Planar Waveguide Filter for CMOS Sensor Diffraction Loss

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Solution Overview

Problem

As complementary metal-oxide semiconductor (CMOS) image sensors are scaled down, microlenses' diffraction effects negatively impact quantum efficiency, leading to reduced performance in focusing incident radiation onto photodetectors.

Innovation Solution

A wave guide filter with a substantially planar upper surface is introduced, comprising a light filter grid structure and light filters with different refractive indices, guiding incident light onto photodetectors to minimize diffraction effects and enhance quantum efficiency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Volume of moving object

If CMOS image sensors are scaled down, then device size and manufacturing cost are reduced, but microlenses' diffraction effects worsen and quantum efficiency decreases

Engineering Contradiction:

Improvedevice sizeVSAvoidquantum efficiency

Core Design Contradiction:

Volume of moving objectVSReliability

Solution Approach 1:

The patent replaces the traditional microlens optical system with a waveguide-based light guiding system. The waveguide uses total internal reflection and refractive index differences to guide light to photodetectors, eliminating diffraction effects that plague scaled-down microlenses. This substitution maintains light focusing capability while avoiding the diffraction limitations that worsen quantum efficiency in miniaturized sensors.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the optical parameters by using materials with specific refractive index differences (first material with higher refractive index, second material with lower refractive index). This parameter change enables waveguide mode propagation and total internal reflection, allowing efficient light guidance without the diffraction effects that occur in conventional microlens systems at small scales.

Inventive Principle:

Principle #35Parameter changes

2Device complexity

If microlenses are used in scaled-down sensors, then device complexity is reduced, but diffraction effects increase and performance deteriorates

Engineering Contradiction:

Improvestructure complexityVSAvoidfocusing precision

Core Design Contradiction:

Device complexityVSManufacturing precision

Solution Approach 1:

The patent substitutes the microlens mechanical/optical system with a waveguide system that uses refractive index contrasts and total internal reflection. This replacement achieves precise light guidance to photodetectors without the diffraction-limited focusing precision that plagues scaled-down microlenses, while maintaining relatively simple device structure.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Device complexity

If traditional light filtering is used, then device structure is simple, but light guidance efficiency is reduced and quantum efficiency is impacted

Engineering Contradiction:

Improvestructure complexityVSAvoidlight energy loss

Core Design Contradiction:

Device complexityVSLoss of energy

Solution Approach 1:

The patent merges the light filtering function with the light guiding function into a single integrated waveguide structure. The waveguide simultaneously guides light from the microlens array and filters it through material absorption characteristics, eliminating the need for separate filter components and reducing overall light energy loss while maintaining simple device structure.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The waveguide structure serves multiple functions: it guides light via total internal reflection, filters specific wavelengths through material properties, and directs light precisely to photodetector pixels. This multi-functionality reduces the number of separate components needed, minimizing light energy loss while keeping the device structure relatively simple.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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

The wave guide filter improves quantum efficiency by effectively focusing incident radiation onto photodetectors, reducing the negative impacts of diffraction in scaled-down CMOS image sensors, thereby enhancing pixel resolution and reducing the form factor.

Implementation Method 1

The light filter comprises a first material having a first refractive index, and the light filter grid structure comprises a second material having a second refractive index that is less than the first refractive index

Methodology Applied

Scientific EffectRefraction: Refraction

Implementation Method 2

the wave guide filter is configured to guide incident light toward the photodetector

Methodology Applied

Scientific EffectTotal internal reflection: Total Internal Reflection

Data Source

PatentUS11862650B2Wave guide filter for semiconductor imaging devices

Publication Date: 2024.01.02 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

In some embodiments, an image sensor is provided. The image sensor includes a photodetector disposed in a semiconductor substrate. A wave guide filter having a substantially planar upper surface is disposed over the photodetector. The wave guide filter includes a light filter disposed in a light filter grid structure. The light filter includes a first material that is translucent and has a first refractive index. The light filter grid structure includes a second material that is translucent and has a second refractive index less than the first refractive index.