Backside-Illuminated CAPD Pixel Layout for Accurate Ranging
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional CAPD sensors face challenges in securing a sufficient photoelectric conversion region due to wiring and control lines on the light-receiving surface, leading to deteriorated pixel sensitivity and ranging accuracy, especially in environments with external light where noise components are significant.
Innovation Solution
A backside illuminated CAPD sensor design with isolated light receiving regions, each having distinct voltage application units and charge detection units, and an isolation portion between them, allowing for improved charge isolation and reduced noise interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If wirings and control lines are arranged on the light-receiving surface side of the photodiode, then charge retrieval and control functions are enabled, but the photoelectric conversion region is limited and pixel sensitivity deteriorates
Solution Approach 1:
The patent inverts the conventional front-side illuminated structure to a backside illuminated structure. The light-receiving surface is formed on the opposite side of the substrate from the wirings and control lines, allowing light to enter the photodiode without being blocked by electrical components. This inversion resolves the contradiction by enabling both comprehensive wiring layout and maximum photoelectric conversion area.
2Reliability
If additional transistors are provided to secure saturation signal capacity, then signal-to-noise ratio is improved, but device complexity increases
Solution Approach 1:
The patent changes the fundamental parameter of light incident direction from front-side to back-side illumination. This parameter change allows the photodiode to achieve higher quantum efficiency and capture more photons, generating sufficient signal charges without requiring additional transistors. The backside illuminated structure inherently provides better signal generation capability, resolving the need for extra components to improve signal-to-noise ratio.
3Productivity
If photoelectric conversion is performed in inactive tap regions, then more signal charges are generated, but ranging accuracy deteriorates due to noise
Solution Approach 1:
The patent segments the pixel structure into distinct regions: an active tap region for signal charge collection and inactive tap regions isolated by deep isolation portions. The backside illuminated structure combined with segmentation ensures that photoelectric conversion primarily occurs in or near the active region, and generated charges are efficiently collected by the active tap before they can diffuse into inactive regions. This resolves the contradiction by spatially separating charge generation and collection functions.
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 solution enhances pixel sensitivity and ranging accuracy by maximizing quantum efficiency and aperture ratio, reducing noise interference, and enabling efficient signal carrier retrieval even at higher drive frequencies.
Implementation Method 1
photoelectric conversion in a Si substrate is considered, although there are differences in the attenuation rate depending on the light wavelength, photoelectric conversion is caused on the light entrance surface side at a higher percentage
Data Source
AI summary
The present technology relates to a light receiving element and a ranging module that can improve characteristics. A light receiving element includes: light receiving regions each including a first voltage application unit to which a first voltage is applied, a first charge detection unit provided around the first voltage application unit, a second voltage application unit to which a second voltage different from the first voltage is applied, and a second charge detection unit provided around the second voltage application unit; and an isolation portion that is arranged at a boundary between the light receiving regions adjacent to each other, and isolates the light receiving regions from each other. The present technology can be applied to a light receiving element.