JP3420729B2 - Field emission display - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a field emission type display device capable of relatively easily forming a pixel capacitance for each pixel and eliminating display unevenness between pixels and greatly improving image quality. .

[0002]

2. Description of the Related Art A field emission type display device is
The basic structure is such that electrons are emitted from the emitter electrode by an electric field between the gate electrode and the emitter electrode, and a high voltage is applied to the anode electrode to accelerate the electrons highly, and then the phosphor provided on the anode electrode is made to emit light by the electrons. I am trying. Therefore, the amount of light emitted from the phosphor can be controlled by the amount of electrons emitted from the emitter electrode.

In a conventional field emission type display device, a pixel is formed by arranging a three-pole circuit as a switching element and a capacitor at each intersection where a plurality of row electrodes and column electrodes are formed, and the pixels are arranged in a matrix. It was built into the display device. The gate of each of these three-pole circuits is connected to an electrode, the emitter is connected to a column electrode, and the capacitor is connected in parallel between the gate and the emitter. The data voltage transmitted through the column electrode accumulates charges in the capacitor, and the potential difference between the gate and the emitter caused by the charges determines the brightness of the pixel.

However, in such a field emission type display device, crosstalk occurs between adjacent pixels. That is, when the capacitor in the second column below is charged after the charging of the capacitor in the first column is completed, the gate of the gate circuit of the three-pole circuit in the first column is crossed through the intersection of the row electrode and the column electrode. The potential fluctuates and the brightness of the pixel fluctuates. When this phenomenon occurs, image quality is deteriorated on the entire screen, such as line-shaped flicker and shading (a phenomenon in which a shadow is drawn in the vertical direction when a window is displayed, a phenomenon often seen in STN). .

[0005]

In the conventional field emission type display device, the data voltage of the pixel being written causes crosstalk through the intersection of the row electrode and the column electrode and the gate of the three-pole circuit being displayed. The potential of the pixel is changed to change the brightness of the pixel, and line-shaped flicker, shading, and the like occur, resulting in deterioration of image quality.

The present invention has been made in order to solve the above problems, and an object of the present invention is to provide a field emission type display device in which the deterioration of the image quality due to the crosstalk which occurs at the time of writing of adjacent pixels is suppressed. .

[0007]

In order to solve the above-mentioned problems, the field emission type display device according to claim 1 is formed with an emitter element, an anode electrode, and
A plurality of pixels each having a gate electrode and a first switching element for controlling charging / discharging of a capacitance formed between the emitter element and the gate electrode by the first switching element, and respective emitters of the plurality of pixels A cathode line electrically connected in common to the cathode line, a cathode line drive circuit for driving the cathode line, and ON / O of the cathode line between the pixels.
A second switching element for controlling an FF, and electrically disconnects the capacitor after charging from the cathode line driving circuit by sequentially turning off the second switching element from a predetermined pixel. A field emission type display device characterized in that

A field emission type display device according to a second aspect is characterized in that, in the first aspect, the electrical disconnection from the predetermined pixel is performed sequentially from the pixel separated from the cathode line driving circuit. Further, this separation may be performed in the case of separating from a pixel close to the cathode line driving circuit, or alternatively, a pixel far from the cathode line driving circuit and a close pixel may be alternately separated. In short, it is necessary to separate them in a certain order in consideration of the improvement in image quality.

A field emission type display device according to a third aspect is the display device according to the first aspect, wherein an auxiliary capacitance connected in parallel with the capacitance is formed for each pixel.

A field emission type display device according to a fourth aspect is the display device according to the first aspect, wherein the emitter element has a pyramidal shape whose tip is exposed from an opening formed in the film-shaped gate electrode. .

According to a fifth aspect of the present invention, in the field emission type display device according to the first aspect, the pixel includes the gate electrode formed by stacking the emitter element on a cathode electrode and forming an insulating film on the cathode electrode. It is characterized in that they are formed separately.

A first aspect of the present invention is that a cathode electrode and a second switching element are electrically connected in series to form one cathode line, and a voltage is applied to the cathode electrode corresponding to a display signal. After the application, the gate line of the cathode electrode is turned on, and the switching element adjacent to the cathode electrode is turned off, whereby the cathode electrode is electrically disconnected between the adjacent cathode electrodes by a driving method.
Electrons are started to be emitted from the emitter element only in the pixel that has the cathode electrode that is the farthest from the cathode line drive circuit and electrically terminates.

According to a second aspect of the present invention, when the electron emission from the emitter element is completed and the voltage difference between the cathode electrode and the gate voltage becomes approximately the threshold voltage, the second portion is provided between the cathode electrodes.
The switching element is turned on to be electrically connected.

According to a third aspect of the present invention, the first gate line for driving the gate electrode and the second gate line for driving the second switching element are the same gate line, and the electric field of the second switching element is the same. By making the effect characteristic opposite to the electric field effect characteristic of the gate electrode and the cathode electrode, the space between the adjacent cathode electrodes is turned off, and at the same time, the second switching element is turned on.

A fourth aspect of the present invention is to provide an auxiliary capacitance in addition to the capacitance formed between the cathode electrode and the gate electrode.

A fifth aspect of the present invention is an FED (hereinafter referred to as vertical type FED) having a conical emitter element on a cathode electrode.
Instead of ED), a planar type emitter element is an FED (hereinafter referred to as planar type FED) formed to face the planar type gate electrode.

[0017]

EXAMPLES The present invention can be better understood by describing the following non-limiting examples. (Embodiment 1) A sectional view of one pixel of a field emission type display device of the present embodiment is shown in FIG. 1, and a plan view of the entire panel is shown in FIG. As shown in FIG. 1, pixels having a plurality of field emission type emitter elements in one pixel are arranged in a matrix in the X and Y directions, and a gate electrode 11 for switching field emission type emitter elements 12 and a plurality of rows are arranged in the row direction. A gate wiring (not shown) for performing common driving for the pixels of 1 and a plurality of cathode electrodes 13 arranged in the column direction for driving the field emission type emitter element 12 are formed on the display substrate 14. Further, a counter substrate 17 having an anode electrode 15 and a phosphor layer 16 is arranged so as to face the display substrate 14.
The configuration shown in FIG. 1 is the internal structure of one pixel.

In the array configuration of the display device according to the first embodiment, as shown in FIG. 2, the first gate line 21 and the first gate line 21 which commonly drive a plurality of pixels in the row direction. A first gate line drive circuit 22 for driving the cathode electrode 23, a cathode electrode 23 for driving the emitter element, and a cathode line drive circuit 24 for driving the cathode electrode 23,
A switching element 25 arranged between the cathode electrodes 23 in the column direction, a second gate line 26 for driving the switching element 25, and a second gate line drive for driving the second gate line 26. A circuit 27 and a display substrate having these portions formed on its surface are prepared. The above-mentioned electrodes are electrically connected to the electrodes of the same name (the numbers are in the 10s) in each pixel shown in FIG.
The display region 29 is formed in a region in the display substrate 14 where the emitter elements are formed in a matrix. The cathode electrode 23 and the adjacent cathode electrode 23 are electrically connected by providing the anode electrode 15 and the counter substrate 17 having the phosphor 16 facing the display substrate and turning on the switching element 25, thereby switching the cathode electrode 23 and the adjacent cathode electrode 23. Element 25 is off
In this state, the cathode electrode 23 and the adjacent cathode electrode 23 are electrically disconnected from each other, and the operation of the pixel having the cathode electrode 23 is controlled by the first gate line 21.

FIG. 3 is a voltage waveform showing a driving sequence according to the present embodiment. The first gate line arranged at the cathode electrode (the bottom end of the display area in FIG. 2) farthest from the cathode line driving circuit. 21 is the n-th line and the second gate line 26 is also the m-th line that controls the switching element farthest from the cathode line drive circuit. The first to drive the first scan line as shown in FIG.
In the scanning period of, all the gate lines from the mth to the first of the second gate lines are in the ON state.
Then, the cathode line driving circuit 24 applies the image information Qn to the cathode electrode located at the electrical end, and the n-th position of the first gate line is turned on. Next, the m-th gate electrode of the second gate line is turned off, so that the cathode electrodes are electrically disconnected from each other, and the cathode electrode at the end moves to the cathode electrode one above. By repeating the same operation, signals are written in all the cathode electrodes, and the wiring length of the cathode lines gradually becomes shorter electrically. This is an advantage that the pixels far from the cathode line driving circuit are sequentially charged, and then the pixels are disconnected from the cathode line driving circuit.

An equivalent circuit diagram of this embodiment is shown in FIG.
And shown in FIG. Figure 4 (a) shows that during the first scan period,
The cathode electrode 23 at the end is in the ON state and the cathode electrode 2
The electrical connection between 3 is in the ON state, but Fig. 4 (b)
Indicates that the electrical connection between the cathode electrodes 23 is OFF
Is. These two states are in the writing state in FIG.
The time interface is sufficient to prevent the signal from the electrode 23 from leaking.
5b from the figure shown in FIG. 5a, which is set globally.
Move to the diagram shown in. Also, the capacitance component C in the figure ₁Is
Formed between the mitter element 12 and the gate electrodes 21 and 26
Indicates capacity. Here, 40 is the emitter element 12 and
It is the resistance between the terminals and electrons are discharged during this period to emit light. Well
Also, 41 is the first connected to the cathode line drive circuit 24.
Switching element, 42 is a second switching element
It These switching elements 41 and 42 are made of polycrystalline silicon.
The active layer is made of silicon or amorphous silicon.
Thin film transistor.

According to this embodiment, the pixels for which writing has been completed by the first switching element 41 and the second switching element 42 are sequentially separated, and there is no crossing portion between the wirings where crosstalk occurs after the writing is completed. Moreover, there is no concern that the image quality will be deteriorated due to the crosstalk that occurs when writing the adjacent pixels. Therefore, the occurrence of line-shaped flicker and shading can be reduced.

Further, according to the present embodiment, although the capacitive driving method using the switching element is used, the cathode electrode is used as a part of the signal line to facilitate the production of the array and to significantly increase the number of pixels in the column direction. Can be increased to a higher vertical resolution.

Further, according to the present embodiment, the capacitance formed between the cathode electrode and the gate electrode is charged with electric charge, and electrons are emitted from the emitter electrode according to the amount of the electric charge, and the cathode is accompanied by the emission of electrons. The unevenness in the display of the pixel feeling can be improved by the mechanism that the electron emission ends when the voltage between the electrode and the gate electrode naturally reaches the electron emission threshold or less. Example 2 The structure of Example 2 is shown in FIG. In the following description of the embodiments, the same parts as those in the first embodiment are designated by the same reference numerals, and detailed description thereof will be omitted. The second embodiment is different from the first embodiment in that the emitter element and the cathode electrode are made of the same material and integrated. The other structure is the same as that of the first embodiment. Here, FIG. 6 ((a) is a plan view,
For a pixel of the size shown in (b) is a sectional view, the capacitance C1 formed between the cathode electrode and the emitter electrode
And the amount of charge Q1 charged by C1 is obtained from the following equation (1). Reference numeral 61 is an emitter element integrated with a cathode electrode (the cathode electrode is a flat plate on which a pyramidal emitter element is formed), and 62 is a gate electrode. Capacity C1 = ε ₀ ε * S / D = 8.8542 × 10 ⁻² * 4 * 150 × 10 ⁻⁶ * 450
× 10 ^-6 / 1 × 10 ^-6 = 2.4 × 10 ^-12 [C / V] Amount of charge Q1 = 2.4 × 10 ^-12 * (90-0) = 2.2 × 10 ^-10 [C ] (Gate voltage Vg = 90 [V], cathode voltage V
c = 0 [V]). In this electric charge, the portion Q2 actually involved in electron emission is Vth = 50 [V], and Q2 = 2.4 × 10 ⁻¹² * (90−50) = 9.6 × 10 ⁻¹¹ [C] .

On the other hand, in order to obtain a brightness of about 300 [cd / m ² ], from a pixel having 50 emitter elements, 6.9 × 10
-30 [n] amount of current per emitter element during ⁵ [s] period
It has been confirmed that it is necessary to emit A], and the amount of charge Q3 emitted from the emitter element, which is necessary from that, is about 100.
It becomes × 10 ^-12 [C]. That is, in order to display a high brightness of 300 [cd / m2], it is sufficient to apply approximately 90 [V] between the gate electrode and the cathode electrode to the cathode electrode. A display device having such an element structure was specifically constructed by the equivalent circuit shown in FIG.

As for the way of emitting light, the voltage of the cathode electrode drops with the discharge of electric charges, and the emission of electrons is stopped when the voltage becomes Vth or less. Therefore, the emission of electrons is automatically stopped, After that, light emission continues for about 3 [ms] only with the afterglow of the phosphor. Even when electrons cannot be emitted from a plurality of elements due to defective fabrication of the emitter element, the electrons are emitted from other elements, so that the luminance proportional to the charge amount can be obtained, that is, the luminance between pixels. No unevenness occurs.

Since all the cathode electrodes become Vth when the emission of electrons is completed, the switching elements between the adjacent cathode electrodes can be turned on to prepare for the next writing. That is, after the writing to the cathode electrode closest to the cathode line drive circuit is completed, the cathode electrode is set to Vt.
The switching elements from the (m-1) th to the 2nd switching elements in the second gate line are turned on until the time becomes h. When the cathode electrode reaches Vth, the first gate line of the second gate line is turned on, so that the terminal end of the cathode line is the farthest from the cathode line drive circuit and the cathode at the bottom end of the panel. Become an electrode.

FIG. 7 shows the signal waveform of each part according to this embodiment. As shown in the figure, the switching element is turned on after both the time Tmax until reaching Vth after applying the voltage required for the maximum brightness and the writing time Tw to the next cathode electrode. To do. With the above configuration, the same effect as that of the first embodiment can be obtained. (Embodiment 3) In Embodiment 3, as shown in FIG. 8, a first gate line for driving a gate electrode and a second gate line for driving a switching element are the same gate line. Only two pixels 88 and 89 are shown here for simplicity. The field effect characteristics of the switching elements 81, 82, 83 are opposite to the field effect characteristics of the gate electrodes 871, 872, 873 and the cathode electrode 86.
When the switching element is turned off, the switching element is turned off.
Set to N state. For example, the switching element 83 exhibits the field effect characteristics of the depletion type P-type FET, and the cathode electrode
The element made up of 86 and the gate electrode is an enhancement type N
If the field effect characteristics of the FET are shown, the gate line 87
When 1 and 872 are Low and the gate line 873 is High, the switching elements 81 and 82 are in the ON state and 83
Is in the OFF state, and the reset voltage is input to the cathode electrodes of the pixels 88 and 89 from the reset drive circuit. Here, in particular, the reset operation necessary for improving the characteristics of the element is performed, and no voltage is applied to those that are not necessary as in the first and second embodiments. Also, since the reset voltage is set to a potential at which electrons are not emitted,
No light is emitted from any of the pixels. Next, gate line 871
Is High and the gate lines 872 and 873 are Low, the switching element 81 is in the OFF state, and 82 and 83 are in the ON state. Then, writing from the cathode line drive circuit to the pixel 89 is performed. Subsequently, in the state where the gate lines 871 and 872 are High and the gate line 873 is Low, the switching element 8
1 and 82 are turned off, and 83 is turned on. Then, writing from the cathode line drive circuit to the pixel 88 is performed. Since the number of gate lines can be halved in this embodiment, the gate line driving circuit can also be halved. With the above configuration, the same effect as that of the first embodiment can be obtained. (Embodiment 4) As shown in FIG. 9, Embodiment 4 is a configuration example in which an auxiliary capacitance C1 is provided in addition to the capacitance C2 formed between the cathode electrode and the gate electrode. This auxiliary capacitance makes it possible to adjust the Tmax and the applied voltage amount.

In FIG. 9 (FIGS. 9 (a) to 9 (b) show the situation of writing in the lowermost pixel), after the image signal is written in the auxiliary capacitance C1 and the capacitance C2, the space between the cathode electrodes is electrically changed. The write switch S2 to the capacitor is turned off so as to be disconnected from the switch S1, and the switch S1 is turned on to write the image signal to the second scanning line. On the other hand, when C1 is sufficiently larger than C2 as shown in (1), a switch S1 can be provided between C2 and C1, and S1 can be turned on after turning off S2. Alternatively, the circuit configuration shown in FIG. 10 (showing the situation of writing to the lowermost pixel in FIGS. 10A to 10B) can be adopted. In either case, the image signal to the second scanning line has a capacitance C of pixels arranged in the first scanning line.
The switches S1 and S2 are controlled so that the switches S1 and S2 are not written. It is needless to say that the same effect as that of the first embodiment can be obtained also by this. (Embodiment 5) As shown in FIGS. 11 and 12, Embodiment 5 is a flat-type emitter instead of an FED having a conical emitter element on a cathode electrode (hereinafter referred to as a vertical-type FED). A configuration example using an FED (hereinafter, referred to as a planar FED) in which an element is formed so as to face a planar gate electrode is shown. Here, 84 is a cathode line drive circuit,
101 is a cathode electrode, 104 is a P-type semiconductor, 105 is a gate line, 106 is an insulating film, and 107 is a display substrate.
As shown, electrons are emitted when the voltage between the emitter electrode 102 and the gate electrode 103 is equal to or higher than the threshold value Vth, and is not emitted when the voltage is equal to or lower than Vth. A display device having such an element structure was constructed by the equivalent circuit shown in FIG. This controls the light emission. As shown, the pixel 100 has a planar emitter electrode 102 and a gate electrode 103 on a cathode electrode 101, and a switching element that electrically connects the cathode electrodes is operated by the gate electrode via a P-type semiconductor 104. Is controlled. The voltage to the gate electrode is applied from the gate line 105, and the gate electrode and the cathode electrode and P
It is electrically insulated from the type semiconductor by the insulating film 106.

Although the present invention has been described with reference to the illustrated embodiments, the method of dividing the cathode wiring, the field effect characteristics and types of the switching elements are not limited to the embodiments of the present invention. Various modifications can be implemented without departing from the scope of the invention.

[0030]

According to the present invention, it is possible to provide a field emission type display device in which the deterioration of the image quality due to the crosstalk occurring at the time of writing the adjacent pixels is suppressed.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an array configuration related to a field emission type display.

FIG. 2 is a schematic panel configuration diagram of a field emission type display.

FIG. 3 is a voltage waveform diagram showing a drive sequence according to the first embodiment of the present invention.

FIG. 4 is an equivalent circuit diagram of an array configuration in the first scanning period of the embodiment.

FIG. 5 is an equivalent circuit diagram of an array configuration in the second scanning period of the embodiment.

FIG. 6 is a schematic diagram of an array configuration according to a second embodiment of the present invention.

FIG. 7 is a signal waveform diagram of each part of the embodiment.

FIG. 8 is a schematic diagram of an array configuration according to a third embodiment of the present invention.

FIG. 9 is an equivalent circuit diagram of an array configuration according to a fourth embodiment of the present invention.

FIG. 10 is an equivalent circuit diagram of an array configuration according to a fourth embodiment of the present invention.

FIG. 11 is a diagram illustrating a display according to Example 5.

FIG. 12 is a diagram illustrating a display according to the fifth embodiment.

[Explanation of symbols]

11 Gate electrode 12 field emission type emitter element 13 Cathode electrode 14 Display board 15 Anode electrode 16 Phosphor layer 17 Counter substrate 21 First gate line 22 First gate line drive circuit 23 Cathode electrode 24 Cathode line drive circuit 25 switching elements 26 Second gate line 27 Second Gate Line Driving Circuit

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ identification code FI H01J 31/12 H01J 31/12 C (58) Fields investigated (Int.Cl. ⁷ , DB name) G09G 3/22 G09G 3 / 20 611 G09G 3/20 623

Claims (5)

(57) [Claims] 1. An emitter element formed apart from each other,
A plurality of pixels having an anode electrode, a gate electrode, and a first switching element for controlling charge / discharge of a capacitance formed between the emitter element and the gate electrode by the first switching element; and the plurality of pixels A cathode line electrically connected to each of the emitters, a cathode line drive circuit for driving the cathode line, and a second switching element for controlling ON / OFF of the cathode line between the pixels. Then, the field emission type display device is characterized in that the electrically charged capacitor is electrically disconnected from the cathode line driving circuit from the predetermined pixels by turning off the second switching element. 2. The field emission type display device according to claim 1, wherein the electrical disconnection from the predetermined pixel is performed sequentially from the pixel separated from the cathode line drive circuit. 3. The field emission type display device according to claim 1, wherein an auxiliary capacitor connected in parallel with the capacitor is formed for each pixel. 4. The field emission type display device according to claim 1, wherein the emitter element has a conical shape whose tip is exposed from an opening formed in a film-shaped gate electrode. 5. The pixel is formed such that the emitter element is laminated on a cathode electrode and separated from the gate electrode formed on the cathode electrode via an insulating film. Field emission type display device described in.