Next, exemplary embodiments of the present invention will be described with reference to appended drawings.
The aspect of the present invention is to reduce problems that are caused by the time lag between charge-discharge times occurring due to the wiring resistance and the capacitance on a drive substrate when it is driven by a constant voltage, that is the time lag between times required for respective light emitting elements to reach predetermined brightness when the image signal voltage is applied to the organic EL element.
Otherwise, the aspect of the present invention is to reduce problems that are caused by the time lag between charge-discharge times, occurring due to the wiring resistance and the capacitance on a drive substrate when it is driven by constant current, that is the time lag between times required for respective light emitting element to reach predetermined brightness with respect to application of the image signal voltage of the organic EL element, when it is driven by constant current.
The main aspect of the present invention is to provide a difference of wiring resistances or wiring capacitances to which pixels having light emitting elements emitting different colors, respectively, are connected.
A matrix display apparatus in which light emitting elements are arranged in row directions and column directions, in many cases, has a stripe arrangement in which different colors are periodically arranged in row directions, and same colors are arranged in column directions. Scanning signal wirings are provided in row directions and a scanning signal is applied to the scanning signal wiring to control the drive of the light emitting element in every row. Moreover, image signal wirings are provided in column directions, and an image signal is supplied to a light emitting element connected to the image signal wiring in a column direction. Even when different colors are arranged in column directions such as in delta arrangement, each image signal wiring is connected to light emitting elements of a same color while being bent in a column direction.
The present invention is applied to such a matrix display apparatus in which each image signal wiring is connected to light emitting elements of a same color.
In general, since the color of the light emitting element is determined by the luminescent material thereof, the light emission efficiency thereof differs every color. For this reason, voltage or current applied to the light emitting element of each color usually differs every color.
Since the voltage or the current is applied to the light emitting element through each image signal wiring from a drive circuit, the voltage or the current of the image signal wiring will differ depending on the color.
A constant amount of capacitance is attached to the image signal wiring, as a load, due to the parasitic capacitance caused by the intersection with the scanning line and the capacitance of a pixel including the light emitting element (hereinafter, the load capacitance is referred to as a wiring capacitance). If the wiring resistance and the wiring capacitance of the image signal wiring has same values, respectively, without depending on the color, rise time until voltage or current reaches to a stable state after they are changed, differs depending on the color. Therefore, even if voltage or current corresponding to a set brightness is applied, practical brightness containing a transitional change will shift from the brightness set by the rise time.
The aspect of the present invention is to cause the wiring resistance and the wiring capacitance of each image signal wiring to differ in a direction where the time rag between rise times during voltage change becomes smaller and uniform.
In order to change the wiring resistance of each image signal wiring according to color, means for, for example, wiring using different materials, wiring so as to be different wiring widths, and wiring so as to be different thicknesses, are used. Moreover, in order to change the wiring capacitance of each image signal wiring according to color, means for, for example, such as wiring the intersection point with respect to the scanning wiring at different wiring widths, wiring insulation layers of different thicknesses between the scanning wirings, and wiring insulation layers made of different materials between the scanning wirings.
This enables the above-mentioned problems to be coped with in view of the material manufacturing the display element, without using a large-scale drive circuit. In other words, even if an organic EL light emitting element, a light emission voltage of which is low and a charge-discharge time of which is short, and an organic EL light emitting element, a light emission voltage of which is high and a charge-discharge time of which is long are present on a panel in a mixed manner, the time lag between charge-discharge times of a capacitance being parasitic through the resistance of the wiring from the image signal voltage source and a hold capacitance, does not act severely on a display. Moreover, even if an organic EL light emitting element, a light emission current of which is large and a charge-discharge time of which is short, and an organic EL light emitting element, a light emission current of which is small and a charge-discharge time of which is long are present on a panel in a mixed manner, the time lag between charge-discharge times of capacitance being parasitic through the resistance of the wiring from the image signal current source, does not act severely on a display.
Accordingly, in a display element in which the drive voltage or the drive current differs depending on the color, it is possible to shorten the time lag between charge-discharge times caused by the wiring resistance and wiring capacitance on the drive substrate, without using a large-scale drive circuit. This enables the current drive display device to display well without smearing except for the display image.
A display system illustrated in
First, image signal voltage is applied through the image signal wiring 32. After that a scanning signal wiring 33 is selected, and TFT 34 in P channel will be in ON state. Thereby, in a capacitance 30, the image signal voltage level applied to the image signal wiring 32 is held. At that time, TFT 36 of N channel flows current corresponding to this setting voltage from an electric power 38 to an organic EL light emitting element 37. After that, the scanning signal wiring 33 is caused to be in a non-selected state, and TFT 34 of P channel will be in OFF state. After that, TFT 36 of N channel also continues to flow current corresponding to gate voltage set in the capacitance 30 to the organic EL light emitting element 37. By means of a series of the above-mentioned operations, the organic EL light emitting element 37 emits light.
Here, in the light emission layer of an organic EL element used for a pixel, materials such as materials emitting phosphorescence in a triplet state, whose structural formula are illustrated in
Pixels having a light emitting element using an organic EL element configured as above, as illustrated in the above-mentioned display element 1 in
In such a substrate, as illustrated in
If there are fluctuations in rise times, the brightness will be shifted from a value set by current. If the rise time is slow, the brightness will be lower than the value set by current, resulting in imbalance of white balance. Therefore, rise times must be equal to each other for R, G and B.
Herein after, specific embodiments of the present invention will be described.
First, First Embodiment of the present invention will be described in detail with reference to the drawings. In this embodiment, an organic EL element is applied to a display element configured to be driven by constant voltage.
In a display element 1 having light emitting pixels of R, G and B, the required brightness when white balance is considered is 50 cd/m2 for R, 100 cd/m2 for G, and 25 cd/m2 for B, the required drive current at that time is 60 μA for R, 166 μA for G, and 159 μA for B, and the voltage applied to the organic EL element for flowing the current, is 6 V for R, 5 V for G, and 4 V for B, as the gate voltage of the drive TFT.
In this embodiment, wirings are arranged so that the wiring width of the corresponding image signal wiring differs every color of pixels. In other words, as illustrated in
At that time, wiring resistances of each image signal wirings are 100 kΩ for R, 120 kΩ for G, and 150 kΩ for B. Since a superposed area at the intersection part between the image signal wiring and the scanning wiring are equal for R, G and B, wiring capacitances for R, G and B will be a same value.
As for the numbers provided in each row in
By assuming that the data line capacitance is 30 pF and the hold capacitance is 5 pF, the capacitance load is assumed to be 35 pF that is the summation of them.
Since the data line resistance of R is set to 100 kΩ, when the gate voltage is 6 V and current is 60 μA, the rise time becomes 19.87 μs. Moreover, since the data line resistance of G is set to 120 kΩ, the rise time when the gate voltage is 5 V and current is 166 μA, also becomes 19.87 μs, and since the data line resistance of B is set to 150 kΩ, the rise time when the gate voltage is 4 V and current is 159 μA, also becomes 19.87 μs.
According to simulation, the rise waveform of image signal wiring for R become such a wave form illustrated in
Next, Second Embodiment of the present invention will be described in detail with reference to the drawings. In this Embodiment, similar to First Embodiment, an organic EL element is also applied to a display element configured to be driven by constant voltage. In addition, descriptions of similar components as those in First Embodiment will be simplified or eliminated.
In this embodiment, wirings are arranged so that the wiring width of the corresponding image signal wiring differs every color of pixels. In other words, as illustrated in
Next, Third Embodiment of the present invention will be described in detail with reference to the drawings. In this Embodiment, similar to First Embodiment, an organic EL element is also applied to a display device configured to be driven by constant voltage. In addition, descriptions of similar components as those in First Embodiment will be simplified or eliminated.
In this embodiment, wirings are arranged so that the material used for wiring the corresponding image signal wiring differs every color of pixels. In other words, as illustrated in
By the difference of wiring materials for each color, the relationship between the drive voltage and the wiring time constant is adjusted every color, thereby, resulting in that the rise waveforms for R, G and B will have substantially a same rise time for the three colors.
Next, Fourth Embodiment of the present invention will be described in detail with reference to the drawings. In this Embodiment, an organic EL element is applied to a display device configured to be driven by constant current. In addition, since the element configuration of the organic EL element is similar to those in
First, a scanning signal wiring 43 is selected, and TFT 45 of N channel turns into ON state. Then, drive current is applied to an organic EL light emitting element 37 through an image signal wiring 42 to cause it to be in an effective state. After that, a hold signal wiring 44 is selected, and TFT 47 of P channel turns into ON state. By this, TFT 46 of P channel flows the drive current into the channel thereof, to generate a conversed voltage level at the gate thereof, and capacitance 40 holds the voltage level generated at the gate of TFT 46. At that time, TFT 48 of P channel flows current set in this time into the organic EL light emitting element 37. Next, when the hold signal wiring 44 is out of selection and TFT 47 is turned into OFF state, TFT 48 of P channel flows constant current corresponding to the voltage level of the hold capacitance 40 into the organic EL light emitting element 37. By the above-mentioned series of operations, the organic EL light emitting element 37 emits light.
Pixels having the light emitting elements are arranged in a matrix, where image signal wirings 104, 105 and 106 are connected in column directions, and scanning signal wirings 107 are connected in row directions, as illustrated in the above-mentioned display element 1 in
In such a substrate, as illustrated in
In a display element 1 having light emitting pixels for R, G and B, required brightnesses by considering white balance are 50 cd/m2 for R, 100 cd/m2 for G, and 25 cd/m2 for B. At that time, current of 161.6 nA flows into the image signal wiring 104 for R, current of 323.2 nA flows into the image signal wiring 105 for G, and current of 1028 nA flows into the image signal wiring 106 for B. Moreover, voltages at that time are 2.1 V, 2.4 V and 2.7 V, respectively. When reading the charge times at that time in
In this embodiment, in order to cause charge times to be equal, wirings are arranged so that, in the image signal wiring, the wiring width of the wiring intersection with respect to the scanning signal wiring differs every color of pixels. In other words, as illustrated in
By this the relationship between the drive current and the wiring time constant is adjusted every color depending on the difference between wiring capacitances. According to simulation, the rise waveform of R image signal wiring became such a wave form illustrated in
Next, Fifth Embodiment of the present invention will be described in detail with reference to the drawings. In this Embodiment, similar to First Embodiment, an organic EL element is also applied to a display element configured to be driven by constant current. In addition, regarding to similar components as those in First Embodiment, descriptions thereof will be simplified or eliminated.
In this embodiment, wirings are arranged so that, in the image signal wiring, the thickness of an insulation film between the image signal wiring and the scanning signal wiring differs every color of pixels. In other words, as illustrated in
By this, the relationship between the drive current and the wiring time constant is adjusted every color depending on the difference between wiring capacitances, thereby, similar to Fourth Embodiment, the rise waveforms for R, G and B become substantially similar to each other.
Next, Sixth Embodiment of the present invention will be described in detail with reference to the drawings. In this Embodiment, similar to First Embodiment, an organic EL element is also applied to a display element configured to be driven by constant current. In addition, regarding to similar components as those in First Embodiment, descriptions thereof will be simplified or eliminated.
In this embodiment, wirings are arranged so that, in the image signal wiring, the material of an insulation film between the image signal wiring and the scanning signal wiring differs every color of pixels. In other words, as illustrated in
The relative dielectric constants of each wiring material are illustrated in
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2006-181667, filed on Jun. 30, 2006, which is hereby incorporated by reference herein in its entirety.
Number | Date | Country | Kind |
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2006/181667 | Jun 2006 | JP | national |