MEMS Anti-Capture Circuit for Electrostatic Beam Restraint
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Micromachined devices, such as accelerometers, face the challenge of electrostatic capture, where the electrostatic force exceeds the restoring forces, causing the movable beam to be captured by the fixed electrode, leading to reduced sensitivity and signal-to-noise ratio, especially under large accelerations or physical shocks.
Innovation Solution
Reducing or eliminating the voltage difference between electrodes when the displacement exceeds a threshold, ensuring no electrostatic force is present to attract and capture the movable electrode, thereby preventing electrostatic capture.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the electrostatic force is increased to improve the restoring force on the beam, then the beam can return to its nominal position more effectively, but the risk of electrostatic capture increases when the beam displaces beyond a threshold
Solution Approach 1:
The patent applies dynamics by making the voltage applied to the fixed electrode dynamic rather than static. The voltage is adjusted based on the real-time position of the movable beam: when the beam is within the safe range, a higher voltage provides strong restoring force; when the beam approaches the capture zone, the voltage is reduced or eliminated. This dynamic adjustment allows the system to adapt its electrostatic force according to operational conditions, resolving the contradiction between needing strong restoring force and avoiding electrostatic capture.
Solution Approach 2:
The patent implements feedback control by monitoring the position of the movable beam and using this information to control the voltage applied to the fixed electrode. A controller receives position information and adjusts the voltage accordingly - maintaining high voltage when the beam is in the safe operating range and reducing or eliminating voltage when the beam approaches the capture threshold. This feedback mechanism enables the system to automatically prevent electrostatic capture while maintaining effective beam restoration during normal operation.
2Reliability
If mechanical stoppers are added to prevent the beam from contacting the fixed electrode, then electrostatic capture is avoided, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent replaces the mechanical stopper system with an electrical control system. Instead of using physical structures to prevent beam contact, the invention uses dynamic voltage control to eliminate electrostatic forces when the beam approaches the capture zone. This substitution of mechanical prevention with electrical control simplifies the mechanical structure while achieving the same protective function through field control.
Solution Approach 2:
The patent changes the electrical parameter (voltage) rather than modifying the mechanical structure. By dynamically adjusting the voltage applied to the fixed electrode based on beam position, the system prevents electrostatic capture through parameter control instead of structural modification. This approach maintains device simplicity while effectively preventing capture.
3Measurement precision
If the voltage difference between electrodes is maintained high to improve sensitivity, then the device can detect smaller displacements, but the beam is more susceptible to electrostatic capture under large accelerations
Solution Approach 1:
The patent applies dynamics by transitioning from a static high-voltage operation to a dynamic voltage adjustment system. During normal operation with small displacements, the system maintains high voltage difference for maximum sensitivity. When large accelerations cause the beam to approach the capture zone, the system dynamically reduces or eliminates the voltage. This dynamic operation allows the device to achieve both high sensitivity during normal use and capture resistance under shock conditions.
Solution Approach 2:
The patent implements preliminary anti-action by detecting when the beam approaches the capture threshold and preemptively reducing or eliminating the voltage before electrostatic capture can occur. This preventive measure allows the system to maintain high voltage and high sensitivity during normal operation, while automatically activating protection when abnormal conditions are detected, thus preventing capture before it happens.
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 effectively minimizes the risk of electrostatic capture, maintaining device sensitivity and signal quality by eliminating electrostatic forces when displacement exceeds a certain level, allowing the beam to return to its nominal position without mechanical stoppers or power shutdown.
Implementation Method 1
The motion of the MEMS device can be detected by a change in capacitance of one or more capacitors within the MEMS device, where the capacitance varies as a function of the displacement of the beam
Implementation Method 2
The supporting tethers also apply a restorative force counter to the external force, which normally pulls the beam back towards its nominal position
Implementation Method 3
If the beam has been displaced from its nominal position, for example by an acceleration, the change in the capacitances discussed above will cause a signal from the fixed electrodes to appear on the beam
Data Source
AI summary
A MEMS device has a movable beam, a differential capacitor with a movable electrode that moves in response to the displacement of the movable beam and that is disposed between two stationary electrodes, and a voltage circuit for applying a first voltage to the first stationary electrode, second voltage to the second stationary electrode, and a third voltage to the moveable electrode. The MEMS device also has a monitor operably coupled with the movable beam to monitor the displacement of the movable beam. In some embodiments, the monitor may monitor the distance between the movable electrode and at least one of the stationary electrodes. The MEMS device further has a voltage reducing circuit operatively coupled with the monitor, the movable electrode, and the stationary electrodes. The voltage reducing circuit reduces the differential between the third voltage and the voltages on the stationary electrodes when the monitor detects that the displacement of the movable beam is greater than or equal to a threshold value.