Double Diaphragm MEMS Microphone Without Backplate
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Solution Overview
Problem
Conventional MEMS microphones with a backplate suffer from increased noise due to parasitic capacitance, which reduces their signal-to-noise ratio, and adding a second backplate further exacerbates this issue while attempting to enhance sensitivity.
Innovation Solution
A double diaphragm MEMS microphone design without a backplate, where two membranes oscillate in anti-phase, creating a volume between them, reducing parasitic capacitance and increasing the signal-to-noise ratio by eliminating the need for a backplate and potentially utilizing a low impedance port for sound entry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a backplate is added to the MEMS microphone, then sensitivity is improved, but parasitic capacitance increases causing electrical noise
Solution Approach 1:
The patent removes the backplate element from the MEMS microphone structure entirely, extracting the source of parasitic capacitance while maintaining the suspended membrane structure for sound detection. This eliminates the harmful electrical noise while preserving sensitivity through alternative design approaches.
Solution Approach 2:
Instead of using a backplate to enhance sensitivity, the patent inverts the approach by using a suspended membrane structure without a backplate. The sensitivity is achieved through the membrane's mechanical properties and suspension design rather than capacitive coupling with a backplate.
2Measurement precision
If a second backplate is added to increase sensitivity, then sensitivity is improved, but noise from parasitic capacitance is increased
Solution Approach 1:
The patent removes both backplates from the conventional MEMS structure, extracting the entire backplate assembly that causes parasitic capacitance. The dual membrane structure replaces the backplate function while eliminating the source of electrical noise.
Solution Approach 2:
The patent divides the single membrane structure into two separate suspended membranes, allowing each to function independently for sound detection. This segmentation enables enhanced sensitivity through differential measurement while avoiding the need for backplates that generate noise.
3Measurement precision
If conventional transduction mechanisms are used in MEMS microphone, then sensitivity is achieved, but electrical noise from parasitic capacitance occurs
Solution Approach 1:
The patent transitions from electrical transduction mechanisms that rely on backplate capacitance to a mechanically-dominated approach where suspended membranes directly convert sound pressure into mechanical displacement. This substitution eliminates parasitic capacitance while maintaining the transduction function through mechanical means.
Solution Approach 2:
The patent employs thin suspended membrane structures that are flexible enough to respond to sound pressure waves while being electrically isolated from fixed electrodes. These thin films serve as both the acoustic sensing element and the electrical isolation barrier, eliminating parasitic capacitance noise.
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 design enhances the signal-to-noise ratio by doubling the signal and minimizing noise, as the membranes' anti-phase oscillation eliminates the need for a backplate, thereby reducing parasitic capacitance and improving microphone sensitivity.
Implementation Method 1
a received pressure wave entering the volume between the first suspended structure and the second suspended structure generates a displacement of the first suspended structure to a first direction and a displacement of the second suspended structure to a second direction different from the first direction
Implementation Method 2
A simple MEMS microphone may be a capacitor consisting of a counter electrode, more commonly referred to as a backplate, and a diaphragm. When a voltage is applied across the backplate/diaphragm capacitive system, and sound waves cause the oscillation of the diaphragm, the sound waves can be converted into useable electrical signals by measuring the change in capacitance
Data Source
AI summary
A sensor structure may include a first suspended structure and a second suspended structure disposed from the first suspended structure to form a volume. The first suspended structure and the second suspended structure may be arranged relative to each other such that a received pressure wave entering the volume between the first suspended structure and the second suspended structure generates a displacement of the first suspended structure to a first direction and a displacement of the second suspended structure to a second direction different from the first direction and the displacement may generate a measurable signal.