JP7565150B2 - Display brightness compensation method and display - Google Patents

Description

The present invention relates to a display brightness compensation method and a display.

In recent years, displays that use organic semiconductor elements, such as organic light-emitting diodes, as light source elements have come into practical use and are now commercially available. In the development of displays that use organic semiconductor elements as light sources, research is still ongoing to further improve performance, such as by increasing brightness, improving resolution, reducing power consumption, and extending life.

Conventionally, the light-emitting elements of an organic EL display are composed of organic light-emitting diodes (also called "OLEDs") and transistors that control the current flowing through the organic light-emitting diodes. Organic light-emitting diodes are devices that emit light in response to the current input from thin-film transistors (also called "TFTs") formed on a substrate to an organic EL layer sandwiched between an anode electrode and a cathode electrode.

However, in contrast to this configuration, Patent Document 1 below describes a vertical organic light-emitting transistor (also called a "VOLET") that is a transistor that adjusts the flowing current by controlling the voltage applied to the gate electrode as an element for reducing the number of control elements and increasing the light-emitting area to increase brightness, and that emits light according to the amount of current flowing through the transistor itself. Patent Document 2 below also describes a display that uses a vertical organic light-emitting transistor, and it is expected that the brightness of the display will be significantly increased.

International Publication No. 2009/036071 Special table 2014-505324 publication

A vertical organic light-emitting transistor, like a field-effect transistor, has a source electrode, a gate electrode, and a drain electrode, with the source electrode corresponding to the anode electrode and the drain electrode corresponding to the cathode electrode. An EL element and an organic semiconductor layer are arranged between the source electrode and the drain electrode, and each electrode is configured so that EL can be emitted by passing a current through the EL element and the organic semiconductor layer, and at least one of the source electrode and the drain electrode is configured to be transparent so that the light obtained by the emission can be emitted to the outside.

It is known that organic light-emitting diodes used in conventional configurations deteriorate in response to the injected current when they are turned on for a long period of time, causing a gradual decrease in brightness. This is thought to be due to factors such as chemical changes and fluctuations in interlayer injection efficiency due to charge accumulation at the interfaces of each organic layer in organic light-emitting diodes. The same is true for vertical organic light-emitting transistors, which emit light by passing a current through an EL element and an organic semiconductor layer sandwiched between a source electrode corresponding to an anode electrode and a drain electrode corresponding to a cathode electrode.

However, the inventors of the present invention have found through intensive research that displays using vertical organic light-emitting transistors have the following problems. When a voltage is applied to the gate electrode of a vertical organic light-emitting transistor to pass a current through the EL element and the organic semiconductor layer to emit EL, charges accumulate at the interface between the gate electrode and the gate insulating film layer, the interface between the source electrode and the organic semiconductor layer and the surface layer, and the gate insulating film layer and the surface layer. Due to the accumulation of charges at these interfaces, even if a predetermined voltage is applied to the gate electrode, the vertical organic light-emitting transistor does not inject the same amount of charge into the organic semiconductor layer as when it was just manufactured or when it was shipped from the factory, and the luminance decreases more quickly than that of an organic light-emitting diode. As a result, displays using vertical organic light-emitting transistors are prone to characteristic fluctuations in a short period of time and have a short lifespan, which makes product reliability an issue.

It is possible to configure a circuit that performs feedback control so that the desired current flows even if there is a change in the current flowing through the vertical organic light-emitting transistor, but this would require the addition of a complex circuit configuration and require an area to place the elements. In other words, this would reduce the light-emitting area and hinder the achievement of high brightness.

In view of the above problems, the present invention aims to provide a luminance compensation method for a display using vertical organic light-emitting transistors that suppresses luminance fluctuations over the long term without adding a complex circuit configuration, and a display.

The method for compensating a luminance of a display of the present invention comprises the steps of:
A luminance compensation method for a display including a plurality of vertical organic light-emitting transistors and a memory unit for storing characteristic information of the vertical organic light-emitting transistors, comprising:
A step (A) of applying a voltage for brightness inspection to a gate electrode of the vertical organic light-emitting transistor to be corrected;
A step (B) of measuring a current flowing through a current supply line that supplies a current to a source electrode of the vertical organic light-emitting transistor by applying a voltage for a luminance inspection to a gate electrode of the vertical organic light-emitting transistor to be corrected;
and a step (C) of determining a correction value of a voltage to be applied to a gate electrode of the vertical organic light-emitting transistor based on the current value measured in the step (B) and the characteristic information of the vertical organic light-emitting transistor stored in the memory unit.

The memory unit stores characteristic information of the vertical organic light-emitting transistor when the display is just manufactured or when it is shipped from the factory. Here, the characteristic information of the vertical organic light-emitting transistor is, for example, the electron mobility (μ), conductance (gm=Id/Vg), threshold voltage (Vt), etc. Id is the current value flowing between the source electrode and drain electrode of the vertical organic light-emitting transistor, and Vg is the voltage applied to the gate electrode of the vertical organic light-emitting transistor.

As described above, the current value of the current flowing through the current supply line or each vertical organic light-emitting transistor is confirmed, and the voltage applied to the gate electrode of each vertical organic light-emitting transistor is corrected based on the characteristic information stored in the memory unit so that the desired current value flows. In other words, the current supplied to the organic semiconductor layer of the vertical organic light-emitting transistor over a long period of time is adjusted to the desired current value. Therefore, fluctuations in brightness due to deterioration of the vertical organic light-emitting transistor itself are suppressed, and brightness is compensated for over a long period of time.

The current value may be measured individually for each vertical organic light-emitting transistor, or may be measured collectively for vertical organic light-emitting transistors arranged in a specific region or on the same line. By measuring the current value of the current flowing to the source electrode of each vertical organic light-emitting transistor and adjusting the voltage applied to the gate electrode, the current flowing to the source electrode can be accurately corrected to obtain the desired brightness.

However, displays with a large number of pixels are composed of millions to tens of millions of vertical organic light-emitting transistors, so if corrections were made individually, it would take a long time to correct all of the vertical organic light-emitting transistors. This would result in differences in brightness between areas where the voltage applied to the gate electrode has been corrected and areas where it has not been corrected, which can easily lead to uneven image quality. Therefore, it is preferable to perform corrections collectively in a short period of time for vertical organic light-emitting transistors arranged in a specific area or on the same line.

The step (A) of the brightness compensation method may include a step (A1) of cutting off the current supply to the vertical organic light-emitting transistor that is not the subject of correction.

When carrying out steps (A) and (B), a voltage for brightness testing is applied to the gate electrode of the vertical organic light-emitting transistor, rather than a voltage corresponding to the image to be displayed, so the screen will momentarily display an unintended image. If a bright screen is displayed momentarily at this time, people looking at the display are likely to notice flickering on the screen. For this reason, it is preferable to carry out the steps on a screen that is as dark as possible.

By using the above method, it is possible to cut off the path that is the source of the current flowing through the vertical organic light-emitting transistor, allowing the correction process to be performed on a darker screen and allowing the current to be measured more accurately.

The above-mentioned steps (A) and (B) of the brightness compensation method are characterized in that they are performed during the image update interval.

The characteristics of vertical organic light-emitting transistors are easily affected by temperature, and when the temperature rises from when the power is turned on, the current value that flows is different even if the same voltage is applied to the gate electrode of a vertical organic light-emitting transistor. Therefore, it is necessary to measure and correct the current value at the operating temperature.

By using the above method, it is possible to correct the voltage applied to the gate electrode of the vertical organic light-emitting transistor to achieve the desired brightness while the display starts operating and the temperature is rising, and while the temperature is rising to the operating temperature, thereby making it possible to emit light with the corrected desired brightness. In addition, after power is turned on, a correction value can be determined by a single current measurement, and the offset voltage of each vertical organic light-emitting transistor can be calculated and stored, and the voltage applied to the gate electrode of the vertical organic light-emitting transistor can be offset according to the passage of time and temperature.

In addition, LCD displays and other displays can reduce the afterimage that occurs when switching from one image to the next by briefly inserting a screen that is different from the image being displayed during the interval between updates of the displayed image.

The step (B) of the above-mentioned brightness compensation method may include a step (B1) of storing the current value measured in the step (B) in the memory unit.

By using the above method, it is possible to correct not only the initial characteristic information of each vertical organic light-emitting transistor stored in the memory unit, but also to adjust the difference between the current value measured in the previous process and the corrected voltage value. Therefore, even immediately after power-on, it is possible to display images and videos in a corrected state based on the current value at the time of the last correction, without measuring the current value to the source electrode of the vertical organic light-emitting transistor.

The display of the present invention comprises:
a plurality of vertical organic light emitting transistors arranged in an array;
a data line for supplying a voltage for controlling gate electrodes of the vertical organic light emitting transistors;
a current supply line for supplying current to source electrodes of the vertical organic light emitting transistors;
a first thin film transistor connected between a gate electrode of each of the vertical organic light emitting transistors and the data line, for controlling a voltage supply to the gate electrode of the vertical organic light emitting transistor;
a first gate line connected to the gate electrode of the first thin film transistor and controlling the first thin film transistor;
A control unit that controls a voltage applied to at least the first gate line;
a current measuring unit for measuring a current flowing through the current supply line;
and a memory unit in which characteristic information of each of the vertical organic light-emitting transistors is stored.
The control unit is
Controlling so that a voltage for brightness inspection is applied to a gate electrode of the vertical organic light-emitting transistor to be corrected;
The current measuring unit is
A voltage for brightness inspection is applied to a gate electrode of the vertical organic light-emitting transistor to be corrected, thereby measuring a current flowing through a source electrode of the vertical organic light-emitting transistor, and storing the measured current value in a memory unit;
The control unit is
The present invention is characterized in that a correction value for the voltage to be applied to the gate electrode of the vertical organic light-emitting transistor is determined based on the measured current value and the characteristic information of the vertical organic light-emitting transistor stored in the memory unit.

For example, the control unit controls the voltage of the first gate line so as to turn on the first thin film transistor connected to the vertical organic light-emitting transistor to be corrected, and in this on state, determines a correction value for the voltage to be applied to the data line from the current value of the current supply line measured by the current measurement unit and the characteristic information of the vertical organic light-emitting transistor stored in the memory unit. This makes it possible to correct the luminance of the vertical organic light-emitting transistor to be corrected.

The above configuration allows the voltage applied to the data line to be adjusted to display the desired image. This allows the current value flowing through the vertical organic light-emitting transistor to be corrected, making it possible to configure a display whose image quality and brightness do not fluctuate even with long-term use, and which can compensate for brightness when the display is turned on for long periods of time.

The display may have a dielectric layer formed between the gate electrode and source electrode of the vertical organic light-emitting transistor.

The image displayed by the display is updated by sequentially switching the on/off state of the first thin film transistor connected to each vertical organic light-emitting transistor and applying a desired voltage to the gate electrode of the vertical organic light-emitting transistor according to each pixel. At this time, after the voltage application to the gate electrode of the vertical organic light-emitting transistor is completed and the first thin film transistor is switched to the off state, the vertical organic light-emitting transistor must maintain its brightness for a predetermined time. In other words, in order to maintain the current flowing through the vertical organic light-emitting transistor, it is necessary to maintain the voltage between the gate electrode and source electrode of the vertical organic light-emitting transistor.

To achieve this, an element that maintains a charge, such as a capacitor, must be connected between the gate and source electrodes of a vertical organic light-emitting transistor. If a capacitance value for maintaining a voltage is to be obtained using a capacitor configured as a semiconductor circuit, the element will become very large, which will put pressure on the light-emitting area.

Therefore, by using the above configuration, a capacitor can be configured as a parasitic element within the vertical organic light-emitting transistor, which is made large to enlarge the light-emitting area. In other words, there is no need to connect a separate capacitor for maintaining voltage, and the light-emitting area is not compressed, making it possible to configure a display with higher brightness.

The source electrode and/or drain electrode of the vertical organic light-emitting transistor of the display may be formed from a conductive material containing carbon.

Furthermore, the vertical organic light-emitting transistor of the display may have a source electrode and/or a drain electrode formed from carbon nanotubes (also called "CNTs").

Carbon-containing conductive materials, particularly carbon nanotubes, have high current density resistance and can form conductive films that are transparent to visible light. Therefore, by using the above-mentioned materials, it is possible to construct vertical organic light-emitting transistors that are transparent to visible light and can pass large currents. In addition, because carbon nanotubes also have high mechanical strength, they can also be used to construct flexible displays.

The above display is
a second thin film transistor connected between the source electrode of the vertical organic light emitting transistor and the current supply line, for controlling the current supply to the source electrode of the vertical organic light emitting transistor;
a second gate line connected to a gate electrode of the second thin film transistor and controlling the second thin film transistor;
The control unit may perform control so that the second thin film transistor connected to the vertical organic light emitting transistor that is not a correction target is turned off.

Furthermore, the second thin-film transistor of the display may be made of an oxide semiconductor.

During normal operation, the second thin-film transistor, which is in the on state, switches to the off state, thereby cutting off the supply path of the current flowing to the vertical organic light-emitting transistor. Furthermore, by configuring the second thin-film transistor from an oxide semiconductor that has a small amount of minute current (leakage current) that flows even in the off state, the current flowing to the vertical organic light-emitting transistor that is not the target of correction can be further reduced.

The present invention provides a luminance compensation method and display using vertical organic light-emitting transistors that suppresses luminance fluctuations over the long term without adding complex circuit configurations.

FIG. 2 is a schematic diagram of a portion of an embodiment of a display. FIG. 2 is a circuit diagram of the light emitting unit of FIG. 1 . FIG. 2 is a configuration diagram of a control unit in FIG. 1 . FIG. 2 is a top view showing a schematic element configuration of a light-emitting section formed on a substrate. FIG. 5 is a side view of the light emitting portion of FIG. 4 . 10 is a flowchart showing a procedure for correcting the luminance of a display. FIG. 11 is a schematic diagram of a portion of another embodiment of a display.

The configuration of the display of the present invention will be described below with reference to the drawings. Note that the drawings are all schematic illustrations, and the dimensional ratios and numbers in the drawings do not necessarily match the actual dimensional ratios and numbers.

[composition]
First, the configuration of the display will be described. Fig. 1 is a schematic diagram of a part of an embodiment of a display 1. As shown in Fig. 1, the display 1 of this embodiment includes a light-emitting section 10 including vertical organic light-emitting transistors arranged in an array, a data line 11 for supplying a voltage to a gate electrode of the vertical organic light-emitting transistor, a current supply line 12 for supplying a current to a source electrode of the vertical organic light-emitting transistor, a first gate line 13 for controlling a first thin film transistor, a second gate line 14 for controlling a second thin film transistor, a control section 15, a current measurement section 16 for measuring a current flowing through the current supply line 12, and a memory section 17.

Figure 2 is a circuit diagram of the light-emitting unit 10 in Figure 1. As shown in Figure 2, the light-emitting unit 10 includes a vertical organic light-emitting transistor 20, a first thin-film transistor 21 that controls the voltage supply to the gate electrode of the vertical organic light-emitting transistor 20, a second thin-film transistor 22 that controls the current supply to the source electrode of the vertical organic light-emitting transistor 20, and a capacitor 23 connected between the source electrode and gate electrode of the vertical organic light-emitting transistor 20.

The data line 11 is a wiring for applying a voltage to the gate electrode of the vertical organic light-emitting transistor 20 via the first thin film transistor 21 in order to adjust the light emission brightness of the vertical organic light-emitting transistor 20 according to the image to be displayed. The current supply line 12 is a wiring for supplying a current to the source electrode of the vertical organic light-emitting transistor 20 via the second thin film transistor 22.

The first gate line 13 is connected to the gate electrode of the first thin film transistor 21 and controls the on/off of the first thin film transistor 21, i.e., controls the electrical conduction between the gate electrode of the vertical organic light-emitting transistor 20 and the data line 11. The second gate line 14 is connected to the gate electrode of the second thin film transistor 22 and controls the on/off of the second thin film transistor 22, i.e., controls the electrical conduction between the source electrode of the vertical organic light-emitting transistor 20 and the current supply line 12.

The current measuring unit 16 is arranged to measure the total amount of current flowing through the light emitting unit 10 (vertical organic light emitting transistor 20) connected to the same current supply line 12.

3 is a block diagram of the control unit 15 in FIG. 1. As shown in FIG. 3, the control unit 15 includes a plurality of gate drivers 15a for driving the data lines 11, a plurality of source drivers 15b for driving the current supply lines 12, a plurality of gate controllers 15c for controlling the voltage of the first gate line 13 and the voltage of the second gate line 14, a data input/output circuit 15d for receiving the current value measured by the current measurement unit 16 and storing it in the memory unit 17, and an arithmetic processing circuit 15e for calculating a correction value of the voltage applied to the gate electrode of the vertical organic light-emitting transistor 20 from the current value measured by the current measurement unit 16 and the characteristic information of the vertical organic light-emitting transistor 20 stored in the memory unit 17. Details regarding the control will be described later in the section on the control method.

The specific configuration of each block constituting the control unit 15 is a dedicated circuit, a processor controlled by a software program, or a combination of these. For example, the dedicated circuit may be a logic circuit that generates a control signal and is configured on the same substrate as the vertical organic light-emitting transistors 20, a driver circuit for driving each vertical organic light-emitting transistor 20, or a dedicated integrated circuit (Application Specific Integrated Circuit, abbreviated as ASIC) configured to be electrically connected to each line (11, 12, 13, 14), or a programmable device (PLD, CPLD, FPGA) that can configure a dedicated circuit by programming.

The processor may be a central processing unit (CPU), other general-purpose processor, digital signal processor (DSP), ASIC, etc. The general-purpose processor may be a microprocessor, and the processor may be any standard processor, etc. Various processing steps may be performed directly by a hardware processor, or may be performed by a combination of hardware and software (or software functional modules) in the processor. Furthermore, a control device such as a microcontroller may be used.

The storage unit 17 may include a high-speed RAM memory, or may be implemented with any type of volatile or non-volatile storage device or combination thereof, such as a static random access memory (SRAM), an electrically erasable programmable read-only memory (EEPROM), an erasable programmable read-only memory (EPROM), a programming read-only memory (PROM), a read-only memory (ROM), a magnetic memory, a flash memory, a magnetic disk, or an optical disk.

The capacitor 23 is a voltage holding element between the gate electrode and source electrode of the vertical organic light-emitting transistor 20, which is arranged to maintain the displayed image for a predetermined period of time while the first thin-film transistor 21 is in the off state.

Next, the structure of each element formed on the substrate will be described. FIG. 4 is a top view of a schematic element configuration of the light-emitting section 10 formed on the substrate 30. FIG. 5 is a side view of the light-emitting section 10 of FIG. 4. As shown in FIG. 4 and FIG. 5, the vertical organic light-emitting transistor 20, the first thin film transistor 21, and the second thin film transistor 22 are formed in an area partitioned by the data line 11, the current supply line 12, the first gate line 13, and the second gate line 14.

The substrate 30 can be made of a material such as glass or a plastic material such as PET (Poly Ethylene Terephthalate), PEN (Poly Ethylene Naphthalate), or polyimide.

In the following explanation, the direction in which the data lines 11 and current supply lines 12 are wired is the X direction, the direction in which the first gate lines 13 and second gate lines 14 are wired is the Y direction, and the direction perpendicular to these is the Z direction, and the direction away from the substrate 30 (+Z direction) is the upper layer side.

The vertical organic light-emitting transistor 20 is configured such that, from the top, a drain electrode layer 20d corresponding to a cathode electrode, an organic EL layer 20c, an organic semiconductor layer 20a, a source electrode layer 20s configured to coat the surface of a surface layer 31 with a conductive material containing carbon (carbon nanotubes in this embodiment), and a gate electrode layer 20g formed below via a gate insulating film layer 20h composed of a dielectric. When a voltage is applied to the gate electrode layer 20g, the Schottky barrier between the organic semiconductor layer 20a and the source electrode layer 20s changes, and when the voltage exceeds a predetermined threshold, a current flows from the source electrode layer 20s to the organic semiconductor layer 20a, causing the vertical organic light-emitting transistor 20 to emit light.

In the display 1 of this embodiment, the substrate 30 is made of a material that is transparent to visible light, and the gate electrode layer 20g and the source electrode layer 20s are configured to have a gap that allows visible light to pass through, so that light emitted from the organic semiconductor layer 20a passes through the substrate 30 and is emitted to the outside, thereby displaying an image. This method of emitting light through the substrate 30 is also called the "bottom emission method," and has the advantage of being easy to connect the wiring between electrodes and easy to manufacture.

The first thin film transistor 21 and the second thin film transistor 22 are connected to a source electrode layer (21s, 22s) and a drain electrode layer (21d, 22d) via an oxide semiconductor layer (21a, 22a), respectively, and a gate electrode layer (21g, 22g) is formed below the oxide semiconductor layer (21a, 22a) via an insulating layer or a dielectric layer. When a voltage is applied to the gate electrode layer (21g, 22g), a channel is formed in the oxide semiconductor layer (21a, 22a), and the source electrode layer (21s, 22s) and the drain electrode layer (21d, 22d) are electrically connected.

The first thin film transistor 21 has a source electrode layer 21s connected to the data line 11, and a drain electrode layer 21d connected to the gate electrode layer 20g of the vertical organic light-emitting transistor 20. The second thin film transistor 22 has a source electrode layer 22s connected to the current supply line 12, and a drain electrode layer 22d connected to the source electrode layer 20s of the vertical organic light-emitting transistor 20. Note that the first thin film transistor 21 may have a source electrode layer 21s connected to the gate electrode layer 20g of the vertical organic light-emitting transistor 20, and a drain electrode layer 21d connected to the data line 11.

As shown in FIG. 4, the vertical organic light-emitting transistor 20 is formed so that the light-emitting area is as large as possible to achieve high brightness, and the first thin film transistor 21 and the second thin film transistor 22 are formed as small as possible in the corners of the partitioned area so as to have minimal effect on the light-emitting area of the vertical organic light-emitting transistor 20.

Although the capacitor 23 is not shown in Fig. 4 and Fig. 5, as shown in Fig. 5, the vertical organic light-emitting transistor 20 of this embodiment has a capacitor 23 as a parasitic element, with the source electrode layer 20s and the gate electrode layer 20g arranged to face each other via the gate insulating film layer 20h. If the capacitance value of such a parasitic element capacitor 23 is insufficient, an additional capacitor may be formed.

The following are examples of materials that can be used for each layer:

The drain electrode layer 20d of the vertical organic light-emitting transistor 20 may be made of single-layer or multi-layer graphene, carbon nanotubes, aluminum (Al), lithium fluoride (LiF), molybdenum oxide (Mo _x O _y ), indium tin oxide (ITO), zinc oxide (ZnO), and the like.

The gate electrode layer 20g of the vertical organic light-emitting transistor 20 may employ materials including zinc oxide (ZnO) doped with metals such as aluminum (Al), tin (Sn), yttrium (Y), scandium (Sc), gallium ( _Ga ), etc., indium oxide ( _In2O3 ), tin dioxide ( _SnO2 ), metal-doped or undoped transparent conductive oxides such as cadmium oxide (CdO), and combinations thereof, or aluminum (Al), gold (Au), silver (Ag), platinum (Pt), cadmium (Cd), nickel (Ni), and tantalum (Ta), and combinations thereof, as well as p- or n-doped silicon (Si), gallium arsenide (GaAs), etc.

The gate insulating film layer 20h between the surface layer 31 and the gate electrode layer 20g of the vertical organic light-emitting transistor 20 may be made of silicon oxide ( _SiOx ), aluminum oxide ( _{Al2O3 )} , silicon nitride ( _Si3N4 ), _yttrium oxide ( _Y2O3 ), lead titanate ( _PbTiOx ), aluminum titanate ( _AlTiOx ), glass _, and organic compounds such as parylene polymer, polystyrene, polyimide, polyvinylphenol, polymethyl methacrylate, and fluoropolymer.

The organic semiconductor layer 20a of the vertical organic light-emitting transistor 20 is made of a linear condensed polycyclic aromatic compound (or acene compound) such as naphthalene, anthracene, rubrene, tetracene, pentacene, hexacene, and derivatives thereof, a pigment such as, for example, a copper phthalocyanine (CuPc)-based compound, an azo compound, a perylene-based compound, and derivatives thereof, and a pigment such as, for example, a hydrazone compound, a triphenylmethane-based compound, a diphenylmethane-based compound, a stilbene-based compound, an allylvinyl compound, a pyrazoline-based compound, a triphenylamine derivative (TPD), an allylamine compound, a low molecular weight amine derivative (a-NPD), 2,2',7,7'-tetrakis(diphenylamino)-9,9'-spirobifluorene (spiro- low molecular weight compounds such as N,N'-di(1-naphthyl)-N,N'-diphenyl-4,4'-diamonobiphenyl (spiro-NPB), 4,4',4"-tris[N-3-methylphenyl-N-phenylamino]triphenylamine (mMTDATA), 2,2',7,7'-tetrakis(2,2-diphenylvinyl)-9,9-spirobifluorene (spiro-DPVBi), 4,4'-bis(2,2-diphenylvinyl)biphenyl (DPVBi), (8-quinolinolato)aluminum (Alq), tris(8-quinolinolato)aluminum (Alq3), tris(4-methyl-8-quinolinolato)aluminum (Almq3), and derivatives thereof; and polythiophenes, poly(p polymer compounds such as poly(N-phenylenevinylene) (PPV), biphenyl group-containing polymers, dialkoxy group-containing polymers, alkoxyphenyl PPV, phenyl PPV, phenyl/dialkoxy PPV copolymers, poly(2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV), poly(ethylenedioxythiophene) (PEDOT), poly(styrenesulfonic acid) (PSS), poly(aniline) (PAM), poly(N-vinylcarbazole), poly(N-vinylcarbazole), poly(vinylpyrene), poly(vinylanthracene), pyrene formaldehyde resins, ethylcarbazole formaldehyde halogenated resins, and modified products thereof; For example, 5,5_-diperfluorohexylcarbonyl-2,2_:5_,2_:5_,2_-quaterthiophene (DFHCO-4T), DFH-4T, DFCO-4T, P(NDI2OD-T2), PDI8-CN2, PDIF-CN2, F16CuPc, and n-type transport organic small molecules, oligomers, or polymers such as fullerene, naphthalene, perylene, and oligothiophene derivatives, as well as aromatic compounds having a thiophene ring such as thieno[3,2-b]thiophene, dinaphthyl[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DNTT), and 2-decyl-7-phenyl[1]benzothieno[3,2-b][1]benzothiophene (BTBT), may be employed.

Here, the vertical organic light-emitting transistor 20 can be suitably used with a hole injection layer, hole transport layer, organic EL layer, electron transport layer, electron injection layer, etc., which are standardly used in OLED displays, by appropriately selecting an organic semiconductor with a suitable energy level. The color of the light emitted to the outside can be adjusted to emit light of a color such as red, green, or blue by selecting the material that constitutes the organic EL layer 20c described above. The vertical organic light-emitting transistor 20 can also be configured to emit white light, or the same vertical organic light-emitting transistor 20 can be used to select and emit light of a desired color using a color filter.

The surface layer 31 is a layer formed on the gate insulating film layer 20h for the purpose of adhering the source electrode layer 20s (particularly the CNT layer). The surface layer 31 can be formed by applying a composition containing a binder resin formed from a silane coupling material, an acrylic resin, or the like.

The oxide semiconductor layers (21a, 22a) formed in the first thin film transistor 21 and the second thin film transistor 22 may be made of an In-Ga-Zn-O based semiconductor, a Zn-O based semiconductor (ZnO), an In-Zn-O based semiconductor (IZO (registered trademark)), a Zn-Ti-O based semiconductor (ZTO), a Cd-Ge-O based semiconductor, a Cd-Pb-O based semiconductor, CdO (cadmium oxide), an Mg-Zn-O based semiconductor, an In-Sn-Zn-O based semiconductor (e.g., _In2O3 - _{SnO2 -} ZnO), an In-Ga-Sn-O based semiconductor, or the like.

In this embodiment, the first thin film transistor 21 and the second thin film transistor 22 are thin film transistors made of oxide semiconductors, but they may be thin film transistors made of amorphous silicon. They may also be either p-type or n-type. Furthermore, as a specific configuration, any of the following configurations may be adopted: staggered type, inverted staggered type, coplanar type, inverted coplanar type, etc.

As the vertical organic light-emitting transistor 20, the vertical organic light-emitting transistor 20 described in Patent Documents 1 and 2 may also be used.

[Control method]
Finally, a method for controlling the display will be described. In this embodiment, as shown in Fig. 1, light-emitting units 10 are arranged in an array, and in a column in the vertical direction in Fig. 1, a data line 11 and a current supply line 12 are shared, and in a column in the horizontal direction in Fig. 1, a first gate line 13 and a second gate line 14 are shared.

In the following explanation, assuming the above-mentioned configuration, the light-emitting units 10 to be corrected at one time will be described as a combination of one horizontal row in FIG. 1 that shares the first gate line 13 and the second gate line 14. However, the light-emitting units 10 to be corrected at one time may be multiple combinations of light-emitting units 10 in the horizontal direction in FIG. 1 that share the first gate line 13, and may be corrected individually in sequence.

The brightness compensation method in this embodiment is performed during the image update interval for displaying the next image from the image currently being displayed when the display 1 is displaying an image. Note that the brightness compensation method described below may be performed at any timing, or may be performed when the power is turned on or at regular time intervals from when the power is turned on.

Figure 5 is a flowchart showing the luminance correction procedure of the display 1. As shown in Figure 5, when the display 1 starts correction control from a state in which it is performing normal image display, the gate controller 15c of the control unit 15 switches the second thin film transistor 22 connected to the vertical organic light emitting transistor 20 to be corrected to the ON state and the second thin film transistor 22 connected to the vertical organic light emitting transistor 20 not to be corrected to the OFF state (S1).

After performing step S1, the gate controller 15c of the control unit 15 switches the first thin film transistor 21 connected to the vertical organic light emitting transistor 20 to be corrected to the on state and the first thin film transistor 21 connected to the vertical organic light emitting transistor 20 not to be corrected to the off state (S2). By controlling in this way by the control unit 15, no voltage is applied to the gate electrode of the vertical organic light emitting transistor 20 not to be corrected, and no current is supplied to the source electrode.

In the above-described controlled state, a luminance inspection voltage is applied to the data line 11 connected to the first thin film transistor 21 in the on state, or to all data lines 11 (S3). Then, the current supply line 12 is caused to flow with the sum of the current values when the luminance inspection voltage is applied to the vertical organic light-emitting transistor 20 to be corrected.

The current measurement unit 16 then measures the current connected to the current supply line 12 connected to the second thin film transistor 22 in the on state, or to all current supply lines 12 (S4). Ideally, when a luminance inspection voltage is applied to the gate electrode of the second thin film transistor 22, the current value measured is the current value that flows from the current supply line 12 to the source electrode multiplied by the number of vertical organic light-emitting transistors 20 that are the subject of correction.

Specific methods for measuring the current value include, for example, measuring the current value using an A/D converter, placing a resistor on the current supply line 12 and comparing the voltage appearing at both ends of the resistor with a desired voltage value, and preparing a shunt path and passing a predetermined current value through the current supply line 12. The current that does not flow through each vertical organic light-emitting transistor but flows through the shunt path is measured with an ammeter, and the difference from the predetermined current value supplied is measured.

The control unit 15 acquires the current value (I ₁ ) for the luminance inspection voltage (Vc) actually measured by the data input/output circuit 15d as characteristic information, and stores it in the memory unit 17. At this time, the data input/output circuit 15d of the control unit 15 reads out the current value (I ₀ ) for the luminance inspection voltage (Vc) in the state just after manufacture or at the time of shipment from the memory unit 17. Then, the arithmetic processing circuit 15e checks the deviation from the characteristic information, and determines a correction value for the voltage to be applied to the data line 11 so that the deviation of the current value (ΔI=I ₁ -I ₀ ) that occurs is reduced (S5). The characteristic information used for the comparison at this time may be the conductance (gm ₁ =I ₁ /Vc) calculated by the conductance of the arithmetic processing circuit 15e, or the like.

Once the correction value has been determined, the process returns to normal image display control, and the gate controller 15c of the control unit 15 switches the second thin film transistor 22 to the on state, and the gate driver 15a of the control unit 15 applies to the data line 11 a voltage that corresponds to the image that the control unit 15 is to display and that has been corrected.

In this way, by applying a corrected voltage value to the gate electrode of the vertical organic light-emitting transistor 20, even if the expected current no longer flows through the source electrode in response to the voltage applied to the gate electrode due to degradation, the control of the gate electrode is corrected to obtain the expected current value, making it possible to suppress changes in luminance and to compensate for luminance over long periods of illumination.

As described above, in the brightness compensation method of this embodiment, almost no current flows through the vertical organic light-emitting transistors 20 that are not the subject of correction. Therefore, when correction control is performed at one time, only one horizontal row in FIG. 1 that shares the first gate line 13 and the second gate line 14 of the light-emitting unit 10 emits light slightly, while the other vertical organic light-emitting transistors 20 are turned off. Therefore, a black screen can be inserted during the image update interval.

By turning the screen black during the image update interval, LCD displays and other displays can briefly insert a screen different from the image being displayed between the image update intervals, reducing the residual image that appears when switching from the previous image to the next. By using the above method, residual images are suppressed, allowing displays to display images and videos more clearly.

[Another embodiment]
Another embodiment will be described below.

<1> The correction value may be determined based on the current value or conductance measured during the previous correction control and stored in the memory unit 17. By basing the correction value on the value measured during the previous correction control, the display 1 can also use the correction value to modify the correction value over time or to detect defects.

<2> Figure 7 is a schematic diagram of a portion of another embodiment of the display 1. As shown in Figure 7, the display 1 of the present invention may not be provided with the second thin film transistor 22. The second thin film transistor 22 blocks the current path so that the current does not flow to the vertical organic light-emitting transistor 20 that is not the subject of correction. In other words, if the current that flows to the vertical organic light-emitting transistor 20 that is not the subject of correction is very small and does not reach a large value that affects the correction calculation, the second thin film transistor 22 does not need to be provided.

By using the above configuration, the wiring and elements can be reduced and the light-emitting area can be further enlarged. Therefore, a display 1 with higher brightness can be realized.

〈3〉 The display 1 may be configured to display an image by emitting light emitted from the organic semiconductor layer 20a to the opposite side of the substrate 30. This configuration is also called a "top emission type" and has the advantage that an element can be configured between the vertical organic light-emitting transistor 20 and the substrate 30.

〈4〉 The configuration of the display 1 described above is merely an example, and the present invention is not limited to the configurations shown in the drawings.

1: Display 10: Light-emitting section 11: Data line 12: Current supply line 13: First gate line 14: Second gate line 15: Control section 15a: Gate driver 15b: Source driver 15c: Gate controller 15d: Data input/output circuit 15e: Arithmetic processing circuit 16: Current measurement section 17: Memory section 20: Vertical organic light-emitting transistor 20a: Organic semiconductor layer 20d: Drain electrode layer 20g: Gate electrode layer 20h: Gate insulating film layer 20s: Source electrode layer 21: First thin film transistor 21a: Oxide semiconductor layer 21d: Drain electrode layer 21g: Gate electrode layer 21s: Source electrode layer 22: Second thin film transistor 22a: Oxide semiconductor layer 22d 22g: Drain electrode layer 22s: Gate electrode layer 23: Capacitor 24: Bank layer 30: Substrate 31: Surface layer

Claims (8)

A luminance compensation method for a display including a plurality of vertical organic light-emitting transistors and a memory unit for storing characteristic information of the vertical organic light-emitting transistors, comprising:
the characteristic information corresponds to a current flowing through a current supply line that supplies a current to a source electrode of the vertical organic light-emitting transistor when a voltage for a luminance test is applied to a gate electrode of the vertical organic light-emitting transistor in an initial stage;
a step (A) of applying a voltage for the luminance inspection to a gate electrode of the vertical organic light-emitting transistor to be corrected and cutting off the supply of current to the vertical organic light-emitting transistor not to be corrected by switching a thin film transistor connected to the vertical organic light-emitting transistor;
a step (B) of measuring a current flowing through a current supply line that supplies a current to a source electrode of the vertical organic light-emitting transistor by applying the voltage for brightness inspection to a gate electrode of the vertical organic light-emitting transistor to be corrected;
and (C) determining a correction value of a voltage to be applied to a gate electrode of the vertical organic light-emitting transistor based on the current value measured in the step (B) and the characteristic information of the vertical organic light-emitting transistor stored in the memory unit,
The method for compensating for brightness of a display, wherein the step (C) is a step of determining a correction value of a voltage to be applied to a gate electrode of the vertical organic light-emitting transistor so as to reduce a deviation between the current value measured in the step (B) and the current value at the initial stage based on the characteristic information of the vertical organic light-emitting transistor . The display luminance compensation method according to claim 1, characterized in that the steps (A) and (B) are performed during an image update interval. The method for compensating for brightness of a display according to claim 1 or 2, characterized in that the step (B) includes a step (B1) of storing the current value measured in the step (B) in the memory unit. a plurality of vertical organic light emitting transistors;
a data line for supplying a voltage for controlling gate electrodes of the vertical organic light emitting transistors;
a current supply line for supplying current to source electrodes of the vertical organic light emitting transistors;
a first thin film transistor connected between a gate electrode of each of the vertical organic light emitting transistors and the data line, for controlling a voltage supply to the gate electrode of the vertical organic light emitting transistor;
a first gate line connected to the gate electrode of the first thin film transistor and controlling the first thin film transistor;
A control unit that controls a voltage applied to at least the first gate line;
a current measuring unit for measuring a current flowing through the current supply line;
A memory unit in which characteristic information of each of the vertical organic light-emitting transistors is stored;
a second thin film transistor connected between a source electrode of the vertical organic light emitting transistor and the current supply line, for controlling current supply to the source electrode of the vertical organic light emitting transistor;
a second gate line connected to a gate electrode of the second thin film transistor and controlling the second thin film transistor;
the characteristic information corresponds to a current flowing through a current supply line that supplies a current to a source electrode of the vertical organic light-emitting transistor when a voltage for a luminance test is applied to a gate electrode of the vertical organic light-emitting transistor in an initial stage;
The control unit is
applying a voltage for brightness inspection to a gate electrode of the vertical organic light-emitting transistor to be corrected, and controlling the second thin film transistor connected to the vertical organic light-emitting transistor not to be corrected to be in an off state;
The current measuring unit is
A voltage for the luminance inspection is applied to a gate electrode of the vertical organic light-emitting transistor to be corrected, thereby measuring a current flowing through a source electrode of the vertical organic light-emitting transistor, and storing the measured current value in a memory unit;
The control unit is
A display characterized in that a correction value of a voltage to be applied to a gate electrode of the vertical organic light-emitting transistor is determined so as to reduce a deviation between a measured current value and a current value at the initial stage based on the characteristic information of the vertical organic light-emitting transistor stored in the memory unit. The display of claim 4, characterized in that a dielectric layer is formed between the gate electrode and the source electrode of the vertical organic light-emitting transistor. The display according to claim 4 or 5, characterized in that at least one of the source electrode and the drain electrode of the vertical organic light-emitting transistor is formed from a conductive material containing carbon. The display according to claim 6, characterized in that at least one of the source electrode and the drain electrode of the vertical organic light-emitting transistor is formed from a carbon nanotube. The display according to any one of claims 5 to 7, characterized in that the second thin film transistor is made of an oxide semiconductor.

Images