CMOS Image Sensor NIR Quantum Efficiency via Dielectric Structures
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Solution Overview
Problem
Conventional image sensors poorly absorb near-infrared (NIR) light due to the band structure of semiconductor materials, leading to reduced performance and increased complexity in fabrication, and materials that effectively absorb NIR light are often expensive, toxic, or less sensitive to the visible spectrum.
Innovation Solution
The implementation of NIR quantum efficiency (QE) enhancement structures, comprising trench-shaped dielectric elements with a refractive index lower than the semiconductor material, arranged in a periodic pattern within the photodiodes to modify and redistribute incident light through diffraction, deflection, and reflection, enhancing optical sensitivity for NIR light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional semiconductor materials are used, then visible spectrum sensitivity is maintained, but near-infrared light absorption is poor
Solution Approach 1:
The patent modifies optical parameters by introducing periodic dielectric structures with specific refractive indices (lower than semiconductor material) to change how NIR light interacts with the semiconductor. This allows conventional semiconductor materials to absorb NIR light effectively without changing the material composition, thus maintaining ease of manufacture while improving NIR sensitivity
Solution Approach 2:
The patent introduces dielectric structures as intermediary elements between the incident NIR light and the semiconductor material. These dielectric structures with lower refractive indices act as optical mediators that enhance light absorption in the semiconductor, resolving the contradiction between maintaining material simplicity and achieving improved NIR sensitivity
2Reliability
If additional semiconductor thickness is added to absorb NIR light, then NIR absorption improves, but fabrication complexity increases and performance may degrade
Solution Approach 1:
Instead of changing the thickness parameter of the semiconductor, the patent changes optical interaction parameters by introducing periodic dielectric structures. This allows achieving enhanced NIR absorption without modifying the semiconductor thickness, thereby avoiding increased fabrication complexity and potential performance degradation
Solution Approach 2:
The patent transitions from solving the NIR absorption problem in the thickness dimension to solving it in the optical interaction dimension through periodic dielectric structures. This dimensional shift allows achieving better NIR absorption without increasing semiconductor thickness or complicating fabrication processes
3Reliability
If materials conductive to absorb NIR light are used, then NIR sensitivity improves, but cost increases and visible spectrum sensitivity may decrease
Solution Approach 1:
The patent changes the optical parameters of conventional semiconductor materials through the introduction of periodic dielectric structures, allowing these materials to achieve enhanced NIR absorption without switching to expensive specialized materials. This maintains cost-effectiveness while improving NIR sensitivity
Solution Approach 2:
The patent makes conventional semiconductor materials multi-functional by enabling them to effectively absorb both visible spectrum light (maintaining original function) and NIR light (enhanced function) through the periodic dielectric structures. This eliminates the need for expensive specialized materials and achieves universal light absorption capability
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
Significantly improves NIR light sensitivity by increasing quantum efficiency from approximately 15% to 40% for 850 nm wavelength and from 11% to 34% for 940 nm wavelength, while maintaining sensitivity to red, blue, and green light, without complicating fabrication or increasing toxicity.
Implementation Method 1
modify and redistribute incident light through diffraction, deflection, and reflection
Implementation Method 2
modify and redistribute incident light through diffraction, deflection, and reflection
Implementation Method 3
CMOS image sensor having enhanced near infrared quantum efficiency
Data Source
AI summary
An image sensor comprises a semiconductor material having an illuminated surface and a non-illuminated surface; a photodiode formed in the semiconductor material extending from the illuminated surface to receive an incident light through the illuminated surface, wherein the received incident light generates charges in the photodiode; a transfer gate electrically coupled to the photodiode to transfer the generated charges from the photodiode in response to a transfer signal; a floating diffusion electrically coupled to the transfer gate to receive the transferred charges from the photodiode; a near infrared (NIR) quantum efficiency (QE) enhancement structure comprising at least two NIR QE enhancement elements within a region of the photodiode, wherein the NIR QE enhancement structure is configured to modify the incident light at the illuminated surface of the semiconductor material by at least one of diffraction, deflection and reflection, to redistribute the incident light within the photodiode to improve an optical sensitivity, including near-infrared light sensitivity, of the image sensor.