Formation of implanted piezoresistors under 100-nm thick for nanoelectromechanical systems

Piezoresistors, with a thickness of 90 nm have been obtained by implanting boron fluorine into germanium-preamorphized silicon. Germanium implantation was carried out at a dose of 10/sup 15/ cm/sup -2/ and an energy of 60 keV to form a 80-nm-thick preamorphized layer prior to BF/sub 2/ implantation at a dose of 5 /spl times/ 10/sup 14/ cm/sup -2/ and an energy of 15 keV. The experimental sensitivity is 80% of the theoretical maximum. This shows that the germanium preamorphization step does not impact the sensitivity of the piezoresistors. Moreover, 1/f noise characteristics have been improved compared to those obtained in a previous work without using a preamorphizing implant.