CMOS Image Sensor NIR QE Enhancement via Dielectric Structures
Find Innovative SolutionsGenerate Solutions
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 can absorb NIR light are often expensive, toxic, or have lower sensitivity to the visible spectrum.
Innovation Solution
Incorporating NIR quantum efficiency (QE) enhancement structures, such as trench-shaped dielectric elements with a refractive index lower than the semiconductor material, into the photodiodes to modify incident light through diffraction, deflection, and reflection, improving optical sensitivity and modulation transfer function (MTF) without increasing semiconductor thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the semiconductor thickness is increased to improve NIR light absorption, then NIR quantum efficiency is improved, but fabrication complexity increases and device performance may deteriorate
Solution Approach 1:
The patent changes the refractive index parameter by introducing dielectric materials with lower refractive indices than the semiconductor substrate. This parameter change enables enhanced NIR light absorption through optical effects (diffraction, deflection, reflection) rather than relying on increased thickness, thus improving NIR quantum efficiency without increasing fabrication complexity
Solution Approach 2:
The patent introduces dielectric materials as intermediary elements between the incident NIR light and the semiconductor photodiode. These dielectric structures (trenches, holes, or layers) act as mediators that modify light propagation through diffraction, deflection, and reflection, enabling improved NIR absorption without requiring thicker semiconductors
2Reliability
If conventional semiconductor materials are used, then fabrication is simpler, but NIR light absorption is poor
Solution Approach 1:
The patent creates a composite structure combining semiconductor material with dielectric materials having lower refractive indices. This composite approach enables enhanced NIR absorption through the optical properties of the dielectric-semiconductor interface while maintaining compatibility with conventional semiconductor fabrication processes
Solution Approach 2:
The patent modifies the optical parameters of the structure by introducing materials with different refractive indices. This parameter change enables the conventional semiconductor to achieve poor NIR absorption performance through optical effects at the dielectric-semiconductor interface, without requiring exotic or difficult-to-fabricate materials
3Reliability
If materials capable of detecting NIR light are used, then NIR sensitivity is improved, but cost increases and visible spectrum sensitivity decreases
Solution Approach 1:
The patent applies local quality enhancement by introducing dielectric structures only in specific locations (trenches, holes, or layers at the illuminated surface) rather than changing the entire semiconductor material. This localized approach enhances NIR sensitivity through optical effects while maintaining the cost-effective and visible-spectrum-sensitive properties of conventional semiconductor materials in the bulk
Solution Approach 2:
The patent changes the local optical parameters (refractive index) at the illuminated surface through dielectric structures, enabling improved NIR sensitivity without changing the bulk semiconductor material. This avoids the need for expensive exotic materials while maintaining visible spectrum sensitivity and fabrication cost-effectiveness
4Reliability
If dielectric structures are added to enhance NIR absorption, then NIR quantum efficiency is improved, but device complexity increases
Solution Approach 1:
The patent segments the dielectric enhancement into discrete, simple geometric structures (trenches, holes, or thin layers) rather than complex continuous structures. This segmentation enables NIR quantum efficiency enhancement through optical effects while keeping each individual structure simple and the overall device complexity manageable
Solution Approach 2:
The patent achieves NIR enhancement by changing optical parameters (refractive index contrast) rather than structural parameters (thickness). This parameter change approach enables improved NIR quantum efficiency with simple geometric dielectric structures, avoiding the need for complex multi-layer or graded-index structures
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 enhances NIR light sensitivity and maintains or improves MTF by redistributing incident light within the photodiode, increasing NIR QE from approximately 15% to 40% at 850 nm and from 11% to 34% at 940 nm, while maintaining sensitivity to red, blue, and green light.
Implementation Method 1
modify incident light by at least one of diffraction, deflection and reflection
Implementation Method 2
modify incident light by at least one of diffraction, deflection and reflection
Implementation Method 3
trench-shaped dielectric elements with a refractive index lower than the semiconductor material
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; and a near infrared (NIR) quantum efficiency (QE) and modulation transfer function(MTF) enhancement structure. The NIR QE and MTF enhancement structure comprises: a NIR QE enhancement sub-structure comprising at least one NIR QE enhancement elements within a photosensitive region of the photodiode, wherein the NIR QE enhancement sub-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 optical sensitivity, including NIR light sensitivity, of the image sensor; and a MTF enhancement sub-structure disposed on the non-illuminated surface of the semiconductor material, facing toward the NIR QE enhancement sub-structure, wherein the MTF enhancement structure has a geometry corresponding to the NIR QE enhancement sub-structure, to ensure the incident light is still within the photodiode after redistribution.