Image Sensor Reflection Structure for Higher Pixel Quantum Efficiency
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Solution Overview
Problem
As semiconductor image sensors shrink and pixels become more densely spaced, the amount of light incident on each pixel decreases, leading to reduced quantum efficiency (QE) and image quality, necessitating a solution to enhance photon detection without compromising image quality.
Innovation Solution
Incorporating a reflection component, such as an air gap or alternating layers of silicon nitride with different refractive indices, on the opposite side of the light sensing element to redirect incident light back towards the pixel, thereby increasing the quantum efficiency by leveraging the refractive index difference between materials like silicon and air or silicon nitride.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pixels are densely spaced to increase resolution, then image resolution is improved, but the amount of incident light per pixel decreases leading to reduced quantum efficiency
Solution Approach 1:
The patent converts the harmful effect of light loss at the back surface into a beneficial reflection mechanism. By introducing a reflection component (air gap or alternating refractive index layers) at the back surface, previously lost light is now reflected back through the light sensing element, transforming the harmful light absorption into useful signal enhancement and resolving the quantum efficiency degradation caused by pixel densification
Solution Approach 2:
The patent adds a dimensional solution by introducing a back surface reflection component perpendicular to the traditional front surface light entry. This back-illuminated architecture with reflection creates an additional optical path dimension, allowing light to traverse the sensing element twice (forward and reflected backward), thereby compensating for reduced incident light in densely packed pixels
2Use of energy by moving object
If a reflection component is added to increase quantum efficiency, then light detection is improved, but device complexity increases
Solution Approach 1:
The patent implements reflection functionality through parameter changes in the back surface structure - specifically using either an air gap (changing the refractive index parameter) or alternating layers of materials with different refractive indices (changing the optical parameter profile). These parameter modifications create natural optical reflection without requiring complex mechanical or electronic components, thus improving quantum efficiency while maintaining relatively simple device structure
Solution Approach 2:
The patent uses composite material structures (alternating layers of high and low refractive index materials such as silicon nitride and silicon oxide) to achieve enhanced reflection. This composite approach at the back surface creates effective optical reflection through material property variations rather than complex geometric structures, balancing improved light detection with manageable device complexity
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 reflection component effectively enhances the quantum efficiency of the semiconductor image sensor, improving image quality by increasing the amount of light available for detection, particularly in pixels sensitive to green light, which the human eye detects at a higher rate, and helps account for manufacturing variations near the edges of the sensor.
Implementation Method 1
a reflection structure between the interconnect and the photodiode, wherein the reflection structure is configured to reflect light passing through the photodiode back toward the photodiode
Implementation Method 2
leveraging the refractive index difference between materials like silicon and air or silicon nitride
Data Source
AI summary
A semiconductor image sensor includes a pixel. The pixel includes a first substrate; and a photodiode in the first substrate. The semiconductor image sensor further includes an interconnect structure electrically connected to the pixel. The semiconductor image sensor further includes a reflection structure between the interconnect and the photodiode, wherein the reflection structure is configured to reflect light passing through the photodiode back toward the photodiode.