JPH10223129A - Ferroelectric cold cathode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ferroelectric cold cathode as an electron-emitting source to work practically with superior control of the electron-emitting amount, concretely to provide its laminated electrode structure including a plane wired electrode structure. SOLUTION: A ferroelectric substance cold cathode has a ferroelectric film 10 which is pinched by a lower electrode 20 and an upper electrode 30, wherein the lower electrode is equipped with patterns on its interface with the ferroelectric film 10 prepared by forming a thermal oxidized SiO2 region 22 on an n-type silicon base board. According to this configuration, the electron emission from the film 10 is restricted to the region where the lower electrode 20 interface with the film 10 consists of n-type silicon 21, and it is practicable to control the electron-emitting amount and the electron-emitting region. An alternative structure is such that the mentioned upper electrode 30 is used as the first upper electrode, thereover a second upper electrode is formed with an insulative film interposed, and that an electron-emitting window, composed of the insulative film and the second upper electrode is furnished on the n-type silicon region.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a ferroelectric cold cathode for emitting electrons, and more particularly to an electrode structure of a ferroelectric cold cathode.

[0002]

2. Description of the Related Art Pb (Zr, Ti) O ₃ (hereinafter abbreviated as PZT) and (Pb, La) (Zr, Ti) O ₃ (hereinafter PL)
Ferroelectrics such as ZT) are materials having spontaneous polarization, and it is known that an emission current density of several A / cm ² or more can be obtained by polarization inversion caused by application of a high-speed pulse.

FIG. 4 is a schematic diagram showing an example of a conventional ferroelectric cold cathode, in which 1 is a ferroelectric, 2 is a lower electrode,
3 is an upper comb-shaped electrode. The ferroelectric cold cathode shown in FIG. Gundel et al. (J. Appl. Phys. 69 (2), pp975,
1990). In the conventional ferroelectric cold cathode configured as described above, when an alternating electric field is applied between the lower electrode 2 and the upper comb-shaped electrode 3, the electric field applied to the inside of the ferroelectric 1 is canceled out. Polarization occurs, and the polarization is reversed with a change in the applied alternating electric field, generating a strong electric field. At this time, when a strong electric field of 10 ⁷ V / cm ² or more is applied to the ferroelectric 1, electrons of the ferroelectric 1 are extracted by the upper electrode 3 and emitted to the outside.

The above-described ferroelectric cold cathode has a simple structure as an element and has a relatively low vacuum (> 10 ^-1 mTorr).
However, since electron emission is possible, application to a printing apparatus (for example, Japanese Patent Application No. 6-291626: image forming apparatus) and a flat display (for example, JP-A-7-64490: light emitting display element) has been proposed. I have.

[0005]

However, in the conventional ferroelectric cold cathode, if a metal wiring is formed directly on the ferroelectric, polarization inversion occurs over the entire ferroelectric under the wiring, and electron emission occurs. The electron emission portion could not be limited, and thus the electron emission area and the electron emission amount could not be controlled. Further, for example, when applied to a display, there is a problem that phosphor emission occurs due to electron emission generated by polarization reversal under a wiring electrode, thereby deteriorating display quality. Also, when applied to an image forming apparatus such as a printing apparatus, a similar problem occurs when forming an electrostatic latent image.

[0006] Such problems can be avoided by processing and wiring the ferroelectric film. However, the above-mentioned composite metal oxide such as PZT is difficult to dry-etch by RIE or the like, or processed without dry-etching. However, new problems such as an increase in leakage current at the processing edge and an increase in the complexity of the process have occurred. Also, the pulse voltage for obtaining electron emission from a ferroelectric cold cathode using PZT ceramics as a ferroelectric is as high as 150 to 300 V, and it is necessary to reduce such a driving voltage for device application. is there.

The present invention has been made in view of the above-mentioned circumstances, and provides a ferroelectric cold cathode as a practical electron emission source which is excellent in controlling the amount of emitted electrons. An object of the present invention is to provide a laminated electrode structure of a ferroelectric cold cathode including a wiring electrode structure.

[0008]

According to a first aspect of the present invention, there is provided a ferroelectric cold cathode having a structure in which a ferroelectric material is sandwiched between a lower electrode and an upper electrode, wherein the lower electrode comprises a silicon substrate. It is characterized by forming a silicon pattern electrode by patterning, so that a ferroelectric cold cathode with excellent control of the amount of emitted electrons can be obtained, and a planar structure ferroelectric emitter without processing the ferroelectric. Can be formed, and the cold cathode fabrication process can be simplified,
Particularly, it is possible to obtain a cold cathode applicable to a flat display or an image forming apparatus excellent in transfer accuracy without a decrease in display quality due to light emission caused by electron emission to a phosphor other than a light emitting portion. It is.

According to a second aspect of the present invention, in the first aspect, the silicon substrate is an n-type silicon substrate, and the silicon pattern electrode is formed by forming a thermally oxidized region on the n-type silicon substrate. An n-type silicon region pattern is formed on the interface side with the body, and the ferroelectric material and the upper electrode are formed in the entire surface area on the lower electrode except for a contact portion in the lower electrode. Characterized in that a more specific configuration for obtaining a ferroelectric cold cathode having excellent control of the amount of emitted electrons is obtained, that is, electron emission is performed on the n-type Si region of the lower electrode. Since the polarization inversion does not occur in the ferroelectric on the thermally oxidized region, and no electron emission from this region occurs, the electron emission area and the electron emission amount are reduced. In addition, since the lower electrode is patterned by thermal oxidation, the electrode and the ferroelectric film have a planar structure with no irregularities, which simplifies the manufacturing process compared to the method of processing the upper electrode and the like. It is made possible.

According to a third aspect of the present invention, in the second aspect of the present invention, the upper electrode is a first upper electrode, and a second upper electrode is laminated on the first upper electrode via an insulating film. And an electron emission window formed by the second upper electrode and the insulating film is provided in at least a part of the region of the upper electrode that coincides with the n-type silicon region in the stacking direction. Electron emission is performed by applying a positive electric field to the second upper electrode. Electron emission pulses from the ferroelectric material are formed by stacking an extraction electric field application electrode (second upper electrode). A high-quality flat display can reduce the voltage, reduce the driving voltage of the element, and control the amount of electron emission at the same pulse voltage by changing the extraction electric field strength. It is obtained to be able to obtain an excellent image forming apparatus to transfer precision.

According to a fourth aspect of the present invention, in the third aspect of the invention, the dielectric constant of the insulating film is 100 or more, and by limiting the dielectric constant of the insulating film, a more effective insulating film can be formed. Specific specifications are obtained.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a ferroelectric cold cathode composed of a ferroelectric material sandwiched between a lower electrode and an upper electrode employs a silicon (Si) substrate having an electrode pattern formed on the lower electrode. doing. 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 lower electrode has a thermally oxidized region (SiO ₂ ) and an n-type Si region on the same surface. The ferroelectric material and the upper electrode are formed on the entire surface excluding the lower electrode contact portion. Further, according to the present invention, in the ferroelectric cold cathode in which the ferroelectric is sandwiched between the lower electrode and the upper electrode, the second upper electrode is laminated on the first upper electrode via an insulating film. And a second upper electrode and an electron emission window formed by an insulating film on the n-type Si region of the lower electrode.
A positive electric field is applied to the upper electrode.

That is, according to the present invention, the lower electrode is composed of a Si substrate in which a pattern of a thermally oxidized SiO ₂ region and an n-type Si region is formed on the interface side with the ferroelectric, and the ferroelectric film and the upper Since the electrode is formed on the entire surface except for the lower electrode contact portion, electron emission is limited only to the n-type Si region of the lower electrode, and polarization inversion occurs in the ferroelectric on the thermally oxidized SiO ₂ region. No electrons are emitted from this region. Thereby, the electron emission area and the electron emission amount can be controlled. In particular, a problem caused by emitted electrons generated by polarization reversal under a conventional wiring electrode. For example, in the case of a display application, a problem such as deterioration of display quality due to light emission due to electron emission to a phosphor other than a light emitting unit is caused. There is no. The same applies to the above image forming apparatus.

Further, in this structure, since the lower electrode is patterned by thermal oxidation, the electrode and the ferroelectric film can be formed in a planar structure without unevenness, and the manufacturing process is more complicated than the method of processing the upper electrode and the like. Can be simplified. Further, by applying an electron extraction electric field to the second upper electrode, the voltage required for emitting electrons from the ferroelectric can be reduced, and the driving voltage of the element can be reduced. Further, the amount of electron emission at the same pulse voltage can be controlled by changing the electron extraction electric field intensity.

Hereinafter, embodiments of the ferroelectric cold cathode according to the present invention will be described in detail with reference to the accompanying drawings. The ferroelectric cold cathode of the present invention is constituted by an aggregate of a plurality of cold cathodes, and a typical element structure thereof is shown in FIG. 1 and FIG. FIG. 1 is a schematic sectional view for explaining an embodiment of a ferroelectric cold cathode according to the present invention.
Is a ferroelectric film, 20 is a lower electrode, 21 is a Si region in the lower electrode, 22 is a thermally oxidized SiO ₂ region in the lower electrode, and 30 is an upper electrode. As shown in FIG. 1, the ferroelectric cold cathode in this embodiment includes a ferroelectric film 10 and an upper electrode 30 and a lower electrode 20 provided on the upper and lower portions of the ferroelectric film. The lower electrode 20 is n-type Si
Consists of a Si substrate having a thermally oxidized SiO ₂ region 22 in the layer 21, the ferroelectric film 10 and the upper electrode 30 is formed on the entire surface except for the lower electrode contact portion, the upper electrode 30
Are grounded, and an alternating pulse voltage is applied to the lower electrode 20 to drive the element.

It is known that electron emission due to polarization reversal of a ferroelectric starts to occur at an applied pulse voltage that is almost twice or more the coercive electric field of the ferroelectric. Therefore, the ferroelectric film 10
And a double layer of a thermally oxidized SiO ₂ region 22,
That is, the thermally oxidized SiO ₂ region 22 is formed on the lower electrode Si substrate surface.
In the region where is formed, the effective voltage applied to the ferroelectric film 10 at the time of driving is reduced, and does not lead to electron emission.
Electron emission occurs only from the region.

FIG. 2 is a schematic structural view for explaining another embodiment of the ferroelectric cold cathode according to the present invention.
a is a first upper electrode, 30b is a second upper electrode, 40 is an insulating film, W is an electron emission window, and other portions having the same function as in FIG. 1 are denoted by the same reference numerals as in FIG. As shown in FIG. 2, in this embodiment, the upper electrode of the ferroelectric cold cathode shown in FIG. 1 is used as a first upper electrode 30a, and
The insulating film 40 and the second upper electrode 30b are stacked, and an electron emission window W is provided at the same position on the n-type Si region of the lower electrode. Second upper electrode 30
When a positive bias electric field is applied to b, the second upper electrode 30b functions as an electron extraction electrode, and the amount of emitted electrons can be increased. Further, if the electron emission amount is fixed, the driving pulse voltage can be reduced. Furthermore, if the driving pulse voltage is fixed and the positive bias electric field is controlled, the amount of emitted electrons can be controlled.

In this embodiment, when a positive voltage is applied to the second upper electrode 30b, the effective voltage applied to the ferroelectric film 10 is preferably not more than 1/2 of the applied voltage. In addition, a dielectric film such as SiO ₂ or SiN can be used as the insulating film 40, and the dielectric film has a low dielectric constant (for example, SiO ₂ to 4). on the other hand,
Ferroelectrics generally have a high dielectric constant (for example, PZT-1
000), and the effective voltage of the ferroelectric film is reduced by 1 /
In order to obtain 2, a thickness of several nm is required. For example,
In the combination of SiO ₂ and PZT, a 1 μm thick P
The SiO ₂ film thickness required for the ZT film is 4 nm, and it is difficult to form such an ultra-thin film having excellent withstand voltage and leak resistance on the ferroelectric film. Therefore, a high dielectric film having a dielectric constant of 100 or more, for example, SrTiO ₃ , Ba
It is desirable to use SrTiO ₃ or the like.

In the present invention, the ferroelectric film 10 is specifically made of PZT, PLZT, SrBi ₂ Ta ₂ O ₉ , BaTi
It is composed of a composite metal oxide such as O ₃ . It is desirable that the ferroelectric film 10 has a thickness of 5 μm or less in order to emit electrons at a low voltage. Also, the upper electrode 30
(30a, 30b) is composed of Pt, Au, and Al.

The construction method of the embodiment shown in FIGS. 1 and 2 will be described below in more detail. First, the configuration shown in FIG. 1 will be described. Using PZT as a material of the ferroelectric film 10, a thin film was formed by a sol-gel method. An n-type Si wafer having a specific resistance of 5 mΩcm is used as a substrate,
After forming a thermally oxidized SiO ₂ layer having a thickness of 100 nm on this substrate to form a SiO ₂ cap layer having a diameter of 2 mm by a photolithography method, a thermally oxidized layer having a thickness of 50 nm is formed.
The cap layer was polished by a (chemical mechanical polishing) method to produce a lower electrode substrate. On this substrate, spin coating (3000 r.
pm × 20 seconds), calcination (400 ° C. × 30 minutes), and main firing (650 ° C. × 20 seconds) are repeated to obtain a PZ of about 800 nm.
A T ferroelectric film 10 was formed. As the upper electrode 30,
Using a metal mask, a Pt electrode having a thickness of 50 nm was formed on the entire surface except for the lower electrode contact portion by a sputtering method.

The device thus fabricated was set in a vacuum chamber and evacuated to 10 ^-5 Torr. At that time, a Pt plate and a fluorescent plate were used as collectors. The driving of the ferroelectric cold cathode was performed by grounding the upper electrode to the ground and applying a positive / negative pulse voltage to the lower electrode as shown in FIG. As a result of evaluating the light emission pattern by the phosphor emission, no bright spots other than the n-type Si region were observed, and the thermally oxidized SiO
It was confirmed that electron emission in _two regions was suppressed.

Next, in order to obtain the configuration shown in FIG. 2, the upper electrode formed by the above process is used as a first upper electrode 30a, and a second upper electrode 30a is formed on the first electrode with an insulating film 40 interposed therebetween.
Of the upper electrode 30b was formed. As the insulating film 40, S
An rTiO ₃ film was adopted and formed to a thickness of 50 nm by RF sputtering under the conditions of a substrate temperature of 400 ° C., RF power of 200 W, oxygen of 100% and gas pressure of 2 mTorr. Sr
TiO ₃ patterning is performed by ordinary photolithography and wet etching (etching solution is hydrochloric acid (HCl)
And a mixed solution of buffered hydrofluoric acid (BHF) and water) to form an electron emission window W having a diameter of 2 mm. Further, Pt (thickness: 200 nm) was formed on the insulating film by a lift-off method using a photoresist as a mask by an EB vapor deposition method to form a second upper electrode having an electron emission window W. The driving of the ferroelectric cold cathode was performed by grounding the first upper electrode 30a to the ground and applying a positive / negative pulse voltage to the lower electrode 20 as shown in FIG. At this time, a positive bias voltage of 0 to 20 V was applied to the second upper electrode 30b.

FIG. 3 is a diagram showing the results of measurement of the electron emission characteristics and the dependence of the electron emission characteristics on the bias electric field. As shown in FIG. 3, it can be seen that the electron emission amount increases as the bias voltage increases. Further, the electron emission start voltage decreases as the bias voltage increases.
Further, according to the above results, it is understood that the electron emission amount can be controlled by the bias voltage by keeping the driving voltage constant. Further, although the pattern of the lower electrode in this embodiment is formed in a circular shape having a diameter of 2 mm, the present invention is not limited to this, and a stripe-shaped electrode for selecting a driving element may be used.

[0024]

【The invention's effect】

Advantageous Effects of Invention: A ferroelectric cold cathode excellent in controlling the amount of emitted electrons can be obtained, and a ferroelectric emitter having a planar structure can be formed without processing the ferroelectric, and a cold cathode manufacturing process Can be simplified. In particular, by using the ferroelectric cold cathode of the present invention, it is possible to obtain a flat display and an image forming apparatus excellent in transfer accuracy without deterioration of display quality due to light emission caused by electron emission to a phosphor other than the light emitting portion. be able to.

Effect of Claim 2 In addition to the effect of Claim 1, a more specific structure for obtaining a ferroelectric cold cathode excellent in controlling the amount of emitted electrons can be obtained. That is, according to the present invention, the lower electrode is formed of an n-type Si substrate on which a thermally oxidized SiO ₂ region is formed, and the ferroelectric film and the upper electrode are formed on the entire surface except for the lower electrode contact portion. Therefore, electron emission is limited only to the n-type Si region of the lower electrode, and no polarization inversion occurs in the ferroelectric on the thermally oxidized region.
Therefore, electron emission from this region does not occur. Thereby, the electron emission area and the electron emission amount can be controlled. Further, since the lower electrode is patterned by thermal oxidation, the structure is a planar structure having no irregularities in the electrode and the ferroelectric film, and the manufacturing process can be simplified as compared with a method of processing the upper electrode and the like. .

Effect of Claim 3 In addition to the effect of Claim 2, by laminating an extraction electric field application electrode (second upper electrode), it is possible to reduce an electron emission pulse voltage from a ferroelectric. In addition, the driving voltage of the element can be reduced. Further, by changing the extraction electric field intensity, the amount of electron emission at the same pulse voltage can be controlled, and a high-quality flat display and an image forming apparatus excellent in transfer accuracy can be obtained.

Effect of Claim 4: In addition to the effect of Claim 3, by limiting the dielectric constant of the insulating film, a more effective specific specification of the insulating film can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram illustrating an embodiment of a ferroelectric cold cathode according to the present invention.

FIG. 2 is a schematic configuration diagram for explaining another embodiment of a ferroelectric cold cathode according to the present invention.

FIG. 3 is a diagram showing electron emission characteristics and bias electric field dependence in the present invention.

FIG. 4 is a schematic configuration diagram illustrating an example of a conventional ferroelectric cold cathode.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Ferroelectric, 2 ... Lower electrode, 3 ... Upper comb-shaped electrode, 10
... ferroelectric film, 20 ... lower electrode, Si regions in 21 ... lower electrode, thermal oxidation SiO ₂ regions in 22 ... lower electrode, 30 ... upper electrode, 30a ... first upper electrode, 30b
... second upper electrode, 40 ... insulating film, W ... electron emission window.

Claims (4)

[Claims] 1. A ferroelectric cold cathode having a configuration in which a ferroelectric is sandwiched between a lower electrode and an upper electrode, wherein the lower electrode forms a silicon pattern electrode by patterning a silicon substrate. A ferroelectric cold cathode characterized in that: 2. The method according to claim 1, wherein the silicon substrate is an n-type silicon substrate, and the silicon pattern electrode has an n-type silicon region pattern on the interface side with the ferroelectric by forming a thermal oxidation region on the n-type silicon substrate. The ferroelectric material and the upper electrode are formed in an entire area on the lower electrode except for a contact portion of the lower electrode, wherein the ferroelectric substance and the upper electrode are formed.
The described ferroelectric cold cathode. 3. A structure in which the upper electrode is a first upper electrode, a second upper electrode is laminated on the first upper electrode via an insulating film, and the n in the laminating direction. An electron emission window formed by the second upper electrode and the insulating film is provided in at least a part of the region of the upper electrode corresponding to the mold silicon region, and a positive electric field is applied to the second upper electrode. 3. The ferroelectric cold cathode according to claim 2, wherein electron emission is performed by performing the following. 4. The ferroelectric cold cathode according to claim 3, wherein the dielectric constant of the insulating film is 100 or more.