Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Lumped type parameters
Reexamination Certificate
2003-05-20
2004-11-09
Tang, Minh N. (Department: 2829)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Lumped type parameters
Reexamination Certificate
active
06815975
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an inspection method and an inspection device for an active matrix substrate used for an organic EL display device and the like, and an inspection program used therefor and an information storage medium.
In recent years, a display device in which self-emitting organic EL elements are arranged in the shape of a matrix array has been extensively developed.
Defect inspection of this type of organic EL display device is carried out before shipment from the factory after forming an organic EL film between an active matrix substrate and a common substrate and assembling all peripheral parts.
A technique of inspecting a display screen by visual inspection by driving the organic EL display device has been known. However, in the case of visual inspection, variation of inspection accuracy easily occurs depending on the condition of the inspector or individual variation. Moreover, it is impossible to determine whether the display defect is caused by an interconnect defect or whether the defect pixel is a dark spot. Furthermore, it is impossible to determine whether luminance nonuniformity of the screen is caused by a defect in an organic EL film, a defect in a drive section, or current leakage from interconnects. Therefore, it is necessary to check the cause of defects for a display device which is determined to be defective after inspection. However, since the display device is manufactured in a plurality of manufacturing steps, the cause of defects may be superimposed between each step. Therefore, data on occurrence of defects cannot be rapidly fed back to the manufacturing steps.
There has been proposed automation of inspection for an organic EL display device (Japanese Patent Application Laid-open No. 10-321367 and Japanese Patent Application Laid-open No. 2000-348861). Japanese Patent Application Laid-open No. 10-321367 discloses a method of evaluating organic EL elements by measuring leakage current flowing through the organic EL elements when applying a reverse bias voltage. In this method, it is necessary to apply a reverse bias voltage to the organic EL elements while suspending display drive which causes constant current to flow through the organic EL elements. Japanese Patent Application Laid-open No. 2000-348861 points out the possibility in which true drive characteristics may not be evaluated by the method disclosed in Japanese Patent Application Laid-open No. 10-321367 due to influence of drive interruption, and proposes inspecting organic EL elements by superimposing an inspection signal during driving in which a forward bias voltage is applied to the organic EL elements. In this method, the organic EL elements are evaluated based on changes in drive voltage and drive current when superimposing the inspection signal.
However, since the inspection is performed in a finished product state in these applications, time and materials used to manufacture the product are lost if defects are detected.
BRIEF SUMMARY OF THE INVENTION
The present invention may provide an inspection method and an inspection device for an active matrix substrate capable of inspecting dot defects, line defects, or luminance defects in the stage of the active matrix substrate, and an inspection program used therefor and an information storage medium.
An inspection method for an active matrix substrate according to a first aspect of the present invention comprises:
a first step of providing an active matrix substrate including a plurality of signal lines, a plurality of scanning lines, a plurality of voltage supply lines, and a plurality of pixels, each of the plurality of pixels being connected with one of the signal lines, one of the scanning lines, and one of the voltage supply lines, each of the plurality of pixels including a pixel select transistor connected with the one signal line and the one scanning line and an operating transistor, a gate of the operating transistor being connected with the pixel select transistor, one of a source and a drain of the operating transistor being connected with the one voltage supply line, and the other of the source and the drain of the operating transistor being in an open state;
a second step of charging a parasitic capacitor between the gate of the operating transistor and the one voltage supply line by supplying a potential from an inspection device;
a third step of measuring discharge current by using the inspection device when discharging the parasitic capacitor; and
a fourth step of determining whether or not a defect exists in each of the plurality of pixels by using the inspection device based on a value of the discharge current.
In the first aspect of the present invention, a voltage is applied between the gate of the operating transistor and the one voltage supply line. This enables the parasitic capacitor between the gate of the operating transistor and the one voltage supply line to be charged even if the source or the drain which is not connected with the one voltage supply line is in an open state. The parasitic capacitor cannot be charged if a defect, such as a breakage of the one voltage supply line or a breakage between the gate of the operating transistor and the one voltage supply line, exists. Therefore, the above defect can be detected by charging the parasitic capacitor and monitoring current when discharging the parasitic capacitor. Since a voltage cannot be normally applied between the gate of the operating transistor and the one voltage supply line in the case where the voltage supply line and the like are short-circuited, the short-circuit can be detected as a defect by monitoring current during discharging. Moreover, a luminance nonuniformity defect caused by a difference in the parasitic capacitors between the pixels can also be detected.
Each of the plurality of pixels may further include a storage capacitor connected with the gate of the operating transistor. In this case, an influence of the storage capacitor may be canceled in the second step and the third step. This is because current must be measured depending only on the parasitic capacitor. The influence of the storage capacitor may be canceled by setting a potential difference between opposite ends of the storage capacitor to be substantially the same in the second step and the third step. This prevents the storage capacitor from being charged and discharged.
A range of capacitance values of the parasitic capacitor between the gate of the operating transistor and the one voltage supply line may have a high-saturation region, a low-saturation region, and a transition region between the high-saturation region and the low-saturation region in which a capacitance value changes depending on an applied voltage. In this case, a voltage may be applied between the gate of the operating transistor and the one voltage supply line in at least one of the second step and the third step, so that a capacitance value of the parasitic capacitor between the gate of the operating transistor and the one voltage supply line is within the high-saturation region.
The amount of charge to be stored in the parasitic capacitor is increased as the capacitance value of the parasitic capacitor is increased during charging, whereby a large amount of discharge current can be obtained. Even if the capacitance value of the parasitic capacitor Cdgo is small during charging, since current flows until the parasitic capacitor is in the equilibrium state if the capacitance value of the parasitic capacitor Cdgo is large during discharging, whereby a large amount of discharge current can also be obtained. This enables a signal
oise ratio (S/N) of monitoring current to be secured sufficiently.
In the first aspect of the present invention, a set of steps consisting of the second to fourth steps may be performed a plurality of times while changing a voltage applied between the gate of the operating transistor and the one voltage supply line.
Luminance nonuniformity of the pixels may be caused by characteristics of the operating transistor (for example, variat
Jiang Hui
Nara Shoji
Yamamoto Wataru
Harness & Dickey & Pierce P.L.C.
Tang Minh N.
Wintest Corporation
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