Amorphous and microcrystalline silicon deposited by hot-wire chemical vapor deposition at low substrate temperatures: application to devices and thin-film microelectromechanical systems

Abstract

Amorphous silicon and microcrystalline silicon have been deposited on glass and plastic (PET) substrates using hot-wire chemical vapor deposition (HW) at substrate temperatures (Tsub) of 100°C and 25°C. The optoelectronic and structural properties of intrinsic and doped films are reviewed. Intrinsic HW a-Si:H is incorporated into a p-i-n diode processed at a maximum temperature of 100°C, achieving a rectification ratio of 106. The mechanical (residual stress) properties of low-Tsub HW layers are compared to those of low-Tsub radio-frequency-deposited layers. Doped-microcrystalline films of low-Tsub HW layers deposited on plastic substrates show piezoresistive behavior. The resistance of n-type films decreases with applied tensile stress and increases with applied compressive stress, while p-type films show the opposite behavior. The mechanical properties of low-Tsub HW layers are adequate for their use as structural layers in thin-film microelectromechanical systems (MEMS). The electrical actuation of surface micromachined bridge structures and the mechanical actuation of thin-film microresonators on large area substrates are demonstrated.