CMOS Compatible Silicon Differential Condenser Microphone
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Solution Overview
Problem
Existing silicon-based MEMS microphones face challenges in achieving high sensitivity and low noise levels while being CMOS-compatible, as previous designs either compromise on size or are not suitable for integration with CMOS circuitry.
Innovation Solution
A CMOS-compatible silicon differential condenser microphone is developed, featuring a silicon substrate with a rigid conductive perforated backplate, a compliant diaphragm, and a second perforated backplate with air gaps, allowing for differential condenser formation and integration with CMOS pre-amplifiers, enhancing signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a sealed capacitive microphone with differential capacitive read-out and high sensitivity is provided, then sensitivity is improved, but common mode change in capacitance occurs and diaphragms become less compliant
Solution Approach 1:
The microphone is divided into two separate sensing elements (first and second capacitive sensors) with independent diaphragms and backplates. Each sensor operates independently to detect acoustic waves, allowing differential processing that eliminates common mode capacitance changes while maintaining high sensitivity through segmented measurement paths.
Solution Approach 2:
The patent changes the electrical configuration from single-ended to differential read-out, transforming the output signal parameters. By measuring the difference between two capacitive sensors instead of absolute capacitance values, the system rejects common mode noise and improves signal quality without sacrificing sensitivity.
2Manufacturing precision
If micro-processing technologies are used to control crucial dimensions, then manufacturing precision is improved, but device complexity increases
Solution Approach 1:
The patent employs universal CMOS-compatible manufacturing processes that serve multiple functions: depositing structural layers, forming electrical connections, creating passivation layers, and fabricating interdigitated electrodes all through standard semiconductor fabrication steps. This multi-functionality reduces device complexity by using a single process platform for diverse manufacturing needs.
Solution Approach 2:
The patent utilizes parameter changes in material properties during processing, such as transitioning from amorphous to crystalline silicon through annealing, and controlling stress states in deposited layers. These parameter changes enable precise dimensional control while maintaining process simplicity through self-organizing material behavior during fabrication.
3Strength
If three poly silicon layers are stacked as diaphragm and dual backplates, then structural integrity is improved, but CMOS compatibility is lost due to low stress poly silicon
Solution Approach 1:
The patent changes the material parameter from low stress poly silicon to high stress silicon nitride for the backplate structure. This parameter change maintains structural integrity through the high mechanical strength of silicon nitride while achieving CMOS compatibility since silicon nitride deposition and processing are fully compatible with standard CMOS fabrication processes.
Solution Approach 2:
The patent employs composite material structures combining silicon nitride layers with metal layers (such as aluminum or copper) to create the backplate and electrode structures. This composite approach provides both the required mechanical strength from silicon nitride and electrical conductivity from metal layers, while remaining compatible with CMOS processing.
4Adaptability or versatility
If a rotational diaphragm center-hinged structure is used, then integration with CMOS circuits is improved, but sound wave direction dependence occurs and air damping increases without perforated backplate
Solution Approach 1:
The patent incorporates perforated backplates with arrays of small holes that allow acoustic waves to pass through while reducing air damping effects. The porous structure enables omnidirectional sound detection by allowing pressure equalization across the backplate, eliminating direction dependence while maintaining effective integration with CMOS circuitry through planar fabrication.
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 solution increases the signal-to-noise ratio and ensures compatibility with CMOS processing, enabling improved noise performance and integration with pre-amplifiers, thus addressing the limitations of previous microphone designs.
Implementation Method 1
the diaphragm vibrates in response to an acoustic wave
Implementation Method 2
the diaphragm and the first backplate form a first variable condenser, the diaphragm and the second backplate form a second variable condenser
Data Source
AI summary
The present invention provides a CMOS compatible silicon differential condenser microphone and a method of manufacturing the same. Said microphone comprises a silicon substrate, wherein a CMOS circuitry is accommodated thereon; a first rigid conductive perforated backplate supported on the silicon substrate with an insulating layer inserted therebetween; a second rigid perforated backplate formed above the first backplate, including CMOS passivation layers and a metal layer sandwiched between the CMOS passivation layers as an electrode plate of the second plate, wherein an air gap, with a spacer forming its boundary, is provided between the opposite perforated areas of the first backplate and the second backplate; a compliant diaphragm provided between the first backplate and the second backplate, wherein a back hole is formed to be open in the silicon substrate underneath the first backplate so as to allow sound pass through, and the diaphragm and the first backplate form a first variable condenser, the diaphragm and the second backplate form a second variable condenser, and the first variable condenser and the second variable condenser form differential condensers.