Backside Illuminated Image Sensor Radiation Shielding
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Solution Overview
Problem
Backside illuminated (BSI) image sensor devices suffer from the hot spot phenomenon due to unwanted radiation from the ASIC substrate, which causes excess charges and degrades pixel performance by making one pixel brighter than adjacent pixels.
Innovation Solution
A high absorption coefficient metal-oxide film is introduced as an absorption layer between the ASIC substrate and the CMOS sensor substrate to absorb and block radiation waves, preventing them from reaching the radiation-sensing region and thus mitigating the hot spot phenomenon.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If transistor devices are shrunk to increase integration density, then device scaling and integration are improved, but electrical or optical crosstalk increases causing hot spot phenomenon
Solution Approach 1:
An absorption layer made of metal-oxide film is introduced as an intermediary between the ASIC substrate and the CMOS sensor substrate. This absorption layer specifically absorbs unwanted radiation (optical crosstalk) generated by the ASIC circuit, preventing it from reaching the image pixels and causing hot spot phenomenon, while allowing the beneficial electrical connections to remain intact.
Solution Approach 2:
The harmful radiation absorption function is extracted from the substrate materials themselves and assigned to a dedicated absorption layer. This separates the harmful optical crosstalk absorption function from the electrical connection function, allowing the transistor scaling to continue while the radiation interference is specifically managed by the extracted absorption layer.
2Object-affected harmful factors
If a blocking layer is added between substrates to prevent radiation, then hot spot phenomenon is reduced, but manufacturing complexity increases
Solution Approach 1:
The absorption layer is formed by changing the material parameter (using metal-oxide film with specific absorption properties) and thickness parameter (50-200 nm) rather than adding a thick blocking structure. This parameter optimization allows effective radiation absorption while maintaining compatibility with existing manufacturing processes and minimizing additional complexity.
Solution Approach 2:
The absorption layer uses composite material structure where metal-oxide film is deposited on the substrate. This composite approach combines the substrate's electrical connection function with the metal-oxide's radiation absorption function, achieving both goals without significantly increasing manufacturing complexity.
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 absorption layer effectively shields radiation waves, preventing them from influencing the image sensor and eliminating the hot spot phenomenon, thereby improving pixel performance by ensuring uniform signal intensity across the image array.
Implementation Method 1
a blocking layer between the first substrate and the second substrate, wherein the blocking layer comprises a metal-oxide film with a higher absorption coefficient
Data Source
AI summary
A backside illuminated (BSI) image sensor device includes: a first substrate including a front side and a back side; a second substrate bonded with the first substrate on the front side; and a blocking layer between the first substrate and the second substrate. The first substrate includes an image sensor, and the image sensor is configured to collect incident light entering from the back side. The second substrate includes a circuit coupled with the image sensor. The blocking layer is configured to block radiation induced by the circuit.