oled pixel measurement & correction · 9/14/2017 · • all oled displays exhibit pixel-level...

Radiant Vision Systems | A Konica Minolta Company

Presented By Alex Podschwit | September 14, 2017OLED PIXEL MEASUREMENT & CORRECTION

Global SupportAutomated Visual InspectionLight & Color

3Radiant Vision Systems | A Konica Minolta Company

© Radiant Vision Systems, LLC.

TODAY’S AGENDA

• The Rise of OLED in Displays

• OLED Drives New Inspection Challenges

• Methods for Pixel-Level Measurement of OLED Displays• Automated Visual Inspection

• Measuring High-Resolution Displays

• The Measurement Process

• Pixel-Level Correction (Demura)

THE RISE OF OLED IN DISPLAYS



Smartphones & Tablets Televisions AR/VR Wearables

ORGANIC LIGHT-EMITTING DIODE (OLED) TECHNOLOGY IN DISPLAYS



DISPLAY TRENDS DRIVE NEW INSPECTION REQUIREMENTS

Increasing Display Size TVs > 70” Smartphones > 5+”

High Resolution Full HD to 4K to 8K

Vivid Picture Quality Full array backlights QD/ OLED

Curved & Non-Curved Form Factors

Growth of Microdisplays

Inspection of large displays while meeting required takt times

Improved accuracy over human inspection on increasingly pixel-dense displays

Pixel-level accuracy Detection of dead, stuck, &

non-uniform pixels OLED pixel-level variation

Automated display correction

Growing Need For:



OLED INTRODUCES NEW CHALLENGES

• Pixel-level variation

• Color dependence on brightness

• Regional non-uniformity (mura) at low grey levels



WHITE OLED DISPLAY



• At high grey levels (bright display), there is strong pixel-level variation, which is noticeable to the observer.

PIXEL-LEVEL VARIATION



COLOR DEPENDENCE ON GREY LEVEL• Response over grey level is different for the red, green, and blue emitters for the

same pixel within an OLED display.

• This response can lead to an overall white point change of the display over grey level, as well as on the pixel level.

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REGIONAL NON-UNIFORMITY

• Mura in OLED displays can appear at low grey levels, while the high-grey level can look uniform.

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WHY CORRECT OLED DISPLAYS?

• Improve yield• The more displays that are corrected, the more product produced,

the greater a supplier’s competitive advantage

• Limit waste due to inevitable quality issues• All OLED displays exhibit pixel-level variation

• Some displays can be corrected, reducing scrapped materials

• Safeguard efficiency• Automated, in-line OLED correction

solutions keep manufacturing processes moving despite quality issues



METHODS FOR PIXEL-LEVEL MEASUREMENT OF OLED DISPLAYS



AUTOMATED VISUAL INSPECTION…

• is proven for testing and grading displays

• consists of an imaging colorimeter and analysis software

• replaces human inspectors

• pin-points and quantifies quality issues and defects

• allows pass/fail determinations to be automated against a consistent standard



MEASUREMENT REQUIREMENTSA 29MP imaging colorimeter can be used to measure a display size up to 1920x1080.

Pitfalls of Alternative Solutions:

• Low-resolution CCD sensors will suffer from aliasing

• When synthetic pixels are sampled with this low resolution, the luminance deviation approaches ±10%

• Larger-resolution sensors exist (>29MP)

• Today these sensors have insufficient SNR for accurate luminance and chromaticity measurement

If the display resolution is greater, we recommend:

• Multiple 29MP imaging colorimeters

• Spaced Pixel Test Patterns (US Patent 9135851)



• Employs several 29MP imaging colorimeters with high signal-to-noise ratio (SNR) to measure displays with resolution higher than 1920x1080.

• Software combines the measurement results of these multiple imaging colorimeters, post-processes, and factorsinto a Synthetic Measurement.

• Synthetic Measurement represents 1 Measurement Pixel = 1 Display Pixel

MULTIPLE IMAGING COLORIMETER SOLUTION



dot matrix test pattern

Pattern 1 Pattern 2 Pattern 3 Pattern 4

• The other test patterns are similar, but with different display pixels turned ON.

• In this example it will take 9x test patterns to ensure that every display pixels is turned ON one time.

• In this method, a series of dot-matrix test patterns will be shown on the display.

• Each pattern has only a small portion of the display pixels turned ON (rest is OFF).

Pattern 9

SPACED PIXEL TEST PATTERNS



THE MEASUREMENT PROCESS



PIXEL MEASUREMENT STEPSRaw Images Synthetic Images Concatenated Image



Software automatically registers the ON-pixels and places Regions-of-Interest (ROI) on each ON-pixel, measuring the pixel luminance and color.

ROIs are placed on the registered ON-pixelsThis measurement is repeated for the different dot-matrix patterns until each display pixel is analyzed.

Each display pixel is tested by many CCD pixels, producing an accurate measurement

AUTO-REGISTRATION OF THE ON-PIXELS

Example from Radiant TrueTest™ Software.



OLED Laptop

OLED Phone 1

OLED Phone 2

OLED Phone 3

OLED Phone 4

OLED Watch 1

OLED Watch 2

LCD Phone 1

FOV: 250um (Full White )

Resolution 2560 x 1440 1440 x 2560 1080 x 1920 1080 x 1920 1080 x 1920 390 x 312 400 x 400 1080 x 1920

Pixel pitch X 0.12 mm 0.05 mm 0.10 mm 0.13 mm 0.07 mm 0.08 mm 0.09 mm 0.08 mm

Pixel pitch Y 0.12 mm 0.05 mm 0.13 mm 0.13 mm 0.07 mm 0.08 mm 0.09 mm 0.08 mm

RGB primary observations at 20% brightness

R = R+GG = G+R+B

No isolated primaries

R = R+G+B G = G+R+B

SUB-PIXEL LAYOUT SUMMARY

Every OLED device arranges pixels differently, with respect to layout and resolution.



The obtained luminance & color values are combined in a Synthetic Image showing all the displays’ pixel rows and columns.

Synthetic Image: 1 Measurement Pixel = 1 Display Pixel

Synthetic Image

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PASS / FAIL testing on luminance values can be applied to find pixel defects.

The location of pixel defects is reported in its row & column number.

SYNTHETIC IMAGE



OLED Phone 1 Device A

OLED Phone 1 Device B

OLED Phone 1 Device C OLED Phone 2 LCD Phone 1

Synthetic Image and Cross Section

Luminance Coefficient of Variation * 2.32% 2.81% 2.57% 2.36% 0.61%Cx Average * 0.309 0.303 0.300 0.296 0.306

Cx Standard Deviation * 0.004 0.003 0.003 0.003 0.000

Cy Average * 0.321 0.333 0.351 0.318 0.321

Cy Standard Deviation * 0.005 0.005 0.005 0.004 0.001

RESULTS COMPARISON: DEVICE TO DEVICE

* Note: Low frequency variation removed



MEASUREMENT RESULTS

• Luminance and color of each display pixel is measured with high accuracy

• Weak stuck-ON/OFF subpixels are easily found and accurately tested

• Different Pass/Fail thresholds can be applied for the different sub-pixels

• The location of display pixels is reported in (Column, Row) coordinates

• Sub-pixels can be tested by using test patterns in the different primary colors (RGB)



NON-UNIFORMITY CAN BE CORRECTED!

AfterBefore

Actual OLED Display Measurements



PIXEL-LEVEL CORRECTION USING RADIANT’S DEMURA SOLUTION



WHAT IS “DEMURA”?

• Even when OLED pixels receive the same electrical signal input, inconsistent luminance and chromaticity can occur from pixel to pixel

• These differences can be resolved using an in-line correction process called “Demura”

• Two steps to the Demura process:1. Use imaging colorimeters to evaluate and

quantify pixel uniformity issues

2. Apply grey-level passes to resolve uniformity based on precise pixel correction coefficients



IN-LINE APPLICATION1

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Measure

Results

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FIXABLE

FAIL

PA

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CORRECTION PROCESS

Select Imaging

ColorimeterTest Set-up Data

CollectionCompute Correction Coefficients

Transfer to OLED Screen

Controller

The correction process requires:

• measurement accuracy,

• measurement repeatability,

• careful definition of performance targets,

• compensation for OLED pixel and measurement geometries,

• and adjustment for human visual perception.



Measurement Hardware

• ProMetric® Imaging Photometer (Y29) or Colorimeter (I29)

• 29MP Sensor (6746 x 4384)

• Broad Dynamic Range (61.4 dB)

Demura Software

• TrueTest™ Demura Process

• Support for Multiple Pixel Layouts

• Proprietary Moiré Pattern Removal

• Grey-Level Correction Coefficients

• Fully-Documented API

RADIANT DEMURA SOLUTION



TrueTest DEMURA

SUPPORT FOR MULTIPLE PIXEL LAYOUTSLaptop Phone 1 Phone 2

Phone 3 Phone 4 Smart Watch



OLED PIXEL CORRECTION PROCEDURE

Utilize a high-resolution imaging colorimeter. Image right was captured with a Radiant 29MP imaging colorimeter.

• Register the sub-pixels within an image of the display

• The yellow ROI represents the location of pixels in the image

• Average the signal for each display’s sub-pixel over yellow ROI

• For each display’s sub-pixel compute luminance vs. grey level

• Compute a correction factor that will perform a uniformity correction for all grey levels



After Moiré removal

Before Moiré removal

• Display Resolution

• Photometer/Colorimeter Resolution

• Lens Design

• Filter

• Software Algorithm

Eliminate moiré due to:

TrueTest DEMURA

PROPRIETARY MOIRÉ PATTERN REMOVAL

Software capable of moiré removal ensures a clear image and enables more accurate pixel-level measurements.



GREY LEVEL CORRECTION COEFFICIENTS

Expected

Measured

Deviation

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Lv)

Gray Level (%)

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• Obtaining precise measurements of each pixel’s response over grey levels is critical to applying accurate correction coefficients for each grey level.

TrueTest DEMURA

GREY-LEVEL CORRECTION COEFFICIENTS

Video Signal In

Video Signal Out



RESULTS OF DEMURA UNIFORMITY IMPROVEMENT



CORRECTION: RED PIXELSBEFORE AFTER



CORRECTION: GREEN PIXELSBEFORE AFTER



CORRECTION: BLUE PIXELSBEFORE AFTER



CORRECTION: WHITE PIXELSBEFORE AFTER



CORRECTION RESULTS: ALL PIXELS

After Correction

Before Correction



SUMMARY

Pixel-level correction has a direct, positive impact on yield of advanced high-resolution OLED displays.

This is important in OLED because each pixel is an independent light emitter, which can behave and age differently than its neighboring pixels.

To perform pixel-level measurements, a colorimeter with very high resolution and high signal-to-noise ratio is critically important.

A Demura solution can be established in-line to measure and route devices based on the severity of mura, and then apply corrections to the fixable devices, reducing waste.

Radiant Vision Systems | A Konica Minolta CompanyRadiant Vision Systems | A Konica Minolta CompanyQuestions? Contact [email protected]

THANK YOU!

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oled pixel measurement & correction · 9/14/2017 · • all oled displays exhibit pixel-level...

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