MEMS Optical Microphone Tilted Back Plate Alignment
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Solution Overview
Problem
MEMS optical microphones face challenges in mass manufacturing due to difficulties in achieving proper alignment of tilted surfaces and layers, which is crucial for optimal operation.
Innovation Solution
A MEMS device design that allows for the tilting of a compliant membrane and back plate with respect to a light source by applying a voltage, using electrostatic forces to adjust the alignment and direct reflected light towards a detector, facilitating the manufacture of MEMS structures with tilted surfaces through MEMS processing techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If tilted surfaces and layers are used in MEMS optical microphones to improve alignment, then alignment precision is improved, but manufacturing complexity increases
Solution Approach 1:
The patent makes the back plate tiltable relative to the diaphragm by providing pivot supports that allow the back plate to rotate about a tilt axis. This dynamic configuration enables alignment adjustment after assembly, resolving the contradiction between needing precise alignment and facing manufacturing complexity. The back plate can be tilted to an optimal angle (e.g., 45 degrees) to direct reflected light toward the detector while maintaining manufacturability through standard MEMS processes.
2Adaptability or versatility
If the back plate is made tiltable to improve light alignment, then alignment flexibility is improved, but structural complexity increases
Solution Approach 1:
The patent segments the microphone structure into functionally independent components: a fixed diaphragm assembly and a separately tiltable back plate. The back plate is divided into a light-reflecting portion and a grating portion, each optimized for its specific function. This segmentation allows the back plate to be tilted independently for alignment without complicating the overall structure, as the tilt mechanism is localized to the back plate assembly.
Solution Approach 2:
The patent introduces pivot supports as intermediary elements that enable the back plate to tilt relative to the diaphragm. These pivot supports act as mediators between the fixed diaphragm and the movable back plate, providing a simple hinge mechanism that allows alignment adjustment without requiring complex mechanical linkages or adjustment mechanisms throughout the entire structure.
3Manufacturing precision
If voltage is applied to tilt the back plate and membrane, then alignment precision is improved, but energy consumption increases
Solution Approach 1:
The patent employs electrostatic actuation to tilt the back plate and/or diaphragm to their optimal alignment positions during the manufacturing or initialization phase. Once tilted to the correct angle, the position is maintained mechanically by the pivot supports and electrostatic holding forces, requiring minimal or no continuous energy input. This preliminary action approach resolves the contradiction by achieving precise alignment through a one-time or occasional energy input rather than continuous energy consumption.
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
Enables the mass production of MEMS optical microphones with improved alignment and performance, allowing for precise detection of sound vibrations using a diffraction-based optical interferometer method, while maintaining a controlled minimal stress region and avoiding stiction issues.
Implementation Method 1
A light emitter and a light detector may be associated with a substrate positioned below the flat surfaces. The light emitter may be a laser (e.g. a vertical cavity surface emitting laser (VCSEL)) configured to direct a light beam toward a reflective portion of the diaphragm. The light beam is diffracted by the grating and reflected off of the reflective portion back to the light detector.
Implementation Method 2
The light beam is diffracted by the grating and reflected off of the reflective portion back to the light detector. The light detector detects the interference pattern created by the diffracted light rays
Implementation Method 3
The light detector detects the interference pattern created by the diffracted light rays and converts the light into an electrical signal, which corresponds to an acoustic vibration of the diaphragm
Implementation Method 4
A MEMS device design that allows for the tilting of a compliant membrane and back plate with respect to a light source by applying a voltage, using electrostatic forces to adjust the alignment
Data Source
AI summary
A micro-electro-mechanical system (MEMS) optical sensor, method of detecting sound using the MEMS optical sensor and method of manufacturing. The MEMS optical sensor including a substrate having a base portion and a vertically extending support portion. The sensor further including a top plate having a compliant membrane configured to vibrate in response to acoustic waves, the top plate connected to the support portion and having a reflective surface. The sensor also includes a back plate connected to the support portion, the back plate having a grating portion positioned below the reflective surface portion and a base plate connected to the support portion at a position below the back plate. A light emitter, a light detector and circuitry operable to tilt the top plate and the back plate with respect to the base plate so as to direct the reflected laser light toward the light detector are further provided.