MEMS Piezoresistive Sensor with Conversion Layer for Planar Stress
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Solution Overview
Problem
Existing force/pressure sensors face challenges with low sensitivity, limited miniaturization, and expensive complex manufacturing processes, particularly when measuring high-range loads, due to the use of high-strength metallic load cells and integrated piezoresistive sensors with complex package structures.
Innovation Solution
A microelectromechanical force/pressure sensor utilizing bulk silicon piezoresistivity, with two semiconductor dies bonded together and a conversion layer to convert applied forces into planar stresses sensed by piezoresistive elements, allowing for high sensitivity and customization, and a simpler manufacturing process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If high strength metallic load cells with strain gauges are used to measure high-range loads, then the sensor can handle high forces, but the sensitivity is low and miniaturization is limited
Solution Approach 1:
The patent replaces the traditional metallic load cell with a silicon-based MEMS structure that utilizes piezoresistive effects. The silicon diaphragm with integrated piezoresistors substitutes the mechanical strain gauge system, enabling higher sensitivity through semiconductor piezoresistivity while maintaining the ability to measure high forces through scalable device geometry.
Solution Approach 2:
The patent changes the material parameter from metallic strain gauge to semiconductor piezoresistor, which has a significantly higher gauge factor. This parameter change enables the sensor to achieve high sensitivity while maintaining force measurement capability, directly resolving the contradiction between force range and measurement precision.
2Measurement precision
If integrated piezoresistive sensors with complex package structures are used, then sensitivity is improved and miniaturization is enabled, but manufacturing complexity and cost increase
Solution Approach 1:
The patent merges the sensing element, the structural element, and the packaging element into a single integrated silicon diaphragm structure. The piezoresistors are directly fabricated on the diaphragm surface, eliminating the need for separate packaging components to convert external pressure to internal stress, thus simplifying the package structure while maintaining high sensitivity.
Solution Approach 2:
The silicon diaphragm serves multiple functions simultaneously: it acts as the structural element that withstands external force, the sensing element that converts force to stress, and the mounting structure for the piezoresistors. This multi-functionality eliminates the need for complex package structures required in traditional sensors.
3Adaptability or versatility
If complex package structures are used to convert applied load to stress on silicon die, then pressure sensing is enabled, but manufacturing cost increases and customization is difficult
Solution Approach 1:
The patent segments the sensor into a simple two-layer structure: the silicon diaphragm and the cap. This segmentation allows independent optimization of each layer and simplifies the manufacturing process, enabling easy customization of the diaphragm thickness and geometry to adapt to different force ranges without increasing overall manufacturing complexity.
Solution Approach 2:
The patent enables dynamic customization by allowing the diaphragm thickness and geometry to be varied based on the required force range. This dynamic adaptability is achieved through standard semiconductor fabrication processes that can easily adjust layer thicknesses, making customization cost-effective and straightforward.
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 solution provides a highly sensitive, easily customizable, and cost-effective force/pressure sensor with a simpler manufacturing process, capable of measuring a wide range of forces and pressures, and is suitable for various applications including high-temperature environments, with improved stability and scalability.
Implementation Method 1
piezoresistive elements (6) are formed in the bulk of the sensor die (2), next to the top surface (2a) thereof... the piezoresistive elements (6) are arranged so as to detect the planar stresses
Data Source
AI summary
A microelectromechanical force/pressure sensor has: a sensor die, of semiconductor material, having a front surface and a bottom surface, extending in a horizontal plane, and made of a compact bulk region having a thickness along a vertical direction, transverse to the horizontal plane; piezoresistive elements, integrated in the bulk region of the sensor die, at the front surface thereof; and a cap die, coupled above the sensor die, covering the piezoresistive elements, having a respective front surface and bottom surface, opposite to each other along the vertical direction, the bottom surface facing the front surface of the sensor die. A conversion layer is arranged between the front surface of the sensor die and the bottom surface of the cap die, patterned to define a groove traversing its entire thickness along the vertical direction; the piezoresistive elements are arranged vertically in correspondence to the groove and the conversion layer is designed to convert a load applied to the front surface of the cap die and/or bottom surface of the sensor die along the vertical direction into a planar stress distribution at the groove, acting in the horizontal plane.