JPH046431A - Vacuum gage - Google Patents

Abstract

PURPOSE:To obtain a vacuum gage characterized by no thermal agitation and stable electron discharge by forming many minute cold cathodes and minute accelerating electrodes on the surface of the same substrate. CONSTITUTION:In a cold-cathode electron discharging mechanism 40, many minute cold cathodes 41 and many minute accelerating electrodes 45 are provided on the surface of a substrate 48. The electrons which are discharged from the projections at the tips of the cold cathodes 41 are made to pass through the electrodes 45 and accelerated along the surface of the substrate 48. The electrons fly in the direction of an arrow 55. The electrons are pulled into a grid electrode 21 and perform the reciprocating movement shown by an arrow 54. The electrons are arrested by the electrode 21. During this period, the electrons collide with gas in a vacuum container 10, and the gas is ionized. The positive ions formed by the ionization are arrested by an ion collector electrode 31. The generated current is measured with an ion current meter 32. The emitter current discharged from the mechanism 10 is measured with ammeter 59. The grid current which flows into the electrode 21 is measured with ammeter 27. Then the pressure in the vacuum container 10 can be obtained based on the ratio between the ion collector current and the emitter current or the grid current.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a vacuum gauge that utilizes the ionization phenomenon of gas.
In particular, it relates to vacuum gauges with a unique cold cathode structure.

[Prior Art] Conventionally, an ionization vacuum gauge equipped with a hot cathode has been known as the most reliable vacuum gauge. Among them, the B-he gauge is often used, and many other types of hot cathode ionization vacuum gauges are known. A hot cathode ionization vacuum gauge ionizes gas using electrons emitted from a hot cathode, and determines the gas pressure based on the amount of ions.

[Problems to be Solved by the Invention] Although the conventional hot cathode ionization vacuum gauge described above has high measurement reliability, it has a problem of thermal disturbance. That is, the hot cathode heats the grid, vacuum gauge container, etc., causing gas to be released from there, and especially in low pressure areas, the pressure may be indicated to be about an order of magnitude higher than the true pressure. Therefore, there is a drawback that pressure measurement in ultra-high vacuum or extremely high vacuum is extremely difficult.

On the other hand, ionization vacuum gauges equipped with a cold cathode do not suffer from the thermal disturbance problem described above, but they use high voltage and have poor cold cathode discharge stability, making measurement reliable. There are low drawbacks. Furthermore, since high voltage is used, the cold cathode is sputtered with positive ions, resulting in a short cathode life.

[Objective] The second object of the invention is to provide a vacuum gauge that takes advantage of the advantages of a cold cathode ionization vacuum gauge, which is basically free from thermal disturbance, and eliminates the above-mentioned drawbacks of the cold cathode ionization vacuum gauge. .

[Means for Solving the Problems] The present invention provides a microfabricated cold cathode emitter (for example,
The above objective is achieved by employing a cold cathode electron emission mechanism including a cold cathode electron emission mechanism (see NIKKEI MICRO DEVICES, November 1989 issue, page 149). That is, the present invention provides a vacuum gauge including a cold cathode electron emission mechanism, a grid mechanism, and an ion collector mechanism, in which the cold cathode electron emission mechanism is configured as follows. This cold cathode electron emission mechanism includes a large number of small cold cathodes and a large number of small accelerating electrodes for accelerating electrons emitted from the small cold cathodes. The microcold cathode and the microacceleration electrode are formed on the surface of the same substrate, and electrons emitted from the cold cathode electron emission mechanism are emitted in a direction along the surface of the substrate.

The microcold cathode and microacceleration electrode are made using micropattern processing technology used in IC manufacturing processes. Therefore, a large number of minute cold cathodes and minute acceleration electrodes can be formed on one substrate.

Generally, the number of microcold cathodes and microacceleration electrodes is the same, but one microacceleration electrode may be associated with two or more tip protrusions that serve as electron emission parts of the microcold cathode. .

The cold cathode electron emission mechanism is formed on a substrate, and if this substrate is made into a flat plate, fine pattern processing becomes easier. Alternatively, the cold cathode electron emitting mechanism may be formed on an annular substrate to surround the coiled grid electrode.

The cold cathode electron emission mechanism may be formed not only on one side of the substrate but also on both sides of the substrate.

Since the minute cold cathode is susceptible to collisions with positive ions, it is preferable to provide a suitable ion shield. For example, an ion shield with a predetermined area is provided on the side surface of the substrate. This ion shield has a potential similar to that of the small cold cathode. Also,
The ion shield may be formed by connecting to the microcold cathode and protruding vertically from the substrate.

[Effect] The basic operation of this vacuum gauge is as follows.

In a cold cathode electron emission mechanism, electrons are emitted from a protrusion at the tip of a minute cold cathode by field radiation, and are accelerated by a minute acceleration electrode. Since the microcold cathode and the microacceleration electrode are formed side by side on the substrate, electrons are emitted along the surface of the substrate. Electrons emitted from the cold cathode electron emission mechanism are pulled by the grid electrode and reciprocate near the grid electrode, colliding with the gas and ionizing it. Positive ions generated by ionization are captured by the ion collector electrode. By measuring this ion collector current, the pressure inside the vacuum gauge can be determined.

In this vacuum gauge, electrons are emitted from many (for example, several thousand to thousands) minute cold cathodes, so even if the emitter current from one minute cold cathode is small, a large emitter current can be obtained in total. I can do it. Furthermore, since the minute accelerating electrode can be placed very close to the minute cold cathode, the electric field strength near the minute cold cathode can be increased. With these configurations, this vacuum gauge can obtain a stable emitter current and has high measurement accuracy despite using a cold cathode. Furthermore, since electrons can be stably supplied by this cold cathode electron emission mechanism, the voltage applied between the cold cathode and the grid electrode does not have to be too high.

[Example] Next, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a longitudinal sectional view of an embodiment of the present invention.

This vacuum gauge mainly includes a vacuum vessel 10, a grid mechanism 20, an ion collector mechanism 30, and a cold cathode emission mechanism 40.

The vacuum container 10 includes a cylindrical vacuum tube 11, an ion collector stem part 12 for penetrating and fixing an ion collector electrode, an electrode stem part 13 for penetrating and fixing other electrode terminals, and a vacuum chamber to be measured. and a connecting pipe 14 for attachment to the holder, and these are integrally formed.

The grid mechanism 20 includes a coil-shaped lid electrode 21, and the lid electrode 21 has a generally cylindrical shape as a whole. Both ends of the grid electrode 21 are connected and fixed to two leats 22 and 23. REIT22.2
3 is connected to an output terminal of an isolation transformer 26, and an AC power supply 25 is connected to an input terminal of the isolation transformer 26. When the AC power supply 25 is operated, the coil-shaped lid electrode 21
A current flows through it, causing it to heat up. Grid electrode 21
The heating operation is performed to release gas from the vacuum gauge, and the grid electrode 21 is not heated during pressure measurement.

For grid heating, the shape of the grid electrode is as follows:
A coiled shape as in this example is suitable.

The leads 22 and 23 are connected to a grid power supply 24 and a grid voltage is applied thereto. The current flowing into the grid can be measured with an ammeter 27.

Ion collector mechanism 30 includes an ion collector electrode 31 and an ion ammeter 32. Ion collector electrode 31
has an elongated needle shape and is located at the center of the coiled grid electrode 21.

In this embodiment, the cold cathode electron emission mechanism 40 is formed on an elongated flat substrate. The cold cathode electron emission mechanism 40 is connected to an ammeter 59 and an emitter power supply 57 via the cold cathode beam 43, and the accelerating electrode of the cold cathode electron emission mechanism 40 is connected to the electron emission control device 50 via the lead wire 47. It is connected to a power source 58. The detailed structure of this cold cathode electron emission mechanism will be explained below with reference to FIGS. 2 to 4.

FIG. 2 is a sectional view taken along the line ■--■ in FIG. Electrons emitted from the substrate surface of the cold cathode electron emission mechanism 40 in the direction of the arrow 55 are pulled by the grid electrode 21 and reciprocate as shown by the arrow 54, and are eventually captured by the grid electrode 21.

FIG. 3 is a schematic enlarged sectional view of the cold cathode electron emission mechanism 40 of FIG. 2, and FIG. 4 is a front view thereof. FIG. 3 is a sectional view taken along the line ■--■ in FIG. 4. On the surface 481 of the substrate 48, a large number of minute cold cathodes 41 (hereinafter referred to as emitters) and minute acceleration electrodes 45 are formed. Board 48
Insulators such as alumina are being used. The tip 411 of the emitter 41 is sharp, and electrons are emitted from the tip 4]1 by field emission.

A large number of emitters 41 are connected to each other at connecting portions 42, and a leait wire 431 is bonded to the end of the connecting portion 42. Lead wire 431 is electrically connected to glue 43 in FIG. The accelerating electrodes 45 have a cylindrical shape and are connected to each other by a connecting portion 46. A lead wire 471 is bonded to the end of the connecting portion 46 . Lead wire 471 is electrically connected to glue 47 in FIG. The row of emitters 4] and the row of accelerating electrodes 45 are parallel to each other, but the position and acceleration of emitters 4]
5 are shifted from each other so that electrons emitted from the emitter 41 pass between the accelerating electrodes 45. Electrons are emitted along the surface 481 of the substrate 48;
It flies in the direction of arrow 55.

In this embodiment, the cold cathode electron emission mechanism is formed on both sides of the substrate, but it may be formed only on one side.

It is preferable to make the radius of curvature of the tip of the emitter 41 as small as possible, which facilitates electric field emission. The radius of curvature is preferably 1 μm or less. The emitter 41 is preferably made of a high melting point metal material such as molybdenum or tungsten, but any material with a small work function (that is, a high ability to emit cold cathode electrons by an electric field) may be used. Further, the work function may be reduced by providing an oxide film on the emitter surface.

To form a large number of minute emitters 41 and accelerating electrodes 45 on the substrate 48, a fine pattern processing technique used in IC manufacturing processes is used. That is, a cold cathode electron emission mechanism as shown in FIGS. 3 and 4 can be formed by combining a film forming process, a patterning process by exposing and developing a photoresist, an etching process, and the like. Using this fine pattern processing technology, it is possible to stably mass-produce a large number of emitters and accelerating electrodes. The size of the emitter 41 and the accelerating electrode 45 is several micrometers to several tens of micrometers, and thousands to hundreds of these are formed on one substrate 48. Note that in FIGS. 3 and 4, the sizes of the emitter 41 and accelerating electrode 45 are exaggerated with respect to the substrate 48.

In addition to the accelerating electrode 45, another accelerating electrode 451 may be provided, and this accelerating electrode 451 is used when it is necessary to further accelerate and guide electrons toward the grid electrode.

An ion shield 44 is formed on the side surface of the substrate 48. The ion shield 44 is maintained at the same potential as the emitter 41 and prevents positive ions generated by ionization of the gas from colliding with the emitter 41. That is, positive ions are captured by the ion shield 44, which has a larger area than the emitter 41, and ion bombardment of the emitter 41 is almost eliminated. This increases the life of the emitter 41. Further, the emitter 41 is located behind the accelerating electrode 45 with respect to positive ions coming from the right side in FIG. 3, and since the accelerating electrode 45 has a higher potential than the emitter 41, In this respect, the ion bombardment is also reduced.

Metal vapor may fly from the direction of the grid (right direction in Figure 3) due to evaporation during grid heating or sputtering of the grid, but even in that case, this metal vapor should fly parallel to the substrate surface 481. Therefore, the substrate surface 481 between the emitter 41 and the grid electrode 45
Metal vapor is less likely to adhere to the emitter 41.
The insulation state between the substrate and the grid electrode 45 will not deteriorate due to metal vapor adhering to the substrate surface.

If necessary, a groove 482 may be provided in the substrate surface 481 so that the insulation state between the emitter 41 and the grid electrode 45 is not affected by the metal vapor described above.

FIG. 5 is an enlarged perspective view of the emitter 41 and its connecting portion 42 shown in FIG. 4. The height of the emitter 41 and the height of the connecting portion 42 are the same. FIG. 6 shows an example of changing the shape of the vicinity of the emitter 41. In this example, the wall 42 is perpendicular to the connection 42.
1 is formed. This wall 421 is at the same potential as the emitter 41 and has a larger area than the emitter 41, so the wall 421 prevents ion bombardment by positive ions.
This has the effect of reducing ion bombardment to the emitter 41.

FIG. 7 shows another example of changing the shape near the emitter. In this example, by making the thickness of the connecting portion 42 thinner than the emitter 41, the electric field is more concentrated at the tip 411 of the emitter 41, and the electric field is easily radiated.

Next, the operation of this vacuum gauge will be explained.

In FIGS. 1 and 2, electrons emitted from the cold cathode electron emission mechanism 40 are pulled by the grid electrode 21 and make a reciprocating motion as indicated by an arrow 54, and eventually the grid electrode 21
captured by During this time, the electrons collide with the gas inside the vacuum gauge and ionize it.

Positive ions generated by ionization are transferred to the ion collector electrode 31
captured by The ion collector current at this time can be measured with an ammeter 32. On the other hand, the current of electrons emitted from the emitter of the cold cathode electron emission mechanism 40 can be measured with an ammeter 59. In addition, electrons flowing into the grid electrode 21 (including electrons emitted from the emitter and electrons generated by ionization of the gas)
The current can be measured with an ammeter 27. The pressure inside the vacuum gauge is
It can be determined from the ratio of ion collector current to emitter current or the ratio of ion collector current to grid current. Alternatively, the pressure may be determined using three of the ion collector current, emitter current, and grid current.

The electron emission control device 50 shown in FIG. 1 is for maintaining the emitter current at a predetermined value. That is, when the emitter current falls below a predetermined value, it acts to increase the emitter current. For example, when the emitter current decreases, the potential of the accelerating electrode is increased.

FIG. 8 shows a modified example of the cold cathode electron emission mechanism, and shows the vicinity of the emitter and accelerating electrode.

In this example, one emitter 41 has two protrusions 413 .
414 is provided. That is, the number of emitters 41 and accelerating electrodes 45 are equal, but the number of protrusions 413 and 414 is twice the number of accelerating electrodes 45. In this case, emitter 41
Electrons emitted from the protrusion 413 of the emitter 41 and the protrusion 414 of the adjacent emitter 41 pass through the same acceleration electrode 45. Of course, three or more emitter protrusions may correspond to one accelerating electrode.

Further, the relative positions of the emitter 41 and the accelerating electrode 45 may be shifted from the illustrated positions.

FIG. 9 shows another modification of the cold cathode electron emission mechanism. In this example, as well as the example shown in FIG. 8, one emitter 41 is provided with two protrusions 413.414.
14 has a more acute angle than the example shown in FIG. 8 to strengthen the electric field at the tip of the protrusion.

FIG. 10 is a perspective view showing various shapes of the substrate of the cold cathode electron emission mechanism, and FIG. 11 is a longitudinal sectional view thereof. The substrates 401, 402, and 403 are configured in a ring shape so as to surround the coil-shaped lid electrode 21. The substrate 401 is in the shape of a hollow disk, and a cold cathode electron emission mechanism is formed on the surface (one or both surfaces) of the hollow disk. The substrate 402 has a hollow cylindrical shape, and a cold cathode electron emission mechanism is formed on the inner peripheral surface of the hollow cylinder. Board 4
03 has a hollow truncated conical shape, and has a cold cathode electron emission mechanism formed on its inner conical surface. The substrate 404 is a hollow cylindrical substrate disposed above the coil-shaped lid electrode 21, and has a cold cathode electron emission mechanism formed on its outer peripheral surface.

The substrate 405 is a flat substrate disposed vertically below the coil-shaped grid electrode 21, and has cold cathode electron emission mechanisms formed on both surfaces thereof.

In FIG. 11, arrows near the various substrates 401 to 405 indicate electron emission directions. In either case, electrons are emitted along the surface of the substrate. Any one of the substrate examples shown in FIGS. 10 and 11 or a combination of two or more can be used.

After all, in this invention, the cold cathode electron emitting mechanism is formed as a solid element on the substrate, so the cold cathode electron emitting mechanism can be formed into any shape, and mass production is also possible.

Since the vacuum gauge of the present invention employs a cold cathode electron emission mechanism and does not cause thermal disturbance, it is possible to measure areas of lower pressure than conventional hot cathode ionization vacuum gauges. By the way, the things that affect the measurement limits of a vacuum gauge are:
In addition to thermal disturbances, there is also the influence of soft X-rays. That is, when electrons are incident on the lid electrode, soft X-rays are generated, and when the soft X-rays hit the ion collector electrode, photoelectrons are emitted from the ion collector electrode. This causes a photocurrent to flow in the ion collector electrode, which defines the measurement limits of the vacuum gauge. Therefore, in the vacuum gauge of the present invention, which has the advantage of not causing thermal disturbance, it is important to further reduce the influence of soft X-rays in order to lower the measurement limit. In consideration of this point, in the modified examples shown in FIGS. 12 and 13 below, the influence of soft X-rays is reduced.

FIG. 12 shows a modification of the ion collector electrode.

In this example, only the tip of the ion collector electrode 31 is exposed in a dotted manner, thereby lowering the measurement limit using soft X-rays. Such an ion collector electrode is disclosed, for example, in Japanese Patent Publication No. 42-14992.

FIG. 13 shows another modification of the ion collector mechanism. In this example, an ion collector electrode 31 having the shape shown in FIG. 12 is used, and an X-ray shield 33 is provided.

This X-ray shield 33 protects against soft X-rays from the grid electrode 21.
It is possible to effectively block the radiation from entering the ion collector electrode 31. Positive ions reach the ion collector electrode 31 through the hole 34. This type of X-ray shield is e.g.
Magazine “Shinku” Vol. 19, w, No. 7 (1,9
76) on pages 229-238.

Although the embodiment shown in FIG. 1 is an example in which various electrodes are arranged in a vacuum container, a so-called nude type may be used in which only the electrode stem portion is left and the vacuum container is removed.

In the above-described embodiment, the grid electrode has a coil shape, but other shapes may be used.

This invention can be applied to any type of vacuum gauge that ionizes gas by electron bombardment. Therefore, it can be applied to Daizo gauges, Schulz gauges, double-electrode vacuum gauges, etc.

[Effects of the Invention] As explained above, the vacuum gauge of the present invention has a cold cathode electron emission mechanism formed by forming a large number of minute cold cathodes and a number of minute accelerating electrodes on the surface of the same substrate, so that the following effects can be achieved. There is.

(1) Since no hot cathode is used, there is no thermal disturbance, and electron emission is stable despite the use of a cold cathode. Therefore, the drawbacks of hot cathode vacuum gauges and conventional cold cathode vacuum gauges can be solved at the same time, and a highly reliable vacuum gauge can be obtained. This allows this vacuum gauge to measure pressure in ultra-high vacuums and extremely high vacuums.

(2) The microcold cathode and microacceleration electrode of the cold cathode electron emission mechanism can be formed on the substrate surface by micropattern processing technology, so stable mass production is possible. In particular, since electrons can be emitted along the substrate surface, microcold cathodes and microacceleration electrodes can be formed in a plane on the substrate, making it suitable for mass production.

(3) Electron emission is performed by field emission at the tip projections of a large number of minute cold cathodes, so there is no need to apply a high voltage between the cold cathode and the grid to obtain a predetermined electron emission current; Cold cathode sputtering due to positive ion bombardment is reduced.

Therefore, the life of the cold cathode is long. Furthermore, if an appropriate ion shield is provided near the cold cathode, the impact of positive ions on the cold cathode will be further reduced.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view of one embodiment of the present invention, and FIG.
Figure 3 is an enlarged plan cross-sectional view of a part of the cold cathode electron emission mechanism; Figure 4 is a front view of the part shown in Figure 3; Figure 5 is a view of the vicinity of the small cold cathode. Perspective view, Figure 6 is a perspective view of a modified example of the vicinity of the cold cathode, Figure 7 is a perspective view of another modified example of the vicinity of the cold cathode, and Figure 8 is a part of a modified example of the cold cathode electron emission mechanism. 9 is a front view of a part of another modified example of the cold cathode electron emission mechanism, FIG. 10 is a perspective view showing various shapes of the substrate of the cold cathode electron emission mechanism, and FIG. 11 is the 10th FIG. 12 is a front sectional view of a modified example of the ion collector electrode, and FIG. 13 is a front sectional view of a modified example of the ion collector mechanism. 21... Grid electrode 31... Ion collector electrode 40... Cold cathode electron emission mechanism 41... Microscopic cold cathode (emitter) 45... Microscopic acceleration electrode 48... Substrate 481... Substrate surface 55 ... Electron emission direction 21゛Grind electrode 31 Ion collector electrode 40゛Cold cathode electron emission mechanism No. 3 Fig. Fig. Fig. 13 Density

Claims (6)

[Claims] (1) In a vacuum gauge including a cold cathode electron emission mechanism, a grid mechanism, and an ion collector mechanism, the cold cathode electron emission mechanism includes a large number of minute cold cathodes and a structure for accelerating electrons emitted from the minute cold cathodes. The micro cold cathode and the micro accelerating electrodes are formed on the surface of the same substrate, and the electrons emitted from the cold cathode electron emission mechanism are directed in the direction along the surface of the substrate. A vacuum gauge characterized by a discharge of (2) The vacuum gauge according to claim 1, characterized in that two or more tip projections serving as electron emitting portions of the cold micro cathode correspond to one micro accelerating electrode. (3) The vacuum gauge according to claim 1, wherein the grid electrode of the grid mechanism has a coil shape, and the cold cathode electron emission mechanism surrounds the grid electrode. (4) The vacuum gauge according to claim 1, wherein the minute cold cathode and the minute acceleration electrode are formed on both sides of the substrate. (5) The vacuum gauge according to claim 1, wherein an ion shield for preventing positive ions from colliding with the minute cold cathode is formed on a side surface of the substrate. (6) An ion shield for preventing positive ions from colliding with the cold minute cathode is connected to the cold minute cathode and is formed to protrude perpendicularly to the substrate. Vacuum gauge.