Abstract:
Detecting statuses of driving units of an active-matrix organic light emitting diode (AMOLED) may reveal defects in the manufacturing process. This helps to detect and remove defective elements earlier in the manufacturing process before forming luminous layers in an AMOLED so as to decrease loss of organic materials and manufacturing time, and to increase yield significantly in the later part of the manufacturing process. The tested AMOLED includes a plurality of voltage sources, a plurality of pixel electrodes, and a plurality of driving units corresponding to the pixel electrodes respectively. Each driving unit includes a first TFT, a second TFT, and a storage capacitor. Defective elements of each driving unit can be detected by checking the detection results.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a method for applying detecting circuits, and more particularly to a method for applying detecting circuits of an active-matrix organic light emitting diode.  
         [0003]     2. Description of the Prior Art  
         [0004]     Please refer to  FIG. 1  showing a diagram of an AMOLED having pixel electrodes and being suitable for detection of a TFT-element matrix, which was published by IBM JAPAN during the 10th International Display Workshop that was held in 2003 (IDW &#39;03). As shown in  FIG. 1 , a pixel circuit  500  of the TFT-element matrix comprises a first transistor  501 , a snubber capacitor (Cs)  503  having one terminal electrically connected to the drain of the first transistor  501 , a second transistor  505  having a gate electrically connected to the drain of the first transistor  501  and the terminal of the snubber capacitor  503 , an organic light emitting diode  507  having an anode electrically connected to the source of the second transistor  505 , and a third transistor  509  having a drain electrically connected to the source of the second transistor  505  and the anode of the organic light emitting diode  507 , wherein the second transistor  505  is a thin film transistor used for driving a circuit, and the third transistor  509  is a bypass thin film transistor. The pixel circuit  500  tests whether the working status of the second transistor  505  is normal with the third transistor  509 , a bypass control electrically connected to the gate of the third transistor  509 , and a ground (GND) electrically connected to the source of the third transistor  509 . Therefore, the organic light emitting diode  507  can be operated normally with the second transistor  505 . Although the design is capable of detecting whether a second transistor  505  works normally, it still cannot be determined which second transistor  505  of the TFT-element matrix has malfunctioned. Furthermore, the third transistor  509  is additionally added to the pixel circuit  500  for assisting the detection so that the aperture ratio of the TFT-element matrix is decreased.  
         [0005]     Please refer to  FIG. 2 , which is a diagram for determining whether a TFT element is working by adding additional current meters. As shown in  FIG. 2 , the active-matrix organic light emitting diode (AMOLED)  600  comprises a first thin film transistor  601 , a storage capacitor  603  having one terminal electrically connected to the drain of the first thin film transistor  601 , a second thin film transistor  605  having a gate electrically connected to the drain of the first thin film transistor  601 , and an organic light emitting diode  607  having an anode electrically connected to the source of the second thin film transistor  605 . In  FIG. 2 , there are further a set of testing apparatuses comprising a first current meter  609  electrically connected to the drain of the second thin film transistor  605 , a first voltage source  611  electrically connected to the first current meter  609 , a second current meter  613  electrically connected to the cathode of the organic light emitting diode  607 , a second voltage source  615  electrically connected to the second current meter  613 , a writing circuit  617  having two outputs electrically connected respectively to the gate and the source of the first thin film transistor  601 , and a decision element  619  electrically connected to the first current meter  609 , wherein the writing circuit  617  is used for writing a binary signal, and the decision element  619  is used for determining whether the statuses of each elements of the active-matrix organic light emitting diode  600  are normal according to the readings of the first current meter  609  and the second current meter  613 . Although the device mentioned in this patent works in theory, however, since the intensity of the bias current applied by the active-matrix organic light emitting diode  600  is too low for both the first current meter  609  and the second current meter  613  to detect the readings of tiny currents so that normal elements may be regarded as malfunctioned elements.  
         [0006]     Please refer to  FIG. 3 , which is a top view for performing an illumination determination in a short-circuit situation by using conductive rubbers after finishing manufacturing an AMOLED and before connecting the AMOLED to a driving integrated circuit. As shown in  FIG. 3 , an organic light emitting diode panel  700  comprises a plurality of display regions  701 , a plurality of conductive plates  703 , and a plurality of conductive rubbers  705  each sticking between a display region  701  and a conductive plate  703 . With disposition of the conductive rubbers  705 , the organic light emitting diode panel  700  is capable of resisting larger voltages and currents, and is capable of finding out defective elements before finishing forming the whole driving circuit for saving losses of defective driving circuits. However, the organic light emitting diode panel  700  is not capable of saving losses of replacing materials of organic light emitting diodes. The organic light emitting diode panel  700  is also not able to save manufacturing time.  
       SUMMARY OF THE INVENTION  
       [0007]     Therefore, an object of the present invention is to provide a method for applying detecting circuits of an active-matrix organic light emitting diode to solve the aforementioned problems.  
         [0008]     The present invention discloses a method for applying detecting circuits of an active-matrix organic light emitting diode comprises providing a pixel electrode, providing a driving unit comprising a first transistor, a second transistor electrically connected to the first transistor and the pixel electrode, and a capacitor electrically connected to the first transistor and the second transistor, and detecting a potential difference between one terminal and another terminal of the capacitor when the first transistor is switched on and the second transistor is switched off.  
         [0009]     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is a diagram of a prior art AMOLED having pixel electrodes and being suitable for detection of a TFT-element matrix.  
         [0011]      FIG. 2  is a diagram for determining whether a TFT element is working by adding additional current meters according to the prior art.  
         [0012]      FIG. 3  is a top view for performing an illumination determination in a short-circuit situation by using conductive rubbers after finishing manufacturing an AMOLED and before connecting the AMOLED to a driving integrated circuit according to the prior art.  
         [0013]      FIG. 4  is a diagram of a first embodiment of an AMOLED for performing the detecting method of the present invention.  
         [0014]      FIG. 5  is a flowchart for detecting a status of the AMOLED of  FIG. 4 .  
         [0015]      FIG. 6  is a diagram of a second embodiment of an AMOLED for performing the detecting method of the present invention.  
         [0016]      FIG. 7  is a flowchart for detecting a status of the AMOLED of  FIG. 6 .  
         [0017]      FIG. 8  is a diagram of an equivalent circuit of each driving unit of the present invention when each second transistor of each driving unit is switch off.  
         [0018]      FIG. 9  is a diagram of an equivalent circuit of each driving unit of the present invention while detecting a status of each second transistor and each pixel electrode corresponding to each driving unit with a non-contact detecting device.  
         [0019]      FIG. 10  is a diagram of input pulses of each voltage source while detecting the status of the second transistor and the pixel electrode with a non-contact detecting device of  FIG. 9 .  
     
    
     DETAILED DESCRIPTION  
       [0020]     Please refer to  FIG. 4 , which is a diagram of a first embodiment of an AMOLED  200  for executing the detecting method of the present invention. The AMOLED  200  comprises a plurality of driving units  201 , a plurality of pixel electrodes  209 , a data voltage source  211 , a gate voltage source  213 , a first voltage source  215  for providing voltage to odd pixels, and a second voltage source  217  for providing voltage to even pixels. Each driving unit  201  comprises a first transistor  203 , a second transistor  205 , and a storage capacitor  207 . In each driving unit  201 , the second transistor  205  is electrically connected to the first transistor  203  and the pixel electrode  209  corresponding to the driving unit  201 . The storage capacitor  207  has a first terminal electrically connected to the first transistor  203  and the second transistor  205 . Each pixel electrode  209  is an OLED, wherein its current provision is manipulated by the second transistor  205  of the corresponding driving unit  201 . Each pixel electrode  209  can be an odd-pixel electrode or an even-pixel electrode according to various positions of its corresponding driving unit  201  inside AMOLED  200 . The data voltage source  211  is electrically connected to the drain of the first transistor  203  of each driving unit  201 . The gate voltage source  213  is electrically connected to the gate of the first transistor  203  of each driving unit  201 . The first voltage source  215  is electrically connected to the drain of the second transistor  205  and a second terminal of the storage capacitor  207  of each driving unit  201  corresponding to each pixel electrode  209  that is an odd-pixel electrode. The second voltage source  217  is electrically connected to the drain of the second transistor  205  and the second terminal of the storage capacitor  207  of each driving unit  201  corresponding to each pixel electrode  209  that is an even-pixel electrode.  
         [0021]     Please refer to  FIG. 5 , which is a flowchart for detecting a status of the AMOLED  200 . The steps are as follows:  
         [0022]     Step  101 : provide a pixel electrode  209 ;  
         [0023]     Step  103 : provide a driving unit  201  corresponding to the pixel electrode  209 ;  
         [0024]     Step  105 : detect a potential difference across the storage capacitor  207  when the first transistor  203  is switched on and the second transistor  205  is switched off;  
         [0025]     Step  107 : detect whether the first transistor  203  is working according to the potential difference across the storage capacitor  207 ;  
         [0026]     Step  109 : if the first transistor  203  is working, perform Step  111 ; otherwise, perform Step  117 ;  
         [0027]     Step  111 : increase the potentials of the drain and the gate of the first transistor  203 ;  
         [0028]     Step  112 : detect whether the second transistor  205  is working;  
         [0029]     Step  113 : if the second transistor  205  is working, perform Step  114 ; otherwise, perform Step  117 ;  
         [0030]     Step  114 : detect whether the pixel electrode  209  is working;  
         [0031]     Step  115 : if the pixel electrode  209  is working, end the procedure; otherwise, perform Step  117 ; and  
         [0032]     Step  117 : analyze the above results to determine malfunction of which suspected element caused the defect, wherein the suspected elements include the first transistor  203 , the second transistor  205 , and the pixel electrode  209 .  
         [0033]     The pixel electrode  209  provided in Step  101  can be an odd-pixel electrode or an even-pixel electrode in the AMOLED  200  and is diagramed in  FIG. 4 .  
         [0034]     The driving unit  201  provided in Step  103  is the fundamental unit while performing the method in the AMOLED  200  and is diagramed in  FIG. 4 . The method for detecting is capable of being performed simultaneously in each driving unit  201  inside the AMOLED  200  to report whether defects happen among the elements inside the AMOLED  200  in a shortest time and to analyze the defects.  
         [0035]     In Steps  105  and  107 , a standard voltage Vcom is inputted into the first voltage source  215  or the second voltage source  217  in the AMOLED  200  to make each second transistor  205  switch off. At this time, the equivalent circuit of each driving unit  201  is shown in  FIG. 8 . After switching on the first transistor  203  by a probe-contact detecting machine, determining whether the first transistor  203  is malfunctioning in the manufacturing process, and calculating the electric quantity of the storage capacitor  207 , the related results are stored as a basis for later analysis. The malfunctions of the transistors of the present invention include malfunction of nodes or wires.  
         [0036]     In Step  109 , if first transistor is malfunctioning, the situation is stored and reported in Step  117  to serve as a basis for determining which element is malfunctioning in the manufacturing process.  
         [0037]     In Step  109 , if the first transistor  203  is working, then a data voltage VSSR and a gate voltage VGSR are inputted into the data voltage source  211  and the gate voltage source  213  respectively in Step  111  so that the storage capacitor  207  is charged by the first transistor  203  until the second transistor  205  is switched on. Then a testing voltage VDD_ODD is inputted into the first voltage source  215 , and a testing voltage VDD_EVEN is inputted into the second voltage source  217  so that each pixel electrode  209  electrically connected to the first voltage source  215  or the second voltage source  217  is charged. A non-contact detecting device is used to determine whether there are any defects in the manufacturing process of the second transistor  205  and the pixel electrode  209  by way of photoelectron transduction or secondary electron collection and to store the related results of detection. Please refer to  FIG. 9 , which is a diagram of the equivalent circuit of each driving unit  201  while detecting a status of the second transistor  205  and the pixel electrode  209  corresponding to the driving unit  201  with a non-contact detecting device. Please refer to  FIG. 10 , which is a diagram of input pulses of each voltage source while detecting a status of the second transistor  205  and the pixel electrode  209  with the non-contact detecting device of  FIG. 9 .  
         [0038]     In Steps  113  and  115 , if there are no defects in the manufacturing process, then the procedure is ended to process procedures of the untested AMOLEDs  200 . If there is any defect found in Step  113  or  115 , the result of the defect is stored and reported as a basis for determining which element is malfunctioning.  
         [0039]     In Step  117 , the stored results about defects in Steps  109 ,  113 ,  115  are analyzed together to determine the precise positions of the malfunctioning elements in the AMOLED  200 . The method is also capable of simultaneously detecting defects of a plurality of the driving units  201  in the AMOLED  200 . So the method is not limited to detecting one defect at a time.  
         [0040]     Please refer to  FIG. 6 , which is a diagram of a second embodiment AMOLED  300  for performing the detecting method of the present invention. The AMOLED  300  comprises a plurality of the driving units  301 , a plurality of pixel electrode  309 , a data voltage source  311 , a gate voltage source  313 , a first voltage source  315  for providing voltage to odd pixels, a second voltage source  317  for providing voltage to even pixels, and a third voltage source  319 . Each driving unit  301  comprises a first transistor  303 , a second transistor  305 , and a storage capacitor  307 . In each driving unit  301 , the second transistor  305  is electrically connected to the first transistor  303  and the pixel electrode  309  corresponding to the driving unit  301 . The storage capacitor  307  has a first terminal electrically connected to the first transistor  303  and the second transistor  305 . Each pixel electrode  309  is an OLED, wherein its current is manipulated by the second transistor  305  of the corresponding driving unit  301 . Each pixel electrode  309  can be an odd-pixel electrode or an even-pixel electrode according to the various positions of the corresponding the driving unit  301  inside the AMOLED  300 . The data voltage source  311  is electrically connected to the drain of the first transistor  303  of each driving unit  301 . The gate voltage source  313  is electrically connected to the gate of the first transistor  303  of each driving unit  301 . The first voltage source  315  is electrically connected to the drain of the second transistor  305  of each driving unit  301  corresponding to each pixel electrode  309  that is an odd-pixel electrode. The second voltage source  317  is electrically connected to the drain of the second transistor  305  and the storage capacitor  307  of each driving unit  301  corresponding to each pixel electrode  309  that is an even-pixel electrode. The third voltage source  319  is electrically connected to the storage capacitor  307 . The differences between the AMOLED  300  and the AMOLED  200  are the position of the storage capacitor  307  and the addition of the third voltage source  319 . In the AMOLED  200 , a second terminal of the storage capacitor  207  is electrically connected to the first voltage source  215  or the second voltage source  217  while a second terminal of the storage capacitor  307  is electrically connected to the additional third voltage source  319  instead of the first voltage source  315  or the second voltage source  317  in the AMOLED  300 . The different arrangements in the AMOLED  200  and the AMOLED  300  are caused by the storage capacitor  307 , which is not a discrete element. The storage capacitor  307  is formed by the structure of the driving unit  301  or between insulation layers inside the driving unit  301 . Therefore, usage of space and the cost of a discrete storage capacitor can be saved, however, the bias voltage of the storage capacitor  307  may be significantly unstable so that there are likely to be inaccurate potentials on elements inside the driving unit  301 . Therefore, a third voltage source  319  is electrically connected to the second terminal of the storage capacitor  307  in the AMOLED  300  so that a standard voltage is provided to the storage capacitor  307  and the bias voltage of the storage capacitor  307  becomes stable. Because of the stable bias voltage of the storage capacitor  307 , the degree of inaccuracy of potentials on elements inside the driving unit  301  is decreased so that all driving units  301  inside the AMOLED  300  are not affected.  
         [0041]     Please refer to  FIG. 7 , which is a flowchart for detecting a status of the AMOLED  300  in  FIG. 6 . The steps are as follows:  
         [0042]     Step  401 : provide a pixel electrode  309 ;  
         [0043]     Step  403 : provide a driving unit  301  corresponding to the pixel electrode  309 ;  
         [0044]     Step  404 : input a standard voltage Vcom into the third voltage source  319  for providing the standard voltage Vcom to the storage capacitor  307 ;  
         [0045]     Step  405 : detect the potential difference across the storage capacitor  307  when the first transistor  303  is switched on and the second transistor  305  is switched off;  
         [0046]     Step  407 : detect whether the first transistor  303  is working according to the potential difference across the storage capacitor  307 ;  
         [0047]     Step  409 : if the first transistor  303  is working, perform Step  411 ; otherwise, perform Step  417 ;  
         [0048]     Step  411 : increase the potentials of the drain and the gate of the first transistor  303 ;  
         [0049]     Step  412 : detect whether the second transistor  305  is working;  
         [0050]     Step  413 : if the second transistor  305  is working, perform Step  414 ; otherwise, perform Step  417 ;  
         [0051]     Step  414 : detect whether the pixel electrode  309  is working;  
         [0052]     Step  415 : if the pixel electrode  309  is working, end the procedure; otherwise, perform Step  417 ; and  
         [0053]     Step  417 : analyze the above results to determine malfunction of which suspected element caused the defect, wherein the suspected elements include the first transistor  303 , the second transistor  305 , and the pixel electrode  309 .  
         [0054]     The pixel electrode  309  provided in Step  401  can be an odd-pixel electrode or an even-pixel electrode in the AMOLED  300  and is diagramed in  FIG. 6 .  
         [0055]     The driving unit  301  provided in Step  403  is the fundamental unit for performing the method and is also shown in  FIG. 6 . The method for detecting is capable of being performed simultaneously in each driving unit  301  inside the AMOLED  300  to quickly report whether defects occur among the elements of the AMOLED  300  and to analyze such defects.  
         [0056]     In Step  404 , the reason for inputting a standard voltage in the third voltage source  319  is the structure of the storage capacitor  307 . The detected results can be affected by the inaccuracy of the bias voltage of the storage capacitor  307 . Therefore the standard voltage Vcom is provided so that the detecting results are not affected by the inaccuracy of bias voltage of the storage capacitor  307 . The above problems have been described above in conjunction with  FIG. 6  and are not explained further here.  
         [0057]     In Steps  405  and  407 , a standard voltage Vcom is inputted into the first voltage source  315  or the second voltage source  317  in the AMOLED  300  to make each second transistor  305  switch off. At this time, the equivalent circuit of each driving unit  301  is shown in  FIG. 8 , wherein the equivalent circuit is the same as for the driving unit  201 . After switching on the first transistor  303  by a probe-contact detecting machine, determining whether the first transistor  303  is malfunctioning in the manufacturing process, and calculating the electric quantity of the storage capacitor  307 , the related results are stored as a basis for later analysis. Possible malfunctions of transistors include malfunction of nodes or wires.  
         [0058]     In Step  409 , if first transistor is malfunctioning, the situation is stored and reported in Step  417  to serve as a basis for determining which element is malfunctioning in the manufacturing process.  
         [0059]     In Step  409 , if the first transistor  303  is working, then a data voltage VSSR and a gate voltage VGSR are inputted into the data voltage source  311  and the gate voltage source  313  respectively in Step  411  so that the storage capacitor  307  is charged by the first transistor  303  until the second transistor  305  is switched on. Then a testing voltage VDD_ODD is inputted into the first voltage source  315 , and a testing voltage VDD_EVEN is inputted into the second voltage source  317  so that each pixel electrode  209  electrically connected to the first voltage source  315  or the second voltage source  317  is charged. A non-contact detecting device determines whether there are any defects in the manufacturing process of the second transistor  305  and the pixel electrode  309  by ways of photoelectron transduction or secondary electron collection and stores the related results of detection. Please refer to  FIG. 9 , which is a diagram of the equivalent circuit of each driving unit  301  that is the same as the equivalent circuit of each driving unit  201 , while detecting a status of the second transistor  305  and the pixel electrode  309  corresponding to the driving unit  301  with a non-contact detecting device. Please refer to  FIG. 10 , which is a diagram of input pulses of each voltage source while detecting a status of the second transistor  305  and the pixel electrode  309  with the non-contact detecting device of  FIG. 9 , wherein the input pulses of each voltage source are the same as in the AMOLED  200 .  
         [0060]     In Steps  413  and  415 , if there are no defects in the manufacturing process, then the procedure is ended to process procedures of the untested AMOLEDs  300 . If there is any defect found in Step  413  or  415 , the result of the defect is stored and reported as a basis for determining which element is malfunctioning.  
         [0061]     In Step  417 , the stored results about defects in Step  409 ,  413 ,  415  are analyzed together to know the precise positions of malfunctioning elements in the AMOLED  300  well. The method is also capable of detecting defects of a plurality of the driving units  301  in the AMOLED  300  at one time. So the method is not limited to detecting one defect at a time.  
         [0062]     The AMOLED of the prior art is not capable of precisely determining whether the TFT elements inside each driving unit are working since the luminance layers of OLEDs have not been formed after forming a TFT-element matrix (also called a driving-unit matrix). The present invention takes advantage of available detecting devices to detect malfunctioned elements earlier in the manufacturing process so that yield of the manufacturing process is improved, and the loss of manufacturing time is decreased. Another advantage of the present invention is that the aperture ratio is not increased since additional TFT elements are not added into AMOLEDs. Moreover, malfunctioned elements are identified by available detecting devices so that the cost of devices is not increased. Combining detecting results of a probe-contact detecting device and a non-contact detecting device, the first transistor of an AMOLED (e.g. the switching TFT) is tested for defects including short circuit, open circuit, and malfunction of nodes. The second transistor (e.g. the driving TFT) is tested for OLED illumination. Furthermore, image processing can also be used to determine the uniformity of properties of the elements and detecting a plurality of malfunctioned elements precisely in the element matrix of an AMOLED.  
         [0063]     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.