Backside Image Sensor Pixel With Vertical Transfer Gate Structure
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Solution Overview
Problem
Back-side illuminated image sensor pixels face disadvantages in their charge transfer devices, particularly in efficiently transferring photogenerated charges from the photosensitive region to the charge collection region.
Innovation Solution
The design includes a doped photosensitive region and a charge collection region more heavily doped, with a vertical stack comprising a transfer gate and an electric insulation wall that penetrates into the substrate, allowing for efficient charge transfer and lateral delimitation of the photosensitive region, and optionally sharing the transfer gate between neighboring pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional charge transfer device is used in back-side illuminated pixels, then the device structure is simpler, but charge transfer efficiency is reduced due to local potential minima causing charge sticking
Solution Approach 1:
The patent transitions from a planar charge transfer gate to a vertical stack configuration where the transfer gate extends in the vertical dimension through the substrate. This vertical arrangement eliminates local potential minima that trap charges in conventional lateral structures, thereby improving charge transfer efficiency without proportionally increasing device complexity
Solution Approach 2:
The transfer gate is nested within a vertical stack structure that includes insulating layers and doping regions. This nested configuration allows the transfer gate to be integrated within the substrate thickness, achieving efficient charge transfer while maintaining a compact device footprint
2Reliability
If the photosensitive region is laterally delimited by conventional means, then manufacturing is easier, but charge transfer efficiency is reduced
Solution Approach 1:
The patent uses vertical stacks of transfer gates and insulating walls to laterally delimit photosensitive regions. This vertical approach provides precise lateral definition of pixel boundaries and charge collection regions, improving charge transfer efficiency while the standardized vertical stack fabrication maintains manufacturing feasibility
3Productivity
If a vertical transfer gate penetrating deeper than the charge collection region is used, then charge sticking is reduced, but the device complexity increases
Solution Approach 1:
The transfer gate extends vertically deeper than the charge collection region to eliminate potential minima that cause charge sticking. This vertical extension ensures complete charge transfer without trapping, improving productivity. The vertical stack integrates multiple functions (transfer gate, insulation, lateral delimitation) into a single structural element, managing complexity through functional integration
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 enhances the efficiency of charge transfer by avoiding local potential minima and improving the transfer of photogenerated charges, reducing charge sticking issues and enhancing the overall performance of the image sensor pixels.
Implementation Method 1
a vertical stack comprising a vertical transfer gate and a vertical electric insulation wall, the stack crossing the substrate and being in contact with the charge collection region
Implementation Method 2
When light is received by the photosensitive area, electron-hole pairs are generated in the photosensitive region
Data Source
AI summary
The present disclosure concerns an image sensor including a plurality of pixels, each including: a doped photosensitive region of a first conductivity type extending vertically in a semiconductor substrate; a charge collection region more heavily doped with the first conductivity type than the photosensitive region, extending vertically in the substrate from an upper surface of the substrate and being arranged above the photosensitive region; and a vertical stack including a vertical transfer gate and a vertical electric insulation wall, the stack crossing the substrate and being in contact with the charge collection region, the gate being arranged on the upper surface side of the substrate and penetrating into the substrate deeper than the charge collection region.