MEMS Microphone Thermal Management for Power Supply Rejection
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Solution Overview
Problem
MEMS microphones face challenges in achieving effective power supply rejection (PSR) performance, as variations and noise in the power supply voltage significantly affect the output signal due to thermoacoustic coupling between the integrated circuitry and the membrane, especially at lower frequencies.
Innovation Solution
The implementation of a MEMS device design that includes a semiconductor die with integrated circuitry and a transducer membrane, where a structure defines a space adjacent to the circuitry to contain heat and reduce thermoacoustic coupling, and a metal layer covering at least 50% of the face with connectors to a heat sink to manage thermal impedance, thereby isolating the membrane from temperature fluctuations caused by power supply changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If integrated circuitry is placed close to the transducer membrane to reduce device size, then device integration and compactness are improved, but power supply noise and thermal coupling affecting the membrane increase
Solution Approach 1:
The device is segmented into distinct functional zones: a first region containing the transducer membrane and acoustic port, and a second region containing the integrated circuitry. This spatial segmentation isolates the sensitive membrane from noise-generating circuitry while maintaining overall device compactness through optimized layout and interconnect structures.
Solution Approach 2:
A low-pass filter is introduced as an intermediary component between the power supply voltage and the integrated circuitry. This filter acts as a mediator that attenuates high-frequency noise from the power supply before it reaches the circuitry, thereby reducing thermal coupling and noise transmission to the membrane while allowing the device to maintain compact dimensions.
2Reliability
If power supply rejection is improved by isolating the membrane from circuitry, then PSR performance is improved, but device integration and size increase
Solution Approach 1:
The device employs dynamic thermal management through the low-pass filter that adapts to varying power supply conditions. The filter's frequency-dependent impedance characteristics dynamically attenuate noise at different frequencies, providing effective power supply rejection across varying operating conditions while maintaining compact device dimensions through optimized filter design.
Solution Approach 2:
The patent addresses the spatial conflict by transitioning to a multi-dimensional layout optimization approach. The first and second regions are arranged in optimized spatial configurations that maximize separation between noise-sensitive and noise-generating components while utilizing three-dimensional space efficiently, thereby achieving good PSR performance without excessive device footprint.
3Stability of the object's composition
If the back volume is sealed to allow free membrane movement, then acoustic response is improved, but pressure equalisation for temperature compensation is prevented
Solution Approach 1:
The back volume is configured with localized pressure equalisation features that maintain sealed conditions for most of the volume to preserve acoustic response, while incorporating specific localized pathways or compliant elements that enable pressure equalisation for thermal compensation. This local quality modification allows the system to simultaneously achieve free membrane movement and temperature adaptability.
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 enhances power supply rejection performance by minimizing the impact of power supply fluctuations and noise on the output signal, particularly at frequencies below 1 kHz, by containing heat within the structural elements and efficiently dissipating thermal energy away from the membrane.
Implementation Method 1
a metal layer covering at least 50% of the face with connectors to a heat sink to manage thermal impedance, thereby isolating the membrane from temperature fluctuations caused by power supply changes
Implementation Method 2
a structure defines a space between the structure and the at least a portion of the circuitry... containing heat within the structural elements
Implementation Method 3
the transducer may be configured so that the flexible membrane is located between first and second volumes... which are sized sufficiently so that the transducer provides the desired acoustic response
Data Source
AI summary
Micro-electro-mechanical system (MEMS) devices are disclosed, including a MEMS device comprising a semiconductor die including integrated circuitry, a structure mounted on the semiconductor die and covering at least a portion of the circuitry, the structure defining a space between the structure and the at least a portion of the circuitry, and a transducer including a membrane, the transducer located outside of the space.