Image Sensor Pixel Element Modulating Quantum Efficiency

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Solution Overview

Problem

Existing image sensor technologies face limitations in efficiently modulating quantum efficiency and collecting charges due to parasitic capacitance, modulation contrast, and signal loss in global shutter imaging, particularly in Time-of-Flight and light field imaging applications.

Innovation Solution

A pixel element design featuring a semiconductor substrate with primary and secondary charge-collection nodes, peripheral nodes, and modulating nodes, where the modulating voltage independently controls the quantum efficiency by altering the reverse bias voltage between the charge-collection nodes and modulating nodes, allowing for efficient charge accumulation and measurement.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If quantum efficiency modulation is implemented using conventional CMOS transistors and capacitors, then charge collection capability is improved, but parasitic capacitance limits modulation speed and accumulated voltage

Engineering Contradiction:

Improvemodulation speedVSAvoidparasitic capacitance

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The patent extracts the charge steering function from conventional CMOS transistors and capacitors, implementing it directly within the pinned photodiode structure using floating diffusions. This removes the parasitic capacitance of external switching components while maintaining the charge collection capability.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent merges the charge collection and modulation functions into a single integrated structure where the pinned photodiode directly steers charge to floating diffusion nodes. This consolidation eliminates the need for separate CMOS switching circuits, reducing parasitic capacitance and simplifying the device architecture.

Inventive Principle:

Principle #5Merging (Combining)

2Speed

If gates extend further above the pinned photodiode to transfer charge rapidly, then charge transfer speed is improved, but transparent gate material is required increasing manufacturing complexity

Engineering Contradiction:

Improvecharge transfer speedVSAvoidgate material requirement

Core Design Contradiction:

SpeedVSEase of manufacture

Solution Approach 1:

Instead of extending gates upward to achieve fast charge transfer, the patent inverts the approach by using the pinned photodiode structure itself to perform the steering function. The floating diffusions are positioned to directly receive charge from the pinned photodiode, eliminating the need for extended transparent gates.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent replaces the mechanical/physical extension of gate structures with an electrical field-based charge steering mechanism. The pinned photodiode uses voltage control to direct charge flow to different floating diffusion nodes, achieving fast transfer without physical gate extensions.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Quantity of substance

If capacitor capacitance is increased to maintain large signal in quantum efficiency modulation, then signal strength is improved, but modulation contrast decreases

Engineering Contradiction:

Improvesignal charge amountVSAvoidmodulation contrast

Core Design Contradiction:

Quantity of substanceVSMeasurement precision

Solution Approach 1:

The patent implements dynamic quantum efficiency modulation by controlling the voltage on the pinned photodiode to alternately attract electrons or holes. This creates a time-varying charge collection efficiency that achieves high modulation contrast while maintaining adequate signal levels through the direct floating diffusion collection path.

Inventive Principle:

Principle #15Dynamics

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 enhances modulation contrast, improves charge collection efficiency, and reduces signal loss, enabling better performance in Time-of-Flight, light field, and High Dynamic Range imaging while maintaining low power consumption and compliance with eye safety regulations.

Implementation Method 1

a semiconductor substrate of a first or second conductivity type, the semiconductor substrate having a front side and a backside, wherein the semiconductor substrate is configured to be exposed to a flux of photons, and to convert the flux of photons to first and second conductivity-type mobile charges

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Data Source

PatentUS11411027B2Systems and methods for modulated image capture

Publication Date: 2022.08.09 KOVILTA OY

AI summary

Disclosed is a pixel element comprising a semiconductor substrate, a primary charge-collection node, a peripheral node, a modulating node, a circuitry and a backside conductive layer. The semiconductor substrate is configured to convert a flux of photons to first and second conductivity-type mobile charges. The peripheral node at least partially surrounds the primary charge-collection node, which at least partially surrounds the modulating node. The circuitry is used to connect and disconnect a reset voltage to/from the primary charge-collection node, provide a peripheral node voltage to the peripheral node, and measure an amount of the first conductivity-type mobile charges collected by the primary charge-collection node. The modulating node is electrically connected to a modulating voltage source, which is independent of the peripheral node voltage. The backside conductive layer is configured to collect and conduct the second conductivity-type mobile charges, and configured to be electrically connected to a bias voltage.