Phased MEMS Plate Lifting via Sequential Electrostatic Peeling
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Solution Overview
Problem
MEMS devices face significant challenges with stiction forces that prevent movable plates from being easily separated from stationary plates, requiring high restoring forces and voltages to overcome these forces, which is inefficient and often unsuccessful.
Innovation Solution
The solution involves a MEMS device design where a flexible top plate is supported by spring structures and driven by phased electrode voltage signals, allowing for sequential release of electrostatic forces to peel the top plate away from electrodes, reducing the maximum force required to break stiction by applying voltage in a phased manner aligned with the resonance properties of the top plate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a high restoring force is applied to overcome stiction forces, then the movable plate can be separated from the stationary plate, but the required voltage increases and the system becomes less efficient
Solution Approach 1:
The patent divides the single large restoring force into multiple smaller phased forces applied sequentially to different regions of the movable plate. By segmenting the plate into multiple zones and applying electrostatic forces in phases to each zone, the system overcomes stiction gradually rather than requiring a single high-voltage impulse, thus reducing overall energy consumption while maintaining effective plate separation.
Solution Approach 2:
The patent employs periodic electrostatic actuation with multiple phases rather than a single continuous force. The electrostatic force is applied in discrete time phases to different regions of the movable plate, creating a periodic action that progressively overcomes stiction. This periodic approach allows the system to build up motion incrementally, reducing the peak voltage requirements compared to a single high-voltage application.
2Reliability
If a single high voltage is applied to overcome stiction, then the plate can be released, but the maximum force required is high and may damage the device
Solution Approach 1:
The patent segments the electrostatic actuation into multiple phases applied to different regions of the movable plate. Instead of applying one high-voltage impulse across the entire plate, the system divides the plate into multiple zones and applies voltage in sequential phases to each zone. This segmentation distributes the mechanical stress and reduces the peak force required, preventing potential damage while maintaining reliable stiction release.
Solution Approach 2:
The patent applies preliminary electrostatic forces to specific regions of the movable plate before attempting full plate separation. By pre-applying force to initiate motion in certain regions first, the system reduces the overall stiction barrier before the final separation phase, thereby lowering the maximum force needed and improving reliability without requiring damaging high-voltage spikes.
3Ease of operation
If the entire top plate is pulled away from the bottom plate simultaneously, then separation is achieved, but the restoring force required is substantially more than spring structures can provide
Solution Approach 1:
The patent divides the plate separation process into multiple sequential phases rather than attempting simultaneous separation. Different regions of the movable plate are actuated in succession, with each phase separating a portion of the plate. This segmentation allows spring structures to provide sufficient restoring force for each smaller phase without requiring an impractically large total force for simultaneous separation of the entire plate.
Solution Approach 2:
The patent implements periodic electrostatic actuation with multiple phases, where each phase separates a different region of the movable plate. This periodic action transforms a single large force requirement into a series of smaller, manageable force applications that the spring structures can handle, thereby improving ease of operation without exceeding mechanical force limits.
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 reduces the force and voltage needed to separate the top plate from the electrodes, allowing for efficient release from stiction forces while minimizing the impact on other device parameters, such as actuator size and manufacturing variability.
Implementation Method 1
an electrostatic drive electrode is located underneath the top plate, providing electrostatic attraction force in response to an applied DC drive voltage in order to pull the top plate down toward the bottom plate
Implementation Method 2
An RF signal applied between top plate 8 and co-planar waveguide CPW also produces an RF electrostatic attraction force. That RF electrostatic attraction force combines with the above-mentioned stiction forces and increases the net force holding top plate 8 tightly against the bottom plate 4
Implementation Method 3
the other plate (e.g., the top plate) is suspended by a spring or elastic suspension element and is free to move
Implementation Method 4
Stiction forces for MEMS devices are well known and are mainly caused by Van der Waals forces, dielectric charging, and other lesser effects
Data Source
AI summary
A MEMS device includes a bottom plate structure supporting a conductive electrode. A flexible conductive top plate movably supported by a flexure is affixed to a small peripheral portion of the top plate that is aligned with the electrode. Drive circuitry applies a high level of a drive voltage signal between the electrode and the top plate to produce an attracting electrostatic force between the top plate and the electrode sufficient to overcome the flexure and draw the top plate against the electrode. The drive circuitry later applies a low level of the drive voltage signal to remove the electrostatic force and allow the flexure to peel the peripheral portion away from the electrode. Additional drive voltage signals may be applied to additional electrodes to draw additional peripheral portions of the top plate against the additional electrodes and successively removed to allow peripheral portions of the top plate to be sequentially peeled away from the electrodes.