Five-axis motion sensor with electrostatic drive and capacitive detection fabricated by silicon bulk micromachining

Abstract

Abstract We have developed a five-axis motion sensor with electrostatic drive and capacitive detection by using silicon bulk-micromachining technique. This sensor has a seismic mass which is constantly vibrated along Z -axis by electrostatic force at the resonant frequency of 1875 Hz. Since the Z -axis acceleration ( A z ) translates a mass parallel and the X -, Y -axis accelerations ( A x , A y ) tilt a mass, three-axis accelerations can be detected by capacitance change. Coriolis force induced by two-axis angular rates ( Ω x , Ω y ) makes tilting vibration of a mass synchronizing with driving frequency. Therefore, two-axis angular rates can be detected separating from the accelerations. Measured sensitivities of Z - and X -( Y -) axis accelerations were approximately 20 and 6 fF/G, respectively, and the cross-axis sensitivity was less than 5%. The sensitivities of two-axis angular rates around X - and Y -axis are approximately 3 aF/(deg/s). The cross-axis sensitivity of Ω x against Ω y was less than 3%, and that of Ω z against Ω x ( Ω y ) was not observed. The chip size of developed sensor is 8.4 mm ×8.0 mm ×1.4 mm.