CMOS Image Sensor Double-Side Absorption Structure
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Solution Overview
Problem
As the number of pixel regions in CMOS image sensor integrated chips increases, the smaller size of each pixel region leads to diminished light intensity, increased sensing times, and reduced signal-to-noise margins due to intervening layers with different indices of refraction causing light to refract and travel away from the desired image sensor.
Innovation Solution
An absorption enhancement structure is placed between the back-side of the substrate and the light sensing element, and a reflection structure comprising semiconductor or dielectric pillars is arranged between the light sensing element and the front-side of the substrate to redirect unabsorbed light back towards the light sensing element, enhancing light absorption and measurement efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the number of pixel regions is increased to improve resolution, then image quality is improved, but the light intensity per pixel is diminished and sensing time increases
Solution Approach 1:
The patent introduces a vertical dimension by placing absorption enhancement structures and reflection structures above and below the pixel region, respectively. This transforms the light absorption problem from a two-dimensional surface issue to a three-dimensional volume issue, allowing light to be absorbed from multiple directions and paths without increasing pixel area.
Solution Approach 2:
The patent introduces intermediary structures (absorption enhancement structures and reflection structures) that mediate between the incident light and the light sensing element. These intermediaries extend the light interaction path and enhance absorption efficiency without requiring larger pixel areas or longer sensing times.
2Measurement precision
If the number of pixel regions is increased, then image resolution is improved, but sensing time increases
Solution Approach 1:
By adding vertical absorption and reflection structures, the patent extends the light interaction path in the vertical dimension, enabling faster absorption of light photons without increasing the horizontal pixel area. This reduces the time required for each pixel to accumulate sufficient signal.
Solution Approach 2:
The intermediary absorption enhancement structures accelerate the light absorption process by providing multiple interaction opportunities for photons, thereby reducing the sensing time required to achieve adequate signal levels for high-resolution imaging.
3Ease of manufacture
If conventional light absorption structures are used, then manufacturing is simpler, but light absorption efficiency is insufficient
Solution Approach 1:
The patent segments the light absorption function into multiple independent components: absorption enhancement structures on the first side, reflection structures on the second side, and the light sensing element in between. This segmentation allows each component to be optimized independently while maintaining overall manufacturing feasibility through standard semiconductor fabrication processes.
Solution Approach 2:
The patent employs composite structures combining different materials with complementary properties: absorption enhancement structures made of materials with high absorption coefficients, reflection structures made of materials with high reflectivity, and the light sensing element made of photoactive materials. This composite approach achieves superior light absorption efficiency while remaining compatible with existing manufacturing processes.
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 solution significantly improves the percentage of incident light absorbed by the image sensor, increasing quantum efficiency and reducing light loss, thereby enhancing image capture resolution and signal quality.
Implementation Method 1
a reflection structure comprising semiconductor or dielectric pillars is arranged between the light sensing element and the front-side of the substrate to redirect unabsorbed light back towards the light sensing element
Implementation Method 2
An absorption enhancement structure is placed between the back-side of the substrate and the light sensing element... significantly improves the percentage of incident light absorbed by the image sensor, increasing quantum efficiency
Data Source
AI summary
The present disclosure relates to an integrated chip that has a light sensing element arranged within a substrate. An absorption enhancement structure is arranged along a back-side of the substrate, and an interconnect structure is arranged along a front-side of the substrate. A reflection structure includes a dielectric structure and a plurality of semiconductor pillars that matingly engage the dielectric structure. The dielectric structure and semiconductor pillars are arranged along the front-side of the substrate and are spaced between the light sensing element and the interconnect structure. The plurality of semiconductor pillars and the dielectric structure are collectively configured to reflect incident light that has passed through the absorption enhancement structure and through the light sensing element back towards the light sensing element before the incident light strikes the interconnect structure.