Metal Pixel Separation Pattern for Dark Current Reduction
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Solution Overview
Problem
Conventional image sensors face challenges in efficiently separating and processing incident light due to high electrical resistance in polysilicon-based pixel separation patterns, leading to increased dark currents and reduced manufacturing efficiency as the aspect ratio of deep trenches increases.
Innovation Solution
The use of a low resistive metallic conductive pattern, such as titanium nitride or tungsten, replaces polysilicon in the pixel separation pattern, allowing stable application of negative bias and minimizing dark currents, while the trapezoidal shape of the separation pattern enhances light reception area and image sensor efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polysilicon-based pixel separation pattern is used, then manufacturing process is conventional and simple, but electrical resistance is high causing increased dark currents
Solution Approach 1:
The patent changes the material parameter from polysilicon to metal (such as titanium nitride or tungsten), fundamentally altering the electrical resistance characteristic. This material substitution enables low resistance in the pixel separation pattern while maintaining compatibility with conventional semiconductor manufacturing processes through established metal deposition techniques.
Solution Approach 2:
The pixel separation pattern is formed as a composite structure combining metal material with the semiconductor substrate. This composite approach allows the metal to provide low electrical resistance for dark current suppression while integrating seamlessly with the surrounding polysilicon-based pixel structures through conventional fabrication processes.
2Reliability
If deep trenches are used for pixel separation, then pixel isolation is improved, but aspect ratio increases reducing manufacturing efficiency
Solution Approach 1:
The patent changes the resistivity parameter of the separation pattern material from high (polysilicon) to low (metal). This parameter change allows shallower trenches to achieve the same level of pixel isolation, thereby reducing the aspect ratio and improving manufacturing efficiency without compromising isolation performance.
3Reliability
If negative bias is applied to pixel separation pattern, then dark currents are reduced, but stable bias application is difficult with polysilicon
Solution Approach 1:
The patent changes the electrical resistance parameter by substituting metal for polysilicon in the pixel separation pattern. This parameter change enables stable negative bias application because the low resistance metal material can effectively conduct and maintain the bias voltage, overcoming the instability inherent in high-resistance polysilicon-based separation patterns.
4Area of stationary object
If conventional pixel separation pattern is used, then manufacturing is simple, but light reception area is reduced
Solution Approach 1:
The patent changes the material parameter to metal with different optical and electrical properties. This enables the pixel separation pattern to be formed with smaller cross-sectional area while maintaining effective isolation, thereby increasing the light reception area of each pixel without significantly complicating the manufacturing process.
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 solution effectively reduces dark currents and improves image quality by stabilizing the negative bias application and increasing the light reception area, enhancing the efficiency of the image sensor module.
Implementation Method 1
a photoelectric converter in a pixel area of the substrate and generating photoelectrons in response to an incident light that is incident onto the pixel area
Implementation Method 2
an insulation pattern having a refractive index smaller than that of the substrate
Data Source
AI summary
An image sensor includes a photoelectric converter in a pixel area of a substrate to generate photoelectrons in response to an incident light that is incident onto the pixel area, a signal generator on a first surface of the substrate in the pixel area to generate electric signals corresponding to image information of an object in accordance with the photoelectrons, and a pixel separation pattern penetrating through the substrate from the first surface of the substrate to a second surface of the substrate opposite to the first surface of the substrate, the pixel separation pattern including an insulation pattern having a refractive index smaller than that of the substrate and a metallic conductive pattern enclosed by the insulation pattern, and the pixel area being enclosed by the pixel separation pattern and isolated from a neighboring pixel area.