Note: Descriptions are shown in the official language in which they were submitted.
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This is a division of copending Canadian Patent
Application Serial No. 356,104 which was filed on ~uly 14,
1980.
Background of the Invention
It is known to peovide a direct viewing bistable
storage t~be that displays write-through informat;on in a
color different from that of stored information. The
target for such a "color write~through" CRT has a storage
dielectric of admixed phosphor materials. The admixture
incl~des two phosphors having different color emission
characteristics - one a storage phosphor/ the other a
phosphor that emits light of a different color and that
has a lower light output efficiency at low ~flood gun3
voltages. In operation, the perceived color of stored
images (which are displayed by flood gun illumination
alone) is mainly determined by the storage phosphor
because of its greater relative efficiency at low
voltages. Unstored write-through images, which are
produced by high energy electrons from the writing gun,
are displayed in a contrasting color resulting from the
combined emissions of both phosphors.
S~ch a target could be produced using an admixture
of a storage phosphor with two other phosphors having
different color emission characteristics. Although this
would make it possible to display write-through images in
either of two different colors, the necessarily reduced
percentage of storage phosphor particles would make stored
image displays undesirably dim and diffic~lt to discern.
Summary of the Invention
The present invention relates to cathode ray
storage t~bes and more particularly to a direct-viewing
bistable storage tube that displays write-through inform-
ation in either of two colors, both of them different from
the color o~ the stored information.
In accordance with an aspect of the invention
there is provided a storage target for a cathode-ray tube,
comprising: a substrate of electrically insulative
material/ means supported by said substrate for collecting
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secondary electrons, and a storage body of phosphor
material on one side of said substrate, said phosphor
material comprising a substantially uniform admixture of
phosphor particles, includiny particles of a first phosphor
capable of bistable storage of charge images and particles
of a second, rare earth phosphor having nonluminescent
material chemically bonded to the surfaces thereof in an
amount sufficient to increase the operating level of said
storage body and thereby increase the brightness of stored
light images~
An embodiment of the present invention can be realized
by a direct-viewing storage CRT target having a storage
dielectric layer o admixed phosphor material. The admixed
material includes two phosphors having different color
emission characteristics; one a low voltage luminescent
phosphor and the other a phosphor that emits light of a
color different at a higher voltage, preferably distinctly
different, from that of the low voltage luminescent
phosphor~ An array of collector electrodes extends through
the storage dielectric layer for collecting secondary
electrons that are emitted from the charge image stored by
the storage phosphor and these col:Lector electrodes are
formed from a conductive non-storing phosphor having a
color different from the phosphors in the admixed
dielectric layer.
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One of the admixed phosphors has a dead layer
which eliminates low voltage lwninance and this dead layer
enables the operating level of the target to be raised
thereby enabling the luminance of the stored information
to be increased. The collector phosphors also have a dead
layer and are conductive thereby collecting secondary
electrons but they do not luminesce unless excited by
higher voltage electrons at which time they luminesce a
different color than the admixed phosphors~
A primary object of the present invention is to
provide a direct-viewing bistable storage tube in which
write-through information may be displayed in two colors.
Another object of the present invention is the
provision of a bistable storage target for use with a
direct-viewing bistable tube which will display write-
through information in two colors and stored information
in a color different from the write~through inormation.
A further object of the present invention is to
provide a bistable storage target that will display stored
information at a h~gher luminance while simultaneously
displaying nonstored information in two different colors
which are different from the color of the stored
information.
An additional object of the present invention is
the provision of a bistable storage target that contains
an array of collector electrode members which are formed
from conductive phosphor particles having a dead layer
surrounding each phosphor particle.
Still a further object of the present invention
is to provide a bistable storage target that has an admix
of two different phosphor particles that emit different
colors forming the storage phosphor layer; one of the
phosphor particles being storage dielectric particles to
emit light of its color, the other phosphor particles
having a dead layer surrounding each of the particles to
inhibit low voltage luminance and to raise the operating
level of the target thereby enabling the stored
information to be displayed with a higher luminance.
Still an additional object of the present
invention is the provision of a bistable storage target
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that can be operatcd to display ref reshed multicolor
infcrmation simultaneously with stored information.
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The present invention taken in conjunction with
the invention disclosed in copending Canadian Patent
Application Serial No. 356 ,104 will be described in detail
hereinbelow wi'ch the aid of the accompanyiny drawings, in
which:
Brie_escri~t~on of the Drawing
] ,~ FIG. 1 is a diagrammatic view of a direct-viewing storage cathode
ray tube in accordance with the present invention, together with associated
circuitry; and
FIG. 2 is a fra~mentary cross-sectional view taken along line 2-2 of
FIG. 1, showing on an enlarged scale a preferred embodiment of a stora~e target
in accordance with the present invention.
Detailed Description of Preferred Embodiment
Referring first to FIG. 1, a direct-viewing bistable storage tube 10
includes an evacuated envelope 12 having a transparent faceplate 14 at one end.
Supported by faceplate 14 is a storage target 16 that includes a conductive
target electrode 18 and a storage dielectric layer 20. Mounted in the opposite
end of the tube is a writing gun 22 comprising a cathode 24, a control grid 26,
and a focusing and accelerating anode structure 28 for formin~ a beam 30 of highvelocity electrons directed toward target 16. Beam 30 is deflected by signals
applied to horizontal deflection plates 32 and vertical deflection plates 34 by
conventional deflection circuits 36. Storage tube 10 is additionally`provided with
one or more flood guns 3g for bombarding the storage dielectric uniformly with
low velocity elec~rons. The cathodes of the flood guns are connected ~o a low
voltage, suitably ground potential (0 volts).
A plurality of electrodes i5 disposed on the inner surface of
envelope 12 intermediate flood guns 38 and target 16. These electrodes
preferably are provided as spaced coatings, or bands, of a conductive material
such as silver, graphite, or the like. A first wall band electrode 40 functions
primarily as a focusing electrode for the flood electrons emitted by guns 38. It is
connected to a suitable positive voltage, about +250 volts, for example. A
second wall band electrode 42 spaced from electrode 40 and connected to a less
positive voltage) e.~., about ~150 volts, functions as a focusing and collimating
electrode. A third wall band electrode 44 spaced from electrode 42 is connected
to a still less positive voltage, e.g., about ~125 volts, and also functions as a
focusing and collimating electrode. A fourth wall band electrode 46 is located
intermediate and spaced from electrode 44 and storage target 16 Electrode 46
4 _
i~ connected to a still less positive voltage (about +75
volts) and functions as a focusing and collimating
electrode, but may also act as an auxiliary collector for
secondary electrons e~itted by the storage target at its
periphery. As a result of the collimating action of the
wall ~and electrodes, flood gun electrons are ~ubstantially
uniformly distributed over the surface of target 16.
It should be noted that a conventional resistive
coating 48, such as Aquadag (trade rnark), is provided on
the interior of the funnel portion of envelope 12 and is
electrically connected to an isolation shield (not shown)
in writing gun 22. Coating 48 thus serves as an extension
of the writing gun's second anode (not shown)~ The
voltages applied to wall band electrodes 40, 42, 44, and
46 are suitably adjusted to provide optimum focusing and
collimation of the flood gun electrons, and the specific
values given herein and shown on the drawing are by way of
example only.
Target electrode 18 is suitably connected to the rnidpoint of a
voltage divider consisting of resistors 50 and 52. Resistor 50 is adjusted so that a
potential of about +200 to +300 volts is applied So the target electrode.
The cathode of writing gun 22 is connected to a high negative D. C.
potential, suitably about -6000 volts via the movable contact of switch 23. The
control grid 26 is connected to the movable contact of a double pole, double
throw switch 53. In the STORE position of switch 53 and switch 23 in connection
with -6KV, grid 26 is connected to a negative D. C. potential -VGI to provide a
suitable grid-to-cathode reverse bias to cause writing beam 30 to bombard target16 with hi~h Yelocity electrons. ~hen struck by the writing beam, dielectric
layer 20 emits secondary electrons, which are then collected by electrode 18.
The written area of the layer is driven positive by the secondary emission, and
retained at a relatively positive potential after beam 30 has passed by low energy
electrons emitted by flood guns 38. In this well known manner a stored char~e
image is formed on the dielectric layer. In the Y/. T. or write-through mode of
operation of switch 53, the control grid is connected to the output of a
rectangular pulse generator 54, which applies positi~e-going voltage pulses 56 to
the grid. Pulses 56 have a maximum voltage level equal to -VGI, and a minimum
(more negative) voltage level sufficient to turn off the writing gun. Switching
the writin~ beam off for a portion of the time it is bombarding a particular area
of the target allows the charge image formed in the storage dielectric to he
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dischar~ed by the flood electrons. The write-through image is thus prevented
frorn being stored. A more compJete description of pulsed write-through
operation may he had by reference to V. S. Patent No. 3,430,093 to
Winningstad.
ReferlinK now to FIG. 2, there is illustrated in cross section the
storage target incorporated in storage tube 10. Target 16 includes a transparentsubstrate body in the form of faceplate l4, which is provided with a thin,
conductive tin oxide film 60. A multiplicity of raised "dots" 62 of a surface-
killed conductive phosphor material is distributed in a regular pattern over the
exposed surface of film 60. The conductive phosphor material is preferably P-22
blue (ZnS:Ag) coated with a cobalt sulfide precipitate that is diffused into thephosphor particles by heat treatment according to the teaching in U. S. Patent
Nos. 3,664,862; 3,767,459 and 3,826,679. The dots, which suitably have a
generally cylindrical or conical configuration, are electrically connected to the
tin oxide film. Thus, conductive film 60 and phosphor dots 62 together form
collector or target electrode 18. Disposed on conductive film 60 and surroundingdots 62 is an at least semi-continuous storage dielectric layer 20. Dots 62 extend
through layer 20 and have their outer ends exposed and they collect secondary
electrons that are emitted from adjacent positively-charged char~e images. Due
to the dead layer surrounding each of the phosphor particles of do~s 62, they will
not luminesce except at -8KV or above dependin~ on the thickness of th`e dead
layer.
According to the present invention, layer 20 comprises an admix-
ture of phosphor particles, including parlticles 64 of a phosphor capable of
bistable storage of charge Images, and particles of another phosphor 66.
Phosphor 66 is a surface-killed~phosphor and it is chosen to have a color emission
different, and preferably substantially different, from that of phosphor 64 when- bombarded by hi~h energy electrons, and to have a substantially lower light
output efficiency when bombarded by low energy flood gun electrons. ~le sur~ace-
killed phosphQr particles 66 present in layer 2~ ~ill ra~se ~he o~erating
level of the storaae target, which will increase the luminance of the
stored information. Suitable phosphors meeting these criteria include the red-
emitting P-22R phosphors, such as Y2O2S:Eu, Y2O3:Eu, Gd2O2S:Eu, Gd2O3:Eu
and YVO4:Eu. The red phosphor particles 66 have their surfaces killed to providea dead layer of a desired thickness. One way in which the dead layer can be
obtained surrounding each of the red phosphor particles of the oxysulfides
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(Gd2O25:Eu and Y2O2S:Eu) is ~o air bake the target at a temperature between
450C and 550C . See J. W. Haynes and JO J. ~rown, "Preparation and
Luminance of selected Eu+3-activated rare earth-oxygen sulfur-compounds",
Journal Electrochem Society, Vol. 115, p 1060 (1969). This produces an
oxysulfate dead layer having a thickness depending on the time of bake at the
prescribed temperature. Another way to obtain the dead layer at the surface of
each of the red phosphor particles for each of the above rare earth oxides or
oxysulfides is to slurry the red phosphor particles in a phosphoric acid solution at
a controlled temperature between room temperature and ~0C and also
controlled phosphor-to-solution concentration so that the pH of the solution
should be less than 4.5. This forces a surface reaction to produce a rare earth
phosphate dead layer having a thickness depending upon the foregoing variables.
See U. S. Patent Nos. 3,607,371 and 3,927,240 for phosphate coating of
phosphors. Phosphor 64 suitably is a green-ernittlng storage phosphor such as P-l
(Zn2SiO4:Mn).
The two types of phosphor particles are uniformly admixed, either
dry or in slurry form, and deposited on conductive film 60 of target electrode 18
in a known manner, for example using the procedure outlined in U. S. Patent No.
3,956,662 to MeTeague, et al. The ratio of the two types of phosphor in the
admixture may range from about 10% to about 80% by weight of phosphor 64,
with the balance being phosphor 66. A preferred composition comprises about
24% by weight P-l, about 56% dead layer red phosphor (or a mixture of P-22R
phosphors) of the rare earth type mentioned above and about 20% of P-22 blue as
the collector electrodes 62. A storage target provided with a dielectric layer of
the preferred composition will exhibit a green display of stored charge images
and an oran~e and a blue display of write-through charge images. The admixed
layer contains about 3396 by wei~ht of P-l phosphor and about 67% by weight of
P-22R phosphor.
1n one mode of write-through operation, switch 23 is connected
with -6KV while switch 53 remains at its W.T. position. This will result in the
stored information being displayed in green color, if information has been stored,
and the write-through information being displayed in an
orange color produced by the combination of the red and
green phosphors.
In another mode of write-through operation,
switch 23 is connected to -8KV while switch 53 is at its
W.T. position. If stored information is displayed
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in its green color, write-through information will be
displayed in a blue color due to emission from phosphors
66, 64 plus dots 62. Thus, a second write through col~r
is produced that is diff erent from the write-through
information when switch 23 is in the -6KV position and
also different from the stored information.
In a further mode of write-through operation, switch 23 is switched
between -6KV and -8KY while switch 53 is at its W.T. position. If stored
information is displayed in its green color, write-through information will be
displayed in the orange and blue colors that are diffcrent from ~he stored
information. The writing gun voltages can be less ~han -61CV or greater
than -8KV depending upon instrument design.
Of course, the tube can operate in a stored mode only or in one or
both color write-through modes as desired. Thus, the CRT can be operated as a
refresh multicolor monitor with bistable stora~e capability.
It will be understood that color coding of write-through information
is not restricted in application to the storage tube target structure exemplified
herein. Other suitable target structures include those descrlbéd in U. S. PatentNos. 3,293,474 to Gibson, Jr.; 3,401,293 to Morris; 3,531,675 to Frankland; and
3,614,820 to Morris.
About 20% of each of the collector electrode members 62 can be
metallic powder instead of 100% conductive phosphor to insure proper operating
range of the CRT because resistance of the phosphor dot collectors may be too
high thereby decreasing the collection efficiency of the secondary electrons andlowering the operating range of the CRT. If desired, about 20% of collector
electrode mernbers 62 can be formed from metallic powder whereas the
remainder can be conductive phosphor. Alternatively, the array of dots can be
made of the admixture of phosphors 64 and 66 surrounded by a layer of
conductive phosphor.
Brighter write-through informa~ion is displayed by the present
target because collectors 62 also emit light at write-through voltages
above -8KV. Also, by killing the surface of the red phosphor particles with a
phosphate layer, this raises the operating level of the storage tar~et thereby
increasing the luminance of the green phosphor particles which also compensates
;5 for the loss in storage luminance of green phosphor particles due to ~he admix of
the red phosphor particles to form the phosphor layer. The killed surfaces of the
conductive phosphor collector electrode members vill collect secondary elec-
trons during storage operation and they will not luminesce except above a
threshold voltage level.
A dual electron gun structure can also be used in
place of the switched voltage sources to a single cathode
if desired.
From the above it should be obvious to one of
ordinary skill in the art that various changes may be made
in the above-described preferred embodiment without
departing from the scope of the invention as defined by
the following claims.
