Electric lamp and discharge devices: systems – Plural power supplies – Plural cathode and/or anode load device
Reexamination Certificate
2001-12-31
2003-10-21
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Plural power supplies
Plural cathode and/or anode load device
C313S504000, C313S506000, C428S690000, C315S368190
Reexamination Certificate
active
06636001
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
The present invention relates to an organic electronic device including a charge-injection-type luminescence device having an organic active layer and a drive circuit therefor formed integrally on a common substrate, and also a nonlinear device having an organic layer therefor.
As a charge injection-type luminescence device, a light-emitting diode (LED) using an inorganic single crystal of CaAs, GaP, GaN, etc., has been widely used, but research work on organic luminescence materials has also been made for a long time. For example, Pope, et al., reported an electric field luminescence phenomenon by using an anthracene single crystal in 1963 (J. Chem. Phys. 38 (1963) 2042). Further, Helfrich and Schneider succeeded in observation of relatively strong EL (electroluminescence) by using a solution electrode system in 1965 (Phys. Rev. Lett. 14 (1965) 229).
Thereafter, various studies for providing organic luminescence materials have been made as reported in, e.g., U.S. Pat. Nos. 3,172,762; 3,173,050; 3,710,167; J. Chem. Phys. 44 (1966) 2902: J. Chem. Phys. 50 (1969) 14364; J. Chem. Phys. 58 (1973) 1542 and Chem. Phys. Lett. 36 (1975) 345, but devices of commercial level have not been provided because of problems, such as weak luminescence intensity and necessity of high voltages for luminescence.
In recent years, however, Tang, et al., have developed an organic EL device comprising very thin vacuum deposition layers (a charge-transporting layer and a luminescence layer) and have realized a high luminance at low drive voltages (Appl. Phys. Lett. 51 (1987) 913 or U.S. Pat. No. 4,356,429). This lamination type of organic luminescence devices have been actively studied since then, and the possibility of various applications thereof, including a flat panel display, is becoming practical recently.
FIG. 9
shows a representative laminate structure of such an organic EL device, including a substrate
500
; a transparent electrode
501
comprising indium/tin oxide (ITO) and functioning as an anode of an organic EL device as a luminescence device; a hole-transporting layer
502
comprising an organic hole-transporting material, such as an aromatic diamine as represented by formula (1) below; an electron-transporting layer
503
comprising an electron-transporting material, such as tris(8-quinolynol)-aluminum complex (or tris(8-quinolynalato)aluminum complex) generally identified as Alq3, is represented by formula (2) below; and a cathode
504
comprising a material having a low work function, such as Al or Mg:Ag alloy.
When a voltage is applied between the anode
501
and the cathode of the organic EL device, holes injected from the anode
401
into the hole-transporting layer
502
and electrons injected from the cathode
504
into the electron-transporting layer
503
(optionally via an optional electron-injection layer) are recombined to cause luminescence.
When such an organic EL device is applied to a flat panel display, it is necessary to arrange a plurality of pixels each comprising such an organic EL device and control the luminescence at the respective pixels independently. For this purpose, it is the simplest way to form a simple matrix structure by forming a plurality of parallel anode stripes on a substrate, forming thereon organic layers including a hole-transporting layer and an electron-transporting layer, and forming thereon a plurality of parallel cathode stripes intersecting with the anode stripes at right angles so as to form a pixel at each intersection of the anodes and the cathodes. For driving the simple matrix device, the mutually parallel cathodes are sequentially connected one at a time to a negative power supply with the other cathodes open, and in synchronism therewith, the anodes are selectively connected to a positive power supply or made open. As a result, only when a certain cathode is connected to the negative power supply, the respective pixels on the cathode are selectively turned on or off depending on whether or not the associated anodes are connected to the positive power supply.
This drive system is simple but is accompanied with a difficulty that the pixel lighting duty is lowered if the number of cathode lines are increased, since in the system only one among the plurality of cathode lines is connected to the negative power supply at a certain instant, and only the pixels on the line are selectively turned on or off depending on whether or not the associated anodes are connected to the positive power supply and the other pixels are extinguished regardless of whether the associated anodes are connected or not. As a result, even if a high luminance is attained at the instant of turn-on, an effective luminance as an average over a certain period is lowered if the number of cathode lines are increased corresponding to an increased number of pixels.
For obviating the above problem, an organic EL device equipped with a transistor at each pixel has been proposed.
FIG. 10
is an equivalent circuit diagram of one pixel of such an organic EL device.
Referring to
FIG. 10
, a pixel unit includes a first thin film transistor (address transistor)
601
, a storage capacitor
602
, a second thin film transistor (drive transistor)
603
, an organic EL device
604
functioning as an organic EL element
604
as a luminescence element, an electrode Pd connected to a source electrode of the address transistor, an electrode Pc connected to a second side of the storage capacitor
602
and a gate electrode of the drive transistor
603
, an electrode Ps connected to a gate electrode of the address transistor
601
, an electrode Pv connected to a first side of the storage capacitor
602
and a source electrode of the drive transistor
603
, and an electrode Pled connected to a cathode of the organic EL element
604
.
Ps is supplied with a selection signal, Pd is supplied with a data, and at Pc is developed a potential depending on the data signal by the charging and discharging of the storage capacitor
602
. Pv and Pled are placed at fixed potentials.
The circuit operates as follows.
When a selection signal supplied to Ps is placed in a selection state (“high”), the potential at Ps is raised. As a result, the source-drain channel of the address transistor
61
is made conductive so that a current corresponding to a data signal supplied to Pd is flowed to the storage capacitor
602
, whereby a potential difference between the source electrode and the gate electrode of the drive transistor
603
, i.e., a potential difference between Pv and Pc, becomes a value corresponding to the data signal supplied to Pd. Accordingly, a current corresponding to the data signal flows through the drive transistor
603
so that the organic EL element
604
causes luminescence at a luminance corresponding to the data signal. When the selection signal supplied to Ps is placed in a non-selection state (“low”), the source-drain channel of the address transistor is made non-conductive, no current flows to the storage capacitor
602
even when the data signal supplied to Pd is changed, so that the potential difference between Pc and Pv is not substantially changed and the luminescence at the organic EL element is not substantially affected thereby.
In such an organic EL device, as described above, each pixel is equipped with an address transistor, a drive transistor and a storage capacitor, and a charge corresponding to a data signal in a selection period is stored at the storage capacitor, whereby the organic EL element at the pixel continually causes luminescence corresponding to the stored charge even in the non-selection period. Accordingly, there is attained an advantage that the luminescence duty at each pixel is kept high without causing a lowering in effective luminance even if the entire device includes a large number of pixels.
The transistors disposed at each pixel are ordinarily thin film electric field-type transistors made of polysilicon or amorphous silicon.
However, in order to form such an organic EL device, after a whole process of forming a
Kawai Tatsundo
Senoo Akihiro
Ueno Kazunori
Lee Wilson
Wong Don
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