SOI Charge-Transfer Pixel Layout for High-Resolution ToF Sensing
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Solution Overview
Problem
Time-of-Flight (ToF) sensors face challenges in enhancing spatial resolution and withstanding outdoor conditions, particularly at eye-safe wavelengths, due to reduced quantum efficiency and time response issues in semiconductor devices used for distance image sensing.
Innovation Solution
A semiconductor device with a silicon-on-insulator (SOI) substrate and a support substrate of a specific conductivity type, featuring a charge collection layer, transfer gates, and a detection electrode, where the transfer electrode and third semiconductor layer are adjacent in plan view, enabling efficient charge transfer and collection, and allowing for self-alignment and fine control of potential gradients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If indirect ToF method is used, then spatial resolution is improved, but quantum efficiency and time response deteriorate
Solution Approach 1:
The semiconductor device is divided into distinct functional regions: a first region for light reception with photodiodes optimized for high quantum efficiency, and a second region for charge transfer and signal processing. This segmentation allows each region to be optimized for its specific function, maintaining high quantum efficiency while enabling precise distance measurement through the indirect ToF method.
Solution Approach 2:
A charge transfer layer is introduced as an intermediary between the photodiode layer and the readout circuitry. This charge transfer layer efficiently transports generated charges to the signal processing region while maintaining charge collection efficiency, thereby preserving quantum efficiency even when using the indirect ToF method which requires complex pixel circuits.
2Speed
If direct ToF method is used, then time response is improved, but pixel circuit complexity increases
Solution Approach 1:
The device separates the photodetection function from the timing measurement function. The first region contains simple photodiodes for light detection, while the second region contains the timing circuitry. This segmentation reduces pixel circuit complexity in the light-receiving region while maintaining fast time response through the dedicated timing processing region.
Solution Approach 2:
The charge transfer layer acts as an intermediary that enables fast charge transport from the photodiode to the timing circuit, achieving rapid time response without requiring complex timing circuits within each pixel. The intermediary layer handles the time-critical charge transport function separately from the pixel circuitry.
3Adaptability or versatility
If eye-safe wavelength (940 nm) is used for outdoor applications, then adaptability is improved, but quantum efficiency deteriorates
Solution Approach 1:
The photodiode structure is optimized for 940 nm wavelength detection by adjusting material composition, layer thickness, and doping profiles. The buried oxide layer thickness and semiconductor layer composition are specifically tuned to maximize quantum efficiency at the eye-safe 940 nm wavelength used for outdoor ToF applications.
Solution Approach 2:
The device uses a composite structure combining silicon-on-insulator (SOI) technology with specifically engineered semiconductor layers and buried oxide layers. This composite material structure enhances light absorption and charge collection efficiency at 940 nm wavelength, maintaining high quantum efficiency for outdoor eye-safe wavelength applications.
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 enhances charge collection efficiency, reduces manufacturing variations, and enables miniaturization, making it suitable for high-resolution distance image sensing in outdoor applications.
Implementation Method 1
an electrode layer of the first conductivity type, which is provided on a surface of the support substrate opposite a surface adjoining the third semiconductor layer and is configured to apply a potential that depletes the support substrate
Implementation Method 2
a transfer electrode configured to transfer charges generated at the support substrate to the third semiconductor layer
Implementation Method 3
pixels equipped with photodiodes for detecting light for distance measurement
Data Source
AI summary
A semiconductor device in which an SOI substrate having an element region in which circuit elements are formed, an insulation layer having a first surface adjoining the SOI substrate, and a support substrate of a first conductivity type are laminated. On the SOI substrate, a transfer electrode configured to transfer charges generated in the support substrate to a third semiconductor layer is formed in a region different from the element region, and the transfer electrode and the third semiconductor layer are adjacent in plan view.