The design of a Fabry Perot interferometer/photodiode (FPI/PD) spectral image sensor in the visible wavelength range using CMOS compatible processes is described. Interdigitated PIN PDs with various geometries were fabricated on Si and tested. The spectral response shows that a quantum efficiency of nearly 80% is achieved by the PD in the visible wavelength range. The quantum efficiency increases with increasing gap-width to pitch-width ratio, and the increase is more significant at shorter wavelengths. The optical performance of FPIs with distributed Bragg reflector mirrors and Ag thin film mirrors are modeled and compared. We find that FPIs with Ag mirrors are more suitable for the applications described here. A transmittance of 0.4 can be achieved using 40 nm Ag mirrors. The effects of the mechanical support of the Ag layer and the PD insulating layer on the transmittance of the FPI are investigated theoretically. After adding the supporting layer or insulating layer, the transmittance changes periodically with the thickness of the respective layers. The changing period and amplitude is a function of the refractive index of the respective layer.
A novel laterally driven mechanism is proposed and studied to solve the pull-in problem of electrostatic actuation in MEMS for use in simple Fabry-Perot interferometers (FPI) with a large tuning range. This method is to build electrodes that are not directly opposite to each other, but rather are laterally shifted. Mathematica calculations show that laterally driven beams require a smaller operating voltage than do some other methods, and cover nearly the full travel range. It is also found that driving performance is influenced by the structure's lateral gap. Too small a lateral gap still yields pull-in failure. For excessively large lateral gap, the pull-in function is not effective. Smaller lateral gaps have lower operating voltage, but larger lateral gaps have better operating stability. A test structure consisting of 40 aluminum beams suspended across two poles has been designed and fabricated. Directly below each test beam is located a capacitive test electrode. Next to each test electrode are two lateral driving electrodes. A driving voltage is applied across the aluminum test beams and lateral electrodes, pulling down the beam and causing the capacitance to change between the test beam and test electrode. By measuring this change, the lateral drive method is verified and characterized.