Image Sensor Contact Resistance Reduction via Area Variation
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Solution Overview
Problem
Contact resistance in image sensors can lead to diminished device performance and potential failure due to non-optimized electrical contacts, particularly in high-resolution and low-power consumption applications where material compatibility and charge carrier density are critical.
Innovation Solution
The solution involves varying the cross-sectional area of electrical contacts to reduce contact resistance, with specific examples including P+ contacts coupled to a grounding metal layer and the use of silicide layers to enhance contact interface properties, and varying the size and extent of electrical contacts to optimize contact resistance across semiconductor-metal junctions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If electrical contacts are optimized for specific performance requirements, then contact resistance is reduced and device performance is improved, but device complexity increases due to tailored material choices and dimensional variations
Solution Approach 1:
The patent applies local quality by varying the cross-sectional area of electrical contacts at different locations within the image sensor. Specifically, electrical contacts in the pixel array region have different dimensions compared to those in the lens array region, allowing each area to be optimized for its specific functional requirements while managing contact resistance effectively
Solution Approach 2:
The patent implements parameter changes by modifying the cross-sectional area dimensions of electrical contacts based on their location. The contact cross-sectional area is adjusted as a variable parameter to optimize electrical performance in different regions of the image sensor, balancing reliability improvement with controlled complexity
2Measurement precision
If higher resolution is achieved through miniaturization, then image sensor performance is improved, but contact resistance becomes more critical and harder to optimize
Solution Approach 1:
The patent addresses the miniaturization challenge by implementing local quality variations in contact dimensions. Different regions of the image sensor (pixel array vs. lens array) receive contacts with cross-sectional areas tailored to their specific resolution and electrical performance requirements, allowing optimization despite overall device miniaturization
Solution Approach 2:
The patent resolves the miniaturization-contact resistance contradiction by introducing dimensional variation in the vertical cross-sectional area of contacts. Rather than uniformly scaling all contacts down with miniaturization, the invention varies contact dimensions in the cross-sectional plane to maintain adequate electrical performance while achieving higher resolution through reduced pixel pitch
Data Source
AI summary
An image sensor includes a plurality of photodiodes disposed in a semiconductor material and a floating diffusion disposed in the semiconductor material adjacent to a photodiode in the plurality of photodiodes. A transfer gate is disposed to transfer image charge generated in the photodiode into the floating diffusion. A first electrical contact with a first cross sectional area is coupled to the transfer gate. A second electrical contact with a second cross sectional area is coupled to the floating diffusion, and the second cross sectional area is greater than the first cross sectional area. The image sensor also includes pixel transistor region disposed in the semiconductor material including a first electrical connection to the semiconductor material. A third electrical contact with a third cross sectional area is coupled to the first electrical connection to the semiconductor material, and the third cross sectional area is greater than the first cross sectional area.