MEMS Transducer Mechanical Support Structure Deflection Control
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Solution Overview
Problem
MEMS capacitive transducers, such as microphones and microspeakers, face issues with pull-in or collapse due to membrane and backplate deflection, leading to potential device failure, and existing designs often result in inefficient active areas and sensitivity limitations.
Innovation Solution
Incorporating a mechanical center post or structure between the backplate and membrane, which shifts the maximum deflection from the center to the perimeter, increasing the active area and preventing collapse, allowing for higher bias voltage application without risk of pull-in, and enhancing sensitivity by altering the harmonic deflection patterns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a voltage is applied to the backplate and the membrane, then the membrane deflects to enable sensing or actuation, but the membrane and backplate may stick together causing pull-in or collapse
Solution Approach 1:
The patent applies preliminary action by pre-positioning mechanical support structures (such as center posts or peripheral supports) on the membrane before operation. These supports are strategically placed to prevent maximum deflection at critical locations, thereby preemptively avoiding pull-in or collapse when voltage is applied and the membrane deflects during normal operation
2Measurement precision
If the membrane is allowed to deflect freely, then the capacitance changes can be maximized for sensing, but the maximum deflection occurs at the center leading to suboptimal sensitivity
Solution Approach 1:
The patent applies local quality by introducing mechanical support structures at specific locations on the membrane (such as the center or peripheral regions) rather than uniformly across the entire membrane. This localized support alters the deflection pattern in specific areas, creating optimal sensitivity zones while maintaining overall membrane functionality for capacitance-based sensing
3Measurement precision
If higher bias voltages are applied to improve the signal output, then the sensitivity increases, but the risk of membrane collapse increases
Solution Approach 1:
The mechanical support structures are pre-installed on the membrane to provide structural reinforcement before high bias voltages are applied. This preliminary structural preparation allows the system to tolerate higher voltages that improve signal output and sensitivity without causing membrane collapse, as the supports prevent excessive deflection at critical locations
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
The center post design increases the active area and sensitivity of MEMS acoustic transducers, preventing membrane collapse and enabling higher voltage application while maintaining structural robustness, thus improving the overall performance and reliability of the devices.
Implementation Method 1
a maximum deflection of the second electrode occurs between the mechanical structure and the perimeter of the second electrode
Implementation Method 2
Many MEMS devices use capacitive sensing techniques for transducing the physical phenomenon into electrical signals. In such applications, the capacitance change in the sensor is converted to a voltage signal using interface circuits
Implementation Method 3
For a microphone, an acoustic signal as a pressure difference causes the membrane to deflect. Generally, the deflection of the membrane causes a change in distance between the membrane and the backplate, thereby changing the capacitance. Thus, the microphone measures the acoustic signal and generates an electrical signal
Implementation Method 4
For a microspeaker, an electrical signal is applied between the backplate and the membrane at a certain frequency. The electrical signal causes the membrane to oscillate at the frequency of the applied electrical signal, which changes the distance between the backplate and the membrane. As the membrane oscillates, the deflections of the membrane cause local pressure changes in the surrounding medium and produce acoustic signals
Data Source
AI summary
According to an embodiment, a microelectromechanical systems (MEMS) transducer includes a first electrode, a second electrode fixed to an anchor at a perimeter of the second electrode, and a mechanical support separate from the anchor at the perimeter of the second electrode and mechanically connected to the first electrode and the second electrode. The mechanical support is fixed to a portion of the second electrode such that, during operation, a maximum deflection of the second electrode occurs between the mechanical structure and the perimeter of the second electrode.