Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2001-02-27
2003-06-24
Hjerpe, Richard (Department: 2674)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S076000, C345S078000, C345S079000, C313S498000, C313S500000, C313S505000
Reexamination Certificate
active
06583776
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an EL panel in which an EL element formed on a substrate is sealed between the substrate and a cover member. Further, the present invention relates to an EL module in which an IC is mounted in the EL panel. Incidentally, in the present specification, the EL panel and the EL module are generally referred to as a light-emitting device. The present invention further relates to an electronic instrument using the light-emitting device.
2. Description of the Related Art
In recent years, a technique for forming a TFT on a substrate has been greatly advanced, and application to an active matrix display device has been advanced. Especially, since a TFT using a polysilicon film has an electron field-effect mobility (also called mobility) higher than that of a TFT using a conventional amorphous silicon film, a high speed operation is possible. Thus, control of a pixel, which is conventionally performed by a driving circuit outside a substrate, can be performed by a driving circuit formed on the same substrate as the pixel.
In this sort of active matrix display device, various merits, such as reduction of manufacturing costs, miniaturization of an electro-optic device, improvement of a yield, and reduction of a throughput, can be obtained by forming various circuits and elements on the same substrate.
Further, research of an active matrix type light-emitting device including an EL element as a self-luminous element has been actively carried out. The light-emitting device (EL display) including the EL element is also called an organic EL display (OELD: Organic EL Display) or an organic light-emitting diode (OLED: Organic Light-emitting Diode).
The light-emitting device is of a self-luminous type differently from a liquid crystal display device. The EL element has such a structure that a layer (hereinafter referred to as an EL layer) containing an organic compound is sandwiched between a pair of electrodes (anode and cathode), and the EL layer has no rmally a laminate structure. Typically, there is cited a laminate structure “hole transporting layer/light-emitting layer/electron transporting layer” proposed by Tang et al. of Eastman Kodak Company. This structure has a very high luminous efficiency, and most of the light-emitting devices on which research and development has been made at present adopt this structure.
In the EL element, luminescence (Electro Luminescence) generated by application of an electric field is obtained, and it includes an anode layer, an EL layer, and a cathode layer. Luminescence in an organic compound includes light emission (fluorescence) generated when a single excited state returns to a ground state and light emission (phosphorescence) generated when a triplet excited state returns to the ground state, and the EL display of the present invention may use either light emission.
In addition, there may be also adopted a structure in which laminating is made on an anode in the order of a hole injecting layer/a hole transporting layer/a light-emitting layer/an electron transporting layer or a hole injecting layer/a hole transporting layer/a light-emitting layer/an electron transporting layer/an electron injecting layer. The light-emitting layer may be doped with a fluorescent pigment or the like.
In the present specification, all layers provided between a cathode and an anode are generally referred to as an EL layer. Thus, all of the foregoing hole injecting layer, hole transporting layer, light-emitting layer, electron transporting layer, electron injecting layer, and the like are included in the EL layer.
Besides, in the present specification, an element formed of an anode, an EL layer and a cathode is referred to as an EL element.
In a light-emitting device, a plurality of pixels are provided in a matrix form, and each of the plurality of pixels includes a thin film transistor (TFT) and an EL element.
FIG. 4
is a circuit diagram of a pixel of a general light-emitting device. A pixel
400
includes a switching TFT
401
, a current controlling TFT
402
, an EL element
403
, a source signal line
404
, a gate signal line
405
, a power supply line
406
, and a capacitor
407
.
A gate electrode of the switching TFT
401
is connected to the gate signal line
405
. One of a source region and a drain region of the switching TFT
401
is connected to the source signal line, and the other is connected to a gate electrode of the current controlling TFT
402
. A source region of the current controlling TFT
402
is connected to the power supply line
406
, and a drain region is connected to an anode or a cathode of the EL element
403
.
In the case where the anode of the EL element
403
is connected to the drain region of the current controlling TFT
402
, the anode of the EL element
403
becomes a pixel electrode, and the cathode becomes a counter electrode. On the contrary, in the case where the cathode of the EL element
403
is connected to the drain region of the current controlling TFT
402
, the anode of the EL element
403
becomes the counter electrode, and the cathode becomes the pixel electrode.
Note that, in the present specification, a potential difference between a potential of a pixel electrode and a potential of a counter electrode is called an EL driving voltage, and this EL driving voltage is applied to the EL layer.
Note that, as shown in
FIG. 4
, the capacitor
407
is provided to be connected to the current controlling TFT
402
and the power supply line
406
.
The potential (power source potential) of the power supply line
406
is kept constant. The potential of the counter electrode of the EL element
403
is also kept constant. The potential of the counter electrode has a potential difference from the power source potential to such a degree that the EL element emits light when the power source potential is applied to the pixel electrode of the EL element.
The switching TFT
401
comes to have an on state by a selection signal inputted to the gate signal line
405
. Incidentally, in the present specification, that a TFT comes to have an on state means that a drain current of the TFT comes to have a state of more than 0.
When the switching TFT
401
comes to have the on state, a video signal inputted from the source signal line
404
is inputted to the gate electrode of the current controlling TFT
402
through the switching TFT
401
. Incidentally, in the present specification, the video signal means an analog signal including image information. Incidentally, that a signal is inputted to the gate electrode of the current controlling TFT
402
through the switching TFT
401
means that a carrier moves through an active layer of the switching TFT
401
, and a potential of a video signal is given to the gate electrode of the current controlling TFT
402
.
The amount of current flowing through the channel formation region of the current controlling TFT
402
is controlled by a gate voltage Vgs of a potential difference between the gate electrode and the source region of the current controlling TFT
402
. Thus, the potential given to the pixel electrode of the EL element
403
is determined by the height of the potential of the video signal inputted to the gate electrode of the current controlling TFT
402
. The emission luminance of the EL element (luminance of light emitted from the EL element) is controlled by the height of the potential given to the pixel electrode. That is, the luminance of the EL element
403
is controlled by the potential of the video signal inputted to the source signal line
404
and a gradation display is carried out.
FIG. 5
shows the relation between the emission luminance (cd/m
2
) of an EL element and the current density (mA/cm
2
). The relation between the emission luminance of the EL element and the current density is linear. That is, when the current density of the EL element becomes high at a constant rate, the emission luminance of the EL element also becomes high at a constant rate. The current density is determined by a drai
Koyama Jun
Osada Mai
Yamazaki Shunpei
Fish & Richardson P.C.
Hjerpe Richard
Lesperance Jean
Semiconductor Energy Laboratory Co,. Ltd.
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