Abstract:
A test method for a liquid crystal display panel in which the pixels providing liquid crystal elements having sealed in liquid crystal material are arranged in a matrix between opposing electrodes is comprised of a charging process for supplying charge to the above-mentioned liquid crystal element of a pixel under test, a measurement process for discharging the charge from the above-mentioned charged liquid crystal element and measuring the amount of charge discharged, and a decision process for determining whether defects are present in the liquid crystal element of the above-mentioned pixel under test from the above-mentioned measurement results.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a manufacturing method, test method, and test apparatus for a display panel, particularly to a manufacturing method, test method, and test apparatus for a liquid crystal display panel that seals in liquid crystal material. 
       DISCUSSION OF THE BACKGROUND ART 
       [0002]    A display apparatus using liquid crystal material is primarily constructed from a backlight as the light source, polarization filters for only transmitting light having specific polarizations, a display panel for controlling the light polarization state of each pixel, and color filters for producing three primary colors. Usually, the display panel is constructed with liquid crystal elements in an active matrix array that forms elements such as transistors and capacitors at each pixel on a substrate such as a glass plate. 
         [0003]      FIG. 2  illustrates the structure of a liquid crystal element  233  of a typical liquid crystal display panel. Liquid crystal element  233  is comprised of a liquid crystal material  302 ; orientation films  301 ,  303  positioned to sandwich liquid crystal material  302  on both sides; and two electrodes  300 ,  304  positioned opposite each other to further sandwich the orientation films  301 ,  303  on the outside. One electrode  304  of the opposing electrodes is provided on a thin-film transistor (TFT) substrate. 
         [0004]    Liquid crystal element  233  functions by rotating the incident polarized light by 90° when a voltage is not applied between electrodes  300 ,  304  and transmits the incident light unmodified when a voltage is applied between electrodes  300 ,  304 . The light shield/transmit states are controlled by inputting the light that has passed through liquid crystal element  233  to the polarization filter. Consequently, when the voltage is not applied, the molecule groups of liquid crystal material  302  are not oriented in a uniform direction, and the shield/transmit states of the light cannot be skillfully controlled. Therefore, orientation films  301 ,  303  are provided between electrodes  300 ,  304  and liquid crystal material  302 , and the liquid crystal molecule groups are oriented in a uniform direction. 
         [0005]    All of the pixels on the liquid crystal display panel should have uniform characteristics. However, current manufacturing techniques have difficulty forming panels having stable characteristics over a wide area. For example, defects that develop due to various causes such as foreign materials exist inside the liquid crystal material; the gap between the opposing electrodes  300 ,  304  is nonuniform; defects arise in the stage of forming orientation films  301 ,  303 ; or the liquid crystal material  302  itself is nonuniform. Therefore, whether the panel has specific characteristics must be tested in the final manufacturing stage of a liquid crystal display panel. 
         [0006]    In this type of test, the primary methods are optical tests as disclosed in Unexamined Japanese Patent Publication No. 2005-55196. In other words, these methods test each pixel in a state where light irradiates the finished liquid crystal panel, analyze the data acquired by image capture elements or light receiving elements from the side opposite the light source, and detect the presence or absence of defects in the liquid crystal display panel. 
         [0007]    However, in optical tests, the positioning of the test apparatus and the liquid crystal display panel before conducting the test must be exact. Furthermore, to test a large area, a portion of the optical system such as the image capture elements and lenses must be physically driven during the test. Therefore, problems encountered include a long testing time and degradation in the measurement accuracy. Consequently, a test method capable of efficient and accurate data collection is sought. 
       SUMMARY OF THE INVENTION 
       [0008]    A test method for a liquid crystal display panel in which the pixels provided with liquid crystal elements that seal in liquid crystal material between opposing electrodes are arranged in a matrix shape and is comprised of a charging process for supplying a charge to charge the above-mentioned liquid crystal element of the pixel under test, a measurement means for measuring the amount of charge discharged from the above-mentioned charged liquid crystal element, and a decision process for deciding whether defects are present in the liquid crystal element of the above-mentioned pixel under test from the above-mentioned measurement results. 
         [0009]    Because the liquid crystal material sealed between the opposing electrodes is a dielectric, when looked at electrically, the entire liquid crystal element has the same structure as a capacitor. Therefore, by detecting the defects produced between the opposing electrodes as abnormalities in the dielectric capacitance (abnormalities in the amount of stored charge), defects may be determined electrically. A test based on electrical methods does not have to exactly position the test apparatus and the panel as with an optical test apparatus because the test apparatus can be run simply by connecting the terminals of the liquid crystal display panel. In addition, a portion of the test apparatus does not have to be driven mechanically during the test. Furthermore, the dynamic characteristics as well as the static characteristics can be measured by changing the method for providing the stored charge. Various data required to identify the sources of defects can be collected. 
         [0010]    A method for efficiently and accurately testing a liquid crystal display panel is provided by the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a schematic diagram of the test apparatus related to the present invention; 
           [0012]      FIG. 2  is a schematic diagram of the liquid crystal display panel, which is the device under test; and 
           [0013]      FIG. 3  is a flow chart of the operation of the test apparatus. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0014]    Typical embodiments of the present invention are explained with reference to the drawings below. 
         [0015]      FIG. 1  is a schematic diagram showing a test apparatus  100  related to the present invention connected to a liquid crystal display panel  200 , which is the device under test. 
         [0016]    Liquid crystal display panel  200  comprises control wires  212 ,  213 ,  214 ,  215  for selecting pixels; signal wires  218 ,  219  that intersect each control wire and transmit analog control signals that control the states of the pixels; a transistor  220  for controlling the connection state between a signal input wire  211  from the outside and signal wire  218  on the basis of the input of control wire  212 ; a transistor  221  for controlling the connection state between signal input wire  211  from the outside and signal wire  219  on the basis of the input of control wire  213 ; pixels ( 230 ,  240 , etc.) arranged at the intersections of the control wires and signal wires; a shared capacitance wire  216  for the reference potential of pixel capacitors ( 232 ,  242 , etc.); and a shared liquid crystal wire  217  for the reference potential of liquid crystal elements ( 233 ,  243 , etc.). 
         [0017]    Pixel  230  comprises a transistor  231  which is a switching element where the gate terminal thereof is connected to control wire  214 , and the drain terminal thereof is connected to signal wire  218 ; and a capacitor  232  and a liquid crystal element  233  connected serially to the source terminal of transistor  231 . The other terminal of capacitor  232  is connected to shared capacitance wire  216 . In liquid crystal element  233 , the electrode on the side of the TFT active matrix substrate (electrode  304  in  FIG. 2 ) connects to the source terminal of transistor  231 , and the other electrode  300  connects to the shared liquid crystal wire  217 . 
         [0018]    The structures of the other pixels ( 240 ,  250 , etc.) in liquid crystal display panel  200  have the same structure as pixel  230 . The structure of the part sealing in the liquid crystal material of each pixel is the same structure as in  FIG. 2  explained earlier. 
         [0019]    Switching element  231  can be appropriately changed to functional elements other than a transistor as long as the element has the function that enables controlling the connection state between signal wire  218  and liquid crystal element  233 . If both transistors  220 ,  221  function to control the connection states of signal input wire  211  and signal wires  218 ,  219 , the transistors can be appropriately changed to, for example, a shift register. 
         [0020]    Liquid crystal display panel  200  is connected to test apparatus  100 . Test apparatus  100  comprises a control apparatus  104  for selecting the pixel under test and controlling the operation of the test apparatus; a power supply  101  for supplying charge to the pixel under test; a charge measurement apparatus  102  for measuring the amount of charge discharged from the pixel under test and deciding whether defects are present in the liquid crystal element; and a switching element  103  for selectively connecting power supply  101  and charge measurement apparatus  102  to signal input wire  211 . Control wires  212 ,  213 ,  214 ,  215  are connected to control apparatus  104 . Shared capacitance wire  216  and shared liquid crystal wire  217  are both connected to ground. 
         [0021]    Next, the operation of test apparatus  100  is explained while referring to the flow chart in  FIG. 3 . 
         [0022]    First, signal input wire  211  and power supply  101  are connected by switching element  103  (Step  401 ). The output of power supply  101  is set to the test voltage of 4 V. In this state, the on voltage is applied to control wire  212  and control wire  214 . Then the pixel  230  placed at the intersection (row  1 , column  1 ) of signal wire  218  connected to transistor  220  controlled by control wire  212  and control wire  214  is selected as the pixel under test. 
         [0023]    The “on voltage” in the present application is the voltage where the switching element enters the conducting state (on state), that is, a voltage above the threshold voltage. In test apparatus  100 , the on voltage of 8 V is given to control wire  214  in order to set transistor  231  in the on state. 
         [0024]    On the other hand, the voltage where the switching element enters the off state is called the “off voltage.” When pixel  230  is tested, the off voltage of −5 V is given to control wire  215  because all of the pixels connected to control wire  215  must be set in the off state. The voltages and polarities of the on voltage and off voltage are appropriately set to match the specifications of the transistors and differ with the channel and type of transistor. 
         [0025]    The operation of test apparatus  100  is explained again. By applying the on voltage to control wire  212 , transistor  220  enters the on state, and signal input wire  211  and signal wire  218  enter the conducting state. By applying the on voltage to control wire  214 , transistor  231  of pixel under test  230  enters the on state. Therefore, the charge supplied from power supply  101  passes through signal input wire  211 , signal wire  218 , and transistor  231 , and is supplied to liquid crystal element  233  of pixel under test  230  (Step  402 ) (charging process). 
         [0026]    Therefore, when the above charging process is executed, a transistor  251  of pixel  250  connected to control wire  214  enters the on state, but charge is not supplied to a liquid crystal element  253  because charge is not supplied to signal wire  219 . In addition, charge is supplied to the drain terminal of a transistor  241  of pixel  240  connected to signal wire  218 . However, charge is not supplied to a liquid crystal element  243  because transistor  241  itself is in the off state. In other words, charge is supplied only to liquid crystal element  233  of pixel under test  230  at row  1 , column  1 . 
         [0027]    When the charging of liquid crystal element  233  ends, the off voltage is applied to control wire  214 , and transistor  231  enters the off state, and signal wire  218  and liquid crystal element  233  are disconnected. After a specific time has elapsed, charge measurement apparatus  102  connects to signal input wire  211 , and transistor  231  enters the on state again (Step  403 ). The charge that charged electrode  304  of pixel under test  230  is discharged through transistor  231  to signal wire  218  (Step  404 ). The discharged charge passes through signal input wire  211 , flows into charge measurement apparatus  102 , and the amount of charge is measured (Step  405 , measurement process). 
         [0028]    Charge measurement apparatus  102  determines whether the measurement result conforms to the specified conditions (Step  406 ). For example, when the amount of charge is extremely small, it is decided that a leak exists between opposing electrodes  300 ,  304 . Even if there is no leakage current when the amount of charge is not in the specified range, it is decided that a foreign material exists inside the liquid crystal material  302 , or the distance between opposing electrodes  300 ,  304  is unsuitable. When a foreign material exists or the distance between opposing electrodes  300 ,  304  is not appropriate, the amount of measured charge differs because the dielectric capacity differs compared to the normal case. 
         [0029]    When faults such as a leakage current or foreign materials are confirmed, defects occur in liquid crystal element  233 , and it is decided that pixel under test  230  is a bad pixel. The position of the pixel under test, the amount of measured charge, and the hypothesized cause of the defect are recorded (Step  407 , decision process). This completes the test of pixel  230  at row  1 , column  1 . 
         [0030]    The same test process sequentially tests pixel  240  at row  1 , column  2 ; and the pixel at row  1 , column  3  (not shown), . . . . When all of the pixels in row  1  have been tested, pixel  250  at row  2 , column  1 ; pixel  260  at row  2 , column  2 , . . . are sequentially tested, and all of the pixels in the second row are tested. Similarly each pixel in the third row and each pixel in the fourth row, . . . are sequentially tested. When all of the pixels have been tested, the test process of display panel  200  ends (Step  408 ). 
         [0031]    The above testing sequence of the pixels is one example, but the testing is not limited to this. For example, after testing pixel  230  at row  1 , column  1 , the test may scan in the row direction and test pixel  250  at row  2 , column  1 ; the pixel at row  3 , column  1 , . . . . In addition, when the stability and the reliability are high in the manufacturing process of the liquid crystal display panel, all of the pixels do not have to be tested, and specific pixels may be sampled and tested. 
         [0032]    In the above embodiment, only the static characteristics of pixel under test  230  were measured. However, the dynamic characteristics may also be measured by measuring the amount of charge discharged a plurality of times over a period of time to measure the temporal variations, by measuring the differences in the amount of charge discharged from liquid crystal element  233  when the test voltage (4 V) is applied after the reversed charge is given to liquid crystal element  233  (applied voltage of power supply  101  set to −4 V and charged), or when the test voltage is applied from the uncharged state as described above. Furthermore, other defect modes, for example, defects of the orientation films or poor liquid crystal material, can be ascertained. 
         [0033]    Above, the technical concepts related to the present invention were explained in detail while referring to specific embodiments. However, a person skilled in the art of the present invention can add various changes and improvements without diverging from the intent and scope of the claims.