JP2006251816A - Image display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a large area and high resolution panel without degrading an organic EL element and without using an active element such as a TFT by driving, by an active driving circuit thin film display elements having a rectifying characteristic which are connected in a reverse direction for composing a display pixel. <P>SOLUTION: A pixel display unit has: a first thin film display element with a hole transport layer, a light emitting layer, an electronic transport layer, and electrodes laminated on a first transparent electrode 2; and a second thin film display element with a hole transport layer, a light emitting layer, an electronic transport layer, and electrodes laminated on a second transparent electrode 2. The first thin film display element and the second thin film display element are connected in parallel through two connecting wires so that their polarities are mutually reversed, and form a pixel. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image display device, and an image in which a thin film display element having a rectifying characteristic, such as an organic electroluminescence (EL) image display device, can be driven without using a thin film transistor (TFT) circuit for switching. The present invention relates to a display device.

As shown in FIG. 6, an organic EL image display device using a conventional TFT active matrix driving circuit includes a screen unit 10 having pixels 10-1, 10-2, 10-3, 10-4,. A shift register 15 for outputting an axis signal and a shift register 16 for outputting a Y-axis signal are provided. A power source E ₀ for organic EL is applied to the screen unit 10.

The pixel 10-1 includes an organic EL element EL ₁ that is a thin film for light emission, a bias TFT 11-1 that controls light emission of the organic EL ₁ , and a capacitor C ₁ connected to the gate electrode of the bias TFT 11-1. configured to the capacitor C ₁ in Y-axis select switch 12-1 for writing a signal is written. Other pixels 10-2, 10-3, 10-4,... Are configured similarly to the pixel 10-1.

The Y coordinate select switch 12-1 is constituted by a TFT, and its gate electrode is connected to the terminal Y ₁ of the shift register 16. The Y coordinate select switch 12-1 is also connected to the X coordinate select switch 13. The X coordinate select switch 13 is also composed of a TFT, and its gate electrode is connected to the terminal X ₁ of the shift register 15. Note that the image data signal Di is input to the X coordinate select switch 13.

Accordingly, in the shift register 16 for the Y-axis, the synchronization signal from the terminal Y ₁ is output, Y-axis select switch 12-1, 12-2 ... it is turned on. At this time, when a synchronization signal is output to the terminal X ₁ in the X-axis shift register 15, the X coordinate select switch 13 is turned on, and the image data signal D ₁ input to the X coordinate select switch 13 is converted to the Y coordinate select switch. It is held in the capacitor C ₁ via 12-1.

Next, when a synchronization signal is output to the terminal X ₂ , the X coordinate select switch 13 is turned off and the X coordinate select switch 14 is turned on at the same time, and the image data signal D ₂ input to the X coordinate select switch 14 at this time is It is held in the capacitor C ₂ via the Y coordinate select switch 12-2. Therefore, Y-axis select switch 12-1, 12-2, ... serves as a select switch for writing for accumulating charge corresponding to the image data signal to the capacitor C _1, C ₂ ···.

In this way, the image data signals D ₁ , D ₂ ... Are held in the capacitors C ₁ , C ₂ ..., And the bias TFTs 11-1, 11-2. The EL elements EL ₁ , EL ₂ ... Are controlled to emit light according to the image data signals D ₁ , D ₂ . In this way, after the pixels 10-1, 10-2,... With respect to the terminal Y ₁ perform the light emission control operation, the Y-axis shift register 16 outputs a synchronization signal to the terminal Y _2. -3, 10-4,... Such an EL image display device is, for example, I.I. E. E. E. Trans. Electron Devices, Vol. ED-22, no. 9, Sept. 1975 (p739-p749).

  By the way, when driving a thin film display element, a line sequential driving type simple matrix driving circuit as shown in FIG. 7 may be used.

In FIG. 7, organic EL elements E ₁₁ , E ₁₂ , E ₂₁ , E ₂₂ are respectively connected as shown, and a voltage V volt or 0 volt pulse voltage via a current limiting resistor R is applied to rows 1 and 2. A voltage of 0 volt or V volt is simultaneously applied to row 1 and row 2.

At time t ₁ , as shown in FIG. 7, when the voltage V volt is applied to the row 1, the row 2 is held in the ground state, and the column 1 and the column 2 are each applied with 0 volt, the organic EL element E ₁₁ and E ₁₂ is a lighting state organic EL element E _21, E ₂₂ becomes off state.

At the next time t ₂ , row 1 is now held at ground, voltage V volts is applied to row 2, column 1 is applied with 0 volts, and column 2 is applied with voltage V volts. Thus the organic EL element E ₂₁ becomes lit, the organic EL element E ₁₁ and E _12, E ₂₂ becomes off state.

If this is repeatedly controlled, for example, at 60 Hz where the human eye cannot follow, only the organic EL element E ₂₂ can be displayed in an off state.

In this way, the organic EL elements E _{11 to} E ₂₂ can be selectively displayed and controlled by sequentially applying the voltage V volts to the rows and the V volts or 0 volts to the columns. The luminance of the EL elements other than E ₂₂ at this time is the time average of the luminance at the time of lighting, and in a panel having two rows as shown in FIG.

  As shown in FIG. 6, the organic EL image display device requires a plurality of TFTs per pixel. Therefore, it is difficult to use TFTs from the viewpoint of capital investment and yield when considering the enlargement of the screen of the organic EL image display device.

  Further, in the line sequential driving type simple matrix driving circuit as shown in FIG. 7, the luminance of the panel is the time average of the luminance at the time of lighting, so that the stronger the light is required from the organic EL element as the number of rows increases. A large applied voltage is required, and the maximum number of rows or the luminance of the panel is limited from the withstand voltage and lifetime of the organic EL element.

  Therefore, an object of the present invention is to provide an image display device in which a TFT select switch is not used for selecting an organic EL element.

  Another object of the present invention is to provide an image display device with high brightness and high resolution without damaging the organic EL element.

In order to achieve the above object, in the related art of the present invention, for example, as shown in FIG. 1A, organic EL elements EL ₁₁ , EL ₁₂ , EL ₂₁ , EL between rows 1, 2, columns 1, and 2 are arranged. ₂₂ , and each organic EL element EL _{11 to} EL ₂₂ is constituted by thin film elements e ₁ and e ₂ connected in parallel with opposite polarities, as the organic EL element EL ₁₁ is typically given a reference numeral.

  Even when this element is used, selective lighting is possible using a line-sequential driving simple matrix driving circuit.

At time t ₁ , as shown in FIG. 1A, a voltage v volt is applied to the row 1 via the current limiting resistor R, the row 2 is held in the ground state, and the columns 1 and 2 are arbitrarily when the voltage -a volts is applied, the organic EL element E ₁₁ and E ₁₂ (v + a) but is sufficiently bright lighting state is applied the organic EL element EL _21, EL ₂₂ is only a is applied Stay in a weakly lit state.

At the next time t ₂ , this time, row 1 is held in the ground state, voltage v volt is applied to row 2 through current limiting resistor R, −a volt is applied to column 1, and column 2 is applied to column 2. A volt is applied. Thus it is only the organic EL element EL ₂₁ is (v + a) but is sufficiently bright lighting state is applied the organic EL element EL _11, the EL ₁₂ a is applied, also the organic EL element EL ₂₂ ( Since only va) is applied, these organic EL elements EL ₁₁ , EL ₁₂ , EL ₂₂ remain weakly lit.

If the period of (t ₁ + t ₂ ) is one cycle, the square value of the effective voltage applied to the organic EL elements EL ₁₁ , EL ₁₂ , EL ₂₁ is (v ² + 2av + 2a ² ) as shown in FIG. ) / 4, and the organic EL element EL ₂₂ becomes (v ² -2av + 2a ² ) / 4. This repetitive control was at 60Hz, for example can not follow the human eye, and the organic EL element of ^{(v 2 + 2av + 2a 2} ) / 4 of the square root of the voltage and brightness (i.e., effective ^{voltage) (v 2 -2av + 2a 2} ) / 4 If the voltage v volt and the voltage a volt are adjusted so as to give a sufficient contrast ratio to the brightness of the square root voltage, only the organic EL element EL ₂₂ can be displayed in the off state. The maximum voltage instantaneously applied to the organic EL element is v + a.

As will be described later in detail, at time t ₁ , a voltage v volt is applied to row 1 and row 2 from the pulse power source through current limiting resistor R, −2a volt is applied to column 1, and 0 volt is applied to column 2. To do. As a result, (v + 2a) is applied to the organic EL elements EL ₁₁ and EL _{21 so that they} are in a sufficiently bright lighting state. However, the organic EL elements EL ₁₂ and EL ₂₂ are only applied with v and remain in a weak lighting state. At the next time t ₂ , a voltage v volt is applied to the row 1 from the pulse power supply through the current limiting resistor R, a voltage −v volt is applied to the row 2, 0 volt is applied to the column 1, and − Apply 2a volts. Thus it is only the organic EL element EL ₁₂ is (v + 2a) but is sufficiently bright lighting state is applied the organic EL element EL _11, EL _21, the v is applied, also the organic EL element EL ₂₂ ( Since only v-2a) is applied, these organic EL elements EL ₁₁ , EL ₂₁ , EL ₂₂ remain in a weakly lit state.

If the period of (t ₁ + t ₂ ) is one cycle, the square value of the effective voltage applied to the organic EL elements EL ₁₁ , EL ₁₂ , EL ₂₁ is 2 (v ² + 2av + 2a as shown in FIG. 1C. ² ) / 4, and the organic EL element EL ₂₂ becomes 2 (v ² -2av + 2a ² ) / 4. If v is adjusted to 1 / √2v and −2a to −√2a, an effective voltage equal to that in FIG. 1B can be obtained. The maximum voltage instantaneously applied to the organic EL element is 1 / √2v + √2a.

  If v and a are selected by this active driving method, an increase due to an increase in the number of rows of the voltage applied to the organic EL element can be suppressed. Thus, a high number of rows, that is, a high resolution panel or a high luminance panel can be manufactured. Moreover, since a TFT select switch is not required, the area can be easily increased.

  As described above, the present invention has the following effects.

  (1): A thin film display element having a rectifying characteristic is connected in the reverse direction to constitute a display pixel, so that it can be driven by an active drive circuit, without using an active element such as a TFT and without damaging the organic EL element. A large-area, high-resolution panel can be provided.

  (2): Since the thin film display elements are arranged in a planar shape, the degree of freedom in selecting the organic material and the electrode material constituting the organic EL element is increased, and an image display apparatus having good characteristics can be provided.

  (3): According to the related art of the present invention, since the thin film display elements are three-dimensionally arranged, it is possible to provide an image display device in which the light source is arranged small and the light source emits light strongly. In addition, the effective light emission area can be increased.

  (4): Since the image display device is driven by an active drive circuit of a plurality of line selection type, the effective voltage that is required can be obtained without increasing the applied voltage in order to continue light emission for the selected long time. A product with a lifetime can be provided.

  The present invention will be described with reference to FIGS. FIG. 1 shows an embodiment of the present invention, and FIG. 2 is an example of a form constituting this organic EL element.

In the embodiment of the present invention, for example, as shown in FIG. 1, in an active drive circuit, organic EL thin film display elements e ₁ and e ₂ arranged in a planar shape shown in FIG. The organic EL elements EL _{11 to} EL ₂₂ are used.

  First, the organic EL element will be described.

In this example, as shown in FIGS. 2A and 2B, one pixel is constituted by thin film display elements e ₁ and e ₂ , and these are arranged on a glass substrate 1 in a planar shape.

The thin film display element e ₁ includes a hole transport layer P, a light emitting layer I, an electron transport layer N, and an electrode E on a transparent electrode 2 formed on a glass substrate 1 as shown in a sectional view in FIG. It is constructed by stacking. The thin film display element e ₂ is formed by laminating a hole transport layer P, a light emitting layer I, an electron transport layer N, and an electrode E on the transparent electrode 2 formed on the glass substrate 1 like the thin film display element e _1. Composed. Since these thin film display elements e ₁ and e ₂ have an n-type electron transport layer N and a p-type hole transport layer P, respectively, they have a rectifying characteristic, so that the thin film display elements e ₁ have opposite polarities. , E ₂ are connected in parallel. For example, the connection lines W ₁ and W ₂ as shown in FIG.

  The hole transport layer P is for injecting and transporting holes from the electrode, and the light emitting layer I is for taking out light emission by efficiently recombining holes and electrons. The electron transport layer N is for transporting electrons injected from the electrodes.

As shown in FIG. 2, when thin film display elements e ₁ and e ₂ are connected in parallel with a reverse polarity in a plane, the area of light emission in one pixel is halved, so that the panel luminance is halved. However, the degree of freedom of selection with respect to the organic material and the electrode material is great, and therefore, a material with good characteristics can be provided. The decrease in panel brightness can be offset by increasing the input voltage.

Next, display control when such organic EL elements EL _{11 to} EL ₂₂ are used will be described in detail with reference to FIG.

In the case of controlling the display of the organic EL elements EL _{11 to} EL ₂₂ , a plurality of lines (two lines of row 1 and row 2 in the example of FIG. 1A) are selected at the same time, and a pulse voltage is applied to them. The voltage applied via the limiting resistor R is applied to the columns 1 and 2 to control the lighting and extinction correspondingly.

First, at time t ₁ , voltage v volts is applied to row 1 and row 2 from the pulse power source via current limiting resistor R, −2 a volts is applied to column 1, and 0 volts is applied to column 2. As a result, the organic EL elements EL ₁₁ and EL ₂₁ are in a sufficiently bright lighting state, but the organic EL elements EL ₁₂ and EL ₂₂ remain in a weak lighting state.

Next, at time t ₂ , a voltage v volt is applied to row 1 from the pulse power source through a current limiting resistor R, a voltage −v volt is applied to row 2, 0 volt is applied to column 1, and − Apply 2a volts. As a result, the organic EL element EL ₁₂ is in a sufficiently bright lighting state, but the organic EL elements EL ₁₁ , EL ₂₁ and EL ₂₂ remain in a weak lighting state.

Therefore, if the time of (t ₁ + t ₂ ) is one cycle, the square value of the effective voltage applied to the organic EL elements EL ₁₁ , EL ₁₂ , EL ₂₁ is 2 (v ² + 2av + 2a) as shown in FIG. ² ) / 4, and the organic EL element EL ₂₂ becomes 2 (v ² -2av + 2a ² ) / 4. This is repeatedly controlled, for example, at 60 Hz that the human eye cannot follow, and the luminance of the square root voltage of the organic EL element (v ² + 2av + 2a ² ) / 4 and the luminance of the square root voltage of (v ² −2av + 2a ² ) / 4. By adjusting v and a so that a sufficient contrast ratio can be obtained, only the organic EL element EL ₂₂ can be displayed in a light-off state. If v is adjusted to 1 / √2v and −2a to −√2a, an effective voltage equal to that in FIG. 1B can be obtained.

Hereinafter, the reason why the thin film display elements e ₁ and e ₂ are connected in parallel in reverse polarity and the active drive is used will be described.

Now, when the emission intensity at which an arbitrary pixel is to be displayed by line sequential scanning using a line buffer is Xcd / m2, if the number of vertical scans (number of rows) is N, an arbitrary pixel is required for each field. Emission intensity Lcd / m ² is Lmax = X · N
It becomes.

For example, when the emission intensity to be displayed is 150 cd / m ² and the number of vertical scanning lines is 640, the emission intensity Lmax required for any pixel for each field is:
Lmax = 150 × 640 = 96000 cd / m ²
become.

Now, assuming that V = 5 volts is input to a circuit having two vertical scanning lines as shown in FIG. 7 via a current limiting resistor R, the light emission luminance of this panel is that the current limiting resistor R is applied to the organic EL element. The brightness is the same as when a constant voltage of 2.5 volts is applied. At this time, a maximum of 5 volts is instantaneously applied to the organic EL elements E _11, E ₁₂ , and E ₂₁ via the current limiting resistor R.

Similarly to this, in order to realize the luminance by the line-sequential driving method with the circuit shown in FIG. 1A, v = 3 volts is input through the current limiting resistor R, and line-sequential driving is performed as described above when a = 1 volt. It may be controlled by the method. At this time, an instantaneous maximum of 4 (3 + 1 = 4) volts is applied to the organic EL elements EL ₁₁ or EL ₁₂ , EL ₂₁ via the current limiting resistor R.

In order to realize the same luminance by the active drive system with the circuit shown in FIG. 1A, v = about 2.1 volts is input through the current limiting resistor R, and a = about 1.4 volts. It may be controlled by the active driving method as described above. At this time, a maximum of about 3.5 volts is applied to the elements EL _11, EL ₁₂ , and EL ₂₁ via the current limiting resistor R.

  As described above, in order to realize the same luminance, the line-sequential driving method is used in the circuit as shown in FIG. 1A than the conventional driving method as shown in FIG. 7, and as shown in FIG. In the circuit, the active drive method can lower the maximum voltage applied instantaneously.

  In the present example, N = 2 is taken up, but these relations are established by an arbitrary N. Now, when line-sequential driving is performed in the circuit of FIG. 1A, the effective voltage Eon during lighting applied to an arbitrary pixel is

に示す（１）式となる。ここでｖは走査線側の駆動電圧の絶対値、ａはデータ線側の駆動電圧の絶対値、Ｎは走査線の本数である。この式は（２）式の様に表すことができる。一方、従来方式の回路での線順次駆動方式の実効電圧はＶ／Ｎで表せる。ここでＶはパルス電源より印加される電圧を表す。今Ｎ＞１であるのでこの２つの実効電圧を等しくするにはこれらの関係よりＶ＞（ｖ＋ａ）の関係が成り立つ。この時の（ｖ＋ａ）は図１（ａ）の回路で線順次駆動を行ったときの最大瞬間の印加電圧に他ならない。

(1) shown in FIG. Here, v is the absolute value of the driving voltage on the scanning line side, a is the absolute value of the driving voltage on the data line side, and N is the number of scanning lines. This equation can be expressed as equation (2). On the other hand, the effective voltage of the line sequential driving method in the conventional circuit can be expressed by V / N. Here, V represents a voltage applied from the pulse power supply. Since N> 1 now, in order to make these two effective voltages equal, the relationship of V> (v + a) is established from these relationships. (V + a) at this time is nothing but the maximum applied voltage when line-sequential driving is performed in the circuit of FIG.

  Further, as described above, the active drive under the condition that all scanning lines are always selected can be achieved by adjusting the line sequential drive in FIG. 1A by adjusting v to (1 / √N) v and a to √N · a. Since effective voltage equal to the case can be obtained, if v and a are selected so that v> √N · a.

という関係が成り立ち、図１（ａ）の回路を用いた線順次駆動よりアクティブ駆動の方が瞬間の最大電圧を低く抑える事ができる。

Thus, the maximum voltage at the moment can be kept lower in the active drive than in the line sequential drive using the circuit of FIG.

  The problem here is that the active drive is a kind of alternating current drive, and therefore it is not possible to use EL, which is usually a rectifying element. However, in the present invention, one pixel is configured by connecting two display elements with opposite polarities, and one display element emits light when the voltage is positive, and the other display element emits light when the voltage is negative. The rectification can be canceled out. However, in the embodiment of the present invention shown in FIG. 2, since the light emission area in one pixel is halved, it is necessary to double the light emission intensity of any pixel to cancel the decrease in average luminance due to the reduction of the light emission area. There is.

An embodiment of the present invention will be described with reference to FIG. Figure in 3, on the transparent electrode 2 formed on the glass substrate 1, an organic EL thin film display element e ₁ of the electron transport layer N and the hole transport layer P and the transparent electrode 2 of the thin film display element e ₂ of the organic EL It is connected by. Thereby, the connection can be easily performed, and these can be easily connected to the reverse polarity. The drive circuit uses an active drive circuit as shown in FIG.

A related art form of the present invention will be described with reference to FIG. FIG. 4A shows a structure in which two organic EL thin film display elements e ₁ and e ₂ are three-dimensionally stacked. In this case, the connection part of the thin film display elements e ₁ and e ₂ is also constituted by the transparent electrode 2. Thereby, the light emission from the light emitting layer of the organic EL elements EL ₁ and EL ₂ can be effectively taken out from the glass substrate 1 side. 4B is an electrical connection diagram when the organic EL thin film display elements e ₁ and e ₂ are driven by the pulse power source PE. The drive circuit uses an active drive circuit as shown in FIG.

  As shown in FIG. 4, the three-dimensional arrangement can avoid the reduction of the light emission area in the pixel. As shown in FIGS. 2 and 3, the light emission intensity of an arbitrary pixel is doubled and the light emission area is reduced. There is no need to cancel the decrease in average luminance, and an increase in applied voltage can be suppressed. Further, since each pixel can be configured with a small area, a higher density panel can be formed.

  In the above description, the 2 × 2 state of the organic EL element has been described. Based on FIG. In this case, as shown in FIG. 5B, the data format indicates a light and dark horizontal stripe pattern in which "-1-1-1-1" (bright) and "0000" (dark) are combined.

As shown in FIG. 5C, at time t ₁ , v volt is applied to all of the rows 1 to 4 and −2 a volt is applied to all of the columns 1 to 4, so that FIG. The organic EL elements EL _{11 to} EL ₄₄ are all in a sufficiently bright lighting state.

At time t ₂ , v volt is applied to row 1 and row 3, −v volt is applied to row 2 and row 4, and −2a volt is applied to all of columns 1 to 4, so FIG. In A), the organic EL elements EL _{11 to} EL ₁₄ and the organic EL elements EL _{31 to} EL ₃₄ in the rows 1 and 3 are sufficiently lit, but the organic EL elements EL _{21 to} EL ₂₄ and the organic in the rows 2 and 4 are organic. The EL elements EL _{41 to} EL ₄₄ are weakly lit.

At time t ₃ , v volt is applied to row 1 and row 2, −v volt is applied to row 3 and row 4, and 0 volt is applied to all of columns 1 to 4, so organic EL element EL _{11 to} EL ₄₄ are all weakly lit.

At time t ₄ , v volt is applied to row 1 and row 4, −v volt is applied to row 2 and row 3, and 0 volt is applied to all of columns 1 to 4, so organic EL element EL ₁₁ All of EL ₄₄ are weakly lit.

  In this way, a bright and dark horizontal stripe pattern can be displayed.

  The display element of the present invention is not limited to these 2 × 2, 4 × 4 and the like. The active drive method is a known one as described in, for example, Nikkei Electronics 1994, 9, 26 (p179 to p191).

It is an embodiment figure of the present invention. It is an embodiment figure of the present invention. It is an embodiment figure of the present invention. It is a form figure of the related technology of this invention. It is an embodiment figure of the present invention. It is a conventional TFT active matrix drive circuit diagram. It is a line sequential drive type drive circuit diagram.

Explanation of symbols

1 Glass substrate 2 Transparent electrode

Claims (2)

A first thin film display element in which a hole transport layer, a light emitting layer, an electron transport layer, and an electrode are laminated on a first transparent electrode;
A second thin film display element in which a hole transport layer, a light emitting layer, an electron transport layer, and an electrode are laminated on the second transparent electrode;
The first thin film display element and the second thin film display element are connected in parallel so as to have opposite polarities through two connection lines and constitute one pixel. An image display device. A first thin film display element in which a hole transport layer, a light emitting layer, an electron transport layer, and an electrode are laminated on a first transparent electrode;
A second thin film display element in which a hole transport layer, a light emitting layer, an electron transport layer, and an electrode are laminated on the second transparent electrode;
The first transparent electrode and the second transparent electrode are provided on the same glass substrate,
The first thin film display element and the second thin film display element are connected in parallel so as to have opposite polarities through two connection lines and constitute one pixel. An image display device.

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