Note: Descriptions are shown in the official language in which they were submitted.
11371Si~
,
DIRECT-VIEWING STORAGE TARGET
FOR A CATHODE RAY TUBE
CROSS REFERENCE TO RELATED APPLICATION
This application is a continuation in part application of Serial No.
6,146 filed January 24, 1979.
BA~KGROUND OF THE INVENTIO,~
U. S. Patent No. 3,293,474 discloses a storage target for a cathode
ray tube that includes a faceplate on the inside surface of which is coated a
collector electrode in the form of a mesh, and phosphor storage dielectric
material is disposed in the openings of the mesh to form islands of dielectric
10 material which are isolated from each other by the mesh electrode.
The islan ls of dielectric material are in contact with the mesh
electrode, and this construction creates a halo or rim of li~ht around these
dielectric islands which provides background luminance which results in an
unacceptable contrast, especially in low light ambient conditions. Even if the
material of the dielectric islands does not contact the mesh electrode, the
dielectric islands are not insulated from the mesh electrode, thus, the halo or rim
lighting around each of the dielectric islands would still occur.
SUM1~1ARY OF THE INVE!~TIO~l
The subject matter of the present invention is related generally to
electron image storage systems, and in particular to a storage target for a
cathode ray tube which stores an electron image formed on such target for an
indefinite controllable time and produces a light image and/or an electrical
25 signal corresponding to such electron image. The storage target include; a mesh-
like electrode of conducting material coated on one side of a support plate of
insulating material, a layer of insulating material covers the mesh electrode
around each opening and covers part of each mesh opening reducing it in size butleaving areas of the mesh electrode exposed between the openings forming
30 collector electrode areas, and dielectric material is disposed in each insulated
mesh opening thereby forming islands of dielectric material isolated from the
mesh electrode to provide near zero background luminance, color write through
or color contrast regarding the displayed information. The dielectric areas may
be made of phosphor material if direct viewing is required and are separated
.
~l37ls4
from each other so that they store a bistal~le charge image formed thereon for an
indefinite controllable time as well as emitting a light image corresponding to
such charge image, in which case the support plate is made of light transparent
material. The present invention also includes photographic methods of
5 manufacture of storage targets employing a mesh electrode, such as that
described above, in order to obtain a fine mesh pattern of conducting material
for such electrode to increase image resolution.
In order for selective erasure of stored information to be
lO accomplished, the storage target can have a thin transparent conductive coating
disposed on the inside surface of the support plate and a thin layer of transparent
insulating material coating. A conductive mesh electrode is formed onto the
insulating layer along with insulating material covering the mesh electrode
around each mesh opening, the insulating material also en~aging the insulating
15 layer thereby reducin~ each mesh opening in size but leaving areas of the mesh
electrode exposed between the mesh openings which form collector electrode
areas. I~ielectric material is disposed in each insulated mesh opening thereby
forming islands of dielectric material isolated from the mesh electrode. ~'hen
selective erasure of information that has been stored on the storage target is
20 desired, the flood guns are turned off, the conductive coating is pulsed from a
low positive level to a high positive level, the electron beam is directed to the
selected area in which erasure of the stored information takes place, the
conductive coating is lowered to its low positive level and the flood guns are
turned on thereby retaining the nonerased information in its stored condition.
A storage target made in accordance with the present invention is
especially useful when employed in a bistable direct-viewing type of storaee tube
which forms part of a cathode ray oscilloscope to store the wave forms of
transient electrical input signals for extended examination. However, such a
30 storage tube can also be utilized in the manner of any conventional storage tube,
such as in radar apparatus, sonar apparatus or electronic computers. The storagetarget of the present invention has several advantages over conventional storagetargets including an increased maximum writing speed due to the high secondary
electron emission ratio of the insu]ating material which covers the regions of the
35 conductive mesh around the dielectric phosphor islands. As the target is scanned
by the writing beam this insulating material will quickly achieve a rest potential
equivalent to the voltage applied to the conductive mesh. Since the insulating
material surrounds and is adjacent to the dielectric phosphor islands, the
11371S4
-3-
phosphor will be brought to the same rest potential due to capacitive coupling.
The higher writing speed is also due in part to the lower capacitance of the
storage target so that such tar8et is capable of storing the electron images of
high frequency information. This reduced capacitance is the result of the use of5 a mesh electrode in the storage target, rather than a continuous electrode
beneath the storage dielectric of such storage target. In addition, a direct
view3ng storage target in accordance with the present invention produces a lightimage of excellent contrast with very low background luminance.
The photographic methods of manufacture of the storage target of
the present invention are simple and economical and even so, produce targets
having image resolution comparable to conventional storage tubes employing
wire mesh electrodes in their storage targets, such as that shown by F. H. Harris
in U. S. Patent ;~o. 2,839,679, issued June 17, 1958. The storage target structure
of the present invention is simple, rugged and reliable because the mesh
electrode, insulating material and the storage dielectric material are applied
onto a common support plate of insulating material. Thus, for large diameter
storage tubes there are no problems of increasing the thickness of the elements
of the mesh electrode as a planar structure in the present storage target, as is20 the case with conventional targets employing a wire mesh electrode. Another
advantage of the present target structure is that it enables the spaced, storagedielectric areas of such target to be substantially uniform so that there is less
noise or shadin~ due to field curvature in the electrical readout signal produced
by scanning the target with a reading beam.
Superior hard copies of the stored information are obtained as a
result of the high resolution of the stored information. The insulating materialcovering the mesh electrode to isolate the dielectric material from the mesh
electrode can be a phosphor material having nonstorage characteristics to enable30 the insulating material to display nonstored information while stored information
is being displayed by the islands of phosphor dielectric material and this is
defined as a write through mode of operation. The color given off by the
phosphor insulating material is different from that of the islands of phosphor
dielectric material to provide an excellent contrast when viewing the stored and35 nonstored information. The insulating material can have storage characteristics
and be a different color from that of the material of the dielectric islands so
that the written and displayed stored information will be a combined color
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113'71S~
representative of the phosphor dieJectric materials and the background wiJI be
the color of the insulatin~ material thereby providing an excellent contrast forviewing the information.
S In addition to the above advantages, the present storage target has
a substantially uniform electrical potential distribution over the rear surface of
the target, even when a charge image is stored thereon, because the conductive
elements forming the mesh electrode are exposed between the storage dielectric
areas of such target. Since the elements of the mesh electrode are the same
potential, the changes in potential of the dielectric areas have little effect on
the over-all potential distribution at the rear surface of the target so that such
potential distribution remains substantially uniform. Previous targets employingan electrode beneath a continuous layer of storage dielectric have a nonuniform
potential distribution on the rear surface of the target due to the different
15 charges stored on adjacent areas of the dielectric layer. This nonuniform
potential distribution effects the transmission of low velocity flood electrons to
the storage target, which are employed to hold the charge image produced
thereon by the writing beam, and produces an effect similar to the "coplanar grid
effect" which distorts the charge image.
~0
It is therefore one object of the present invention to provide an
improved structure for storing electron images of excellent contrast.
Another object of the invention is to provide an improved storage
25 target for storing an electron charge image thereon which has a low target
capacitance and an increased maximum writing speed.
` A further object of the present invention is to provide an improved
direct-viewing storage target in which a phosphor material is employed as the
~ 30 storage dielectric for storing an electron image formed thereon and for
`~ producing a light image corresponding to the electron image of excellent
brightness, increased contrast, high resolution and near zero background
luminance.
.
An additional object of the invention is to provide an improved
cathode ray storage tube in which a storage target having a simple structure
which is rugged and reliable is employed thus enabling a storage tube of large
size to be produced without decreasing the resolution of the image stored on such
target.
~137154
-5--
Still another object of the invention is to provide an improved
storage target in which a mesh electrode in the form of a conductive coating is
disposed on a support member of insulating material, a layer of insulating
material covers the mesh electrode except for exposed areas thereof with the
5 insulating material extending part way into the mesh apertures into engagementwith the support member thereby reducing the size of the apertures and a
storage dielectric material including a plurality of spaced storage areas is
contained within the insulated apertures of such mesh electrode.
A still further object of the present invention is the provision of an
improved storage target wherein the insulated mesh electrode and islands of
dielectric material within the insulated mesh openings are located on an
insulating layer covering a conductive layer to enable selective erasure of stored
information that is displayed on the storage target.
BRIEF DESCRIPTION OF THE DRAWINGS
Other objects and advantages of the present invention will be
apparent from the following detailed description of preferred embodiments
thereof and from the attached drawing of which:
FIG. I is a diagrammatic view of one embodiment of a storage tube
in accordance with the present invention and associated electrical circuitrv:
FIG. 2 is a part horizontal sectional view taken along the line 2--2
of FIG. I showing on an enlarged scale a storage target in accordance with the
present invention;
FIG. ~ is a view taken along the line 3--3 of FIG. 2 showing the rear
surface of the storage target on an enlarged scale;
FIGS. 4 and 5 are views similar to FIGS. 2 and 3 of another
embodiment of the storage target; and
FIG. 6 is a view similar to FIG. 2 of a further embodiment of the
30 storage target.
DESCRIPTION OF TllE PREFERRED EMBODIMENTS
A direct-viewing, bistable storage tube 10 having a storage target
12 made in accordance with the present invention is shown in FIG. 1. This
35 storage tube may have a single electron gun including a cathode 14, a controlgrid 16, a focusing anode structure 18 as welJ as a pair of horizontal deflection
plates 20 and a pair of vertical deflection plates 22. This single electron gun
may be empJoyed to produce either a writing beam or a reading beam 23 of
7154
electrons by changing the positions of each of three ganged switches 24, 26 and
28 connected, respectively, to the control grid 16, horizontal deflection plates 20
and vertical deflection plates 22 between a "WRITE" position and the "READ"
position, in a manner hereafter described. However, it should be understood that5 a pair of separate electron guns may be employed to form the writing beam and
the reading beam. The writing beam forms an electron charge image on the
storage target 12 by deflection of the writing beam across such stora~e target in
accordance with an input signal applied to the vertical deflection plates 12. The
reading beam is employed to produce an electrical readout signal on the storage
10 target of the storage tube by scanning the charge image stored on the storagetarget 12, for example, in accordance with a conventional television raster
pattern.
One or more flood guns 30 may be provided within the envelope of
15 the storage tube 10 in order to bombard the surface of the storage target 12
substantially uniformJy with low velocity flood electrons in order to maintain or
hold the charge image produced on such storage target by the writing beam after
such writing beam no longer bombards such target.
The storage target 12 includes a mesh electrode 32 shown in FIGS.
2 and 3 which is connected to a D. C. target voJtage across load resistor 34, a
layer of insulating material 37 covering the mesh electrode except for exposed
areas 39 of the mesh electrode and part of each mesh opening and a storage
dielectric 36 in the form of an array of spaced islands or dots of rectangular,
25 circular or other suitable configuration disposed within the insulated openings of
mesh electrode 32 so that the storage dielectric islands 36 are isolated from
mesh electrode 32. Exposed areas 39 of mesh electrode 32 define collector
electrode areas. \Vhen the target voltage applied to mesh electrode 32 is withinthe "stable range" of target voltages over which the islands of dielectric 35 of30 the storage target will store a charge image for an indefinite controllable time,
the writing beam of high velocity electrons produces by secondary emission a
charge image on the dielectric 36 which is more positive than the areas as a
result of the attraction thereto of the low velocity flood electrons which are
collected by exposed areas 39 of mesh electrode 32. The potential of the
35 "written" charge image is above a critical voltage corresponding to the firstcross-over point on the secondary emission curve of such dielectric, while the
remaining "unwritten" areas of such dielectric layer have a potential below suchcritical voltage. The flood electrons bombarding the storage target drive the
- . ... . .. .
~137154
potential of the "written" areas of the dielectric 36 to a high voltage stable state
corresponding to the potential on the mesh electrode, and drive the potential ofthe "unwritten" areas to a low voltage stable state corresponding to the voltageapplied to the cathode of the flood guns 30. This bistable storage operation hasbeen previously described in U. S. Patent No. 3,293,473.
The load resistor 34 is connected to a D. C. voltage source of ~500
volts through a variable bias resistor 38 whose setting controls the target voltage
applied to the mesh electrode 32. In order to erase the charge image stored on
target 12 the variable resistor 38 is decreased in value until the voltage applied
through the mesh electrode exceeds the "fade positive" voltage of the dielectric36 so that the flood electrons cause the potential of the dielectric layer to
become uniformly written positive. Next the resistance of the variable resisitor38 is increased until the target voltage applied to the mesh electrode 32 is below
the "retention threshold" voltage for the dielectric 36 below which the storage
target will not store a charge image. Then the voltage applied to the mesh
electrode is raised above the "retention threshold" voltage for the dielectric 36
below which the storage target will not store a charge image. Then the voltage
applied to the mesh electrode is raised above the "retention threshold" voltage to
a voltage within the "stable range" of target voltages over which the dielectriclayer will store a charge image and the target is ready to receive another charge
image.
During the writing operation of the storage tube of FIG. I the
control grid 16 is connected by a switch 24 to a source of D. C. voltage of -3,025
volts which is slightly negative with respect to the D. C. voltage of -3,000 volts
applied to cathode 14. The horizontal deflection plates 20 are connected by a
switch 26 to a horizontal sweep generator 40, while the vertical deflection plates
22 are connected by a switch 28 to a vertical amplifier 42, which may be of the
conventional type employed in cathode ray oscilloscopes. The input signal whose
wave form is to be stored on the storage target 12, is applied to the input
terminal 44 of the vertical amplifier 42.
The dielectric 36 of the storage target 12 may be made of phosphor
material including conventional phosphors, such as P-l type phosphor, rare earth-
activated rare earth oxides or oxysulfides and even photoconductive phosphors
such as Pl l, P20, P22, or P31 t~pe phosphors, so that the dielectric layer
1137~54
--8-
produces a light image corresponding to the charge image stored thereon when
the storage tube is of a direct-viewing type. In this case it is not necessary to
provide the storage tube with an electrical readout circuit since the wave form
of the input signal can be observed directly through the face plate of the storage
5 tube, but it may also be desirable to view the stored information and make a hard
copy of the stored information in accordance with the teaching of U. S. Patent
No. 3,679,824. Photoconductive phosphors may be used as the storage dielectric
because such dielectric is in the form of a plurality of separate spaced islands or
dots which are insulated from the target electrode by insulating material 37 to
10 prevent the charge image stored on such dielectric from spreading due to
photoconductivity.
Insulating material 37 can be a suitable nonphosphor insulating
material such as aluminum oxide, thorium oxide, silica or the like, but it can also
15 be a nonstoring phosphor material such as a rare earth-activated rare earth oxide
or oxysulfide with its surface killed by oxidation having a different color thanthat of dielectric 36 to enable nonstored information to be displayed in a colordifferent from the stored information for ease of comparison therebetween and
this is defined as a color write tllrough mode of operation. Insulating material 37
20 can also be a storage phosphor material such as a rare earth-activated rare earth
oxide or oxysulfide having a different color than that of dielectric 36 so that the
information that is stored on dielectric 36 is displayed in a combined color of
dielectric 36 and insulating material 37 and insulating material 37 provides on
each side of the displayed stored information a background color of the insulating
2S material 37 which provides a color contrast between the stored information and
the background. The insulating material 37 can be, for example, rare earth-
activated rare earth oxide or oxysulfide materials which, for example, can be
europium-activated yttrium oxide or oxysulfide which is a red color. The
dielectric storage material can, for example, be Pl or terbium-activated yttrium30 oxide or oxysulfide which are a green color. Conductive phosphors such as P31,
P22, Pl 1, or the like can also be used for dielectric material 36 to store
information thereon.
A collimating electrode 45 may be provided as a wall coatin~ of
35 conductive material on the interior surface of the funnel portion of the envelope
adjacent the storage target 12. This collimating electrode may be connected to
a D. C. voltage of +S0 volts to focus the flood electrons onto the storage target
11~7154
and to prevent distortion of the stored image due to the copJanar grid effect
discussed previously by which the positive target areas attract some of the flood
electrons away from the adjacent negative areas.
~lowever, if the dielectric layer 36 is not of phosphor, but is of
another secondary emissive material such as aluminum oxide, magnesium oxide
or the like, tlle storage tube must be provided with a readout circuit to produce
an electrical readout si~nal corresponding to the charge image stored on the
storage target. This may be accomplished by connecting the control grid 16 by
switch 24 to a source of D. C. voltage of -3,050 volts in order to reduce the
current density of the electron beam transmitted from the cathode 14 to target
12 in order to prevent such reading beam from producing a stored image on the
target. In addition, the horizontal deflection plates 20 and the vertical
deflection plates 22 may be connected by switches 26 and 28, respectively, to a
raster signal generator 46. The raster signal generator applies conventional sawtooth signals of different frequency to the horizontal plates and to the vertical
plates in order to produce a conventional television raster scanning pattern forthe reading oeam. This raster pattern can be controlled to cover all, or only a
portion of the storage target 12 in order to magnify a portion of the image stored
thereon- This image magnification operation can be performed automatically by
adjusting the raster signal generator so that the vertical raster signal applied to
the deflection plates 22 of the storage tube runs between two voltage limits
which correspond to voltages on opposite sides of the wave form portion sought
to be magnified. The electrical readout signal produced on the mesh electrode
32 is transmitted through a coupling capacitor 48, a low impedance preamplifier
50 and a high gain amplifier 52 to the Z-axis input of a remotely-positioned
television monitor tube 54 or other recording device. The horizontal and vertical
deflection plates of the monitor tube 54 are also connected to the raster signalgenerator 46 so that the monitor tube displays the entire wave form image storedon the storage target 12 of the storage tube, or only a magnified portion of such
wave form. Of course, it may be desirable to employ such a television monitor
tube and electrical readout circuit even when the storage dielectric layer 36 ofthe target 12 is phosphor material in order to enable the remote observation of
the stored wave form or to enable magnification of a portion thereof as indicated
or to make hard copies of the displayed and stored information in accordance
with the teaching of U. S. Patent No. 3,679,824.
~13'715~
-10-
As shown in FIGS. 2 and 3, the storage target 12 of the present
invention employs the mesh electrode 32 as a coating of conductive material on
the surface of one side of a li~ht transparent support plate S6 of insùlating
material which may be the glass face plate portion of a cathode ray tube
S envelope. The envelope may include a funnel portion S8 of ceramic material
which is sealed to the face plate 56 by a glass frit seal 60. The mesh electrode32 may be formed of a light opaque conductive material, such as aluminum, or
Nichrome, or silver, or a light transparent conductive material, such as tin oxide.
A section of mesh electrode 32 extends through the seal 60 to the exterior of the
10 envelope in order to provide an electrical lead portion 61 connected to the mesh
electrode within the envelope. The dielectric 36 of the storage target is
provided as a plurality of spaced areas of phosphor or other dielectric materialwhich are coated on the inner surface of the face plate 56 within the apertures
of the mesh electrode 32 which are insulated by insulating material 37 so that
such storage areas are separated from each other by the insulated elements of
such mesh electrode and collector electrode areas 39 are exposed through
insulating material 37. The storage dielectric areas are disposed laterally of the
insulated mesh electrode elements directly in contact with the face plate 56, and
are not between the writing beam and a continuous conductive layer on such face
20 plate as in some prior targets, so that the capacitance formed by such dielectric
areas, which must be charged by the writing beam bombarding the storage
target, is materially reduced. The dielectric areas may be rectan~ular, circularor of any other suitable configuration and they are all of approximately the same
thickness to provide a substantially uniform low capacitance over the surface of25 the storage target. Also the outer edges on the rear surface of these areas may
be formed with rounded corners rather than square corners in order to produce
this uniform capacitance because of the increased electrostatic fields produced
at sharp corners. The present storage target can be readily made in large sizes
and on flat or curved surfaces.
Depending on the type o~ material insulating material 37 is will
determine its mode of operation. If it is a nonphosphor, the background
luminance will be near 2ero. If material 37 is a nonstoring phosphor, color write
through will occur. If material 37 is a storing phosphor, color contrast will take
35 place. In each mode of operation, excellent contrast will be obtained. The
storage target shown by FIGS. 2 and 3 Is the desired structure when insulating
material 37 is a nonphosphor to increase phosphor area which results in higher
written luminance and low background luminance. The FIGS. 2 and 3 target can
'
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113~715~
, I
also be used for color write through operation. Dielectric islands 36 cover about
70~ of the total tar~et area, the insulating material 37 covers about 20% and the
collector electrode area 39 about lO%. The structure for the storage target as
shown in FIGS. 4 and 5 is desired when a color contrast mode of operation is to
5 be utilized, but a color write through mode of operation can also be used on this
structure. The target of FIGS. 4 and 5 is the same as that of FIGS. 2 and 3
except that mesh electrode 32a is made of transparent conductive material such
as tin oxide or the like and dots 41 of nontransparent or opaque conductive
material such as an alloy of nickel and chromium are adhered onto the
10 conductive elements of mesh electrode 32a to form an array of exposed collector
electrode areas 41 as shown in FIG. 5. Insulating material 37a extends into the
apertures of mesh electrode 32a into engagement with the surface of faceplate
56a making the size of these apertures smaller and isolating the islands of
phosphor storage dielectric material 36a. Insulating material 37a covers all of
15 the conductive areas 39 and it is either a storage or nonstorage phosphor
dielectric material of different color from that of the dielectric material of
islands 36a for color contrast or color write through modes of operation. The
dielectric islands 36a cover about 50% of the total target area, the insulating
material 37a covers about 40% and the collector electrode areas 41 about 109~.
20 The transparent conductive material 32a also covers 40% of the target area and
its transparency is reduced by one fourth due to the pattern of nontransparent
collector electrode dots 41 secured thereon.
A graticule scale 64 in the form of a plurality of scribed lines may
25 be provided on the Inner surface of the face plate 56 beneath the storage target
12 when the dielectric layer 36 is of phosphor in order to provide an internal
graticule for examining the light image produced on the storage target. This
internal graticule may be edged lighted by projecting light through the
surrounding edge of the face plate 56. In addition, the graticule scale 64 may
30 also be provided by deposits of glass frit printed on the inner surface of such face
plate to produce the graticule lines. Face plate 56a can also have a graticule
scale.
The following steps are set forth to make the storage target
35 structure of FIGS. 2 and 3: (1) An opaque, conductive material such as
chromium, nickel or an alloy of nickel and chromium is coated on one side of thefaceplate. (2) A layer of photo-sensitive material (photoresise) is applied ontothe conductive coating. (3) This photoresist is exposed by transmission of light
1137~.54
through a mask which is patterned in the configuration of a conductive mesh. (4)This exposed image is developed and the underlying areas of the conductive
coatings are etched. (A typical etchant is a solution of ceric ammonium sulfate
in nitric acid.) (5) The photoresist in the unexposed areas is then removed
S (typically by washing in acetone or similar solvents). Steps 1-5 results in an opaque, conductive mesh on the glass faceplate. (6) A second layer of
photoresist material is applied over the conductive mesh and the glass faceplate.
(7) The photoresist is then exposed by transmission of light through another mask
adjacent to the photoresist and developed to define a pattern of polymerized
10 photoresist "dots" which will form the collector regions. (8) The conductive
mesh is made the cathode in an electrolyte solution (typically isopropyl alcoholand aluminum nitrate) in which is suspended small positively-charged particles of
insulating material (typically aluminum oxide or thorium dioxide, or silicon
dioxide). When a voltage is applied to the mesh, these particles of insulating
15 material migrate and adhere to all areas of the conductive mesh which are notprotected by the previously-applied photoresist dots which will form the
collector regions. This insulating material is deposited to a thickness of greater
than one micron ar.d it covers the exposed edges of the mesh apertures. (9)
Phosphor may be deposited on this target by any of the customary photographic
20 deposition techniques. One method is to apply a wet slurry laver which consists
of 100 grams phosphor, 100 grams polyvinyl alcohol, 1000 ml. water, 1.0 ml.
isopropanol, and 20 grams of ammonium dichromate. This slurry is photo-
sensitive and so may be polymerized by exposure to light. The phosphor pattern
is defined by exposure through the conductive mesh which acts as a photo-mask.
25 (10~ The phosphor in the unexposed areas is developed by water rinse. (11) The
faceplate is baked to remove all organic binders from the phosphor and
photoresist from collector regions.
The following steps are described to make the color contrast
30 storage target of FIGS. 4 and 5: (1) A conductive transparent material such as
tin oxide is coated on one side of the faceplate glass. (2) Over this transparent
material is coated an opaque conductive material such as an aJloy of nicke! and
chromium. (3) A layer of photoresist is applied onto the nickel-chromium
coating. (4) The photoresist is exposed by transmission of light through a mask
35 which is patterned in a configuration of a mesh. (5) The exposed image of thephotoresist is developed and the underlying layers of opaque conductive materialand transparent conductive material are etched (typical etchants are: ceric
ammonium sulfate in nitric acid followed by powder zinc metal and hydrochloric
113~1s4
acid!. t5~ The photoresist in the unexposed areas is then removed. (Acetone or
similar solvent) (7) A layer of photoresist is then exposed by transmission of
light through a mask adjacent to the photoresist and developed to define a
pattern of photoresist dots to form the collector regions. (9) The storage
5 phosphor for this target is deposited photographically by standard techniques to
provide a pattern of phosphor islands surrounded by a conductive opaque mesh.
(10) The opaque conductive material in the areas not protected by photoresist isthen removed by etching in a solution which is selective to this material and not
for the transparent conductive material. (Typically the etchant is ceric
10 ammonium sulfate in nitric acid. This step defines a pattern of opaque
conductive dots which are protected by photoresist and are secured on the
transparent conductive mesh.) (Il) The conductive transparent mesh is made
the cathode in an electrolyte solution (typically isopropyl alcohol and aluminumnitrate) in which is suspended finely divided positively-charged particles of
15 dielectric phosphor. (A typical phosphor is eurpoium-activated yttrium oxysul-
fide.) If the target is to be made as a color write through tar~et, the phosphorwill be pre-treated in a manner such that it will not be luminescent at typical
storage voltages but will luminesce at higher voltages. When a voltage is
applied to the mesh, these particles of phosphor will migrate and adhere to the
20 transparent conductive mesh in all regions not protected by photoresist. The
particles will not migrate to the previously applied phosphor islands, since these
islands are electrically isolated from the mesh. (12) The faceplate is then baked
to remove all organic binders and photoresist from the phosphor and collector
regions.
FIG. 6 illustrates a further embodiment of the storage target.
Faceplate 56b has a thin layer 62 of transparent conductive material applied onto
its inner surface by vapor deposition or vacuum evaporation. The material is
about 0.2 micron thick and it can be tin oxide or indium tin oxide. A thin layer30 64 of transparent insulating material is applied onto conductive layer 52 and it
has a thickness of about one micron. The transparent insulating material can be
silicon oxide, silicon dioxide or aluminum oxide and it is preferably vacuum
evaporated onto conductive layer 62. Conductive layer 62 and insulating layer 64constitute a laminate structure.
Mesh electrode 32b, insulating material 37b and storage dielectric
islands 36b are formulated onto insulating layer 64 in the same manner as
1137iS4
--14--
hereinabove described in relation with the storage targets of FIGS. 2 and 3 and
FIGS. 4 and 5 to complete the storage target structure.
Mesh electrode 32b is connected to load resistor 34 via lead portion
S 61b and conductive layer 62 is connected to a conventional pulse generator
circuit 66 via lead portion 68. Pulse generator circuit 66 applies a rectangularerase pulse 70 t~ conductive layer or target electrode 62 when selective erasureof displayed stored information is to be undertaken.
Selective erasure of stored information on the storage target of
FIG. 6 is performed in the same manner as that disclosed in U. S. Patent No.
4,139,800 wherein flood guns 30 are turned off, pulse target electrode 62 to +400
volts which capacitively couples the surface of the phosphor layer containing
phosphor islands 36b above the potential of the collector electrode 32b, the
15 writing electron beam 23 is directed to the area on the storage target to be
erased for a predetermined time which will cause the phosphor islands in this
area to be changed to the potential of collector electrode 32b by secondary -
emission, target electrode 62 is returned to OV. which will capacitively couple
the surface of the phosphor islands to a potential below the voltage level at
20 which storage takes place and flood guns 30 are turned on which restores the
written information to its stored condition and the unwritten and erased areas
are at a voltage below the voltage level at which storage takes place.
If complete erasure of the storage target is desired, an erase pulse
25 is applied to collector electrode 32b which causes the entire target to be written
and restored to its writing threshold level ready for storage of information to be
written thereon via the writing electron beam 23. If desired, an erase pulse canalso be applied to target electrode 62 at the same time when the erase pulse is
applied to collector electrode 32b for faster complete erasure.
All of the methods for making the storage target described above
have at least one photographic exposure step in which a photosensitive layer is
exposed to the light of a mesh pattern in order to produce the mesh electrodes
32, 32a and 32b. This enables such mesh electrode to be provided with a plurality
3S of substantially uniform, small apertures and with a plurality of mesh elements
so that a lar~e number of small phosphor areas 36, 36a and 36b may be provided
within the insulated apertures of the mesh electrode. The result is a fine mesh
11371S4
-15-
storage target which enables the storage of electron images and the production
of light images of extremely high resolution which has not been possible with
conventional mesh storage targets formed by a plurality of interwoven wires.
It will be obvious to those having ordinary skill in the art that many
changes may be made in the details of the above-described preferred embodi-
ments of the present invention without departing from the spirit of the invention.
Therefore, the scope of the present invention should only be determined by the
following claims.
