CMOS Image Sensor Passivation Layer Exposure for Light Sensitivity
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Solution Overview
Problem
CMOS image sensors suffer from reduced sensitivity due to the high photon absorption and refraction effects caused by silicon nitride passivation layers, which reduce the amount of incident light reaching the photosensing elements.
Innovation Solution
The passivation layer is selectively omitted from the main pixel array region of the CMOS image sensor, allowing incident light to reach the photosensing elements without absorption and refraction, while still providing protection in the control circuit and pad regions using a silicon nitride layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a silicon nitride passivation layer is used to protect internal circuits from environmental effects, then reliability is improved, but sensitivity deteriorates due to high photon absorption and refraction
Solution Approach 1:
The device is divided into different regions with different passivation layer configurations: the pixel array region has no passivation layer to maximize light sensitivity, while the circuit region has a passivation layer for protection. This spatial segmentation resolves the contradiction by applying protection only where needed without compromising optical performance.
Solution Approach 2:
Different regions of the device are given different properties: the pixel region is kept exposed for optimal light detection, while the circuit region is protected by the passivation layer. This local differentiation allows each region to have the quality it needs without compromising the other.
2Reliability
If a passivation layer is formed over the entire device, then protection is improved, but light transmission deteriorates
Solution Approach 1:
The passivation layer coverage is segmented to be present only in the circuit region and absent in the pixel array region. This selective segmentation allows protection where electronics are located while maintaining full light transmission where photosensing occurs.
Solution Approach 2:
The passivation layer is extracted or removed from the pixel array region where it would interfere with light transmission. This extraction eliminates the harmful optical effects in the critical light-receiving area while preserving protection in non-optical areas.
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 approach enhances the sensitivity of the image sensor by eliminating the absorption and refraction effects, resulting in improved light detection capabilities.
Implementation Method 1
Silicon nitride (SiN) has a higher photon absorption rate and a higher refractive index than other commonly used dielectric films such as silicon dioxide (SiO2). As a result, the amount of incident light 29 that reaches the photosensing elements 8 for detection by the sensor is reduced by absorption and refraction as the light passes through the passivation layer 19.
Implementation Method 2
Silicon nitride (SiN) has a higher photon absorption rate and a higher refractive index than other commonly used dielectric films such as silicon dioxide (SiO2). As a result, the amount of incident light 29 that reaches the photosensing elements 8 for detection by the sensor is reduced by absorption and refraction as the light passes through the passivation layer 19.
Data Source
AI summary
A CMOS image sensor with improved sensitivity includes a main pixel array region of an active pixel array region formed on a semiconductor substrate. A passivation layer is formed over the sensor, and it is at least partially removed from the main pixel array region, such that incident light being detected by the main pixel array does not pass through the passivation layer. Optical absorption and refraction caused by the material of the passivation layer are eliminated, resulting in an image sensor with improved optical sensitivity.