Autofocus Pixel Isolation Structure to Reduce Alignment Error
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Solution Overview
Problem
Image sensors face alignment errors and saturation issues due to misalignment of pixel internal isolation layers, which affect the autofocusing function and overall image quality.
Innovation Solution
The image sensor design includes a pixel array with a substrate, pixels, and a logic circuit, featuring a pixel internal isolation layer formed from a different material than the pixel isolation layer, extending from the substrate's surface to minimize alignment errors and prevent photodiode saturation, with autofocusing pixels utilizing a microlens and separated photodiodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a pixel internal isolation layer is formed between photodiodes to improve autofocusing function, then alignment errors occur and photodiode saturation is caused
Solution Approach 1:
The pixel internal isolation layer is divided into a first pixel internal isolation layer and a second pixel internal isolation layer that are separated from each other in the first direction (vertical direction). This segmentation allows each layer to be formed with appropriate thickness and material properties, reducing alignment errors while maintaining the autofocusing function.
Solution Approach 2:
The first pixel internal isolation layer and the second pixel internal isolation layer are formed with different materials. This composite material approach enables optimization of each layer's electrical and optical properties, preventing photodiode saturation while maintaining reliable autofocusing operation.
2Measurement precision
If pixel area is decreased to increase resolution, then sensitivity is improved, but photodiode saturation occurs more easily
Solution Approach 1:
The pixel internal isolation layer structure extends in the vertical direction (first direction) with two separated layers, creating a three-dimensional charge management structure. This vertical dimensionality allows better charge separation and prevents saturation even when horizontal pixel area is reduced for higher resolution.
3Manufacturing precision
If different materials are used for first and second pixel internal isolation layers to reduce alignment errors, then manufacturing complexity increases
Solution Approach 1:
The first pixel internal isolation layer is formed before the second pixel internal isolation layer in a sequential manufacturing process. This preliminary action allows each layer to be optimized independently with appropriate materials and thickness, achieving reduced alignment errors while managing manufacturing complexity through a systematic multi-step process.
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 design reduces alignment errors and improves autofocusing functionality while maintaining high image resolution, effectively preventing photodiode saturation and enhancing sensitivity.
Implementation Method 1
a pixel internal isolation layer extending from the first surface in the first direction between the first photodiode and the second photodiode
Implementation Method 2
a microlens on the second surface
Implementation Method 3
each of the plurality of pixels including at least one photodiode
Data Source
AI summary
An image sensor includes a pixel array and a logic circuit. The pixel array includes a pixel isolation layer between a plurality of pixels. Each of the plurality of pixels include a pixel circuit below at least one photodiode. The logic circuit acquires a pixel signal from the plurality of pixels. The pixel array includes at least one autofocusing pixel, which includes a first photodiode, a second photodiode, a pixel internal isolation layer between the first and second photodiodes, and a microlens on the first and second photodiodes. The pixel internal isolation layer includes a first pixel internal isolation layer and a second pixel internal isolation layer, separated from each other in a first direction, perpendicular to the upper surface of the substrate, and the first pixel internal isolation layer and the second pixel internal isolation layer include different materials.