Back-Illuminated Light Receiving Element for Higher Pixel Sensitivity
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Solution Overview
Problem
Current CAPD sensors face challenges in securing a sufficient photoelectric conversion region due to wiring lines on the light receiving surface, leading to degraded pixel sensitivity and accuracy in ranging systems, especially under external light conditions and with near-infrared light sources.
Innovation Solution
A light receiving element with an on-chip lens, a wiring layer, and a semiconductor layer that includes a photodiode, transfer transistors, and interpixel separation portions, where the wiring layer incorporates a light blocking member to overlap with the photodiode, enhancing light blocking and quantum efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If wiring lines are disposed on the light receiving surface side of the photodiode to extract charges and provide control signals, then charge extraction and control functions are enabled, but the photoelectric conversion region is limited and pixel sensitivity is degraded
Solution Approach 1:
The patent transitions from a surface-illuminated structure to a back-illuminated structure, moving the light receiving surface to the opposite side of the substrate from the wiring layer. This dimensional change allows light to enter the photodiode without being blocked by wiring lines, thereby maximizing the photoelectric conversion region and pixel sensitivity while maintaining charge extraction functionality through the transferred electron mechanism.
2Device complexity
If a surface-illuminated CAPD sensor structure is used, then wiring layout flexibility is maintained, but the aperture ratio is limited and signal-to-noise ratio is degraded
Solution Approach 1:
By switching to a back-illuminated structure, the patent eliminates the blocking effect of wiring lines on the light receiving surface. The light enters through the back surface where no wiring obstructs the path, maximizing the aperture ratio and allowing more signal photons to reach the photodiode, thereby improving the signal-to-noise ratio.
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 improves the sensitivity and accuracy of the light receiving element by maximizing quantum efficiency and aperture ratio, reducing noise, and enhancing ranging characteristics.
Implementation Method 1
a photodiode; a first transfer transistor that transfers electric charge generated in the photodiode
Implementation Method 2
the wiring layer has at least one layer including a light blocking member, and the light blocking member is disposed to overlap with the photodiode in a plan view
Data Source
AI summary
Disclosed is a light receiving element including an on-chip lens, a wiring layer, and a semiconductor layer disposed between the on-chip lens and the wiring layer. The semiconductor layer includes a photodiode, a first transfer transistor that transfers electric charge generated in the photodiode to a first charge storage portion, a second transfer transistor that transfers electric charge generated in the photodiode to a second charge storage portion, and an interpixel separation portion that separates the semiconductor layers of adjacent pixels from each other, for at least part of the semiconductor layer in the depth direction. The wiring layer has at least one layer including a light blocking member. The light blocking member is disposed to overlap with the photodiode in a plan view.