Capacitance MEMS Sensor Recessed Diaphragm Design
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Solution Overview
Problem
Existing capacitance type MEMS sensors face challenges in increasing sensitivity while maintaining a small size and reducing manufacturing costs, as larger electrode areas require larger device sizes and costly gas-phase etching processes for sacrificing layer removal.
Innovation Solution
A capacitance type MEMS sensor design featuring a semiconductor substrate with a recessed diaphragm and insulating film, where the diaphragm is positioned within the recess to face the sidewall as a movable electrode, allowing for increased facing area without the need for a sacrificing layer, enabling enhanced sensitivity and reduced manufacturing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the area of movable electrode and fixed electrode is increased to enhance sensitivity, then the sensitivity is improved, but the device size grows larger
Solution Approach 1:
The patent transitions from a planar electrode arrangement to a three-dimensional configuration by forming the movable electrode as a vertical pillar structure within a recess. This dimensional change allows the electrode facing area to be increased in the vertical direction while maintaining a compact planar footprint, thereby improving sensitivity without significantly increasing device size.
Solution Approach 2:
The movable electrode pillar is nested within the recess formed in the semiconductor substrate. This nesting arrangement allows the electrode to extend vertically into the substrate, increasing the facing area between the movable and fixed electrodes while keeping the overall device footprint small.
2Reliability
If a polysilicon layer is formed as a sacrificing layer to support the diaphragm in a movable state, then the diaphragm can be supported, but the manufacturing cost increases due to costly gas-phase etching processes
Solution Approach 1:
The patent removes the polysilicon sacrificing layer and the associated costly gas-phase etching process entirely. Instead, the diaphragm is directly formed as a silicon pillar using standard semiconductor fabrication processes, and the recess structure provides mechanical support without requiring a separate sacrificing layer.
Solution Approach 2:
The silicon substrate itself serves as both the structural support and the material for the movable electrode. The recess formed in the substrate provides the necessary mechanical support for the diaphragm pillar, eliminating the need for external sacrificing layers and complex release processes.
3Device complexity
If the diaphragm is made from the same material as the semiconductor substrate, then manufacturing complexity is reduced, but the diaphragm may adhere to the substrate during processing
Solution Approach 1:
The patent applies different surface treatments or structural configurations to specific regions. The recess walls may have different surface properties or geometries compared to the bulk substrate, creating local conditions that prevent adhesion while maintaining material uniformity throughout the structure.
Solution Approach 2:
The recess structure creates a geometric configuration where the diaphragm pillar is suspended within the recess space, maintaining equal spacing from the substrate surface. This equipotential geometric arrangement prevents adhesion by ensuring no point of the diaphragm is in direct contact with the substrate during processing.
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 achieves high sensitivity and reduced manufacturing costs by allowing the diaphragm to vibrate freely and expand/contract in response to sound waves, temperature, or humidity, while maintaining a small sensor size and eliminating the need for costly etching processes.
Implementation Method 1
If a sound wave is inputted, the diaphragm vibrates to thereby change the capacitance between the metal layer on the front surface of the diaphragm and the back plate
Implementation Method 2
If a sound wave is inputted, the diaphragm vibrates
Implementation Method 3
if the diaphragm is expanded and contracted by the change in temperature or humidity, it is possible to convert the change in temperature or humidity to an electric signal
Implementation Method 4
if the diaphragm is expanded and contracted by the change in temperature or humidity
Data Source
AI summary
A capacitance type MEMS sensor has a first electrode portion and a second electrode portion facing each other. The sensor includes a semiconductor substrate having a recess dug in a thickness direction of the semiconductor substrate, the recess having sidewalls, one of which serves as the first electrode portion. The sensor further includes a diaphragm serving as the second electrode portion, the diaphragm arranged within the recess to face the first electrode portion in a posture extending along a depth direction of the recess, the diaphragm having a lower edge spaced apart from the bottom surface of the recess, and is made of the same material as the semiconductor substrate. The sensor further includes an insulating film arranged to join the diaphragm to the semiconductor substrate.