Silicon Condenser Microphone Diaphragm Parasitic Capacitance Reduction
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Solution Overview
Problem
Miniature microphones, such as silicon condenser microphones, face challenges due to variability in sensitivity caused by non-uniform stamping and assembly processes, as well as long-term performance drifts from temperature and humidity effects on organic diaphragm films, leading to inconsistent performance.
Innovation Solution
A silicon condenser microphone design featuring a diaphragm with an inner vibrating part and an outer part, where a gap between them reduces parasitic capacitance by electrically connecting the inner part to bias voltage and the outer part to ground, enhancing sensitivity and reducing unwanted capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a one-piece diaphragm is fixed to the silicon base, then the microphone structure is simplified and easier to manufacture, but parasitic capacitance increases and sensitivity decreases
Solution Approach 1:
The diaphragm is divided into two distinct parts: an inner vibrating part and an outer part. The outer part is separated from the silicon base through a gap structure, while the inner vibrating part remains connected. This segmentation allows the outer part to be electrically isolated (connected to ground) while the inner part responds to acoustic signals, thereby reducing parasitic capacitance without complicating the manufacturing process.
2Ease of manufacture
If organic diaphragm films and electret films are used, then the microphone can be manufactured with traditional techniques, but temperature and humidity effects cause long term drift in performance
Solution Approach 1:
The patent transitions from organic materials (mylar, polyester, electret films) to inorganic silicon-based materials. This parameter change in material composition eliminates the temperature and humidity sensitivity inherent in organic films, providing long-term performance stability while maintaining compatibility with existing semiconductor manufacturing techniques.
3Strength
If the diaphragm periphery is fixed to the silicon base, then the diaphragm is mechanically supported, but parasitic capacitance occurs between the diaphragm and silicon base
Solution Approach 1:
The harmful parasitic capacitance pathway is extracted by creating a gap between the outer part of the diaphragm and the silicon base. This physical separation removes the source of parasitic capacitance while the inner vibrating part maintains necessary mechanical connection for acoustic signal detection. The outer part is reconnected to the system through electrical grounding rather than mechanical attachment.
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 improves microphone sensitivity and stability by minimizing parasitic capacitance, leading to more reliable and consistent sound wave conversion to electrical signals.
Implementation Method 1
a sensing element and a pre-amplifier IC device. The sensing element is basically a variable capacitor constructed with a movable compliant diaphragm, a rigid and fixed perforated backplate, and a dielectric spacer to form an air gap between the diaphragm and backplate. When the diaphragm vibrates, capacitance of the capacitor varies, by which sound waves are converted to electric signals.
Implementation Method 2
When the diaphragm vibrates, a parasitic capacitor will occur between the diaphragm and the silicon base. The inner vibrating part is provided with a first electrode pad electrically connected to a bias voltage, and the outer part is provided with a second electrode pad connected to the ground.
Data Source
AI summary
Disclosed is a silicon condenser microphone including a backplate having a plurality of perforations therethrough, a diaphragm opposed from the backplate for forming a capacitor. The diaphragm includes a first part and a second part received in the first part, the second part being capable of vibrating relative to the backplate. The first part is connected to the ground and the second part is connected to a bias voltage.