Image Sensor Overflow Charge Storage for Dynamic Range and Leakage Control
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Solution Overview
Problem
Current image sensors face challenges in effectively managing and reading out electric charge overflowing from photoelectric conversion layers, leading to limitations in dynamic range and increased leakage of electrical charge.
Innovation Solution
The proposed image sensor design includes a substrate with a photoelectric conversion layer, an isolation film, a storage conductive pattern, a transfer gate, and impurity-injected areas to store and read out electric charge, utilizing a capacitor and transfer transistor to manage and store charges, allowing for expanded dynamic range without charge loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional photoelectric conversion layer is used without additional storage structures, then the device complexity is low, but the dynamic range is limited and charge leakage occurs
Solution Approach 1:
The photoelectric conversion layer is divided into multiple regions with different impurity concentrations (first and second impurity-injected areas), creating specialized zones for charge storage and transfer. This segmentation allows different functional areas to handle charge management tasks, improving retention while maintaining manageable complexity through functional division
Solution Approach 2:
The patent implements a nested structure where the storage conductive pattern is embedded within the isolation film, which itself is integrated with the substrate and photoelectric conversion layer. This nesting approach allows multiple functional elements to occupy overlapping spatial volumes, increasing effective storage capacity without proportionally increasing overall device footprint or complexity
2Quantity of substance
If the photoelectric conversion layer is enlarged to capture more light, then the light sensitivity improves, but the charge leakage increases
Solution Approach 1:
Different regions of the photoelectric conversion layer are doped with different impurity concentrations to create localized functional zones. The first impurity-injected area has higher doping concentration for efficient charge collection, while the second area has lower concentration to reduce leakage. This local quality variation allows the layer to simultaneously achieve high light capture and low charge loss in different spatial regions
Solution Approach 2:
The isolation film acts as an intermediary barrier between the photoelectric conversion layer and the storage conductive pattern. It provides electrical isolation that prevents direct charge leakage paths while still allowing the system to function as an integrated unit. This intermediary structure enables the photoelectric conversion layer to be enlarged for better light capture without proportionally increasing charge leakage
3Productivity
If impurity injection is increased to improve charge collection, then the charge transfer efficiency improves, but the charge leakage also increases
Solution Approach 1:
The patent applies different impurity injection levels to different spatial regions: the first impurity-injected area receives higher concentration doping to maximize charge collection and transfer efficiency, while the second impurity-injected area receives lower concentration doping to minimize leakage. This localized quality differentiation resolves the contradiction by optimizing each region for its specific function rather than applying a uniform doping strategy
Solution Approach 2:
The photoelectric conversion layer is segmented into multiple impurity-injected areas with distinct doping characteristics. This segmentation allows the system to achieve high overall charge transfer efficiency through the first area while the second area contributes to leakage reduction, demonstrating how functional division can simultaneously optimize competing performance metrics
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 design enhances the dynamic range of image sensors by effectively storing and reading out electric charge, reducing leakage and improving overall image signal processing efficiency.
Implementation Method 1
The photodiode converts incident light into an electrical signal
Implementation Method 2
a capacitor configured to receive the second electric charge from the photoelectric conversion layer and store the second electric charge
Data Source
AI summary
An image sensor, which stores electric charge overflowing from a photoelectric conversion layer, includes: (1) a substrate including a first surface and a second surface, which is opposite to the first surface and upon which light is incident, (2) a photoelectric conversion layer in the substrate, (3) an isolation film disposed on the substrate, along the photoelectric conversion layer, (4) a storage conductive pattern disposed in the isolation film, (5) a transfer gate disposed on a first surface of the substrate, (6) a first impurity-injected area disposed between the photoelectric conversion layer and the isolation film, and (7) a second impurity-injected area disposed on the first surface of the substrate and connected to the transfer gate. The first and second impurity-injected areas are electrically connected.