Back-Illuminated Light Receiver Layout for NIR Ranging Pixels
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Solution Overview
Problem
Existing CAPD sensors face challenges in securing a sufficient photoelectric conversion region due to wiring lines and control lines on the light receiving surface, leading to degraded pixel sensitivity and signal-to-noise ratio, especially in external light conditions. Additionally, near-infrared light with low quantum efficiency requires thicker silicon layers, resulting in longer charge transfer times and potential erroneous signals.
Innovation Solution
A back-illuminated light receiving element with a semiconductor substrate between on-chip lenses and a multilayer wiring layer, where transfer transistors and floating diffusion regions are formed on the front surface, and interpixel separation portions are used to prevent light leakage. This design enhances quantum efficiency and aperture ratio, improving ranging characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If wiring lines and control lines are disposed on the light receiving surface side of the photodiode, then charge extraction and control functions are achieved, but the photoelectric conversion region is limited and pixel sensitivity is degraded
Solution Approach 1:
The patent inverts the conventional surface-illuminated structure by adopting a back-illuminated structure where light enters through the rear surface of the substrate. This allows wiring lines and control lines to be disposed on the front surface while the photodiode's light receiving surface remains on the rear surface, eliminating the conflict between wiring and photoelectric conversion regions.
Solution Approach 2:
The patent utilizes the third dimension (depth) by creating a through-substrate structure where light passes through the entire substrate thickness. The photodiode is positioned such that its light receiving surface is on the rear surface while wiring is on the front surface, effectively using vertical separation to resolve the spatial conflict.
2Reliability
If the silicon layer is made thicker to improve quantum efficiency for near-infrared light, then photoelectric conversion efficiency is improved, but charge transfer time increases and erroneous signals occur
Solution Approach 1:
The patent changes the structural parameters by optimizing the substrate thickness to a specific range (50-200 μm) and positioning the photodiode's light receiving surface on the rear surface. This configuration achieves high quantum efficiency for near-infrared light while maintaining sufficiently short charge transfer times by reducing the distance charges must travel through the substrate.
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 back-illuminated design maximizes quantum efficiency and aperture ratio, enhancing the sensitivity and accuracy of the light receiving element, thereby improving the ranging characteristics and reducing erroneous signals.
Implementation Method 1
a photodiode PD as a photoelectric conversion portion
Data Source
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AI summary
Disclosed is a light receiving element (10) including an on-chip lens (47), a wiring layer (42), and a semiconductor layer (41) disposed between the on-chip lens and the wiring layer. The semiconductor layer includes a photodiode (PD), a first transfer transistor (TRG1) that transfers electric charge generated in the photodiode to a first charge storage portion (FD1), a second transfer transistor (TRG2) that transfers electric charge generated in the photodiode to a second charge storage portion (FD2), and an interpixel separation portion (61) 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 (63). The light blocking member is disposed to overlap with the photodiode in a plan view.