Rectangular Microlens Design for CMOS Phase Difference Pixels

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Solution Overview

Problem

In solid-state imaging apparatuses, the conventional microlens design for phase difference detection pixels leads to gaps between adjacent pixels, causing light leakage and flare, which deteriorates image quality and affects Auto Focus (AF) performance.

Innovation Solution

A microlens design with a substantially spherical surface and a rectangular shape in a planar view, where the bottom surface near the opposite-side boundary is higher than near the diagonal boundary, and the curvature radii of the lens surface are approximately equal in both directions, with a pixel size of 3 μm or larger and a curvature radius ratio between 0.98 and 1.20, and an antireflection inorganic film is applied to minimize differences in curvature radii.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If the microlens is formed with a circular shape to achieve front-focus state, then the AF performance is improved, but gaps are formed between adjacent pixels causing light leakage and flare

Engineering Contradiction:

ImproveAF performanceVSAvoidlight leakage and flare

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The microlens is designed with an asymmetric shape where the bottom surface near the opposite-side boundary is higher than near the diagonal boundary. This asymmetric configuration allows the microlens to maintain rectangular shape filling the pixel region without gaps, while still achieving the front-focus state necessary for phase difference detection, thereby eliminating light leakage and flare between adjacent pixels.

Inventive Principle:

Principle #4Asymmetry

Solution Approach 2:

The microlens employs different curvature radii in different regions: a first curvature radius in the opposite-side center portion and a second curvature radius in the diagonal boundary portion. This local variation in optical properties allows the lens to maintain both the rectangular shape that fills the pixel region and the front-focus characteristic, preventing light from entering gaps between adjacent pixels.

Inventive Principle:

Principle #3Local quality

2Measurement precision

If the opening of the light-shielding film is made smaller than the imaging pixel, then the phase difference detection sensitivity is improved, but the image quality deteriorates due to gaps between pixels

Engineering Contradiction:

Improvephase difference detection sensitivityVSAvoidcolor mixing and flare

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The microlens is designed to have a rectangular shape that completely fills the pixel region, merging the lens boundary with the pixel boundary. This eliminates gaps between adjacent pixels, preventing light from leaking into neighboring pixels and causing color mixing or flare, while the microlens still maintains the front-focus state for sensitive phase difference detection.

Inventive Principle:

Principle #5Merging (Combining)

3Ease of manufacture

If the microlens bottom surface is made flat, then the manufacturing is simplified, but light cannot be properly collected and reflected to wiring metal causing flare

Engineering Contradiction:

Improvemicrolens fabricationVSAvoidflare

Core Design Contradiction:

Ease of manufactureVSObject-affected harmful factors

Solution Approach 1:

Inventive Principle:

Principle #3Local quality

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 AF performance while preventing light leakage and flare, thereby maintaining image quality and improving the sensitivity characteristics of phase difference detection pixels.

Implementation Method 1

a microlens that is formed corresponding to a phase difference detection pixel, the microlens being formed such that a lens surface thereof is a substantially spherical surface

Methodology Applied

Scientific EffectSpherical surface focusing: Lens

Implementation Method 2

an antireflection inorganic film is applied to minimize differences in curvature radii

Methodology Applied

Scientific EffectAntireflection: Anti-Reflective Coating

Data Source

PatentUS10088608B2Lens array and manufacturing method therefor, solid-state imaging apparatus, and electronic apparatus

Publication Date: 2018.10.02 SONY GROUP CORP

AI summary

The present technology relates to a lens array and a manufacturing method therefor, a solid-state imaging apparatus, and an electronic apparatus that can improve the AF performance while suppressing the deterioration of image quality. A lens array includes microlenses that are formed corresponding to phase difference detection pixels that are provided to be mixed in imaging pixels. Each of the microlenses is formed such that a lens surface thereof is a substantially spherical surface, the microlens has a rectangular shape in a planar view and four corners are not substantially rounded, and a bottom surface in vicinity of an opposite-side boundary portion that includes an opposite-side center portion of a pixel boundary portion in a cross-sectional view is higher than a bottom surface in vicinity of a diagonal boundary portion that includes a diagonal boundary portion. The present technology is applicable to a lens array of a CMOS image sensor, for example.