Design and sensitivity optimization of vibration sensors for tool state monitoring

A novel vibration sensor in silicon technology for monitoring the tool state of a lathe was developed. The high acceleration amplitudes of up to 4000 g required a careful design of the piezoresistive vibration sensors, based on a silicon membrane, in order to achieve a maximum sensitivity in a wide frequency range. The Finite Element Method (FEM) program ANSYS as well as ICECREM, a simulation program for processing steps in semiconductor production, were used for the optimization of the sensor device shape and internal structure. By ICECREM simulations the process specifications for the piezoresistors and for the silicon membrane were determined. The FEM analyses showed that a proper design of the seismic mass and placement of the piezoresistors can reach a sensitivity of up to 30 mu V/Vg for vibration sensors operating in the above-mentioned acceleration range at a resonance frequency of 14 kHz in the undamped state. This is the highest sensitivity known for this working range. Given the geometrical deviations caused by the production in a CMOS-compatible process, test results correspond well with the simulation.