JPH1027539A - Ferroelectric cold cathode and its driving method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make controllable the emission area and amount of electrons emitted and the spread of the emitted electrons by providing a portion where an insulating film intervenes between a ferroelectric and an upper electrode and a portion where the ferroelectric makes contact with the upper electrode to form an electron emitting window. SOLUTION: This ferroelectric cold cathode has lower and upper electrodes 2, 3 placed respectively at the bottom and top of a ferroelectric 1, and has between the ferroelectric 1 and the electrode 3 a portion where an insulating film 4 is formed and a portion where the ferroelectric 1 makes contact with the electrode 3, with an electron emitting window formed in the portion where they make contact. Electron emission by the polarization reversal of the ferroelectric is known to start to occur from an applied pulse voltage that is about twice the resisting electric field of the ferroelectric or greater. Thus when a driving pulse voltage 6 is applied to the electrode 3, an effective voltage applied to the ferroelectric 1 during drive is lowered enough under wiring where the ferroelectric 1 and the film 4 form double layers, so that electron emission is not started, while electron emission can be effected only from the electron emitting window.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ferroelectric cold cathode for emitting electrons which is applied to an image forming apparatus such as a printing apparatus, a flat display, and the like, and a driving method thereof.

[0002]

2. Description of the Related Art Conventionally, Pb (Zr, Ti) O ₃ (hereinafter referred to as PZT) and (Pb, La) (Zr, Ti) O ₃
A ferroelectric such as (hereinafter, referred to as PLZT) is a material having spontaneous polarization, and it is known that an emission current density of several A / cm ² or more can be obtained by polarization reversal by applying a high-speed pulse.

Here, a conventional ferroelectric cold cathode that emits an electron beam, which is reported by H. Gundel et al., Will be described with reference to FIG. 5 which is a schematic configuration diagram thereof (J. Appl. Phys. 69 (2), pp975, 1991). As shown in FIG. 5, the ferroelectric cold cathode has a structure in which a ferroelectric material 101 is sandwiched between a lower electrode 102 and an upper comb electrode 103. When an alternating electric field 106 is applied between the lower electrode 102 and the upper comb-shaped electrode 103, polarization occurs in such a direction as to cancel the electric field applied inside the ferroelectric material 101,
This polarization is reversed with a change in the applied alternating electric field 106, and a strong electric field is generated. When a strong electric field of 10 ⁷ V / cm ² or more is applied to the ferroelectric substance 101, the ferroelectric substance 1
The electrons 01 are extracted by the upper comb-shaped electrode 103 and emitted to the outside.

The above-mentioned ferroelectric cold cathode has a simple element structure and can emit electrons even in a relatively low vacuum (10 ^-1 mTorr or more). Therefore, an image forming apparatus such as a printing apparatus or a flat display is used. An application to it has been proposed.

[0005]

However, in the above-mentioned conventional ferroelectric cold cathode, when a metal wiring is formed directly on the ferroelectric and operated, the entire ferroelectric under the wiring is inverted and the electron emission occurs. Then, since the electron emission portion cannot be limited, the electron emission area and the electron emission amount cannot be controlled. Further, for example, when applied to a display, electron emission generated by polarization reversal in the ferroelectric under the wiring electrode causes phosphor emission due to electron emission in the wiring portion, which reduces display quality. There was a problem of inviting. Further, even in a case where the present invention is applied to an image forming apparatus such as a printing apparatus, a similar problem occurs in forming a latent image.

[0006] Such a problem can be avoided by wiring a ferroelectric material. However, composite metal oxides such as PZT have other problems such as difficulty in dry etching such as RIE, an increase in leakage current at the processing edge, and a complicated process.

[0007] In the case of a ferroelectric cold cathode using PZT ceramics, the pulse voltage for obtaining electron emission is as high as 150 to 300 V, and it is necessary to reduce the driving voltage for device application.

[0008] The electron emission from the ferroelectric cold cathode is
There is a spread angle due to the scattering of the ferroelectric and the electrode surface, and the spread of the emitted electrons cannot be suppressed. Therefore, high image quality cannot be obtained in a flat display application or the like.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and can control the emission area and emission amount of emitted electrons, suppress the spread of emitted electrons, and perform low-voltage driving. It is an object of the present invention to provide a ferroelectric cold cathode and a driving method thereof.

[0010]

According to the present invention, there is provided a ferroelectric cold cathode comprising a ferroelectric material sandwiched between a lower electrode and an upper electrode. Between the ferroelectric material and the upper electrode to form an electron emission window.

Further, according to the present invention, a ferroelectric cold cathode comprising a ferroelectric material sandwiched between a lower electrode and an upper electrode includes a first upper electrode and a second upper electrode as upper electrodes, A portion having a first insulating film interposed between the ferroelectric and the first upper electrode; and a portion forming an electron emission window when the ferroelectric and the first upper electrode are in contact with each other. A second upper electrode is provided on a portion of the first electrode between the first upper electrode and the first insulating film via a second insulating film.

According to the present invention, in a ferroelectric cold cathode in which a ferroelectric material is sandwiched between a lower electrode and an upper electrode, the first upper electrode, the second upper electrode, and the third A first insulating film interposed between the ferroelectric and the first upper electrode;
And a portion that forms an electron emission window in contact with the upper electrode of
A second insulating film is interposed between the ferroelectric and the first upper electrode via a second insulating film on a portion of the first electrode where the first insulating film is interposed.
Is provided, and a third upper electrode is provided on the second upper electrode via a second insulating film.

Further, in the present invention, in the above-mentioned ferroelectric cold cathode, the dielectric constant of the insulating film is set to 100 or more.

Further, according to the present invention, a ferroelectric cold cathode comprising a ferroelectric material sandwiched between a lower electrode and an upper electrode includes a first upper electrode and a second upper electrode as upper electrodes, A portion having a first insulating film interposed between the ferroelectric and the first upper electrode; and a portion forming an electron emission window when the ferroelectric and the first upper electrode are in contact with each other. Driving method of a ferroelectric cold cathode in which a second upper electrode is provided on a portion of the first electrode with a first insulating film interposed between the first upper electrode and a second upper electrode via a second insulating film In this case, a positive electric field is applied to the second upper electrode.

Further, according to the present invention, in a ferroelectric cold cathode in which a ferroelectric material is sandwiched between a lower electrode and an upper electrode, the first upper electrode, the second upper electrode, and the third A first insulating film interposed between the ferroelectric and the first upper electrode;
And a portion that forms an electron emission window in contact with the upper electrode of
A second insulating film is interposed between the ferroelectric and the first upper electrode via a second insulating film on a portion of the first electrode where the first insulating film is interposed.
A method of driving a ferroelectric cold cathode in which an upper electrode is provided and a third upper electrode is further provided on the second upper electrode with a second insulating film interposed therebetween. Is applied, and a negative electric field is applied to the third upper electrode.

According to the present invention, since the electron emission window is provided on the ferroelectric, the electron emission can be limited to only the electron emission window, and the electron emission is not directly formed on the ferroelectric. No polarization inversion occurs in the ferroelectric under the wiring metal, and no electron emission from under the wiring occurs. This makes it possible to control the electron emission area and the electron emission amount. Therefore, for example, in the case of a display application, it is possible to prevent light emission due to electron emission to a phosphor other than the light emitting portion, and it is possible to improve display quality. To play.

Further, by applying an electron extraction electric field by the second upper electrode, the electron emission voltage from the ferroelectric can be reduced, and the driving voltage of the element can be reduced. Further, by changing the electron extraction electric field intensity, the amount of electron emission at the same pulse voltage can be controlled.

Further, by applying a negative electric field to the third upper electrode, the spread of emitted electrons can be suppressed, and a high-quality flat display or an image forming apparatus such as a printing apparatus excellent in transfer accuracy can be provided. Can be realized.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. The ferroelectric cold cathode of the present invention is constituted by an aggregate of a plurality of cold cathodes. Hereinafter, a diagram showing a single element structure will be used.

FIG. 1 is a schematic sectional view of a ferroelectric cold cathode according to a first embodiment of the present invention. As shown in FIG. 1, this ferroelectric cold cathode has a lower electrode 2 and an upper electrode 3 arranged at a lower portion and an upper portion of a ferroelectric 1 respectively, and between the ferroelectric 1 and the upper electrode 3. There is a portion where the insulating film 4 is formed, and a portion where the ferroelectric 1 and the upper electrode 3 are in contact, and an electron emission window is formed by a portion where the ferroelectric 1 and the upper electrode 3 are in contact. Although FIG. 1 shows a cross-sectional structure of the ferroelectric cold cathode, in practice, the insulating film 4 and the upper electrode 3 are formed so as to surround the electron emission window.

It is known that electron emission due to polarization reversal of a ferroelectric starts to occur at an applied pulse voltage that is at least approximately twice the coercive electric field of the ferroelectric. Therefore, this first
In the ferroelectric cold cathode of the embodiment, when a drive pulse voltage 6 is applied to the upper electrode 3, the ferroelectric 1 and the upper electrode are placed under the wiring which is a double layer of the ferroelectric 1 and the insulating film 4. In a portion where the insulating film 4 is formed between the ferroelectric layer 3 and the gate electrode 3, the effective voltage applied to the ferroelectric 1 is reduced during driving, so that electron emission does not occur, and electrons can be emitted only from the electron emission window.

Next, as a second embodiment, as shown in FIG. 2, a second upper electrode 13 is formed on the upper electrode 3 of the first ferroelectric cold cathode via a second insulating film 14. Will be described. Although FIG. 2 also shows the cross-sectional structure of the ferroelectric cold cathode, actually, the insulating film 4, the upper electrode 3, the second insulating film 14, and the second upper electrode 13 are shown.
Are formed so as to surround the periphery of the electron emission window.

When a positive bias electric field 7 is applied to the second upper electrode 13 of the ferroelectric cold cathode according to the second embodiment, the second upper electrode 13 functions as an electron extraction electrode and emits electrons. The amount can be increased. Also,
Even if the drive pulse voltage 6 is reduced, it is possible to obtain substantially the same electron emission amount as that of the first embodiment, and it is also possible to reduce the drive voltage. Further, the driving pulse voltage 6
Is constant, and the amount of electron emission can be controlled by controlling the positive bias electric field 7 applied to the second upper electrode 13.

Next, as a third embodiment, as shown in FIG. 3, the second upper electrode 1 of the second ferroelectric cold cathode is used.
A structure in which a third upper electrode 23 is provided on the substrate 3 via a third insulating film 24 will be described. Although FIG. 3 also shows the cross-sectional structure of the ferroelectric cold cathode, in practice, the insulating film 4, the upper electrode 3, the second insulating film 14, the second upper electrode 13, and the third The insulating film 24 and the third upper electrode 23 are formed so as to surround the electron emission window.

When a negative bias electric field 8 is applied to the third upper electrode 23 of the ferroelectric cold cathode according to the third embodiment, the third upper electrode 23 acts as an electrostatic lens and emits electrons. Can be controlled.

In the first to third embodiments, a dielectric film such as SiO ₂ or SiN can be used as the insulating film 4, but these dielectric films have relatively low dielectric constants. Low (for example, about 4 SiO ₂ ). On the other hand, the dielectric constant of the ferroelectric 1 is generally high (for example, PZT is about 1000), and the effective voltage of the ferroelectric at the portion where the ferroelectric 1 and the insulating film 4 are stacked is と. To do so, a thickness of several nm is required as the insulating film thickness. For example, SiO
_With the combination of ₂ and PZT, the SiO ₂ film thickness becomes 4 nm for a 1 μm thick PZT film, but such an ultra-thin film is formed on a ferroelectric material with excellent withstand voltage and leak resistance. It is difficult. Therefore, as the insulating film 4, a high dielectric film having a dielectric constant of 100 or more is desirable.
Specific materials include SrTiO ₃ and BaSrTiO ₃ .

Further, as the ferroelectric 1 of the ferroelectric cold cathode of the first to third embodiments, PZT, PLZT, Sr
It can be composed of a composite metal oxide such as Bi ₂ Ta ₂ O ₉ and BaTiO ₃ . Also, the upper electrodes 3, 13, 2
For 3, a metal material such as Pt, Au, or Al can be used.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, more specific embodiments of the present invention will be described with reference to the drawings. First, as a first example, a method using a PZT ferroelectric film as the ferroelectric 1 of the second embodiment (see FIG. 2) will be described from a manufacturing method thereof.

A thermally oxidized SiO _{2 was} formed on the surface of the Si substrate, and a 10-nm-thick Ti thin film and a 200-nm-thick Pt electrode film as the lower electrode 2 were sequentially formed thereon by RF sputtering.

Then, spin coating (3000 rpm × 20 seconds), preliminary baking (400 ° C. × 30 minutes), and main baking (650 ° C. × 20 seconds) are sequentially repeated on the substrate by a sol-gel method to obtain a film of about 800 nm. A PZT ferroelectric film as the ferroelectric 1 was formed.

Thereafter, an SrTiO ₃ film is adopted as the insulating film 4 and the substrate temperature is set to 400 ° C. by RF sputtering.
Sputtering power 200W, 100% oxygen in sputter gas
At a gas pressure of 2 mTorr and a film thickness of about 50
nm. Then, in order to form the electron emission window 5, the SrTiO ₃ film was patterned.
This patterning is performed by ordinary photolithography and wet etching (etching solution: a mixed solution of hydrochloric acid (HCl), buffered fluorine (BHF) and water).
A window of mm × 2 mm was formed.

On the insulating film 4 thus formed, a 50 nm-thick Pt film is formed by EB evaporation as the upper electrode 3, and then a 300 μm-thick second insulating film 14 is formed.
A SiO ₂ film having a thickness of 10 nm was formed by an RF sputtering method. Then, in order to form the electron emission window 5, the SiO ₂ film was patterned by photolithography and wet etching (etching solution: BHF) in the same manner as described above.

Further, a film thickness of 2 is formed on the second insulating film 14 by a lift-off method using a photoresist as a mask.
A Pt film having a thickness of 00 nm was formed by using the EB evaporation method, the second upper electrode 13 was formed so as to have the electron emission window 5, and the fabrication of the ferroelectric cold cathode of this example was completed.

Next, evaluation of the electric characteristics of the ferroelectric cold cathode manufactured as described above will be described. The ferroelectric cold cathode of this example was placed in a vacuum chamber, and 10 ⁻⁵ Torr
The device was driven using a Pt plate and a fluorescent plate as collectors. As shown in FIG. 2, the upper electrode 3 was grounded, and a positive bias voltage (drive pulse voltage 6) of 0 to 20 V was applied to the lower electrode 2 as shown in FIG. At this time, as a result of evaluating the light emission pattern of the phosphor plate due to the phosphor emission, it was confirmed that no bright spot was observed except for the electron emission window 5, and that the electron emission under the wiring was suppressed.

Next, FIG. 4 shows the results of measuring the electron emission characteristics and the dependence of the electron emission characteristics on the bias electric field (positive bias electric field 7). FIG. 4 shows that the electron emission start voltage decreases as the positive bias electric field 7 to the second upper electrode 13 increases. From the above results, it is understood that the electron emission amount can be controlled by the positive bias electric field 7 to the second upper electrode 13 when the driving voltage is fixed.

In the first embodiment, the lower electrode 2 is formed on the entire surface of the element. However, the present invention is not limited to this. The lower electrode 2 is formed as a stripe-shaped electrode for selecting a driving element. For example, it can be freely designed according to an actual application device.

Next, the second embodiment corresponding to the third embodiment will be described.
As an example of the second embodiment, the second upper electrode 1 of the first embodiment described above is used.
A second embodiment will be described in which a third insulating layer 24 made of a SiO ₂ film and a third upper electrode 23 made of a Pt film are sequentially formed on the substrate 3 in the same manner as in the first embodiment. .

With respect to the ferroelectric cold cathode of the second embodiment, as shown in FIG.
0V negative bias electric field 8 is applied.
The electrical characteristics were evaluated in the same manner as in the Examples, except that the electrical connection was made. Here, a fluorescent plate was used for the anode. As a result of the evaluation, the phosphor emission pattern on the phosphor plate increases the voltage of the negative bias electric field 8 applied to the third upper electrode 23 in the negative direction (from 0 V to −20 V).
, The emission electrons were observed to converge, confirming the lens effect of acting as an electrostatic lens.

[0039]

As described above, according to the present invention, the electron emission region by the ferroelectric cold cathode is limited to only the electron emission window, and the ferroelectric under the wiring metal which is not directly formed on the ferroelectric. Since the polarization inversion of the dielectric does not occur, the electron emission from under the wiring does not occur. As a result, a ferroelectric cold cathode having excellent control of the amount of emitted electrons can be realized.

Further, a ferroelectric emitter having a planar structure can be formed without processing the ferroelectric, thereby simplifying a cold cathode manufacturing process.

Therefore, when the ferroelectric cold cathode of the present invention is used, a high-quality flat display having no deterioration in display quality caused by electron emission to a phosphor other than the light emitting portion, and excellent transfer accuracy are obtained. An image forming apparatus such as a printing apparatus can be realized.

Further, according to the present invention, by providing the second upper electrode as the electrode for applying the electron extraction electric field, the pulse voltage applied for emitting electrons from the ferroelectric can be reduced. Can be reduced. In addition, the electric field strength of the electron extraction, that is, the second
By changing the electric field strength applied to the upper electrode of
It is possible to control the amount of electron emission at the same pulse voltage.

Further, according to the present invention, by providing the third upper electrode, the spread of emitted electrons can be suppressed, and an image forming apparatus such as a high-quality flat display or a printing apparatus excellent in transfer accuracy can be provided. Can be realized.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part showing a schematic structure of a first embodiment according to the present invention.

FIG. 2 is a sectional view showing a main part of a schematic structure of a second embodiment according to the present invention.

FIG. 3 is a cross-sectional view of a main part showing a schematic structure of a third embodiment according to the present invention.

FIG. 4 is a view showing the results of measuring the electron emission characteristics of the first example corresponding to the second embodiment and the dependence of the electron emission characteristics on the bias electric field applied to the second upper electrode.

FIG. 5 is a sectional view of a main part showing a schematic structure of a conventional ferroelectric cold cathode.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ferroelectric 2 Lower electrode 3, 13, 23 Upper electrode 4, 14, 24 Insulating layer 5 Electron emission window 6 Drive pulse voltage 7 Positive bias electric field 8 Negative bias electric field

Claims (6)

[Claims] 1. A ferroelectric cold cathode comprising a ferroelectric material sandwiched between a lower electrode and an upper electrode, wherein a portion of the ferroelectric material having an insulating film interposed between the ferroelectric material and the upper electrode; A portion forming an electron emission window in contact with the upper electrode. 2. A ferroelectric cold cathode comprising a ferroelectric material sandwiched between a lower electrode and an upper electrode, comprising: a first upper electrode and a second upper electrode as upper electrodes; A portion having a first insulating film interposed between the first upper electrode and a portion forming an electron emission window when the ferroelectric and the first upper electrode are in contact with each other; A ferroelectric cold cathode characterized in that a second upper electrode is provided on a portion of the first electrode with a first insulating film interposed between the upper electrode and the second upper electrode with a second insulating film interposed therebetween. 3. A ferroelectric cold cathode comprising a ferroelectric material sandwiched between a lower electrode and an upper electrode, wherein the first upper electrode, the second upper electrode, and the third
A portion where a first insulating film is interposed between the ferroelectric and the first upper electrode; and a portion where the ferroelectric and the first upper electrode are in contact with each other to form an electron emission window. And providing a second upper electrode via a second insulating film on a portion of the first electrode via a first insulating film between the ferroelectric and the first upper electrode, further comprising: A ferroelectric cold cathode comprising a third upper electrode provided on a second upper electrode via a second insulating film. 4. The ferroelectric cold cathode according to claim 1, wherein said insulating film has a dielectric constant of 100.
A ferroelectric cold cathode characterized by the above. 5. The method for driving a ferroelectric cold cathode according to claim 2, wherein a positive electric field is applied to the second upper electrode. 6. The method of driving a ferroelectric cold cathode according to claim 3, wherein a positive electric field is applied to the second upper electrode, and a negative electric field is applied to the third upper electrode. A method of driving a ferroelectric cold cathode.