Carbon Nanotube Transparent Conductive Coating for Backside Illuminated Image Sensors
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Solution Overview
Problem
Backside illuminated image sensors face challenges with traditional Tin doped Indium Oxide (ITO) transparent conductive coatings, including high thermal processing requirements that can degrade the sensor, mechanical fragility of thinned substrates, and increasing costs, which affect the fill factor and reliability of the image sensor.
Innovation Solution
A carbon nanotube transparent conductive coating is applied using a low-temperature process, providing flexibility and acting as a wavelength-selective optical filter to enhance the image sensor's performance while maintaining high transparency and electrical conductivity, potentially replacing ITO coatings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ITO transparent conductive coating is used on BSI image sensor, then electrical conductivity and transparency are improved, but thermal processing requirements cause substrate degradation and increase manufacturing complexity
Solution Approach 1:
The patent changes the material composition from ITO to a composite of transparent resin and conductive particles (silver, aluminum, or carbon). This parameter change allows the coating to achieve the required electrical conductivity without requiring high-temperature annealing processes, thereby eliminating thermal degradation of the thinned substrate while maintaining the necessary transparent conductive properties.
Solution Approach 2:
The patent employs a composite material system consisting of transparent resin combined with conductive particles (silver particles, aluminum particles, or carbon particles). This composite approach enables the coating to simultaneously provide electrical conductivity, optical transparency, and mechanical flexibility without the thermal processing requirements of conventional ITO, thus resolving the contradiction between conductivity and thermal stability.
2Reliability
If ITO transparent conductive coating is applied, then uniform voltage bias is achieved, but the coating rigidity stresses the thinned substrate
Solution Approach 1:
The patent replaces rigid ITO with a flexible composite coating comprising transparent resin and conductive particles. This flexible thin film can accommodate the mechanical stresses and deformations of the thinned substrate without causing stress concentration or cracking, while still maintaining uniform electrical contact across the substrate surface for consistent voltage bias distribution.
3Productivity
If substrate is thinned to reduce optical absorption, then fill factor is improved, but mechanical fragility increases
Solution Approach 1:
The flexible composite transparent conductive coating acts as a protective layer on the thinned substrate. The resin matrix and particle composition provide mechanical reinforcement that compensates for the reduced substrate thickness, preventing cracking and damage during handling and processing while maintaining the high fill factor achieved through substrate thinning.
4Reliability
If ITO coating is used, then transparent conductive properties are achieved, but manufacturing cost increases
Solution Approach 1:
The patent replaces expensive ITO materials and complex vacuum sputtering processes with a cost-effective composite formulation using readily available transparent resins and conductive particles (silver, aluminum, or carbon). The coating can be applied using simple dip-coating or spin-coating methods, eliminating the need for expensive vacuum equipment and reducing manufacturing costs while achieving comparable or superior transparent conductive properties.
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 carbon nanotube coating improves the reliability and efficiency of the image sensor by reducing thermal stress on the substrate, maintaining high transparency, and offering flexibility, which enhances the sensor's ability to detect visible light while filtering out deleterious wavelengths like infrared, thus improving the signal-to-noise ratio and fill factor.
Implementation Method 1
The image sensor is designed to detect visible light... the carbon nanotube transparent conductive coating has characteristics selected so that the coating is at least semi-transparent to each wavelength of visible light that the image sensor is designed to detect
Implementation Method 2
The carbon nanotube transparent conductive coating may also have characteristics selected so that the carbon nanotube transparent conductive coating acts as a wavelength selective optical filter to filter wavelengths of light that degrade performance of the image sensor, such as infrared light
Data Source
AI summary
A backside illuminated image sensor has a carbon nanotube transparent conductive coating formed on the backside of the image sensor. In one implementation the carbon nanotube transparent conductive coating acts as a wavelength selective filter to filter out infrared light. In one implementation the carbon nanotube transparent conductive coating has an optical transparency between 50% and 80% for blue and green color bands.