Back-Illuminated Light Receiver Layout for Accurate Ranging
Find Innovative SolutionsGenerate Solutions
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 limited saturation signal amount, which affects the signal-to-noise ratio and ranging accuracy.
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, enhancing quantum efficiency and aperture ratio.
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 a photodiode in a surface-illuminated CAPD sensor, 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 illumination direction from surface-illuminated to back-illuminated structure. By making light incident from the back surface of the semiconductor substrate, the wiring lines disposed on the front surface no longer block the light path, thereby securing a sufficient photoelectric conversion region while maintaining the necessary wiring layout for charge extraction and control functions
2Reliability
If the silicon photoelectric conversion region is made thick to improve quantum efficiency for near-infrared light, then absorption of incident light is improved, but charge extraction time increases and ranging accuracy decreases
Solution Approach 1:
By inverting the illumination direction to back-illuminated structure, the patent enables efficient charge extraction from a relatively thin photoelectric conversion region. The light incident from the back surface generates charges that can be quickly collected by the front surface electrodes, maintaining both high quantum efficiency and fast charge extraction speed for accurate ranging
3Adaptability or versatility
If a surface-illuminated CAPD sensor is used in a place subjected to external light, then the sensor can operate in various environments, but external light becomes a noise component and signal-to-noise ratio decreases
Solution Approach 1:
The back-illuminated structure combined with interpixel separation portions effectively blocks external light from reaching adjacent pixels. The light incident from the back surface is directed through the semiconductor substrate to the photodiode, while the interpixel separation portions prevent lateral light propagation, thereby maintaining environmental adaptability while significantly improving signal-to-noise ratio by eliminating external light noise
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 improves quantum efficiency and aperture ratio, leading to enhanced ranging characteristics, increased sensitivity, and better signal-to-noise ratio, while also allowing for thinner substrates and higher electron extraction efficiency.
Implementation Method 1
a photodiode PD as a photoelectric conversion portion
Data Source
Figure 1
Figure 2
Figure 3
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 (10) 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.