Research Of Pull-in Accelerometer Based On Cantilever Beam Mass Structure

Micro-electro-mechanical accelerometer is one of the most important types of silicon-based sensors. But suffering from parasitic effects and pull-in effects, it's difficult to scale down the structure further. In this dissertation, a novel digital accelerometer which works in the pull-in operation mode is presented. The acceleration is obtained by measuring the pull-in time. As the pull-in time signal can be read out by digital circuit, no analog circuit is needed. The system can be scaled down further since it has no limit of pull-in and parasitical capacitance effect.A model of the pull-in accelerometer based on cantilever beam mass structure is developed. Theoretical analysis indicates that the difference of the pull-in time from detected electrode 1 to 2 and 2 to 1 is proportional to the input acceleration, and the sensitivity and the non-linearity of the accelerometer are comparable to the traditional capacitive accelerometers. The damping ratio, the ratio of the beam length and the mass length and the range of the mass movement can also affect the sensitivity and the non-linearity.A quasi-LIGA progress consisted of thick film photolithography and electroplating is accomplished. The stress characterization of electroplated gold layers is found to be affected by the current density while electroplating and the length of the structure. Two types of accelerometers made of silicon and gold are designed and fabricated. The capacitive and the digital interface circuits are both applied to the test. The test results show that the pull-in time changes as the acceleration.