Electro luminescence display device and method of testing the same
AssigneeSemiconductor Energy Laboratory Co., Ltd.
InventorJun Koyama
Life of this patent
Estimating the term…
Abstract
To increase the proportion of the perfects to the whole lot of final products and to reduce the cost for active matrix EL display devices by checking the operation of a TFT substrate before depositing an EL material. A capacitor for testing is connected to a drain terminal of a driving TFT in a pixel portion to observe charging and discharging of the capacitor. Whether the driving TFT is normal or not is judged by the observation, so that the rejects can be removed before the manufacturing process is completed.
Claims20
An electro luminescence display device comprising:
- a plurality of source signal lines;
- a plurality of gate signal lines;
- a plurality of power supply lines;
- a plurality of switching thin film transistors;
- a plurality of driving thin film transistors;
- and a plurality of testing capacitors which are all formed on an insulating substrate,
- wherein one end of each of said testing capacitors is connected to a drain region of each of the driving thin film transistors and the other end of said each testing capacitor is connected to one of the gate signal lines, and
- wherein the power supply lines are led out of the insulating substrate through switches.
An electro luminescence display device comprising:
- a pixel region comprising a plurality of source signal lines;
- a plurality of gate signal lines;
- a plurality of power supply lines;
- a plurality of switching thin film transistors;
- a plurality of driving thin film transistors;
- a plurality of electro luminescence elements, a plurality of storage capacitors;
- and a plurality of testing capacitors which are all formed over a substrate;
- and
- driver circuits comprising at least a gate signal line driver circuit, a source signal line driver circuit, and a testing driver circuit which are all formed over said substrate,
- wherein one end of each of said testing capacitors is connected to a drain region of one of the driving thin film transistors and the other end of said each testing capacitor is connected to one of the gate signal lines, and
- wherein the power supply lines are connected to said testing driver circuit through switches.
A method of testing an electro luminescence display device comprising the steps of:
- operating a thin film transistor to charge a testing capacitor until it reaches and keeps a certain level of electric potential;
- turning the driving thin film transistor OFF and then setting the electric potential of the power supply lines to a level different from the electric potential of the testing capacitor;
- leading the electric charges charged in the testing capacitor out for each pixel through its associated power supply line;
- and
- detecting a change in the electric potential.
A method of testing an electro luminescence display device comprising the steps of:
- applying a voltage corresponding to a signal “Hi” to the power supply lines;
- turning a driving thin film transistor in each pixel ON to write the voltage of the power supply lines in each testing capacitor;
- turning said driving thin film transistor OFF so that an electric potential of the power supply lines is set to a voltage corresponding to a signal “Lo”;
- and then
- turning said driving thin film transistor ON, thereby electric charges held in the testing capacitor are discharged to the power supply lines;
- and
- detecting the discharged voltage using a testing circuit connected to the power supply line lead out terminal.
Dependencies are inferred from the claim text.