Testing flat panel display plates using high frequency AC signals

Abstract

Methods of and apparatus for detecting pixel element defects in flat panel display (FPDs). Floating pixel elements (fpes) of uncompleted active plates in a manufacturing process are activated with high frequency AC test signals. In response to the activation signal, a high frequency output signal is produced by a voltage divider formed by an impedance of the fpe under test and an impedance presented by high frequency elements (e.g. stray capacitances) associated with the fpe under test. A signal characteristic (e.g. the amplitude) of the output signal is compared to an expected characteristic to determine the presence of pixel element defects. The methods of the present invention may be performed prior to completion of the active plate, e.g., prior to forming a liquid crystal between plates of a passive matrix LCD and prior to coating a partially formed OLED active plate with light emitting organic material layers. Use of high frequency activation signals allows detection of pixel element defects that are invisible to DC test methods. Additionally, because the methods and apparatus of the present invention allow testing prior to FPD plates being completely manufactured and prior to FPD final assembly, pixel defects can be detected early in the display manufacturing process, thereby resulting in a substantial reduction in production costs.

1 . A method of determining pixel defects in an FPD plate, comprising: 
 activating an FPD plate with an AC test signal;    at a point on the FPD plate corresponding to a location of a pixel element, measuring the amplitude of a signal that is responsive to the AC test signal;    comparing the amplitude of the measured signal to a predetermined amplitude; and    determining whether the difference between the measured and predetermined amplitudes represents that the pixel element is defective.    
   
   
       2 . The method of  claim 1  wherein the FPD plate is an OLED FPD plate.  
   
   
       3 . The method of  claim 2  wherein the OLED FPD plate is part of a down-emitting OLED FPD structure.  
   
   
       4 . The method of  claim 2  wherein the OLED FPD plate is part of an up-emitting OLED FPD structure.  
   
   
       5 . The method of  claim 2  wherein the OLED FPD plate comprises a substrate upon which one or more pixel elements are disposed.  
   
   
       6 . The method of  claim 5  wherein the substrate is a polymer or a plastic.  
   
   
       7 . (canceled)  
   
   
       8 . (canceled)  
   
   
       9 . (canceled)  
   
   
       10 . The method of  claim 1  wherein the step of measuring is performed using an electron beam probe.  
   
   
       11 . The method of  claim 10 , further comprising collecting secondary electrons emitted from the point on the FPD plate corresponding to a location of a pixel element.  
   
   
       12 . The method of  claim 10  wherein the energy of an electron beam from the electron beam probe is about 500 eV or less.  
   
   
       13 . The method of  claim 10  wherein a current of an electron beam from the electron beam probe is about 5 nA or less.  
   
   
       14 . A method of testing an electrically floating pixel element of an FPD plate, comprising: 
 applying an AC test signal to an input of an electrically floating pixel element (fpe);    directing an electron beam to a surface of said fpe;    collecting electrons emitted from the surface of said fpe;    forming an electrical signal from the collected electrons; and    comparing a measured characteristic of the electrical signal to an expected characteristic.    
   
   
       15 . The method of  claim 14 , further comprising determining whether said fpe is defective, based on results obtained from the step of comparing.  
   
   
       16 . The method of  claim 14  wherein the measured characteristic is an amplitude of the electrical signal and the expected characteristic is an expected amplitude of the electrical signal.  
   
   
       17 . The method of  claim 14  wherein said fpe comprises one of a plurality of fpes of the FPD plate.  
   
   
       18 . The method of  claim 14  wherein the FPD plate is an OLED FPD plate.  
   
   
       19 . The method of  claim 18  wherein the OLED FPD plate is part of a down-emitting OLED FPD structure.  
   
   
       20 . The method of  claim 18  wherein the OLED FPD plate is part of an up-emitting OLED FPD structure.  
   
   
       21 . The method of  claim 18  wherein the OLED FPD plate comprises a substrate upon which said fpe and other fpes are formed.  
   
   
       22 . The method of  claim 21  wherein the substrate is a polymer or a plastic.  
   
   
       23 . The method of  claim 14  wherein the energy of said electron is about 500 eV or less.  
   
   
       24 . The method of  claim 14  wherein a current of said electron beam is about 5 nA or less.  
   
   
       25 . A method of testing a floating pixel element (fpe) of an FPD, comprising: 
 applying an AC signal to a power input of an fpe of a FPD;    providing a first activation signal to a current controlling device of said fpe, to activate said fpe to a first activation level; and    measuring characteristics of a first output signal provided at an output of said fpe.    
   
   
       26 . The method of  claim 25  wherein the step of measuring is performed using an electron beam probe.  
   
   
       27 . The method of  claim 25 , further comprising: 
 providing a second activation signal to said controlling device of said fpe, to activate said fpe to a second activation level; and    measuring characteristics of a second output signal provided at the output of said fpe.    
   
   
       28 . The method of  claim 27 , further comprising comparing the characteristics of said first and second output signals, to determine a transconductance of said current controlling device.  
   
   
       29 . The method of  claim 25 , further comprising: 
 applying a second AC signal to the power input of said fpe, the amplitude of said second AC signal having a different value than the amplitude of said first AC signal; and    measuring characteristics of a second output signal provided at the output of said fpe.    
   
   
       30 . The method of  claim 29 , further comprising comparing the characteristics of said first and second output signals, to determine a drain conductance of said current controlling device.  
   
   
       31 . An apparatus for determining pixel defects in an FPD plate, comprising: 
 means for activating an FPD plate with an AC test signal;    means for measuring the amplitude of a signal that is responsive to the AC test signal, at a point on the FPD plate corresponding to a location of a pixel element;    means for comparing the amplitude of the measured signal to a predetermined amplitude; and    means for determining whether the difference between the measured and predetermined amplitudes represents that a pixel element is defective.    
   
   
       32 . The apparatus of  claim 31  wherein the FPD plate is an OLED FPD plate.  
   
   
       33 . The apparatus of  claim 32  wherein the OLED FPD plate is part of a down-emitting OLED FPD structure.  
   
   
       34 . The apparatus of  claim 32  wherein the OLED FPD plate is part of an up-emitting OLED FPD structure.  
   
   
       35 . The apparatus of  claim 32  wherein the OLED FPD plate comprises a substrate upon which one or more pixel elements are disposed.  
   
   
       36 . The apparatus of  claim 35  wherein the substrate is a polymer or a plastic.  
   
   
       37 . A test apparatus for testing an electrically floating pixel element of an FPD plate, comprising: 
 means for applying an AC test signal to an input of an electrically floating pixel element (fpe);    means for directing an electron beam to a surface of said fpe;    means for collecting electrons emitted from the surface of said fpe;    means for forming an electrical signal from the collected electrons; and    means for comparing a measured characteristic of the electrical signal to an expected characteristic.    
   
   
       38 . The apparatus of  claim 37  wherein the measured characteristic is an amplitude of the electrical signal and the expected characteristic is an expected amplitude of the electrical signal.  
   
   
       39 . The apparatus of  claim 37  wherein the FPD plate is an OLED FPD plate.  
   
   
       40 . The apparatus of  claim 39  wherein the OLED FPD plate is part of a down-emitting OLED FPD structure.  
   
   
       41 . The apparatus of  claim 39  wherein the OLED FPD plate is part of an up-emitting OLED FPD structure.  
   
   
       42 . The apparatus of  claim 39  wherein the OLED FPD plate comprises a substrate upon which said fpe and other fpes are formed.  
   
   
       43 . The apparatus of  claim 42  wherein the substrate is a polymer or a plastic.  
   
   
       44 . An apparatus for testing a floating pixel element (fpe) of an FPD, comprising: 
 means for applying an AC signal to a power input of an fpe of a FPD;    means for providing a first activation signal to a current controlling device of said fpe, to activate said fpe to a first activation level; and    means for measuring characteristics of a first output signal provided at an output of said fpe.    
   
   
       45 . The apparatus of  claim 44  wherein said means for measuring characteristics of a first output signal is an electron beam probe.  
   
   
       46 . An apparatus for testing floating pixel elements (fpes) of an FPD plate, comprising: 
 an AC signal generator operable to provide an AC test signal to an input of an fpe of an active plate of an FPD; and    a measuring instrument operable to measure an amplitude of an fpe output signal that is responsive to said AC test signal.    
   
   
       47 . The apparatus of  claim 46  wherein the measuring instrument comprises an electron beam probe.  
   
   
       48 . The apparatus of  claim 46  wherein the FPD plate is an OLDED FPD plate.  
   
   
       49 . The apparatus of  claim 48  wherein the OLED FPD plate comprises a substrate upon which said fpe and other fpes are formed.  
   
   
       50 . The apparatus of  claim 49  wherein the substrate is a polymer or a plastic.  
   
   
       51 . The apparatus of  claim 46  wherein the measured amplitude of the output signal of the fpe is compared to an expected amplitude, to determine whether the fpe is defective.