D-ILA™ Projector Technology: The Path to High Resolution Projection Displays

advertisement
D-ILA™ Projector Technology:
The Path to High Resolution Projection
Displays
William P. Bleha, PhD
Senior Research Scientist
JVC North America R&D Center
Projection Technology Group
20984 Bake Parkway, Suite 102
Lake Forest CA 92630
[email protected]
www.jvcdig.com
D-ILA™ Projector Technology:
The Path to High Resolution Projection Displays
William P. Bleha, PhD
Senior Research Scientist
JVC North America R&D Center
Projection Technology Group
20984 Bake Parkway, Suite 102
Lake Forest CA 92630
Introduction
JVC is leading the industry in high-resolution large screen projection displays with the continuing
development of the D-ILA™ technology. The D-ILA technology builds on the high luminance, high
resolution Hughes-JVC ILA™ Super Projectors that established new standards of projector excellence for
the first generation of high resolution solid state projection displays in the 1990s..
With the benchmark JVC G1000 D-ILA projector (Fig. 1), the path to the future of
compact ultra-high resolution displays began in 1998. Now projectors, the QX-1 (Fig. 2), SX-21, HX-1
(Fig. 3) and the all- new HD-2K (Fig. 4), carry the D-ILA technology to performance maxims in
resolution and overall image quality.
SID 1998 Display Product of the Year Award
Fig. 1. G1000 D-ILA Projector: The World’s First LCOS Projector (1998)
2
Fig. 2. QX-1 D-ILA Projector with QXGA 2048 x 1536 pixel resolution
(A)
(B)
Fig. 3. (A) Compact SX-21 D-ILA Projector with SXGA+ 1400 x 1050 pixel
resolution; (B) HX-1 D-ILA Projector with 1400 x 780 pixel resolution for Home Theatre
applications.
Fig 4. New HD-2K D-ILA Projector with full native HDTV 1920 x 1080 pixel
Resolution.
3
D-ILA is JVC’s proprietary reflective-mode active matrix liquid crystal display
referred to as LCOS (liquid crystal on single crystal silicon). LCOS display technology has many inherent
advantages over competing technologies:
♦
The unique high performance and small dimensions of single crystal silicon backplane circuitry allows
a high level of integration of driver and processing circuitry. This is coupled with the high electrooptic efficiency and reliability of liquid crystal materials.
♦ Adaptability and scalability: With LCOS technology, in contrast to micromirror technology, pixel size
and format can be readily adjusted to meet optical system requirements.
♦ High performance reflective-mode displays fill the display surface with closely spaced pixel elements
thus minimizing the pixel border “screen door” look of transmissive LCD displays. In additiont the
liquid crystal acts to bridge the pixels resulting in near-structureless image compared to other reflective
image modulators using micromirrors.
♦ Thermal stability: the silicon backplane can be thermally controlled across the entire aperture for
stability,optical uniformity, and reliability in operation which is key to applications using multikilowatt
Xenon arc lamps.
JVC has developed a technology that combines the high performance of the Hughes-JVC ILA®
technology and the lightweight features of the TFT-LCD. Fig. 5 shows a photograph of the D-ILA display
modulators and Table 1, a chart of modulator characteristics. Resolution from SXGA+ to QHDTV
characterize the D-ILA devices.. Fig. 6 graphically compares the significant increase in image
information achieved with the high resolution D-ILA modulators.
Fig. 4. D-ILA Image Modulators
Table 1. D-ILA Modulator Types
4
Fig 5 Photograph of D-ILA Modulators
QXGA 3.2M
2048×1536
HDTV 2.1M
1920×1080
SXGA 1.4M
1365×1024
QHDTV 8.3M
3840x2160
Fig. 6. Comparison of Image Formats.
5
Fig. 7. Schematic of image information flow in the D-ILA device
D-ILA device
The D-ILA, or Digital Image Light Amplifier, is a reflective liquid-crystal design where
electronic signals are directly addressed to the device.1,2 The light valves use active matrix addressing of
the liquid crystal to achieve the spatial modulation. The active matrix consists of an array of electrical
switches, (MOS transistors) and addressing electronics. The sources and drains of the transistors are
connected to the columns and pixel electrodes. The gates are connected to the row electrode. The
electrical image signal is sampled successively into a sample-and-hold circuit (S/H) in the columns. When
a full line of data has been sampled, a row electrode is enabled, opening the channels of all the transistors
on this selected row. The charges on the S/Hs are transferred to the capacitor of the corresponding pixel.
The gate pulse is then removed, isolating the charge. The process is repeated for successive rows. The
image information is updated at the vertical refresh rate. The D-ILA device can be driven with high speed
image signals resulting from the high carrier mobility of the crystalline silicon.
This is shown schematically in Fig. 7. Since the nematic liquid crystal responds to voltage level
directly, the gray scale is determined by the value of voltage set on each pixel. This reduces the transfer
characteristic bit depth required to address the multi-gray levels without contouring or spatial noise in
comparison with the time-sequential mode (pulse code modulation) used in bi-stable devices such as the
DMD or plasma panels..
The D-ILA X-Y matrix of pixels is configured on a C-MOS substrate using planar processes
standard in IC technology. Each pixel is covered, except for a small border, with an aluminum reflective
pixel electrode. The driving transistor is connected to this reflective pixel electrode through the center via.
The vertically aligned nematic (VAN) (homeotropic) mode liquid crystal is sandwiched between the
reflective pixel electrode and continuous transparent ITO electrode. The thickness of the liquid crystal
layer is ~ 3 micrometers. The liquid crystal material has a negative dielectric constant necessary for VAN
alignment and low viscosity for video-rate response. The voltage applied to the selected pixel of the
matrix makes the liquid crystal above the pixel change birefringence and thus modify the polarization state
of the projection light in the D-ILA. See the discussion in the section on D-ILA projector technology on
D-ILA optical systems.
Since the nematic liquid crystal responds to voltage level directly, the gray scale is determined by
the value of the analog voltage set on each pixel. The transfer characteristic also complements the typical
signal gamma characteristic of 2.2-2.6 This reduces the transfer characteristic bit depth required to address
the multi-gray levels without contouring or spatial noise found in time-sequential mode operation (pulse
width modulation) used in bi-stable devices such as DMD™ . These devices have have a digital linear
6
transfer characteristic that does not provide decompression of the black levels caused by the signal gamma.
Thus high bit depth approaching infinity at zero signal level is required. Thus for DLP projectors both
spatial and temporal dithering are used to generate additional bits which can be noticeable in the image as
noise. In Fig. 8 the calculated bit depth requirements are shown for digital and analog systems. The
increased bit dept necessary for a linear digital system is particularly severe in the dark levels.
100
100
Gradation accuracy dB
Gradation accuracy dB
14 bit
80
10 bit
60
9 bit
8 bit
40
20
0
80
60
12 bit
10 bit
系列1
系列2
系列3
多項式 ( 系列1)
多項式 ( 系列2)
40
多項式 ( 系列3)
多項式 ( 系列2)
20
0
0.0
0.2
0.4
0.6
0.8
1.0
Input level
0.0
0.2
0.4
0.6
0.8
1.0
Input level
(a)
(b)
Fig. 8 Calculated transfer characteristic accuracy as a function of bit depth for
digital and analog projectors: (a) analog; (b) digital.
Device structure
Fig. 9 shows a cross sectional image of the D-ILA device. Three metal layers are
formed on the silicon chip; the first metal layer for the driving circuit, the second for the light blocking
layer and the third for reflective pixel electrode. For example in the array of 1400 x 1050 pixels,
electrodes, with a size of 10.1 x 10.1 micrometers, are separated by 0.3 micrometers.
7
Glass Substrate
ITO Electrode
Liquid Crystal
Alignment Layer
Third Metal
(Reflective Electrode)
Second Metal (Wiring Shield)
First Metal (Wiring)
Silicon Substrate
Capacitor Polysilicon
Gate
Source
Drain
Capacitor Diffusion
Fig. 9. Cross-section of D-ILA device
The reflectivity and light blocking structure of the silicon chip substrate are important
factors in achieving a projected image of 4000 lumens. The pixel electrodes of the D-ILA device have a
93% aperture ratio, and have high intrinsic reflectivity. The insulating layers formed between each metal
layer are made flat and smooth by chemo-mechanical polishing techniques. The final pixel mirror
approaches a reflectivity of 98%.
The light blocking layer is formed under the mirror electrode in order to prevent light
leakage to the transistor located on the first metal layer in the silicon chip. Light leakage would activate the
transistor. Each metal layer also has anti-reflective layers on both sides. A light-induced voltage drop in
the pixel electrode could cause decreased projection light output due to decreasing liquid crystal
modulation. With anti-reflection layers, no voltage drop was observed with high light input from the
illumination system. It will be possible to produce projection systems with greater than 20,000 lumens
using D-ILA devices.
Liquid Crystal Alignment
Vertically aligned nematic(VAN) LC alignment allows high device contrast
ratio across the entire visible light spectrum range since, in a tunable birefringence operational mode 3, the
birefringence of the liquid crystal is near zero at the threshold off-state voltage. This allows the
theoretically highest contrast ratio for any liquid crystal device using a broad spectrum projection light
source. The liquid crystal molecules are aligned almost perpendicular to the surface with a small pre-tilt
angle at off state. A low pre-tilt angle is an important factor in achieving high contrast ratios and good
quality in the projected image. Figure 10 shows a schematic of the VAN liquid crystal alignment. There
is a range of pre-tilt angles best suited for producing a high contrast ratio and a good uniform image
without LC disclination. With optimized pre-tilt the intrinsic device contrast ratio for a ƒ/2.4 optical
system is greater than 5000:1. As shown in Figure 10, the molecules are rotated away from the
perpendicular state by the electric field from the pixel corresponding to input image signal. This
movement of the molecules changes the amount of rotation of the polarized projection light .
The JVC alignment method uses no organic layers common in other LC devices. Thus high stability is
achieved under conditions that degrade organic layers and cause short operating lifetimes. This is shown in
Figure 11 where the results of subjecting D-ILA modulators with different alignment methods to an high
intensity visible light source are given. The JVC inorganic method shows no degradation during the
accelerated test whereas the samples using organic (polyamide) alignment quickly degrade. In the graph
the voltage holding ratio of the liquid crystal (VHR) is used as a figure of merit for the stability of the
alignment method.
8
LIQUID CRYSTAL
INPUT
OUTPUT
LIGHT
LIGHT
OFF-STATE
( BLACK )
ON-STATE
( BRIGHT )
ALIGNMENT LAYER
SUBTRATE
Fig. 10. VAN LC alignment used in the D-ILA device
Photo- stability of SiO2 Alignment layer
15W/ cm2- White light
100
VHR(%)
80
60
40
SiO2
Poly- imide A
Poly- imide B
20
0
0
200
400
600
800
1000
1200
exposure time (h)
Figure 11. Photostability of liquid crystal alignnment techniques showing high
stability of D-ILA inorganic SiO2 method compared with organic polyamide
methods.
Temporal response time
The D-ILA device has a true video-rate response time (the rise time plus fall time equals less than
12 milliseconds). In general, the response time of liquid crystal layers is strongly related to the layer
thickness. Reflective mode permits a thinner liquid crystal cell gap compared to transmissive mode LCDs
because in this mode the light passes through the liquid crystal twice - effectively doubling the modulation.
9
In addition the pre-tilt angle of liquid crystal is a determining factor for response time. The pre-tilt angle is
set at a high enough value to avoid potential liquid crystal artifacts that can occur at very low tilt angles
while maintaining video-rate response.
Thermal stability
Figure 10 shows the voltage versus transmission curve changes with various temperatures
of T curve at a wide range of temperatures. This is a measure of how the light transmitted by the liquid
crystal varies as a function of voltage driving each pixel. There is almost no change in the front slope of the
V-T curves with temperature. This thermal stability of the device is required in projection systems so that
ambient temperature variations do not change the image characteristics.
O
36 C
O
40 C
TR
AN 100
SM
IS
SI 80
ON
[ % 60
]
50
60
65
70
75
80
O
C
C
C
O
C
O
C
O
C
O
O
40
20
0
0
1
2
3
4
5
6
APPLIED VOLTAGE [ V ]
Fig. 12. D-ILA Liquid Crystal Transfer
Characteristic as a function of temperature
MTBF of D-ILA Modulator
The ruggedness and reliability of the D-ILA modulator has been demonstrated in
actual operation in the field since production started in 1998. Table 2 summarizes the MTBF
performance.
10
2002/10/24
JVC ILA Center
Life-time of D-ILA panel
Configuration
Life-time coefficient
Actual performance data
Life-time
IC
10% decreasing rate of MOS
anplification ratio(gm)
(Degradation of transistor
characteristic by hot electron)
180 years at 15V
(120 years at 50 degree C)
Over 10 years
LC
Timing of 10% degradation in LCD
holding rate by UV element
574,200 Hrs at 0.1mW/cm2
Over 10 years
Sealing
material
Reduce by half time of adhesion
strength by UV light
Over 8 years at room temperature
storage
Over 8 years
ACF
connection
Insulation resistance of terminal 108
ohms, connnecting resistance
over 300 ohms
Over 100,000 Hrs at 85 degree C,
85% moisture
Over 100,000 Hrs
Table 2.
MTBF of D-ILA modulator components.
D-ILA Projector Technology
As previously discussed in the D-ILA device section, the driving IC controls the voltage
across the liquid crystal layer between reflective pixel electrode and transparent electrode based on image
signal level. This signal level determines the intermediate levels, or gray scale, of the image. Polarized
light from the light source (Xenon lamp or other high intensity discharge lamp) passes through the
activated liquid crystal and is reflected by reflective pixel electrode for each selected pixel. The liquid
crystal molecules change birefringence according to the signal voltage, changing the polarization direction
of the illumination light.
A schematic of the optical system to read the image on a single D-ILA device is shown in Fig.13.
The individual operation for each of the RGB D-ILAs is the same. The light from the arc lamp is
separated into two linear polarization states by the polarizing beam splitter (PBS) before it reaches the DILA. One state is reflected by the interface in the PBS and reaches the D-ILA device. To improve the
contrast ratio of the PBS a nominal quarter wave plate retarder is inserted between the PBS and the D-ILA.
Then the polarized light is reflected by pixel electrode and modulated by the liquid crystal again thus
receiving the gray scale image information.
Quarter Wave Plate
Screen
Beam Splitter
Polarizer
Projection
Lens
D-ILA
Arc Lamp
Fig 13. Optical Schematic of Basic D-ILA projector
Operation.
11
For pixels that have image information (highlight and gray level), the polarized light is rotated
through 90 degrees for highlight and partially rotated for gray level.The rotated light is transmitted through
the PBS to the projection lens to be finally imaged on the projection screen. For the pixels that have no
image information (black), the polarized light remains unchanged after leaving the D-ILA and then
reflected back to the lamp by the PBS. Full color D-ILA projectors have 3 D-ILAs for R (red), (G) (green),
and B (Blue). In most systems each device has its own PBS.
Figure 14 shows the optical schematic of a full color 3-PBS RGB system. This type of system
is used in the QX-1 projector. The white projection light from the high intensity light source (xenon lamp
or UHP-type lamp) is collimated and sent to an integrator and polarization recovery optical elements . The
integrator improves the uniformity of the illumination across the aperture of the D-ILA modulators and the
polarization recovery element rotates some of the orthogonal polarization state to the state used for
projection. The beam is then split into RGB components by crossed dichroic plates ,prepolarized, and sent
through the PBS beamsplitters (discussed above) to the D-ILA modulators. The image-modulated output
projection light from the 3 D-ILAs is analyzed by the same PBS elements and combined by a crossed
dichroic prism, which transmits the full color image to the projection lens. The projection lens then
images and magnifies the converged RGB image components on a projection screen.4
Fig. 14. RGB optical system used in D-ILA projectors.
Figure 15 shows a schematic of the new compact D-ILA projector color management
architecture using ColorQuad ™ technology. This is representative of many possible ColorQuad ™
system configurations. This type of optical engine is used in the SX-21, HX-1 and HD-2K projectors.
Four PBS are used to split the polarized white light into three primary color beams. The Color Select™
filters separate the color beams into orthogonal polarizations before the PBS to efficiently channel the
light through the system. The colors are determined by the angle insensitive Color Select™ filters. Thus
no degradation in color results from the use of low f/number systems down to f/2.
.
12
Fig. 15. Schematic of ColorQuad™ color management system architecture.
Color Gamut
The color gamut of the QX-1 projector is shown in Fig. 16. The color is reproduced at 10 bits per color.
The color reproduction corresponds closely to SPMTE 240M.
Chromaticity diagram
1
0.8
G
y
0.6
0.4
D55
R
SMPTE240
0.2
B
0
0
0.2
0.4
0.6
0.8
x
Fig. 16. Color Gamut of QX-1 D-ILA Projector
Future development
The JVC Reseach Division has used the inherent scalablility of D-ILA technology to
demonstrate a research projector incorporating 3 QHDTV D-ILA modulators shown in Fig.17. Each
modulator is 1.7 inches in diagonal and has a resolution of 3840 x 2048 pixels. Thus 4 native HDTV
images of 1920 x 1080 pixels can be shown simultaneously as shown in Fig. 18. This significant
development show that true 35mm ultimate quality photographic projection displays will be possible in the
future.
13
Fig. 17. Research Implementation of QHDTV (3840 x 2160 pixel) D-ILA Projector
Fig. 18. Four Native Resolution HDTV Images Projected Simultaneously on QHDTV D-ILA
Projector
References:
1.
Atsushi Nakano, Akira Honma, Shintaro Nakagaki and Keiichiro Doi, “Reflective active matrix
LCD: D-ILA.” SPIE Proceedings 1998, Vol 3296, p. 100.
2.
H. Kurogane, K. Doi, T. Nishihata, A. Honma, M. Furuya, S. Nakagaki, I. Takanashi, “Reflective
AMLCD for Projection Displays: D-ILA™, Society for Information Display International
Symposium Digest of Technical Papers, Vol. XXIX, 1998, p. 33.
3.
A.M. Lackner, J.D. Margerum, L.J. Miller, “Photostable Tilted-Perpendicular Alignment of
Liquid Crystals for Light Valves,” Society for Information Display International Symposium
Digest of Technical Papers, Vol. XXI, 1990, p. 98.
4.
F. Tatsumi, S. Moriya, Y. Ishizaka, “Optical System Using 3 Pieces of D-ILA Panel Module,”
Proceedings of the International Display Workshops 1998, p. 753.
14
15
Download