MEMS Sensor Beam System Stress Compensation
Solution Overview
Problem
The natural frequency of MEMS sensors, such as angular velocity and acceleration sensors, fluctuates due to stress from adhesive agents and thermal expansion differences, leading to reduced measurement accuracy and reliability.
Innovation Solution
The design incorporates elastically deformable beams and a spring system structure where the movable body is supported by multiple beams connected to fixed portions, with specific arrangements to offset tensile and compressive stresses, maintaining consistent spring constants despite substrate deformation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the sensor element is adhered to the package body using an adhesive agent, then the sensor element can be mounted and connected, but stress occurs due to volume change causing the natural frequency to fluctuate and measurement accuracy to degrade
Solution Approach 1:
The patent applies parameter changes by modifying the adhesive agent's properties - specifically using an adhesive with low modulus of elasticity and low glass transition temperature. This changes the physical parameters of the adhesive to reduce stress transmission to the sensor element during mounting, thereby maintaining measurement accuracy while enabling proper mounting.
Solution Approach 2:
The adhesive agent acts as an intermediary between the package body and sensor element. By selecting an adhesive with specific properties (low modulus, low Tg), it serves as a stress-absorbing mediator that prevents direct stress transmission to the sensor element, resolving the contradiction between secure mounting and measurement precision.
2Ease of manufacture
If the sensor element is adhered to the package body, then mounting is achieved, but stress from adhesive setting causes natural frequency fluctuation
Solution Approach 1:
The patent changes the physical parameters of the adhesive agent - specifically using materials with low modulus of elasticity and low glass transition temperature. This parameter change ensures that the adhesive remains flexible during setting, preventing stress-induced natural frequency fluctuations while maintaining secure mounting.
Solution Approach 2:
The patent applies beforehand cushioning by pre-selecting an adhesive agent with stress-absorbing properties before the mounting process. The adhesive's low modulus and low Tg characteristics provide built-in cushioning against stress during setting, preventing natural frequency instability before it occurs.
3Adaptability or versatility
If ambient temperature changes, then thermal expansion difference causes stress, but the natural frequency fluctuates and detection sensitivity changes
Solution Approach 1:
The patent applies parameter changes by selecting materials with matched thermal expansion coefficients - the package body and sensor element are designed to have similar thermal expansion characteristics. This parameter matching reduces thermal stress during temperature changes, maintaining detection sensitivity across different temperatures.
Solution Approach 2:
The patent employs composite materials strategy by carefully selecting the combination of package body material and sensor element material to achieve compatible thermal expansion properties. This material compatibility reduces differential thermal expansion stress, allowing the system to adapt to temperature changes while maintaining measurement precision.
4Adaptability or versatility
If the natural frequency fluctuates, then the detection sensitivity changes, but measurement accuracy degrades
Solution Approach 1:
The patent applies parameter changes by modifying the adhesive agent's physical parameters - using low modulus and low glass transition temperature materials. This changes the stress transmission characteristics, allowing the system to adapt to environmental changes without natural frequency fluctuation, thereby maintaining measurement accuracy.
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 approach stabilizes the natural frequency of MEMS sensors, enhancing measurement accuracy and reliability by minimizing fluctuations caused by stress and thermal changes, thus providing robust performance against environmental variations.
Implementation Method 1
a beam (4a to 4d) extending from each of the fixed portions (3a to 3d) and supporting the movable body (5) in a movable state
Implementation Method 2
stress occurs from the adhesive agent to the sensor element in general due to volume change caused by the setting of the adhesive agent
Implementation Method 3
by applying an angular velocity Ω around the z-axis externally, a Coriolis force Fc represented by Expression (2) is generated, and the Coriolis force Fc displaces the oscillator in a y-axis direction perpendicular to the x-axis
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
In order to provide a technology capable of suppressing degradation of measurement accuracy due to fluctuation of detection sensitivity of an MEMS by suppressing fluctuation in natural frequency of the MEMS caused by a stress, first, fixed portions 3a to 3d are displaced outward in a y-direction of a semiconductor substrate 2 by deformation of the semiconductor substrate 2. Since a movable body 5 is disposed in a state of floating above the semiconductor substrate 2, it is not affected and displaced by the deformation of the semiconductor substrate 2. Therefore, a tensile stress (+σ1) occurs in the beam 4a and a compressive stress (-σ2) occurs in the beam 4b. At this time, in terms of a spring system made by combining the beam 4a and the beam 4b, increase in spring constant due to the tensile stress acting on the beam 4a and decrease in spring constant due to the compressive stress acting on the beam 4b are offset against each other.