Physical Quantity Sensor Protrusion Stress Distribution
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Solution Overview
Problem
Existing physical quantity sensors, particularly those using the rocker lever principle, face structural damage and breakage due to etching gas during the Deep Reactive Ion Etching process, leading to reduced reliability and impact resistance.
Innovation Solution
The design incorporates a movable body with a rotation shaft, a coupling portion, and a mass portion connected via a protrusion on the support substrate, where the protrusion is strategically positioned to distribute bending stress and prevent breakage by convexly bending the movable body when excessive impact is applied, with the protrusion located between 0.5L and 3.1L from the connection point, enhancing impact resistance and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If through-etching is performed on the silicon substrate to form the movable body, then the mass portion can be formed with precise dimensions, but the rear surface of the silicon substrate receives damage from etching gas that wraps around the gap between the substrate and glass, causing the structure to break easily
Solution Approach 1:
A protrusion is formed on the glass substrate at a predetermined position before the through-etching process. This protrusion serves as a preliminary structural feature that will later function to suppress breakage by controlling the bending behavior of the movable body during impact events.
Solution Approach 2:
The invention converts the harmful effect of etching gas wrapping around the gap into a beneficial outcome. By strategically positioning the protrusion, the design allows the movable body to bend convexly during impact, which prevents breakage at the coupling portion boundary. The protrusion transforms the potential damage mechanism into a protective feature that enhances reliability.
2Ease of operation
If the movable body is designed with a coupling portion connecting the rotation shaft and mass portion, then the sensor can measure acceleration through electrostatic capacitance changes, but the boundary portion between coupling and mass portions becomes vulnerable to breakage under impact
Solution Approach 1:
The protrusion acts as an intermediary element between the glass substrate and the silicon movable body. It provides a mechanical interface that controls the interaction between these two components during impact events, mediating the stress distribution to prevent breakage at the vulnerable coupling portion boundary.
Solution Approach 2:
The invention changes the geometric parameter of the system by introducing a protrusion with specific dimensions and position. The distance L1 from the protrusion to the end portion of the mass portion is controlled to be within a specific range, which changes the bending characteristics of the movable body from concave to convex during impact, thereby preventing breakage.
3Ease of manufacture
If no protrusion is provided on the glass substrate, then the manufacturing process is simpler, but the movable body lacks the ability to bend convexly under impact, making it prone to breakage
Solution Approach 1:
The protrusion is formed on the glass substrate as a preliminary structural feature during the manufacturing process. This preliminary action enables the movable body to achieve the desired convex bending behavior under impact without requiring complex post-processing or additional components.
Solution Approach 2:
The protrusion converts the potential harm of impact forces into a beneficial protective mechanism. By providing this simple structural feature on the glass substrate, the design enables the movable body to bend convexly during impact events, transforming the impact energy into a protective deformation that prevents breakage rather than causing damage.
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 configuration effectively suppresses breakage at the boundary portion between the coupling and mass portions, improving the physical quantity sensor's impact resistance and reliability by managing stress distribution and preventing contact-induced damage.
Implementation Method 1
measures the acceleration from electrostatic capacitance that changes according to the acceleration applied in a vertical direction
Data Source
AI summary
A physical quantity sensor includes: a movable body that includes a beam, a coupling portion that is connected with the beam and is provided in a direction intersecting with the beam, and a first and second mass portions that are connected with the coupling portion at connection positions; a first and second fixed electrodes are opposed to the first and second mass portions; and a protrusion are provided and protrude toward the first and second mass portions. In the intersecting direction, in a case where a distance from connection positions to end portions of the first and second mass portions opposite to the beam is L, and a distance from the protrusions to end portions of the first and second mass portions opposite to the beam is L1, the distance L1 is 0.5 L or longer and 3.1 L or shorter.