Display apparatus and imaging apparatus

A display apparatus comprises a pixel including a plurality of sub pixels. Each of the sub pixels includes a current driven light emitting device, a transistor for supplying an electric current to the light emitting device and a capacitive element for maintaining a gate voltage of the transistor. The capacitive element of one sub pixel and the capacitive element of the other sub pixel at least partially overlap each other.

BACKGROUND

Field of the Disclosure

The present invention relates to a display apparatus and an imaging apparatus having the display apparatus.

Description of the Related Art

There is an active matrix type organic EL display apparatus that controls signals for video, which are supplied to display elements, by using transistors in pixels, as one example of an organic EL display apparatus having a self-luminous light-emitting device, in particular, an organic EL display apparatus that includes an organic electroluminescence element (hereinafter referred to as “organic EL element” in some cases) which is a current control element, as a light emitting device.

In the organic EL display apparatus, there is a scheme of separately applying organic EL materials of red (R), green (G) and blue (B) by vapor deposition while using a mask. In addition, there is a scheme of extracting each color light of RGB by combining an organic EL element that emits white light with color filters, instead of separately applying each of RGB organic EL materials.

According to Japanese Patent Application Laid-Open No. 2010-2476 (Patent Document 1), a display apparatus is structured so that a size of a pixel circuit element provided in each sub pixel is different among each sub pixel according to a required driving current, and a size of a capacitive element is also different among each of the sub pixels. The display apparatus is structured so as to suppress the increase in pattern defects due to dust or the like and improve a yield by preventing the pixel pattern density from increasing in a particular sub pixel.

In a current driven light-emitting device, the larger capacitance a capacitive element for maintaining the gate voltage of a transistor which is connected to the light emitting device, the better the capacitive element can suppress a voltage fluctuation of a pixel electrode during a light emitting period. If the voltage fluctuation of the pixel electrode can be suppressed, the display apparatus can suppress an increase in the amount of light emission, which is caused by the voltage fluctuation at low luminance levels. If an unexpected increase in the amount of light emission is suppressed, which occurs at low luminance levels, the contrast can be improved. In order to increase the capacitance of the capacitive element, it is acceptable to increase an area of the capacitive element, but when the capacitive element is provided in each sub pixel, the space at which the capacitive element can be arranged is limited. Therefore, if the capacitive element is separated into a plurality of layers for each sub pixel and the capacitive elements are electrically connected to each other, the capacitive element can increase the capacitance. However, because it is necessary to distinguish capacitive elements in each sub pixel by patterning the capacitive elements among sub pixels, the size of the capacitive element results in decreasing correspondingly to the space necessary for patterning.

SUMMARY

Accordingly, an object of the present invention is to provide a display apparatus that has sufficiently large capacity of a capacitive element provided in each sub pixel, suppresses a voltage fluctuation of a pixel electrode, and can suppress an increase in the amount of light emission due to the voltage fluctuation, which occurs at low luminance levels.

According to an aspect of the present invention, the display apparatus comprises a pixel that has a first sub pixel and a second sub pixel which emits a color different from that of the first sub pixel, on a substrate, wherein each of the first sub pixel and the second sub pixel includes a light-emitting device, a transistor connected to the light emitting device, and a capacitive element connected to the transistor, wherein the capacitive element of the first sub pixel and the capacitive element of the second sub pixel at least partially overlap each other.

DESCRIPTION OF THE EMBODIMENTS

First Embodiment

Preferable Embodiments of the display apparatus of the present invention will be described with reference to the drawings.

FIG. 1illustrates an overall schematic diagram illustrating a display apparatus of the present embodiment. The display apparatus ofFIG. 1has a display region1, a horizontal drive circuit2, a vertical drive circuit3and a connection terminal unit4, on a substrate5. In the display region1, a plurality of pixels are arranged in a form of a matrix. The pixels have each a plurality of sub pixels. The plurality of sub pixels each have a first sub pixel and a second sub pixel which emits a different color from that of the first sub pixel, and further can have each a third sub pixel which emits a different color from those of both of the first sub pixel and the second sub pixel. The horizontal drive circuit2is a circuit which outputs a data signal, and is connected to an output line. The vertical drive circuit3is a circuit which outputs a selection signal. The connection terminal unit4is a terminal which inputs a clock signal, an image data signal and the like to the horizontal drive circuit2and the vertical drive circuit3, and is connected to the horizontal drive circuit2and the vertical drive circuit3by wires (unillustrated).

Each of the sub pixels has a current driven light-emitting device, a transistor for supplying an electric current to the light emitting device, and a capacitive element for maintaining a gate voltage of the transistor. The light emitting device which the sub pixel has may be an organic light-emitting device such as an organic electroluminescence device (organic EL device) which has a pair of electrodes and an organic compound layer arranged between the pair of electrodes. Examples of the pair of electrodes include an anode and a cathode.

The organic compound layer which the organic light-emitting device has may be formed of a single layer or a plurality of layers, as long as the organic compound layer has a light emitting layer. When the organic compound layer is formed of the plurality of layers, examples of the layers include a hole injection layer, a hole transporting layer, an electron blocking layer, a light emitting layer, a hole blocking layer, an electron transporting layer and an electron injecting layer.

The light emitting layer may be formed of a plurality of light emitting layers. When having the plurality of light emitting layers, the light emitting layer may come in contact with another light emitting layer. An intermediate layer may be provided between the light emitting layer and another light emitting layer.

The emission color of the light emitting layer is not limited in particular, but may be a white color due to light emissions of a plurality of light emitting layers. Combinations by which the light emitting layers emit white light include combinations of red, green and blue, combinations of blue and yellow or yellow-green, and the like. The yellow or the yellow-green may be formed by having both of red and green light emitting materials in the same light emitting layer.

In the case of the combination of the red, the green and the blue light emitting layers, an intermediate layer may be provided between the blue light emitting layer and another light emitting layer. More specifically, when the light emitting layers are arranged in order of red, blue and green from the anode side, an intermediate layer may be arranged between red and blue light emitting layers.

The light emitting device may have a protective layer on a pair of electrodes. The protective layer may be a plurality of layers. The protective layer may be formed by a CVD method, a sputtering method, an ALD method or the like. When the protective layer is formed of a plurality of layers, a plurality of production methods may be combined. For example, the first protective layer may be formed by the CVD method, and the second protective layer may be formed by the ALD method. Furthermore, the constituent materials of the plurality of protective layers may be different. Usable constituent materials of the protective layer include SiN, SiO, Al2O3and SiON.

The light emitting device may further have a color filter. The color filter may be color filters of red, green and blue. The red, green and blue color filters may be arranged in any way, but can be a delta arrangement. The delta arrangement includes an arrangement illustrated inFIG. 2. InFIG. 2, a pixel30and sub pixels10R,10G and10B are illustrated which emit colors of red (R), green (G) and blue (B), respectively.

Hereinafter, the case will be described as an example, where the light emitting device is an organic EL element and the pixel30has the sub pixels10R,10G and10B which emit the respective colors of R, G and B, but the present invention is not limited to the present example.

Firstly, a circuit connected to the sub pixel of the display apparatus of the present embodiment will be described with reference toFIG. 3.FIG. 3illustrates an equivalent circuit diagram of the pixel circuit connected to the sub pixel. InFIG. 3, the sub pixel10includes a current driving type organic EL element11of which the light emission luminance changes according to a flowing current, and a driving circuit which drives the organic EL element11.

In the organic EL element11, the cathode electrode is connected to a common power source25wired in common with all of the sub pixels10.

The driving circuit which drives the organic EL element11includes a driving transistor12, a selection transistor13, switching transistors14and15, a first capacitive element16and a second capacitive element17. A P-channel transistor is used for each of the driving transistor12, the selection transistor13, and the switching transistors14and15.

The driving transistor12is a transistor which supplies an electric current to the light emitting device, and supplies a driving current to the organic EL element11by being connected to the organic EL element11in series. Specifically, a drain electrode of the driving transistor12is connected to an anode electrode (pixel electrode) of the organic EL element11.

In the selection transistor13, the gate electrode is connected to a scanning line21, the source electrode is connected to a signal line24, and the drain electrode is connected to the gate electrode of the driving transistor12. To the gate electrode of the selection transistor13, written signals are applied from the vertical drive circuit3through the scanning line21.

In the switching transistor14, the gate electrode is connected to the scanning line22, the source electrode is connected to the first power supply potential VDD, and the drain electrode is connected to the source electrode of the driving transistor12. To the gate electrode of the switching transistor14, a signal for controlling luminescence is applied from the vertical drive circuit3through the scanning line22. In the other switching transistor15, the gate electrode is connected to the scanning line23, the source electrode is connected to a second power supply potential VSS, and the drain electrode is connected to the anode electrode of the organic EL element11. To the gate electrode of the switching transistor15, a signal for controlling a potential of the anode electrode of the organic EL element11is applied from the vertical drive circuit3through the scanning line23.

The first capacitive element16is a capacitive element which maintains the gate voltage of the transistor, and is connected to between the gate electrode and the source electrode of the driving transistor12. The second capacitive element17is connected to between the source electrode of the driving transistor12and the first power supply potential VDD. InFIG. 3, both of the first capacitive element16and the second capacitive element17are each illustrated as one capacitive element, but it is acceptable to use different capacitive elements which are electrically connected in parallel, as one capacitive element.

The vertical drive circuit3to which the scanning lines21,22and23are connected supplies signals sequentially row by row, thereby make the first capacitive element16of each of the sub pixels maintain the signal voltage and the reference voltage, and control the sub pixels so that the sub pixels emit light having luminance corresponding to the signal voltage.

InFIG. 3, a PMOS is used as a MOS transistor, but an NMOS may be used. In addition, the driving circuit is not limited to such a 4Tr2C circuit configuration as to include four transistors and two capacitive elements. In addition, a transistor formed on a silicon wafer may be used as the MOS transistor, or a thin film transistor formed on a glass substrate may be used.

In the sub pixel10having the above described configuration, the selection transistor13becomes a conductive state in response to a write signal which is applied from the vertical drive circuit3to the gate electrode through the scanning line21. By this operation, the selection transistor13samples the signal voltage or the reference voltage corresponding to the luminance information and writes the voltages in the sub pixel10. By applying the reference voltage, the vertical drive circuit3corrects the variation of threshold voltages of the driving transistors12in each of the sub pixels, and can reduce the variation of luminance of each of the sub pixels, which is caused by the variation of the threshold voltages. The written signal voltage or reference voltage is applied to the gate electrode of the driving transistor12, and also is maintained by the first capacitive element16.

The driving transistor12is designed so as to operate in a saturation region. The driving transistor12receives a supply of an electric current from the first power supply potential VDD via the switching transistor14, and makes the organic EL element11emit light by the current drive. At this time, the amount of electric current flowing through the organic EL element11is determined according to the voltage maintained by the first capacitive element16, and accordingly the driving transistor12can control the amount of light emission of the organic EL element11.

The switching transistor14becomes a conductive state in response to a signal for controlling light emission, which is applied to the gate electrode from the vertical drive circuit3through the scanning line22. Specifically, the switching transistor14has a function of controlling the luminescence and non-luminescence of the organic EL element11.

The switching transistor15selectively supplies the second power supply potential VSS to the anode electrode of the organic EL element11in response to a signal for controlling the potential of the anode electrode, which is applied to the gate electrode from the vertical drive circuit3through the scanning line23. Assuming that the common power source25connected to the cathode electrode of the organic EL element11is represented by Vcath and a threshold voltage of the organic EL element11is represented by Vthel, the second power source potential VSS is designed so as to satisfy the condition of VSS<Vcath+Vthel. Thereby, when the switching transistor15is in the conductive state, the VSS applies a reverse bias to the organic EL element11, and can control the organic EL element11to the non-luminescent state.

Next, in order to describe an arrangement relationship among the capacitive elements in the pixel of the present embodiment, firstly, a display apparatus of a comparative embodiment will be described below.

FIG. 7is an equivalent circuit diagram of a pixel circuit connected to a sub pixel of the display apparatus of the comparative embodiment. The difference from the pixel circuit illustrated inFIG. 3is a point that the first capacitive element16is configured as a capacitive element in which a plurality of capacitive elements16a,16band16care electrically connected in parallel.

FIGS. 8A and 8Bare views for describing the arrangement relationship among the capacitive elements in the pixel of the comparative embodiment.FIG. 8Aschematically illustrates a cross section of the first capacitive element16of the three sub pixels10R,10G and10B of RGB in a pixel30, and other elements in the pixel circuit are omitted. The cross section illustrated inFIG. 8Ais a plane which is perpendicular to the substrate plane (XY plane) and is along the arrayed direction (X direction) of the sub pixels10R,10G and10B, and an unillustrated substrate is positioned at a lower part of the page.FIG. 8Bis a sectional view taken along line8B-8B inFIG. 8A.

InFIG. 8A, a case of the R sub pixel10R will be described. Capacitive elements16aR,16bR, and16cR correspond to the capacitive elements16a,16band16cofFIG. 7, respectively. The capacitive element16aR is a capacitive element having a stacked structure, which includes an insulating layer32R stacked on the upper part of the lower electrode31R, and an upper electrode33R stacked on the upper part of the insulating layer32R. The capacitive elements16bR and16cR having a similar structure are provided with the use of other wiring layers and insulating layers, and the capacitive elements16aR,16bR and16cR in the R sub pixel10R can be used as one capacitive element (first capacitive element16) by being electrically connected in parallel. Also concerning a G sub pixel10G and a B sub pixel10B, similarly to the R sub pixel10R, three capacitive elements16a,16band16care electrically connected in parallel in each of the sub pixels10, and constitute the first capacitive element16.

In the comparative embodiment, the plurality of capacitive elements16a,16band16cwhich are stacked along a direction (Z direction) perpendicular to the substrate plane are connected in parallel in the sub pixel10with the use of different wiring layers and insulating layers, and thereby the capacity is increased in a limited planar space in the sub pixel10.

However, it is necessary to electrically distinguish the capacitive elements of different sub pixels10from each other, and accordingly in the comparative embodiment, the size of the capacitive element results in being decreased by an amount for securing the space therefor. In the comparative embodiment, the capacitive elements of the different sub pixels10are electrically distinguished from each other by patterning wiring layers for forming the lower electrode31and the upper electrode33. Specifically, as for the lower electrode31, a space35is provided between the lower electrodes31, in order to distinguish the capacitive elements of the different sub pixels10from each other, as illustrated inFIG. 8B. The arrangement of an upper electrode32is also similar, and as a result, the capacitive elements16aR,16aG and16aB are electrically insulated from each other. When a pixel size decreases because of high definition, the size of the capacitive element decreases by the amount of a space necessary for patterning the capacitive element, and there is a limit in increasing the capacitance of the capacitive element.

Incidentally, the comparative embodiment has been described with reference to the first capacitive element16, but all the capacitive elements using the wiring layer can be similarly described as in the above.

Next, the capacitive element in the pixel of the present embodiment will be described below with reference toFIGS. 4A and 4B.

FIGS. 4A and 4Billustrate views for describing an arrangement relationship among the capacitive elements in the pixel of the present embodiment.FIG. 4Aschematically illustrates a cross section of the first capacitive element16of the three sub pixels10R,10G and10B of RGB in the pixel30, and other elements in the pixel circuit are omitted. The cross section illustrated inFIG. 4Aillustrates a plane which is perpendicular to the substrate plane (XY plane) and is along the arrayed direction (X direction) of the sub pixels10R,10G and10B, and an unillustrated substrate is positioned at a lower part of the page.FIG. 4Billustrates a sectional view taken along the line4B-4B inFIG. 4A.

InFIG. 4A, a case of R sub pixel10R will be described. A first capacitive element16R corresponds to the first capacitive element16inFIG. 3. The first capacitive element16R is a capacitive element having a stacked structure, which includes an insulating layer32R stacked on the upper part of a lower electrode31R, and an upper electrode33R stacked on the upper part of the insulating layer32R. The first capacitive elements16G and16B of a G sub pixel10G and a B sub pixel10B are also similar to the R sub pixel10R.

The difference from the comparative embodiment is a point that the first capacitive elements16of the different sub pixels10overlap each other at least partially, can overlap each other totally, and specifically overlap when viewed from a direction (Z direction) perpendicular to a substrate plane. Specifically, the first capacitive element16is arranged so as to astride a planar region of another sub pixel10, similarly to all in the R sub pixel10R, the G sub pixel10G and the B sub pixel10B. In other words, a first capacitive element16G of the G sub pixel10G is stacked on the upper part of a first capacitive element16R of the R sub pixel10R, and a first capacitive element16B of the B sub pixel10B is stacked on the upper part of the capacitive element16G of the G sub pixel10G, so as to be electrically distinguished from each other, for example, by an insulating layer or the like.

In the present specification, to overlap can be also said to be stacked. In addition, to overlap also can mean that the capacitive element of the first sub pixel is arranged between the substrate and the capacitive element of the second sub pixel.

In the present embodiment, positions at which the first capacitive elements16are arranged are not partitioned by a planar area for each of the sub pixels10, but are partitioned with the use of a plurality of layers; and regions in which the first capacitive elements16are arranged are shared among different sub pixels10in a plane direction (XY plane direction). Because of this, the display apparatus can reduce a space for electrically distinguishing the first capacitive elements16between the different sub pixels10in the planar direction, and accordingly can form a size of the first capacitive element16large which is provided in each of the sub pixels10. If the capacity of the first capacitive element16increases, the resultant capacitive element16suppresses the voltage fluctuation of the pixel electrode, can prevent the amount of light emission from increasing due to the voltage fluctuation at low luminance levels, and can enhance the contrast.

In the present embodiment, the first capacitive elements16of the sub pixel10in the same pixel30are stacked so as to overlap each other planarly, and the first capacitive elements16of the sub pixels10of the different pixels30are electrically distinguished from each other by the patterning of the wiring layers, which forms the lower electrode31and the upper electrode33. However, the sub pixels10which are stacked so as to planarly overlap each other are not limited to the sub pixels10in the same pixel30, but, for example, the first capacitive elements16of the sub pixel10of the different pixels30may be stacked so as to planarly overlap each other. In addition, the order in which the first capacitive element16is stacked is not limited to the present embodiment, but, for example, the first capacitive element16B may be arranged on the upper part of the first capacitive element16R, and the first capacitive element16G may be stacked on the upper part of the first capacitive element162B.

The present embodiment has been described with reference to the first capacitive element16, but all the capacitive elements using the wiring layer can be similarly described, and for example, the present embodiment may be applied to a second capacitive element17. In addition, as in the comparative embodiment, it is acceptable to form a capacitive element which combines a structure in which capacitive elements in the same sub pixel are connected in parallel with each other, with a structure according to the present embodiment.

Second Embodiment

The present embodiment will be described with reference toFIG. 5.FIG. 5illustrates a view for describing an arrangement relationship among capacitive elements in a pixel of the present embodiment, and illustrates a cross section similar toFIG. 4A; and other elements in the pixel circuit are omitted similarly to that inFIG. 4A. The structure and description of the first embodiment can be similarly applied also to the present embodiment. The difference from the first embodiment of the present embodiment is that a conductive layer36is arranged between the first capacitive elements16of the different sub pixels10.

In the present embodiment, the conductive layer36is arranged between the first capacitive element16R and the first capacitive element16G, and between the first capacitive element16G and the first capacitive element16B. Due to the conductive layer36being arranged between the first capacitive elements16of the different sub pixels10, the display apparatus can suppress the capacitive coupling which occurs between the first capacitive elements16, and can reduce crosstalk between the sub pixels10. Because of this, the display apparatus can improve color reproducibility. It is desirable that the potential of the conductive layer36is fixed, and for example, the same potential as the second power supply potential VSS or the first power supply potential VDD can be supplied. The conductive layer36can be also referred to as a shield layer.

In the present embodiment, the conductive layer36is arranged not in a planar direction (XY plane direction) between the first capacitive elements16of the different sub pixels10, but in a space in a direction (Z direction) perpendicular to the planar direction. Thereby the display apparatus can reduce the crosstalk without reducing an area of the first capacitive element16.

Third Embodiment

The present embodiment will be described with reference toFIG. 6.FIG. 6is a view for describing an arrangement relationship among capacitive elements in a pixel of the present embodiment, and illustrates a cross section similar toFIG. 4A; and other elements in the pixel circuit are omitted similarly to that inFIG. 4A. The structure and description of the first embodiment can be similarly applied also to the present embodiment. The difference from the first embodiment of the present embodiment is that such a relationship that the first capacitive elements16of the different sub pixels10are stacked so as to planarly overlap each other holds for only sub pixels10of particular colors.

In the present embodiment, only the first capacitive element16R of the R sub pixel10R and the first capacitive element16G of the G sub pixel10G are stacked so as to planarly overlap each other. In the first capacitive element16B of the B sub pixel10B, the capacitive elements16aB and16bB are electrically connected in parallel. Because of this, though in the first embodiment, the first capacitive element16is formed by three layers in the direction perpendicular to the planar direction (XY plane direction), in the present embodiment, the first capacitive element16can be formed by two layers, and the capacitive elements to be stacked are reduced. Accordingly, the number of steps for forming the first capacitive elements16can be reduced, and accordingly an effect of improving the yield can be obtained.

In the present embodiment, only the first capacitive element of the B sub pixel10B is arranged so as not to planarly overlap the first capacitive elements16R and16G of the other sub pixels10R and10G, but the present embodiment is not limited to this combination, and the combination may be changed according to characteristics of the display element. For example, if it is necessary to increase the capacity of the first capacitive elements16of the G sub pixel10G and the B sub pixel10B as compared with the R sub pixel10R, the first capacitive elements16G and16B of the G sub pixel10G and the B sub pixel10B may be stacked so as to planarly overlap each other.

The display apparatus of the present invention may be used for a display unit of a television, a PC monitor, a display unit inside an automobile, a display unit of a mobile terminal, a display unit of a smartphone, and a display unit of a tablet terminal.

The display apparatus of the present invention may be used for a display unit of an imaging apparatus. The imaging apparatus may include an optical system having a plurality of lenses, and an imaging device which receives light passing through the optical system. The display unit displays an image photographed by the imaging device.

The imaging apparatus may be a digital still camera, a network camera or the like. In the case, the display unit may be a back face display unit of a digital still camera, a view finder, or a display unit showing a photographed image of another camera and/or a state of the camera.

As described above, according to the present invention, the display apparatus can increase the capacity of the capacitive elements provided in each of the sub pixels, accordingly can suppress the voltage fluctuation of the pixel electrode, and can suppress an increase of the amount of light emission due to the voltage fluctuation at low luminance levels.

According to the present invention, the display apparatus can increase the capacity of the capacitive elements provided in each of the sub pixels, accordingly can suppress the voltage fluctuation of the pixel electrode, and can suppress the increase of the amount of light emission due to the voltage fluctuation at low luminance levels.

This application claims the benefit of Japanese Patent Application No. 2018-001601, filed Jan. 10, 2018, which is hereby incorporated by reference herein in its entirety.