Background Statement for SEMI Draft Document 4913A

Background Statement for SEMI Draft Document 4913A

Revision to SEMI D31-1102, with title change from “Definition of Measurement Index (SEMU) for Luminance Mura in FPD Image Quality Inspection” to “Definition of Measurement Index (DSEMU) for Luminance Mura in FPD Image Quality Inspection”

Notice: This background statement is not part of the balloted item. It is provided solely to assist the recipient in reaching an informed decision based on the rationale of the activity that preceded the creation of this Document.

Notice: Recipients of this Document are invited to submit, with their comments, notification of any relevant patented technology or copyrighted items of which they are aware and to provide supporting documentation. In this context, “patented technology” is defined as technology for which a patent has issued or has been applied for. In the latter case, only publicly available information on the contents of the patent application is to be provided.

Background:

SEMI D31 is the standard regarding FPD Mura, which was published in 2002. At that time, the panels up to 20 inches had predominated in the FPD industry, which resulted in viewing distance limited to 50 cm. However, recently, panels up to 100 inches have been on the market. As the panel size becomes larger, the viewing distance changes accordingly. As a result, there have been many cases where SEMI D31 is not applicable.

Revision of SEMI D31 is proposed in this ballot to redefine the level of Mura by changing viewing distance according to the size of panels.

This document was voted at the cycles 1 in 2011 and was rejected by the mismatch among formulas of DSEMU Definition.This mismatch has been discussed carefully and corrected by the D31 Revision Task Force under the Japan FPD Metrology Committee and Doc.#4913A has been prepared.

The voting results of Doc.#4913Awill be reviewed by the D31 Revision Task Force and will be adjudicated at the Japan FPD Metrology Committee on November, 2 at SEMI Japan, Tokyo, Japan

Finally, the D31 Revision Task Force and the Japan FPD Metrology Committee would like to thank and acknowledge the Taiwan FPD committee for their great support to revise D31.

If you have any questions, please contact the D31 Revision Task Force co-leaders as shown below:

- Keizo Ochi (Konica Minolta Optics) ,

- Kosei Tanahashi (Samsung Electronics)

- Masao Kochi (Highland)

SEMI Staff

Naoko Tejima (SEMI Japan) at

Semiconductor Equipment and Materials International

3081 Zanker Road

San Jose, CA 95134-2127

Phone: 408.943.6900, Fax: 408.943.7943

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SEMI Draft Document 4913A

1 Purpose

1.1 This standard defines the index of measurement for mura in FPD image quality inspection.

1.2 This standard defines distance factor.

1.3 Based on the result of investigation for human eye’s sensitivity to mura in ergonomics approach, this standard proposes an index for level of mura by expressing the function of the major axis and contrast of mura.

2 Scope

2.1 This standard is applicable to Flat Panel Display (FPD) excluding Cathode-ray Tube (CRT) and Head Mount Display (HMD). Applicable display sizes are from Type 10 (10" diagonal) to Type 100 (100" diagonal). Viewing distance ranges from 0.5 m to 5 m.

NOTICE: SEMI Standards and Safety Guidelines do not purport to address all safety issues associated with their use. It is the responsibility of the users of the Documents to establish appropriate safety and health practices, and determine the applicability of regulatory or other limitations prior to use.

3 Limitations

3.1 Mura to be measured is limited as below:

3.1.1 This standard is not applicable to line defects narrower than 300 µm and pixel dot defects.

3.1.2 Background display is limited to monochromedisplays/intermediate gray scale level.This standard is not applicable to color background such as RGBand L0/L63 background.

4 Referenced Standards and Documents

4.1 SEMI Standard

SEMI D57 ― Definition of Measurement Index (VCT) for Mura in FPD Image Quality Inspection

NOTICE: Unless otherwise indicated, all documents cited shall be the latest published versions.

5 Terminology

5.1 Abbreviations and Acronyms

5.1.1 DSEMU ― distance-considered SEMI Mura

5.1.2 JND ― just noticeable difference

5.2 Definitions

5.2.1 distance-considered SEMI Mura(DSEMU) ―measurement index for distance-linked mura

5.2.2 just noticeable difference (JND) ―used in the field of Psychophysics; for a certain stimulus, the smallest change in stimulus (luminance, for example) where a difference can be perceived. Specifically, it is often used to indicate a statistical value where the probability of the difference being “perceptible” is 50% and the probability of the difference “not being perceptible” is 50%. This is also expressed as j.n.d. using lower case letters.

6 DSEMU Definition

6.1 Under specific conditions, the below regressive relationship isshown between the major axis and contrast for Human Mura JND (Refer to Related Information 1).

Cjnd = F(d)

=2.2K(1/d0.33)(1)

Cjnd: Contrast of mura at JND (Unit: %, relative to background [=100%])

d:Major axis of mura at above contrast (Unit: mm)

6.1.1 In the above equation, contrast at JND is inversely proportional to the major axis powered by 0.33. In short, it indicates that as muramajor axis gets shorter, darker murasare sensed.

6.2 For the subject mura, the mura level, DSEMU, is calculated using the below formula, from equation (R1-1), (R2-1), (R1-3), (R1-4)

DSEMU= |Cx| / Cjnd[d=dx]

= |Cx| /F(dx)

= |Cx| /(2.2K(1/ dx0.33)) (2)

Cx:Average contrast of mura being measured (Unit: %, relative to background [=100%])

dx: Major axis of mura being measured (Unit: mm)

K:Distance factor (Unit: m): 0.2D2-0.2D+1

D: Viewing Distance

7 Notation

7.1 DSEMU is a comparison ratio between contrast of the measurement target and its major axis, and thus has no unit.

8 Test Methods

8.1 Comparative Measurement and Direct Measurement — The two methods for determining DSEMU levels on panels are comparative measurement and direct measurement.

8.1.1 Comparative Measurement

8.1.1.1 The comparative measurement method involves a panel and software which simulate DSEMU level, to which a person compares a mura on an actual panel, making adjustments, until a level which appears similar is determined. This is a method that is used in the actual production site easily using the DSEMU simulation panel as the variable level limit sample.

8.1.2 Direct Measurement

8.1.2.1 The direct measurement method captures the actual panel with a CCD camera, or the like, and is a method of measuring the DSEMU level of the mura section, making it possible to directly determine the DSEMU from the major axis and contrast of the mura section that is captured.

8.2 Measurement Equipment

8.2.1 DSEMU measurement consists of measurement of the major axis of Mura on the display surface and contrast measurement, and needs to be appropriately calibrated.

8.3 Measurement Environment

8.3.1 DSEMU measurement is conducted in a darkroom environment.

8.4 Display Conditions

8.4.1 Background luminance for DSEMU measurement shall be 50±5cd/m2.

8.5 Contrast Measurement

8.5.1 The average contrast of the mura section shall be measured, and the contrast ratio of the mura section will be expressed as a percentage, while the background = 100%.

APPENDIX 1

Definition of Measurement Index (SEMU) for Luminance Mura in FPD Image Quality Inspection

NOTICE: The material in this Appendix is an official part of SEMI [designation number] and was approved by full letter ballot procedures on [A&R approval date].

A1-1 Terminology

A1-1.1 Definitions

A1-1.1.1 Semu―Semi Mura, Mmeasurement index for mura

A1-2 SEMU Definition

A1-2.1 Under specific conditions, the below regressive relationship can be seen between area and contrast for Human Mura JND. (Refer to Related Information.)

Cjnd = F(S)=1.97/S0.33 + 0.72(A1-1)

Cjnd: Contrast of mura at JND (Unit: %, relative to background [=100%])

S: Area of mura at above contrast (Unit: mm2)

A1-2.1.1 In the above equation, contrast at JND is inversely proportional to area raised to the 0.33 power. In short, it indicates that as mura area gets smaller, only darker murasare sensed.

A1-2.2 For the subject mura, the muralevelandSemu are be calculated using the below formula.

Semu = |Cx| / Cjnd[S=Sx]

= |Cx| / F(Sx)

= |Cx| /(1.97/Sx0.33 + 0.72)(A1-2)

Cx: Average contrast of mura being measured (Unit: %, relative to background [=100%])

Sx: Surface area of mura being measured (Unit: mm2)

RELATED INFORMATION 1
EXPERIMENT OUTLINE FOR CALCULATION OF MEASUREMENT INDEX FOR LUMINANCE MURA IN FPD IMAGE QUALITY INSPECTION

NOTICE: This Related Information is not an official part of SEMI [designation number] and was derived from the work of the global [committee name] Technical Committee. This Related Information was approved for publication by full letter ballot procedures on [A&R approval date].

R1-1 Purpose

R1-1.1 It has been reported that under the range of certain conditions, a basic expression of FPD mura quality level can be made, using their size and contrast. Here, recreating those experiments, we verified their reproducibility, conducting the experiment with a goal of calculating a measurement index for luminance mura for standardization.

R1-2 Experiment Method

R1-2.1 Experiment Equipment

R1-2.1.1 The experiment utilized a 19.0 inch, 1240 X 768 pixel backlit TFT/LCD. As there was a need to display low contrast luminance muras, it was reworked to display 256 gradations in a 43 cd/m2 ~ 54 cd/m2 range. A program capable of displaying rectangular and round muras as desired was created, and the muras were displayed in the center of the prepared LCD. The subjects could freely adjust the luminance of the displayed luminance muras using a keyboard.

R1-2.2 Experiment Conditions

R1-2.2.1 21 types of muras were used. These were six round types (diameter: 2 mm, 5 mm, 10 mm, 25 mm, 50 mm, 100 mm) Observation conditions were a viewing distance of 0.5 m, 1 m, 2 m and view angle normal to the center of the LCD. The experiment room was a darkroom, and the background luminance of the luminance mura was 50 cd/m2. As for ellipse types (2:1 or 3:1), they were observed for reference.

R1-2.3 Subjects/Experiment Procedure

R1-2.3.1 The subjects for the experiment were randomly-selected 66 adults. Of the 66 subjects, there was an Expert group of 20, consisting of engineers from LCD makers, who regularly conduct mura inspections and analysis. The remaining 46 subjects were college students and working people, a Novice group who conducted luminance mura evaluation for the first time. Using the keyboard, the subjects adjusted the luminance of mura, to a point “where mura can just no longer be detected” (referred to as “jnd”: just noticeable difference below) and to a “point where mura can clearly be detected”. The contrasts were recorded at these times. Muras brighter than the background and lighter than the background were both targeted. For the purpose of getting data from wide range of people, subjects were randomly selected.

R1-3 Experiment Results

R1-3.1 It became clear from the experiment that thelonger the major axis is, the smaller the contrast (C) became (Muras are more visible as the major axis becomes longer).

R1-3.2 The relation between muramajor axis and contrast showed the same trend as in past experience, and the quality of reproducibility was confirmed. Therefore at this point, for the sake of standardization, we examined the function for muramajor axis, and tried linear regression for it with contrast. Figure R1-1 shows the results. When the horizontal axis is 1/(d)0.33(d is the major axis of mura. Unit is mm), and the vertical axis is contrast, the bold line shows a strong correlation coefficient, understood through linear regression. However, when mura is larger than a specific size, it is not always the case.

R1-3.3 Regression equation in Figure R1-1 is proposed as a basis for standardization.

Cjnd = 2.2 f(d)(R1-1)

f(d) = 1/(d)0.33(R1-2)

Multiply the above value by distance factor: K. This is the final equation.

Cjnd= 2.2f(d)K(R1-3)

K = 0.2D2-0.2D+1 (R1-4)

D: Viewing Distance

R1-4 Summary

R1-4.1 A proposal was made regarding the quantization of FPD luminance mura. The quality level of a murais expressed as a function between muramajor axis and contrast, using the contrast at the jnd point as criteria.

f(d)

Figure R1-1
Relation between the Major Axis of Luminance Mura and Contrast (Viewing Distance: 0.5 m)

f(d)

Figure R1-2
Relation between the Major Axis of Luminance Mura and Contrast (Viewing Distance: 1.0 m)

f(d)

Figure R1-3
Relation between the Major Axis of Luminance Mura and Contrast (Viewing Distance: 2.0 m)

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