Image Sensor Blue Light Absorption Depth Control
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Solution Overview
Problem
Conventional photoelectric conversion image sensors using organic material devices react poorly with blue and red light, leading to noise in photoelectric conversion current and color distortion in captured images due to changes in external quantum efficiency with bias voltage.
Innovation Solution
The image sensor design includes a first transparent electrode layer, an active layer, and a second transparent electrode layer, with specific refractive index and thickness conditions, and an optical buffer layer to absorb blue light within a depth of 1/5 of the active layer's thickness from both surfaces, along with a P-type doping layer and hole transport layer, to stabilize photoelectric conversion current across varying bias voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional organic photoelectric conversion devices are used, then the device structure is simple, but the external quantum efficiency changes with bias voltage causing color distortion
Solution Approach 1:
The photoelectric conversion device is divided into multiple functional layers including a first transparent electrode layer, an active layer, and a second transparent electrode layer. Each layer has specific thickness and refractive index requirements to control light absorption at different depths, thereby stabilizing the external quantum efficiency across varying bias voltages.
Solution Approach 2:
The patent applies different refractive indices and thicknesses to specific layers to achieve localized optical control. The first transparent electrode layer has a refractive index and thickness satisfying 120N-(30-5N) ≤ refractive index × thickness ≤ 120N+(30-5N), while the active layer has optimized thickness to absorb blue light within 1/5 of its total thickness from both surfaces.
2Productivity
If the active layer thickness is increased to improve light absorption, then the absorption efficiency improves, but the blue light absorption depth increases causing noise
Solution Approach 1:
The patent optimizes the active layer thickness and the refractive index-thickness product of the first transparent electrode layer to control the absorption depth of blue light. By satisfying specific parameter ranges, blue light is absorbed within 1/5 of the active layer thickness from both surfaces, maintaining high absorption efficiency while preventing excessive penetration that would cause noise.
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 configuration reduces the impact of bias voltage changes on photoelectric conversion current, minimizing color distortion and maintaining consistent image quality across varying ambient light intensities.
Implementation Method 1
The first transparent electrode layer and the optical buffer layer may satisfy: 120N−(30−5N)≦refractive index of first transparent electrode layer×thickness (nm) of first transparent electrode layer+refractive index of optical buffer layer×thickness (nm) of optical buffer layer≦120N+(30−5N), wherein N is a natural number
Implementation Method 2
light having a wavelength of about 440 nm-480 nm is absorbed within a depth of about 1⁄5 of an entire thickness of the active layer from both the top and bottom surfaces of the active layer
Implementation Method 3
The image sensor separates incident light into three primary colors of red, green, and blue, and converts each of them into an electrical signal. The image sensor may also sense light by using a photodiode reacting with one of the three primary colors.
Data Source
AI summary
A photoelectric conversion device of an image sensor includes a first transparent electrode layer, an active layer, and a second transparent electrode layer, which are sequentially stacked. A light having a wavelength of about 440 nm-480 nm is absorbed within a depth of about ⅕ of an entire thickness of the active layer from both the top and bottom surfaces of the active layer.