Microphone Back Chamber Volume via Substrate Cavity
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Solution Overview
Problem
Existing microphones face challenges in achieving a low profile while simultaneously enhancing the signal-to-noise ratio (SNR) and frequency characteristics, particularly in the low frequency band, due to the limitations in adjusting the volume of the back chamber without increasing the microphone's height.
Innovation Solution
A microphone design that includes a base substrate with a hollow space between the acoustic sensor and the circuit element, featuring a cavity in the sensor substrate and a through-hole in the base substrate, which communicates with the hollow space to form an acoustic port, allowing for a larger back chamber volume without increasing the overall height, and is sealed by a sealing member to maintain acoustic integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the height of the bump contact is increased to enlarge the back chamber volume, then the signal-to-noise ratio and frequency characteristic are improved, but the overall height of the microphone is increased
Solution Approach 1:
The patent transitions from a vertical expansion approach (increasing bump contact height) to a horizontal/lateral expansion approach by forming the back chamber as a cavity within the circuit element substrate. This allows the back chamber volume to be increased without increasing the overall height of the microphone, resolving the contradiction between improved acoustic performance and compact form factor.
Solution Approach 2:
The back chamber is nested within the circuit element structure itself, specifically formed as a cavity in the substrate. This nesting approach allows the back chamber to occupy space that would otherwise be unused, enabling volume increase without external dimensional expansion.
2Reliability
If the height of the bump contact is increased to enlarge the back chamber volume, then the frequency characteristic in low frequency band is improved, but the profile of the microphone is increased
Solution Approach 1:
The patent resolves the profile contradiction by changing the dimensional approach from vertical (height) to lateral (in-plane) expansion. The back chamber cavity is formed within the circuit element substrate, allowing low frequency characteristic improvement through increased volume without compromising the low-profile shape.
3Volume of stationary object
If a cavity is formed in the circuit element to create back chamber, then the back chamber volume is defined by cavity volume, but the overall height cannot be reduced further
Solution Approach 1:
The patent achieves increased back chamber volume without height increase by forming the cavity within the circuit element substrate's planar structure. This lateral/cross-sectional expansion approach allows volume increase while maintaining a compact height profile.
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 achieves both a low profile and improved acoustic characteristics by increasing the back chamber volume, enhancing the SNR and frequency response in the low frequency band, while maintaining the microphone's compactness.
Implementation Method 1
A through-hole is made in the base substrate while piercing the base substrate in a thickness direction. A communication hole is made in the sensor substrate while piercing the sensor substrate from the first surface to the second surface, and causes the through-hole and the hollow space to communicate with each other.
Data Source
AI summary
A microphone has a base substrate comprising a main surface, an acoustic sensor mounted on the main surface, and a circuit element stacked on the acoustic sensor. A hollow space is formed between the acoustic sensor and the circuit element. The acoustic sensor has a sensor substrate having a first surface opposed to the base substrate, a second surface on a side opposite to the first surface, and a cavity formed while recessed with respect to the second surface, and a movable electrode that covers the cavity from the second surface side. A through-hole is formed in the base substrate while piercing the base substrate in a thickness direction. A communication hole is formed in the sensor substrate while piercing the sensor substrate from the first surface to the second surface. The communication hole causes the through-hole and the hollow space to communicate with each other.