Photovoltaic Pixel Element Isolation for Crosstalk Reduction
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Solution Overview
Problem
Photovoltaic type pixels suffer from crosstalk, large temperature-dependent pixel signal variations, low low-illuminance sensitivity, and increased dark current due to the PN junction diode's characteristics, limiting dynamic range and image quality.
Innovation Solution
Incorporating element isolation regions between photoelectric conversion regions of adjacent pixels to block signal charge diffusion and using a combination of photovoltaic and accumulation type pixels with a PN junction diode, transfer gate, and floating diffusion to generate and process photovoltaic power, thereby suppressing crosstalk and enhancing sensitivity and signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If photovoltaic type pixels with PN junction diodes are used, then dynamic range is improved and saturation is avoided, but crosstalk occurs due to electron diffusion from N-type region to P-type substrate
Solution Approach 1:
An element isolation region is introduced as an intermediary structure between adjacent photovoltaic type pixels. This isolation region acts as a barrier that prevents electron diffusion from the N-type region of one pixel to the P-type substrate of an adjacent pixel, thereby eliminating crosstalk while preserving the photovoltaic effect and wide dynamic range capabilities of the original pixel structure.
2Adaptability or versatility
If photovoltaic type pixels are used, then saturation is avoided, but pixel signal voltage decreases markedly with temperature increase due to exponential increase in reverse saturated current
Solution Approach 1:
The patent introduces element isolation regions that modify the electrical parameters of the pixel structure by providing controlled isolation paths. This changes the current flow characteristics and reduces the temperature-dependent variations in pixel signal voltage while maintaining the photovoltaic power generation mechanism.
3Object-generated harmful factors
If element isolation regions are added to block electron diffusion, then crosstalk is suppressed, but device complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the semiconductor substrate into isolated pixel regions using element isolation regions. Each pixel is segmented from its neighbors by these isolation structures, which are formed as standardized regions between pixels. This segmentation approach systematically addresses crosstalk while maintaining manufacturing feasibility through regular, repeating patterns.
4Adaptability or versatility
If accumulation type operation is used, then saturation charge amount limits dynamic range, but photovoltaic type operation avoids saturation
Solution Approach 1:
The patent enables the pixel to function universally in both accumulation type and photovoltaic type operations. The same pixel structure with the added element isolation region can operate in accumulation mode for standard imaging or switch to photovoltaic mode for high dynamic range applications, providing multi-functionality without requiring separate dedicated pixel structures for each operation mode.
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 reduces crosstalk, improves low-illuminance sensitivity, and maintains image quality by isolating signal charges and utilizing dual pixel types, achieving a wider dynamic range and better signal-to-noise performance.
Implementation Method 1
photovoltaic power proportional to a logarithm of a photocurrent value depending on incident light 2 is generated by a PN junction diode 3
Implementation Method 2
element isolation region that is provided between the photoelectric conversion regions of adjacent pixels and in a state of substantially surrounding the photoelectric conversion region
Data Source
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AI summary
There is provided an imaging device that includes photovoltaic type pixels that have photoelectric conversion regions generating photovoltaic power for each pixel depending on irradiation light; and an element isolation region that is provided between the photoelectric conversion regions of adjacent pixels and in a state of substantially surrounding the photoelectric conversion region.