A MICROMACHINED PRESSURE SENSOR WITH FIBEROPTIC INTERFEROMETRIC READOUT

A high sensitivity, batch fabricated, fiber-optic pressure sensor has been fabricated using silicon micromachining technology. The transduce r consists of a fiber positioning v-groove, a 45-degrees stationary mi rror and a silicon membrane, micromachined in silicon by anisotropic e tching in KOH solution, and a single mode optical fiber. The membrane and optical fiber end form a Fabry-Perot cavity whose length varies wi th pressure. The generated optical interference fringes are used to de tect and measure the change in membrane deflection. Pressure range of operation is dictated by the thickness, size and material of the membr ane. The sensor described here was designed for low pressure range (0- 25 mm Hg) applications. Temperature sensitivity and stability problems which are commonly encountered with currently available piezoresistiv e and capacitive pressure sensors are significantly reduced by the inh erent differential nature of interferometric measurement and the use o f all silicon construction. The fabrication, packaging and testing of the sensor are described in this paper. The performance of the sensor was evaluated and found to compare favorably with theoretical predicti ons.