UBG ToF Photodiode Structure for Uniform Multi-Tap Charge Transit
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Solution Overview
Problem
Conventional time-of-flight (ToF) photodiodes face limitations in accuracy due to device non-idealities and sub-optimal design, which affect the correlation between charge collection and distance measurements in depth sensing applications.
Innovation Solution
The implementation of a uniform-bridge-gradient (UBG) ToF photodiode design, featuring a photodiode region with a photodiode-defining implant, shallow and deep bridging implants, and a pinning implant, which creates a uniform doping gradient across multiple taps to enhance photocarrier transit time and minimize charge accumulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional ToF photodiode design is used, then device simplicity is maintained, but measurement precision deteriorates due to device non-idealities and sub-optimal design
Solution Approach 1:
The patent applies local quality by creating a uniform doping gradient specifically in the bridging region between taps, while maintaining other photodiode regions with conventional structures. The bridging implants are strategically placed to provide localized doping control that enhances photocarrier transit without requiring complete redesign of the entire photodiode structure.
Solution Approach 2:
The patent changes the doping parameter by introducing a uniform doping gradient through bridging implants with controlled doping concentrations. This parameter change creates optimized electric field distributions that accelerate photocarrier transit while maintaining overall device functionality and compatibility with standard CMOS fabrication processes.
2Loss of time
If rapid photocarrier transit is achieved through enhanced fields, then shuttle time is reduced, but device complexity increases due to multiple bridging implants
Solution Approach 1:
The patent segments the bridging structure into multiple implants at different depths (first bridging implant and second bridging implant). This segmentation allows each implant to contribute to different aspects of the electric field distribution, creating a comprehensive solution for rapid photocarrier transit while maintaining manufacturability through standard ion implantation processes.
Solution Approach 2:
The patent extends the solution into the vertical dimension by placing bridging implants at different depths within the photodiode structure. The first bridging implant is positioned at a shallower depth while the second bridging implant is positioned deeper, creating a three-dimensional doping profile that optimizes electric field distribution throughout the photocarrier transit path.
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 design improves the accuracy of distance measurements by ensuring rapid and equivalent photocarrier transit across all taps, reducing shuttle time and enhancing demodulation efficiency, quantum efficiency, and minimizing temporal readout noise.
Implementation Method 1
The bridging implants provide lateral bridging with a uniform doping gradient near and across the multiple taps
Implementation Method 2
The deeper bridging implant can generate an enhanced band of fringing fields near the taps to improve lateral and vertical photocharge transit time
Implementation Method 3
The shallower bridging implant can have a uniform bridging critical dimension that creates a lateral field to improve photocarrier transit time
Implementation Method 4
Received photons are converted into photocarriers (i.e., electrons or holes)
Data Source
AI summary
A uniform bridge gradient (UBG) time-of-flight (ToF) photodiode block is described, such as for integration with image sensor pixels. The UBG ToF photodiode block can be part of a UBG ToF pixel, and an image sensor can include an array of such pixels. Each UGB ToF photosensor block has multiple taps for selective activation, and a photodiode region designed for complete and rapid transit of photocarriers, as they are generated, via the multiple taps. Embodiments of the photodiode region include a photodiode-defining implant, a relatively shallow first bridging implant, and relatively deep second bridging implant. The bridging implants provide lateral bridging with a uniform doping gradient near and across the multiple taps.