Central Collection Photodiode with Tri-Gate Charge Transfer
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Solution Overview
Problem
Time of flight cameras face challenges in balancing performance parameters with physical size and power constraints, particularly due to high power requirements and long charge transfer paths, which affect miniaturization and increase response time.
Innovation Solution
The implementation of a time of flight light sensing system with a central collection photodiode and tri-gate charge transfer block, which reduces power consumption and improves charge transfer speeds by using a central collection photodiode and tri-gate charge transfer block to transfer image charges with low power consumption and short image charge paths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional time of flight cameras operate at very high frequencies to achieve high performance, then measurement precision and depth resolution are improved, but power consumption increases significantly
Solution Approach 1:
The pixel structure is segmented into distinct functional regions: a photodiode for light detection, a charge collection gate for charge accumulation, and a tri-gate charge transfer block for charge transfer. This segmentation allows each component to be optimized independently, enabling high-frequency operation with reduced power consumption by minimizing the charge transfer path length between these segmented regions.
Solution Approach 2:
The invention transitions from conventional lateral charge transfer to vertical charge transfer through the use of a tri-gate charge transfer block positioned directly above the photodiode. This dimensional change from horizontal to vertical charge transfer reduces the charge transfer path length, enabling faster operation at lower power consumption while maintaining depth resolution.
2Reliability
If charge transfer paths are made longer to improve charge collection efficiency, then quantum efficiency is improved, but response time increases
Solution Approach 1:
The tri-gate charge transfer block acts as an intermediary structure between the photodiode and the readout circuitry. It provides a direct vertical charge transfer path that is both short and efficient, using the gate structure to create strong electric fields that rapidly collect and transfer charges without requiring long lateral paths, thus maintaining charge collection efficiency while reducing response time.
Solution Approach 2:
The invention changes the electric field distribution parameters by using a tri-gate structure with specific doping profiles and gate voltages. This creates optimized electric field patterns that enhance charge collection efficiency in the vertical direction while keeping the transfer path short, thereby reducing response time without sacrificing charge collection efficiency.
3Productivity
If pixel size is increased to accommodate longer charge transfer paths, then charge transfer efficiency is improved, but device miniaturization is hindered
Solution Approach 1:
The invention moves the charge transfer path from the lateral plane to the vertical dimension by positioning the tri-gate charge transfer block directly above the photodiode. This vertical arrangement enables efficient charge transfer within a compact pixel area, achieving high charge transfer efficiency without increasing pixel size and thus supporting device miniaturization.
Solution Approach 2:
The tri-gate charge transfer block is nested vertically above the photodiode, with the gate structure encompassing the charge collection region. This nested configuration allows the charge transfer function to be integrated within the vertical profile of the pixel rather than extending laterally, maintaining compact pixel size while achieving efficient charge transfer.
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 solution enables reduced power consumption and faster charge transfer without increasing pixel size, improving the performance of time of flight cameras while maintaining miniaturization and reducing response time.
Implementation Method 1
a photodiode to accumulate image charge in response to light
Data Source
AI summary
A pixel circuit includes a photodiode disposed in a semiconductor material layer to accumulate image charge in response to light incident upon the photodiode. A charge collection gate is coupled to the photodiode. The charge collection gate is disposed over the photodiode to generate an inversion layer in the semiconductor material layer under the charge collection gate to collect the image charge from the photodiode. A first transfer gate is disposed proximate to the charge collection gate, wherein the first transfer gate is coupled to transfer the image charge from in the inversion layer in response to a first transfer signal.