Dual Conversion Gain Gate Capacitor Pixel Architecture
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Solution Overview
Problem
Conventional CMOS imager pixel cells have a limited fill factor and charge storage capacity, leading to inefficiencies in light conversion and potential 'blooming' issues, where excess charge escapes to other areas or adjacent cells, reducing dynamic range and sensitivity.
Innovation Solution
A dual conversion gain element is introduced, acting as both a control gate and the bottom plate of a storage capacitor, allowing for increased charge storage capacity and improved light performance by switching capacitance to change conversion gain, thereby enhancing the fill factor and dynamic range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a capacitor is added to increase charge storage capacity, then storage capacity is improved, but the photosensor area decreases
Solution Approach 1:
The patent merges the capacitor bottom plate with the transfer gate structure, making the transfer gate serve dual functions: charge transfer control and capacitor plate. This integration eliminates the need for a separate capacitor structure, increasing charge storage capacity without reducing photosensor area.
Solution Approach 2:
The transfer gate is given multiple functions: it controls charge transfer from the photosensor and simultaneously serves as the bottom plate of the storage capacitor. This multi-functionality resolves the contradiction by providing both charge transfer control and increased storage capacity within the same structural element.
2Area of stationary object
If the pixel cell area is reduced for scaling, then device density is improved, but the photosensor area proportion decreases
Solution Approach 1:
By merging the capacitor bottom plate with the transfer gate, the patent reduces the total area required for charge storage functionality. This allows the photosensor to occupy a larger proportion of the pixel cell area, maintaining high fill factor even as overall pixel dimensions are reduced for scaling.
Solution Approach 2:
The patent optimizes the local arrangement of components within the pixel cell, positioning the transfer gate and capacitor structure to maximize the photosensor area. The merged structure is strategically placed to minimize interference with the photosensor region while providing adequate charge storage capacity.
3Ease of operation
If conventional separate capacitor and transfer gate structures are used, then charge transfer control is achieved, but the fill factor decreases
Solution Approach 1:
The patent combines the transfer gate and capacitor bottom plate into a single integrated structure. This merger maintains effective charge transfer control through the gate while eliminating the additional area that would be required for a separate capacitor, thereby preserving a high fill factor.
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 dual conversion gain element increases the fill factor and storage capacity of pixel cells, providing improved sensitivity at both low and high light conditions while minimizing space usage and preventing blooming.
Implementation Method 1
when incident light 187 strikes the surface of a photodiode photosensor 120, electron/hole pairs are generated in the p-n junction of the photodiode photosensor 120
Implementation Method 2
a capacitor which is connected to the floating diffusion region 110. The capacitor is used to store the additional over-capacity charges
Data Source
AI summary
A pixel cell array architecture having a dual conversion gain. A dual conversion gain element is coupled between a floating diffusion region and a respective storage capacitor. The dual conversion gain element having a control gate switches in the capacitance of the capacitor to change the conversion gain of the floating diffusion region from a first conversion gain to a second conversion gain. In order to increase the efficient use of space, the dual conversion gain element gate also functions as the bottom plate of the capacitor. In one particular embodiment of the invention, a high dynamic range transistor is used in conjunction with a pixel cell having a capacitor-DCG gate combination; in another embodiment, adjacent pixels share pixel components, including the capacitor-DCG combination.