Infrared Sensor Pixel Isolation via Bandgap Segmentation
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Solution Overview
Problem
Infrared image sensors experience signal charge migration between adjacent pixels, leading to crosstalk and increased dark currents due to crystal defects, which existing technologies fail to effectively mitigate.
Innovation Solution
A photoelectric conversion device and imaging device design incorporating a light absorption layer with a compound semiconductor material, a first semiconductor layer of a higher bandgap energy, a second semiconductor layer of a different conductive type, and a diffusion region between pixels to form a p-n junction and depletion layer, electrically separating pixels and reducing dark currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a light absorption layer using compound semiconductor material is used for infrared detection, then infrared sensitivity is improved, but signal charges migrate between adjacent pixels causing crosstalk
Solution Approach 1:
The patent divides the semiconductor structure into multiple layers with different bandgap energies (first semiconductor layer with larger bandgap, second semiconductor layer with intermediate bandgap, and light absorption layer with smaller bandgap). This segmentation creates energy barriers that segment and contain signal charges within specific pixel regions, preventing migration between adjacent pixels while maintaining infrared sensitivity.
Solution Approach 2:
The patent introduces intermediate semiconductor layers with bandgap energies between the light absorption layer and the first semiconductor layer. These intermediary layers act as energy barriers that block signal charge migration while allowing infrared light to pass through to the absorption layer, thus serving as mediators that prevent harmful charge migration without compromising detection sensitivity.
2Device complexity
If conventional pixel structure is used, then device simplicity is maintained, but dark currents increase due to crystal defects
Solution Approach 1:
The patent changes the bandgap energy parameter across different semiconductor layers, creating a gradient from larger bandgap (first semiconductor layer) to intermediate bandgap (second semiconductor layer) to smaller bandgap (light absorption layer). This parameter change creates potential wells and barriers that confine carriers and reduce dark current generation from crystal defects while maintaining a relatively simple layered structure.
Solution Approach 2:
The patent employs a composite semiconductor structure consisting of multiple materials with different bandgap energies (e.g., InP, InGaAs, InAlAs layers). This composite material approach creates a heterostructure that reduces dark currents through band alignment effects while maintaining structural simplicity and compatibility with existing infrared detection technology.
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 solution effectively restrains signal charge migration between pixels and reduces dark currents, enhancing the signal-to-noise ratio and sensitivity of the imaging device.
Implementation Method 1
This light absorption layer absorbs infrared light to generate electrical charges, i.e., performs photoelectric conversion
Implementation Method 2
a junction of the first conductive type and the second conductive type (a p-n junction) is provided by the first semiconductor layer and the second semiconductor layer. This allows a depletion layer to be formed near between the semiconductor layers
Data Source
AI summary
A photoelectric conversion device includes: a light absorption layer that has a light entrance surface and a compound semiconductor material; a first electrode provided for each of the pixels, in opposed relation to an opposite surface to the light entrance surface; a first semiconductor layer of a first conductive type, with a bandgap energy larger than bandgap energy of the light absorption layer and that is provided between the light absorption layer and the first electrode; a second semiconductor layer of a second conductive type, with a bandgap energy larger than the bandgap energy of the light absorption layer and that is provided between the first semiconductor layer and the light absorption layer; and a first diffusion region of the second conductive type, in which the first diffusion region is provided between adjacent ones of the pixels and across the second semiconductor layer and the light absorption layer.