Sense Node Capacitive Structure for 3D Time-of-Flight Sensor
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Solution Overview
Problem
Three-dimensional time-of-flight cameras face limitations in distance resolution due to the limited storage capacity of pixels, which affects signal quality and background light suppression, especially as the number of storage nodes increases, reducing the optical fill factor and sensitivity.
Innovation Solution
A pixel structure combining gate and diffusion capacitances for enhanced electron storage, allowing higher capacitance per unit area and reduced noise, with a floating n+ diffusion region as a sense node and an amplifier for readout, enabling efficient storage and minimization of the sense node area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If diffusion capacitance is used for electron storage in sense nodes, then the pixel can store charge carriers, but the capacitance per unit area is limited by technology parameters and cannot be increased further
Solution Approach 1:
The patent merges gate capacitance and diffusion capacitance into a hybrid storage structure. The gate electrode creates a depletion region that provides additional capacitance beyond what diffusion alone can provide, effectively combining both mechanisms to achieve higher capacitance per unit area in the sense node.
Solution Approach 2:
The patent changes the electrical parameters of the sense node by introducing a gate electrode that modifies the capacitance characteristics. By controlling the gate voltage, the depletion region width and capacitance can be dynamically adjusted, enabling higher storage capacity without increasing physical area.
2Measurement precision
If the number of storage nodes is increased to improve distance resolution, then measurement precision improves, but the optical fill factor decreases and sensitivity is reduced
Solution Approach 1:
The patent merges multiple storage functions into a single sense node by implementing multiple integration nodes within one pixel. This allows the pixel to perform multiple integration operations sequentially, effectively increasing the number of storage operations without adding separate physical storage nodes that would reduce fill factor.
Solution Approach 2:
The patent transitions from spatial multiplication of storage nodes to temporal multiplication through sequential integration cycles. By using time-domain multiplexing with multiple integration phases, the system achieves enhanced measurement precision without increasing the spatial footprint of the pixel array.
3Quantity of substance
If larger sense node area is used to increase capacitance, then more electrons can be stored, but the pixel area occupied increases reducing overall array density
Solution Approach 1:
The patent changes the capacitance parameter through electrical control rather than physical scaling. By applying gate voltages to create depletion regions, the effective capacitance volume is increased without proportionally increasing the physical pixel area, maintaining high array density while improving storage capacity.
Solution Approach 2:
The patent creates a composite capacitance structure combining gate-controlled depletion region capacitance with diffusion capacitance. This composite approach leverages both mechanisms to achieve superior capacitance density, storing more charge carriers within the same pixel footprint compared to diffusion-only structures.
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 increases the overall capacitance, allowing more charge carriers to be stored while reducing noise and maintaining high sensitivity, thus improving distance resolution and background light suppression.
Implementation Method 1
a photosensitive area (5) that converts light into photogenerated charges
Implementation Method 2
a storage structure comprising an integration gate (2) and a diffusion capacitance (3) that stores the photogenerated charges
Data Source
AI summary
An increased sense node capacitance, mainly for 3D time-of-flight (TOF) applications, includes a storage structure that combines the advantages of gate and diffusion capacitance in order to improve the overall capacitance. The storage structure provides higher capacitance per unit area and accordingly a better fill-factor/sensitivity of the pixel; improved noise behaviour because of the use of gate capacitances, better protection against interacting signals and thus better signal quality.