Vertical Transfer Gate for Global Shutter CMOS Image Sensors
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Solution Overview
Problem
Existing CMOS image sensors with global shutter systems require a reset period, which can limit their performance in capturing images with uniform exposure across all pixels.
Innovation Solution
The implementation of a vertical transfer gate in the image sensor that controls the transfer of charge from a light-sensing element to a storage diode and then to a floating diffusion region, allowing for simultaneous or sequential transfer signals to achieve global shutter operation without the need for separate gates, thereby reducing the area occupied on the substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a global shutter system is implemented using conventional structures, then simultaneous exposure across all pixels is achieved, but the device requires additional reset periods and larger substrate area
Solution Approach 1:
The patent merges the functions of multiple gates into a single transfer gate structure. The transfer gate is positioned to control charge transfer from both first and second charge storage regions to their respective floating diffusion regions, eliminating the need for separate gates and reducing overall device area while maintaining global shutter functionality
Solution Approach 2:
The transfer gate serves multiple functions simultaneously: it controls charge transfer from the first charge storage region to the first floating diffusion region, and also controls charge transfer from the second charge storage region to the second floating diffusion region. This multi-functional design reduces the number of components needed
2Ease of operation
If separate gates are used for each charge transfer path, then precise control is achieved, but the device complexity and area increase
Solution Approach 1:
The patent combines multiple gate functions into a single transfer gate. The transfer gate is strategically positioned to control charge transfer from both first and second charge storage regions, reducing device complexity while maintaining operational control through unified gate management
Solution Approach 2:
The transfer gate is divided into a first transfer gate portion and a second transfer gate portion, where each portion controls a specific charge transfer path. This segmentation allows precise control of individual transfer paths while using a unified gate structure, balancing control precision with device simplicity
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 solution enables efficient global shutter operation with reduced substrate area, improving image capture uniformity and integration capabilities, enhancing the performance of CMOS image sensors.
Implementation Method 1
a light-sensing element that generates charge in response to incident light
Implementation Method 2
a transfer gate at least partially buried under the top surface of the substrate, wherein the transfer gate controls the transfer of the charge from the storage diode to the floating diffusion region
Data Source
AI summary
An image sensor includes a light-sensing element that generates charge in response to incident light, a storage diode formed in a substrate, wherein the storage diode stores the charge generated by the light-sensing element, a floating diffusion region formed in a top surface of the substrate and spaced apart from the storage diode, and a transfer gate at least partially buried under the top surface of the substrate, wherein the transfer gate controls the transfer of the charge from the storage diode to the floating diffusion region.