Image Sensor Microlens Array Using Hydrophilic-Hydrophobic Segregation

Solution Overview

Problem

Current microlens formation processes in image sensors are limited by the formation of lens bridges due to the use of hydrophobic photoresist materials, which restrict the minimum gap width to about 50 nm and prevent the creation of zero-gap microlenses, impacting photo sensitivity and device performance.

Innovation Solution

The use of a hydrophilic and hydrophobic material combination for microlenses, where the first set is formed of a hydrophilic material and the second set of microlenses is formed of a hydrophobic material, allowing for the creation of a microlens array with zero gaps by adjusting their sizes and shapes through thermal reflow, preventing lens bridges by exploiting the non-mixing properties of hydrophilic and hydrophobic materials.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If hydrophobic photoresist material is used for microlens formation, then the microlens can be formed through thermal reflow, but lens bridges form between neighboring microlenses due to material mixing

Engineering Contradiction:

Improvemicrolens formationVSAvoidlens bridge prevention

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent applies local quality by using different material properties (hydrophobic vs. hydrophilic) for different sets of microlenses within the same array. Specifically, first sets of microlenses are formed from hydrophobic photoresist material while second sets are formed from hydrophilic photoresist material, creating local material differentiation that prevents lens bridge formation at interfaces between neighboring microlenses of the same material type.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent employs composite materials by combining hydrophobic and hydrophilic photoresist materials in a microlens array. This composite approach creates distinct material regions where hydrophobic microlenses are separated from hydrophilic microlenses, preventing the mixing phenomenon that causes lens bridges while maintaining the optical functionality of the entire array.

Inventive Principle:

Principle #40Composite materials

2Quantity of substance

If photolithography pattern width is reduced to minimize gaps, then photo sensitivity improves, but minimum gap width is limited to about 50 nm due to lithography resolution limitations

Engineering Contradiction:

Improvephoto sensitivityVSAvoidgap width control

Core Design Contradiction:

Quantity of substanceVSManufacturing precision

Solution Approach 1:

The patent applies parameter changes by utilizing the contact angle parameter difference between hydrophobic and hydrophilic materials during thermal reflow. This parameter difference causes the materials to segregate and form distinct regions, enabling gap widths smaller than the lithography resolution limit (50 nm) to be achieved through self-organization of the materials during the reflow process.

Inventive Principle:

Principle #35Parameter changes

3Quantity of substance

If gap width between microlenses is reduced to less than 50 nm, then photo sensitivity improves by more than 15%, but neighboring microlenses merge during reflow forming lens bridges

Engineering Contradiction:

Improvephoto sensitivityVSAvoidmicrolens separation

Core Design Contradiction:

Quantity of substanceVSShape

Solution Approach 1:

The patent applies local quality by using different material properties (hydrophobic vs. hydrophilic) for different sets of microlenses within the same array. Specifically, first sets of microlenses are formed from hydrophobic photoresist material while second sets are formed from hydrophilic photoresist material, creating local material differentiation that prevents lens bridge formation at interfaces between neighboring microlenses of the same material type.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent employs composite materials by combining hydrophobic and hydrophilic photoresist materials in a microlens array. This composite approach creates distinct material regions where hydrophobic microlenses are separated from hydrophilic microlenses, preventing the mixing phenomenon that causes lens bridges while maintaining the optical functionality of the entire array.

Inventive Principle:

Principle #40Composite materials

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 effectively inhibits lens bridge formation between neighboring pixels, enabling the fabrication of microlenses with zero gaps, thereby enhancing the image sensor's performance and photo sensitivity.

Implementation Method 1

heat is applied to the material to reflow it so that a spherical curve is formed

Methodology Applied

Scientific EffectThermal reflow: Heating

Implementation Method 2

a first set of microlenses formed of a hydrophilic material and a second set of microlenses formed of a hydrophobic material

Methodology Applied

Scientific EffectHydrophobic effect: Hydrophobe

Implementation Method 3

a first set of microlenses formed of a hydrophilic material and a second set of microlenses formed of a hydrophobic material

Methodology Applied

Scientific EffectHydrophilic effect: Hydrophile

Data Source

PatentUS7538949B2Image sensor and manufacturing method thereof

Publication Date: 2009.05.26 III HOLDINGS 4 LLC

AI summary

An image sensor and method for fabricating an image sensor are provided. The image sensor includes a substrate and a microlens array in a checkerboard pattern. In some embodiments, the checkerboard pattern involves alternating hydrophilic and hydrophobic microlenses.