Abstract:
There are disclosed systems and methods in which a liquid dispensing head is positioned above the contact area of the device under test (DUT). A stream of liquid is dispensed from the head such that a continuous column of liquid extends from the head to the contact area of the test device. This column of liquid completes a circuit which allows current to flow thereby allowing for current measurement.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     The present application is related to concurrently filed, co-pending, and commonly assigned U.S. patent application Ser. No. ______, Attorney Docket No. 10041037-1, entitled “NON-CONTACT ELECTRICAL PROBE UTILIZING CHARGED FLUID DROPLETS,” and U.S. patent application Ser. No. ______, Attorney Docket No. 10041087-1, entitled “SYSTEMS AND METHODS FOR AN ELECTRICAL PROBING MEDIUM USING AN IONIZED GAS CREATED BY AN ATMOSPHERIC DISCHARGE,” the disclosures of which are hereby incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     Organic light emitting diode (OLED) flat panel displays use an emissive flat panel display technology that is an extension of the existing thin film transistor (TFT) liquid crystal display (LCD) technology. While OLED technology is similar to TFT technology, the emissive property of the OLED displays leads to greater complexity, particularly for testing during manufacturing. One difference, as it applies to testing, is that the OLED pixel brightness is controlled with a current signal, as opposed to being controlled with a voltage as are existing LCD displays. This results in the OLED display having one additional transistor per pixel.  
         [0003]     To test existing LCD displays, the voltage controlling each pixel can be directly measured even without touching the active area of the display&#39;s surface. However, in order to test each pixel of the OLED display, it is necessary to measure current on the display at each pixel also without actually touching the display surface.  
         [0004]     While, several techniques are known to sense voltage without actually touching the surface, current sensing without touching presents a problem. For example, voltage can be sensed by using an electron beam to image the surface, such that, voltage differences on the surface show as contrast differences. One technique to measure current is to incorporate an additional capacitor per pixel on the OLED display circuit and to measure the charging of this added capacitor through a resistor. This works because the charging rate of the capacitor is a direct function of the resistance value of the resistor. This technique adds complexity to the circuitry and adds a component that will not be used again after testing.  
         [0005]     A second technique is to use an electron beam as a contactless probe. This technique requires placing the OLED in a vacuum chamber which is expense and time consuming.  
       BRIEF SUMMARY OF THE INVENTION  
       [0006]     There are disclosed systems and methods in accordance with the invention in which a liquid dispensing head is positioned above the contact area of the device under test (DUT). A stream of liquid is dispensed from the head such that a continuous column of liquid extends from the head to the contact area of the test device. This column of liquid completes a circuit which allows current to flow thereby allowing for current measurement. In this manner, for example, the transistor at each pixel of an OLED can be tested. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]     For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawing, in which:  
         [0008]      FIG. 1  shows one embodiment of a test system in accordance with the invention; and  
         [0009]      FIG. 2  shows one embodiment of a test system in accordance with the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0010]      FIG. 1  shows one embodiment of test system  10  in accordance with the invention where test head  1   1  selectively allows fluid  102  to flow therefrom to form a pool of fluid  105  on a contact pad, such as on contact pad  13 , of DUT  12 . Contact pad is in contact with device  14  to be tested (in this case the device is a transistor which is part of DUT  12 ), DUT  12  can be, for example, an OLED display panel or any other device that must be tested without direct physical contact. Display panel  12 , in turn, rests in this embodiment on test bed  17 , which can be any type of test bed. In other embodiments display panel  12  can be self-supporting, if desired.  
         [0011]     Test head  11  in the embodiment shown is a piezoelectric inkjet head having control element  101 , fluid  102 , and control orifice  103 , which selectively allows fluid  102  to flow which result in pool of fluid  105  on contact  13 . Fluid  102  is a conductive fluid so that it forms a continuous electric path from test head  11  to contact pad  13 . The fluid must also be easy to clean from the contact pad after the measurement. An ionic conductor would be acceptable as would water with ionic impurities or perhaps mercury or other elements that are conductive but that also have the properties of water. Neither the fluid nor the impurities must react with the contact pad surface and must be readily removed from the surface after the test.  
         [0012]     Conductive fluid  104  would complete an electrical path from voltage source  111  through meter  110 , head  11 , fluid pool  105 , and transistor  14  to ground, thereby allowing for the measurement of current flow through transistor  14  of OLED  12 . A processor, such as processor  15 , could control both the application of the current as well as the flow of the liquid such that the liquid can be selectively controlled, if desired. Note that processor  15  could be part of control  16  or could be separate therefrom, or can be part of test head  11 , if desired. The system could be adapted to measure voltage instead of current, if desired, all without the test probe touching the surface of the DUT.  
         [0013]     When the test of display panel  12  is complete, the conductive liquid is stopped; the liquid in pool  105  is wiped clean from the surface, the panel is removed, and another panel inserted in its place. Note that in the embodiment, it is contemplated that test head  11  and test bed  17 , as well as the circuitry that controls the test fixture, is permanently in place. Alternatively, the system can be hand held such that the test head is part of a portable device, such that liquid can be squirted from the head to the display to complete a circuit for the purpose of measuring current flow between the test head and the device under test.  
         [0014]     In device  10  liquid stream  104  is shown falling by gravity from head  11 . However, liquid can be under power and controlled by head  11  or by orifice  103  which can operate much like a squeeze bottle to pulse liquid through orifice  103  in a steady stream. For horizontal operation this might be preferable. Orifice  103  could be arranged to selectively direct the liquid stream, if desired.  
         [0015]      FIG. 2  shows the same DUT  12  as shown in  FIG. 1  except that in the embodiment of  FIG. 2  test system  20  uses fluid  202  falling in stream  204  to pool  205 . Fluid  202  is nonconductive (or of low conductivity) as it emerges from head  11  until such time as energy from an external energy source, such as energy source  22 , impacts stream  204 . In the embodiment, energy source  22  is light, impacting fluid  202 , which charges the fluid making it conductive only while energy source  22  is on. Energy source  22  could be light or any other type of energy source, such as ultraviolet, infrared, etc. Using this arrangement, movement of the uncharged fluid (light off) across panel  12  will not interact with the electronics except when desired. One problem that a conductive fluid would encounter is the shorting of electronics on the DUT. When the pool of liquid on the surface spreads, multiple devices can become shorted together, making the measurement difficult or impossible. If the fluid is selectively conductive, only the fluid that is receiving external energy (which can be precisely focused) would be conductive, and thus, the liquid pool will not cause problems with the electronics. This allows much more fluid to be used to make a connection between the head and the panel. If more fluid can be used, the distance between the inkjet head and panel can be increased. It is contemplated that the distance between orifice  103  and contact  13  will be approximately 100 microns.  
         [0016]     Note that while the disclosure has been framed in context to testing an OLED panel, the concepts discussed herein could be used to test any device without actually touching that device.  
         [0017]     Also, it should be understood that while a single aperture is shown forming a single column, a plurality of apertures could be used to control multiple columns, or a single aperture could be used to direct the droplets to different contact locations.  
         [0018]     Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one will readily appreciate from the disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.