MEMS Sensor GND Plane Stress Isolation
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Solution Overview
Problem
Silicon MEMS physical quantity sensors face issues with temperature hysteresis and radiation noise due to residual stress from differences in linear expansion coefficients between the bottom plate and GND plane, leading to distorted measurements.
Innovation Solution
A physical quantity sensor design where the GND plane is positioned apart from the inner bottom surface, with a multilayered substrate configuration and a GND plane that overlaps with the sensor element, reducing the propagation of stress-induced distortions and radiation noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the GND plane is formed on the inner bottom surface of the package, then radiation noise can be reduced, but temperature hysteresis arises due to residual stress from linear expansion coefficient differences
Solution Approach 1:
The patent introduces a vertical separation between the GND plane and the inner bottom surface by forming an insulating film layer. This dimensional change in the Z-axis direction allows the GND plane to be positioned above the inner bottom surface, reducing stress propagation to the sensor element while maintaining radiation noise shielding effectiveness.
Solution Approach 2:
The patent introduces an insulating film as an intermediary layer between the inner bottom surface and the GND plane. This mediator layer prevents direct stress transmission from the bottom plate to the GND plane and sensor element, while still allowing the GND plane to provide electromagnetic shielding. The insulating film acts as a buffer that decouples the mechanical stress path while maintaining electrical shielding function.
2Measurement precision
If the GND plane is positioned apart from the inner bottom surface, then temperature hysteresis is reduced, but radiation noise shielding effectiveness may be compromised
Solution Approach 1:
The patent makes the insulating film layer serve multiple functions: it provides mechanical decoupling to reduce stress propagation, acts as an electrical insulator, and contributes to electromagnetic shielding when combined with the GND plane. This multi-functionality ensures that separating the GND plane from the bottom surface does not compromise radiation noise shielding.
Solution Approach 2:
The patent creates a composite structure consisting of the inner bottom surface, insulating film layer, and GND plane. This composite configuration combines the mechanical stability of the bottom plate with the electromagnetic shielding of the GND plane, while the insulating film provides stress isolation. The composite structure achieves both temperature stability and radiation noise reduction.
3Object-affected harmful factors
If a metallic cover and GND plane are electrically connected to shut off radiation noise, then radiation noise influence is reduced, but manufacturing complexity increases
Solution Approach 1:
The patent merges the GND plane formation process with the existing bottom plate manufacturing process. By forming the GND plane on top of the insulating film that is already on the bottom plate, the patent eliminates the need for separate metallic cover assembly and electrical connection processes, thereby reducing manufacturing complexity while maintaining radiation noise shielding.
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 reduces temperature hysteresis and radiation noise interference, enhancing the accuracy and reliability of the sensor measurements.
Implementation Method 1
the GND plane is disposed to overlap with the sensor element in a plan view, the radiation noise from outside the container affecting the sensor element from a side of the bottom plate can be shut off by the GND plane
Implementation Method 2
unevenness and distortion of the GND plane surface caused by a residual stress resulting from a difference in a linear expansion coefficient between the GND plane and bottom plate are relaxed by a part of the bottom plate existing between the GND plane and the inner bottom surface
Implementation Method 3
an electrostatic capacitance type physical quantity sensor (mechanical quantity sensor) that includes an element having a movable electrode and a fixed electrode disposed so as to face each other in a comb teeth shape and measures a physical quantity based on electrostatic capacitance generated between these two electrodes
Data Source
AI summary
A physical quantity sensor includes: a container that includes a storage space and a bottom plate that configures an inner bottom surface of the storage space; a sensor element that is attached to the inner bottom surface; a circuit element that is attached to a surface of the sensor element on the opposite side of the inner bottom surface, and is electrically connected with the sensor element; and a ground plane that is provided on the bottom plate. The ground GND plane is provided apart from the inner bottom surface.