JPH0743236A - Vacuum gauge of constant-current operating field emission type - Google Patents

Abstract

PURPOSE:To provide a field emission type vacuum gauge which has an extremely simple structure and small size and can accurately measure a pressure in an ultra-high vacuum region or lower than the region. CONSTITUTION:A constant-current power source 3 which automatically applies a required high-voltage V across an anode 1 and field emission cathode 2 in accordance with a set field emission current 1 is connected between the anode 1 and cathode 2 and a differentiating circuit 4 which differentiates the voltage V and squaring circuit 5 which squares the voltage V are connected to the power source 3. Then a divider circuit 6 which obtains a pressure P by inputting the outputs of the circuits 4 and 5 is connected to the circuits 4 and 5 and a displaying section 7 which displays the pressure P is connected to the circuit 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention detects changes in physical constants on a material surface due to a gas adsorption phenomenon, and can measure ultrahigh vacuum or lower pressures, and has an effect on a system under test as compared with conventional measuring instruments. The present invention relates to a two-pole structure vacuum gauge that is significantly less in number.

[0002]

2. Description of the Related Art Conventionally, a BA gauge or a quadrupole mass spectrometer, which is a typical vacuum gauge used as a pressure gauge in a pressure range of ultrahigh vacuum or lower, is radiated from a hot cathode. The principle is to read the pressure by accelerating electrons and irradiating them to gas molecules in a vacuum, counting the number of molecules ionized thereby.

[0003]

In the above-mentioned conventional example, a new gas is generated by catalytic decomposition of a gas by a high temperature filament as a thermoelectron source, and a new gas is generated from warming the container wall. The operation of the instrument seriously affects the measurement system, and in the ultra-high vacuum region, especially in the pressure of 1 × 10 ⁻⁸ Pa or less, the number of gas molecules in the gas phase is originally small, so the above-mentioned effect is serious. It's a problem. Further, as long as the number of ions is measured, it is unavoidable to introduce a complicated electrode structure and a structure that becomes a new gas source such as an electron multiplier to compensate for the number of ions that decreases with the decrease in pressure. For this reason, it has been reported that the pressure produced by the pressure gauge is often measured instead of the original pressure of the vacuum device. In order to make up for such drawbacks of the conventional vacuum gauge, a vacuum gauge based on a new principle other than ionization is required.

[0004]

The vacuum gauge of the present invention has been made in order to solve the above-mentioned problems and meet the above-mentioned demands. As shown in FIG. 1, an anode 1 and a field emission cathode 2 are provided. A constant current power supply 3 for automatically applying a required high voltage V according to the set field emission current I is connected between the two, and the constant current power supply 3 is squared with a differentiation circuit 4 for differentiating the high voltage V. A square circuit 5 is connected, a division circuit 6 is connected to the differentiation circuit 4 and the outputs of the square circuit 5 to obtain the pressure P, and a display unit 7 for displaying the pressure is connected to the division circuit 6. Become.

[0005]

[Operation] Since the vacuum gauge of the present invention has such a configuration,
As the gas molecules are adsorbed on the surface of the clean field emission cathode 2 by being installed in the vacuum device to be measured and the surface is contaminated, the surface physical quantities such as the work function of the cathode surface and the effective electron emission area change. The rate at which the surface is contaminated is a function of the number of gas phase molecules, or pressure. Therefore, the pressure can be calculated from the surface contamination rate. That is, the voltage is changed so as to keep the field emission current constant, and the pressure is measured from the change in the voltage. Now, the field emission current I at a certain time
(T) is expressed as follows, assuming that the effective radiation area mainly decreases due to the adsorption of gas molecules. I (t) = a (t) cV (t) ² exp (−bφ ^3/2 / V (t)) (1) where a (t) is the effective radiation area and c and b are A constant, φ is the work function of the cathode, and V (t) is the high voltage. The effective radiation area is given from the experiment as a (t) = a _o exp (−t / τ) (2), where the time constant τ is inversely proportional to the pressure P, and P = Σ / τ (3) where σ is a constant and the condition that the emission current does not depend on time is
It is given from the condition that Eq. (1) is differentiated with respect to time and becomes zero. Since V (t) ^{2 in the} previous term of the exponent has a small effect on the current fluctuation, the constant V (o) ² is given as

[Equation 1] The work function is a value specific to the cathode material and is a constant.

[Equation 2] It is represented by. However, m = bφ ^3/2 σ. Of the equation (5), dV / dt is obtained by the differentiating circuit 4, and V ² is obtained by the squaring circuit 5. These outputs are division circuits 6
The pressure P is calculated by dividing by, and is multiplied by an appropriate coefficient m and displayed on the display unit 7.

[0006]

1 is a block diagram showing the configuration of a first embodiment of the vacuum gauge of the present invention, in which a field emission current extracted by a high electric field generated on the surface of a field emission cathode 2 by applying a positive high voltage to the anode 1 is shown. An example of a method of detecting on the cathode side will be shown. FIG. 2 is a cross-sectional view showing a mounting example of the anode and the field emission cathode in the first embodiment. A positive high voltage (depending on the radius of the cathode tip, several kv) is applied to the anode 1 to obtain a radiation current. An example of attachment of both electrodes when used for connection is shown. In FIGS. 1 and 2, reference numeral 1 denotes an anode, which may be coated with a normal conductor or a phosphor to allow observation of a field emission image. A field emission cathode 2 is a heat-resistant conductor wire whose tip is sharply polished to about 0.1 μm. Reference numeral 9 denotes a cathode supporting wire, which also serves as an electrode for electric heating for heating and cleaning the cathode 2 before pressure measurement. Reference numeral 12 is a vacuum flange, which is used to attach the vacuum device to be measured. A current introducing terminal 10 supporting a field emission cathode 2 via a cathode supporting electrode 9 and an anode terminal 8 of an anode 1 for applying a positive high voltage V to the cathode 2 are insulated by an insulator 11 to form a vacuum flange. It is attached to 12.

Between the anode 1 and the field emission cathode 2 is connected a constant current power source 3 which automatically applies a required high voltage V according to the set field emission current I. The field emission current I can be set arbitrarily, but in consideration of the response of the current detection circuit, the influence of noise, the emission of gas from the anode due to the emission current, etc., select between 0.1 nA and 100 uA. Seems appropriate. A differential circuit 4 for differentiating the high voltage V and a square circuit 5 for squaring are connected to the constant current power source 3, and a dividing circuit 6 for inputting their outputs to the differential circuit 4 and the square circuit 5 to obtain a pressure P is provided. The division circuit 6 is connected to a display unit 7 for displaying the pressure.

The operation of the first embodiment having the above structure will be described. The vacuum flange 12 is attached to the vacuum device to be measured, and the constant voltage power supply 3 connected between the anode 1 and the field emission cathode 2 changes the high voltage V so as to keep the field emission current I constant. The high voltage V is input to the differentiating circuit 4 and differentiated, and also input to the squaring circuit 5 to be squared. The outputs are divided by the division circuit 6 to calculate the pressure P, which is then multiplied by an appropriate coefficient m and displayed on the display unit 7.

FIG. 3 is a block diagram showing the configuration of the second embodiment of the vacuum gauge of the present invention, which is an example in which a negative high voltage is applied to the field emission cathode 2 to detect the current in the constant current power supply 3. Others are the same as those in the first embodiment shown in FIG. FIG. 4 is a cross-sectional view showing a mounting example of the anode and the field emission cathode in the second embodiment. The anode 1 may be a normal conductor or a phosphor may be coated on the conductor to observe a field emission image. As the field emission cathode 2, a conductor wire whose tip is sharply polished to about 0.1 μm is used. In this second embodiment, the anode terminal 8 of the anode 1 is
Is directly attached to the vacuum flange 12, and the field emission cathode 2 for applying a negative high voltage to the anode 1 is attached to the cathode support electrode 9
The same operation as that of the first embodiment, except that the current introducing terminal 10 supported through the insulator is attached to the vacuum flange 12 with the insulator 11, the anode 1 is grounded, and the negative high voltage V is applied to the field emission cathode 2. It is what makes up.

[0010]

As described above, according to the present invention, since it is a field emission type vacuum gauge of a constant current operation mode, (1) the heat source is not used during the operation, so the influence on the system to be measured is extremely small. (2) Since the adsorption phenomenon itself is an integral action, an extremely low measurement lower limit can be obtained. (3) There is almost no shape dependency of sensitivity, which can be arbitrarily downsized. (4) Very simple anode / cathode bipolar structure. In addition to the features such as the simple structure, it is easy to discharge gas from the sensor part, (5) Selectivity of adsorption, and the partial pressure can be measured from the characteristics of each gas species in the field emission image. Compared to the constant voltage mode in which pressure is measured from current changes, (6) When the cathode surface state changes rapidly due to sputtering, etc., and the local electric field on the cathode surface increases, causing a significant increase in the emission current. (Many field emission cathode applications Oite only major uncertainties and going on) even voltage is reduced, it is possible to prevent damage to the cathode due to excessive current. (7) Since the applied voltage is automatically set even when the conditions such as the cathode material and the cathode radius are changed, it is not necessary to change the measurement conditions, and no specialized knowledge is required for using. (8) Further advantageous features can be obtained when the vacuum gauge is used as a practical vacuum gauge, because the control circuit is simplified without the need for a protection circuit.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a first embodiment of a vacuum gauge according to the present invention.

FIG. 2 is a cross-sectional view showing a mounting example of an anode and a field emission cathode in the first embodiment.

FIG. 3 is a block diagram showing the configuration of a second embodiment of the vacuum gauge of the present invention.

FIG. 4 is a sectional view showing a mounting example of an anode and a field emission cathode in the second embodiment.

[Explanation of Codes] 1 Anode 2 Field emission cathode 3 Constant current power supply 4 Differentiation circuit 5 Square circuit 6 Division circuit 7 Display section 8 Anode terminal 9 Cathode support electrode 10 Current introduction terminal 11 Insulator 12 Vacuum flange

Claims (3)

[Claims] 1. A high voltage (V) required according to a set field emission current (I) between an anode (1) and a field emission cathode (2).
Is connected to a constant current power source (3) for automatically applying a voltage, and a differential circuit (4) for differentiating the high voltage (V) and a square circuit (5) for squaring are connected to the constant current power source (3), A display unit (7) for displaying the pressure in the division circuit (6) is connected to the division circuit (4) and the squaring circuit (5) to connect the outputs thereof to obtain the pressure (P). ) Connected constant current operation field emission type vacuum gauge. 2. A current introducing terminal (10) supporting a field emission cathode (2) via a cathode supporting electrode (9) and an anode (1) for applying a positive high voltage to the cathode (2). Vacuum anode flange (12) with insulator (11) for anode terminal (8)
The constant current operating field emission type vacuum gauge according to claim 1, which is attached to the. 3. The anode terminal (8) of the anode (1) is connected to a vacuum flange (12) which is at ground potential, and the anode (1) is connected to the vacuum flange (12).
A current-introducing terminal (10) supporting a field emission cathode (2) for applying a negative high voltage to it via a cathode supporting electrode (9).
The constant current operating field emission type vacuum gauge according to claim 1, wherein the vacuum is attached to the vacuum flange (12) with an insulator (11).