Pixel With Shared Memory Gate For Global Shutter
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Solution Overview
Problem
Existing pixel structures suffer from a rolling shutter effect due to asynchronous readout of pixels in a sensor array, leading to image distortion, and require additional components like a memory gate and extra transistors that decrease the fill-factor and increase complexity.
Innovation Solution
A five-transistor pixel structure with a memory gate acting as both a storage capacitor and a control gate, using a control signal to alternate between high and intermediate voltages to transfer and hold photo charges, eliminating the need for a separate reset transistor and reducing wiring complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a memory gate and extra transistors are added to achieve global shutter functionality, then image distortion is reduced, but the fill-factor decreases and device complexity increases
Solution Approach 1:
The memory gate electrode is merged with the transfer gate electrode to form a single shared electrode structure. This combining of functions allows the same physical structure to serve as both the memory gate for storing photocharges and the transfer gate for moving charges to the sense node, thereby achieving global shutter functionality without adding extra transistors or components that would increase device complexity
Solution Approach 2:
The shared gate electrode performs multiple functions: it acts as a memory gate electrode to store photocharges during the integration period, and simultaneously serves as a transfer gate electrode to transfer charges to the sense node during readout. This multi-functionality eliminates the need for separate dedicated structures, maintaining fill-factor while enabling global shutter operation
2Reliability
If a memory gate and extra transistors are added to achieve global shutter functionality, then image distortion is reduced, but the fill-factor decreases
Solution Approach 1:
The memory gate electrode is merged with the transfer gate electrode to form a single shared electrode structure. This combining of functions allows the same physical structure to serve as both the memory gate for storing photocharges and the transfer gate for moving charges to the sense node, thereby achieving global shutter functionality without adding extra transistors or components that would increase device complexity
Solution Approach 2:
The shared gate electrode performs multiple functions: it acts as a memory gate electrode to store photocharges during the integration period, and simultaneously serves as a transfer gate electrode to transfer charges to the sense node during readout. This multi-functionality eliminates the need for separate dedicated structures, maintaining fill-factor while enabling global shutter operation
3Reliability
If additional components are added to eliminate rolling shutter effect, then image distortion is minimized, but manufacturing complexity increases
Solution Approach 1:
The memory gate electrode is merged with the transfer gate electrode to form a single shared electrode structure. This combining of functions allows the same physical structure to serve as both the memory gate for storing photocharges and the transfer gate for moving charges to the sense node, thereby achieving global shutter functionality without adding extra transistors or components that would increase device complexity
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
Improves the fill-factor and reduces reset capacitance noise, enabling simultaneous charge transfer and storage across the pixel array, thereby minimizing image distortion and enhancing the dynamic range of light intensity capture.
Implementation Method 1
When illuminated, the photodiode accumulates photo generated electrons that migrate in the n region to be adjacent to the p+ region
Implementation Method 2
A positive TG voltage will create an electrical field that penetrates down into the substrate and attracts the accumulated electrons from out of the photodiode which are then transported laterally to the higher potential of the n+ sense node
Data Source
AI summary
A method of scanning pixels, each pixel including a photodiode and a sense node formed in the substrate, including a transfer gate coupled between the photodiode and the sense node, and including a memory gate coupled between the photodiode and the transfer gate. The method switches a control signal, connected to a memory gate electrode of all pixels, alternately between a first voltage and a second voltage that is intermediate between the first voltage and a substrate voltage. The first voltage transfers all photo charge in each photodiode into the respective memory gate. The second voltage both (1) holds all photo charge already transferred into the memory gate and (2) blocks further transfer of photo charges into each memory gate. The method further includes reading out photo charge from the memory gate on a row-by-row basis while the control signal is at the second voltage.