Direct TOF Pixel With Deep Trench Isolation for Low Power
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Time of flight (TOF) image sensors face challenges in balancing performance parameters with physical size and power constraints, particularly in achieving reduced power consumption and improved charge transfer speeds while maintaining miniaturization and high accuracy, due to high power consumption and long image charge transfer paths in existing photogate indirect TOF pixel structures.
Innovation Solution
The implementation of deep trench isolation (DTI) light blocking structures and central collection photodiodes in TOF pixels, which separate light collection volumes from readout circuit structures, reducing power consumption and enhancing charge transfer speeds without increasing pixel sizes, and using shallow trench isolation (STI) to further improve fill factor and optical isolation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If photogate indirect TOF pixel structures are used, then depth measurement capability is achieved, but power consumption is high
Solution Approach 1:
The patent extracts and removes the photogate structures from the pixel design, transitioning to a direct TOF pixel structure where photons are directly converted to electrical signals without requiring photogate modulation. This elimination of the photogate component directly reduces power consumption while maintaining depth measurement capability through direct time-of-flight measurement of photons.
Solution Approach 2:
The patent inverts the conventional indirect TOF approach by implementing a direct TOF measurement method. Instead of using photogates to modulate light and infer depth from modulation changes, the system directly measures the time of flight of individual photons, fundamentally reversing the measurement paradigm to achieve lower power consumption.
2Measurement precision
If photogate indirect TOF pixel structures are used, then depth measurement capability is achieved, but charge transfer path length is long
Solution Approach 1:
By removing the photogate structures and associated charge transfer pathways, the patent directly converts incident photons to electrical signals at the pixel site. This extraction of the photogate component eliminates the long charge transfer paths required in indirect TOF systems, reducing the distance charges must travel and associated transfer time.
3Area of moving object
If pixel size is reduced for miniaturization, then device size is reduced, but performance parameters deteriorate
Solution Approach 1:
The patent inverts the conventional approach by using direct TOF measurement that is inherently more area-efficient than indirect TOF methods. The direct photon-to-signal conversion requires fewer structural components and less pixel area, allowing miniaturization without sacrificing depth measurement precision or other performance parameters.
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 results in reduced power consumption, faster charge transfer, and improved fill factor, enabling more efficient 3D image acquisition with reduced pixel sizes and lower power usage, effectively addressing the constraints of size and power in TOF image sensors.
Implementation Method 1
a sensor that detects the light that is reflected from the object
Data Source
AI summary
A time-of-flight pixel array comprises multiple pixel cells. The pixel cell comprises a light collection region, a light shielded region, and a deep trench isolation (DTI) structure that encircles the light collection region to prevent light from entering the light shielded region. Photogate in the light collection region is disposed above a photodiode to accumulate the photo-generated electrical charges. A doped region disposed near the photogate collects the attracted charges. The doped region extends to the light shielded region and transfers the collected charges to a floating diffusion through a shutter transistor also in the light shielded region. DTI or similar structures are deployed to the entire pixel array to prevent light from exchanging between different light collection regions and light from entering the light shielded regions of all pixel cells. Interference between the shielded regions of different pixel cells is also minimized.