Backplateless Silicon Microphone Design
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The fabrication of silicon condenser microphones is complicated by the inclusion of a dedicated backplate, leading to high costs and complex manufacturing processes due to the need for multiple masking levels and precise overlay and spacing between the diaphragm and backplate.
Innovation Solution
A microphone sensing element is designed without a dedicated backplate, featuring a movable diaphragm supported by mechanical springs anchored to a conductive substrate through dielectric pads, with perforated plates attached to the diaphragm, eliminating the need for a separate backplate and simplifying the fabrication process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a dedicated backplate is included in the microphone sensing element, then the structural stability and acoustic performance are improved, but the manufacturing complexity and cost increase due to multiple masking levels and precise overlay requirements
Solution Approach 1:
The invention extracts and removes the dedicated backplate component from the microphone sensing element. The backplate function is eliminated by forming the microphone cavity directly in the substrate, thereby simplifying the structure and manufacturing process while maintaining acoustic performance through the substrate's inherent rigidity and the precisely controlled air gap.
Solution Approach 2:
The invention merges the backplate function with the substrate itself. The substrate serves dual purposes: as the mechanical support structure and as the acoustic reference surface that replaces the traditional backplate. This integration eliminates the need for separate backplate fabrication and assembly, reducing manufacturing complexity.
2Reliability
If a dedicated backplate is included in the microphone sensing element, then the acoustic performance is maintained, but the production cost increases due to complex fabrication processes
Solution Approach 1:
The dedicated backplate component is extracted and removed from the design. The substrate alone provides the necessary acoustic reference surface, eliminating material costs and processing steps associated with backplate fabrication, thereby reducing production cost.
Solution Approach 2:
The substrate is given multiple functions: it serves as the mechanical support, the acoustic reference surface (replacing the backplate), and the mounting platform for the diaphragm. This multi-functionality reduces the total component count and production cost.
3Manufacturing precision
If multiple masking levels are used for precise overlay and spacing between diaphragm and backplate, then the manufacturing precision is improved, but the device complexity and production time increase
Solution Approach 1:
The backplate component is removed, eliminating the need for masking levels required to define backplate geometry and its precise overlay with the diaphragm. The air gap is formed by direct etching of the substrate, simplifying the photolithography process.
Solution Approach 2:
The air gap is formed as a preliminary feature during substrate preparation, before diaphragm fabrication. This preliminary etching establishes the precise spacing between the diaphragm and substrate without requiring subsequent overlay operations, thereby reducing the number of masking levels.
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 reduces the number of masking levels required, lowers production costs, and maintains performance comparable to microphones with a dedicated backplate, while allowing for a more straightforward and efficient manufacturing process.
Implementation Method 1
a dielectric spacer (12) supported by the conductive substrate (11) and having a top surface defining an air gap (28)
Implementation Method 2
a movable diaphragm (13a) made from a membrane film (13) and suspended above the conductive substrate (11) by mechanical springs (13b)
Implementation Method 3
forming a variable capacitor between the diaphragm and substrate
Data Source
AI summary
A silicon based microphone sensing element and a method for making the same are disclosed. The microphone sensing element has a diaphragm with adjoining perforated plates on the front side of a conductive substrate. The diaphragm is aligned above a back hole in the substrate wherein the front opening of the back hole is smaller than the diaphragm. The diaphragm is supported by mechanical springs each having one end attached to the diaphragm and another end connected to a rigid pad anchored on a dielectric spacer. The diaphragm, perforated plates, and mechanical springs are preferably made of the same film and are suspended above an air gap that overlies the substrate. A first electrode is formed on one or more rigid pads and a second electrode is formed at one or more locations on the substrate to establish a variable capacitor circuit. Different embodiments are shown that reduce parasitic capacitance.