MEMS Microphone Back Plate Sag Prevention via Flat Insulation Layer
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Capacitive MEMS microphones face reduced sensitivity due to sagging of the back plate, which is caused by stress concentration at the bent portion in the chamber, making it difficult to increase the air gap and thus limiting the bias voltage and sensitivity of the microphone.
Innovation Solution
A MEMS microphone design that includes a substrate with a cavity and a diaphragm supported by an anchor, a back plate spaced apart from the diaphragm with an upper insulation layer having a flat plate shape to prevent sagging, and a method of manufacturing that omits the strut forming process, allowing for increased widths of the lower and sacrificial layers to stabilize the back plate and maintain the air gap.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the air gap between the back plate and diaphragm is increased to increase bias voltage and sensitivity, then the sensitivity of the MEMS microphone is improved, but the back plate sags downward due to stress concentration at the bent portion in the chamber
Solution Approach 1:
The chamber structure is modified to have different properties at different locations: the bent portion is eliminated and replaced with a localized support structure (lower insulation layer pattern) at the specific location where stress concentration occurs, while the rest of the chamber maintains its original configuration. This localized structural reinforcement prevents back plate sagging without compromising the overall air gap and sensitivity.
Solution Approach 2:
A lower insulation layer pattern is introduced as an intermediary support structure between the substrate and the back plate. This intermediate element provides localized support at the bent portion location, preventing stress concentration and back plate sagging, while allowing the rest of the back plate to maintain its spacing from the diaphragm for optimal sensitivity.
2Stability of the object's composition
If a strut is formed to support the back plate and prevent sagging, then the back plate stability is improved, but the manufacturing process complexity increases due to additional forming steps
Solution Approach 1:
The support function is merged with the existing lower insulation layer by forming a lower insulation layer pattern. Instead of adding a separate strut structure requiring additional forming steps, the insulation layer itself is patterned to provide structural support at the bent portion, combining the insulation and support functions into a single element that can be formed during the existing manufacturing process.
Solution Approach 2:
The problematic bent portion is extracted or removed from the chamber structure, and replaced with a simplified configuration that includes the lower insulation layer pattern. This eliminates the need for complex strut forming while maintaining the support function, as the lower insulation layer pattern is integrated into the existing manufacturing flow without requiring separate strut formation steps.
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 design effectively prevents back plate sagging, maintains the air gap, and enhances the sensitivity of the MEMS microphone by stabilizing the back plate, reducing the risk of decreased sensitivity due to bias voltage drops and simplifying the manufacturing process by omitting the strut forming steps.
Implementation Method 1
a diaphragm being spaced apart from the substrate, covering the cavity, and being configured to generate a displacement thereof in response to an applied acoustic pressure
Implementation Method 2
an upper insulation layer provided on the substrate, covering the back plate, and holding the back plate to space the back plate from the diaphragm, the upper insulation layer having a flat plate shape to prevent a sagging of the back plate
Implementation Method 3
capacitive MEMS microphones that are capable of transmitting signals related to an acoustic signal using a displacement which may be generated due to an acoustic pressure
Data Source
AI summary
A MEMS microphone includes a substrate defining a cavity, a diaphragm being spaced apart from the substrate, covering the cavity, and being configured to generate a displacement thereof in response to an applied acoustic pressure, an anchor extending from an end portion of the diaphragm, the anchor including a lower surface in contact with an upper surface of the substrate to support the diaphragm, a back plate disposed over the diaphragm, the back plate being spaced apart from the diaphragm such that an air gap is maintained between the back plate and the diaphragm, and defining a plurality of acoustic holes and an upper insulation layer provided on the substrate, covering the back plate, and holding the back plate to space the back plate from the diaphragm, the upper insulation layer having a flat plate shape to prevent sagging of the back plate.