Seebeck and piezoresistance effects in amorphous-microcrystalline mixed-phase silicon films and applications to power sensors and strain gauges

Abstract

Highly conductive films of amorphous-microcrystalline mixed-phase fluorinated hydrogenated silicon (conductivity, more than 1 S cm -1) were prepared by d.c. glow discharge and studied. The maximum conductivity obtained was about 20 S cm -1 for both p- and n- type films. Raman scattering spectroscopy andHall effect measurements showed that the highly conductive films included 15%–80% of a crystalline phase in an amorphous silicon network and has a carrier concentration of over 10 18 cm -3 which was derived from a conventional Hall effect analysis. The absolute value of the Seebeck coefficient was 150–200 μV K -1 at room temperature which is two orders of magnitude higher than those of metals. We demonstrated the fabrication of a power sensor using the Seebeck effect and obtained a sensitivity of 1.5 mV mW -1 when d.c. input power was applied. From the results of measurements of the piezoresistance effect, the gauge factor is found to be 30 for p-type films and - 20 for n-type films, which is sufficiently high for the films to be used in strain gauges. This suggests the possibility of application to thin film pressure sensors.