Mol. Cryst. Liq. Cryst., Vol. 410, pp. 255=[783]–274=[802], 2004
`Copyright # Taylor & Francis Inc.
`ISSN: 1542-1406 print=1563-5287 online
`DOI: 10.1080=15421400490432993
`
`VERTICALLY ALIGNED TFT-LCDs
`H. Yoshida , A. Takeda, Y. Taniguchi, Y. Tasaka, S. Kataoka,
`Y. Nakanishi, Y. Koike, and K. Okamoto
`Fujitsu Display Technologies Corp.,
`4-1-1 Kami-odanaka, Nakahara-ku, Kawasaki 211-8588, Japan
`
`types of vertically aligned TFT-LCD: with
`Fujitsu has developed several
`protrusion; with photo-alignment; and with comb-shaped electrodes. The pro-
`trusion-type TFT-LCD has the best balance of specifications and is in mass-
`production. It has a transmittance of 5% for a 15-inch XGA LCD, a response
`of 25 ms ðson þ soffÞ, and a contrast ratio of over 400. The photo-aligned type
`gives highest transmittance (7.5%) with dual domains. The lamp for UV
`irradiation can be a tube type and non-polarized UV is possible. We think it
`is a good candidate for notebook-type applications. The comb-shaped electrode
`type has the fastest response of better than 17 ms for any gray-scale switching.
`We think it is a good candidate for video applications.
`
`1. INTRODUCTION
`
`Liquid crystal displays (LCDs) are now finding a wider range of applica-
`tions. In addition to devices such as cellular phones, personal computers,
`and PDAs, they are being applied to audiovisual equipment including
`wide-screen television sets. The primary advantages prompting the
`expanded application of LCDs have been their space- and power-saving fea-
`tures. Further expansion of these devices will depend on the progress
`made in solving problems in their display characteristics. The performance
`of a display device is usually evaluated in terms of its contrast, brightness,
`viewing angle, color reproduction, resolution, and response speed. Among
`these parameters, the conventional LCD has a very tough time at achieving
`a superior viewing angle, brightness, and response speed [1–31]. We have
`developed three types of VA LCDs; VA TFT-LCD with protrusions offers a
`well-balanced specification [21,26,29,30], VA TFT-LCD with photo-
`alignment offers a high transmittance [19,20,23,30], VA TFT-LCD with
`comb-shape electrodes and oblique electric field offers a fast response [27,28].
`
`Received July 1, 2002
` Corresponding author. Tel.: þ 81-44-754-3491, Fax: þ 81-44-754-3846, E-mail: yoshida.
`h@jp.fujitsu.com
`
`255=[783]
`
`Page 1 of 20
`
`Tianma Exhibit 1010
`
`

`

`256=[784]
`
`H. Yoshida et al.
`
`2. VA TFT-LCD WITH PROTRUSIONS
`
`A new alignment control technology with protrusions has been developed.
`The principle is illustrated in Figure 2-1. Instead of processing the surface
`of alignment layer, as done in the conventional approach, this technology
`adopts the new concept of processing the underlying structure beneath
`the alignment layer. Structures installed partly beneath the alignment layer
`form protrusions. When the voltage supply is turned OFF, most of the liquid
`crystal molecules align themselves vertically to the substrate, but those
`positioned above the protrusions incline slightly towards the substrate
`due to the slope of the protrusions beneath them. When the voltage is
`turned ON, the molecules on the sloped protrusions initially start tilting
`in the direction shown by the arrow in Figure 2-2, and then the molecules
`in the regions without protrusions are affected by the tilting molecules and
`align themselves in the same direction. In this way, stabilized alignment is
`attained in the entire pixel.
`In other words, controlled alignment is
`achieved over the entire display area starting from the protrusions.
`
`FIGURE 2-1 Principal structure of new LCDs.
`
`FIGURE 2-2 Tilting of LC molecules.
`
`Page 2 of 20
`
`

`

`Vertically Aligned TFT-LCDs
`
`257=[785]
`
`Figure 2-3 illustrates alignment control by a combination of electrode
`slits and protrusions on color filter (CF) substrate. As can be seen from
`the figure, the TFT substrate has no protrusion formed on the surface,
`and parts of the ITO pixel electrode are etched off (electrode slits). When
`voltage is supplied, a deformed electric field (diagonal electric field) is gen-
`erated in the vicinity of the individual slits, providing field distribution and
`alignment control of the liquid crystal molecules similar to those attained
`when protrusions are installed. The simultaneous formation of slits with
`ITO pixel electrodes can eliminate the need for additional processes.
`Figure 2-4 shows the micro-photograph of the real TFT pixels with pro-
`trusions and slits of ITO. Slits are fabrication in ITO electrode in stead of
`protrusions on ITOs. The liquid crystal molecular alignment is divided into
`four domains, North-East, North-West, South-East, South-West.
`Actual photograph of the pixel when the voltage is applied (white state)
`is shown in Figure 2-5. The big disclination lines are seen at specific posi-
`tion near the pixel edge. This results in the reduced transmittance of the
`multi-domain vertically aligned (MVA) panels. The tilted directions of the
`
`FIGURE 2-3 Alignment control by electrode slits and protrusions.
`
`FIGURE 2-4 Real pixel design with protrusions or slits.
`
`Page 3 of 20
`
`

`

`258=[786]
`
`H. Yoshida et al.
`
`FIGURE 2-5 Actual micro-photograph of pixel and alignment.
`
`LC molecules are also illustrated in Figure 2-5. The tilted directions are
`opposite way for domains divided by the disclination line and the cause
`can be estimated by the edge field effect of the pixel ITO.
`To remove this disclination line, we put additional protrusion on the coun-
`ter electrode which is placed just in front of the pixel edge (Figs. 2-6, 7).
`
`FIGURE 2-6 Cross sectional view of protrusion wing.
`
`FIGURE 2-7 Previous and new design with protrusion wing.
`
`Page 4 of 20
`
`

`

`Vertically Aligned TFT-LCDs
`
`259=[787]
`
`The newly adopted protrusion is called protrusion wing and the ability to
`control the tilted direction is much bigger than that of the edge field effect
`due to distorted electrical field.
`Figure 2-8 shows the newly designed columnar spacer panel. The layers
`of Red, Green, and Blue resin filters are stacked only on the pixel borders
`to minimize the leakage of light rays from the borders (stacked RGB color
`filters prevent the transmission of light rays). This eliminates the need for
`black matrix required in the existing manufacturing processes. In addition,
`a protrusion is formed on the color filter-stacked point to provide a cell
`spacer and create a cell gap. This protrusion acts as a spacer and an align-
`ment controller. This approach eliminates the black matrix forming process
`and spacer distributing process, simplifying the process on the whole.
`Figure 2-9 shows SEM photograph of spacer. The protrusion layer stacked
`on ITO enables to avoid an electrical short between CF and TFT substrates
`and to keep an appropriate cell-gap.
`
`FIGURE 2-8 Multi-layer color filter resin spacer.
`
`FIGURE 2-9 SEM photograph of spacer.
`
`Page 5 of 20
`
`

`

`260=[788]
`
`H. Yoshida et al.
`
`It is pointed out that the switching characteristic from black to dark gray
`levels is disadvantageous (Fig. 2-10). Figure 2-11 shows LC switching
`mechanism of MVA-LCDs. The direction of the vertically aligned LC mole-
`cules is determined by protrusions on CF substrates or by ITO slits on TFT
`substrates. In this technology, when a voltage is applied, the LC molecules
`around the protrusions tilt at first because they initially have a tilted align-
`ment due to the slope of the protrusions and also the oblique electrical field
`created around them is consistent with the initial tilting. We call this situa-
`tion as ‘‘partial control’’ in Figure 2-11. Subsequently, the remaining LC
`molecules between the protrusions and the ITO silts gradually tilt to the
`same direction from both sides. This is the propagation of LC alignment.
`Consequently, in conventional MVA mode, the response time for turning
`on contains this extra propagation time or sleeping time.
`Figure 2-12 illustrates the technology, in which ITO pixel electrodes
`have a jagged shape and a main fringe structure at the center. The LC
`
`FIGURE 2-10 Response characteristics of conventional MVA.
`
`FIGURE 2-11 LC molecular switching.
`
`Page 6 of 20
`
`

`

`Vertically Aligned TFT-LCDs
`
`261=[789]
`
`FIGURE 2-12 New pixel design and LC molecular tilt.
`
`molecules tend to tilt by the deformation of the electric field around the
`jagged ITO pattern. As the minutely patterned ITO cover most of the
`display domain area, we are able to obtain a remarkable improvement in
`response time by reducing the propagation time. Figure 2-13 shows the
`high-speed camera photograph of the response from black to a grey-scale
`level. With the jagged shape electrode, the transmittance changes almost
`simultaneously in the whole pixel area.
`Figure 2-14 shows the measured response characteristics for the new
`MVA panel in comparison with the conventional MVA and a Super-IPS
`[10] panel. The starting level of the switching is black, which is the weakest
`case in the MVA-LCDs. The response speed to 20% of the white transmit-
`tance is about three times as fast as that of the conventional one.
`Figure 2-15 shows the fabricated 1700 diagonal wide-screen TFT-LCD.
`
`FIGURE 2-13 High-speed camera photograph of switching.
`
`Page 7 of 20
`
`

`

`262=[790]
`
`H. Yoshida et al.
`
`FIGURE 2-14 Response characteristics improved.
`
`FIGURE 2-15 17W inch diagonal TFT-LCDs.
`
`This MVA mode has balanced specification; high contrast ratio, rather
`fast response speed, sufficient transmittance for monitors.
`
`3. VA TFT-LCD WITH PHOTOALIGNMENT
`
`We have developed TFT-LCDs with high transmittance with photo-align-
`ment technology. We think that VA-TFT LCD can be used as screens for
`note-book type PCs.
`Figure 3-1 shows the photo-alignment principle. Polyimide layer with
`alkyl side chain is irradiated with unpolarized UV light. A part of side alkyl
`chain is deformed and the liquid crystal molecules are aligned by the
`residual alkyl-side chains.
`
`Page 8 of 20
`
`

`

`Vertically Aligned TFT-LCDs
`
`263=[791]
`
`FIGURE 3-1 Photo-alignment principle.
`
`Figure 3-2 shows the pretilt angle of the fabricated cell vs. UV irradiation
`energy characteristics of the fabricated cell. The pretilt angle decreased as
`the UV irradiation energy increased. Figure 3-2 also shows photographs of
`the fabricated cell between a pair of crossed polarizers with an intermediate
`voltage. When the UV irradiation energy was too low, black spots appeared
`around spacers. When the UV was irradiated in excess, defects appeared par-
`allel to the LC filling direction. With an appropriate UV dosage, no such black
`spots appeared and the tilt angle of the liquid crystal was around 89 degrees.
`Figure 3-3 shows the response speed of fabricated LC panel. The re-
`sponse time between several gray scale level were almost the same or
`rather faster than the LC panel with rubbing technology.
`Next, we tried to develop dual-domain TFT-LCDs. Figure 3-4 shows the
`UV irradiation system. We used a tube-type fluorescent lamp to irradiate
`the surface of the vertical alignment layer with unpolarized UV. Since the
`lamp house is small, the equipment size is quite small and inexpensive.
`Figure 3-5 shows how we irradiated with UV light through an optical
`mask and shows the cross sectional panel configuration. The aperture of
`the optical mask is less than half of the pixel pitch. The UV is irradiated
`
`FIGURE 3-2 UV irradiation and pretilt angle.
`
`Page 9 of 20
`
`

`

`264=[792]
`
`H. Yoshida et al.
`
`FIGURE 3-3 Response time.
`
`FIGURE 3-4 UV irradiation system.
`
`through this aperture from two directions simultaneously. By scanning the
`UV lamp, we can irradiate at the same dose over the whole area. After irra-
`diating the surface of a pair of substrates, we stacked and filled them with
`liquid crystal with negative dielectric anisotropy. We fabricated protrusions
`on the CF substrate at the pixel centers to produce dual-domain TFT-LCDs.
`
`FIGURE 3-5 How to irradiate UV through an optical mask.
`
`Page 10 of 20
`
`

`

`Vertically Aligned TFT-LCDs
`
`265=[793]
`
`With prototype TFT-LCDs, disclinations appeared parallel to the gate
`bus line or CS (subsidiary capacitance) bus lines (Fig. 3-6). This disclina-
`tion is due to distortion of the optical mask. If the optical mask is distorted
`by 20 mm, the gap between the mask and LCD substrate changes and the
`irradiation area can move by 20 mm. When the surface of the alignment
`layer is irradiated twice with UV light, the anchoring of the alignment layer
`is damaged and the disclinations appear. To solve this problem, we nar-
`rowed the aperture of the optical mask to less than half the pixel pitch
`so that the alignment cannot be irradiated twice at one position and
`achieved alignment without disclinations.
`There appeared other disclinations (Fig. 3-7) along the data bus lines
`caused by the oblique electric field from the data bus lines. Figure 3-8
`shows the cross section alogn line X in Figure 3-7. We fabricated subsidiary
`protrusions parallel and along the bus lines to reduce these disclinations
`
`FIGURE 3-6 Disclination due to distortion of optical mask.
`
`FIGURE 3-7 Disclination due to oblique electric field from data bus.
`
`Page 11 of 20
`
`

`

`266=[794]
`
`H. Yoshida et al.
`
`FIGURE 3-8 Cross section along line X in Figure 3-7.
`
`(Figure 3-9). Since the oblique electric field around and from the data
`bus line (shown in circle in Figure 3-8) is suppressed by the subsidiary
`protrusions, the disclinations are reduced.
`Figure 3-10 shows the TFT pixels. There is no disclination and the
`transmittance is high. Figure 3-11 shows an example of the display of the
`
`FIGURE 3-9 Subsidial protrusion to reduce disclination.
`
`FIGURE 3-10 Micro-photograph of new pixel.
`
`Page 12 of 20
`
`

`

`Vertically Aligned TFT-LCDs
`
`267=[795]
`
`FIGURE 3-11 15 inch diagonal TFT-LCD.
`
`TABLE 3-1 Specification
`
`Size
`Pixels
`Transmittance
`Color gamut
`Contrast ratio
`Response time
`Viewing angle
`
`1500
`XGA (1024 768)
`7.4%
`54%(NTSC)
`500:1
`25 ms
`> 160 degrees
`
`fabricated 15-inch diagonal XGA TFT-LCD and Table 3-1 shows the speci-
`fications. The contrast ratio in the normal direction is better than 500 and
`the transmittance is 7.4%. This transmittance is twice that of IPS LCD
`[9,10], 1.5 times that of conventional MVA-LCD [21] and 1.1 times that of
`TN-LCDs with Wide-View film [14]. In this case, we used a color filter
`layer to achieve a wide color gamut (54% of NTSC). We think this newly
`developed TFT LCD is excellent candidate for the display of notebook
`computers with multi-media application.
`
`4. VA TFT-LCDS DRIVEN BY OBLIQUE ELECTRIC FIELD
`
`We have developed Vertically Aligned TFT-LCDs driven by oblique electric
`field which has sufficiently fast response speed for any gray-scale switching.
`Figure 4-1 shows the cross section of the LCDs. The LCD is composed of
`interdigital electrodes like the IPS mode, a transparent electrode (ITO) on
`the CF substrate like the MVA-LCD, and a dielectric layer on the ITO layer.
`It contains liquid crystal with positive dielectric anisotropy and is initially
`
`Page 13 of 20
`
`

`

`268=[796]
`
`H. Yoshida et al.
`
`FIGURE 4-1 Cross sectional view of newly developed LCDs.
`
`aligned vertically. A pair of crossed polarizers are stacked on the sub-
`strates. Because the new LCD has an ITO electrode inside the LC cell, it
`does not suffer from the electrostatic-charge problem of the IPS mode.
`Figure 4-2 shows a microphotograph of VA-IPS (without ITO electrode
`and dielectric layer on CF substrate) and the new LCD. There are disclina-
`tion lines between the source and common electrodes in case of VA-IPS.
`However, the new LCD mode has no disclination lines and the screen
`brightness is higher. When voltage is applied, the electric field from the
`source electrode extends to both the common electrodes on the TFT and
`CF substrates (Fig. 4-3). Since the electric field is asymmetrical, the LC
`molecules are parallel to the electric field asymmetrically and there is no
`disclination.
`Figures 4-4 show the effect of the dielectric layer on ITO. Without the
`dielectric layer, the line of equipotential is only in the LC layer, so the
`direction of the field is almost perpendicular to the glass substrate. The
`LC molecules are not inclined parallel to the substrate, resulting in a low
`brightness level. With the dielectric layer, the line of equipotential extends
`
`FIGURE 4-2 Microphotograph of VA-IPS and new LCD mode.
`
`Page 14 of 20
`
`

`

`Vertically Aligned TFT-LCDs
`
`269=[797]
`
`FIGURE 4-3 Electric field with VA-IPS and new LCD.
`
`to the dielectric layer. The ratio of the electric field parallel to the substrate
`is higher, so more LC molecules are parallel to the substrate, resulting in
`higher brightness.
`Figure 4-5 shows the measured response characteristics of the new
`LCD. The x- and y-axes show the gray scales before and after switching
`and the z-axis shows the rising and decaying response times. The response
`time for black-and-white switching is 13 ms for rising (from 0th to 63rd gray
`level) and 4 ms for decaying (from 63rd to 0th gray level). The slowest
`response time for gray-scale images was 17 ms for rising (from black
`(0th) to gray (16th)) and 11 ms for decaying (from white (63rd) to gray
`(48th)). Almost every response time is shorter than the frame period
`(16 ms) and is sufficient for multimedia use.
`Figure 4-6 shows the calculated electric field when 2 V and 10 V are
`applied for a dark-gray image and white image respectively. When 2 V is
`applied, only the liquid crystal around the source electrodes is switched
`and the electric field is 0.325 V=m. When 10 V is applied, the liquid crystal
`of the whole area between the electrodes is switched and the electric field
`is 0.765 V=m. The lower voltage (2 V) is 20% that of the higher voltage
`
`FIGURE 4-4 Effect of dielectric layer on ITO layer.
`
`Page 15 of 20
`
`

`

`270=[798]
`
`H. Yoshida et al.
`
`FIGURE 4-5 Response speed.
`
`(10 V), but the electric field is almost half. In the case of an LCD switched
`by a parallel field to the substrate, the movement of the LC molecules is
`determined by the strength of the electric field, not the applied voltage.
`For example,
`
`son ¼ cd2=fðA2 1Þp2Kg
`c: viscosity, d: cell gap, A: E=Eth, E: Electric Field, K ¼ K1 ¼ K3 (for sim-
`plifying the equation.)
`The small difference in the electric field with low and high driving
`voltages explains the small difference in the response between various
`gray-scale levels.
`Figure 4-7 shows a schematic pixel structure of fabricated TFT-LCDs.
`Half the comb-shaped electrodes have an azimuth angle at 45 degrees,
`and the other half have an azimuth angle at 135 degrees, so the LC mole-
`cules incline in four directions.
`The first sample had lower transmittance than expected. There
`appeared dark regions in the aperture areas. Figure 4-8 shows the
`microscope photograph of the pixel whose area is shown in Figure 4-7 by
`dotted line. As the electrodes are kinked at an acute angle, the electric field
`
`FIGURE 4-6 Electric field and reason of the fast response.
`
`Page 16 of 20
`
`

`

`Vertically Aligned TFT-LCDs
`
`271=[799]
`
`FIGURE 4-7 Schematic pixel structure of fabricated TFT-LCDs.
`
`FIGURE 4-8 Microphotograph of pixel.
`
`is not applied on these regions and the liquid crystal molecules are not
`inclined.
`We developed wing-shaped electrodes (Fig. 4-9). Some source electro-
`des were extended over common electrodes and common electrodes were
`
`FIGURE 4-9 Wing-shaped electrode.
`
`Page 17 of 20
`
`

`

`272=[800]
`
`H. Yoshida et al.
`
`extended along source electrodes. Figure 4-10 shows the electric field
`when a common electrode or a source electrode is extended to apply
`electric field on the liquid crystal layer. The common electrodes should
`be extended longer than the source electrodes because the common
`electrodes are located beneath the source electrodes.
`We fabricated the new LCD with the wing-shaped electrodes. Figure 4-11
`shows the microscope photograph of the TFT-LCD with the new pixel
`structure. There are no dark regions inside the aperture areas.
`
`FIGURE 4-10 Cross section of wing-shape electrodes.
`
`FIGURE 4-11 Electrode design and microphotograph of pixel.
`
`Page 18 of 20
`
`

`

`Vertically Aligned TFT-LCDs
`
`273=[801]
`
`FIGURE 4-12 15 inch diagonal TFT-LCD.
`
`TABLE 4-1 Specification
`
`Display area
`Number of pixels
`Viewing angle
`(CR > 10, no reversed image)
`Response time (black=white)
`(slowest between gray scale)
`Transmittance
`Brightness
`
`New LCD
`
`1500diagonal
`XGA (1024 RGB 768)
`> 160 (up-down)
`> 160 (right-left)
`17 msðsr þ sdÞ
`17 ms
`3.5%
`200 cd=m2
`
`VA-IPS
`
`
`
`
`40 ms
`—
`< 1%
`—
`
`Figure 4-12 shows the fabricated 15 diagonal XGA TFT-LCDs and
`Table 4-1 shows the specifications. It has a wide viewing range, fast
`response and good light transmittance, making it a potential candidate
`for use in video applications.
`
`5. SUMMARY
`
`Three types of vertically aligned TFT-LCDs are reviewed.
`VA TFT-LCD with protrusion has balanced specification. The transmit-
`tance is sufficiently high for monitors, and the response speed is compara-
`ble with TN-LCDs, and the contrast ratio is so high (500). It has been
`manufactured and used for various size of LCD monitors.
`VA TFT-LCD with photo-alignment has 1.5 times higher transmittance
`than that with protrusions. It is a great candidate as a screen for notebook
`type PCs.
`
`Page 19 of 20
`
`

`

`274=[802]
`
`H. Yoshida et al.
`
`VA TFT-LCD with interdigital electrode has fast response for any
`gray-scale switching. It is a great candidate as a screen for TV application.
`The VA TFT-LCDs can be used for any application; monitors, TVs,
`note-type PCs, cellular phone, PDA, Auto-motive, Avionics, Digital video
`etc. We think that the future of the VA TFT-LCDs are so bright.
`
`REFERENCES
`
`[1] Yamagishi, N. et al. (1989). Digest of SID 89, 316.
`[2] Hirai, H. et al. (1989). Prodeedings of IDRC 9, 184.
`[3] Gibbons, W. M. et al. (1991). Nature, 351, 49.
`[4] Yang, K. H. (1992). Jpn. J. Appl. Phys., 31, L1603.
`[5] Koike, Y. et al. (1992). Digest of SID 92, 798.
`[6] Schadt, M. et al. (1992). Jpn. J. Appl. Phys., 31, 2155.
`[7] Yoshida, H. et al. (1993). Journal of the SID, 63.
`[8] Yoshida, H. et al. (1994). Journal of the SID, 135.
`[9] Ohta, M. et al. (1995). Proceedings of IDRC, 707.
`[10] Ohe, M. et al. (1995). Digest of Asia Display 95, 577.
`[11] West, J. L. et al. (1995). Digest of SID 95, 703.
`[12] Yamamoto, T. et al. (1996). Digest of SID 96, 642.
`[13] Saito, T. et al. (1996). Digest of 22nd Japanese Liquid Crystal Conf., 19.
`[14] Mori, H. et al. (1996). Digest of AM-LCD 96, 189.
`[15] Ohmuro, K. et al. (1997). Digest of SID 97, 845.
`[16] Nam, M. S. et al. (1997). Digest of SID 97, 933.
`[17] Chen, J. et al. (1997). Digest of SID 97, 936.
`[18] Iimura, Y. et al. (1997). Digest of SID 97, 311.
`[19] Yoshida, H. et al. (1997). Jpn. J. Appl. Phys., 36, L428.
`[20] Yoshida, H. et al. (1997). Jpn. J. Appl. Phys., 36, L1449.
`[21] Takeda, A. et al. (1998). Digest of SID 98, 1077.
`[22] Lien, A. et al. (1998). Digest of SID 98, 1123.
`[23] Tasaka, Y. et al. (1998). Digest of AM-LCD 98, 35.
`[24] Kim, K.-H. et al. (1998). Digest of SID 98, 1085.
`[25] Lee, S.-H. et al. (1998). Digest of SID 98, 838.
`[26] Tanaka, Y. et al. (1999). Digest of SID 99, 206.
`[27] Yoshida, H. et al. (2000). Digest of SID 00, 334.
`[28] Nakanishi, Y. et al. (2000). Digest of AM-LCD 00, 13.
`[29] Taniguchi, Y. et al. (2000). Digest of SID 00, 378.
`[30] Kataoka, S. et al. (2001). Digest of SID 01, 1066.
`[31] Yoshida, H. et al. (2002). Digest of SID 02, 758.
`
`Page 20 of 20
`
`