Depth Sensor Storage Gate Structure for Small Pixels and Low PLS
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Solution Overview
Problem
Existing depth sensors face challenges in increasing resolution while maintaining a reduced pixel size and minimizing parasitic light sensitivity (PLS).
Innovation Solution
A depth sensor design with a substrate structure that includes a photoelectric conversion element and taps, featuring storage transistors with extensions and barrier areas to reduce pixel size and enhance charge storage capacity, thereby reducing PLS.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the pixel size is decreased to increase resolution, then the resolution is improved, but the charge storage capacity is reduced
Solution Approach 1:
The storage gate electrode extends in the depth direction (third direction) of the substrate, utilizing the vertical dimension to increase storage volume without expanding the pixel's planar footprint. This allows charge storage capacity to increase while maintaining small pixel size for high resolution.
Solution Approach 2:
The storage gate electrode is embedded within the substrate structure, with its extension nested between the first and second faces of the substrate. This nested configuration maximizes space utilization within the pixel volume, enabling increased charge storage without increasing pixel area.
2Measurement precision
If the pixel size is decreased to increase resolution, then the resolution is improved, but the parasitic light sensitivity increases
Solution Approach 1:
The barrier area is positioned to overlap the storage transistor in the depth direction, creating a three-dimensional shielding structure. This vertical barrier effectively blocks parasitic light from reaching the storage transistor without increasing the pixel's planar dimensions, thus maintaining high resolution while reducing PLS.
Solution Approach 2:
The barrier area acts as an intermediary structure between the photoelectric conversion element and the storage transistor, blocking parasitic light paths while allowing the pixel to maintain its compact size for high resolution imaging.
3Quantity of substance
If the charge storage capacity is increased, then the charge storage capacity is improved, but the pixel size increases
Solution Approach 1:
The storage gate electrode utilizes the depth direction (third direction) of the substrate to increase charge storage capacity. By extending vertically between the first and second faces, the storage volume increases without expanding the pixel's area in the first and second directions, thus maintaining small pixel size for high resolution.
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 design achieves improved resolution and reduced PLS, enhancing the performance of depth sensors by increasing charge storage capacity and minimizing external light interference.
Implementation Method 1
a photoelectric conversion element disposed in the substrate
Data Source
AI summary
A depth sensor includes a substrate that includes a first face and a second face opposite to each other in a first direction; a photoelectric conversion element disposed in the substrate; and first and second taps connected to the photoelectric conversion element. Each of the first and second taps includes: a floating diffusion area disposed in the substrate; a transfer transistor connected to the floating diffusion area; a photo transistor connected to the photoelectric conversion element; a tap transfer transistor connected to the photo transistor; and a storage transistor connected to the tap transfer transistor and the transfer transistor. The storage transistor includes a storage gate electrode. The storage gate electrode includes a first extension and a second extension that extend from the first face of the substrate toward the second face, and the first extension and the second extension are spaced apart from each other in a second direction.