Vertical-Gate LOFIC Pixel Layout for High Dynamic Range CMOS Sensors
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
CMOS image sensors face challenges in downsizing due to the complexity of lateral overflow integration capacitor (LOFIC) pixels, which require additional components and hinder efficient pixel miniaturization.
Innovation Solution
The use of vertical gate transistors for both the transfer and LOFIC select transistors, allowing for a shared configuration that reduces the number of components needed, enabling more compact pixel design by eliminating the need for additional transistors typically required in source follower shared LOFIC pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional LOFIC pixels are used to process large amounts of signal charge, then tolerance against saturation is improved, but pixel size increases due to additional components
Solution Approach 1:
The patent merges the transfer transistor and LOFIC select transistor into a single integrated structure where both functions are performed by shared components. The transfer transistor transfers charge from the photodiode to either the floating diffusion or LOFIC node, while the LOFIC select transistor controls the overflow path to the LOFIC capacitor, eliminating the need for separate dedicated transistors for each function.
Solution Approach 2:
The transfer transistor and LOFIC select transistor are designed to serve multiple functions simultaneously. The transfer transistor acts as both a charge transfer element and a select element for the LOFIC path, while the LOFIC select transistor functions as both an overflow control element and a readout select element, reducing the total component count.
2Area of moving object
If source follower shared LOFIC pixel is used to reduce components, then some downsizing is achieved, but additional LOFIC overflow and select transistors are still required
Solution Approach 1:
The patent merges the transfer transistor and LOFIC select transistor into a single integrated structure where both functions are performed by shared components. The transfer transistor transfers charge from the photodiode to either the floating diffusion or LOFIC node, while the LOFIC select transistor controls the overflow path to the LOFIC capacitor, eliminating the need for separate dedicated transistors for each function.
Solution Approach 2:
The transfer transistor and LOFIC select transistor are designed to serve multiple functions simultaneously. The transfer transistor acts as both a charge transfer element and a select element for the LOFIC path, while the LOFIC select transistor functions as both an overflow control element and a readout select element, reducing the total component count.
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 configuration allows for the downsizing of LOFIC pixels while maintaining their functionality, increasing conversion gain and preventing image saturation and blooming, thus enhancing the dynamic range and image quality.
Implementation Method 1
A third end of the transfer transistor and a third end of the LOFIC select transistor are connected in common to a photodiode
Data Source
AI summary
An image sensor element includes a transfer transistor TX, a LOFIC select transistor LF, a photodiode PD, and a first overflow path OFP. The transfer transistor TX outputs a readout signal from a first end. The LOFIC select transistor LF includes a first end connected to a second end of the transfer transistor TX, and a second end connected to a capacitor. The photodiode PD is connected in common to a third end of the transfer transistor and a third end of the LOFIC select transistor LF. The first overflow path OFP is formed between the photodiode PD and a second end of the LOFIC select transistor LF. Each of the transfer transistor TX and the LOFIC select transistor LF is configured with a vertical gate transistor.