Photodiode Impurity Gradient for Complete Charge Transfer
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Solution Overview
Problem
Conventional MOS solid-state image capturing elements face challenges in complete electric charge transfer due to low power supply voltage, leading to difficulties in signal charge reading from a wide photodiode area, which affects sensitivity and dynamic range, especially in applications requiring larger pixel sizes for cameras like monitoring and television telephone devices.
Innovation Solution
A solid-state image capturing element with a photodiode section comprising multiple impurity concentration regions, where the impurity concentration incrementally increases towards the transfer gate, facilitating easier electric charge transfer and enabling wider photodiode areas without signal charge residency, thus enhancing sensitivity and dynamic range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If the photodiode area is enlarged to improve sensitivity and dynamic range, then the light receiving capability is improved, but the electric charge transfer completeness deteriorates due to low power supply voltage
Solution Approach 1:
The patent applies local quality by creating multiple impurity concentration regions within the photodiode section, where each region has a different impurity concentration tailored to its specific function. The first region has higher impurity concentration to facilitate charge transfer, while the second region has lower impurity concentration to maintain photoelectric conversion efficiency, resolving the contradiction between large area and complete charge transfer.
Solution Approach 2:
The patent changes the impurity concentration parameter across different regions of the photodiode section. By varying the impurity concentration from the first region to the second region, the patent optimizes both the charge transfer capability and the photoelectric conversion efficiency, enabling large photodiode area to work effectively with complete charge transfer.
2Use of energy by moving object
If the power supply voltage is kept low to reduce power consumption, then the energy efficiency is improved, but the electric potential modulation under transfer gate deteriorates
Solution Approach 1:
The patent applies local quality by creating specific impurity concentration regions that enhance the electric potential modulation effect locally under the transfer gate. The first impurity concentration region with higher doping creates a stronger electric field in the charge transfer path, compensating for the low power supply voltage and enabling complete charge transfer without increasing overall power consumption.
Solution Approach 2:
The patent changes the impurity concentration parameter to optimize the electric potential modulation. By adjusting the impurity concentration in the first region, the patent enhances the electric field strength locally, allowing effective charge transfer at low power supply voltage, thus maintaining low power consumption while improving power delivery where needed.
3Area of moving object
If the pixel size is increased for monitoring and television telephone applications, then the image quality is improved, but the signal charge transfer difficulty increases
Solution Approach 1:
The patent applies segmentation by dividing the photodiode section into multiple impurity concentration regions. This segmentation allows each region to perform its specific function optimally: the first region facilitates charge transfer to the transfer gate, while the second region maintains photoelectric conversion. This resolves the charge transfer difficulty in large pixel sizes by creating a staged charge transfer path.
Solution Approach 2:
The patent applies local quality by optimizing different regions of the large pixel structure with different impurity concentrations. The first region has higher impurity concentration to aid charge transfer across the larger distance, while the second region has lower concentration for efficient photoelectric conversion, enabling large pixel size to achieve both good image quality and easy charge transfer.
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 allows for efficient electric charge transfer even with enlarged photodiode areas, improving sensitivity and dynamic range, enabling effective image capture in devices with larger pixel sizes, such as monitoring and television telephone cameras.
Implementation Method 1
a photodiode section (4), constituted of a plurality of one conductivity type regions with successively different impurity concentrations, for complete electric charge transferring
Implementation Method 2
a potential inclination is provided towards the transfer gate with the plurality of impurity regions of incrementally changing impurity concentrations
Data Source
AI summary
A solid-state image capturing element according to the present invention includes a one conductivity type semiconductor substrate; an opposite conductivity type well region formed on the one conductivity type semiconductor substrate; a photodiode section formed on the opposite conductivity type well region, constituted of a plurality of one conductivity type regions with successively different impurity concentrations for complete electric charge transferring; a one conductive drain region capable of reading out signal charges from the photodiode section; and a transfer gate formed above a substrate between the one conductivity drain region and the photodiode section.