Electrophoretic display panel with arc driven individual pixels

An electrophoretic display includes a laminated triple pane construction with an electrophoretic fluid-containing envelope formed between the first and second panes and an ionizable gas-containing envelope between the second and third panes. A transparent reference electrode coats the first pane internal to the fluid envelope. A matrix of discrete pixels are disposed upon the second pane within the fluid envelope. Each pixel has a probe extending therefrom through the second pane and into the gas envelope. A plurality of row electrodes are disposed upon the second pane in the gas envelope in close proximity to corresponding rows of probes. A plurality of column electrodes disposed upon the third pane within the gas envelope perpendicular to the row lines establishes an addressable X-Y matrix. By impressing a sufficient voltage differential at selected intersections of the matrix, a local ionization of gas biases a proximate probe to the ionization potential. The probe potential is shared by the corresponding pixel, setting up an electrostatic field relative to the reference electrode for controlling the movement of pigment within the fluid. A capacitive effect is realized upon removal of ionization potential whereupon the gas deionizes leaving the pixel and probe to discharge slowly through the dielectric fluid.

FIELD OF THE INVENTION 
The present invention relates to an electrophoretic display panel apparatus 
and, more particularly, to an electrophoretic display having independent 
pixel elements driven by an arc through an ionizable gas. 
BACKGROUND OF THE INVENTION 
Electrophoretic displays (EPIDS) are now well known. A variety of display 
types and features are taught in several patents issued in the names of 
the inventors herein, Frank J. DiSanto and Denis A. Krusos and assigned to 
the assignee herein, Copytele, Inc. of Huntington Station, N.Y. For 
example, U.S. Pat. Nos. 4,655,897 and 4,732,830, each entitled 
ELECTROPHORETIC DISPLAY PANELS AND ASSOCIATED METHODS describe the basic 
operation and construction of an electrophoretic display. U.S. Pat. No. 
4,742,345, entitled ELECTROPHORETIC DISPLAY PANELS AND METHODS THEREFOR, 
describes a display having improved alignment and contrast. Many other 
patents regarding such displays are also assigned to Copytele, Inc. 
The display panels shown in the above-mentioned patents operate upon the 
same basic principle, viz., if a suspension of electrically charged 
pigment particles in a dielectric fluid is subjected to an applied 
electrostatic field, the pigment particles will migrate through the fluid 
in response, to the electrostatic field. Given a substantially homogeneous 
suspension of particles having a pigment color different from that of the 
dielectric fluid, if the applied electrostatic field is localized it will 
cause a visually observable localized pigment particle migration. The 
localized pigment particle migration results either in a localized area of 
concentration or rarefaction of particles depending upon the polarity and 
direction of the electrostatic field and the charge on the pigment 
particles. The electrophoretic display apparatus taught in the foregoing 
U.S. Patents are "triode-type" displays having a plurality of independent, 
parallel, cathode row conductor elements or "lines" deposited in the 
horizontal on one surface of a glass viewing screen. A layer of insulating 
photoresist material deposited over the cathode elements and photoetched 
down to the cathode elements to yield a plurality of insulator strips 
positioned at right angles to the cathode elements, forms the substrate 
for a plurality of independent, parallel column or grid conductor elements 
or "lines" running in the vertical direction. A glass cap member forms a 
fluid-tight seal with the viewing window along the cap's peripheral edge 
for containing the fluid suspension and also; acts as a substrate for an 
anode plate deposited on the interior flat surface of the cap. When the 
cap is in place, the anode surface is in spaced parallel relation to both 
the cathode elements and the grid elements. Given a specific particulate 
suspension, the sign of the electrostatic charge which will attract and 
repel the pigment particles will be known. The cathode element voltage, 
the anode voltage, and the grid element voltage can then be ascertained 
such that when a particular voltage is applied to the cathode and another 
voltage is applied to the grid, the area proximate their intersection will 
assume a net charge :sufficient to attract or repel pigment particles in 
suspension in the dielectric fluid. Since numerous cathode and grid lines 
are employed, there are numerous discrete intersection points which can be 
controlled by varying the voltage on the cathode and grid elements to 
cause localized visible regions of pigment concentration and rarefaction. 
Essentially then, the operating voltages on both cathode and grid must be 
able to assume at least two states corresponding to a logical one and a 
logical zero. Logical one for the cathode may either correspond to 
attraction or repulsion of pigment. Typically, the cathode and grid 
voltages are selected such that only when both are a logical one at a 
particular intersection point, will a sufficient electrostatic field be 
present at the intersection relative to the anode to cause the writing of 
a visual bit of information on the display through migration of pigment 
particles. The bit may be erased, e.g., upon a reversal of polarity and a 
logical zero-zero state occurring at the intersection coordinated with an 
erase voltage gradient between anode and cathode. In this manner, 
digitized data can be displayed on the electrophoretic display. 
Besides the triode-type display, the applicant's herein have proposed a 
variety of EPID structures for utilizing the electrophoretic effect. For 
example, an alternative EPID construction is described in application Ser. 
No. 07/345,825, now U.S. Pat. No. 5,053,763, entitled DUAL ANODE FLAT 
PANEL-ELECTROPHORETIC DISPLAY APATUS, which relates to an 
electrophoretic display in which the cathode/grid matrix as found in 
triode-type displays is overlayed by a plurality of independent, 
separately addressable "local" anode lines. The local anode lines are 
deposited upon and aligned with the grid lines and are insulated therefrom 
by interstitial lines of photoresist. The local anode lines are in 
addition to the "remote" anode, which is the layer deposited upon the 
anode faceplate or cap as in triode displays. The dual anode structure 
aforesaid provides enhanced operation by eliminating unwanted variations 
in display brightness between frames, increasing the speed of the display 
and decreasing the anode voltage required during Write and Hold cycles, 
all as explained therein. 
In general, it can be noted that a variety of EPID configurations have been 
proposed by the prior art. In the quest for better EPID's, improvements in 
resolution, speed of operation, simplicity of construction, reliability 
and economy continue to be sought. 
An object of the present invention is to achieve an improved EPID structure 
and function. 
SUMMARY OF THE INVENTION 
The problems and disadvantages associated with conventional electrophoretic 
displays are overcome by the present invention which includes a first 
receptacle containing electrophoretic fluid and a second receptacle 
containing an ionizable gas. The first and second receptacles share a 
common barrier wall and a plurality of conductive pathways penetrate the 
barrier wall. A first end of the conductive pathways is disposed proximate 
the fluid while a second end is in contact with the gas. Apparatus is 
provided for ionizing the gas proximate selected conductive pathways to 
bias those selected pathways in order to induce movement of pigment in the 
fluid proximate the first end of the selected conductive pathways.

DETAILED DESCRIPTION OF THE FIGURES 
FIG. 1 shows an electrophoretic display or EPID 10 having a front faceplate 
12, an intermediate pixel carrier plate 14 and a backplate 16. Typically, 
the plates 12, 14 and 16 would be formed from glass due to its 
transparency, dielectric strength and compatibility with photoetching 
processes. The plates are separated by spacers 18 which join the 
respective plates about their periphery forming a pair separate internal 
envelopes or receptacles, a first for containing electrophoretic fluid and 
a second for containing an ionizable gas, as shall be seen and described 
more fully below. The spacers are typically mylar and are bonded to the 
respective plates making up the EPID 10 by epoxy which flows under the 
influence of pressure and heat and upon cooling bonds to form an airtight 
and fluid tight seal. The faceplate of the EPID 10 has a substantially 
clear indium-tin-oxide (ITO) electrode 20 deposited on the interior 
surface thereof through which the electrophoretic effect may be 
visualized, A plurality of individual pixels 22 disposed on the 
intermediate pixel carrier plate 14 are depicted in dashed lines. Like the 
faceplate electrode 20, the individual pixels 22 may be formed of indium- 
tin-oxide (ITO) and are electrically conductive. In the alternative, 
metals such as chrome could be employed. Methods for depositing and 
shaping indium-tin-oxide on glass substrates are known in the art and are 
described, e.g., in the above-referenced U.S. Pat. Nos. 4,655,897 and 
4,732,830. 
FIG. 2 illustrates the interior components of the EPID 10. An anterior 
sealed chamber 24 receives electrophoretic fluid which includes a 
dielectric fluid and suspended therein a dispersion of colloidal 
surface-charged pigment particles, as is known in the art. Examples of 
typical electrophoretic fluids are referred to in U.S. Pat. Nos. 4,655,897 
and 4,732,830. One such typical fluid employs a dark blue or black 
dielectric along with yellow negatively surface-charged pigment particles. 
A posterior chamber 26 formed by the sealing of mylar seals 18 to plates 
14 and 16 contains an ionizable gas such as Argon, Xenon or Neon or a 
mixture of such gases. The rear plate 16 supports a plurality of parallel 
column conductor lines 28 disposed in this view in the "vertical 
direction". The conductor lines 28 may be formed from ITO, chrome or any 
other conductor material in a manner which is conventional in the art, 
such as photoetching, plasma etching, etc. The individual pixel elements 
22 disposed upon the intermediate pixel carrier plate 14 are electrically 
connected to associated conductor pins 30 formed from copper or any other 
suitable conductor. The conductor pins 30 penetrate the intermediate pixel 
carrier plate 14 such that a portion protrudes toward the backplate 16 
within the posterior chamber 26 and a portion protrudes toward the 
interior chamber to establish contact with an associated individual pixel 
22. If the vertical conductor members or column lines 28 are arbitrarily 
described as "vertical", the individual pixels may be said to be 
horizontally grouped in rows which are disposed at right angles to the 
vertical conductor lines 28. The grouping of the individual pixels 22 and 
associated conductor pins 30 is established by row conductor lines 32 
which traverse the intermediate pixel carrier plate 14 proximate to but 
not in conductive association with the conductor pins 30. Preferably, a 
row conductor line 32 is disposed on either side of a set or row of 
conductor pins 30 as shall be seen more conveniently in FIG. 3. A pair of 
driver circuits 33, 35 for driving the respective electrodes 20, 28 and 32 
are shown diagrammatically and are such as are known in the art as, e.g., 
represented by the teachings of U.S. Pat. Nos. 4,655,897 and 4,732,830. 
FIG. 3 shows the rear portion of the intermediate pixel carrier plate 14 
with the conductor pins 30 penetrating the plate and projecting towards 
the viewer. The conductor pins 30 are organized into rows by pairs of row 
conductor lines 32 which traverse the intermediate pixel carrier plate 14 
proximate to but not touching the conductor pins 30. In order to provide a 
uniform electrostatic field proximate the individual conductor pins 30, 
each of a pair of the row conductor lines assumes a semicircular shape 
proximate thereto which semicircles are conjoined to encircle the pins 30 
and coaxial spacing 33. 
FIG. 4 shows the front portion of backplate 16 upon which is disposed a 
plurality of vertical conductor lines 28. As can be seen by referring to 
FIGS. 2, 3 and 4, the vertical conductor lines 28 align with individual 
pixel members 22 and corresponding conductor pins 30 thereby forming a 
matrix with the horizontal row conductor lines 32. The conductor pins 30 
are disposed at each intersection of the matrix. In this respect, an X, Y 
addressable matrix is formed with the individual pixels 22 disposed at the 
addressable points on the matrix. 
FIG. 5 shows an enlarged fragment of the display 10 shown in FIG. 2 with 
one of the conductor pins 30 supporting an electric arc 34 traversing the 
gap between itself and an associated vertical conductor line 28. The 
electric arc is supported by the local ionization of the gas filling the 
posterior chamber 26 and originates from row conductor line 32. Given a 
voltage drop between a particular row conductor line 32 and an 
intersecting vertical conductor line 28 which is equal to or greater than 
the threshold voltage to create ionization across a particular physical 
gap, an electric discharge will occur as illustrated by electric arc 34. 
The threshold voltage is dependent upon the gas and the size of the gap. 
Since the conductor pin 30 is interposed into the arc pathway from the row 
conductor lines 32 to the vertical conductor column lines 28, the 
conductor pin 30 is raised to a voltage level corresponding to that of the 
electric are 34 at the point where the arc enters the conductor pin 30. 
Given that the conductor pin 30 is in electrical continuity with a single 
pixel 22, the potential of pixel 22 is also raised or lowered to the 
voltage of the conductor pin. In this manner, the pigment particles can be 
controlled, that is by setting the voltage of the individual pixels 22 in 
accordance with the voltage level of the electric arc 26. In FIG. 5, the 
electric are is induced by a positive voltage gradient from the row 
conductor line 32 to the vertical conductor line 28 such that the 
conductor pin 30 is raised to a high positive voltage thereby attracting 
the pigment particles 36 towards the individual pixel 22. This can be 
described as writing the pixel. The remainder of the pigment particles 36 
are retained on the faceplate electrode 20 by a zero or slightly positive 
voltage in areas adjacent to pixels 22 not influenced by the electric arc. 
It should be recalled that the anterior chamber 24 contains 
electrophoretic fluid which is a dielectric fluid suspending pigment 
particles 36 therein. In accordance with the operation of electrophoretic 
displays, the concentration of pigment particles proximate to or distal to 
the faceplate 12 is responsible for the display characteristics, namely if 
yellow pigment particles 36 are adhered to the faceplate electrode 20, the 
resultant image will appear yellow in all areas with pigment particles 36 
so adhered. In areas where the pigment particles are removed, that is, 
towards the pixels 22, the background dielectric solution color, for 
example black, will be evidenced. Thus, a convention is usually 
established in describing the electrophoretic display operation wherein a 
written pixel is either the absence of pigment particles, that is, a black 
pixel upon a yellow background defined by the presence of pigment 
particles, or vice-versa. In the present example, we will use the 
convention that a written pixel will be black and that the pigment 
particles 36 are yellow and negatively charged. What has been described 
then is an apparatus for creating an electric arc at a selected 
intersection of row conductor lines 32 and vertical conductor lines 28 to 
thereby influence pigment particles in an electrophoretic fluid which are 
further controlled by a planar faceplate electrode 20. By way of further 
example and explanation, assume that V.sub.1 volts is necessary to cause 
the gas between a conductor pin 30 and a vertical conductor line 28 to 
ionize and that V.sub.2 is equal to 1/2V.sub.1. If all the row conductor 
lines 32 are set at V.sub.1 volts, and all the vertical conductor members 
are set at V.sub.2, the gas will not ionize at any intersection. If the 
horizontal row conductor lines 32 are sequentially placed at V.sub.1 volts 
and the vertical conductor lines 28 are either left at V.sub.2 or placed 
at 0 volts in accordance with a data pattern, then the gas between the 
electrodes which have a potential difference of V.sub.1 volts will ionize. 
The conductor pins 30 which are in contact with the ionized gas will 
therefore be at a potential approximating V.sub.1 and the charged pigment 
particles 36 will move in a direction consistent with the polarity of 
V.sub.1 since the ITO of the faceplate electrode 20 is maintained close to 
zero potential. For example, if the row conductor lines 32 are 
sequentially placed at +100 volts and the vertical conductor lines 28 are 
maintained at +50 volts with a 100 volt differential required for 
ionization to occur, all vertical conductor lines which are placed at zero 
volts will then cause an ionization at that location. It should be 
appreciated that a negative voltage of, e.g., -100 volts imposed on row 
lines 32 would reach the ionization threshold at intersections with column 
lines 28 at 0 volts. This would result in the associated pixel at that 
intersection acquiring a potential approximating -100 volts thus repelling 
pigment particles to the faceplate electrodes 20 and thereby "erasing" the 
pixel. After each row of individual pixels 22 is written or erased, the 
gas is deionized setting up a capacitive effect between the individual 
pixels 22 and the faceplate electrode 20 since the pixels remain at the 
arc threshold voltage V.sub.1 until discharged through the resistance of 
the electrophoretic fluid. The pixels 22, as capacitors, charge quickly 
through the low resistance of the ionized gas and discharge slowly through 
the high resistance of the electrophoretic fluid. If, for example, the 
pixels 22 are 0.0045 inches by 0.0045 inches and the space between the 
faceplate electrode 20 and the pixel 22 is approximately 0.0045 inches 
then the effective capacitance at each pixel is on the order of 8 
microfarrads. Thus, a current in the micro-amp range can easily charge the 
capacitor in 50 microseconds even to a voltage of 100 volts. The same 
capacitive pixel 22 will require many milliseconds to discharge because of 
the high resistance of the suspension. In this manner, a unique TFT 
arrangement can be achieved and the panel can be written at very fast 
rates approaching those of video. In accordance with an alternative 
embodiment, holes of approximately 0.0036 inches in diameter in the 
intermediate pixel carrier plate 14 could be employed instead of the 
conductor pins 30 which traverse the plate from the pixel to the gas 
envelope in the posterior chamber 26. The holes would form a matrix of 
individual gas discharge lamps. This configuration can readily be 
envisioned by simply removing the probes 30 shown in FIG. 5. 
It should be understood that the embodiments described herein are merely 
exemplary and that a person skilled in the art may make many variations 
and modifications without departing from the spirit and scope of the 
invention as defined in the appended claims.