Embedded Spring Stoppers for Shock-Robust Thermal Sensor Pixels
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Solution Overview
Problem
Conventional thermal sensing pixels face issues with mechanical robustness during shock testing due to flexible springs that can damage the device or limit sensitivity and field-of-view, necessitating improved mechanical stoppers.
Innovation Solution
A method of forming thermal sensing pixels with laterally extending stoppers that constrain spring movement, using multiple metal layers as etch stops to define frame, springs, and central structures, ensuring mechanical stability without obstructing the field-of-view.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If flexible springs are used to suspend the mass, then thermal isolation is achieved, but mechanical robustness deteriorates during shock testing
Solution Approach 1:
The patent applies beforehand cushioning by forming stopper structures that extend into the cavity to limit the range of motion of the springs before mechanical damage can occur. These stoppers are positioned to prevent the mass from contacting the interior surface of the top cap or bottom cap during shock events, thereby cushioning against potential mechanical failure while maintaining the flexible suspension needed for thermal isolation.
2Reliability
If projections are added to the top cap to act as stoppers, then mechanical robustness is improved, but sensitivity and field-of-view deteriorate
Solution Approach 1:
The patent resolves this contradiction by moving the stopper structures from the top cap surface (which would block the field of view) into the cavity space along the sides. This dimensional relocation allows the stoppers to perform their mechanical protection function without interfering with the optical path to the sensing elements, thereby maintaining both mechanical robustness and measurement precision.
3Adaptability or versatility
If the mass is allowed to bounce freely during mechanical shock, then spring flexibility is maintained, but device yield deteriorates
Solution Approach 1:
The patent applies preliminary anti-action by pre-positioning stopper structures that will counteract excessive spring motion before it can cause damage. The stoppers are configured to engage only when the springs exceed their normal operational range during shock events, thereby allowing normal flexibility and adaptation while preventing catastrophic failure that would reduce device yield.
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 enhances mechanical robustness by constraining spring movement, preventing damage and maintaining sensitivity, thus improving device reliability and performance under mechanical stress.
Implementation Method 1
The springs 14 serve to thermally isolate the mass 13 from the frame 12 due to the springs 14 having a low thermal conductivity
Implementation Method 2
When there is a temperature difference between the sensing junction and the reference junction, a temperature-dependent voltage is generated as a result of the Seebeck effect
Data Source
AI summary
Disclosed herein are thermal sensor devices including TMOS devices with a mass suspended over a cavity by springs extending between a frame and the mass. The thermal sensor devices include stoppers that limit upward and/or downward movement of the springs and therefore the mass. These stoppers are formed from sidewalls supporting a top cap over the frame, springs, and mass. The stoppers are constructed by using various overlapping metal layers during fabrication. Details of forming the stoppers using these overlapping metal layers are contained here.