BSI Image Sensor Pixel Structure for Quantum Efficiency and Dynamic Range
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Solution Overview
Problem
Backside illuminated (BSI) image sensors face challenges in detecting low irradiance targets under strong background irradiance due to insufficient quantum efficiency and dynamic range, leading to saturation issues.
Innovation Solution
The image sensor is designed with two types of pixels: high quantum efficiency pixels featuring a metal grid structure with apertures and groove patterns, and high saturation level pixels with a blocking metal layer to reduce incident light intensity, enhancing the sensor's ability to detect low irradiance targets amidst strong background illumination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a BSI image sensor uses a conventional single pixel design, then the structure is simple, but the quantum efficiency and dynamic range are insufficient for detecting low irradiance targets under strong background irradiance
Solution Approach 1:
The pixel array is segmented into two distinct types: high quantum efficiency pixels and high saturation level pixels. Each pixel type is independently optimized with specific structures (metal grid with apertures for high QE pixels, blocking metal layer for high saturation pixels) to handle different irradiance conditions, thereby improving overall detection capability without requiring a completely new complex design
2Measurement precision
If high quantum efficiency pixels with metal grid structure and apertures are used, then the signal-to-noise ratio is improved, but the saturation level is reduced for high irradiance targets
Solution Approach 1:
Different local structures are applied to different pixel types based on their specific functions: high quantum efficiency pixels use metal grid structures with apertures optimized for low irradiance detection with high signal-to-noise ratio, while high saturation level pixels use blocking metal layers optimized for high irradiance detection. Each pixel type has locally optimized properties matched to its detection requirements
3Illumination intensity
If high saturation level pixels with blocking metal layer are used, then the dynamic range is improved, but the quantum efficiency is reduced for low irradiance targets
Solution Approach 1:
The blocking metal layer in high saturation level pixels is locally optimized to provide appropriate light attenuation for high irradiance conditions while maintaining sufficient quantum efficiency. The layer's thickness and material properties are specifically tuned to achieve the right balance between saturation prevention and light detection efficiency
4Adaptability or versatility
If the image sensor detects both low and high irradiance targets, then the versatility is improved, but the device complexity increases due to multiple pixel types
Solution Approach 1:
The pixel array is divided into two functional segments that can be independently optimized and manufactured. This segmentation allows each pixel type to be designed for its specific detection range (low or high irradiance) while maintaining overall system versatility through the combination of both types in the same sensor array
Solution Approach 2:
Both high quantum efficiency pixels and high saturation level pixels are integrated into the same image sensor device, creating a multi-functional system that can detect targets across a wide range of irradiance conditions. The universal platform supports multiple detection modes within a single 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 configuration improves the image sensor's quantum efficiency and dynamic range, enabling effective detection of targets with a wide range of illumination intensities by optimizing both signal-to-noise ratio and saturation levels.
Implementation Method 1
an array of pixels that absorb (e.g., sense) the incoming radiation and convert it into electrical signals
Implementation Method 2
high saturation level pixels with a blocking metal layer to reduce incident light intensity
Implementation Method 3
pixels that absorb (e.g., sense) the incoming radiation and convert it into electrical signals
Data Source
AI summary
The present disclosure describes an image sensor device and a method for forming the same. The image sensor device can include a semiconductor layer. The semiconductor layer can include a first surface and a second surface. The image sensor device can further include an interconnect structure formed over the first surface of the semiconductor layer, first and second radiation sensing regions formed in the second surface of the semiconductor layer, a metal stack formed over the second radiation sensing region, and a passivation layer formed through the metal stack and over a top surface of the first radiation sensing region. The metal stack can be between the passivation layer and an other top surface of the second radiation sensing region.