Deep Trench Isolation Passivation for Pixel Sensor Crosstalk
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Solution Overview
Problem
Optical crosstalk between adjacent pixel sensors in a CMOS image sensor array degrades spatial resolution, sensitivity, and increases dark current, noise, and color mixing, due to photons passing through deep trench isolation (DTI) structures.
Innovation Solution
A boron layer is formed as a passivation layer in a recess of the DTI structure, creating a boron-silicon interface that reduces photon transmission by forming strong chemical bonds with silicon, thereby minimizing optical crosstalk through its heterojunction properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If deep trench isolation structures are used to isolate pixel sensors, then optical crosstalk between adjacent pixels is reduced, but photons can still pass through the DTI structure causing residual optical crosstalk
Solution Approach 1:
The patent applies composite materials by forming a multi-layer structure consisting of a first dielectric material layer and a second dielectric material layer within the deep trench isolation structure. The second dielectric material has different optical properties (refractive index) than the first, creating a composite structure that reduces photon transmission more effectively than a single material layer. This composite approach directly addresses the residual optical crosstalk problem by combining materials with complementary optical characteristics to block photons that penetrate the first layer.
Solution Approach 2:
The patent implements local quality by positioning the second dielectric material layer specifically at regions where photon penetration is most problematic. The alternating layer structure creates localized optical property variations within the DTI structure, with each layer configured to address specific optical transmission pathways. This localized optimization allows the structure to effectively block photons in critical areas while maintaining the overall isolation function.
2Measurement precision
If deep trench isolation structures are used to increase photon absorption in pixel sensors, then spatial resolution is improved, but dark current and image noise increase
Solution Approach 1:
The alternating dielectric material layers create a composite structure with optimized optical and electrical properties. The different dielectric materials have varying electrical characteristics that can be selected to minimize dark current generation at the interfaces, while their optical characteristics (refractive index differences) enhance photon absorption in the pixel sensor. This composite approach allows simultaneous optimization of both spatial resolution and noise reduction.
Solution Approach 2:
The patent changes material parameters by selecting dielectric materials with specific refractive indices and electrical properties. By adjusting the optical parameters (refractive index contrast between layers) and electrical parameters (dielectric constant, charge trapping characteristics) of the alternating layers, the structure achieves enhanced photon absorption while controlling dark current generation. The thickness and composition of each layer are optimized to balance optical and electrical performance.
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 boron-silicon interface effectively reduces optical crosstalk, enhancing spatial resolution, sensitivity, and optical responsivity while decreasing dark current and image noise in the CMOS image sensor.
Implementation Method 1
A boron layer is formed as a passivation layer in a recess of the DTI structure, creating a boron-silicon interface that reduces photon transmission by forming strong chemical bonds with silicon
Implementation Method 2
creating a boron-silicon interface that reduces photon transmission by forming strong chemical bonds with silicon, thereby minimizing optical crosstalk through its heterojunction properties
Data Source
AI summary
A boron layer may be formed as a passivation layer in a recess in which a deep trench isolation structure (DTI) structure is to be formed. The boron layer results in formation of a boron-silicon interface between the DTI structure and a photodiode of a pixel sensor included in a pixel array. The boron-silicon interface functions as a diode junction, which resists penetration of photons into the DTI structure. This reduces and/or minimizes photon transmission through the DTI structure, which reduces and/or minimizes optical crosstalk between pixel sensors of the pixel array.