimensional large-scale integration and flexible device applications on poly-crystalline Ge.