MEMS Sensor Mechanical Decoupling via Air Gap and Trenches
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Microintegrated MEMS sensors face challenges in packaging due to stress-induced performance degradation, particularly in piezoresistive sensors, where common packaging methods like molding generate high stresses that affect reliability and stability, and existing low-stress encapsulation solutions may not fully address these issues.
Innovation Solution
A microintegrated encapsulated MEMS sensor design featuring a layer stack with a sensor layer, cap layer, and insulating layer, including an air gap and through trenches that mechanically decouple the sensor from the package, allowing for fluidic paths without perforating the sensitive membrane, enabling stress relief and reliable operation even with high-stress packaging techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If traditional molding packaging is used, then manufacturing cost is reduced and productivity is improved, but high stresses are generated during resin injection and cooling that adversely affect sensor performance and reliability
Solution Approach 1:
The sensor structure is segmented into distinct functional layers (sensor layer, insulating layer, cap layer) with through-trenches creating separate stress zones. This segmentation allows the package to be divided into stress-bearing structural portions and stress-isolated sensitive portions, enabling high-stress packaging processes while protecting the sensor element.
Solution Approach 2:
The air gap formed by the through-trenches acts as an intermediary layer between the sensor element and the package structure. This intermediate space mechanically decouples the sensitive element from stress-generating packaging processes, allowing the sensor to maintain performance stability while enabling robust packaging methods.
2Productivity
If package size and dice size are increased, then manufacturing efficiency is improved, but stress effects from packaging become increasingly severe
Solution Approach 1:
The increased package and dice sizes are accommodated by segmenting the structure into stress-isolated regions. The through-trenches create localized stress management zones that prevent stress propagation across the entire enlarged structure, allowing scaling while maintaining stress control.
Solution Approach 2:
Different regions of the enlarged package are given different structural qualities - the sensor layer and cap layer provide structural integrity for large sizes, while the air gap regions provide localized stress relief. This local quality differentiation allows large dimensions without proportionally increased stress effects.
3Strength
If mechanical coupling between sensor and package is strengthened, then mechanical strength is improved, but stress transmission to the sensor element increases
Solution Approach 1:
The mechanical coupling is segmented into two functional paths: the sensor layer and cap layer provide strong mechanical coupling for overall structural strength, while the through-trenches with air gaps create discontinuities that block stress transmission paths to the sensitive element.
Solution Approach 2:
The air gap within the through-trenches serves as a mechanical intermediary that transmits load-bearing capacity while blocking stress propagation. This allows the package to maintain mechanical strength for handling and mounting while preventing stress transmission to the sensor element.
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 effectively reduces stress-induced performance degradation, allowing the sensor to accurately detect environmental forces like pressure without disturbance from packaging-related stresses, and supports high-stress packaging methods without compromising the sensitive element's integrity.
Implementation Method 1
An air gap extends between the central portions of the sensor layer and of the cap layer
Implementation Method 2
sensors based upon piezoresistive characteristics of silicon, wherein the stresses are directly involved in the transduction mechanism
Data Source
AI summary
The microintegrated sensor comprises a stack formed by a sensor layer, of semiconductor material, by a cap layer, of semiconductor material, and by an insulating layer. The sensor layer and the cap layer have a respective peripheral portion surrounding a central portion, and the insulating layer extends between the peripheral portions of the sensor layer and of the cap layer. An air gap extends between the central portions of the sensor layer and of the protection layer. A through trench extends into the central portion of the sensor layer as far as the air gap and surrounds a platform housing a sensitive element. The cap layer has through holes in the insulating layer that extend from the air gap and form a fluidic path with the air gap and the through trench.