Plasma addressed liquid crystal display with glass spacers

Details Plasma addressed liquid crystal display with glass spacers Plasma addressed liquid crystal display with glass spacers

1996-01-19

2002-08-13

Patel, Vip (Department: 2879)

Electric lamp and discharge devices

With luminescent solid or liquid material

C313S484000, C313S582000, C313S584000, C313S495000

Reexamination Certificate

active

06433471

ABSTRACT:

BACKGROUND OF INVENTION
This invention relates to plasma channels, to display devices comprising plasma channels, and to plasma-addressed liquid crystal display panels commonly referred to as “PALC” display devices using such channels. PALC devices comprise, typically, a sandwich of: a first substrate having deposited on it parallel transparent column electrodes, commonly referred to as “ITO” columns or electrodes since indium-tin oxides are typically used, on which is deposited a color filter layer; a second substrate comprising parallel sealed plasma channels corresponding to rows of the display crossing all of the ITO columns and each of which is filled with a low pressure ionizable gas, such as helium, neon and/or argon, and containing spaced cathode and anode electrodes along the channel for ionizing the gas to create a plasma, which channels are closed off by a thin transparent dielectric sheet; and a liquid crystal (LC) material located between the substrates. The structure behaves like an active matrix liquid crystal display in which the thin film transistor switches at each pixel are replaced by a plasma channel acting as a row switch and capable of selectively addressing a row of LC pixel elements. In operation, successive lines of data signals representing an image to be displayed are sampled at column positions and the sampled data voltages are respectively applied to the ITO columns. All but one of the row plasma channels are in the de-ionized or non-conducting state. The plasma of the one ionized selected channel is conducting and, in effect, establishes a reference potential on the adjacent side of a row of pixels of the LC layer, causing each LC pixel to charge up to the applied column potential of the data signal. The ionized channel is turned off, isolating the LC pixel charge and storing the data voltage for a frame period. When the next row of data appears on the ITO columns, only the succeeding plasma channel row is ionized to store the data voltages in the succeeding row of LC pixels, and so on. As is well known, the attenuation of the backlight or incident light to each LC pixel is a function of the stored voltage across the pixel. A more detailed description is unnecessary because the construction, fabrication, and operation of such PALC devices have been described in detail in the following U.S. patents and publication, the contents of which are hereby incorporated by reference: U.S. Pat. Nos. 4,896,149; 5,077,553; 5,272,472; 5,276,384; and Buzak et al., “A 16-Inch Full Color Plasma Addressed Liquid Crystal Display”, Digest of Tech. Papers, 1993 SID Int. Symp., Soc. for Info. Displ. pp. 883-886.
FIG. 1
shows a flat panel display system
10
, which represents a typical PALC display device and the operating electronic circuitry. With reference to
FIG. 1
, the flat panel display system comprises a display panel
12
having a display surface
14
that contains a pattern formed by a rectangular planar array of nominally identical data storage or display elements
16
mutually spaced apart by predetermined distances in the vertical and horizontal directions. Each display element
16
in the array represents the overlapping portions of thin, narrow electrodes
18
arranged in vertical columns and elongate, narrow channels
20
arranged in horizontal rows. (The electrodes
18
are hereinafter referred to from time to time as “column electrodes”). The display elements
16
in each of the rows of channels
20
represent one line of data.
The widths of column electrodes
18
and channels
20
determine the dimensions of display elements
16
, which are typically of rectangular shape. Column electrodes
18
are deposited on a major surface of a first electrically nonconductive, optically transparent substrate
34
(FIG.
2
), and the channel rows are usually built into a second transparent substrate
36
. Skilled persons will appreciate that certain systems, such as a reflective display of either the direct view or projection type, would require that only one substrate be optically transparent.
Column electrodes
18
receive data drive signals of the analog voltage type developed on parallel output conductors
22
′ by different ones of output amplifiers
23
(
FIG. 2
) of a data driver or drive circuit
24
, and channels
20
receive data strobe signals of the voltage pulse type developed on parallel output conductors
26
′ by different ones of output amplifiers
21
(
FIG. 2
) of a data strobe or strobe means or strobe circuit
28
. Each of the channels
20
includes a reference electrode
30
(
FIG. 2
) to which a reference potential, such as ground, common to each channel
20
and data strobe
28
is applied.
To synthesize an image on the entire area of display surface
14
, display system
10
employs a scan control circuit
32
that coordinates the functions of data driver
24
and data strobe
28
so that all columns of display elements
16
of display panel
12
are addressed row by row in row scan fashion as had been described. Display panel
12
may employ electro-optic materials of different types. For example, if it uses such material that changes the polarization state of incident light rays, display panel
12
is positioned between a pair of light polarizing filters, which cooperate with display panel
12
to change the luminance of light propagating through them. The use of a scattering liquid crystal cell as the electro-optic material would not require the use of polarizing filters, however. All such materials or layers of materials which attenuate transmitted or reflected light in response to the voltage across it are referred to herein as electro-optic materials. As LC materials are presently the most common example, the detailed description will refer to LC materials but it will be understood that the invention is not limited thereto. A color filter (not shown) may be positioned within display panel
12
to develop multi-colored images of controllable color intensity. For a projection display, color can also be achieved by using three separate monochrome panels
12
, each of which controls one primary color.
A partial perspective view of the PALC display described in the 1993 SID Digest is shown in FIG.
2
.
FIG. 2
illustrates the PALC version of such a flat display panel using LC material. Only
3
of the column electrodes
18
are shown. The row electrodes
20
are constituted by a plurality of parallel elongated sealed channels underlying (in
FIG. 2
) a layer
42
of the LC material. Each of the channels
20
is filled with an ionizable gas
44
, closed off with a thin dielectric sheet
45
typically of glass, and contains on an interior channel surface first and second spaced elongated electrodes
30
,
31
which extend the full length of each channel. The first electrode
30
is grounded and is commonly called the anode. The second electrode
31
is called the cathode, because to it will be supplied relative to the anode electrode a negative strobe pulse sufficient to cause electrons to be emitted from the cathode
31
to ionize the gas. As explained above, each channel
20
, in turn, has its gas ionized with a strobe pulse to form a plasma and a grounded line connection to a row of pixels in the LC layer
42
above. When the strobe pulse terminates, and after deionization has occurred, the next channel is strobed and turned on. Since the column electrodes
18
each cross a whole column of pixels, typically only one plasma row connection at a time is allowed on to avoid crosstalk.
Fabrication of a PALC device is typically done as described in the 1993 SID digest paper by providing first and second substrates
34
,
36
with the first substrate
34
comprising a glass panel on which is deposited the ITO column electrodes
18
, followed by color filter processing over the ITO electrodes to produce the RGB stripes (not shown), followed by the black surround processing and liquid crystal alignment processing. The second substrate
36
, also a glass panel, is masked and etched to form the channels
20
, following which the plasm

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