Vertical ToF Pixel Photogates for Higher Quantum Efficiency
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Solution Overview
Problem
Current time-of-flight (ToF) camera pixels with planar photogates face challenges such as reduced quantum efficiency, increased power consumption, and limited resolution due to longer photoelectron transit times and larger pixel area, which are exacerbated by thicker photoelectron generation regions.
Innovation Solution
The use of vertical photogates, which allow for a thicker photoelectron generation region without increasing electron migration distances or transit times, and the application of negative bias to one photogate to suppress dark current noise, enabling higher quantum efficiency and resolution while reducing power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If planar photogates are used in ToF camera pixels, then the pixel structure is simple and easy to manufacture, but the photoelectron transit time increases and quantum efficiency decreases
Solution Approach 1:
The patent transitions from planar (2D) photogate structures to vertical (3D) photogate structures. The vertical photogates extend through the thickness of the pixel, creating electric fields that efficiently collect photoelectrons generated at any depth within the photoelectron generation region. This dimensional change reduces photoelectron transit time and increases quantum efficiency without complicating the manufacturing process.
2Reliability
If the photoelectron generation region is made thicker to increase quantum efficiency, then more photoelectrons are generated, but the photoelectron transit time increases and power consumption increases
Solution Approach 1:
By implementing vertical photogates that extend through the photoelectron generation region, the patent creates efficient charge collection pathways in the vertical dimension. This allows the photoelectron generation region to be made thicker for increased quantum efficiency while maintaining short transit times, as the vertical electric field directly collects electrons regardless of their generation depth.
Solution Approach 2:
The patent applies different bias voltages to different vertical photogates to create localized electric field regions optimized for charge collection. By controlling the bias applied to each vertical photogate, the system efficiently collects photoelectrons from thick generation regions without requiring uniformly high voltages across the entire pixel, thus reducing power consumption.
3Reliability
If higher photogate voltage is applied to reduce photoelectron transit time, then quantum efficiency improves, but power consumption increases
Solution Approach 1:
The patent applies different bias voltages to different vertical photogates based on their specific function and position. Not all vertical photogates require the same high voltage; the bias is optimized locally for each photogate region, maintaining effective charge collection while minimizing overall power consumption.
Solution Approach 2:
The system dynamically adjusts photogate bias voltages based on operational requirements. By changing the voltage parameters adaptively rather than maintaining constantly high voltages, the patent achieves high quantum efficiency when needed while reducing power consumption during normal operation.
4Ease of manufacture
If planar photogates are used, then the manufacturing process is simpler, but the pixel area increases reducing resolution
Solution Approach 1:
The transition to vertical photogates allows charge collection to occur in the vertical dimension rather than requiring large horizontal collection areas. This enables smaller pixel pitches and higher resolution while maintaining simple manufacturing processes, as the vertical structure efficiently collects electrons without requiring large lateral photogate dimensions.
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 achieves higher quantum efficiency, better demodulation contrast, and lower power consumption, allowing for smaller pixel pitches and higher resolution imaging without the need for increased photogate voltage, thus enhancing the performance of ToF cameras.
Implementation Method 1
each addressable pixel comprising a first vertical photogate and a second vertical photogate... apply a first relative bias to the first vertical photogate and the second vertical photogate to collect charge at a first pixel tap
Implementation Method 2
application of negative bias to one photogate to suppress dark current noise
Data Source
AI summary
Examples are disclosed that relate to time-of-flight camera systems comprising vertical photogates. One example provides a time-of-flight camera comprising a plurality of addressable pixels configured for backside illumination, each addressable pixel comprising a first vertical photogate and a second vertical photogate. The time-of-flight camera further comprises a processor and a storage device storing instructions executable on the processor to, during an integration period, apply a first relative bias to the first vertical photogate and the second vertical photogate to collect charge at a first pixel tap, apply a second relative bias to the first vertical photogate and the second vertical photogate to collect charge at a second pixel tap, and determine a distance value for the addressable pixel based at least upon the charge collected at the first pixel tap and the charge collected at the second pixel tap.