Patent Publication Number: US-6033281-A

Title: System for testing field emission flat panel displays

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to testing systems, and more particularly, to a testing system for Field Emission Flat Panel Display (FEFPD) devices. 
     2. Description of Related Art 
     Flat panel displays, and specifically Field Emission Flat Panel Displays (FEFPDs), are technologically viable alternatives to cathode ray tubes (CRTs) for display of electronic information. They provide several advantages over CRTs, including smaller weight and size and lower power consumption. However, some manufacturing problems, such as the capability to test their expected performance, often make them more expensive than typical CRTs. 
     FIG. 1 shows a magnified cross-section schematic of a typical FEFPD 20. A substrate 11 is manufactured with several microscopic conical structures or Field Emitter (FE) cathodes 13. An electrode gate layer 15 confronts the substrate 11 and is provided with holes 17 just at the tip of the FE cathodes 13. The gate layer 15 is biased to a relatively high voltage (on the order of a few hundred of volts), causing the field emission and acceleration of electrons 19 located at the tip of the FE cathodes 13. The cathodes 13 are also biased to a positive voltage to control the amount of electrons emitted once the gate layer 15 enables their flow. Electrons 19 impact the inner surface 21 of a phosphorous-coated plate 23. Plate 23 is disposed in close proximity to gate layer 15, while the region between the substrate 11 and plate 23 is held under vacuum conditions to facilitate the emission process. 
     The impact of electrons 19 on the phosphorous-coated plate 23 causes photon emission at the outer surface 25 of plate 23, as indicated by arrows 27. By modulating an arrangement of row and column of FE pixels, a controlled light image can be generated. 
     FIG. 2 shows schematically the pixel arrangement of FEFPD 20. The panel is divided into a set of columns 31 and rows 33. One of these sets electrically comprises the FE cathode substrate while the other set comprises the FE gates. Pixels 39 are selectively activated by applying a voltage to the row and column intersection via a set of column and row drivers (35 and 37, respectively). Each pixel 39 contains more than one FE cathode, and a typical pixel arrangement contains an array of about 10×10 cathodes electrically connected in parallel. This redundant amount of cathode emitters increases the probability that the pixel display performance will be acceptable even with a few of the cathodes not operating properly. One of the purposes of this invention is to assess the amount of FEs that are operative for each pixel 39 by measuring the emission uniformity of all the pixels of the display. 
     It is recognized that for replacing CRTs in consumer applications such as TVs and computers, FEFPD manufacturing costs, which include costs of inspection during the manufacturing process to insure quality control and a functional product, must be reduced. 
     SUMMARY OF THE INVENTION 
     The invention overcomes the deficiencies of the prior art by providing an inspection system for field effect flat panel displays (FEFPDs) which activates the pixels of the flat panel display to emit electron current streams for measurement by a detector. The FEFPD is disposed in a vacuum and is scanned to sequentially activate the pixels thereof. 
     In a preferred embodiment of the invention, scanning is effected by an activation mechanism comprising a pair of selective activation linear stage mechanisms disposed in the vacuum chamber, which also houses the FEFPD. The linear stage mechanisms each comprise a sliding assembly guided by a rail and drive assembly. Motion is induced by a drive means which comprises either a manual dial or an appropriate motor. Each sliding assembly is provide with a ball bearing rotatably mounted therein, the ball bearing being urged toward contacts comprising the contact pads of the FEFPD to thereby complete an electrical circuit between an activation signal source and the contacts, which are each in connection with electrodes of the pixels of the FEFPD. 
     In another embodiment, the invention comprises a selective activation device comprising a stage mechanism which guides the motion of a sliding assembly. A ball bearing is rotatably mounted on the sliding assembly. The ball bearing is electrically conducting and is connected to an activation source. By rolling across the contact pads of an FEFPD and sequentially contacting electrically discrete portions thereof, the ball bearing selectively activates electrodes of the FEFPD. 
     One advantage provided by the arrangement of the invention is that testing of the active substrate array before the panel is completed provides manufacturing cost savings because scrap material due to defective active substrates can be detected before all the manufacturing expense is incurred. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Many advantages of the present invention will be apparent to those skilled in the art with a reading of this specification in conjunction with the attached drawings, wherein like reference numerals are applied to like elements and wherein: 
     FIG. 1 is a perspective schematic view a pixel of a field effect flat panel display (FEFPD); 
     FIG. 2 is a schematic view of a pixel arrangement of an FEFPD of FIG. 1; and 
     FIG. 3 is a schematic perspective view of an FEFPD testing device in accordance with the preferred embodiment of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention is used to test the uniformity of emission of the active substrate section of an FEFPD before panel manufacture is complete. The test is performed in a controlled vacuum environment. 
     FIG. 3 shows a three-dimensional schematic of an arrangement for testing an FEFPD in accordance with the invention. An FEFPD substrate 30 is shown placed inside a high vacuum chamber 41. For simplicity, only a section of the chamber 41 enclosure is shown. The FEFPD 30 comprises pixel column 43 and row 45 row contact pads 43 and 45, respectively, each comprising a plurality of individually addressable contacts 43 1-N , 45 1-N . 
     In accordance with the invention, pixels of the FEFPD 30 are selectively activated for testing. This is accomplished in the preferred embodiment by using a selective activation device comprising a pair of linear stage mechanisms 47 and 49 each associated with a corresponding contact pad of the FEFPD 30. Column contacts 43 1-N  are contacted by a ball bearing 51 that rolls over the contacts in the direction shown by arrow a. The rolling action is achieved using linear stage mechanism 55 shown schematically as comprising sliding assembly 53, rail and drive assembly 47, and drive source 57 comprising for instance a manual dial or a motor assembly preferably located outside the vacuum chamber 41. An appropriate mechanical linkage (not shown) translates rotary motion of drive source 57 to linear motion of sliding assembly 53. For simplicity, the vacuum chamber feedthrough of the drive source 57 is not shown. Ball bearing 51 is rotatably mounted in sliding assembly 53 and is electrically isolated from the linear stage mechanism 55 while being in electrical communication with the exterior of vacuum chamber 41 via conductor 59 passing through a conductor feedthrough 61. The electrical signal necessary to activate the columns of the FEFPD 30 is conducted into the vacuum chamber via this electrical connection and may be provided by an appropriate activation source (not shown). 
     The rows of the FEFPD 30 are activated using row contact pad ball bearing 63 electrically connected to the exterior of vacuum chamber 41 via conductor 65 passing through feed through 67. It should be noted that the system in accordance with the invention can be configured such that conductors 59 and 65 share a common feedthrough. Ball bearing 63 is rolled over contacts 45 1-N  of row contact pad 45 in the direction indicated by arrow b using linear stage mechanism 68, which comprises sliding assembly 69, rail and drive assembly 49 and a drive source 71. The vacuum chamber feedthrough of drive source 71, which may comprise a motor or a manual dial mechanism, is not shown for simplicity. 
     Row and column contact pad ball bearings 51 and 63 are configured to be minimally biased against their corresponding contact pads such that reliable electrical contact between the ball bearings 51 and 63 and the respective contacts 43 1-N  and 45 1-N  is achieved without damaging the substrate of the FEFPD 30. A spring biasing mechanism (not shown) or other means of urging electrical contact is contemplated. Also, ball bearings 51 and 63 are subject to low rotational friction and designed with a diameter which is of an appropriate relation to the distance between contacts 43 1-N  and 45 1-N  such that only one contact at a time is electrically contacted by each ball bearing. In this manner any pixel of FEFPD 30 can be individually addressed, with the rolling motion of ball bearings 51 and 63 in the respective a and b directions across contact pads 43 and 45 causing the sequential activation of the addressed pixels of FEFPD 30. The activation signal is provided by an activation signal source (not shown) controlled by a control device (not shown) which correlates the position of the ball bearings 51 and 63, and thus the identity of the particular pixel under test, with the output signal of the detector 77 to thereby provide an indication of the condition of the pixel array. The process may be further automated by provision of a comparison expedient between the detected signal from detector 77 and a standard signal representative of a defect-free pixel. 
     Although in the preferred embodiment ball bearings are used as rolling members to electrically contact the contacts 43 1-N , 45 1-N , those skilled in the art will recognize that any circular rotating object, taking the form of a wheel for instance, can be substituted therefor. Similarly, any pointing stylus that slides across the contacts 43 and 45 can also be used, with the rolling action being dispensed with altogether. 
     By individually contacting contacts 43 1-N  and 45 1-N , selective addressing of the array of pixels of FEFPD 30 is achieved. The pixels can thus be activated for testing their performance during the manufacturing process. In FIG. 3, the row and column contact pad ball bearings 51 and 63 are shown activating the gate and FE cathode electrodes of pixel 73. Thus activated, pixel 73, referred to as the pixel under test, emits an electronic current stream 75 towards detector 77, which is preferably an Everhart-Thornel type-high sensitivity electron detector. The electron detector 77 is provided with a detection region comprising a scintillator disk 81 that is biased to a voltage which is on the order of 10 KV. This voltage generates a high acceleration field inside the chamber 41 that attracts electrons emitted by any of the addressed pixels of FEFPD 30. The scintillator disc 81 operates to convert the electron impacts thereon to photons which are directed to photomultiplier tube (PMT) 79 via a light pipe 83. Light pipe 83 also acts as a feedthrough from the PMT 79 into the vacuum chamber 41, relying on a circular O-ring 85 to maintain hermetical sealing of the interior of the vacuum chamber. PMT 79 converts the photon emission stimulated in scintillator disk 81 by electronic current stream 75 into an electrical signal which is transferred to appropriate measuring and analysis equipment (not shown) via electrical conductor 87. The measuring and analysis equipment will operate to correlate the position of the particular pixel under test with the output signal 77 by for instance tracking the position of the row and column contact ball bearings 51 and 63 and comparing the signal generated by the pixel associated with these positions with a standard signal indicative of a properly functioning pixel. The electrical output signal of the detector 77 will vary in direct proportion to the magnitude of the emitted electronic current stream of the addressed pixel. In this manner, pixel performance can be assessed. Sequential scanning of each pixel of the FEFPD 30 can be used to generate uniformity data across the whole FEFPD 30. This process can be automated by having a computer system control drive sources 57 and 71 in synchrony with the reading the output of electron detector 77 using an analog to digital converter and other electronic expedients. 
     The above are exemplary modes of carrying out the invention and are not intended to be limiting. It will be apparent to those skilled in the art that modifications thereto can be made without departure from the spirit and scope of the invention as set forth in the following claims.