Wafer-Bonded Piezoelectric Chemical Sensor Fabrication
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing chemical sensor fabrication methods face challenges in forming reliable sensing layers that maintain functionality under varying temperatures and mechanical stresses, particularly when integrating piezoelectric materials and nano-composite structures.
Innovation Solution
A method involving the formation of a sensor structure between two wafers, where a piezoelectric material is used in one wafer and a sensing layer is deposited through a hole in the other, using techniques like direct printing and thermo-compression bonding with spacer materials that match thermal expansion coefficients, to create a stable and sensitive chemical detection system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sensing layers are formed using conventional fabrication methods, then the sensor structure can be created, but the sensing layers suffer from mechanical and thermal stress that reduces their sensitivity and functionality
Solution Approach 1:
The fabrication process is divided into separate stages: first forming the piezoelectric substrate and sensor structures, then adding the sensing layer in a subsequent step. This segmentation allows each component to be optimized independently and reduces cumulative stress on the sensing layer.
Solution Approach 2:
The piezoelectric substrate and sensor structures are fully formed and stabilized before the sensing layer is deposited. This preliminary action ensures that the substrate is ready to provide mechanical support and stress compensation before the sensitive sensing layer is introduced.
2Manufacturing precision
If the sensing layer is deposited after wafer bonding, then the sensor structure is already formed, but accessing the sensing layer requires removing or modifying the wafer structure
Solution Approach 1:
A hole is drilled through the first wafer to provide direct access to the sensing layer location. This extraction approach allows the sensing layer to be deposited and accessed without requiring complex modifications to the bonded wafer structure.
Solution Approach 2:
The hole in the first wafer acts as an intermediary access path, allowing deposition materials to reach the sensing layer through a simple aperture rather than requiring the sensing layer to be exposed by complex structural modifications.
3Ease of manufacture
If spacer materials with mismatched thermal expansion coefficients are used, then the wafer bonding process is simpler, but the sensor experiences thermal stress that damages the sensing layer
Solution Approach 1:
The thermal expansion coefficient is changed to match between the spacer material and the wafer materials. This parameter matching eliminates differential thermal expansion and the associated stresses that would damage the sensing layer during temperature variations.
Solution Approach 2:
The spacer material is specifically selected or engineered to have a thermal expansion coefficient that matches the average of the two wafer materials. This thermal expansion matching prevents stress buildup during thermal cycling and maintains sensing layer integrity.
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 enables the creation of chemical sensors that effectively detect and measure chemical presence/concentration with reduced mechanical and thermal stress, preserving the sensitivity and functionality of the sensing layers, even at high temperatures.
Implementation Method 1
The second wafer includes a piezoelectric material
Implementation Method 2
The spacer material could include frit glass paste that is cured into frit glass, where the frit glass has a thermal coefficient of expansion at least approximately equal to average thermal coefficients of expansion for the first and second wafers
Implementation Method 3
forming the hole through the first wafer includes using ultrasonic milling
Data Source
AI summary
A method includes forming a hole in a first wafer and forming a sensor structure in or on a second wafer. The second wafer includes a piezoelectric material. The method also includes bonding the first wafer and the second wafer, where the sensor structure is located between the wafers. The method further includes forming a sensing layer by depositing material between the wafers through the hole in the first wafer. The sensing layer could be formed by depositing a sensing layer material on the second wafer using direct printing. Also, the hole through the first wafer could be formed using ultrasonic milling, micro-drilling, laser drilling, wet etching, and/or plasma etching. A spacer material could be used to bond the wafers together, such as frit glass paste or an organic adhesive. Trenches could be formed in the first wafer to facilitate easier separation of multiple sensors.