Curved Image Sensor Reflector for Light Capture
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Solution Overview
Problem
As image sensors and their pixels become smaller, existing technologies face challenges in efficiently capturing incident light, leading to reduced sensitivity and increased crosstalk and blooming effects due to the thickness of the silicon substrate and obstructions in traditional image sensors.
Innovation Solution
A frontside illuminated image sensor design with a reflector having multiple angles of reflection, such as concave, convex, or trapezoidal shapes, is used to redirect unabsorbed incident light back towards the photodiode, increasing light absorption and reducing crosstalk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the pixel size is reduced to increase sensor density, then the area occupied by each pixel decreases, but the ability to efficiently capture incident light deteriorates
Solution Approach 1:
The patent employs a curved reflector with a concave or convex surface geometry to redirect incident light. The curvature of the reflector surface enables effective light redirection in smaller pixel structures, maintaining light capture efficiency despite reduced pixel area. The curved surface focuses or disperses light appropriately to ensure sufficient light reaches the photodiode even in compact pixel designs.
2Ease of manufacture
If the silicon substrate thickness is increased to improve manufacturing, then the ease of manufacture improves, but light absorption efficiency deteriorates due to light being absorbed or scattered before reaching the photodiode
Solution Approach 1:
The patent introduces a vertical dimension solution by implementing a curved reflector beneath the photodiode. This reflector redirects light that would otherwise be lost in the substrate back toward the photodiode active region. By adding this reflective dimension, the system compensates for the light loss caused by increased substrate thickness, allowing thicker substrates to be used without sacrificing light absorption efficiency.
3Device complexity
If traditional flat reflectors are used, then the device complexity is low, but light redirection efficiency deteriorates leading to increased crosstalk and blooming
Solution Approach 1:
The patent replaces flat reflectors with curved (concave or convex) reflector surfaces to improve light redirection efficiency. The curvature enables better focusing and directional control of reflected light, reducing crosstalk and blooming effects. This geometric modification significantly enhances optical performance while adding minimal structural complexity to the overall device.
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 enhances light absorption and reduces crosstalk, improving the sensitivity and image quality of image sensors by focusing unabsorbed light onto the photodiode, thereby maintaining or improving image quality despite the smaller pixel sizes.
Implementation Method 1
a reflector (140) for reflecting incident light that was not initially absorbed by the photodiode (102), wherein the reflector (140) has a shape having multiple angles of reflection such that incident light that has not been initially absorbed by the photodiode (102) is focused and reflected towards the photodiode (102)
Data Source
Figure 1
Figure 2
Figure 3A~3C
AI summary
An array of pixels is formed using a substrate, (101) where each pixel has a substrate having an incident side for receiving incident light, (150) a photosensitive region (102, 104, 106) formed in the substrate, and a reflector (140, 142, 144) having a complex-shaped surface. The reflector is formed in a portion of the substrate that is opposed to the incident side such that light (150) incident on the complex- shaped surface of the reflector is reflected towards the photosensitive region.