Monolithic Multi Degree of Freedom (MDoF) Capacitive MEMS Accelerometers

Abstract

With the continuous advancements in microelectromechanical systems (MEMS) fabrication technology, inertial sensors like accelerometers and gyroscopes can be designed and manufactured with smaller footprint and lower power consumption. In the literature, there are several reported accelerometer designs based on MEMS technology and utilizing various transductions like capacitive, piezoelectric, optical, thermal, among several others. In particular, capacitive accelerometers are the most popular and highly researched due to several advantages like high sensitivity, low noise, low temperature sensitivity, linearity, and small footprint. Accelerometers can be designed to sense acceleration in all the three directions (X, Y, and Z-axis). Single-axis accelerometers are the most common and are often integrated orthogonally and combined as multiple-degree-of-freedom (MDoF) packages for sensing acceleration in the three directions. This type of MDoF increases the overall device footprint and cost. It also causes calibration errors and may require expensive compensations. Another type of MDoF accelerometers is based on monolithic integration and is proving to be effective in solving the footprint and calibration problems. There are mainly two classes of such monolithic MDoF accelerometers, depending on the number of proof masses used. The first class uses multiple proof masses with the main advantage being zero calibration issues. The second class uses a single proof mass, which results in compact device with a reduced noise floor. The latter class, however, suffers from high cross-axis sensitivity. It also requires very innovative layout designs, owing to the complicated mechanical structures and electrical contact placement. The performance complications due to nonlinearity, post fabrication process, and readout electronics affects both classes of accelerometers. In order to effectively compare them, we have used metrics such as sensitivity per unit area and noise-area product. This paper is devoted to an in-depth review of monolithic multi-axis capacitive MEMS accelerometers, including a detailed analysis of recent advancements aimed at solving their problems such as size, noise floor, cross-axis sensitivity, and process aware modeling.

Capacitive‐Type Two‐Axis Accelerometer with Liquid‐Type Proof Mass

“…When acceleration is applied to accelerometers, the mass moves deforming the spring, and the input acceleration is calculated by measuring the position of mass. [ 2 ] To measure the position, various accelerometers have been developed, such as capacitive, [ 3–14 ] piezoresistive, [ 15,16 ] resonant, [ 17,18 ] and optical [ 19,20 ] accelerometers. However, accelerometers with such microscale solid spring‐like silicon structures can suffer from mechanical fatigue.…”

Strain-controlled power devices as inspired by human reflex

“…One of the critical parts of the field of AI is to realize the accelerate-feedback-control. Emerging AI applications, such as autopilot or robot walking, require effectively control output power according to the changes of environment, e.g., acceleration [31][32][33][34][35] . In a self-driving car, the output power of engine needs to be realized at the self-adjusted and unsupervised conditions in rapid response to emergency braking or other accidents, as schematically shown in Fig.…”

Cantilever Type Acceleration Sensors Made by Roll-to-Roll Slot-Die Coating

“…The repeatability characteristic of the acceleration sensor thus needs to be improved, which can be obtained by employing materials with stronger restoration and elastic force than epoxy resin for the structural layer. Compared to conventional MEMS air gap-based cantilever type capacitive acceleration sensors [66][67][68] and printed micro-sized acceleration sensors [69], the roll-to-roll slot-die coated sensor samples have lower electrical sensitivity and higher hysteresis error. This result is due to the relatively large size of the sensor samples.…”