Electrostatic MEMS Double-Resonance Actuation for Lower Voltage
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Solution Overview
Problem
Electrostatic micro-electro-mechanical systems (MEMS) require high actuation voltages for operation, which limits their adoption in applications like RF switches and MEMS resonator-based sensors, and previous methods to reduce voltage often compromise MEMS performance or introduce new issues such as squeeze-film-damping and stiction.
Innovation Solution
The method involves driving MEMS devices with two alternating current (AC) signals, where one frequency is within the internal electrical resonance frequency bandwidth and the difference between the frequencies is near the natural mechanical resonance frequency, allowing for double resonance actuation that amplifies the effective voltage without altering the MEMS device configuration or operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If high voltage is applied to actuate electrostatic MEMS devices, then the MEMS structure can be moved, but the device requires very high voltage which limits adoption in promising applications
Solution Approach 1:
The patent applies mechanical vibration by driving the MEMS device at its natural mechanical resonance frequency. This resonance amplifies the mechanical response of the MEMS structure, allowing smaller actuation voltages to produce the same displacement effect that would otherwise require very high voltages. The vibrational approach converts electrical energy more efficiently into mechanical motion.
Solution Approach 2:
The patent changes the operating parameters by utilizing the electrical resonance frequency of the MEMS device. By tuning the AC signal frequency to match the electrical resonance, the system achieves maximum current amplitude and voltage amplification across the capacitive structure, thereby reducing the required input voltage while maintaining adequate actuation force.
2Use of energy by moving object
If the air gap between MEMS structure and substrate is reduced to lower actuation voltage, then voltage is reduced, but squeeze-film-damping increases
Solution Approach 1:
By operating at mechanical resonance, the system achieves large amplitude vibrations that overcome the damping effects. The resonant oscillation creates dynamic conditions where the inertial forces dominate over the squeeze-film damping forces, allowing the MEMS to achieve sufficient displacement even with smaller air gaps without being severely penalized by increased damping.
3Use of energy by moving object
If the MEMS actuation area is increased to reduce actuation voltage, then voltage is reduced, but squeeze-film-damping increases
Solution Approach 1:
The resonant vibration approach allows the system to achieve adequate actuation with smaller electrode areas. The resonance amplification compensates for the reduced actuation area, maintaining sufficient electrostatic force while minimizing the area that would otherwise generate excessive squeeze-film damping.
4Use of energy by moving object
If MEMS stiffness is reduced to lower actuation voltage, then voltage is reduced, but immunity to stiction decreases
Solution Approach 1:
Operating at mechanical resonance provides large amplitude oscillations that continuously overcome static friction and adhesion forces. The dynamic motion generated by resonance prevents the MEMS structure from sticking to the substrate, maintaining reliability even with lower stiffness designs that would otherwise be more susceptible to stiction.
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 can amplify the voltage across the MEMS device by up to an order of magnitude, reducing the need for high input voltages and maintaining the MEMS device's operational integrity, as demonstrated through experimental validation showing significant voltage amplification and mechanical vibration enhancement.
Implementation Method 1
an electrostatic MEMS device requires very high voltage to move its structure
Implementation Method 2
the MEMS device has a natural mechanical resonance frequency
Implementation Method 3
the MEMS device has an internal electrical resonance frequency
Data Source
AI summary
Systems and methods to amplify the response of a MEMS micro-oscillator by driving the MEMS device at its electrical and mechanical resonance frequencies, simultaneously. This enhances the MEMS mechanical sensitivity to electrical excitation and increases the voltage across the MEMS capacitor. Moreover, using a combination of two input signals at different frequencies (beat signal) may be used to achieve double resonance in any MEMS device, even if its natural frequency is far from its electrical resonance.