Abstract:
The present invention provides a method of electron beam testing of liquid crystal displays comprising non-uniform electrodes having a conductive portion and a dielectric portion. In accordance with methods of the present invention, the diameter of the electron beam is increased so that the beam is less focused, i.e., enlarged or “blurred,” over a non-uniform electrode area. The diameter of the beam is increased so that the beam generates secondary electrons from the conductive portion of the non-uniform electrode area. The configured test beam may be circular, elliptical, or other suitable shapes.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims priority to a U.S. Provisional Patent Application No. 60/598,667 filed on Aug. 3, 2004, which is entitled “Method for Testing Multi-Domain Vertical Alignment Pixels for TFT Displays,” and is incorporated by reference herein in its entirety. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to testing of pixels of a flat panel display. In particular, embodiments of the invention relate to the testing of pixels by directing an electron beam onto a non-uniform electrode area.  
         [0004]     2. Description of the Related Art  
         [0005]     In years past, a common display for computers and other electronic products has been the cathode ray tube, or CRT. The CRT served as the standard display for personal computers (PC&#39;s) and televisions during the last half of the twentieth century. The CRT generally operates on a curved glass panel to form a display.  
         [0006]     Recently, active matrix liquid crystal displays, or LCD&#39;s, have been commercially developed. The LCD has several advantages over the CRT, including higher picture quality, lighter weight, lower voltage requirements, and low power consumption. LCD displays are beneficial for flat panel displays, and have been commercialized of late in many portable electronic devices such as calculator screens, personal digital assistant (PDA) screens, portable computer (notebook) screens, mobile telephone displays, and small computer and television screens. In addition, larger LCD displays are now being employed in flat-screen televisions for the consumer market.  
         [0007]     One type of active matrix LCD comprises liquid crystal material sandwiched between a TFT-array substrate and a color filter substrate. The TFT-array substrate comprises an array of thin film transistors (TFT&#39;s) each coupled to a pixel electrode. The color filter substrate comprises different color filter portions and a common electrode. When a certain voltage is applied to a pixel electrode, an electric field is created between the pixel electrode and the common electrode, orienting the liquid crystal material to allow light to pass therethrough for that particular pixel.  
         [0008]      FIG. 1  is a schematic diagram showing one pixel of a liquid crystal display  100  comprising a uniform pixel electrode. This diagram is taken from the web site of Fujitsu, found currently at http://www.fine.fujitsu.com/products/displays/lcdvatech.html. Liquid crystal material  120  is sandwiched between the TFT-array substrate  110 ′ and the color filter substrate  110 ″. Since the TFT-array substrate  110 ′ comprises a uniform pixel electrode  112 ′, the molecules of the liquid crystal orient in a single direction when a certain voltage is applied to the pixel electrode. The light intensity of the display  100  is dependent on the view direction in reference to the liquid crystal orientation. Thus, the TFT-LCD having a uniform pixel electrode has a drawback in that the effective viewing angle is narrow.  
         [0009]      FIG. 2  is a schematic diagram showing one embodiment of one pixel of a liquid crystal display  200  comprising a non-uniform electrode. This diagram is taken from the web site of Fujitsu, found currently at http://www.fine.fujitsu.com/products/displays/lcdvatech.html. Liquid crystal material  220 A and  220 B is sandwiched between the TFT-array substrate  210 ′ and the color filter substrate  210 ″. The TFT-array substrate  210 ′ comprises a non-uniform electrode  212 ′. The non-uniform electrode comprises dielectric lines formed over a conductive portion. The dielectric lines cause the liquid crystal material to orient in multiple directions. As a consequence, the display  200  seems bright when viewed at different angles by the viewer. This type of display having a non-uniform electrode comprising dielectric lines formed over a conductive portion is referred to as a multi-domain vertical alignment (MVA) display.  
         [0010]      FIG. 3  and  FIG. 4  are schematic diagrams of one example of a MVA display in which the liquid crystal can be oriented in four directions, designated as domains A, B, C, and D. In  FIG. 4 , six pixels can be seen having dielectric lines  218  formed over conductive portions  220 B, G, and R. The dielectric lines  218  are used to divide and align the liquid crystal in a pixel into a plurality of alignment orientations.  
         [0011]     Another type of display having a non-uniform electrode is referred to as an In Plane Switching (IPS) display. The display comprises a pair of electrodes formed over the TFT-array substrate. In one arrangement, the IPS display employs a pair of electrodes shaped as interlocking fingers. The liquid crystal molecules remain parallel to the substrates. As a consequence, the viewing angle of the display is increased.  
         [0012]     As sizes increase for MVA-type and IPS-type displays, manufacturers must add more pixels and transistors to the substrate. Those of ordinary skill in the art appreciate that even moderately-sized color displays may employ transistors that number in the millions. If there is a problem with any of the transistors, it creates a defective pixel on the display. As the number of transistors increases, the likelihood that a bad transistor might be created within a display also increases. Therefore, manufacturers of large LCD&#39;s will test all or a percentage of pixels in a display as part of quality control.  
         [0013]     Electron beam testing (EBT) can be used to monitor and troubleshoot defects during the manufacturing process. In a typical EBT process, TFT response within the pixels is monitored to provide defect information. For example, in EBT testing, certain voltages are applied to the thin film transistors, and the electron beam is directed to the individual pixel electrodes under investigation. Secondary electrons emitted from the pixel electrode area are sensed to determine the TFT voltages.  
         [0014]     During testing, an electron beam is positioned over each pixel electrode of the TFT array, one after the other. To accomplish this movement, a substrate is first positioned on a table below an electron beam column. A substrate area (sometimes referred to as a sub-display area) may be moved under the electron beam column. Once a sub-display area of a substrate area is under the beam column, the beam is moved sequentially over each pixel electrode within the substrate area. After this area has been tested, the table is moved for testing of the next area. In some newer systems, two to four beams are utilized in parallel to simultaneously test separate substrate areas.  
         [0015]     Electron beam testing of displays comprising non-uniform electrodes is problematic due to the conductive portions and dielectric portions of the non-uniform electrode. As a consequence, an improved method of testing displays comprising non-uniform electrodes is needed.  
       SUMMARY OF THE INVENTION  
       [0016]     The present invention provides a method of electron beam testing of liquid crystal display comprising non-uniform electrodes having a conductive portion and a dielectric portion. In accordance with methods of the present invention, the diameter of the electron beam is increased so that the beam is less focused, i.e., enlarged or “blurred,” over a non-uniform electrode area. The diameter of the beam is increased so that the beam generates secondary electrons from the conductive portion of the non-uniform electrode area. The configured test beam may be circular, elliptical, or other suitable shapes. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.  
         [0018]      FIG. 1  is a schematic diagram showing one pixel of a liquid crystal display comprising a uniform pixel electrode.  
         [0019]      FIG. 2  is a schematic diagram showing one embodiment of one pixel of a liquid crystal display comprising a non-uniform electrode.  
         [0020]      FIG. 3  and  FIG. 4  are schematic diagrams of one example of a MVA display in which the liquid crystal can be oriented in four directions  
         [0021]      FIG. 5  is a schematic perspective view of an exemplary electron beam test (EBT) system.  
         [0022]      FIG. 6  is a schematic perspective view of one embodiment of a non-uniform electrode area  
         [0023]      FIG. 7  is a schematic perspective view of another embodiment of a non-uniform electrode area.  
         [0024]      FIG. 8  is a schematic plan view of a still another non-uniform electrode area.  
         [0025]      FIG. 9  is a schematic plan view of yet another non-uniform electrode area. 
     
    
     DETAILED DESCRIPTION  
       [0026]      FIG. 5  is a schematic perspective view of an exemplary electron beam test (EBT) system  500 . The illustrated EBT system  500  is capable of testing large panel substrates, up to and exceeding 1.9 meters by 2.2 meters. The EBT system  500  is for purposes of illustration, it being understood that any EBT system of any size may be modified to practice the methods disclosed here.  
         [0027]     The electron beam test system  500  generally includes a prober storage assembly  520 , a prober transfer assembly  530 , a load lock chamber  540 , and a testing chamber  550 . The prober storage assembly  520  houses one or more probers  505  proximal the test chamber  550  for easy use and retrieval. Preferably, the prober storage assembly  520  is disposed beneath the test chamber  550  as shown in  FIG. 1 , reducing the clean room space needed for a contaminant free and efficient operation. The prober storage assembly  520  preferably has dimensions approximating those of the testing chamber  550  and is disposed on a mainframe  510  supporting the testing chamber  550 . The prober storage assembly  520  includes a shelf  522  disposed about the mainframe  510  to provide a support for the one or more probers  505 . The prober storage assembly  520  may further include a retractable door  524  that can seal off the storage area and protect the stored probers  505  when not in use.  
         [0028]     The prober transfer assembly  530  is a modular unit disposable near the testing chamber  550  for transferring a prober  505  between the prober storage assembly  520  and the test chamber  550 . The prober transfer assembly  530  includes a base  305  connected to two or more vertical support members  310 A,  310 B (two are shown). Wheels or casters  315  may be arranged on a bottom surface of the base  305  to easily maneuver the assembly  530  when desired.  
         [0029]     The prober transfer assembly  530  further includes a lift arm  320  that is attached at one end thereof to the support members  310 A,  310 B. The support members  310 A,  310 B each include a recessed track  312  (one is shown in this view) for mating engagement with the lift arm  320 . One or both of the recessed tracks  312  may house a linear actuator, a pneumatic cylinder, a hydraulic cylinder, a magnetic drive, a stepper or servo motor, or other type of motion device (not shown). The recessed tracks  312 , working in conjunction with the motion device (not shown), guide and facilitate the vertical movement of the lift arm  320 . The lift arm  320  is configured to be inserted into the test chamber  550  or within the storage assembly  520  to retrieve and deliver the prober  505 .  
         [0030]     The load lock chamber  540  is disposed adjacent and connected to the testing chamber  550 . These chambers  540 ,  550  share a common environment which is typically maintained at vacuum conditions by a pump (not shown) coupled through the testing chamber  550 . The load lock chamber  540  transfers substrates between the testing chamber  550  and the outside which is typically a clean room at atmospheric pressure. The load lock chamber  540  may function as an isolated processing environment that is capable of being heated or cooled as well as pressurized or de-pressurized, depending on system requirements. Consequently, load lock chamber  540  enables the transfer of substrates into and out of the testing chamber  550  without exposure to outside contaminants.  
         [0031]     Four EBT columns  525  A, B, C, D are shown in  FIG. 5 . The EBT columns  525 A/B/C/D are disposed on an upper surface of the test chamber  550 . When actuated, the columns deliver a beam of electrons onto the electrodes on the substrate in order to excite the electrodes during testing.  
         [0032]     Additional details concerning the testing of pixels and the operation and features of the illustrative EBT test system  500  are disclosed in pending U.S. patent application Ser. No. 10/778,982, filed Feb. 12, 2004. That application is entitled “Electron Beam Test System with Integrated Substrate Transfer Module.” That application is incorporated herein in its entirety by reference.  
         [0033]     During testing, a substrate is positioned on a table below the beam and the beam is moved to sequentially test the electrodes of the TFT array. It has been observed that during EBT testing of an MVA-type display, the insulator lines formed on the TFT-array substrate interfere with the electron responses. For example, in reference to  FIG. 4 , during EBT testing of an MVA-type display, it is desired that the electron beam excite electrons on the exposed conductive portions  220  BIGIR between the dielectric lines  218 . However, a beam may be unintentionally directed primarily on one of the insulator lines  218  rather than a conductive portion, thereby interfering with the electron responses from the conductive area. Similarly, it has been observed that the conductive line fingers structure of an IPS display interferes with the electron responses. For example, a beam may find itself directed primarily on a dielectric portion formed between the pair of electrodes, thereby interfering with the electron responses. In either instance, the secondary electron signal detected when a beam is positioned solely on the dielectric portion is different than when the beam is positioned on the conductive portion.  
         [0034]     It is desirable to avoid a situation where different electron signal values are generated depending on the position of the electron beam within a non-uniform electrode area. Therefore, the methods of the present invention employ an enlarged or “defocused” test beam that essentially generates an average or blended signal. Stated another way, increasing the diameter of the test beam allows the signal interference of the dielectric portion to be substantially reduced.  
         [0035]      FIG. 6  is a schematic perspective view of one embodiment of a non-uniform electrode area  600 . The non-uniform electrode area  600  is intended to represent a single pixel in an MVA-type display. The dielectric lines  618  are formed over a conductive portion  622  and  624 . In the illustrative non-uniform electrode  600 , conductive portion  624  is exposed between the insulating lines  618 .  
         [0036]     To overcome the problem of inconsistent electron beam response for the MVA-type display, the electron beam diameter is increased, or “blurred,” between two times and ten times (or more) than the width of the dielectric lines  618 . In one aspect, the electron beam diameter is increased between about four times and eight times more than the width of the dielectric lines  618 . In one non-limiting example, the width of the dielectric lines  618  may be about 10 μm. In this instance, the electron beam diameter is increased to between about 20 μm and about 100 μm. Increasing the diameter of the electron beam causes less proportional charging of the dielectric lines  618 , and essentially averages out the effect of the dielectric lines  618  on electrode excitement.  
         [0037]     An electron beam  625  is shown in  FIG. 6  being directed over a portion of the non-uniform electrode  600  during testing. Here, the electron beam  625  is generally circular in shape. The beam  625  has a diameter that is significantly greater than a width of the various dielectric lines  618 .  
         [0038]     Other beam configurations may be employed.  FIG. 7  is a schematic perspective view of another embodiment of a non-uniform electrode area  700 . Here, the electron beam  725  is generally elliptical in shape. The diameter of the beam  725  is measured across its minor axis.  
         [0039]     The size of the “blurred” beam may also be measured in comparison to the area of the pixel electrode area itself. In one embodiment of the methods herein, the area of the beam is increased to have a size that is at least about 50% of the non-uniform electrode area being tested.  FIG. 8  is a schematic plan view of a still another non-uniform electrode area  800 . Two adjacent lines  818  are shown over the non-uniform electrode area  800 . The pixel area is intended to be generic such that the lines  818  may be either dielectric or conductive, and the adjacent areas between the lines  818  are either conductive or dielectric respectively. It can be seen in  FIG. 8  that an electron test beam  825  is being directed onto the non-uniform electrode area  800 . The beam  825  is covering portions of both a line  818  and an area adjacent the line  818 . The beam  825  has a diameter that is sufficient to generate secondary electrons from a conductive portion. Moreover, the beam is of sufficient diameter so that the electron signal will be substantially the same when the beam  825  is moved to a different non-uniform electrode within the same TFT array.  
         [0040]     In the view of  FIG. 8 , the beam area is at least 50% of the entire non-uniform electrode area. In one embodiment, the area of the beam  825  could be as large as the distance from line  818  to an adjacent line  818 . In one aspect, the electron beam has an area that is between about 50% and 90% of the non-uniform electrode area  800  under investigation.  
         [0041]      FIG. 9  is a schematic plan view of yet another non-uniform electrode area  900 , such as an IPS-type cell. The non-uniform electrode area  900  comprises a pair of electrodes  918 ′,  918 ″ forming an interlacing finger structure. A width is defined between the electrodes  918 ′,  918 ″ with the width traversing an dielectric portion  924 .  
         [0042]     An electron test beam  925  is being directed onto the non-uniform electrode area  900 . The beam  925  is at least covering portions of the electrode  918 ′, the electrode  918 ″, and a dielectric portion  924  between the electrodes  918 ′,  918 ″. The beam is of sufficient diameter so that the electron signal will be substantially the same when the beam  925  is moved to a different non-uniform electrode within the same TFT array.  
         [0043]     The diameter of electron beam  925  is increased, or “blurred,” between two times and ten times (or more) than the diameter of the width of one of the electrodes  918 ′,  918 ″. In one aspect, the electron beam diameter is increased between about four times and eight times more than the width of one of the electrodes  918 ′,  918 ″. Increasing the diameter of the electron beam causes less proportional charging of the dielectric portion  924 , and essentially averages out the effect of the dielectric portion  924  on electrode excitement.  
         [0044]     In another embodiment of the methods described herein, a focused beam is used to first scan over a positioning/alignment mark on the substrate. Since the display substrate position under the beam is typically shifted by substrate loading errors, table positioning errors, and other errors, and since the beam positioning control has an error margin, scanning over a positioning/alignment mark on the substrate helps to eliminate these positional errors and correct the beam position in reference to the substrate. For example, the beam may be focused to an area about 20% or less than the area of the non-uniform electrode, then, the electron beam is scanned over the positioning/alignment mark. Then, the beam may be defocused by altering the current in the focusing lens and/or altering the current in a magnetic focusing coil. The electron beam may be defocused to an area greater than about 20% than the area of the non-uniform electrode or to other sizes as disclosed herein. Then, the defocused beam is directed sequentially over the targeted non-uniformed electrode area of the TFT-array.  
         [0045]     The inventions herein have been described primarily with reference to MVA-type and IPS-type displays. However, it is understood that the present inventions are not limited to these types of devices, and that these devices are described merely for purposes of illustration. In this respect, the methods described herein have utility in testing devices of any other type where the display has non=uniform electrodes.  
         [0046]     While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.