A method to measure the micro-capacitance for MEMS comb actuators

Abstract

A method is introduced to measure the micro-capacitance for MEMS comb actuators whose value is in pF even fF magnitude. This method uses so called peak detection measuring technology to realize this purpose. It is mainly composed of the signal generating circuits, C/V (Capacitance/Voltage) converting part, peak detector circuits and the digital solution element. In order to verify the correctness of the design, detailed theory analysis and simulation are made for every composed portion and corresponding mathematical model is built. It is concluded from the analyzed result that precision of the system can reach 237 aF for 0.98–2 pF measuring range. When corresponding measuring electric circuits is fabricated and debugged, high precision calibration device named Agilent E4980A is used to calibrate it. It is concluded from the calibrated result that the output voltage of the measurement circuit and the micro capacitance have good linear relationship, which verifies the correctness of the pertinent theory. Finally, in order to verify the correctness of the design, dynamic characters of a resonant MEMS gyroscope, which is fabricated with bulk technology and bonding process, is tested with this device. It is concluded from the measured result that relative error of the resonant frequency between the ideal value and the measured result is just 0.02%. Quality factor of this sensor is 312.5. Experimental results indicate this scheme is feasible to measure the static and dynamic characters of micro capacitors.