MEMS Pressure Sensor Recess Structure for Sensitivity and Die Size
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Solution Overview
Problem
Existing Micro-Electro-Mechanical Systems (MEMS) devices with recess or cavity structures face challenges in reducing die size while maintaining performance, particularly in pressure sensors where the structure of the recess or cavity drives die size and affects sensitivity.
Innovation Solution
The proposed solution involves an improved recess or cavity structure in MEMS devices, including a sensing diaphragm with bosses extending from the bottom wall into the recess, formed using silicon-on-insulator (SOI) technology, where the bosses are perpendicular to the bottom wall and can extend laterally across the diaphragm, enhancing sensitivity and allowing for a smaller device footprint.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the recess or cavity structure is made larger to improve sensing performance, then sensitivity is improved, but die size increases
Solution Approach 1:
The patent transitions from a conventional planar recess structure to a three-dimensional cavity structure with vertical side walls extending downward from the diaphragm surface. This vertical dimension allows the sensing volume to extend into the depth of the substrate, improving sensitivity without increasing the lateral die footprint. The cavity depth and volume can be optimized independently of the die area, resolving the contradiction between sensitivity and die size.
Solution Approach 2:
The cavity structure is nested within the substrate thickness, utilizing the vertical space inside the die rather than expanding the external dimensions. The cavity is formed by etching downward into the substrate, nesting the sensing volume within the existing die structure. This allows the sensing performance to be improved by utilizing internal volume rather than external area.
2Measurement precision
If the diaphragm is made thinner to increase sensitivity, then sensitivity is improved, but mechanical strength decreases
Solution Approach 1:
The patent applies local quality by creating a non-uniform thickness profile in the diaphragm region. The diaphragm is thinned locally over the cavity area to maximize sensitivity where needed, while maintaining full thickness at the edges and surrounding areas to provide mechanical support and strength. This localized thinning allows the diaphragm to be more sensitive to pressure changes without compromising overall structural integrity.
Solution Approach 2:
The diaphragm structure is segmented into different thickness zones: a thin central region over the cavity for high sensitivity, and thicker edge regions for mechanical support. This segmentation allows different parts of the diaphragm to serve different functions - the thin center region detects pressure changes while the thick edge regions provide structural strength and mounting support.
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 increased sensitivity and reduced die size for MEMS devices, such as pressure sensors, by optimizing the recess and cavity structure, enabling more compact devices with comparable or improved performance.
Implementation Method 1
The diaphragm deflects according to the magnitude of the input pressure, and this deflection creates a change in the resistance of the piezoresistors
Implementation Method 2
Pressure sensors are often formed by anisotropically etching a recess into a back side of a silicon substrate die
Data Source
AI summary
A sensor includes a first substrate and a second substrate. The first substrate includes a first side and an opposing second side, with the first side having a recess. The recess is defined by one or more side walls and a bottom wall. One or more of the side walls are substantially perpendicular to the bottom wall. A sensing diaphragm is defined between the second side of the first substrate and the bottom wall of the recess. A boss extends from the bottom wall of the recess. The second substrate may include a first side and an opposing second side, where the first side has a recess. The first side of the first substrate may be secured to the first side of the second substrate such that the recess in the first substrate faces and is in fluid communication with the recess in the second substrate.