Thermomechanical noise of arrayed capacitive accelerometers with 300-NM-gap sensing electrodes

2017 19th International Conference on Solid-State Sensors, Actuators and Microsystems (TRANSDUCERS), 18-22 June 2017.Thermomechanical noise of arrayed capacitive accelerometers with sub-micrometer sensing electrodes was evaluated. The unit accelerometer of the array was 80-μm square, designed as a proportional scale-down of a conventional single-axis accelerometer. Since the size effect shows the capacitance sensitivity per unit volume increases by proportional downsizing, a 10-by-10 array of the one-tenth sized unit accelerometer would have the same sensitivity of a single accelerometer of same occupied area. However, the thermomechanical noise needs to be controlled and reduced by vacuum encapsulation because size reduction causes noise increase. By measuring the electrical impedance at the resonant frequency, the damping coefficient was estimated using electrical equivalent circuit modeling. The estimated thermomechanical noise was reduced below 3 μg√VHZ by encapsulating at 100 Pa, which is low enough for instrumentation applications

Self-dependent Equivalent Circuit Modeling of Electrostatic Comb Transducers for Integrated MEMS

International audienceThe article presents a new equivalent circuit model of electrostatic comb transducers for an integration of MEMS into LSI. The model detects the displacement using a dummy spring to express the current induced by the movement, and the model parameters can be derived from only its dimensions not from external parameters, such as acting force and applied voltage. In addition, being composed from basic circuit components, the model is easily utilized in conventional circuit simulation software. The in-plane two-degree-of-freedom comb model was applied to a simple SOI coupled resonator and the measured and simulated electrical and mechanical properties showed good agreement with each other. The model was also applied to a decoupled two-axis resonator for a vibrating gyroscope made on silicon-on-glass substrate. Frequency tuning and oscillating circuit with constant amplitude control have been tested and the tuning results and transient responses showed good agreement as well