Proximity Focused Image Sensor Sealing for Thermal Expansion Mismatch
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Solution Overview
Problem
Existing photocathode-based image sensors face challenges due to thermal coefficient of expansion mismatches between glass-bonded III-V semiconductor photocathodes and silicon substrates, leading to degraded performance and manufacturing issues.
Innovation Solution
A compact proximity focused image sensor design featuring a malleable metal seal that bonds the photocathode window assembly and silicon substrate, creating a vacuum gap with defined height, allowing for thermal expansion mismatch accommodation and eliminating the need for a separate vacuum body component, thereby reducing sensor size, weight, and cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If glass-bonded III-V semiconductor photocathodes are used, then photocathode performance is improved, but thermal coefficient of expansion mismatch with silicon substrate degrades performance
Solution Approach 1:
The patent introduces a malleable metal seal as an intermediary component between the glass-bonded III-V semiconductor photocathode and the silicon substrate. This seal layer acts as a buffer that accommodates the thermal coefficient of expansion mismatch between the two materials, allowing both to be bonded without direct thermal stress contact, thereby preserving photocathode performance while enabling compatibility with silicon substrates
2Reliability
If separate vacuum body component is used, then vacuum seal integrity is maintained, but sensor size, weight, and part count increase
Solution Approach 1:
The patent merges the vacuum body function with the malleable metal seal by making the seal itself form the vacuum enclosure. The malleable metal seal bonds the photocathode window assembly and silicon substrate together while simultaneously creating the vacuum gap and maintaining vacuum integrity, eliminating the need for a separate vacuum body component and reducing overall device complexity
3Reliability
If glass-bonded III-V semiconductor photocathodes are used, then photocathode performance is improved, but manufacturing complexity increases due to thermal budget constraints
Solution Approach 1:
The malleable metal seal serves as a manufacturing-friendly intermediary that allows assembly at lower temperatures compatible with both glass-bonded photocathodes and silicon substrates. This intermediary enables a simplified thermal budget process where components can be bonded without exposing the photocathode to excessive heat that would degrade performance, thereby improving ease of manufacture
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 design achieves reliable thermal expansion mismatch accommodation, enhances manufacturing efficiency, and minimizes image sensor part count, size, and weight, while maintaining ultra-high vacuum seal integrity and high voltage bias reliability.
Implementation Method 1
One constraint associated with the previously cited glass bonded III-V semiconductor photocathodes is that the thermal coefficient of expansion (TCE) of the glass bonded window must closely match that of the semiconductor used in the photocathode structure. A significant mismatch in thermal expansion coefficient results in degraded photocathode performance
Data Source
AI summary
An image sensor has a photocathode window assembly, an anode assembly, and a malleable metal seal. The photocathode window assembly has a photocathode layer. The anode assembly includes a silicon substrate that has an electron sensitive surface. The malleable metal seal bonds the photocathode window assembly and the silicon substrate to each other. A vacuum gap separates the photocathode layer from the electron sensitive surface. A first electrical connection and a second electrical connection are for a voltage bias of the photocathode layer relative to the electron sensitive surface.