Stacked MEMS Microphone Assembly for Compact Acoustic Design
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Solution Overview
Problem
Current assembly methods for MEMS capacitive microphones face challenges in achieving low manufacturing costs, high acoustic performance, and small dimensions, with existing solutions either being complex, large in size, or lacking flexibility in chamber sizing and protection from external agents.
Innovation Solution
A stacked assembly of a first die integrating the MEMS sensing structure and a second die integrating the reading electronics, where the second die has through holes for acoustic access and EMI shielding, and the package contributes to defining the acoustic chambers, allowing for reduced dimensions and improved protection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the MEMS sensing structure and reading electronics are assembled using conventional methods, then the assembly can be manufactured, but the overall size becomes large and manufacturing complexity increases
Solution Approach 1:
The patent merges the MEMS sensing structure die and the reading electronics die into a single integrated unit by stacking them together and sealing them within a common package. This integration reduces the overall volume by eliminating separate housing requirements and simplifies the assembly process by pre-configuring both components in a compact stacked arrangement that can be manufactured using standardized techniques.
Solution Approach 2:
The patent implements nesting by placing the first die (MEMS sensing structure) and second die (reading electronics) one on top of the other in a vertical stack, with each die nested within the package cavity. This nested arrangement maximizes space utilization and reduces the lateral footprint of the microphone while maintaining functional separation between the sensing and processing components.
2Object-affected harmful factors
If the package is designed to protect the assembly from external agents, then protection is improved, but the acoustic performance may be compromised
Solution Approach 1:
The package is designed with locally differentiated properties: the package cavity provides enclosed protection for the stacked dies from external agents such as moisture and contaminants, while the back plate is configured with specific acoustic properties (porosity, permeability, or acoustic transmission characteristics) that allow acoustic waves to pass through to the membrane. This local quality differentiation enables simultaneous achievement of environmental protection and acoustic performance.
3Reliability
If the acoustic chamber volume is increased for better performance, then acoustic performance improves, but the overall dimensions of the microphone increase
Solution Approach 1:
The patent transitions from a lateral expansion approach to a vertical stacking approach. By stacking the MEMS die and electronics die vertically and utilizing the vertical space within the package cavity, the design creates sufficient acoustic chamber volume for optimal performance without increasing the lateral footprint of the microphone. This dimensional reorganization allows the acoustic chamber to be formed in the vertical dimension rather than requiring large horizontal space.
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 approach reduces the overall size of the microphone, enhances electrical characteristics, and provides greater freedom in designing the acoustic chambers for improved performance while offering effective protection from external factors.
Implementation Method 1
a microelectromechanical sensing structure (MEMS) of a capacitive type and comprising a membrane, which is mobile, is made of conductive material and faces a back plate
Implementation Method 2
designed to transduce acoustic-pressure waves into an electrical quantity (in particular, a capacitive variation)
Implementation Method 3
The second die has through holes for acoustic access
Implementation Method 4
the package contributes to defining the acoustic chambers
Data Source
AI summary
A microelectromechanical-acoustic-transducer assembly has: a first die integrating a MEMS sensing structure having a membrane, which has a first surface in fluid communication with a front chamber and a second surface, opposite to the first surface, in fluid communication with a back chamber of the microelectromechanical acoustic transducer, is able to undergo deformation as a function of incident acoustic-pressure waves, and faces a rigid electrode so as to form a variable-capacitance capacitor; a second die, integrating an electronic reading circuit operatively coupled to the MEMS sensing structure and supplying an electrical output signal as a function of the capacitive variation; and a package, housing the first die and the second die and having a base substrate with external electrical contacts. The first and second dice are stacked in the package and directly connected together mechanically and electrically; the package delimits at least one of the front and back chambers.