Force balanced micromachined pressure sensors

This paper discusses the fabrication and testing of two low-voltage force-balanced pressure sensors. In these devices the force acting on a diaphragm under external pressure and its corresponding deflection are counterbalanced with the force and deflection generated in a parallel plate electrostatic actuator mechanically coupled to the diaphragm. The low balancing voltage is attained using a force multiplication scheme. The first device is implemented using an open gap actuator constructed on top of a vacuum sealed sense diaphragm. The open gap design is exposed to the measurement environment hence susceptible to contamination. The second device eliminates this problem by enclosing the actuator in an hermetically-sealed cavity. Both devices have a full scale pressure range of 1 atmosphere (1.013 bar). The open actuator device has a nominal capacitance of 0.34 pF and a full scale range of 70 fF. The sealed actuator device a nominal capacitance of 2.12 pF and a full scale range of 100 fF. The pressure is balanced by voltages in the range of 12-25 V demonstrating the feasibility of force balanced pressure sensor compatible with low-voltage electronics.