Lateral Photodetector Structure for Higher-Density Image Sensors
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Solution Overview
Problem
Reducing the lateral distance between pixels in image sensors without diminishing the performance of photodetectors, which is challenging due to the lateral extension of the p-n junction in existing CMOS image sensors.
Innovation Solution
The image sensor design features a first and second doped region laterally beside each other, forming a p-n junction that extends vertically, allowing for a reduction in pixel width without reducing the size of the p-n junction, and includes a second semiconductor layer that increases the photosensitive area and sensitivity, particularly at short-wave infrared wavelengths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the lateral distance between pixels is reduced, then the pixel density increases, but the photodetector performance deteriorates due to the lateral extension of the p-n junction
Solution Approach 1:
The patent transforms the conventional lateral (horizontal) p-n junction configuration into a vertical configuration. The first doped region and second doped region are positioned at different vertical levels within the semiconductor substrate, creating a vertical p-n junction that extends in the depth direction rather than laterally. This dimensional change allows pixels to be placed closer together horizontally while maintaining adequate photodetector performance, as the vertical junction no longer occupies lateral space that would interfere with adjacent pixels.
2Length of moving object
If the pixel width is reduced, then the lateral distance between pixels decreases, but the p-n junction size is reduced compromising detector performance
Solution Approach 1:
The patent relocates the p-n junction from a lateral configuration to a vertical configuration. The first doped region and second doped region are positioned at different depths within the substrate, allowing the junction to maintain its functional size and performance characteristics while occupying vertical rather than lateral space. This enables pixel width to be reduced without compromising the p-n junction dimensions or performance.
Solution Approach 2:
The patent embeds the p-n junction structure within the vertical depth of the semiconductor substrate. The first doped region and second doped region are nested at different vertical levels, with the junction forming in the depth direction between them. This nesting approach allows the junction to be contained within the pixel structure without extending laterally, enabling smaller pixel widths while preserving junction performance.
3Length of moving object
If a vertical p-n junction configuration is used, then the lateral distance between pixels can be reduced, but the photosensitive area may be limited
Solution Approach 1:
The patent embeds an additional second semiconductor layer within the vertical structure of the pixel. This second layer, positioned between the first doped region and the substrate surface, contains additional photosensitive material that contributes to the overall photosensitive area. The nested configuration allows the vertical p-n junction to enable smaller pixel spacing while the embedded second layer maintains adequate light-sensitive volume within the constrained lateral dimensions.
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 enables a reduction in the lateral distance between pixels without compromising performance, improving the fill factor and sensitivity of the image sensor.
Implementation Method 1
The first doped region and the second doped region form a p-n junction... The image sensor design features a first and second doped region laterally beside each other, forming a p-n junction that extends vertically
Implementation Method 2
Some CMOS image sensors are based on avalanche photodiodes (APD) and single-photon avalanche photodiodes (SPAD)
Data Source
AI summary
The present disclosure relates to an image sensor including a first semiconductor layer having a first doping type. A second semiconductor layer having the first doping type is between sidewalls of the first semiconductor layer and extends vertically along the sidewalls of the first semiconductor layer from a bottom side of the first semiconductor layer toward a top side of the first semiconductor layer. A first doped region having the first doping type is in the first semiconductor layer and laterally beside the second semiconductor layer. The first doped region extends vertically along a sidewall of the second semiconductor layer. A second doped region having a second doping type is in the first semiconductor layer and laterally beside the first doped region. The second doped region extends vertically along a side of the first doped region and forms a p-n junction with the first doped region.