Patent Application
20060139041
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.
To test existing LCD displays, the voltage controlling each pixel can be directly measured even without touching the active area of the display'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.
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.
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.
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.
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:
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.
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.
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.
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.
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.
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.
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.
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.
