Patent Application
20080231183
This application relates to a hermetically sealed flat panel display maintained at a high vacuum utilizing a getter enclosed in a low profile containment.
Flat panel display (FPD) technology is one of the fastest growing display technologies in the world, with a potential to surpass and replace cathode ray tubes (CRTs) in the near future. As a result of this growth, a large variety of FPDs exist, which range from very small virtual reality eye tools to large hang-on-the-wall television displays.
The FPD generally includes a hermetically sealed vacuum container or envelope formed by sealing an anode substrate to a cathode substrate. A display employs phosphors at pixel locations which emit light when energized.
The anode substrate and the cathode substrate of such displays are made of thin glass plates each having a thickness as small as, for example, between 0.5 to 2.5 millimeters (mm) and are spaced from each other at a distance as small as 0.2 mm, resulting in the envelope being highly reduced in thickness. The substrates are rectangular and each of the same size. The substrates can be any size. Viewing areas vary accordingly and can be used as automotive, telephone, computer and other displays requiring small (or large) size and high (or low) resolution and larger sizes for computer and television devices, for example. However, the attachment of devices to insure the evacuation of residual gases in the envelope often compromise the overall thickness of the construction. U.S. Pat. No. 6,084,344 ('344 patent) issued on Jul. 4, 2000 to T. Kishino et al. and entitled “Reduced Thickness Vacuum Container With Getter” and assigned to Futaba Denshi Kogyo K.K. of Japan, describes prior art techniques used to evacuate such displays having anode and cathode substrates. The patent also describes a problem which is inherent in making thin displays. For example, as indicated above, such displays may have a spacing as small as 0.2 millimeters. The evacuation tube which goes to the evacuation pump has an inside diameter which is approximately 2 mm and an outside diameter of 4 mm. Therefore, since the evacuation tube has a diameter (outside) of 4 mm, one cannot easily evacuate the display via the thin bonded sides or the periphery, which sides are bonded by a glass frit joining the anode plate (or substrate) to the cathode plate. This cannot be done because of the fact that if the glass is, for example 0.7 mm in thickness, the entire display including the spacing is about 1.6 millimeters in thickness (0.7 mm cathode+0.7 mm anode+0.2 mm spacing). Therefore, the tube from the pump is of a diameter greater than the thickness of the display. The above-noted '344 patent discloses a first series of solutions that involve putting a through-hole in the cathode or the anode substrate with no hole in the periphery. When placing a hole or aperture in the periphery of the display one had to extend the anode or cathode structure so that one could place a getter box over the display, which getter box as shown in
The present invention involves placing a getter box at the sides or periphery of the display, which getter box is attached to the periphery of the display without the need to extend the cathode or anode substrate.
According to an aspect of the present invention, a vacuum container is formed from two substrates arranged opposite to each other, spaced from each other at a predetermined distance, and sealed about the periphery. A getter box is attached to the side of the display and a hole (e.g. rectangular) in the periphery of the display is surrounded by the getter box which has a separate aperture for communicating with the evacuation tube while enabling efficient exhaust.
According to another aspect of the invention, a vacuum container comprises: a first and second substrate of relatively the same dimensions and areas, a peripheral seal positioned about the outer periphery of each substrate for bonding the first substrate to the second substrate to form a composite stacked member of a given height with the first substrate bonded to the second substrate with the seal sandwiched between the substrates, the substrates separated one from the other by the width of the seal to create an internal hollow between the substrates, the seal having an elongated aperture between the substrates, a getter box having a top and a bottom surface with a first and a second side joining the top and bottom surfaces, with a front opening of the box having a length greater than the length of the aperture and a width greater than the thickness of the composite member, the box joined to the substrates to cover and enclose the aperture in the seal, the box having a vacuum aperture in one side with an evacuation tube of a given diameter opening to enclose the vacuum aperture, the tube joined to the box about the opening and having a sealed end remote from the box, the getter box having a getter source in the box hollow to absorb any residual gasses in the display hollow after the display hollow has been evacuated to a desired vacuum before sealing the end of the evacuation tube, wherein the area of the aperture is equal to or greater than π(D/2)2 where D is the diameter of the evacuation tube opening.
In another aspect of the present invention, an FPD comprises a vacuum envelope formed from a cathode substrate and an anode substrate joined by one or more outer peripheral members that provide at least one access hole to a getter box, and an associated evacuation tube further including within the envelope a plurality of electrically addressable pixels; a plurality of thin-film transistor (TFT) driver circuits each being electrically coupled to an associated at least one of the pixels, respectively; a passivating layer on the thin-film transistor driver circuits and at least partially around the pixels; and, a cathode; wherein addressing one of the pixels using the associated driver circuit causes the cathode to emit electrons that induce the one of the pixels to emit light.
It is to be understood that the accompanying drawings are solely for purposes of illustrating the concepts of the invention and are not drawn to scale. The embodiments shown in the accompanying drawings, and described in the accompanying detailed description, are to be used as illustrative embodiments and should not be construed as the only manner of practicing the invention.
a illustrates a perspective view of a display vacuum container showing the top substrates and side members according to an embodiment of the present invention;
b illustrates a side view of a display device showing a getter box and evacuation tube according to an embodiment of the present invention;
c illustrates a cross sectional view Al of a display device showing a getter box and evacuation tube according to an embodiment of the present invention;
a illustrates a perspective view of an exemplary getter box according to an embodiment of the present invention;
a illustrates a vacuum container and a getter box according to another embodiment of the present invention.
b shows a perspective view of the getter box of
It is to be understood that the figures and descriptions of the present invention have been simplified to illustrate elements that are relevant for a clear understanding of the present invention, while eliminating, for the purpose of clarity, many other elements found in typical FPD systems and methods of making and using the same. Those of ordinary skill in the art may recognize that other elements and/or steps are desirable and/or required in implementing the present invention. However, because such elements and steps are well known in the art, and because they do not facilitate a better understanding of the present invention, a discussion of such elements and steps is not provided herein.
Referring to
For example in the case of a low voltage phosphor display the vacuum permits the field emission cathode to emit electrons which impinge upon the anode at high efficiencies. Such a display should have a vacuum anywhere from 10−5 Torr to 10−6 Torr. Spacing 109 is on the order of 0.2 mm. An aperture 216 which is made on a peripheral portion of the display between the anode and the cathode is rectangular and is selected in accordance with the diameter of the evacuation tube. The dimension of the aperture 216 which as seen is rectangular in shape, is selected so that the evacuation pump in conjunction with the evacuation tube can operate to efficiently and quickly evacuate the space between the anode and cathode. Instead of aperture 216 a hole in the side would only be 0.2 mm in diameter. This diameter is unacceptable because of the fact that the exhaust mechanism which includes the exhaust tube cannot and will not be able to create a vacuum due to the small sized aperture.
b shows the partial view of the anode substrate 110 which as indicated is a glass substrate. The cathode substrate 160 which is also a glass substrate is joined or sealed to the anode by spacer member 109 formed of a suitable adhesive such as a low melting glass or a glass frit or other suitable adhesive, which firmly seals the anode 110 to the cathode 160. The aperture 216 is shown. The aperture 216 has a width which again is equal to the width of the spacer 109, and as indicated is 0.2 mm. It also has a length L. The length L is selected as follows. A typical exhaust tube has an inner diameter of 2 mm. This inner diameter is specified because of the exhaust port associated with the exhaust motor which thereby draws air from the spacing in the envelope and produces a vacuum. The exhaust tube has an inner diameter of 2 mm with an outer diameter of 4 mm. The 2 mm diameter specifies an area of exhaust for proper operation. The area of exhaust equals πD2. Therefore, for an outer diameter of 2 millimeters, πD2 is approximately equal to 12 square millimeters. Thus, the aperture 216 would have a length of 60 millimeters (0.2 mm×60 mm=12 sq. millimeters). This area of 12 square millimeters is provided by aperture 216 which therefore enables the pump to evacuate the spacing between the anode and cathode at the appropriate exhaust with the correct air flow.
c illustrates a cross sectional view of one embodiment of the vacuum container 100 housing a TFT anode/cold cathode FPD according to an embodiment of the present invention. In this exemplary embodiment, the FPD includes cathode 104 positioned on the glass substrate 110. The cathode acts as a low-voltage source of electrons. While not shown in this embodiment, it is nevertheless understood that both the cathode and anode may be on the same plate or substrate (such as for example in a nanotube emitter configuration). The glass anode substrate 160 employs TFT circuitry to control the attraction of electrons 140 emitted from the cathode 104. As shown in
The evacuation tube 212 is cone-like in geometric shape. The cone shape of the evacuation tube 212 with the apex 220 is formed after the display envelope is evacuated. The evacuation tube has an inner diameter (A) of 2 mm and an outer diameter (B) of 4 mm. The tube is made of glass and is connected at one end to an evacuation pump (not shown). After evacuation to the desired vacuum (10−5-10−6 Torr) the glass evacuation tube is heated and drawn closed by pulling and compressing as the glass becomes molten, hence forming the conical like shape. In the embodiment shown, the through-hole 216 is arranged at a left side end portion of the peripheral seal joining the glass members. It is recognized that the through-hole 216 may be formed on any one of the four sides of the vacuum container 100.
As indicated, the through-hole 216 functions as a port through which the gas (i.e., air) in container 100 is withdrawn under pressure from the external pump, through the evacuation tube 212 and discharged. After the pump has discharged the air content to a particular low level, the getter 214 (after activation) substantially absorbs the gas remaining in the container 100. Getters are typically composed of materials of the non-vaporization type such as Ti-Zr-Al alloy, Ti-Zr-V—Fe alloy or any material of the vaporization type such as Ba—Al alloy. In each of the embodiments described herein, the getter 214 is arranged on a side of the getter box 218. Multiple getters may be installed and arranged in the getter box 218 depending on the requirements for the particular FPD. Furthermore, the getter 214 may be formed into any suitable shape such as a pill-like cylinder, bar, or ring-like member, provided it can be housed in the getter box 218. In
Anode substrate 160 includes a plurality of conductive pads 170 fabricated in a matrix of substantially parallel rows and columns on substrate 160 using known fabrication methods. Column conductors 177 are associated with each of the corresponding conductive pads 170. In this illustrated embodiment substrate 160 is a transparent material such as glass. Conductive pads 170 are also composed of a transparent material, such as Indium Titanium Oxide (ITO). The getter box 218 and the envelope 100 are also fabricated from a material such as glass. It is of course recognized that the pixels may range from opaque to transparent according to the desired application and/or viewing perspective.
Deposited on each conductive pad 170 is phosphor layer 175. Phosphor layer 175 may be selected from materials that emit light 195 of a specific color. In a conventional RGB display, phosphor layer 175 may be selected from materials that produce red light, green light or blue light 195 when struck by electrons 140. As will be appreciated by those skilled in the art, the terms “light” and “photon” are used synonymously and interchangeably herein. A matrix organization of conductive pads and phosphor layers allows for X-Y addressing of each of the individual pixel elements in the display will be understood by one skilled in the pertinent arts.
Associated with each conductive pad 170/phosphor layer 175 pixel is a TFT circuit 180 and associated TFT final passivation layer 179, that serve to apply a known voltage to the associated conductive pad 170/phosphor layer 175 pixel. For example, TFT circuit 180 operates to apply either a first voltage to bias an associated pixel element to maintain it in an “off state or a second voltage to bias an associated pixel element to maintain it in an “on” state, or an intermediate state. In this illustrated case, conductive pad 170 is inhibited from attracting electrons 140 emitted by cathode 104 when in an “off” state, and attracts electrons 140 when in an “on” state or an intermediate state.
The use of TFT circuitry 180 for biasing conductive pad 170 provides the dual function of addressing pixel elements and maintaining the pixel element in a condition to attract electrons for a desired time period, i.e. time-frame or sub-periods of a time-frame. Cathode 104 is fabricated by progressively depositing onto substrate 110, conventionally a glass, an insulating material 115, such as a silicon dioxide (SiO2), an edge emitter material 120 operable to emit electrons, a second insulating layer 125, such as SiO2, and a second conductive material 130, such as Mo. Emitter material 120 may be selected from known materials that have a low work function for emitting electrons 140. Emitter material 120 may comprise a metal such as Molybdenum (Mo), for example. Wells 136 are formed through the deposited second conductive layer 130, insulating layer 125, emitter layer 120, and insulating layer 115 using well-known techniques, such as photo-etching. In this case, edges 135 of emitter material 120 are exposed and generate electrons 140 under excitation. Second conductive material 130 operates as a gate electrode to draw electrons 140 from the edges of emitter material 120 when a sufficient potential difference exists between conductive material 130 and emitter layer 120.
Referring to
The getter pill 306 operates to chemically absorb the remaining gas in the envelope of the vacuum container 100 following the evacuation of gases by pumping means. The getter 306 may be installed in a space in the getter box 218 where the getter 306 is fixedly supported therein. As illustrated, the getter pill 306 is provided, on a portion of an inner surface of the getter box 218. There may be multiple getter pills 306 placed in the getter box 218.
Referring to
Typically the front surface of the getter box as shown in
As seen in
It is expressly intended that all combinations of those elements that perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Substitutions of elements from one described embodiment to another are also fully intended and contemplated.
