Chapter 4 Simulation results and discussions
4.5 Comparison
The structures of the other two prior arts, as illustrated in table 4.1, are listed here for comparison. The dimension of our proposed ALEL pixel was about 300 µm, which fitted the pixel of light source. Other variables were determined by optimized results and process limitation. The optimal pixel spacing was equal to Dr. Wei’s result and the height was larger than the other two prior arts. As a result, the gain factor of our proposed structure is as high as 1.70.
Table 4.1 Gain factor of OLED panels with various microlens geometry.
Journal Mao-Kuo Wei,
OPTICS EXPRESS, No 23, Vol. 12, 2004
S. Moller, J. Appl. Phys.,
V9, 2002
NCTU
Spherical geometry Arc geometry pyramid-shaped geometry (55o)
Microlen Dimension (µm) 100 10 ~ 300
Pixel Spacing (µm) 11 ~ 0 15
Height (µm) 50 5 200
ALEL Material PMMA PDMS PDMS
Gain factor 1.56 1.50 1.70
Structure
4.6 Summary
We have designed and optimized the array light-enhancing layer on an OLED panel.
From the mentioned analyses, thus the structure of ALEL has the distinguished capability to eliminate the total internal reflection (TIR) effect, thus, light efficiency and gain factor of OLED panel can be increased significantly. Optimized pyramidal ALEL yields a gain factor of 1.7. A pyramidal ALEL on OLED panel produces higher light efficiency than other structures in our simulation results.
Additionally, according to the simulated results, three important features of design rules for ALEL on OLED panel can be derived:
In ideal alignment cases, the gain factor can be optimized with (a) Narrower pixel spacing
(b) Tilt angle of 50º to 55º
(c) Opening area ratio smaller than 30 %.
For alignment issue, the area of pixel spacing cross light source was the main factor of the gain factor loss.
Chapter 5
Experimental Results and Discussions
5.1 Introduction
Based on the simulation and fabrication presented in the previous chapters, the experimental results and discussions will be shown in this chapter. Optical microscope (OM) and SEM were utilized to examine the mold and ALEL. The optical performances of a Chung Hwa Picture Tube, Ltd (CPT) OLED panel with ALEL, such as luminance, were measured by Chromameter CS-100 and Conoscope. Finally, the gain factors of ALEL-attached OLED panels with two different pixel sizes are compared.
5.1.1 Mold examination
Optical microscope was used to examine the fabricated structures of silicon mold. The spacing between two adjacent pixels and the pixel size were checked, as illustrated in Figs. 5.1 (a) and (b). The height (H) of each ALEL pixel was also inspected as illustrated in Fig. 5.2 (a).
Wet etching rate on the {111} crystal lattice direction, as illustrated in Fig. 5.2 (b), is 400 times slower than the {100} direction [22]. Since the angle between {100} and {111} crystal lattice is well-know as 54.74º, which fits our optimized TILT, the relationship between the height of the ALEL pixel (H) and the width of the slope (W) can be derived by the following equation:
H = W tan (54.74º ) (1)
Spacing between two adjacent pixels
15 µm 40 µm
(a)
Pixel size
Pixel size of ALEL : Pixel size of OLED panel1:1 0.5 : 1 0.2 : 1
(b)
Fig. 5.1 Photographs of fabricated structure on molds from optical microscope (a) different spacing between two adjacent pixels and (b) different pixel size.
Height of ALEL pixel
W
H
H = W tan (54.74º )
W
H
{111}
{100 }
54.74o
Si-mold
{111}
{100 }
54.74o
Si-mold
(a) (b)
Fig. 5.2 Illustrations of fabricated structure on molds from optical microscope (a) height of ALEL pixel and (b) cross-section and crystal lattice direction of a silicon mold.
5.1.2 Replication examination
Optical microscope and SEM were used to examine the replicated ALEL. The overviews of ALEL are shown in Figs. 5.3 and 5.4, while various variables of ALEL are illustrated in Fig.
5.5.
Fig. 5.3 A photograph of ALEL.
Fig. 5.4 SEM photographs of ALEL.
~
Tilt angle of pyramidal pixel
TILT
TILT ~~
Tilt angle of pyramidal pixel
TILT TILT
(a)
LEL_S LEL_S
Spacing between two adjacent pixels
15 µm 30 µm 40 µm
(b)
(d)
Fig. 5.5 Photographs of ALEL by optical microscope (a) tilt angle of ALEL pixel, (b) various spacing between two adjacent pixels, (c) various height of two ALEL pixel, and (d) various pixel size.
5.1.3 Measurement System
The measurement system was illustrated in Fig. 5.6. The optical performance, the luminance of ALEL region at the direction normal to CPT OLED panel, was measured by Chromameter CS-100 and Conoscope in a dark room.
Detector
( MINOCTA Chroma Meter CS-100 ) OLED Panel (CPT)
Power Supply
Detector
( MINOCTA Chroma Meter CS-100 ) OLED Panel (CPT)
Power Supply
(a)
Detector (Conoscope)
(b)
Fig. 5.6 Photographs of measurement systems (a) Chromameter CS-100 and (b) Conoscope.
5.2 Results and discussions
5.2.1 Alignment issue
5.2.1.1 Moire pattern
According to the measured luminance, we studied the alignment issue first. Several alignment cases, as illustrated in table 5.1, are listed here for comparison. Free from moire pattern is the desired optical performance as shown in the left alignment of the case 1. Moire pattern are serious in the cases 2 and 3. We checked the periods of pixel size of ALEL and the pixel size of the OLED panel, they were different along x and y axes. Therefore, the experimental results show that when one ALEL pixel fitting with one OLED pixel and without rotational misalignment, both ALEL shifts along x and y axes are allowed for the OLED panel to be free from moiré pattern.
Table 5.1 Moire pattern between various alignment cases for comparison.
Alignment Image Moire Pattern
5.2.1.2 Gain factor loss
According to the experimental results of gain factor loss, larger cross region of pixel spacing and light source caused a lower gain factor, as illustrated in Fig. 5.7. Hence, the area of pixel spacing of ALEL cross the light source of OLED panel was the dominant factor in alignment, so called the pixel spacing effect in this thesis.
(a)
(b)
(c)
Fig. 5.7 Illustration of gain factor loss for various ALEL alignment cases (a) alignment mark aimed at the center of ALEL pixel, (b) various alignment cases (c) the corresponding photographs from conoscope and gain factor.
The luminance of the OLED panel measured by chromameter CS-100 was 55 cd/cm2.
Gain factor 1.95
Gain factor 1.62
Gain factor 0.93
5.2.2 Height and pixel spacing of pyramidal pixel
n
and simulated results. Besides, the relative curves can be transferred to the relationship between gain factor and opening area ratio, as illustrated in Fig. 5.9. As the results, the smaller opening area ratio can provide a higher gain factor, which agrees with the simulated result.
Fig. 5.8 Illustration of the relationship between gain factor and Height. The tilt angle is 55o. The relationship between gain factor and height, as illustrated in Fig. 5.8, was the studied for ideal alignment. The tendencies of relative curves are similar in both experimental
0.8 1.0
G 1.2
1.4 1.6 1.8 2.2
0 50 100 150 200 250
Height (µm)
a in F acto r
2.0
Spacing = 15 µm Spacing = 30 µm Spacing = 40 µm Spacing = 15 µm Simulation result
1.0 1.2 1.4 1.6 1.8 2.0 2.2
0 10 20 30 40 50 60 70
Opening area ratio (%)
G a in F acto r
Spacing = 15 µm Spacing = 30 µm Spacing = 40 µm
Fig. 5.9 Illustration of the relationship between gain factor and opening area ratio.
The tilt angle is 55o.
5.2.3 Pixel size of pyramidal pixel
In addition, the relationship between gain factor and pixel size of ALEL, as illustrated in Fig. 5.10, was investingated. From the results, the case of the pixel size of ALEL equal to the pixel size of OLED panel obtained the maximal gain factor, and the pixel spacing effect appeared in the smaller pixel size of ALEL.
0.8
Pixel size of ALEL : Pixel size of OLED panel = 1:1
Pixel
Fig. 5.10 Illustration of the relationship between gain factor and pixel size.
5.3 Comparison
For comparison, two OLED panels with ALELs were demonstrated in Fig. 5.11, and the CPT OLED panel with the optimized ALEL showed a gain factor of 2.03, which was based on the process limitation. Because the pixel size of ALEL was different from that of X company, pixel spacing effect would cause more serious moire patterns and larger gain factor loss on X company’s OLED panel.
Fig. 5.11 Photographs of OLED panels with ALELs (a) CPT 7” OLED panel and (b) ‘X’
company 1.5” OLED panel.
‘X' company 1.5” OLED Panel
Gain factor 1.05OLED Panel ALEL
CPT 7” OLED Panel
Gain factor 2.03CPT 7” OLED Panel
Gain factor 2.035.4 Summary
The experiments, including ALEL fabrication, measurements from Chromameter and Conoscope, were implemented and successfully demonstrated the improvements of luminance and angular distribution of the proposed ALEL, designed for the CPT OLED panel. Based on one pixel size of ALEL fitting one pixel size of OLED panel, ALEL shifts along x and y axes are allowed for the OLED panel to be free from moiré pattern. Meanwhile, the measured results of several alignment cases were investigated and explained as the pixel spacing effect.
According to the experimental curves of gain factor versus variables of ALEL, the higher luminance efficiency correlates to smaller opening area ratio, narrower pixel spacing, which agrees with the simulated results. Furthermore, the CPT OLED panel with the optimized pyramidal ALEL yields a gain factor of 2.0.
Chapter 6
Conclusions and future work
hancing layer designed for on CPT OLED panel was proposed and successfully demonstrated. In simulations, we analyzed the transmittance at the interface between the top-glass substrate and air to confirm that the Fresnel equations are necessary for modelling a pyramidal ALEL. Several important features of design rules for ideal ALEL alignment on OLED panel can be derived from the results:
(a) smaller opening area ratio (b) narrower pixel spacing (c) tilt angle of 50º~55º.
Optimized pyramidal ALEL yields a gain factor of 1.7 which produces higher light efficiency than other structures in our simulation results. For alignment issue, the area of pixel spacing cross light source was the main factor of the gain factor loss (pixel spacing effect).
The entire fabrication processes we utilized to fabricate the ALEL include the typical
material, p S), for replication is considered to have a similar refraction index as optical glass. As a result, based on one pixel size of ALEL fitting one pixel size of OLED panel, ALEL shifts along x and y axes are allowed for the OLED panel to be free from moiré pattern. Meanwhile, the measured results of several alignment cases were investigated and explained as the pixel spacing effect. According to the experimental results of gain factor versus variables of ALEL, the higher luminance efficiency correlates to smaller 6.1 Conclusions
The pyramidal array light-en
semiconductor fabrication processes and plastic modeling replication techniques. The plastic oly-dimethyl-siloxane (PDM
opening area ratio, narrower pixel spacing, which agrees with the simulated results.
OLED panel with the optimized pyramidal ALEL yields a gain factor of 2.0. From
red by UV light simultaneously. Thereafter the UV-gel-coated substrate is peeled off from the roller and then the prisms are formed. The materials are considered for high throughput and yield rate of mass production. The future work is to replicate the ALEL by various thicknesses of PET and various recipes of UV gel and to evaluate improvements of luminance efficiency of the PET-based ALEL on CPT OLED panel.
Fig. 6.1 The current manufacturing process and materials of BEF.
Furthermore, the CPT
the mentioned analyses, the structure of ALEL has the distinguished capability to eliminate the total internal reflection effect, thus, light efficiency and gain factor of OLED panel can be increased significantly.
6.2 Future work
6.2.1 New ALEL fabrication process
A fabrication process to manufacture brightness enhancing film(BEF) is as illustrated in Fig.6.1. The thin film of UV gel coated on a polyethylene terephthalate (PET) substrate is pressed by a roller with microstructures and cu
Polyethylene terephthalate (PET)
6.2.2 New pixel size design for ALEL
t to fit one pixel of an OLED panel, and m. However, in order to keep high yield ass production, the height of microstructure should be limited to match the demolding process. For example, the height of BEF is optimized to be less than 30 µm. T
In this study, the pixel size of ALEL had been se the height of ALEL had been optimized as 150~200 µ rate and high throughput of m
herefore, the new pixel size of ALEL will be designed to fit the “subpixel” of an OLED panel, as shown in Fig. 6.2. The future works are to simulate the new design by ASAPTM and to fabricate new ALEL in order to obtain the maximum gain factor.
~200 µm
1 pixel
1
1 subpixel size of OLED panel
size of ALEL
pixel size of OLED panel
Fig. 6.2 The new pixel size design for ALEL.
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Vita
A. GENERAL INFORMATION Name: Ming-Lung Chen / 陳明倫
E-mail Address : amitaallen.iod93g@nctu.edu.tw B. EDUCATION
◆M.S. in Photonics and Display Technologies Chiao Tung University, Hsinchu, Taiwan Advisor: Prof. Han-Ping D. Shieh
Feb.05’~ July 06’
◆M.S. in Chemical Engineering & Materials Science Yuan Ze University, Taoyuan, Taiwan
Advisor: Prof. Sheng-Hsiung Lin
Sep. 94’~ June 96’
◆B.S. in Chemical Engineering & Materials Science Yuan Ze University, Taoyuan, Taiwan.
Sep. 90’~ June 94’
C. AWARD
◆ Student Paper Award, Optics & Photonics Taiwan 2005 D. PUBLICATION
◆ Ming-Lung Chen, An-Chi Wei, and Han-Ping D. Shieh, "Optimization of micro-structured light-enhanced layer for OLED panel," OPT 2005.
◆ Ming-Lung Chen, An-Chi Wei, and Han-Ping D. Shieh, "Improved output coupling efficiency of OLED panel using array light-enhanced layer," TDC 2006.