High-resolution MEMS inertial sensor combining large-displacement buckling behaviour with integrated capacitive readout.

TLDR: The design of a bulk micromachined MEMS device exploiting non-linear buckling behaviour is described, aiming for n∕Hz resolution by maximising mechanical and capacitive sensitivity.

Abstract: Commercially available gravimeters and seismometers can be used for measuring Earth’s acceleration at resolution levels in the order of $${\mathrm{ng}}/\sqrt {\mathrm{Hz}}$$ (where g represents earth’s gravity) but they are typically high-cost and bulky. In this work the design of a bulk micromachined MEMS device exploiting non-linear buckling behaviour is described, aiming for $${\mathrm{ng}}/\sqrt {\mathrm{Hz}}$$ resolution by maximising mechanical and capacitive sensitivity. High mechanical sensitivity is obtained through low structural stiffness. Near-zero stiffness is achieved through geometric design and large deformation into a region where the mechanism is statically balanced or neutrally stable. Moreover, the device has an integrated capacitive comb transducer and makes use of a high-resolution impedance readout ASIC. The sensitivity from displacement to a change in capacitance was maximised within the design and process boundaries given, by making use of a trench isolation technique and exploiting the large-displacement behaviour of the device. The measurement results demonstrate that the resonance frequency can be tuned from 8.7 Hz–18.7 Hz, depending on the process parameters and the tilt of the device. In this system, which combines an integrated capacitive transducer with a sensitivity of 2.55 aF/nm and an impedance readout chip, the theoretically achievable system resolution equals 17.02 $${\mathrm{ng}}/\sqrt {\mathrm{Hz}}$$ . The small size of the device and the use of integrated readout electronics allow for a wide range of practical applications for data collection aimed at the internet of things. A micromechanical system (MEMS) has been developed that allows accurate measurement of acceleration at high-resolution levels. Commercially available gravimeters and seismometers can be used for high-resolution measurement of the earth’s acceleration, but they are typically very expensive and bulky. However, a team headed by Guo Qi Zhang at Delft University of Technology, Netherlands was able to design, simulate, fabricate and test a low-cost MEMS device with an integrated miniaturized high-sensitivity transducer for high-resolution acceleration measurements. The team was able to process and package its device by wirebonding it to a printed circuit board containing an application-specific integrated circuit. The authors believe that their extremely compact, low-power inertial sensor has considerable potential for a wide range of practical applications for data collection with the Internet of things.