Piezoelectric-Capacitive Combined MEMS Microphone Design
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Solution Overview
Problem
Capacitive type MEMS microphones face performance bottlenecks, are susceptible to dust, water, and high sound pressure, and have complex fabrication processes and high production costs, limiting their reliability and sensitivity.
Innovation Solution
A piezoelectric type and capacitive type combined MEMS microphone design featuring a piezoelectric diaphragm structure between the capacitor system and the base, with acoustic holes for communication between sound cavities, enhancing sensitivity and dust resistance by generating dual electric signals from both the capacitor system and the piezoelectric diaphragm.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a capacitive type MEMS microphone is used, then the microphone can be fabricated with micro-machining technology, but the sensitivity is limited and performance has reached a bottleneck
Solution Approach 1:
The patent combines two different transduction mechanisms - capacitive type and piezoelectric type - into a single MEMS microphone device. The capacitive diaphragm and piezoelectric diaphragm are integrated to work simultaneously, allowing the device to benefit from both transduction principles and overcome the sensitivity limitations of pure capacitive designs
Solution Approach 2:
The invention uses composite material structures by integrating piezoelectric materials with the capacitive diaphragm system. The piezoelectric diaphragm structure incorporates piezoelectric elements that generate electrical charge in response to mechanical stress, creating a composite transduction system that enhances overall sensitivity
2Ease of operation
If a capacitive type MEMS microphone is used, then the microphone can convert sound waves to electric signals, but it is greatly affected by dust, water and pollutants
Solution Approach 1:
The piezoelectric diaphragm structure serves as a sacrificial or protective element that can be designed to withstand environmental contaminants. The robust piezoelectric structure protects the more sensitive capacitive components while maintaining signal conversion functionality
Solution Approach 2:
The piezoelectric diaphragm acts as an intermediary between the external environment (dust, water, pollutants) and the internal capacitive sensing mechanism. It transmits acoustic signals while blocking or filtering out harmful environmental factors before they reach the sensitive capacitive components
3Stress or pressure
If the diaphragm works at a high sound pressure environment, then the microphone can handle loud sounds, but reliability will be getting worse
Solution Approach 1:
The piezoelectric material properties are utilized to change the mechanical-to-electrical conversion characteristics under high sound pressure. The piezoelectric effect provides a linear response that maintains reliability even when subjected to high acoustic pressures that would distort capacitive measurements
4Ease of manufacture
If a capacitive type MEMS microphone is used, then the microphone can be fabricated with micro-machining technology, but the fabrication process is relatively complex and production cost is relatively high
Solution Approach 1:
The fabrication process is segmented into distinct stages: first forming the capacitive diaphragm structure, then adding the piezoelectric diaphragm layer, and finally integrating the back plate and acoustic holes. This segmentation allows each component to be optimized independently while simplifying the overall manufacturing workflow
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 combined design improves microphone sensitivity and reliability by converting sound waves into electric signals through both capacitive and piezoelectric mechanisms, while providing dustproofing and reducing noise through acoustic hole arrangements.
Implementation Method 1
sound pressure acts on the piezoelectric diaphragm structure to deform the piezoelectric diaphragm structure, thereby generating charge output
Implementation Method 2
The diaphragm vibrates under an action of a sound wave, causing the distance between the diaphragm and the back plate to change, and causing capacitance of the plate capacitor to change, thereby converting a sound wave signal into an electric signal
Data Source
AI summary
Provided is a piezoelectric type and capacitive type combined MEMS microphone, comprising a base with a back cavity and a capacitor system arranged on the base; wherein, the capacitor system comprises a back plate and a diaphragm; the back plate is opposite to and apart from the diaphragm to form a first sound cavity; a piezoelectric diaphragm structure is between the capacitor system and the base; a second sound cavity is formed between the capacitor system and the piezoelectric diaphragm structure; the second sound cavity is at least in communication with the first sound cavity or the back cavity; the piezoelectric type and capacitive type combined MEMS microphone can output two groups of electric signals comprising a group of electric signals output from the capacitor system and a group of electric signals output from the piezoelectric diaphragm structure, thus improving sensitivity of the microphone.