Backside-Illuminated Pixel Sensor Spacer for Optical Filter Gap Control
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Solution Overview
Problem
Conventional methods for mounting optical filters in pixel matrix sensors face challenges in controlling the gap width between the filter and the sensor, particularly for sensors made of different materials, leading to difficulties in managing etaloning effects and restricting the types and applications of image sensors.
Innovation Solution
A method involving a substrate spacer is used, where the substrate is partially removed to create a gap, allowing for precise attachment of the optical filter, which serves as both a mechanical spacer and holder, ensuring a well-defined gap width and parallelism between the filter and sensor layer, thereby controlling etaloning effects and enabling easier mounting across various materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a dedicated filter holder is used to mount the optical filter, then the optical filter can be mounted before the optical sensors, but the gap width between the filter and sensor is difficult to control due to tolerance chain accumulation
Solution Approach 1:
The substrate is selectively removed (etched away) in the central area to create a precise gap between the optical filter and the sensor layer. This extraction of substrate material allows direct control of the gap width through the etching depth, eliminating the tolerance chain issues associated with mechanical filter holders.
Solution Approach 2:
The remaining substrate edges act as an intermediary mechanical stop that defines the gap width. By controlling the substrate thickness and etching depth, the substrate itself becomes the precision spacer, replacing the need for separate filter holders and their associated tolerance accumulations.
2Manufacturing precision
If an optical filter is directly deposited onto the sensor layer, then the gap width can be precisely controlled, but this method is limited to specific materials and sensor types
Solution Approach 1:
The substrate is segmented into different functional zones: the central area is completely removed to create the optical gap, while the peripheral areas are retained as mechanical supports and alignment references. This segmentation allows the gap to be precisely defined by the substrate thickness in the remaining peripheral regions, enabling universal application across different sensor materials.
Solution Approach 2:
The substrate serves multiple functions: it provides mechanical support for the sensor layer, defines the gap width through its thickness, and creates the precise optical path by selective removal. This multi-functional approach makes the method universally applicable to different sensor materials (Silicon, InGaAs, HgCdTe) without requiring material-specific deposition processes.
3Loss of energy
If the substrate is completely removed in the central area, then light absorption by the substrate is reduced, but the structural support is weakened
Solution Approach 1:
The substrate exhibits different qualities in different regions: the central area is completely removed to minimize light absorption and improve optical transmission, while the peripheral areas retain full substrate thickness to provide mechanical strength and structural support. This local differentiation resolves the contradiction between optical performance and structural integrity.
Solution Approach 2:
The substrate is segmented into a central optical region (completely removed) and peripheral support regions (retained). This segmentation allows the structure to simultaneously achieve high optical transmission in the center while maintaining mechanical strength through the peripheral remnants, which also serve as alignment references for the optical filter.
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 provides a cost-efficient, robust, and precise method for mounting optical filters, reducing light absorption, controlling etaloning effects, and allowing for the use of diverse sensor materials, resulting in improved optical properties and reduced sensor size and cost.
Implementation Method 1
removing completely the substrate in the central area from the second side of the substrate to create a gap in the central area
Implementation Method 2
attaching an optical filter to the substrate spacer
Implementation Method 3
sensor layer including an optical sensor in a photoactive region of the sensor layer
Data Source
Figure 1
Figure 2
Figure 3A~3C
AI summary
The invention relates to a method of preparing a pixel matrix sensor with a backside-illuminated geometry. After depositing (S12) a sensor layer on a second side of the substrate, a substrate spacer is prepared (S14), including removing completely the substrate in the central area from the second side of the substrate to create a gap in a central area above a photoactive region of the sensor layer and leaving the substrate spacer on the second side of the substrate and outside of the central area. An optical filter is then attached (S15) to the substrate spacer. The substrate spacer serves as a mechanical spacer for mounting the optical filter and facilitates maintaining the spatial homogeneity of the width of a gap between the optical filter and the sensor layer, without requiring additional holder structures for mounting the optical filter.