Results of capacitance and current-voltage measurements are reported. A new surface-micromachining technique is explored in which porous silicon is grown laterally in a thin film of polycrystalline silicon constrained between two insulating layers of silicon nitride. Direct observation of the etch front and pore structure are demonstrated. Finally, the feasibility of forming a porous layer over a suspended silicon nitride membrane is demonstrated. This high sensitivity can be accounted for by an increased permittivity in the space-charge region owing to condensation within the pores.
Transient behavior is characterized in detail.
Surface-modification techniques are employed to improve the stability of the RH sensor.