Chapter 3 Fabrication and measurement instruments
3.3 Measurement system
3.3.2 Measurement systems for light efficiency
3.3.2.2 Conoscope
Conoscope is a measurement system which utilizes Fourier transform lens to transfer the light beams emitted (or reflected) from the test area of different angles to the CCD array, as shown in Fig. 3.5. Every light beam emitted from the test area with a θ incident angle will be focused on the focal plane at the same azimuthal angle and at a position x = F(θ).
Therefore, the angular characteristics of the sample are thus measured simply and quickly, without any mechanical movement. Particularly, which kind of light source, i.e. collimated or diffuse illumination, is provided depending on the needs.Besides, by equipped with a fast photometer system and a high-sensitivity spectrometer, its functions are extended to comprise not only the simultaneous measurement of luminance and chromaticity versus viewing direction, evaluation of the data yields, i.e. luminance contras ratio, grey-scale inversion and reduction, color shift and many more characteristics, but also the spectra and temporal luminance variances.
C: cone of converging elementary parallel beams A: variable aperture Fig. 3.5 Schematic diagram of Conoscope.
Chapter 4
Simulated Results and Discussions
4.1 Introduction
In chapter 2, we had 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. We established a simulation model to characterize the features of the array light-enhancing layer on OLED panel.
First, the parameters of pyramidal ALEL, including the height of each ALEL pixel, the tilt angle of pyramidal pixel and the spacing between two adjacent pixels, were designed and optimized. After that, the alignment issue of the array light-enhancing layer on OLED panel was also discussed.
4.2 Simulation Software
The optical simulator Advanced Systems Analysis Program (ASAPTM), developed by Breault Research Organization (BRO) was used to optimize the array light-enhancing layer on OLED panel and simulate its light efficiency.
4.3 Simulation description
4.3.1 Optical Model
In order to consider the whole effect of the array light-enhancing layer on an OLED panel, all the design and optimization were carried out under the complete system framework.
bottom glass substrates, as shown in Fig. 4.1. Ribs and insulators were set with 60 % transmittance. Since the organic layers, including the electron injection layer, the electron transport layer, the active layer (the emitting layer), the hole transport layer and the hole injection layer, are much thinner (~0.15 µm) than other layers, they are assumed as one “source layer” in our simulation, as shown in Fig. 4.2. Metal cathode was set with 90 % reflectance.
Fig. 4.1 Schematic diagram of OLED structure.
Glass Substrate
Cathode
Electron Transport Layer Electron Injection Layer
Hole Transport Layer Hole Injection Layer
Anode
Emitting Layer Organic Layers
Fig. 4.2 Schematic diagram for organic layers of OLED structure.
Lights from active layer was assumed to emit in the form of pixel array and was set as an isotropic light source. The array light-enhancing layer consists of the base substrate and microlens array. The pixel size of ALEL, as shown in Fig. 4.3, was set to fit one of OLED panel. The size of ALEL and OLED panel are W×L. In addition, a flat detector with the diameter of 3cm was located at a distance of 3.5cm above the OLED panel, as shown in Fig.
4.4.
1 Pixel size of OLED Panel 1 Pixel size of
OLED Panel
1 Pixel size of ALEL
1 Pixel size of
ALEL Alignment
Fig. 4.3 Schematic diagram for designing pixel size of light source and ALEL.
L
OLED panel ALEL
W
Detector 3 cm
Fig. 4.4 Schematic diagram of measurement.
Light efficiency is defined as the detected flux over the generated one. Furthermore, gain factor was defined as the ratio of the light efficiency of an OLED panel with ALEL to that of a panel without ALEL, which were served as the bases of the optimizations.
(1) = detected flux light efficiencyof OLED panel with ALEL
Gain Factor =
light efficiencyof OLED panel
light efficiencyof OLED panel with ALEL Gain Factor
light efficiencyof OLED panel
=
4.3.2 Parameters
In order to obtain to maximum gain factor, several variables, as shown in Fig. 4.5, such as the height of each ALEL pixel (LEL_H), the tilt angle of pyramidal pixel (TILT) and the spacing between two adjacent pixels (LEL_S), need to be designed properly. A simulation tool, ASAPTM, with the Fresnel equations assigned was used to perform the following simulation.
LEL_H
Fig. 4.5 Illustration of parameters for designing array light-enhancing layer.
4.4 Results and discussions
4.4.1 Tilt angle and spacing of pyramidal pixel
First, the relationship between the gain factor and the tilt angle (TILT) will be discussed.
Height and spacing are kept constant, and TILT is changed from 90° to the minimum angle where the two slopes meet at the intersection point, and then the relationship between the gain factor and TILT is formed. Besides, spacing is kept as different constants to represent the
relationship between the gain factor and spacing. The green sub-pixel light source is turned on.
From the simulated results, as illustrated in Fig. 4.6, the maximal gain factor can be derived at 50° to 55° and smaller spacing.
1.0 1.2 1.4 1.6 1.8 2.0
40 50 60 70 80 90
TILT (degrees)
Ga in Fa c to r
Spacing = 10 µm Spacing = 25 µm Spacing = 40 µm
Fig. 4.6 Illustration of the relationship between gain factor and TILT. The height is 125 µm.
4.4.2 Height of pyramidal pixel
Next, the relationship between the gain factor and the height is discussed. From the simulated results, as illustrated in Fig. 4.7, the curve of gain factor becomes stable when the height is higher than 100 µm. Since the lower height can bring higher yield rate during the demolding process, the optimized height is set as around 150 µm.
1.0 1.2 1.4 1.6 1.8 2.0
0 50 100 150 200 250
Height (µm)
G a in F acto r
TILT = 40 TILT = 50 TILT = 60 o o o
Fig. 4.7 Illustration of the relationship between gain factor and Height. The spacing is 10 µm.
4.4.3 Opening area ratio
We further broaden the analysis of the relationship between gain factor and the parameters of ALEL. Opening area ratio is defined as the sum of the flat areas A over the pixel size of ALEL, as illustrated in Fig. 4.8.
Fig. 4.8 Definition of opening area ratio.
The relationship between the gain factor and the parameters of ALEL, as illustrated in Figs. 4.6 and 4.7, will be transferred to the relationship between the gain factor and the opening area ratio.
First, the relative curves of gain factor versus opening area ratio are obtained by converting the gain-TILT curve (Fig. 4.6). Maximal opening area ratios, as illustrated in Fig.
4.9, are different at various spacing. Therefore, the relationship between the gain factor and TILT is still the suitable method to obtain proper directionalities.
1.0 1.2 1.4 1.6 1.8 2.0
0 20 40 60 80 100
Opening area ratio (%)
G a in F acto r
Spacing= 10 µm Spacing= 25 µm Spacing= 40 µm
Fig. 4.9 Illustration of the relationship between gain factor and opening area ratio (transfromed from gain-TILT curve). The height is 125 µm.
Moreover, the relationship between gain factor and height was also transferred to the relative curves of gain factor versus opening area ratio. From the results, as illustrated in Fig. 4.10, it can be concluded that smaller opening area ratio produces higher gain factor. In addition, the gain factor is similar when opening area ratio is smaller than 30 % at the optimized TILT angle of 50°. It could be the reference for designing lower height of ALEL to bring higher yield rate during the demolding process.
1.0 1.2 1.4 1.6 1.8 2.0
0 20 40 60 80 100
Opening area ratio (%)
Ga in Fa c to r
TILT = 40 TILT = 50 TILT = 60 o o o
Fig. 4.10 Illustration of the relationship between gain factor and opening area ratio (transferred by various height). The spacing is 10 µm.
4.4.4 Alignment issue
In our design, the pixel size of ALEL is set to fit the one OLED pixel. As a result, the alignment issue should be considered in the mass production. Fig. 4.11 shows the result of gain factor loss versus ALEL shift. ALEL shift is defined as the same shift on X and Y axes as illustrated in Fig. 4.12. The space between adjacent sub-pixels on OLED panel is about 40 µm. When ALEL are 60 µm and 90 µm shifted, as illustrated in Figs. 4.13 (c) and (d), their regions of the pixel spacing of ALEL crossing the green sub-pixel source are similar. There is about 15 % loss of gain factor when ALEL is shifted 90 µm along X and Y axis. The gain factor losses of 60 µm and 90 µm misalignments are also approximated. Therefore, the pixel
Fig. 4.11 Illustration of the relationship between gain factor loss a spacing of ALEL crossing light source is the main factor of alignment.
nd ALEL shift.
0 5 10 15 20 25
0 30 60 9
X & Y Shift (µm) Ga in Fa c to r L o ss ( % )
Spacing = 40 µm , TILT = 55Height =125 µm,
o
0
OLED panel
ALEL
Y
X
OLED panel
ALEL
Y
X
Fig. 4.12 Illustration of ALEL misalignment.
Pixel spacing (a) (b) (c) (d)
Fig. 4.13 Schematic diagram of ALEL shift on X and Y axis: (a) ideal case, (b) 30 µm, (c) 60 µm, and (d) 90 µm.
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
herefore, the new pixel size of ALEL will be designed to fit the “subpixel” of an OLED