JPH0748346B2 - Field emission cold cathode device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cold cathode which serves as an electron emission source, and more particularly to a field emission cold cathode device which emits electrons from a sharp tip.

[0002]

2. Description of the Related Art Cold cathodes (Journal of Applies) in which microscopic cold cathodes composed of a minute conical emitter and a gate electrode formed in the immediate vicinity of the emitter and having a current extraction and current control function are arranged in an array form
d Physics, Vol. 47, No. 12, p
p. 5248, 1976) has been proposed. This Spindt-type cold cathode has advantages that a higher current density can be obtained and the velocity dispersion of emitted electrons is smaller than that of a hot cathode. Further, it is said that the current noise is smaller than that of a single field emission emitter, it operates at a low voltage of several tens to 200 V, and it operates even in an environment of relatively poor vacuum degree.

FIG. 7 shows the structure of one minute cold cathode of the Spindt-type cold cathode of the prior art. Reference numeral 101 denotes a conductive substrate on which a minute conical emitter 102 is formed.
Is formed by a film deposition method, and an insulating layer 103 and a gate electrode 104 are formed around the emitter 102. The substrate 101 and the emitter 102 are electrically connected, and a voltage of about 100 V is applied between the substrate 101 (and the emitter 102) and the gate electrode 104. The distance between the substrate 101 and the gate electrode 104 is as narrow as about 1 μm, and the tip of the emitter 102 is made extremely sharp, so that a strong electric field is applied to the tip of the emitter 102. When the electric field becomes 2 to 5 × 10 ⁷ V / cm or more, electrons are emitted from the tip of the emitter 102.

The micro cold cathode having such a structure is used as the substrate 101.
By arranging them in an array on top, a planar cathode that emits a large current is formed.

In FIG. 7, the alternate long and short dash line and the alternate long and two short dashes line indicate the equipotential lines formed from the positions of 10% and 50% from the bottom of the insulating layer, respectively, and the numerals indicate the potentials of these equipotential lines. The ratio of V to the voltage V ₀ between the substrate and the emitter is shown. Insulating layer 103, since a uniform potential of equipotential lines formed between 10% and 50% of the positions from the bottom of the insulating layer are respectively 0.1 V _0, becomes 0.5V _0.

FIG. 8 shows a manufacturing method and structure of a conventional technique (Japanese Patent Laid-Open No. 4-94033) of a field emission cold cathode called a gray type. In FIG. 8, 110 is an insulating film mask pattern, 111 is a silicon substrate, 112 is a silicon thermal oxide film, 113 is an insulating film, 114 is a gate electrode, 11
5 is an emitter. The basic operation is similar to that of the Spindt type shown in FIG. 7, except that the emitter 115 is integrated with the silicon substrate 111 by the same material.
In order to manufacture this cold cathode, the silicon substrate 111 is isotropically etched through the insulating film mask pattern 110 having substantially the same size as the opening of the gate electrode 114 to form the conical emitter 115 (FIG. 8C). )).

Next, the surface of the silicon substrate 111 including the emitter 115 is thermally oxidized to form a thermal oxide film 112 (FIG. 8 (d)). Then, the insulating film 113 and the gate electrode 1
14 is deposited (FIG. 8E), and the thermal oxide film and the insulating film mask pattern 110 in the emitter 115 portion are removed (FIG. 8E).
(F)) By patterning the gate electrode 114, the structure shown in FIG.

By forming the thermal oxide film 112 on the emitter 115 and removing it, an emitter having a sharp tip, which cannot be realized by isotropic etching, can be formed with high accuracy. The insulating film 113 is the gate electrode 1
The thickness is selected so as to properly set the position of 14 with respect to the tip of the emitter. In the conventional example shown in FIG. 8, since the emitter having a sharp tip is manufactured with high accuracy and good reproducibility, the insulating layer has a two-layer structure. Thermal oxide film 1 for the purpose of making different layers
12 and the insulating film 119 are not formed.

FIG. 9 is a known example of a lateral field emission cold cathode obtained by modifying a Spindt-type cathode (Technical Dig).
est of IVMC 91, pp. 46,199
It is the structure of 1). In FIG. 9, an insulating substrate 11 made of quartz is used.
6, a planar emitter 117 is formed on the first surface on 6,
A planar gate electrode 119 is formed on a second surface slightly lower than the first surface of the insulating substrate 116. Although not shown in the figure, the emitter 117 is processed into a comb shape and has many corners or edges. Since the tip end of the emitter 117 and the tip end of the gate electrode 119 are formed extremely close to each other, the gate electrode 119 and
When a positive voltage is applied to, electrons are emitted from the vicinity of the tip of the emitter 117.

[0010]

A voltage between the emitter 102 and the gate electrode 104 (hereinafter referred to as a gate voltage).
Influences the insulating property between the emitter 102 and the gate electrode 104 and affects the stability of the cathode for a long time.
It is desirable that the gate voltage be as low as possible. Also,
The cathode emission current is controlled by the gate voltage, so
In order to control the gate electrode 104 with the output of a semiconductor integrated circuit or the like, it is desirable to similarly lower the gate voltage.

Further, the emitter 102 having such a structure.
The positive ions that impact the electron emission part at the tip of the
Since it is generated in the vicinity of 02 (within several μm), the impact energy of positive ions is mainly determined by the gate voltage. Further, the mechanical deformation of the tip of the emitter 102, which is caused by the impact of positive ions, is drastically reduced as the gate voltage is lowered when the accelerating voltage is 100 V or less. Therefore, the life of the emitter 102 is extended and the environment resistance related to the degree of vacuum is improved. The reduction of the gate voltage is also important for improving.

To reduce the gate voltage, the tip of the emitter is sharpened and the apex angle of the cone is reduced (T
hird International Vacuum
Microelectronics Confere
nce, Keynote Address, 1990,
Japanese Patent Laid-Open No. 4-94033), a method for reducing the structure of the entire micro cold cathode based on the scaling rule (Thir).
d International Vacuum Mi
croelectronics Conference
e, Keynote Address, 1990),
A method of using a material having a small work function for the emitter body, tip, or emitter surface (Japanese Patent Laid-Open No. 3-18711).
No. 9, JP-A-51-21471, JP-A-51
No. 54,358) has been proposed.

If the tip of the emitter is sharpened, the characteristics are likely to change due to positive ion bombardment, and if the apex angle of the cone is made smaller, the heat dissipation at the tip of the emitter 102 is reduced and the temperature rise of the tip is increased. , The maximum emission current per emitter is limited. In order to reduce the size of the entire structure, a highly accurate microfabrication system is required to manufacture the device, which may cause problems such as uniformity and yield. Further, the emitter material that can be used is limited by factors such as the element manufacturing process and the operating environment.

An object of the present invention is to provide a field emission cold cathode device in which the electric field strength near the emitter tip is increased, the gate voltage for emitting the same current is lowered, and the mechanical deformation of the emitter tip due to positive ion bombardment is reduced. Especially.

[0015]

In order to achieve the above object, a field emission cold cathode device according to the present invention is a field emission cold cathode device having a substrate, an electron emission electrode, an insulating layer, and a control electrode. The substrate is a substrate having conductivity or a substrate in which a conductive layer is laminated on an insulating material, and the electron emission electrode is formed in a pyramidal shape on the substrate and is electrically connected to the substrate. The insulating layer surrounds the periphery of the electron emission electrode and is formed in multiple layers having different dielectric constants, and the dielectric constant of the insulating layer close to the substrate is smaller than that of other insulating layers. The control electrode is laminated on the insulating layer and has an opening surrounding the electron emission electrode.

Of the laminated layers, the insulating layer close to the substrate and having a dielectric constant smaller than that of the other insulating layers has a smaller film thickness than the other insulating layers.

The field emission cold cathode device according to the present invention is a field emission cold cathode device having a thin film type electron emission electrode, a control electrode and an insulator, and the thin film type electron emission electrode emits electrons. The control electrode applies a voltage for extracting electrons to the electron emission electrode, and the insulator is composed of at least two insulators and separates the electron emission electrode from the control electrode. The dielectric constant of the insulator close to the electron emission electrode is smaller than that of other insulators.

[0018]

In the present invention, the insulating layer between the substrate and the gate electrode has at least a two-layer structure with different permittivities, an insulating material with a low permittivity is provided on the substrate or emitter side, and an insulator with a high permittivity is provided on the gate electrode side. Use material.

As a result, the electric field strength in the vicinity of the tip of the emitter becomes larger than that in the case of the uniform insulating layer, so that a low gate voltage is sufficient to obtain the same emission current. For this reason,
Even if positive ions are accelerated by the gate voltage and impact the electron emission part of the emitter, the possibility that mechanical deformation of the emitter tip will occur will be small, and stable operation with little change in electrical characteristics over a long time is expected. it can. In addition, the possibility of increase in leakage current between the emitter and the gate electrode is reduced, and stable operation can be expected. Furthermore, since the signal voltage amplitude for controlling the emission current can be reduced, there is an advantage that the load of the external circuit that drives the gate electrode and the like is reduced.

[0020]

Embodiments of the present invention will be described in detail with reference to the drawings.

(Embodiment 1) FIG. 1 is a structural view of a field emission cold cathode device showing a first embodiment of the present invention. In FIG. 1, 1 is a conductive substrate, 2 is a conical emitter that emits electrons, and the emitter 2 is electrically connected to the substrate 1. Reference numeral 3 is a first insulating layer, 4 is a second insulating layer, and 5 is a gate electrode.

During normal operation, a positive voltage of several tens of volts is applied to the gate electrode 5 with respect to the emitter 2 having the same potential as the substrate 1. The tip of the emitter 2 is formed to be extremely sharp, and the tip of the emitter 2 and the gate electrode 5 are extremely close to each other. Therefore, a strong electric field is applied to the tip of the emitter 2 to emit electrons. .
A micro cold cathode is constituted by one emitter 2 and the opening 5a of the gate electrode 5 around the emitter 2, and a single micro cold cathode or a set of a plurality of micro cold cathodes serves as a cold cathode.

The insulating layer between the substrate 1 and the gate electrode 5 has a two-layer structure of a first insulating layer 3 and a second insulating layer 4,
The first insulating layer 3 is a silicon oxide film (Si having a relative dielectric constant of 3.9).
O ₂ ) and the second insulating layer 4 are composed of a silicon nitride film (Si ₃ N ₄ ) having a relative dielectric constant of 7.5.

Now, assuming that the voltage between the substrate 1 and the gate electrode 5 is V ₀ , the distance between the substrate 1 and the gate electrode 5, that is, the thickness of the entire insulating layer is t, both ends of the first insulating layer 3 are Voltage,
The thickness and relative permittivity are V ₁ , ta ₁ , and ε ₁ , respectively, and the electric field in the first insulating layer 3 is E ₁ . Similarly, the second insulating layer 4
Voltage, thickness, relative permittivity, and electric field of V ₂ and ta ₂ respectively.
(= T (1-a ₁ )), ε ₂ , E ₂ . At this time, the electric field E ₁ and the voltage V ₁ of the first insulating layer 3 are expressed by the following equations, respectively. _{E 1 = V 0 / {t} · [1- (1-a 1) (1-ε 1 / ε 2)]} ... (1) V 1 = V 0 · a 1 / [1- (1-a 1 ) (1-ε ₁ / ε ₂ )] (2) The first insulating layer 3 and the second insulating layer 4 have the same thickness (a ₁ =
When 0.5), and _{E 1 = 1.32V 0 / t V} 1 = 0.66V 0.

On the other hand, when the dielectric constant of the insulating layer is uniform,
That is, when ε ₁ = ε ₂ (a ₁ = 0.5), E ₁ = 1.0V ₀ / t V ₁ = 0.5V ₀ , and the first insulating layer 3 has uniform voltage and electric field. The value is 30% or more higher than that in the case of.

In FIG. 1, the alternate long and short dash line and the alternate long and two short dashes line show the equipotential lines formed from the positions of 10% and 50% from the bottom of the insulating layer, respectively, and the numeral indicates the substrate of the potential of these equipotential lines. And the voltage V ₀ between the emitter and the emitter are shown. The potential of the equipotential line formed from the same 10% position is 1.3 times the potential of the conventional equipotential line in FIG.

In the case of the embodiment shown in FIG. 1, the electric field in the portion of the insulating layer around the emitter 2 close to the substrate 1 is 1.3 times as large as that in the conventional technique in which the entire insulating layer is also uniform. Has become. The electric field in the space in which the emitter 2 is housed, which is sandwiched by the insulating layer, strongly reflects the electric field in this insulating layer, and the electric fields near the surface of the substrate 1 and the surface of the emitter 2 are also compared with the case of a uniform insulating layer. And grow bigger. Since the electric field is 30% higher at the same gate voltage, the gate voltage applied may be about 25% lower in order to realize the same electric field.

As is clear from the equation (1), the dielectric constant of the first insulating layer 3 is smaller than that of the uniform insulating layer, and the dielectric constants of the first insulating layer and the second insulating layer are The larger the ratio and the smaller the thickness of the first insulating layer 3, the stronger the electric field near the tip of the emitter and the lower the gate voltage.

(Embodiment 2) FIG. 2 is a sectional view showing Embodiment 2 of the present invention. 2, the same components as those of FIG. 1 are designated by the same reference numerals. 2 is different from FIG. 1 in that the thickness of the first insulating layer 3 is 0.1 t and the thickness of the second insulating layer 4 is 0.9 t. That is, the lowermost 10% of the insulating layer in contact with the substrate 1 is the silicon oxide film (first insulating layer 3), and the remaining 90% is the silicon nitride film (second insulating layer 4). In this case, the potential of the equipotential line formed from the position of 10% from the lowermost end of the insulating layer indicated by the one-dot chain line is 0.18 V ₀ , and the electric field E in the first insulating layer 3 is
₁ is 0.18, which is about 1.2 as compared with the case of the uniform insulating layer.
8 times. Therefore, the gate voltage can be reduced by about 40% as compared with a device having a uniform insulating layer that forms the same electric field.

3A to 3D are sectional views showing a method of manufacturing the field emission device showing the first and second embodiments of the present invention in the order of steps. First, as shown in FIG.
The insulating layer 3, the second insulating layer 4, and the thin film layers to be the gate electrode 5 are sequentially formed to a predetermined thickness, for example, in the case of the first embodiment, the first insulating layer 3 is 0.5 μm and the second insulating layer 4 is 0. 0.5 μm, and the gate electrode 5 is laminated to 0.2 μm.

Next, as shown in FIG. 3B, a resist pattern having an opening having substantially the same size as the gate opening is formed on the gate electrode 5, and reactive ion etching is performed through the resist to form the gate electrode 5, A hole is formed in the second insulating layer 4 and the first insulating layer 3. At this time, the gate electrode 5
In order to increase the breakdown voltage between the emitter 2 and the emitter 2, the second insulating layer 4 and the first insulating layer 3 are processed under the condition that they are slightly overetched.

Next, as shown in FIG. 3C, while sacrificing the entire wafer, the sacrificial layer 6 is laminated in an oblique direction to form the sacrificial layer 6 on the gate electrode 5 and on the side surface of the opening 5a.

Next, as shown in FIG. 3D, when an emitter metal material such as molybdenum or dangsten is deposited by vapor deposition, an emitter metal layer 7 is formed on the sacrificial layer 6, and at the same time, on the substrate 1. The conical emitter 2 is formed at a position corresponding to the gate opening 5a. Next, as shown in FIG. 3E, the sacrificial layer 6 and the emitter metal layer 7 are removed.

In the first and second embodiments, the substrate 1 is made of a conductor such as metal or semiconductor, but a substrate having a conductive thin film formed on an insulator can also be used.

(Embodiment 3) FIG. 4 is a structural view of a field emission device showing a third embodiment of the present invention. FIG. 4 shows an embodiment in which the present invention is applied to the conventional field emission device whose manufacturing method and structure are shown in FIG. 8, and 8 is a thermal oxide film required in the process of forming the tip of the emitter 2. Also in the case of a multi-layered insulating layer structure of three or more layers as shown in this figure, the electric field strength at the tip of the emitter 2 is strongly influenced by the electric field in the thermal oxide film 8 of the lowermost layer. A weighted average dielectric constant considering the dielectric constants and thicknesses of the first insulating layer 3 and the second insulating layer 4, and the first insulating layer 3 and the second insulating layer 4.
The electric field in the thermal oxide film 8 can be calculated from the equation (1) assuming that the insulating layer 4 is a single insulating layer having the sum of the thicknesses.
Therefore, the effect of the present invention can be realized if the weighted average dielectric constant is larger than that of the lowermost insulating layer in contact with the emitter 2.

To manufacture the field emission device shown in FIG.
In FIG. 8, the step of depositing the insulating layer 113 is divided into two steps, and different insulating materials such as silicon nitride and titanium oxide (relative dielectric constant of about 100) may be sequentially deposited.

In the third embodiment, the case where the emitter made of the same material as that of the substrate is formed has been described. However, even when the emitter is formed by the deposition method as in the first and second embodiments, the case where the emitter is formed is 3 The same idea can be applied to more than one insulating layer.

(Embodiment 4) FIG. 5 is a structural view of a field emission device showing a fourth embodiment of the present invention. In FIG.
16 is an insulating substrate, 17 is a thin film emitter, 18 is a first insulating layer formed between the insulating substrate 16 and the emitter 17, 1
Reference numeral 9 is a gate electrode, which is different from the conventional structure shown in FIG.
The difference is that a first insulating layer 18 is added between the insulating substrate 16 and the emitter 17. The tip of the emitter 17 and the gate electrode 19 are formed very close to each other, and a strong electric field is applied to the corner or edge of the emitter 17,
Electrons are emitted from here. The insulating substrate 16 is made of quartz having a relative dielectric constant of about 4, and the first insulating layer 18 is made of quartz having a relative dielectric constant of about 2.
The porous silicon oxide film is used. Also in this case,
The electric field in the first insulating layer 18 having a small dielectric constant is larger than that in the conventional example shown in FIG. 7 in which the first insulating layer 18 and the insulating substrate 16 are made of the same material, and the tip of the emitter 17 is The nearby electric field also becomes stronger.

(Embodiment 5) FIG. 6 is a structural view of a field emission device showing a fifth embodiment of the present invention. The names of the constituent elements in FIG. 6 are the same as the constituent elements with the same numbers in FIG. The emitter 2 is formed on the conductive substrate 1 and has a rectangular cross section. Emitter 2 and gate electrode 5
Face each other through a narrow gap, and a strong electric field is applied to the corner or edge of the gate electrode, and electrons are emitted from this. The insulating layer between the gate electrode 5 and the substrate 1 is the first
It is composed of an insulating layer 3 and a second insulating layer 4, the first insulating layer 3 is made of a silicon oxide film, and the second insulating layer 4 is made of a silicon nitride film. The electric field in the first insulating layer 3 having a small dielectric constant is stronger than the electric field in the uniform insulating layer, and a strong electric field is also applied to the electron discharge part of the emitter 2.

Even if the present invention is used in combination with the method conventionally proposed for reducing the gate voltage, each of them exhibits its effect. Therefore, if these methods are used in combination, a large gate voltage reducing effect can be obtained. Is obtained.

Although examples of the silicon oxide film, the porous silicon oxide film, the silicon nitride, and the titanium oxide have been shown as the insulating material, it is obvious that the concept of the present invention can be applied to other insulating materials. .

Further, in the embodiment, the example in which the insulating layer is made of two kinds and three kinds of insulating materials is shown, but the present invention is also applied to the case of being made of four kinds or more of insulating materials. . Further, even in the case of an insulating layer whose permittivity changes continuously, it is clear that the idea of the present invention is applied if the permittivity near the substrate or the emitter is small and the permittivity near the gate electrode is large. .

Further, regardless of whether the change in permittivity is continuous or discontinuous, the change in permittivity in the middle of the layer is such that the permittivity is small near the substrate or the emitter and near the gate electrode. Even if it does not partially match the principle that the dielectric constant is large, the dielectric constant of the insulating layer near the emitter is compared with that of the other insulating layers by comparing the weighted average dielectric constants of the insulating layers near the emitter with other insulating layers. Obviously, the present invention can be applied if it is smaller than the average dielectric constant.

[0044]

As described above, in the cold cathode of the present invention, the tip of the emitter is not particularly sharpened, the shape of the microcathode is miniaturized, and no special material is used for the emitter. The gate voltage that discharges the same current can be reduced. Further, according to the present invention, it is possible to manufacture without significantly changing the conventional manufacturing method and without complicating the element structure and manufacturing method.

As a result, the possibility of instability due to the reduction of the insulation between the emitter and the gate is reduced, and the mechanical deformation of the tip of the emitter due to the impact of the positive electron on the emitter electron-emitting portion is greatly reduced, and the Can be operated. Further, the load on the gate electrode drive circuit that controls the emission current can be reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing a structure of a cold cathode device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a structure of a cold cathode device according to a second embodiment of the present invention.

FIG. 3 is a view showing a structure of a cold cathode device showing first and second embodiments of the present invention.

FIG. 4 is a diagram showing a structure of a cold cathode device showing a third embodiment of the present invention.

FIG. 5 is a diagram showing a structure of a cold cathode device according to a fourth embodiment of the present invention.

FIG. 6 is a diagram showing a structure of a cold cathode device according to a fifth embodiment of the present invention.

FIG. 7 is a diagram showing a structure of a conventional example.

FIG. 8 is a diagram showing a structure of a conventional example.

FIG. 9 is a diagram showing a structure of a conventional example.

[Explanation of symbols]

 1 Substrate 2 Emitter 3 First Insulating Film 4 Second Insulating Film 5 Gate Electrode 6 Sacrificial Layer 7 Emitter Metal Layer 8 Thermal Oxide Film 16 Insulating Substrate 17 Emitter 18 First Insulating Layer 19 Gate Electrode 101 Substrate 102 Emitter 103 Insulating Layer 104 Gate Electrode 110 Insulating film mask pattern 111 Silicon substrate 112 Thermal oxide film 113 Insulating film 114 Gate electrode 115 Emitter 116 Insulating substrate 117 Emitter 119 Gate electrode

Claims (3)

[Claims] 1. A field emission cold cathode device having a substrate, an electron emission electrode, an insulating layer, and a control electrode, wherein the substrate is a conductive substrate or a conductive layer is laminated on an insulating material. The electron emission electrode is formed in a pyramidal shape on the substrate and electrically connected to the substrate, and the insulating layer surrounds the periphery of the electron emission electrode, The dielectric constant of an insulating layer formed in multiple layers having different dielectric constants and close to the substrate is
A field emission cold cathode device, which is smaller than those of other insulating layers, wherein the control electrode is laminated on the insulating layer and has an opening surrounding the electron emitting electrode. 2. The insulating layer of the laminated layer, which is closer to the substrate and has a dielectric constant smaller than that of the other insulating layers, has a thickness smaller than that of the other insulating layers. The field emission cold cathode device described. 3. A field emission cold cathode device having a thin film type electron emission electrode, a control electrode, and an insulator, wherein the thin film type electron emission electrode emits electrons, and the control electrode is an electron. A voltage for extracting electrons is applied to the emission electrode, and the insulator is composed of at least two insulators and separates the electron emission electrode from the control electrode. The dielectric of the insulator close to the electron emission electrode is used. The field emission cold cathode device is characterized in that its rate is smaller than that of other insulators.