MEMS Out-of-Plane Actuator Linear Force via Levitation
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Solution Overview
Problem
MEMS devices, such as inertial sensors, face challenges in out-of-plane actuation due to non-linear forces from existing methods like comb drives and parallel plate electrodes, which are not suitable for devices with electrodes beneath the comb drive or result in unstable actuation at higher voltages.
Innovation Solution
A MEMS sensor device utilizing a combination of levitation and parallel plate forces, where the levitation force acts in the opposite direction of the parallel plate force, achieving a linear out-of-plane actuation dependent only on applied voltage, by designing the drive comb and parallel plate actuator to ensure forces act in opposite directions and are independent of in-plane and out-of-plane displacement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a comb drive is used to create an out-of-plane force, then vibration reduction is achieved, but the approach is not usable for devices with electrodes beneath the comb drive and the force produced is non-linear around zero deflection
Solution Approach 1:
The patent transitions from using a comb drive (which operates in a plane) to using a parallel plate electrode structure (which operates in the out-of-plane dimension). This dimensional change allows the actuator to function beneath the proof mass without interfering with in-plane comb drive electrodes, while still providing effective vibration reduction through out-of-plane electrostatic forces.
2Measurement precision
If parallel plate electrodes are used to compensate for quadrature movement, then motion compensation is achieved, but the force produced is non-linear and the actuator becomes unstable for higher actuation voltages
Solution Approach 1:
The patent employs an asymmetric electrode configuration where the parallel plate electrodes are positioned offset from the center of the proof mass. This asymmetric placement creates a restoring force that is linear with displacement, improving stability at higher voltages while maintaining effective motion compensation capability.
3Ease of operation
If out-of-plane actuators based on parallel plate electrodes are used, then actuation in out-of-plane direction is achieved, but the actuation is inherently non-linear
Solution Approach 1:
The patent modifies the geometric parameters of the parallel plate electrode structure, specifically the plate area and spacing, to linearize the electrostatic force-displacement relationship. By carefully selecting these parameters, the actuator achieves both effective out-of-plane actuation and improved linearity, enabling precise control for high-performance inertial sensors.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables higher yield and performance in MEMS inertial sensors by providing a linear out-of-plane actuation suitable for high-performance accelerometers and gyroscopes, reducing vibration sensitivity and improving dynamics through force feedback loops.
Implementation Method 1
The first and second drive combs, and the parallel plate sense electrode, are each electrically charged and configured with respect to the proof mass such that a combination of a levitation force and a parallel plate force produces a linear out-of-plane actuation
Data Source
AI summary
A MEMS sensor device comprises a support substrate, a proof mass movably connected to the support substrate, a first drive comb fixedly connected to the support substrate in a first orientation and adjacent to the proof mass, and a second drive comb fixedly connected to the support substrate in a second orientation and adjacent to the proof mass. The second orientation is opposite of the first orientation such that the first and second drive combs face toward each other. A parallel plate sense electrode is located under the proof mass on the support substrate. The drive combs and the parallel plate sense electrode are each electrically charged and configured with respect to the proof mass such that a combination of a levitation force and a parallel plate force produces a linear out-of-plane actuation that depends only on an applied voltage.