Fast Flexible Electronics Based on Printable Thin Mono-Crystalline Silicon

Traditional flexible electronics employ amorphous Si, poly Si and organic materials, but these materials cannot be used for fast (radio-frequency, RF) flexible electronics due to their low carrier mobilities. Instead, we employ monocrystalline Si as the active materials. These high quality materials were released from silicon-on-insulator by undercutting the buried oxide layer. They have equivalent mobility values as their bulk counterpart, yet with high mechanical flexibility. We realized the first RF flexible thin-film transistors by performing pre-release doping and changing the transistor fabrication process to gate-after-source/drain to avoid high temperature process on plastic substrate and achieve low source/drain contact resistance. We further increased the device speed with reduced source/drain access resistance through careful device structure design. By realizing smaller feature size (1µm) with local gate alignment and higher fidelity membrane registration/transfer technique, 12 GHz flexible thin-film transistors were demonstrated. Strained channel and nanolithography are projected to further increase device speed.