Always-Depleted Photodiode for ToF Sensor Power Efficiency
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Solution Overview
Problem
Time-of-flight (ToF) cameras face challenges in achieving power efficiency while maintaining modulation contrast and distance accuracy, particularly at smaller pixel sizes, due to the trade-offs between voltage bias and semiconductor material resistivity, which can lead to increased dark current and signal noise.
Innovation Solution
The use of an always-depleted photodiode with a doped first region and a more lightly-doped second region creates a permanent electric field that separates electron-hole pairs without the need for high-resistivity materials, allowing for lower power operation without sacrificing modulation contrast, and enables selective operation of pixels to reduce power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high-resistivity semiconductor material is used in the photocharge generation region, then modulation contrast is improved, but power consumption increases and dark current increases
Solution Approach 1:
The patent changes the doping concentration parameter in the semiconductor material, using a moderately-doped region instead of high-resistivity material. This parameter change achieves the necessary photocharge separation while reducing power consumption and dark current, resolving the contradiction between measurement precision and energy use.
2Measurement precision
If high voltage bias is applied to the photocharge generation region, then photocharge separation is improved, but power consumption increases
Solution Approach 1:
The patent changes the electrical parameter by applying a reduced voltage bias to the moderately-doped photocharge generation region. The moderate doping level enables effective photocharge separation at lower voltages, improving photocharge separation while reducing power consumption.
3Area of moving object
If smaller pixel sizes are used, then device integration is improved, but signal noise increases
Solution Approach 1:
The patent changes the material parameter by using moderately-doped semiconductor material with optimized carrier concentration. This enables smaller pixel sizes to maintain adequate photocharge separation efficiency and signal quality, reducing signal noise while improving device integration.
4Use of energy by moving object
If always-depleted photodiode structure is used, then power consumption is reduced, but manufacturing complexity increases
Solution Approach 1:
The patent achieves the always-depleted condition by optimizing the doping concentration parameter in the photocharge generation region. This parameter optimization enables the photodiode to remain depleted without additional control circuitry, reducing power consumption while maintaining manufacturing simplicity.
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 approach allows for lower power consumption in ToF cameras while maintaining high modulation contrast and distance accuracy, reducing dark current and signal noise, and enabling higher in-pixel storage capacity and modulation frequencies.
Implementation Method 1
receiving photons in a photocharge generation region of the pixel, the photocharge generation region of the pixel comprising an always-depleted photodiode formed by a doped first region comprising one of p-doping or n-doping and a more lightly-doped second region comprising the other of p-doping or n-doping
Implementation Method 2
creates a permanent electric field that separates electron-hole pairs
Data Source
AI summary
Examples are disclosed that relate to the use of an always-depleted photodiode in a ToF depth image sensor. One example provides a method of operating a pixel of a depth image sensor, the method comprising receiving photons in a photocharge generation region of the pixel, the photocharge generation region of the pixel comprising an always-depleted photodiode formed by a doped first region comprising one of p-doping or n-doping and a more lightly-doped second region comprising the other of p-doping or n-doping. The method further comprises, during an integration phase, energizing a clock gate for a pixel tap, thereby directing photocharge generated in the photocharge generation region to an in-pixel storage comprising a capacitor, and in a readout phase, reading charge out from the in-pixel storage.