Light-Trapping Image Sensor Cavities for Near-Infrared Quantum Efficiency
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional image sensors, particularly silicon-based CMOS sensors, exhibit low quantum efficiency in the near-infrared spectrum, limiting their performance in low-light conditions such as night vision applications where near-infrared light is used.
Innovation Solution
A light-trapping image sensor design featuring a pixel array with cavities formed by reflective material around semiconductor material, coupled with a lens array that focuses light into these cavities, effectively increasing the path length of incident photons within the semiconductor substrate, thereby enhancing quantum efficiency in wavelengths where silicon absorption is low.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional silicon-based image sensors are used, then manufacturing and integration are straightforward, but quantum efficiency in the near-infrared spectrum is low
Solution Approach 1:
The patent introduces a third dimension by forming cavities extending from the front surface into the substrate, creating a vertical light-trapping structure. This dimensional change allows light to travel a longer path through the silicon material, increasing absorption probability in the near-infrared spectrum where silicon has low absorption coefficient.
Solution Approach 2:
The patent converts the naturally occurring light reflection at the silicon-air interface, which normally causes light loss, into a beneficial effect. By creating cavities with reflective material at the bottom and using the air-silicon interface as a reflective ceiling, the structure traps light through multiple reflections, turning the harmful reflection into a light-trapping mechanism that enhances near-infrared absorption.
2Reliability
If the photodiode depth is increased to improve light absorption, then quantum efficiency improves, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent segments the light absorption function into two distinct components: the cavity structure that traps and redirects light, and the photodiode that converts photons to electrical signals. This segmentation allows the photodiode to maintain a reasonable depth while the cavity structure provides the extended light path, thereby improving quantum efficiency without proportionally increasing device complexity.
Solution Approach 2:
The cavity structure acts as an intermediary between the incident light and the photodiode. It pre-processes the light by trapping and redirecting it multiple times through the silicon material before the light reaches the photodiode, thereby enhancing absorption without requiring the photodiode itself to be excessively deep or complex.
3Reliability
If the aperture size is increased to allow more light entry, then light trapping efficiency improves, but spatial resolution deteriorates
Solution Approach 1:
The patent applies local quality by making each cavity's aperture size specifically optimized for its function while maintaining appropriate spacing from adjacent cavities. The aperture dimensions are locally tuned to balance light trapping efficiency with spatial resolution, allowing each pixel element to function optimally without compromising the overall image quality.
Solution Approach 2:
By extending the light-trapping mechanism into the vertical dimension through deep cavities, the patent decouples the aperture size constraint from the light trapping efficiency. Light can enter through relatively small apertures and then be trapped and redirected multiple times within the cavity volume, achieving high trapping efficiency without sacrificing spatial resolution that would result from overly large apertures.
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 light-trapping design significantly improves quantum efficiency, especially in the near-infrared range, allowing for better image capture in low-light conditions by increasing the absorption of near-infrared light, thus compensating for the low absorption coefficient of silicon.
Implementation Method 1
a reflective material forming a cavity around a portion of semiconductor material to at least partly trap light that has entered the cavity
Implementation Method 2
the cavity... to at least partly trap light that has entered the cavity
Implementation Method 3
Each lens of the lens array is aligned to the aperture of a respective cavity to focus the light into the cavity through the aperture
Implementation Method 4
Each lens of the lens array is aligned to the aperture of a respective cavity to focus the light into the cavity through the aperture
Implementation Method 5
an image sensor, such as a charge coupled device (CCD) image sensor or a complementary metal oxide semiconductor (CMOS) image sensor, converts incident light to electrical charge
Data Source
AI summary
A light-trapping image sensor includes a pixel array and a lens array. The pixel array is formed in and on a semiconductor substrate and including photosensitive pixels each including a reflective material forming a cavity around a portion of semiconductor material to at least partly trap light that has entered the cavity. The cavity has a ceiling at a light-receiving surface of the semiconductor substrate, and the ceiling forms an aperture for receiving the light into the cavity. The lens array is disposed on the pixel array. Each lens of the lens array is aligned to the aperture of a respective cavity to focus the light into the cavity through the aperture.