Microscale Sensor Backside Contacts Eliminate Flow Disturbances
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Solution Overview
Problem
Existing microscale sensors face challenges in accurately measuring wall shear stress due to flow disturbances caused by traditional wire bonds and bump bonding methods, which result in measurement errors and increased fabrication complexity and cost.
Innovation Solution
The development of microscale sensor structures with backside contacts and packaging that eliminate the need for electrical through-wafer vias (TWVs) by using a support substrate with openings for backside electrical connections, allowing for flush mounting and minimizing surface roughness, thereby reducing flow disturbances and fabrication complexities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If wire bonds are placed on the front side of the sensor, then electrical connection to conditioning electronics is achieved, but flow disturbances occur due to wire bond loop heights exceeding 100 μm, resulting in measurement errors and increased drag
Solution Approach 1:
The patent inverts the conventional approach by moving electrical connections from the front side to the back side of the sensor. The sensing element is mounted flush on the front surface with connections routed through the backside, eliminating wire bond loops that cause flow disturbances. This inversion resolves the contradiction by achieving electrical connectivity without compromising measurement precision.
Solution Approach 2:
The patent transitions electrical connections from the front surface dimension to the backside dimension. By routing connections through the thickness of the sensor substrate rather than along the surface, the solution eliminates the harmful wire bond loops while maintaining electrical connectivity, thus resolving the measurement precision issue.
2Measurement precision
If bump bonding with electrical through-wafer vias is used, then flow disturbance is circumvented, but rigid connection causes large packaging stresses resulting in increased measurement error
Solution Approach 1:
The patent employs a thin flexible sensing element that can deflect in response to wall shear stress while maintaining electrical connections through the backside. This flexible thin film approach allows the sensor to accurately measure flow conditions without the rigid packaging stresses that plague through-wafer via solutions, thereby resolving the contradiction between flow measurement accuracy and measurement reliability.
3Ease of manufacture
If bump bonding and through-wafer vias are implemented, then electrical connection is achieved, but fabrication complexity and cost increase due to larger number of processing steps
Solution Approach 1:
The patent extracts the electrical connection function from the front surface mounting process and relocates it to the backside. By separating the sensing function (front surface) from the connection function (backside), the fabrication process is simplified, eliminating the need for complex through-wafer via formation and bump bonding steps while maintaining electrical connectivity.
Data Source
AI summary
A microscale sensor structure is provided that enables backside electrical connection to flush-mounted microscale sensors without through-wafer-vias (TWVs). A flush-mounted microscale sensor can be fabricated without TWVs by providing a sensor support substrate with openings for electrical connection access to the backside of a device layer. Backside electrical connection is made to the sensing element(s) of the device layer through the openings in the support substrate. Electrical isolation of the sensing element(s) from the support substrate is accomplished through use of an insulating support substrate and/or an insulating layer between the support substrate and the device layer.