Si-gate CMOS devices on a Si/CaF2/Si structure

Si-gate CMOS inverter chains and 1/8 dynamic frequency dividers have been fabricated on a Si/CaF2/Si structure. A high-quality heteroepitaxial Si/CaF2/Si structure was formed by successive molecular-beam epitaxy of CaF2and Si. Transistors have been fabricated with an improved CMOS process that prevents crystal degradation during the fabrication process as much as possible. The maximum effective mobilities are about 570 and 240 cm²/V . s for n-channel and p-channel transistors, respectively. The inverter chain with an effective channel length of 2.0 µm has a delay time per gate of 360 ps. A maximum operating frequency of 300 MHz is obtained in the divider with an effective channel length of 2.5µm at a supply voltage of 5 V. These results indicate that the Si/CaF2/Si structure has potential for the fabrication of high-speed silicon-on-insulator devices.