Backside Illuminated Image Sensor Refractive Index Layering
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Solution Overview
Problem
Current image sensor technologies are not optimized for radiation absorption by pixels, leading to reduced quantum efficiency and suboptimal performance in sensing light, especially as the wavelength of the radiation increases.
Innovation Solution
A semiconductor image sensor device is fabricated with a substrate having a radiation-sensing region and multiple dielectric layers with specific refractive indices and thicknesses, forming a distributed Bragg reflector to enhance radiation absorption by reflecting unabsorbed light back towards the pixel, thereby increasing quantum efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If current fabrication technologies are used for image sensors, then the devices can be manufactured with standard processes, but the radiation absorption by pixels is not optimized leading to reduced quantum efficiency
Solution Approach 1:
The image sensor is divided into front-side pixel regions and back-side circuit regions, with light incident on the front side and unabsorbed light reflected back through the substrate to the pixels. This segmentation allows optimization of light absorption paths while maintaining standard fabrication processes for each region
Solution Approach 2:
A reflective structure is introduced as an intermediary element on the back side of the substrate to reflect unabsorbed light back toward the pixels. This mediator component enables enhanced radiation absorption without requiring fundamental changes to the pixel fabrication process
2Reliability
If the substrate is made thinner to improve light absorption, then more light can reach the pixels, but the mechanical strength and structural integrity of the device is reduced
Solution Approach 1:
The back-side reflective structure acts as a counterbalancing element that compensates for the reduced mechanical strength caused by thinning the substrate. The reflective layer provides structural support while performing its optical function of reflecting unabsorbed light back to the pixels
3Reliability
If multiple dielectric layers with different refractive indices are added to enhance radiation reflection, then quantum efficiency is improved, but the device complexity and manufacturing precision requirements increase
Solution Approach 1:
The thickness of each dielectric layer is specifically designed based on the wavelength of incident light and the refractive index of the materials. By optimizing these parameters, the reflective structure achieves enhanced quantum efficiency while using standard fabrication techniques that can maintain the required precision
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 enhances the quantum efficiency of the image sensor by reflecting unabsorbed radiation back towards the pixel, improving the photo response characteristics and performance, particularly for longer wavelengths.
Implementation Method 1
forming a distributed Bragg reflector to enhance radiation absorption by reflecting unabsorbed light back towards the pixel
Implementation Method 2
a first layer formed over the front side of the device substrate, the first layer having a first refractive index and a first thickness that is a function of the first refractive index; and a second layer formed over the first layer, the second layer being different from the first layer and having a second refractive index
Data Source
AI summary
Provided is an image sensor device. The image sensor device includes a device substrate having a front side and a back side. The device substrate has a radiation-sensing region that can sense radiation that has a corresponding wavelength. The image sensor also includes a first layer formed over the front side of the device substrate. The first layer has a first refractive index and a first thickness that is a function of the first refractive index. The image sensor also has a second layer formed over the first layer. The second layer is different from the first layer and has a second refractive index and a second thickness that is a function of the second refractive index.