Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure – Plural light emitting devices
Reexamination Certificate
1999-04-23
2002-02-26
Tran, Minh Loan (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
Plural light emitting devices
C257S080000, C257S081000, C257S084000, C257S103000, C257S040000
Reexamination Certificate
active
06350996
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a light emitting diode device used for a copying machine, a printer, a display, an original illuminating light source of an image reading apparatus, and the like, and a method of manufacturing the light emitting diode device.
2. Description of the Related Art
A light emitting diode device, in which a plurality of pixels each comprising a micro light emitting portion are arranged to permit the emission of light from each of the pixels to be independently controlled, is conventionally used as a panel or a back light of a display device or the like; an internal writing head of an image forming apparatus such as a copying machine, a printer, or the like; or an original illuminating light source of an image reading apparatus.
Such a conventional light emitting diode device is produced by a method comprising arranging light emitting diode chips comprising an inorganic semiconductor crystal such as GaAs or AlInGaP in a one-dimensional or two-dimensional form, or a method comprising depositing a thin film of an inorganic material such as ZnS or the like on a substrate, and then patterning the thin film to form pixels.
An example of a display device using light emitting diode chips which is brought into practical use is a large outdoor display device of a several meters square in which packages of respective light emitting diode chips are arranged in a two-dimensional form.
Also an internal reading head of an image forming apparatus such as a copying machine, a printer, or the like is brought into practical use, in which light emitting chips each having many micro light emitting portions provided thereon are arranged in a one-dimensional form.
However, the method of arranging light emitting chips has the problem of causing difficulties in miniaturizing the apparatus and improving arrangement precision.
The method of depositing a thin film of an inorganic material such as ZnS or the like on a substrate, and then patterning the thin film to form pixels is suitable for miniaturizing the apparatus, and permits photolithographic patterning or the like with high precision. This method does not have the above-described problem, but has a problem in which the device cannot be driven with a direct current at a low voltage suitable for design of an electronic apparatus.
On the other hand, an organic thin film light emitting diode (organic light emitting element) has recently been developed, which can be formed in a thin film on a substrate of a large area, and which can be driven with a direct current. In order to solve the above problems, therefore, the use of an organic light emitting device as a light emitting device is proposed, in which light emitting portions comprising organic light emitting elements are arranged in a one-dimensional or two-dimensional form.
FIG. 70
shows a typical structure of an organic light emitting diode.
Referring to
FIG. 70
, the organic light emitting diode comprises a substrate
100
, a transparent electrode
401
made of indium/tin oxide (ITO), a hole transport layer
403
made of an organic hole transport material such as an aromatic diamine (Formula 2) or the like, and an organic electron transport layer
404
made of an organic electron transport material such as tris(8-quinolinolato)aluminum complex (Formula 3).
The organic light emitting diode further comprises a cathode made of a material having a low work function, such as Al, a Mg:Ag alloy, or the like. When a voltage is applied between an anode and cathode, holes injected into the hole transport layer from the anode are recombined with electrons injected into the electron transport layer from the cathode through an electron injection layer to emit light.
As the simplest method for arranging a plurality of micro pixels each comprising such a light emitting diode to enable independent control of the emission of light from each of the pixels, a plurality of parallel stripe anodes are formed on a substrate, the hole transport layer and the electron transport layer are laminated on the anode, and stripe cathodes are further formed on the hole and electron transport layers perpendicularly to the anodes to form a simple matrix in which a pixel is formed at each of the intersections of the anodes and the cathodes. In order to drive this structure, for example, the lines of the cathodes formed in parallel stripes are successively connected to a negative power source and disconnected therefrom, and in synchronism therewith, the anodes are successively connected to a positive power source or disconnected therefrom. By this operation, each of the pixels is flashed only at a moment when the cathode connected to the corresponding pixel is connected to the negative power source depending upon whether or not the anode is connected to the positive power source at that moment.
In this simple method, since only one of the plurality of cathode lines is connected to the negative power source at a moment, only the pixels connected to the line connected to the negative power source are flashed depending upon whether or not the anodes are connected to the positive power source, all other pixels being turned off regardless of whether the anodes are connected to the positive power source. This operation has the property that the lighting duty of the pixels decreases with an increase in the number of lines of the cathodes.
Therefore, this method has the drawback that although the luminance is high at a lighting moment, the effective luminance as an average luminance for a predetermined time decreases as the number of pixels increases to increase the number of cathode lines.
In order to improve this point, a light emitting diode device has been proposed in which a non-linear element such as a transistor or capacitor is provided on each of the pixels.
Of devices using the above-mentioned organic light emitting diode, an example of light emitting diode devices in which light emitting portions used in a display device are arranged in a two-dimensional form is described below.
FIG. 71
is a drawing showing an equivalent circuit of a single pixel in such a light emitting diode device.
The circuit shown in
FIG. 71
comprises a first thin film transistor (address transistor)
1
which constitutes a pixel, a storage capacitor
2
, a second thin film transistor (driving transistor), and an organic light emitting diode
4
. The circuit further comprises an electrode Ps connected to the source electrode of the address transistor, an electrode Pm connected to the second side of the storage capacitor and the gate electrode of the driving transistor, an electrode Pg connected to the gate electrode of the address transistor, an electrode Pc connected to the first side of the storage capacitor and the source electrode of the driving transistor, and an electrode Pled connected to a cathode of the organic light emitting diode
4
.
A selection signal is applied to the electrode Pg, a data signal is applied to the electrode Ps, and a potential appears in the electrode Pm by charge and discharge of the storage capacitor according to the data signal. The electrodes Pc and Pled are at fixed potentials.
The circuit is operated as described below.
When the selection signal applied to the electrode Pg is brought to a selection state (high-potential state), the potential of the electrode Pg decreases. As a result, conduction occurs between the source and drain of the address transistor, and a current flows in and out of the storage capacitor
2
according to the data signal applied to the electrode Ps to set a potential difference between the source and gate electrodes of the driving transistor, i.e., a potential difference between the electrodes Pc and Pm, to a value corresponding to the data signal applied to the electrode Ps. Therefore, a current flows through the driving transistor
3
according to the data signal, and the organic light emitting diode
4
emits light with a luminance corresponding to the data signal. When the selection signal applied to the electr
Kawai Tatsundo
Ueno Kazunori
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Tran Minh Loan
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