Fin Transfer Gate for Image Sensor Charge Lag Reduction
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Solution Overview
Problem
Image sensors face challenges in efficiently capturing incident light due to image lag, which degrades image quality as charge from previous images is not fully removed from photodiode regions.
Innovation Solution
The introduction of fin-like structures in transfer gates increases the effective channel width, allowing for high-speed transfer of charges from photodiodes to the floating diffusion region, reducing image lag and improving leakage control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the pixel size is decreased to increase the number of pixels in the sensing array, then the resolution is improved, but the light capture efficiency deteriorates and image lag increases
Solution Approach 1:
The transfer gate is extended vertically into the substrate to form fin structures, transitioning from a two-dimensional planar gate to a three-dimensional structure. This vertical extension increases the effective channel width without increasing the lateral footprint, allowing more pixels to be packed in the same area while maintaining adequate charge transfer capability for each pixel
Solution Approach 2:
The transfer gate channel is segmented into multiple fin structures that extend vertically into the substrate. These fins are spaced apart laterally but connected through the substrate depth, creating multiple parallel charge transfer pathways that increase the effective channel width while maintaining a compact lateral footprint
2Speed
If the transfer gate channel width is increased to improve charge transfer speed, then image lag is reduced, but the pixel area increases
Solution Approach 1:
The transfer gate channel is extended into the third dimension (vertical depth) by forming fins that penetrate into the substrate. This allows the effective channel width to be increased by adding more fin structures vertically, while the lateral footprint of each pixel remains constrained, thus improving charge transfer speed without proportionally increasing pixel area
Solution Approach 2:
Multiple fin structures are merged into a single integrated transfer gate device. The fins are electrically connected through the substrate and function as a unified channel, combining their individual charge transfer capabilities to achieve high-speed transfer while maintaining a compact overall structure
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 enhances the speed and accuracy of charge transfer, improving image quality by reducing image lag and maintaining or improving the quality of electronic images captured by ever-decreasing pixel sizes.
Implementation Method 1
each photosensitive element absorbs a portion of incident image light. Photosensitive elements included in the image sensor, such as photodiodes, each generate image charge upon absorption of the image light
Data Source
AI summary
A device includes a photodiode, a floating diffusion region, a transfer gate, and a channel region. The photodiode is disposed in a semiconductor material. The photodiode is coupled to generate charge in response to incident light. The floating diffusion region is disposed in the semiconductor material. The transfer gate is disposed between the photodiode and the floating diffusion region. The channel region associated with the transfer gate is in the semiconductor material proximate to the transfer gate. The transfer gate is coupled to transfer the charge from the photodiode to the floating diffusion region through the channel region in response to a transfer signal coupled to be received by the transfer gate. The transfer gate includes a plurality of fin structures that extend into the semiconductor material and the photodiode.