Architecture for isolating display grids in a field emission display

The present invention teaches a field emission display ("FED") architecture for isolating display grids, wherein an FED has a plurality of pixels. Each of the pixels comprise at least two field emitter tips for displaying information to the pixel and a pixelator for driving the field emitter tips. Further, an isolated display grid is incorporated for each of the field emitter tips. Each display grids is coupled to a bus having a predetermined voltage by a link. In one embodiment of the present invention, the link can be disintegrated by internal or external means. In a second embodiment, the FED comprises a first and second bus, each of bus having a predetermined voltage, whereby a first isolated display grid is coupled to the first bus by a first link and a second isolated display grids is coupled to the second bus by a second link.

FIELD OF THE INVENTION 
The present invention relates to Field Emission Displays (FEDs), and more 
particularly, an architecture for isolating display grids in an FED. 
BACKGROUND OF THE INVENTION 
Until recently, the cathode ray tube ("CRT") has been the primary device 
for displaying information. While having sufficient display 
characteristics with respect to color, brightness, contrast and 
resolution, CRTs are relatively bulky and power hungry. In view of the 
advent of portable laptop computers, the demand has intensified for a 
display technology which is lightweight, compact, and power efficient. 
One available technology is flat panel displays, and more particularly, 
Liquid Crystal Display ("LCD") devices. LCDs are currently used for laptop 
computers. However, these LCD devices provide poor contrast in comparison 
to CRT technology. Further, LCDs offer only a limited angular display 
range. Moreover, color LCD devices consume power at rates incompatible 
with extended battery operation. In addition, a color LCD type screen 
tends to be far more costly than an equivalent CRT. 
In light of these shortcomings, there have been several developments 
recently in thin film, Field Emission Display ("FED") technology. In U.S. 
Pat. No. 5,210,472, commonly assigned with the present invention and 
incorporated herein by reference, a FED design is disclosed which utilizes 
a matrix-addressable array of pointed, thin-film, cold emission cathodes 
in combination with a phosphor luminescent screen. Here, the FED 
incorporates a column signal to activate a column switching driver and a 
row signal to activate a row switching driver. At the intersection of both 
an activated column and an activated row, a grid-to-emitter voltage 
differential exists sufficient to induce a field emission, thereby causing 
illumination of the associated phosphor of a pixel on the phosphorescent 
screen. By employing this design, the bus line associated with the current 
regulator has a low parasitic capacitance, thus being easier to control. 
Extensive research has recently made the manufacture of an inexpensive, low 
power, high resolution, high contrast, full color FED a more feasible 
alternative to LCDs. However, in order to produce a high resolution FED, a 
greater number of pixels per unit of area measured--i.e., square 
inches--are required. Thus, resolution is inversely proportional to the 
number of field emitter tips per pixel. For example, while a lower 
resolution FED may comprise 1000 tips per pixel, a higher resolution FED 
will comprise 1, 2, 3 or 4 tips per pixel. 
Several problems may arise where a number of field emitter tips relate to a 
single pixel. Referring to FIG. 1, an FED is illustrated having a four tip 
per pixel design. In this architecture, four emitter tips, 20, 20', 20", 
and 20'", are each coupled together at a common node 25. Emitter tips 20, 
20', 20", and 20'" are additionally coupled through a singular grid 15 to 
form a singular pixel 10 on an FED 5. Further, a pixelator 30 is coupled 
between a drive resistor 35 and common node 25. 
The problems associated with this architecture can best be viewed from a 
topographical perspective. Referring to FIG. 2, pixel is illustrated 
comprising field emitter tips 20, 20', 20", and 20'". Further, each tip, 
20, 20', 20", and 20'" is positioned within the singular grid 15, which is 
coupled to a power bus 45 by means of a via or link 40. Given this 
structural configuration, should one emitter tip of tips 20, 20', 20", and 
20'" be inoperative, the entire pixel 10 will fail. This can be realized 
because tips 20, 20', 20" and 20'" are each coupled to common node 25. 
Thus, should one tip electrically short, the remaining tips and the pixel 
as a whole will be inoperative as well. As there is no present design 
enabling the removal of the malfunctioning pixel, the entire FED, 
depending on the specifications, may be unusable. As such, the yield of an 
FED utilizing this design may be substantially impacted. 
In light of these limitations, presently there is a need for an FED 
architecture which provides a means for decoupling a nonfunctional field 
emitter tip or tips. Ideally, this structural design must not increase 
manufacturing and labor costs. Thus, a circuit design solution 
incorporated into current FED is preferred. 
SUMMARY OF THE INVENTION 
In order to achieve the hereinabove advantage, as well as others which will 
become apparent hereafter, an architecture for isolating display grids in 
a field emission displays having a plurality of pixels is disclosed. Each 
of the pixels comprise at least two field emitter tips for displaying 
information to the pixel and a pixelator for driving the field emitter 
tips. Further, an isolated display grid is incorporated for each of the 
field emitter tips or for a group of tips. Each display grid is coupled by 
a link to a bus having a predetermined voltage. 
In one embodiment of the present invention, the link comprises a fusible 
region which disintegrates when a predetermined level of current is being 
driven by the pixelator to the tip. Nonetheless, an external means can 
also be employed to disintegrate the link. 
In a second embodiment, the FED comprises a first and second bus, each bus 
having a predetermined voltage, whereby a first isolated display grid is 
coupled to the first bus by a first link and a second isolated display 
grid is coupled to the second bus by a second link. 
Other aspects and advantages will become apparent to those skilled in the 
art from the following detailed description read in conjunction with the 
appended claims and the drawings attached hereto.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to FIG. 3, a schematic representation of the present invention is 
illustrated. A high resolution FED 5 is shown having a four tip per pixel 
design. It should be obvious to one of ordinary skill in the art that the 
present invention is applicable to any multiple tips per pixel design, and 
not simply the four tip per pixel arrangement described herein. 
As a high resolution FED architecture, four emitter tips, 20, 20', 20", or 
20'", are each coupled together at a common node 25. To properly drive 
each tip, 20, 20', 20", or 20'", a pixelator 30 is coupled between a drive 
resistor 35 and common node 25. However, in each pixel 10, unlike known 
high resolution FED designs, each of the emitter tips, 20, 20', 20", or 
20'" are coupled through a singular isolated grid, 16, 17, 18 and 19. 
Referring to FIG. 4, a topographical perspective of the present invention 
is depicted. As field emitter tips is disclosed. Being directly accessible 
to light emissions, the link associated with a failed tip can be 
disintegrated by directly exposing it to light emissions. These emissions 
should be generated by a laser, though other energy forms are also 
employable. The power necessary from a laser to sufficiently disintegrate 
the link through this approach is substantially in the range of 0.1 
.mu.Watt and 10 mWatt. However, there is a direct relationship between 
power and the dimensions of the links themselves. While a thicker link 
requires greater power, a thinner will require less power. 
In an alternate embodiment of the present invention, the link associated 
with a failed tip can be dissolved by applying an acid etch. The acid 
employed should comprise H.sub.2 SO.sub.4, H.sub.2 SO.sub.4 and H.sub.2 
O.sub.2, or H.sub.2 PO.sub.4, though other acids can also be used. 
However, when using acid, consideration must be given to the potential 
damage to the remainder of the chip. As such, only a limited amount of 
acid can be used. A special applicator may be required to allow for the 
application of the acid. 
In the preferred embodiment of the present invention, the link is directly 
disintegrated by relying on fuse-type technology. Referring to FIG. 5, a 
link 50 is shown coupling an isolated display grid 19 to a power bus 75. 
Link 50 comprises a fusible region 70 having predetermined dimensions. 
Fusible region 70 is incorporated in link 50 for the purpose of 
disintegrating the coupling between isolated display grid 19 and bus 75 
when a predetermined level of current begins to pass. For example, the 
dimensions of region 70 can be calibrated to disintegrate when a short has 
formed in the associated emitter tip 19. 
Referring to FIG. 6, still another embodiment of the present invention is 
illustrated from a topographical perspective. As described above, a one to 
one relationship exists between the number of emitter tips and the number 
of singular isolated grids. It should, however, be obvious to one of 
ordinary skill in the art that an architecture could be designed wherein a 
one to one relationship exists between the number of isolated display 
grids and the number of power buses. Thus, it is conceivable that, in a 
four tip per pixel arrangement, each of the four isolated display grids 
has its own power bus. Other relationships, such as varying the number of 
tips per isolated display grid, are similarly devisable. 
Furthermore, isolated grids 16, 17, 18 and 19, are coupled into pairs of 
grids, wherein grid 16 and 18 form the first pair, and 17 and 19 form the 
second pair. Each pair of grids are then independently coupled to one of 
two power buses, 60 or 65, by means of a via or link, 55, 55', 56 and 56'. 
Both power buses, 60 and 65, have a predetermined voltage for the purposes 
of properly biasing each grid. 
In the event one or more of emitter tips, 20, 20', 20", or 20'" should 
malfunction, this embodiment enables the remaining functioning emitter 
tips to properly operate and facilitate further usage of the pixel. This 
is achieved by removing the malfunctioning tip through its associated 
link. Thus, in pixel 10, should emitter tip 20, 20', 20" or 20'" fail, the 
present invention provides described above, a one to one relationship 
exists between the number of emitter tips and the number of singular 
isolated grids. By this design, each singular isolated grid 16, 17, 18 and 
19, is coupled, by means of a via or link, 50, 50', 50" and 50'", to a bus 
45 having a predetermined voltage for the purposes of properly biasing 
each grid. 
Relying on the structural configuration of FIGS. 3 and 4, the advantages of 
the present invention should become more evident. In the event one or more 
of emitter tips, 20, 20', 20", or 20'" should malfunction, the present 
invention enables the remaining functioning emitter tips to properly 
operate and facilitate further usage of the pixel. This is achieved by 
removing the malfunctioning tip through its associated link. Thus, in 
pixel 10, should emitter tip 20, 20', 20", or 20'" fail, the present 
invention provides means for decoupling the failed tips associated 
isolated grid, 50, 50', 50", or 50'" from bus 45. This condition is of 
particular significance when the failed tip ultimately causes the 
remaining tips to fail. This issue can arise when the tip fails because of 
a short. 
By removing the failed tip from the pixel, the remaining operating tips can 
provide sufficient current to enable the pixel to properly function. Thus, 
it should be noted that while lowering the resolution of pixel 10, this 
decoupling step enables the pixel to properly operate. Furthermore, by the 
disintegration of the link of a failed tip, the need to remove the 
otherwise failed pixel from the display itself is overcome. 
Prior to disintegrating the link of a failed tip, each pixel must be 
properly tested to ascertain -which tips of that pixel are properly 
functioning. Several means for evaluating the operability of each of the 
field emitter tips are available to properly test each pixel. In one 
embodiment of the present invention, the operability of each tip is made 
apparent by stressing the entire display or specific pixels. Tips which 
are inoperative emit infrared light after shorting as a result of 
stressing. Thus, by means of an infrared sensor, such as an emission 
microscope for multilevel inspection ("EMMI"), a failing emitter tip which 
has shorted can be detected. As such, utilizing an EMMI, the coordinates 
of an inoperative tip can be ascertained and stored to enable the 
subsequent disintegration of its associated link. 
Further, upon stressing a pixel, a second phenomenon has been observed. The 
isolated display grid of a properly functioning tip comprises a negligible 
current to its associated bus. However, the isolated display grid of a 
failed tip generates a current substantially within the range of 100 nA 
and 10 .mu.A. Given this event, in a second embodiment of the present 
invention, a failing emitter tip which has shorted can be detected, by 
means of a current sensor, whereby the coordinates of an inoperative tip 
can be ascertained and stored to enable the subsequent disintegration of 
its associated link. 
The disintegration of the link associated with a failed tip can be achieved 
utilizing several methods. In one embodiment of the present invention, a 
system for decoupling each of the inoperable means for decoupling the 
failed tips from the pixel by disintegrating the relevant link. This 
condition is of particular significance when the failed tip ultimately 
causes the remaining tips to fail. This issue can arise when the tip fails 
because of a short. By removing the failed tip from the pixel, the 
remaining operating tips can provide sufficient energy to enable the pixel 
to properly function. Thus, it should be noted that while lowering the 
resolution of pixel 10, this decoupling step enables the pixel to properly 
operate. Furthermore, by the disintegration of the link of a failed tip, 
the need to remove the otherwise failed pixel from the display itself is 
overcome. 
The structural configuration of FIG. 6 has several additional advantages. 
Firstly, by subdividing each pixel into two pairs of isolated display 
grids, identifying a malfunctioning tip within a pixel is simplified. By 
biasing only one power bus, a shorted tip can be detected. This is 
achieved by subsequently measuring the current flow through the bus and 
the shorted pixel As the other power bus is disabled, this approach 
enables the determination of which pair of tips is shorted. While this 
technique can be used for more than two tips per pixel resolution, to 
directly identify a particular shorted tip, a one to one relationship is 
required between the number of isolated display grids and the number of 
buses. 
Similarly, a method for decoupling inoperative field emitter tips can be 
formulated. Initially, a field emission display is provided having a 
plurality of pixels. Each of the pixels of the display comprises at least 
two field emitter tips for displaying information to the pixel, a 
pixelator for driving the field emitter tips, a bus having a predetermined 
voltage, and an isolated display grid for each of the field emitter tips. 
Each isolated display grid is coupled to the bus by a link. 
Second, the step of testing each of the tips for operability is performed. 
This testing step involves the generation of a signal identifying which of 
the elements are inoperable. This step of testing can be achieved in one 
embodiment by sensing infrared energy emitted from each inoperative field 
emitter tip. Thus, by using an emission microscope for multilevel 
inspection ("EMMI"), those tips which are inoperable can be identified. In 
an alternate embodiment, the testing step can be achieved by sensing a 
current between said inoperative tip and said display grid. 
Third, the step of decoupling each of the inoperable tips is performed. 
This is achieved by disintegrating the link between the isolated display 
and bus of the failed tip in response to the signal. In one embodiment, 
disintegrating the link is accomplished by exposing the link to external 
energy substantially in the range of 0.1 .mu.Watt and 10 mWatt. This 
energy is generated by a laser. In a second embodiment, disintegration is 
achieved by exposing the link to an acid etch. The acid etch preferably 
comprises at least one of H.sub.2 SO.sub.4, H.sub.2 SO.sub.4 diluted with 
H.sub.2 O.sub.2, and H.sub.2 PO.sub.4, though other acids may also be 
suitable. 
While the particular invention has been described with reference to 
illustrative embodiments, this description is not meant to be construed in 
a limiting sense. It is understood that although the present invention has 
been described in a preferred embodiment, various modifications of the 
illustrative embodiments, as well as additional embodiments of the 
invention, will be apparent to persons skilled in the art upon reference 
to this description without departing from the spirit of the invention, as 
recited in the claims appended hereto. For example, it should be obvious 
to one of ordinary skill in the art that the ratio of tips per isolated 
display grid could be increased to greater than one to one. It is 
therefore contemplated that the appended claims will cover any such 
modifications or embodiments as fall within the true scope of the 
invention. 
All of the U.S. Patents cited herein are hereby incorporated by reference 
as if set forth in their entirety.