Infrared Pixel Reflective Structures for Quantum Efficiency
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Solution Overview
Problem
Conventional image sensors suffer from low quantum efficiency and optical crosstalk issues when capturing images in both infrared and visible spectral ranges, leading to degraded image quality.
Innovation Solution
Incorporating reflective structures in infrared pixels, such as upper and lower reflectors, to create an optical cavity that increases sensitivity to infrared light while minimizing crosstalk with color pixels, using materials like copper or dielectric layers to form interference filters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional image sensors are used to capture infrared light, then infrared imaging is enabled, but quantum efficiency remains low
Solution Approach 1:
The patent introduces a vertical optical cavity structure with upper and lower reflective structures beneath the photodiode, transforming the planar light detection into a three-dimensional optical path. This dimensional change allows infrared light to be reflected multiple times through the photodiode, increasing absorption probability and quantum efficiency without expanding the pixel area horizontally.
Solution Approach 2:
The reflective structures create a continuous optical path that repeatedly directs infrared light through the photodiode region. Instead of a single-pass detection, the light undergoes multiple reflections and transmissions, ensuring continuous interaction with the photodiode until absorbed or directed to the infrared pixel, thereby maximizing energy utilization and quantum efficiency.
2Adaptability or versatility
If image sensors capture both infrared and visible light, then dual spectral imaging is enabled, but optical crosstalk degrades image quality
Solution Approach 1:
The patent divides the pixel array into distinct regions: color pixels with full color filters for visible light detection, and dedicated infrared pixels for infrared detection. The selective infrared absorption layer in color pixels further segments the spectral response, allowing visible light to pass through to color filters while blocking infrared, thereby preventing crosstalk between the two spectral domains.
Solution Approach 2:
The selective infrared absorption layer acts as an intermediary element between the optical lens and the color filters. It selectively absorbs infrared light before it reaches the color filters, preventing infrared contamination in color pixel signals, while allowing visible light to pass through to the color filters for normal color imaging.
3Measurement precision
If reflective structures are added to increase infrared sensitivity, then quantum efficiency improves, but device complexity increases
Solution Approach 1:
The lower reflective structure serves multiple functions: it reflects infrared light upward toward the photodiode to enhance sensitivity, and it also acts as a common ground or reference plane for the entire pixel array. By making the reflective structure universal across all pixels rather than individualized, the patent reduces overall device complexity while maintaining enhanced infrared detection capability.
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
Significantly enhances quantum efficiency of infrared pixels by four to five times, reducing optical crosstalk and improving image quality in both infrared and visible spectral ranges.
Implementation Method 1
The pixel array may include first and second reflective structures positioned in the pixel array such that the photodiode in the infrared pixel is between the first and second reflective structures. Infrared light received by the infrared pixel may be reflected by the first and second reflective structures until the infrared light is absorbed by the photodiode in the infrared pixel.
Implementation Method 2
Each pixel may include a photosensor such as a photodiode that receives incident photons (light) and converts the photons into electrical signals.
Implementation Method 3
using materials like copper or dielectric layers to form interference filters
Data Source
AI summary
An imaging device may include an image sensor having an array of image pixels. The array of image pixels may include one or more infrared pixels that are configured to detect infrared light. The infrared pixels may include reflective structures for increasing quantum efficiency in the infrared spectral range. The reflective structures may include first and second parallel structures formed on opposing sides of a photodiode in an infrared pixel. The reflective structures may be partially transparent to infrared light and non-transparent to visible light. The reflective structures may form an optical cavity so that infrared light that enters an infrared pixel is reflected back and forth between the reflective structures until it is absorbed by the photodiode in the infrared pixel. Reflective structures may also be formed between infrared filters and color filters to suppress optical crosstalk between infrared pixels and color pixels.