Dean P. Neikirk
Dept. of Elec. and Comput. Eng., Univ. of Texas, Austin, TX 78712
A new class of optically interrogated pressure microsensors with tailored dielectric film mirrors will be discussed. The sensors are based on the well-established combination of a pressure sensitive membrane serving as the sensing element with an optical fiber as the interconnect. The pressure sensitive element consists of a Fabry--Perot cavity monolithically built by etching a polysilicon sacrifical layer that lies between dielectric film stacks. The size of the cavity can be precisely adjusted by controlling the thickness of the sacrificial layer grown using LPCVD. Using LPCVD, multiple dielectric films (typically consisting of silicon dioxide and silicon nitride) can be deposited to form wavelength selective dielectric mirrors. This batch fabrication technique allows excellent alignment and parallelism of the two mirrors in the cavity, which has been a problem in devices using hybrid assembly. A guiding structure for the optical fiber can also be formed using anisotropic silicon etching. The structure allows accurate alignment between the pressure sensitive Fabry--Perot cavity and the fiber. Similar fabrication techniques can be applied to construct a tunable optical filter that allows the use of optical wavelength modulation detection techniques, which are much less sensitive to light loss during interrogation.