MEMS Microphone Spacer Layer Capacitance Reduction
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Solution Overview
Problem
In corrugated encapsulated microelectromechanical system microphones, the high dielectric constant of silicon nitride spacer layers leads to excessive plate-to-plate capacitance between membranes, negatively impacting microphone performance.
Innovation Solution
A process involving a spacer layer with counter electrode walls and support walls made of silicon nitride, where the spaces between these walls are filled with a material having a lower dielectric constant, such as silicon oxide, to reduce unwanted capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the spacer layer is made of silicon nitride to ensure superior mechanical properties, then the mechanical strength and stability are improved, but the dielectric constant increases to 9.5 which generates excessive plate-to-plate capacitance
Solution Approach 1:
The spacer layer is divided into multiple discrete support walls instead of a continuous solid structure. This segmentation reduces the overall dielectric material volume between the membranes, thereby reducing plate-to-plate capacitance while maintaining mechanical support function through the distributed wall structure.
Solution Approach 2:
Different regions of the spacer layer have different structures - solid support walls provide mechanical strength where needed, while the spaces between walls use lower dielectric constant material (silicon oxide) to reduce capacitance. This local differentiation optimizes both mechanical properties and electrical performance in different areas.
2Stability of the object's composition
If solid nitride support walls are used to maintain structural integrity, then mechanical stability is improved, but unwanted capacitance increases by 50% compared to the improved structure
Solution Approach 1:
The continuous solid nitride spacer layer is segmented into discrete support walls. This reduces the total dielectric material volume and creates air gaps or low-dielectric regions between walls, significantly reducing unwanted capacitance while the distributed wall structure maintains structural stability.
Solution Approach 2:
The spacer layer uses a composite structure combining silicon nitride support walls (for mechanical strength) with silicon oxide fill material (for low dielectric constant). This composite approach achieves both structural integrity and reduced capacitance by leveraging the complementary properties of different materials.
3Object-generated harmful factors
If the spaces between support walls are filled with low dielectric constant material to reduce capacitance by 80%, then unwanted capacitance is reduced, but the manufacturing process complexity increases due to additional etching steps
Solution Approach 1:
The low dielectric constant material (silicon oxide) is deposited as a filler material during the fabrication process before final release. This preliminary filling of spaces between support walls prepares the structure for subsequent release steps, enabling capacitance reduction without requiring complex post-processing modifications.
Solution Approach 2:
The process involves depositing filler material that will later be selectively removed (released) through etching through the membranes. This temporary material presence during fabrication enables capacitance optimization, and the final release step discards the filler material to achieve the desired low-capacitance structure.
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 unwanted capacitance by 50% compared to solid nitride support walls and can further reduce it by 80% by releasing fillers between support walls, thereby improving microphone performance.
Implementation Method 1
the second material having a dielectric constant less than that of the first material
Implementation Method 2
releasing the second material around the counter electrode walls by etching
Data Source
AI summary
A microelectromechanical system includes a lower membrane including a plurality of troughs and crests arranged alternately, an upper membrane including a plurality of troughs and crests arranged alternately, and a spacer layer disposed between the lower membrane and the upper membrane. The spacer layer includes counter electrode walls and support walls made of nitride, the counter electrode walls being provided with conductive elements. Chambers are formed between the troughs of the lower membrane and the crest of the upper membrane and the counter electrode walls are suspended in the chambers respectively. The support walls are sandwiched between the crests of the lower membrane and the troughs of the upper membrane with a space formed between adjacent support walls. The spaces between adjacent support walls may be empty or filled with oxide. Unwanted capacitance between the upper and lower membranes is reduced significantly.