JP5315382B2 - Display device - Google Patents

Description

  The present invention relates to a display device using an organic light emitting element and a driving method thereof. More specifically, the present invention relates to a display device that drives an organic light emitting element with an alternating current and a driving method thereof.

  In recent years, a technology for forming a transistor, for example, a TFT (Thin Film Transistor) on a substrate has greatly advanced, and an active matrix display device has been developed. Since the active matrix type can solve the problem of crosstalk seen in the simple matrix type, display with higher definition and higher contrast than the simple matrix type can be realized.

  In particular, a TFT using polysilicon as an active layer has a higher field effect mobility than a conventional TFT using amorphous silicon, and can operate at high speed. For this reason, it is possible to control the luminance of a pixel, which has been conventionally performed by attaching a drive circuit to the substrate, using a drive circuit formed on the same substrate as the pixel. In such an active matrix display device, various circuits and elements can be formed over the same substrate, and the display device can be downsized.

  Further, in recent years, development of display devices using organic light-emitting elements (hereinafter referred to as organic light-emitting displays) has become active. The organic light-emitting element is self-luminous and does not require a light source such as a backlight unlike a liquid crystal display device. For this reason, it is considered promising as a means for realizing a lighter and thinner display device, and is expected to be used for a mobile phone, a personal digital assistant (PDA) for personal use, and the like.

  An organic light-emitting device has a diode structure in which an organic compound layer is sandwiched between two electrodes, and holes are injected from one electrode and electrons are injected from the other electrode, whereby an organic compound layer A light emitter that emits light by recombination of electrons and holes inside. The organic light emitting device emits electroluminescence (EL), for example, fluorescence, phosphorescence, and the like. An organic light emitting element is also called an organic light emitting diode (OLED) because of its diode structure.

  In many cases, the organic light emitting device has an anode / hole transport layer / light emitting layer / electron transport layer / cathode structure. This configuration has a very high luminous efficiency, and almost all organic light emitting devices that are currently under research and development employ this configuration. One or both of the hole injection layer and the electron injection layer may not be provided. However, the light-emitting layer is an indispensable component for the organic light-emitting layer because carriers are recombined when a current flows therethrough to emit light.

  The organic compound layer is a generic name for a carrier transport layer such as electrons and holes, and a light emitting layer made of a material having a high quantum yield. Therefore, the light emitting layer, the hole injection layer, and the electron injection layer described above are included in the organic compound layer.

  The organic light emitting element has high rectification characteristics. When the anode is set to a higher potential than the cathode, a current flows through the organic compound layer, and light emission occurs due to recombination of carriers. Conversely, when the anode is at a lower potential than the cathode, no current flows through the organic compound layer and no light emission occurs. In a diode structure such as an organic light emitting element, a voltage applied in a direction in which current easily flows is referred to as forward bias, and a voltage applied in a direction in which current does not easily flow is referred to as reverse bias.

  FIG. 19 shows an equivalent circuit of a pixel portion of a conventional active matrix organic light emitting display.

The gate signal lines (G _{1 to} G _n ) are connected to the gate electrode of the switching TFT 901 included in each pixel 900. The source of the switching TFT, and drains and is the one of the source signal line for inputting a data signal (S ₁ ~S _n), a gate electrode and each pixel of the current control TFT902 the other has each pixel Each is connected to one electrode of the capacitor 903. The other electrode of the capacitor is connected to a power supply line (V _{1 to} V _m ).

  One of the source and the drain of the current control TFT is connected to the power supply line, and the other is connected to the pixel electrode of the organic light emitting element 905 included in each pixel. The counter electrode of the organic light emitting element is an electrode that is provided facing the pixel electrode of the organic light emitting element and serves as a reference potential of the pixel electrode.

  It is assumed that the counter electrode is connected to the counter power source 906 for convenience of explanation. The potential difference between the power supply line and the counter power supply is set to about the voltage at which the organic light emitting element emits light.

  One of the anode and the cathode of the organic light emitting element 905 is a pixel electrode, and the other is a counter electrode. When the anode of the organic light emitting element is connected to the source or drain of the current control TFT, the anode of the organic light emitting element serves as a pixel electrode, and the cathode of the organic light emitting element serves as a counter electrode. On the other hand, when the cathode is connected to the source or drain of the current control TFT, the cathode of the organic light emitting element is the pixel electrode, and the anode of the organic light emitting element is the counter electrode.

The luminance of the light emitted from the organic light emitting device is determined as follows. A selection signal is input from the gate signal line to the gate electrode of the switching TFT 901, and the switching TFT is turned on (conductive state). Then, the data signal input to the source signal line is input to the gate electrode of the current control TFT 902 via the switching TFT. The potential of the gate electrode of the current control TFT is held by the capacitor 903. Therefore, the potential difference between the gate electrode of the current control TFT 902 and the power supply line (V _{1 to} V _m ), that is, the gate voltage of the current control TFT is kept constant until a data signal is input to the pixel next time. Maintained.

  When the current control TFT is turned on, a current flows from the semiconductor layer of the current control TFT to the organic light emitting element connected in series to the semiconductor layer of the current control TFT. The intensity of light emitted from the organic light emitting device is determined according to the amount of current flowing through the organic light emitting device. Since the amount of current flowing through the current control TFT is controlled by a data signal input to each pixel, the luminance of light emission of each pixel can be controlled by the potential of the data signal.

  In general, driving an organic light-emitting element with a direct current means that when either the counter electrode or the pixel electrode is a cathode and the other electrode is an anode, the anode is maintained at a higher potential than the cathode and the direct current is applied. This means that the light emission is sustained by flowing the light.

  However, when the organic light emitting device is driven with a direct current, the luminance of light emitted from the organic light emitting device decreases with time. The causes of luminance degradation when driven by direct current are due to the accumulation of ionic impurities at the interface of the organic compound layer and the organic light emission due to the molecules that make up the organic compound layer being polarized in a uniform direction along the electric field. It is considered that an electric field opposite to the electric field applied from the pixel electrode and the counter electrode of the element is generated inside the organic compound layer.

  In particular, when the organic light emitting device is driven with a constant voltage applied between the cathode and the anode of the organic light emitting device (hereinafter, referred to as a constant voltage method), the light emission of the organic light emitting device is remarkably increased as time passes. The brightness of the light is reduced. In the constant voltage method, the strength of the voltage applied to the anode and the cathode is always constant, so that the effective voltage applied to the organic compound layer decreases as the electric field strength generated inside the organic light emitting layer increases, and the organic The luminance of light emitted from the light emitting element is reduced.

In order to suppress this luminance deterioration, it is necessary to drive the organic light emitting element with an alternating current.
Driving the organic light emitting element with alternating current means that voltages having different polarities are alternately applied to the organic light emitting element. That is, in addition to the forward bias necessary for light emission, it means adding a reverse bias. The forward bias and the reverse bias are not necessarily equal in strength and application time. Even if only a slight reverse bias is applied, it will be referred to as alternating current.

  However, in the conventional circuit described above, even if an AC power supply is provided connected to the counter electrode of the organic light emitting element and the power supply line, the organic light emitting element may not be sufficiently reverse-biased. This will be described below.

The circuit shown in FIG. 19 is a closed circuit in which the source or drain of the current control TFT 902 and the organic light emitting element 905 are connected in series between the counter power supply 906 and the power supply lines (V _{1 to} V _m ). Configure. In this closed circuit, the operation when a voltage is applied to the organic light emitting element by alternating current will be described. In order to simplify the description, the current control TFT is hereinafter referred to as a p-channel type. A p-channel TFT is turned on when the gate potential is lowered by a value exceeding a threshold value than the potential of the source, that is, the power supply line.

  Therefore, when forward biasing is applied to the organic light emitting element, the potential of the counter electrode of the organic light emitting element 905 is set to Lo level, the potential of the power supply line is set to Hi level, and the power supply line (of the current control TFT) is set. The potential of the gate of the current control TFT is made lower than the potential of the source by a value exceeding the threshold value. Then, the current control TFT is turned on, that is, in a conductive state, a current flows through the organic light emitting element 905, and the organic light emitting element emits light.

  When stopping the current flowing through the organic light emitting element without changing the potentials of the power supply line and the counter electrode, the gate potential of the current control TFT is made higher than the source potential to turn off the current TFT. .

  It is assumed that the current control TFT is turned on and the potentials of the power supply line and the counter electrode are inverted in order to reverse bias the organic light emitting element. That is, the potential of the counter electrode of the organic light emitting element 905 is set to the Hi level, and the potential of the power supply line is set to the Lo level. At this time, a series circuit including the counter electrode, the organic light emitting element, the current control TFT, and the power supply line is equivalent to a source follower. Therefore, since the gate potential of the current control TFT is a low value, a large voltage drop occurs here, and the organic light emitting element is not sufficiently reverse-biased.

As described above, even if an AC waveform is output between the counter power source 906 and the power supply line, the organic light emitting element may not be sufficiently reverse-biased. This is the same even when the current control TFT is an n-channel type so that current flows from the anode to the cathode of the organic light emitting device when the pixel electrode of the organic light emitting device is the cathode and the counter electrode is the anode. .

  As described above, in the conventional circuit configuration described above, it is difficult to drive the organic light emitting element with an alternating current, and there is a problem in that the luminance of the organic light emitting element is significantly decreased with time by application of a direct current voltage.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a display device configured to drive an organic light emitting element by applying an alternating voltage, prevent a decrease in luminance of the organic light emitting element, and improve display quality, and a driving method thereof. And

  By adding an element having a rectifying characteristic (hereinafter referred to as a rectifying element) to a conventional circuit, the organic light emitting element can be driven with an alternating current.

  If the circuit in which the rectifier element and the semiconductor layer of the current control TFT are connected in parallel, even if one of the rectifier element and the semiconductor layer of the current control TFT has a high resistance, the other has a low resistance. The voltage corresponding to the low resistance can be applied to the organic light emitting device.

  The rectifying element is an element having a rectifying characteristic in which a characteristic curve representing a relationship between an applied voltage and a current flowing through the rectifying element is asymmetric with respect to the origin. When a voltage with one polarity is applied to the rectifying element, current flows, but when a voltage with the other polarity is applied to the rectifying element, almost no current flows. The direction in which current flows easily is called the forward direction, and the direction in which current does not flow easily is called the reverse direction.

  An example of a circuit to which the present invention is applied will be described with reference to FIG. FIG. 17 is an equivalent circuit of the pixel 100. The present invention has a configuration in which a rectifying element 109 is provided in parallel with the semiconductor layer of the current control TFT 102 in a conventional closed circuit in which the semiconductor layer of the current control TFT 102 and the organic light emitting element 105 are connected in series to the AC power source 106. is there. For convenience of explanation, the conductivity type of the current control TFT is a p-channel type.

In FIG. 17, the AC power supply 106 and the power supply line (V _i ) are connected, and the AC power supply 106 and the organic light emitting element 105 are connected by a dotted line. This is because an AC power supply is arranged outside the pixel portion where the pixels 100 are arranged in a matrix, and an AC waveform is supplied from the AC power source to the pixel 100 via a connection wiring 113 that connects the AC power supply and the pixel portion. Is meant to do.

The forward bias is applied to the organic light emitting device as follows. The potential of the counter electrode of the organic light emitting element 105 is set to the Lo level, the potential of the power supply line (V _i ) is set to the Hi level, and the potential of the gate of the current control TFT 102 is made higher than the potential of the power supply line. Lower the threshold or more. Then, the current control TFT is turned on, that is, becomes conductive. As a result, a forward bias is applied to the organic light emitting element, and a voltage is applied to the rectifying element 109 in the reverse direction.

The reverse bias is applied to the organic light emitting device as follows. The potential of the counter electrode of the organic light emitting element 105 is set to the Hi level, and the potential of the power supply line (V _i ) is set to the Lo level. At this time, regardless of whether the gate potential of the current control TFT is high or low, a voltage is applied to the rectifying element 109 in the forward direction, and a reverse bias is applied to the organic light emitting element.

  As described above, in a circuit in which the rectifier element 109 and the semiconductor layer of the current control TFT 102 are connected in parallel, at least one of the rectifier element and the semiconductor layer of the current control TFT depends on the polarity of the voltage output from the AC power source 106. However, the resistance becomes low enough to allow current to flow there. In this way, either forward bias or reverse bias can be applied to the organic light emitting element by the AC power supply.

  In order to enable AC driving, the forward direction of the rectifying element 109 is opposite to the direction of the current flowing when the current control TFT 102 is turned on. In other words, the forward direction of the rectifying element 109 is opposite to the forward direction of the organic light emitting element 105 having a diode structure.

  The circuit shown in FIG. 17 is an example of the present invention, and the conductivity type of the current control TFT 102, the rectifying direction of the rectifying element 109, and the rectifying direction of the organic light emitting element 105 having a diode structure are within the range where the effects of the present invention are exhibited. It can be decided freely.

18A to 18B show examples of waveform diagrams when the organic light emitting element is driven by alternating current. The horizontal axis represents time, and the vertical axis represents voltage. The driving method shown in FIG. 18A, in which the potential (V _c ) of the counter electrode is made constant and the potential (V _Vi ) of the power supply line is changed when driving by inputting a signal from the AC power source, the potential of the counter electrode Any of the driving methods shown in FIG. 18B for changing both the potential (V _c ) and the potential (V _Vi ) of the power supply line can be employed.

  However, in general, it is more preferable to adopt the driving method shown in FIG. 18B in which the potentials of both the counter electrode and the power supply line are changed. In FIG. 18B, since the amplitude of the voltage output from the AC power supply is smaller than that in the driving method of FIG. 18A, a low-voltage driven AC power supply can be used, and the cost of the AC power supply can be reduced. It becomes possible. When the amplitude of the voltage of the AC power supply is reduced, the load applied to the circuit constituting the AC power supply is reduced and the reliability of the AC power supply is improved. Furthermore, it is advantageous from the viewpoint of low cost that the total number of power supply systems is reduced.

The configuration of the display device of the present invention will be described below.
A display device including a plurality of pixels, wherein each of the pixels includes a transistor, an organic light emitting element, and an element having a rectifying characteristic, and one of the source and drain of the transistor is the organic light emitting element. And the other is connected to one of the AC power supplies, and the element having the rectifying characteristic is connected to the one of the AC power supplies and the pixel electrode of the organic light emitting element. The counter electrode of the organic light emitting element is connected to the other side of the AC power supply, and the forward direction of the element having the rectifying characteristic and the forward bias of the organic light emitting element are opposite to each other. Display device.

  A display device including a plurality of pixels, each of which includes a switching transistor, a current control transistor, a rectifying transistor, and an organic light emitting element, and a gate of the switching transistor. Is connected to the gate signal line, one of the source and drain is connected to the source signal line, and the other is connected to the gate of the current control transistor, and one of the source and drain of the current control transistor is connected to one of the AC power supplies, The other is connected to the pixel electrode of the organic light emitting element, the gate of the rectifying transistor is one of the AC power supplies, the source or drain is one of the AC power supplies, and the other is the pixel electrode of the organic light emitting element. The counter electrode of the organic light emitting element is connected to the other of the AC power supply, The flow control transistor and the rectifier transistor, a display device conductivity type, characterized in that the same.

  In the above structure, the pixel electrode of the organic light emitting element is an anode, the counter electrode is a cathode, and the conductivity type of the current control transistor and the rectifying transistor is a p-channel type. Alternatively, the pixel electrode of the organic light emitting element is a cathode and the counter electrode is an anode, and the conductivity type of the current control transistor and the rectifying transistor is an n-channel type.

  In each of the above structures, the transistor or the switching transistor, the current control transistor, and the rectification transistor are thin film transistors.

  In each of the above structures, the plurality of pixels are integrally formed with a driving circuit for the pixels on a glass substrate.

  Alternatively, each pixel includes a transistor, an element having a rectifying characteristic, and an organic light emitting element, and one of the source and drain of the transistor is one of an AC power supply and the other is the organic light emitting element. One of the elements having the rectifying characteristic is connected to one of the AC power supplies and the other is connected to the pixel electrode of the organic light emitting element, and the counter electrode of the organic light emitting element is connected to the AC power supply. A driving method of a display device connected to the other of the above, wherein when a voltage is applied in the forward direction of the element having the rectification characteristic with the AC power source, a reverse bias is applied to the organic light emitting element, and the rectification characteristic is obtained. A driving method of a display device, wherein the reverse bias applied to the organic light emitting element is removed when a voltage is applied in the reverse direction of the element.

  Each of the pixels includes a switching transistor, a current control transistor, a rectifying transistor, and an organic light emitting element. The gate of the switching transistor is a gate signal line, and one of the source and drain is The other is connected to the source signal line and the other is connected to the gate of the current control transistor. One of the source and drain of the current control transistor is connected to one of the AC power supplies, and the other is connected to the pixel electrode of the organic light emitting element. The rectifying transistor has a gate connected to one of the AC power supplies, a source or drain connected to one of the AC power supplies and the other connected to a pixel electrode of the organic light emitting element, and facing the organic light emitting element. An electrode is a driving method of a display device connected to the other side of the AC power source, and the AC power source The reverse bias is applied to the organic light emitting device when a voltage is applied in the forward direction of the rectifying transistor, and the reverse bias applied to the organic light emitting device is removed when a voltage is applied in the reverse direction of the rectifying transistor. A driving method of a display device.

  In each of the above configurations, an address period in which a data signal is input to the organic light emitting element, and a sustain period in which the organic light emitting element emits light or does not emit light according to the data signal. A method for driving a display device, characterized in that the polarity of a voltage output from the AC power supply changes when changing to a sustain period.

  In each of the above structures, there is a standby period in which a voltage having the same polarity as the address period is output from an AC power source between the address period and the sustain period.

  In each of the above-described structures, a driving method of a display device, characterized in that a plurality of the address periods and the sustain periods having different lengths are provided to form one frame period and time-division gray scale display is performed.

  In each configuration, when the reverse bias and the forward bias are applied to the organic light emitting element with the AC power supply, the potential of the pixel electrode of the organic light emitting element and the potential of the counter electrode change simultaneously. A display device driving method.

  The present invention having the above configuration will be described in detail in the following embodiments and examples. Note that the embodiments and examples can be used in appropriate combinations. Further, the configuration of the present invention is not limited to the following embodiments and examples.

  In the pixel of the organic light emitting display of the present invention, a reverse bias can be easily applied to the organic light emitting element by using a rectifying element. As a result, it is possible to suppress a decrease in the luminance of the organic light emitting element that is generated by direct current driving and to ensure good display quality.

  In addition, when driving the organic light emitting element with an alternating current, if the driving that changes both the counter electrode of the organic light emitting element and the potential of the power supply line is used, the alternating current power source that outputs an alternating current waveform can be driven with a low voltage. It is possible to realize stability of long-term operation of the AC power supply and cost reduction of the AC power supply.

An example of the circuit diagram of the pixel of the organic light emitting display of this invention, and a pixel part. 3 is a timing chart of driving for performing time-division gradation display according to the first embodiment. 3 is a timing chart of driving for performing time-division gradation display according to the first embodiment. An example of the wave form diagram which shows the method of alternating current drive of the organic light emitting element of Embodiment 2. FIG. 10 is a timing chart of driving for performing time-division gradation display according to the third embodiment. FIG. 6 is an example of a circuit diagram of a pixel and a pixel unit of the organic light emitting display according to the fourth embodiment. 10 is a timing chart of driving for analog gradation display according to the fourth embodiment. 10 is a timing chart of driving for analog gradation display according to the fourth embodiment. 10 is a timing chart of driving for analog gradation display according to the fifth embodiment. Sectional drawing of the pixel part of the organic light emitting display of Example 1, and a drive circuit part. FIG. 3 is a top view of a pixel portion of the organic light emitting display according to the first embodiment. FIG. 3 is a top view of a pixel portion of the organic light emitting display according to the first embodiment. FIG. 3 is a circuit diagram of a pixel of the organic light emitting display according to the first embodiment. FIG. 6 is a perspective view showing an appearance of an organic light emitting display according to Example 3. FIG. 10 is a perspective view illustrating an example of an electronic apparatus according to a fifth embodiment. FIG. 10 is a perspective view illustrating an example of an electronic apparatus according to a fifth embodiment. An example of the circuit diagram of the pixel of the organic light emitting display of this invention. An example of the wave form diagram which shows the method of the alternating current drive of this invention. An example of the circuit diagram of the pixel of the conventional organic light emitting display.

[Embodiment 1] An example in which the configuration of the present invention is applied to an organic light emitting display that performs gradation display by time division driving will be described. Gradation display by time-division driving is a gradation display method for controlling the gradation of each pixel by combining a plurality of periods with different light emission times.

FIG. 1A is an equivalent circuit of a pixel. Signals are input to each pixel 100 from the gate signal line (G _j ) and the source signal line (S _i ). Each pixel includes a switching TFT 101, a current control TFT 102, a capacitor 103, a rectifying TFT 104, and an organic light emitting element 105. The AC power supply 106 applies a potential to the power supply line (V _i ) and the counter electrode of the organic light emitting element 105.

The gate electrode of the switching TFT 101 is connected to a gate signal line (Gj) for inputting a selection signal. One of the source and the drain of the switching TFT is connected to the source signal line (S _i ) for inputting a digital image data signal (hereinafter referred to as a digital data signal) having information “0” or “1”. Are connected to the gate electrode of the current control TFT 102 and one electrode of the capacitor 103 of each pixel. The other electrode of the capacitor is connected to the power supply line (V _i ). The capacitor 103 is provided to hold the gate voltage of the current control TFT 102 when the switching TFT 102 is in a non-selected state.

The current control TFT 102 has a source and a drain, one connected to the power supply line (V _i ) and the other connected to the pixel electrode of the organic light emitting element 105.

One of the source and the drain of the rectifying TFT 104 is connected to the power supply line (V _i ), and the other is connected to the pixel electrode of the organic light emitting element 106. The gate electrode of the rectifying TFT 104 is connected to the power supply line (V _i ). The rectifying TFT 104 has a rectifying characteristic in which current flows only in one direction because the gate electrode and one of the source and the drain are connected.

  It is desirable that the rectifying TFT 104 and the current control TFT 102 have the same conductivity type. In this embodiment mode, the conductivity type of the current control TFT and the rectification TFT is a p-channel type. Note that the conductivity type of the switching TFT 101 may be an n-channel type or a p-channel type.

  The rectifying characteristic of the rectifying TFT 104 is that the rectifying TFT is a p-channel type, and one of the gate and the source or drain is connected, so that current easily flows only from the organic light emitting element side to the power supply line side. It is a characteristic.

  The organic light emitting element 105 includes an organic compound layer, and a cathode and an anode that sandwich the organic compound layer. In this embodiment, the pixel electrode of the organic light emitting element connected to the current control TFT 102 and the rectifying TFT 104 is used as an anode, the counter electrode of the organic light emitting element is used as a cathode, and a current flows from the pixel electrode to the counter electrode. The element is configured to emit light.

The AC power source 106 is connected to the counter electrode of the organic light emitting element 105 and the power supply line (V _i ). In this embodiment mode, AC driving is performed by simultaneously changing the potential of the counter electrode and the potential of the power supply line. A potential difference is provided between the counter electrode and the power supply line so that the organic light emitting element emits light when the current control TFT is turned on.

  Contrary to this embodiment, the current control TFT and the rectifying TFT are used as an n-channel type, the pixel electrode of the organic light emitting element is used as a cathode, the counter electrode is used as an anode, and the organic light emitting element is formed from the counter electrode to the pixel electrode. You may make it light-emit and to light-emit.

FIG. 1B is an equivalent circuit of the pixel portion. The pixel unit 110 includes pixels 100 arranged in a matrix, and includes gate signal lines (G _{1 to} G _n ) and source signal lines (S _{1 to} S _m ).
In addition, a signal is input to each pixel from an AC power source (not shown) to control the luminance of each pixel.

The gate signal lines (G _{1 to} G _n ) are connected to the gate electrode of the switching TFT included in each pixel. One of the source and drain of the switching TFT is connected to the source signal line (S _{1 to} S _m ), and the other is connected to the capacitor and the gate electrode of the current control TFT.

One of the source or drain of the current control TFT is connected to the power supply line (V _{1 to} V _m ), and the other is connected to the pixel electrode of the organic light emitting element. The gate electrode of the rectifying TFT is connected to a power supply line (V _{1 to} V _m ). One of the source or drain of the rectifying TFT is connected to the power supply line (V _{1 to} V _m ), and the other is connected to the pixel electrode of the organic light emitting element. The counter electrode of the organic light emitting element and the power supply line (V _{1 to} V _m ) are connected to an AC power source.

In the present embodiment, for the sake of simplicity, a single color pixel is used, and the relationship between the voltage applied to the organic light emitting element and the light emission intensity of the organic light emitting element is the same in all pixels arranged in a matrix in the pixel portion. Will be described. Therefore, the power supply line (V ₁ ~V _m)
Is a common potential for all the pixels provided in the pixel portion. The counter electrode also has a common potential in all the pixels provided in the pixel portion.

  Next, a driving method of the organic light emitting display having the circuit of the pixel portion of FIG. 1 will be described. First, an example of gradation display by time division driving according to the present embodiment will be described with reference to FIG.

One frame period (F) is divided into _n subframe periods (SF _{1 to} SF _n ). For simplicity, only the first subframe period (F ₁ ) and the second subframe period (F ₂ ) are shown. One frame period refers to a period during which one image whose gradation is controlled is formed. In this embodiment, 60 or more frame periods are provided per second. When the number of images displayed per second is less than 60, images such as flicker visually start to stand out.

The subframe period (SF _{1 to} SF _n ) is a period obtained by further dividing one frame period. As the number of gradations increases, the number of divisions in one frame period also increases, and the drive circuit must be driven at a high frequency.

One subframe period includes an address period (Ta) and a subframe period (Ts).
And divided. The address period is a period required to input data to all the pixels in one subframe period, and the sustain period is displayed by flowing a constant current through the organic light emitting element according to the data input to the pixels. It is a period to perform.

The lengths of the address periods (Ta _{1 to} Tan) included in the _n subframe periods (SF _{1 to} SF _n ) are constant. The lengths of the sustain periods (Ts) included in the _n subframe periods (SF _{1 to} SF _n ) are different. The lengths of the subframe periods (SF _{1 to} SF _n ) are Ts _{1 to} Ts _n , respectively.

The length of the sustain period is as follows: Ts ₁ : Ts ₂ : Ts ₃ :...: Ts _(n−2) : Ts _(n−1) : Ts _n = 2 ¹ : 2 ² : 2 ^{3 :. 2)} : Set to 2 ^(n-1) . Although the length of the sustain period varies depending on the subframe period, the order in which the subframe periods (SF _{1 to} SF _n ) appear may be any way. A desired gradation display among 2 ⁿ gradations can be performed by combining the sustain periods.

  Next, a signal input to the pixel in order to perform time-division gradation display at the timing shown in FIG. 2 will be described with reference to the timing chart of FIG. In order to simplify the description, only the first subframe period and the second subframe period are illustrated in one frame period.

The first subframe period (SF ₁ ) includes a first address period (Ta ₁ ) and a first sustain period (Ts ₁ ). The address period is divided into a _first line period (L ₁ ) to an nth line period (L _n ).

The first line period (L ₁₎ is supplied with the selection signal to the gate signal line (G _1), a period in which all of the switching TFT is turned on, which is connected to the gate signal line (G ₁₎ is there.

With the switching TFT connected to the gate signal line (G ₁ ) turned on, digital data signals are sequentially input to the source signal lines (S _{1 to} S _m ). The digital data signal is input to the gate electrode of the current control TFT through the switching TFT that is turned on.

Then, the digital data signal input to the source signal lines (S _{1 to} S _m ) is input to the gate electrode of the current control TFT via the switching TFT in the ON state. In addition, a digital data signal is input and held in the capacitor.

Since the digital data signal is held in the capacitor, the potential of the gate electrode of the current control TFT is held even when the switching TFT connected to the gate signal line (G ₁ ) is turned off.

When a digital data signal is input to the m-th column source signal line (S _m ), the first line period (L ₁ ) ends. The period until the input of the digital data signal to the source signal lines (S _{1 to} S _m ) and the horizontal blanking period may be combined into one line period.

The second line period (L ₂ ) is a period in which a selection signal is input to the gate signal line (G ₂ ) and all the switching TFTs connected to the gate signal line G ₂ are in an on state. Then, digital data signals are sequentially input to the signal lines (S _{1 to} S _n ) with the switching TFT turned on. The digital data signal is input to the gate electrode of the current control TFT via the switching TFT. In addition, a digital data signal is input and held in the capacitor.

  The above-described operation is repeated until the n-th line period, and digital data signals are input to all pixels. That is, the period until the digital data signal is input to all the pixels is the address period. Note that a period in which digital data signals are input to all pixels and a vertical blanking period may be combined to form an address period.

During the address period, the potential of the power supply lines (V _{1 to} V _n ) is kept lower than the potential of the gate electrode of the current control TFT. For this reason, the current control TFT is turned off. However, a voltage is applied in the forward direction to the rectifying TFT, and a reverse bias is applied to the organic light emitting element through the rectifying TFT. At this time, since no current flows through the organic light emitting device, the organic light emitting device is kept in a non-light emitting state.

When the first address period (Ta ₁ ) ends, the first sustain period (Ts ₁ ) starts. When the sustain period starts, the polarity of the voltage output from the AC power supply changes. By changing the waveform input from the AC power supply, the potential (V _{1 to} V _n ) of the power supply line becomes higher than the potential (C) of the counter electrode.

  When the current control TFT is turned on during the sustain period and a voltage higher than the threshold is applied to the organic light emitting element, the organic light emitting element emits light. However, the off state is maintained in the pixel in which the non-light-emitting digital data signal is written in the gate of the current control TFT. In any case, the reverse bias of the organic light emitting element applied during the address period is removed.

  In this manner, in an arbitrary sub-frame period in which the organic light emitting element emits light, voltages having different polarities in the address period and the sustain period are driven by alternating current applied to the organic light emitting element. Note that the AC driving method using the circuit of the present invention is not limited to this.

  When the first sustain period ends, the polarity of the voltage output from the AC power supply changes, and the first subframe period ends. When the first subframe period ends, the second subframe period begins.

  When the polarity of the voltage output from the AC power supply is changed after the first sustain period is over, the potential of the gate of the current control TFT becomes lower than the threshold value by the potential of the power supply line, and the transistor is turned off. Then, the rectifying TFT is turned on, and the organic light emitting elements of all the pixels are in a non-light emitting state due to reverse bias.

  In the second subframe period, the second address period starts, and when the digital data signal is sequentially input to the pixels and the digital data signal is input to all the pixels from the first line period to the nth line period, the second address period starts. 2 address period ends, and the second sustain period starts. When the second sustain period ends, the second subframe period ends.

  Thereafter, the same operation is repeated from the third subframe to the nth subframe, an address period and a sustain period are sequentially set, and display is performed in each sustain period.

  When the nth subframe period ends, the first frame period ends. At this time, the gradation of the pixel is determined by integrating the length of the sustain period during which the pixel is emitting light.

  As described above, the organic light emitting element can be driven with an alternating current while driving the organic light emitting display. The present invention can be applied to a time-division driven organic light emitting display.

According to the present embodiment, the polarity of the voltage applied to the organic light-emitting element can be set by simple means by simply providing a rectifying TFT in each pixel and changing both the power supply line and the potential of the counter electrode using an AC power supply. It can be changed and AC driven.

[Embodiment 2] In a color organic light-emitting display, the material of the light-emitting layer is different for pixels that display red, blue, and green light. When they are different, one of the potentials of the power supply line or the counter electrode may be changed for each color displayed by the pixel.

For example, the driving method of the organic light emitting display shown in the waveform diagram of FIG. 4 can be used. The potential applied from the AC power source to the power supply line and the counter electrode of the organic light emitting element is shown. The potential of the power supply line is changed depending on the color displayed by the pixel. The horizontal axis represents time, and the vertical axis represents voltage. For simplicity, only the first subframe (SF ₁ ) and the second subframe (SF ₂ ) are shown. The plurality of subframe periods constituting the first frame period are divided into an address period (Ta _{1 to} Ta ₂ ) and a sustain period (Ts _{1 to} Ts ₂ ). When changing from the address period to the sustain period, the waveform output from the AC power supply changes. The potential of the counter electrode potential of (V _c) power supply line relative to the, the potential (V _ViR) of the power supply line of the pixel for emitting red light, the potential of the power supply line of the pixel that emits blue (V _ViB) , _And varies depending on the potential (V _ViG ) of the power supply line of the pixel emitting green light.

In addition, when the organic light emitting element emits white light and performs color display by passing through a color filter, or in the case of monocolor display, the material of the light emitting layer of the organic light emitting element is common to all pixels. . In this case, it is preferable that the potential of the counter electrode and the potential of the power supply line are common to all the pixels. An example in which the potentials of the power supply lines (V ₁ to _m ) and the counter electrode (C) are made common is Embodiment 1 and has already been described with reference to FIG.

[Embodiment 3] In the present embodiment, the sustain period is started by changing the polarity of the AC voltage output from the AC power supply after a certain waiting period after the address period ends.

The circuit of the pixel portion of the organic light emitting display of the present embodiment is the same as that of the first embodiment. The driving method of the organic light emitting display is different from that of the first embodiment. Therefore, a difference from the first embodiment will be described with reference to a timing chart of FIG. 5 showing driving of the organic light emitting display. The parts having the same functions as those in FIG. For convenience of explanation, only the first subframe period (SF ₁ ) and the second subframe period (SF ₂ ) are illustrated. The subframe period (SF) is divided into an address period (Ta), a standby period (Tw), and a sustain period (Ts).

For example, in the first address period (Ta ₁ ) and the first standby period (Tw ₁ ), a voltage is applied in the forward direction to the rectifying TFT, so that a reverse bias is applied to the organic light emitting element. Therefore, the organic light emitting device does not emit light.

After the first standby period (Tw ₁ ) ends, the waveform output from the AC power supply is changed to start the first sustain period (Ts ₁ ). When the waveform output from the AC power supply changes, the potentials of the counter electrode (C) and the power supply lines (V _{1 to} V _m ) of the organic light emitting element change.

In the first sustain period, ON / OFF of the current control TFT is determined according to the digital data signal input to the pixel. The organic light emitting device emits light when the current control TFT is on, and does not emit light when the current control TFT is off. In any case, the reverse bias applied to the organic light emitting element is removed.

By adjusting the length of the standby period according to the present embodiment, it is possible to adjust the time during which reverse bias is applied to the organic light emitting element in one subframe period.
Switching from the standby period to the sustain period only requires changing the waveform output from the AC power supply, and does not require a complicated circuit.

[Embodiment 4] In this embodiment, an example of a method of driving an organic light emitting display that displays gradation by analog driving will be described. The analog drive is a method of performing gradation display by controlling the intensity of light emitted from the organic light emitting element by changing the amount of current flowing through the organic light emitting element in an analog manner.

A circuit of the pixel portion of this embodiment is shown in FIGS. The gate signal lines (G _{1 to} G _n ) are connected to the gate electrode of the switching TFT 101 included in each pixel. One of the source and drain of the switching TFT is connected to the source signal lines (S _{1 to} S _m ), and the other is connected to the gate electrode of the current control TFT 102 and the capacitor 103 included in each pixel. One of the source and drain of the current control TFT is connected to the power supply line (V _{1 to} V _m ), and the other is connected to the organic light emitting element 105 of each pixel. The power supply line is connected to the gate electrode of the rectifying TFT 104 and the capacitor 103. One of the source and drain of the rectifying TFT is connected to the power supply line, and the other is connected to the pixel electrode of the organic light emitting element.

In the present embodiment, the organic light emitting element has a pixel electrode as a cathode and a counter electrode as an anode. The current control TFT is an n-channel type in order to allow a current to flow through the organic light emitting element in the forward direction. Similarly to the current control TFT, the rectification TFT is an n-channel type and has a rectification action in the direction opposite to the direction of the current flowing when the current control TFT is in the ON state.
The switching TFT may be either an n-channel type or a p-channel type.

  Since the current control TFT is an n-channel type, when the potential of the gate of the current control TFT is higher than the threshold value and higher than the potential of the power supply line, the current control TFT is turned on.

  Since the rectifying TFT is an n-channel type and its gate electrode is at the same potential as the power supply line, the direction of the forward current is such that the current flows from the organic light emitting element side to the power supply line side. Become.

  A timing chart for driving an organic light emitting display having the circuit shown in FIG. 6 with analog gradation will be described with reference to FIGS.

  As shown in the timing chart of FIG. 7, each frame period is divided into one address period (Ta) and one sustain period (Ts). The address period is a period in which analog signals are sequentially input to all pixels. The sustain period is a period in which a current flows through the organic light emitting element in accordance with the potential of the analog signal input to the pixel and gradation display is performed in accordance with the potential of the analog signal input to the pixel.

FIG. 8 shows signals input to each pixel. The first line period (L ₁ ) starts simultaneously with the start of the address period (Ta ₁ ) of the first frame (F ₁ ). The first line period is a period during which the gate signal line (G ₁ ) is selected.

  Since there are n gate signal lines, n line periods are provided in the address period. As the resolution increases, the number of line periods also increases and the drive circuit must be driven at a high frequency.

In the first line period, a selection signal is input to the gate signal line. A data signal (analog data signal) whose potential is changed in an analog manner is input to the source signal lines (S _{1 to} S _m ). Since the selection signal is input to the gate signal line and the switching TFT is turned on, an analog data signal is input from the source signal line to the gate electrode of the current control TFT via the switching TFT. The potential of the analog data signal is held by a capacitor connected to one of the source and drain of the current control TFT and the power supply line.

When a signal is input from the source signal line (S _m ) to the pixel, the first line period (L ₁ ) ends. The period until the input of the analog video signal to the source signal lines (S _{1 to} Sm) and the horizontal blanking period may be combined into one line period. Simultaneously with the end of the first line period, the second line period begins.

When the second line period (L ₂ ) starts, a selection signal is input to the gate signal line (G ₂ ). Similarly to the first line period (L ₁ ), analog video signals are sequentially input to the source signal lines (S _{1 to} Sm).

When selection signals are input to all the gate signal lines (G _{1 to} Gn), all the line periods (L _{1 to} L _n ) are finished. When all the line periods are finished, the address period is finished. All the line periods (L _{1 to} L _n ) and the vertical blanking period may be combined as an address period.

  In the address period, since a voltage is applied in the forward direction to the rectifying TFT having the rectifying characteristics, a reverse bias is applied to the organic light emitting element. Therefore, the organic light emitting device is in a non-light emitting state.

  When the address period ends, the sustain period begins. When the sustain period begins, the polarity of the voltage output from the AC power supply is reversed.

  When the polarity of the voltage output from the AC power supply is reversed, a current flows through the current control TFT according to the magnitude of the gate voltage of the current control TFT. The amount of current flowing through the current control TFT is controlled by the height of the potential of the analog data signal input to the gate during the address period.

  The intensity of light emitted from the organic light emitting element is controlled in accordance with the amount of current flowing through the current control TFT. When the address period starts again, a reverse bias is applied to the organic light emitting element, and voltages having different polarities are applied to the organic light emitting element during the sustain period and the address period, thereby driving alternating current.

  Since the rectifying TFT has a rectifying characteristic and a voltage is applied in the reverse direction of the rectifying characteristic during the sustain period, no current flows through the rectifying TFT during the sustain period.

  When the sustain period ends, the polarity of the voltage output from the AC power supply changes. Simultaneously with the end of the sustain period of the first frame, the second frame period begins and the address period of the second frame period begins. Thereafter, the same operation is repeated to display an image whose gradation is controlled for each frame period.

  In the present embodiment, the example in which the organic light emitting element is reverse-biased in the address period has been described above, but the present invention is not limited to this. It is also possible to apply a forward bias to the organic light emitting element during the address period and the sustain period and reverse bias during the standby period by appropriately changing the waveform output from the AC power supply.

[Embodiment 5] The present invention provides a time for freely applying voltages having different polarities to an organic light emitting element by changing the time of inverting the potential of the power supply line and the counter electrode of the organic light emitting element when performing analog driving. Can be changed.

  The circuit of the pixel portion in this embodiment is the same as that described with reference to FIG.

  An embodiment of the present invention will be described with reference to the drawings. FIG. 9 is a timing chart of the driving method of the present embodiment. Portions having functions equivalent to those in FIG. 8 are denoted by the same reference numerals, and portions different from those in FIG. 8 are described.

  When the address period (Ta) ends, the waiting period (Tw) starts, and when the waiting period ends, the sustain period (Ts) starts. The potential of the power supply line and the counter electrode of the organic light emitting element is maintained at a constant potential during the address period and the standby period, and is inverted when the standby period ends and the sustain period starts.

  In the address period and the standby period, the organic light emitting element is in a non-light emitting state because a reverse bias is applied to the organic light emitting element having a diode structure. During the sustain period, a forward bias is applied to the organic light emitting device having a diode structure. Thus, the polarity of the voltage applied to the organic light emitting element can be changed between the address period, the standby period, and the sustain period.

  A voltage is applied to the rectifying TFT in the reverse direction and a forward bias is applied to the organic light emitting element, and a case in which a voltage is applied in the forward direction to the rectifying TFT and the organic light emitting element is applied with a reverse bias. It can be controlled by changing the potential of the counter electrode using an AC power source. That is, the polarity of the voltage applied to the organic light emitting element is determined by the polarity of the voltage output from the AC power supply.

In this example, by setting the length of the standby period, it is possible to freely determine the time for applying voltages of different polarities to the organic light emitting elements.

  The present invention can be applied to any display device using an organic light emitting element. FIG. 10 shows an example thereof, which shows an example of an active matrix display device manufactured using TFTs.

  The TFT of the embodiment may be distinguished from an amorphous silicon TFT or a polysilicon TFT depending on the material of the semiconductor layer forming the channel formation region, but the present invention can be applied to either of them. However, since it is possible to increase the light emission intensity of the organic light emitting device when using a polysilicon TFT having a high electric field mobility, it is preferable to use a polysilicon TFT as the TFT of this embodiment.

  As the substrate 401, a substrate made of glass such as quartz, barium borosilicate glass typified by Corning # 7059 glass or # 1737 glass, or aluminoborosilicate glass is used.

Next, a base film 402 made of an insulating film such as a silicon oxide film, a silicon nitride film, or a silicon oxynitride film is provided. For example, a silicon oxynitride film 402a formed from SiH ₄ , NH ₃ , and N ₂ O by plasma CVD is formed to a thickness of 10 to 200 nm (preferably 50 to 100 nm), and similarly formed from SiH ₄ and N ₂ O. A silicon oxynitride film 402b is formed to a thickness of 50 to 200 nm (preferably 100 to 150 nm). Although the base film 402 is shown as a two-layer structure in this embodiment, it may be formed as a single-layer film of the insulating film or a structure in which two or more layers are stacked.

  Next, a semiconductor layer is formed and patterned, and the first semiconductor layer 403, the second semiconductor layer 404, the third semiconductor layer 405, the fourth semiconductor layer 406, the fifth semiconductor layer 407, and the sixth semiconductor layer are patterned. The semiconductor layer 408 is formed.

Further, a gate insulating film 409 is formed so as to cover these semiconductor layers. The gate insulating film is a silicon nitride oxide film manufactured from SiH ₄ and N ₂ O, and is formed here with a thickness of 10 to 200 nm, preferably 50 to 150 nm.

  Further, tantalum nitride (TaN) is formed by sputtering, and then an aluminum alloy containing aluminum (Al) as a main component is formed. The conductive film stacked in the two layers is patterned to form a gate signal line 410, an island-shaped gate electrode 411, a capacitor electrode 412, and a gate electrode 413, and an impurity element is added in a self-aligning manner using these electrodes as a mask. To do.

Next, a silicon oxynitride film formed from SiH ₄ , NH ₃ , and N ₂ O is formed by plasma CVD as a first interlayer insulating film 414 with a thickness of 10 to 200 nm (preferably 50 to 100 nm). It is also possible to form an oxynitride film as the first interlayer insulating film. Further, a second interlayer insulating film 415 made of an organic resin film is formed to 0.5 to 10 μm (preferably 1 to 3 μm). As the second interlayer insulating film, an acrylic resin film, a polyimide resin film, or the like can be preferably used. It is desirable that the second interlayer insulating film has a thickness sufficient to flatten unevenness caused by the semiconductor layer, the gate electrode, and the like.

Further, a silicon oxynitride film manufactured from SiH ₄ , NH ₃ , and N ₂ O by plasma CVD is used as a protective film 416 to have a thickness of 10 to 200 nm (preferably 50 to 100 nm)
The thickness is formed. The cathode, which is an electrode material constituting the organic light-emitting element described later, contains an alkali component, but the protective film prevents the alkali component from flowing out and degrading the electrical characteristics of the TFT. In this embodiment, the protective film is formed of a silicon oxynitride film, but a silicon nitride film may be used instead of the silicon oxynitride film.

  Next, the first interlayer insulating film, the second interlayer insulating film, the protective film, and the gate insulating film are selectively etched to form a contact hole, and a conductor film is formed so as to cover the contact hole. Then, patterning is performed. This conductor film has a laminated structure of a Ti film having a thickness of 50 nm and an alloy film (alloy film of Al and Ti) having a thickness of 500 nm.

  In the driver circuit portion 438, wirings 417 to 420 are formed. In the pixel portion, a source signal line 421, a connection electrode 422, a drain side electrode 423, and a power supply line 424 are formed. A source signal line 421 is connected to the source of the switching TFT 434, and a connection electrode 422 is connected to the drain. Although not shown, the connection electrode 422 is connected to the gate electrode 412 of the current control TFT 436. A power supply wiring 424 is connected to the source of the current control TFT 436, and a drain-side electrode 423 is connected to the drain. The gate electrode 412 and the drain of the rectifying TFT are connected to the power supply line 424, and the source is connected to the drain-side electrode 423. Note that the switching TFT is an n-channel TFT, and the current control TFT and the rectifying TFT are p-channel TFTs.

  The power supply line is a common electrode for each of red, blue, and green pixels from which the organic light emitting element emits light. That is, the power supply line is provided for each color emitted by the organic light emitting element in the pixel portion.

  As described above, the driver circuit portion 438 including the n-channel TFT 432 and the p-channel TFT 433, the switching TFT 434, the rectifying TFT 435, the current control TFT 436, and the pixel portion 439 including the storage capacitor 437 are formed over the same substrate. Can be formed.

  Next, an ITO (Indium Tin Oxide) film is formed by a vacuum sputtering method, and this ITO film is patterned for each pixel so as to be in contact with the drain-side electrode 423 to form an anode (pixel electrode) of the organic light emitting device. ) 426 is formed. ITO has a high work function of 4.5 to 5.0 eV, and can efficiently inject holes into the organic light emitting layer.

  Next, a photosensitive resin film is formed, and this photosensitive resin film inside the peripheral edge of the anode is removed by patterning to form a bank 425. The bank forms an organic compound layer, which will be described later, along the smooth inclined surface of the bank, so that the organic compound layer is disconnected at the peripheral edge of the pixel electrode of the organic light emitting element, and the pixel electrode and the counter electrode are disconnected at the disconnected portion. Preventing short circuit.

  Next, an organic compound layer 427 of the organic light emitting element is formed by an evaporation method. The organic compound layer is used in a single layer or a stacked structure, but the light emission efficiency is better when used in a stacked structure. Generally, the hole injection layer / hole transport layer / light emitting layer / electron transport layer are formed on the anode in this order, but the hole transport layer / light emitting layer / electron transport layer, or hole injection layer / hole are formed. A structure such as a transport layer / a light emitting layer / an electron transport layer / an electron injection layer may be used. In the present invention, any known structure may be used.

  In this embodiment, color display is performed by depositing three types of light emitting layers corresponding to RGB. As a specific light emitting layer, cyanopolyphenylene may be used for a light emitting layer that emits red light, polyphenylene vinylene may be used for a light emitting layer that emits green light, and polyphenylene vinylene or polyalkylphenylene may be used for a light emitting layer that emits blue light. The thickness of the light emitting layer may be 30 to 150 nm. The above example is an example of an organic compound that can be used as the light emitting layer, and is not limited thereto.

  Next, a cathode (counter electrode) 428 of the organic light emitting element is formed by vapor deposition. For the cathode, a light reflective material containing a small amount of an alkali component such as MgAg or LiF is used. The thickness of the cathode is 100 nm to 200 nm. The counter electrode is formed as an electrode common to each pixel so as to cover the entire surface of the pixel portion, and is electrically connected to an FPC (Flexible Print Circuit) via a wiring.

  Thus, an organic light emitting device having a structure in which the organic compound layer is sandwiched between the anode and the cathode is formed. The pixel electrode of the organic light emitting element 429 is a transparent electrode, and a light reflective counter electrode is formed on the anode. For this reason, the light which an organic light emitting element light-emits can be radiated | emitted from the side shown by the arrow of FIG.

  Next, a DLC (Diamond Like Carbon) film is formed as the protective film 430 to prevent the organic light emitting element from being deteriorated by water vapor, oxygen or the like entering the sealing region of the organic light emitting display.

  The substrate formed with the above structure is referred to as an active matrix substrate in this specification.

  Next, a filler 440 is formed so as to cover the pixel portion 439 and the driver circuit portion 438. As this filler, an adhesive having a function of adhering the sealing substrate is used. As the filler, PVC (polyvinyl chloride), epoxy resin, silicone resin, PVB (polyvinyl butyral) or EVA (ethylene vinyl acetate) can be used. It is preferable to provide a desiccant inside the filler because the moisture absorption effect can be maintained.

  Further, the sealing substrate 431 is bonded to the active matrix substrate with an adhesive filler, and the encapsulation of the organic light emitting element is completed.

  Further, an FPC (Flexible Print Circuit) is connected to the connection wiring using an anisotropic conductive resin by a known method. The connection wiring receives a signal from the FPC serving as a connection terminal with an external device, and transmits the signal to the pixel and the driving circuit.

  FIGS. 11 to 12 are top views of the pixel portion of the organic light emitting display of this example fabricated as described above. The configuration of the pixel portion of this embodiment will be described with reference to FIGS.

  In FIG. 11 to FIG. 12, elements common to FIG. 10 are denoted by the same reference numerals. FIG. 10 shows a cross section obtained by cutting FIGS. 11 to 12 along a chain line AA ′, a chain line BB ′, a chain line CC ′, and a chain line DD ′.

  A first semiconductor layer 403, a second semiconductor layer 404, a third semiconductor layer 405, and a fourth semiconductor layer 406 are formed in each pixel on the substrate.

  A gate signal line 410 arranged in the row direction in contact with a gate insulating film (not shown) formed on these semiconductor layers, an island-shaped gate electrode 411, and a capacitor arranged in an island shape in the column direction An electrode 412 is formed.

  An impurity element is added to the semiconductor layer in a self-aligning manner using these gate signal lines, island-shaped gate electrodes, and capacitor electrodes as a mask, and a source or drain is formed in the semiconductor layer.

  A first interlayer insulating film made of an inorganic material, a second interlayer insulating film made of an organic material, and a protective film (both not shown) are formed so as to cover these wirings, electrodes and the like (FIG. 11). .

  Contact holes 501 to 509 are formed. A conductive film is formed in contact with the protective film, and the conductive film is patterned to form a source signal line 421, a connection electrode 422, a drain-side electrode 423, and a power supply line 424.

  The source signal line 421 arranged in the column direction is in contact with the first semiconductor layer 403 through the contact hole 501. The connection electrode 422 is in contact with the first semiconductor layer 401 through the contact hole 502 and is further in contact with the capacitor electrode 412 through the contact hole 503. The power supply line 424 arranged in the column direction is in contact with the island-shaped gate electrode 411 through the contact hole 504, is further in contact with the second semiconductor layer 404 through the contact hole 505, and is further in contact with the contact hole. It is in contact with the fourth semiconductor layer 406 through 506. The drain-side electrode 423 is in contact with the second semiconductor layer 404 through the contact hole 508 and is further in contact with the third semiconductor layer 405 through the contact hole 412.

  When a selection signal is input from the gate signal line 410 that is the gate electrode of the switching TFT, the data signal input to the source signal line 421 is connected to the connection electrode via a channel formed in the first semiconductor layer. 422 is entered.

  A data signal input from the source signal line to the connection electrode 422 through the switching TFT is input to the capacitor electrode 412 connected to the connection electrode.

  When a data signal is input to the capacitor electrode 412 that is the gate electrode of the current control TFT, a current flows between the power supply line 424 and the drain-side electrode 423 in accordance with the potential of the data signal. This current flows to the organic light emitting device connected in series with the current control TFT.

  The rectifying TFT has an island-shaped gate electrode 411 as its gate electrode and one of a source and a drain connected to the power supply line 424 and has a rectifying characteristic in which a current easily flows in the forward direction.

  In the capacitor, the potential of the power supply line is applied to the fourth semiconductor layer 406 which is one electrode, and a capacitor is formed in a region overlapping with the capacitor electrode 412 which is the other electrode and a gate insulating film (not shown) therebetween. To do.

  A pixel electrode (anode) 426 of the organic light emitting element is formed by patterning for each pixel so that the ITO film is in contact with the drain side electrode 423. The bank made of the photosensitive resin film is formed outside the region surrounded by the dotted line in FIG.

  The organic compound layer of the organic light emitting element is composed only of a light emitting layer, and a light emitting layer that emits light emission colors corresponding to red, green, and blue pixels is formed inside a region surrounded by a dotted line in FIG.

  The cathode of the organic light emitting element is formed as an electrode common to each pixel so as to cover the entire surface of the pixel portion, and is electrically connected to the FPC via a wiring.

  An equivalent circuit of such a pixel is shown in FIG. 13, and elements common to those in FIG. 10 are denoted by the same reference numerals. The switching TFT 434 has a multi-gate structure, and the current control TFT 436 is provided with an LDD overlapping the gate electrode. Since a TFT using polysilicon exhibits a high operation speed, deterioration such as hot carrier injection is likely to occur. Therefore, it is highly reliable to form TFTs with different structures (switching TFTs with sufficiently low off-state current and TFTs for current control strong against hot carrier injection) having different structures depending on functions in the pixels, and This is very effective in manufacturing a display device capable of displaying a good image (high operation performance).

In the present invention, the organic material used as the organic compound layer of the organic light emitting device may be a low molecular weight organic material or a high molecular weight organic material. As the low molecular weight organic materials, materials centering on Alq ₃ (tri-8-quinolinite-aluminum), TPD (triphenyleramine derivative) and the like are known. Examples of the high molecular weight organic material include a π-conjugated polymer material. Typically, PPV (polyphenylene vinylene), PVK (polyvinyl carbazole), polycarbonate, and the like can be given.

  The high molecular weight organic material can be formed by a simple thin film forming method such as a spin coating method, a dipping method, a dispensing method, a printing method, or an ink jet method, and has higher heat resistance than a low molecular weight organic material.

In the organic light-emitting device of the organic light-emitting display of the present invention, when the organic compound layer of the organic light-emitting device has an electron transport layer and a hole transport layer, an electron transport layer and a successful transport layer are provided. inorganic materials, for example may be constituted by an amorphous semiconductor layer such as amorphous Si or amorphous Si _1-x C _x.

  Many trap states exist in an amorphous semiconductor, and a large amount of interface states are formed at the interface where the amorphous semiconductor is in contact with other layers. Therefore, the organic light emitting device can emit light at a low voltage and can also increase the luminance.

  Further, a dopant may be added to the organic compound layer to change the light emission color of the organic light emitting element. Examples of the dopant include DCM1, Nile red, rubrene, coumarin 6, TPB, quinacridone and the like.

  In this embodiment, an example of an external view of the organic light emitting display of the present invention will be described with reference to FIG. FIG. 14 is a perspective view showing a state where an organic light emitting element is encapsulated and an FPC (Flexible Print Circuit) is further provided in an active matrix substrate on which the organic light emitting element is formed. Parts having the same functions as those in FIG. 438a surrounded by a dotted line is a gate signal side driver circuit portion, 438b is a source signal side driver circuit portion, and 439 is a pixel portion. Reference numeral 431 denotes a sealing substrate. Although not illustrated, a filler may be provided in a gap between the sealing substrate and the substrate 401.

  Note that reference numeral 441 denotes a connection wiring for transmitting a signal input to the gate signal side driver circuit portion 438a, the source signal side driver circuit portion 438b, and the pixel portion 439, and a signal is transmitted from the FPC 442 serving as a connection terminal with an external device. receive.

  The source signal side driver circuit portion and the gate signal side driver circuit portion are formed using a CMOS circuit in which an n-channel TFT and a p-channel TFT are complementarily combined.

  For the source signal side drive circuit unit and the gate signal side drive circuit unit, a known circuit is adopted according to the driving method of the organic light emitting display such as time division driving and analog driving.

  A light-emitting device formed by implementing the present invention is incorporated in various electric appliances, and a pixel portion is used as an image display portion. Examples of the electronic device of the present invention include a mobile phone, a PDA, an electronic book, a video camera, a notebook personal computer, and an image reproducing device provided with a recording medium, such as a DVD (Digital Versatile Disc) player and a digital camera. Specific examples of these electronic devices are shown in FIGS.

  FIG. 15A illustrates a mobile phone, which includes a display panel 9001, an operation panel 9002, and a connection portion 9003. The display panel 9001 is provided with a display device 9004, an audio output portion 9005, an antenna 9009, and the like. . The operation panel 9002 is provided with operation keys 9006, a power switch 9007, a voice input unit 9008, and the like. The present invention can be applied to the display device 9004.

FIG. 15B illustrates a mobile computer or a portable information terminal, which includes a main body 9201, a camera portion 9202, an image receiving portion 9203, operation switches 9204, and a display device 9205. The present invention can be applied to the display device 9205.
For such an electronic device, a 3 inch to 5 inch class display device is used; however, by using the display device of the present invention, the weight of the portable information terminal can be reduced.

  FIG. 15C illustrates a portable book, which includes a main body 9301, display devices 9202 to 9303, a storage medium 9304, operation switches 9305, and an antenna 9306, and data stored in a minidisc (MD) or DVD, The data received by the antenna is displayed. The present invention can be used for the display devices 9302 to 9303. A portable book uses a 4-inch to 12-inch class display device, but by using the display device of the present invention, the portable book can be reduced in weight and thickness.

  FIG. 15D illustrates a video camera which includes a main body 9401, a display device 9402, an audio input portion 9403, operation switches 9404, a battery 9405, an image receiving portion 9406, and the like. The present invention can be applied to the display device 9402.

  FIG. 16A illustrates a personal computer which includes a main body 9601, an image input portion 9602, a display device 9603, and a keyboard 9604. The present invention can be applied to the display device 9603.

  FIG. 16B shows a player using a recording medium (hereinafter referred to as a recording medium) in which a program is recorded. The player includes a main body 9701, a display device 9702, a speaker portion 9703, a recording medium 9704, and operation switches 9705. This apparatus uses a DVD (Digital Versatile Disc), CD, or the like as a recording medium, and can perform music appreciation, movie appreciation, games, and the Internet. The present invention can be applied to the display device 9702.

  FIG. 16C illustrates a digital camera which includes a main body 9801, a display device 9802, an eyepiece unit 9803, an operation switch 9804, and an image receiving unit (not shown). The present invention can be applied to the display device 9802.

  The display device of the present invention is used for the mobile phone shown in FIG. 15A, the mobile computer or portable information terminal shown in FIG. 15B, the portable book shown in FIG. 15C, and the personal computer shown in FIG. By displaying a black background in the mode, the power consumption of the device can be suppressed.

  In the cellular phone operation shown in FIG. 15A, the power consumption can be reduced by decreasing the luminance when the operation key is used and increasing the luminance when the operation switch is used. Further, the power consumption can be reduced by increasing the brightness of the display device when an incoming call is received and decreasing the brightness during a call. Further, in the case of continuous use, it is possible to reduce power consumption by providing a function that turns off display by time control unless resetting. Note that these may be manual control.

  Although not shown here, the present invention can also be applied to a display device incorporated in a navigation system, a refrigerator, a washing machine, a microwave oven, a fixed telephone, a facsimile, and the like. Thus, the application range of the present invention is very wide and can be applied to various products.

100 pixel 101 switching TFT
102 Current control TFT
103 Capacitor 104 Rectifying TFT
105 Organic Light Emitting Element 106 AC Power Supply 109 Rectifier

Claims (2)

The pixel has a first transistor, and an organic light emitting element, a second transistor, a third transistor, a,
A gate of the third transistor is electrically connected to a gate signal line; one of a source and a drain is electrically connected to the source signal line; the other is electrically connected to a gate of the first transistor;
Wherein one of a source and a drain of the first transistor is electrically connected to the first wiring, the other is electrically connected to the pixel electrode of the organic light emitting element,
The gate of the second transistor is electrically connected to one of a source and a drain of the second transistor is electrically connected to said first wiring, said source and said drain of said second transistor Is electrically connected to the pixel electrode,
The counter electrode of the organic light emitting element is electrically connected to the second wiring ,
The first wiring has a function of supplying a potential of one end of a first power source,
The second wiring has a function of supplying a potential of the other end of the first power source,
The first power source has a function of alternately supplying voltages having different polarities,
A high potential is supplied before Symbol counter electrode, when a low potential is supplied to one of said source and said drain of said second transistor, a reverse bias is characterized in that it is applied to the organic light emitting element Display device. The display device according to claim 1 , wherein the first transistor and the second transistor are transistors of the same conductivity type.

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