JP3300775B2 - Field emission vacuum gauge with constant current operation - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention detects a change in the physical constant of a material surface due to a gas adsorption phenomenon, and can measure an ultra-high vacuum or a pressure lower than that. The present invention relates to a vacuum gauge having a two-pole structure, which is much smaller than that of the vacuum gauge.

[0002]

2. Description of the Related Art Conventionally, BA gauges and quadrupole mass spectrometers, which are typical vacuum gauges used as pressure gauges in an ultrahigh vacuum or lower pressure range, emit light from a hot cathode. The principle is that electrons are accelerated and applied to gas molecules in a vacuum, and the pressure is read by counting the number of ionized molecules.

[0003]

In the above conventional example, a new gas is generated by catalytic decomposition of a gas by a high temperature filament as a thermionic electron source, and a new gas is generated from the container by warming the container wall. The influence on the measurement system becomes serious due to the operation of the instrument, and the above-described influence is significant because the number of gas molecules in the gas phase is originally small in an ultra-high vacuum region, particularly at a pressure of 1 × 10 ⁻⁸ Pa or less. It is a problem. Further, as long as the number of ions is measured, it is inevitable to introduce a complicated electrode structure and a structure serving as a new gas source such as an electron multiplier in order to compensate for the number of ions decreasing with a decrease in pressure. For this reason, it has been reported that the pressure created by a pressure gauge is often measured instead of the original pressure of the vacuum device. In order to compensate for such a drawback of the conventional vacuum gauge, a vacuum gauge based on a new principle other than ionization is required.

[0004]

SUMMARY OF THE INVENTION A vacuum gauge according to the present invention has been made in response to the above-mentioned demands by solving the above-mentioned problems, and comprises an anode 1 and a field emission cathode 2 as shown in FIG. A constant current power supply 3 for automatically applying a required high voltage V in accordance with the set field emission current I is connected between the two, and a differentiation circuit 4 for differentiating the high voltage V to the constant current power supply 3 is squared. A squaring circuit 5 is connected, a dividing circuit 6 for obtaining the pressure P by inputting their outputs to the differentiating circuit 4 and the squaring circuit 5 is connected, and a display unit 7 for displaying the pressure is connected to the dividing 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 clean surface of the field emission cathode 2 by being installed in the vacuum device to be measured and the surface is contaminated, the physical function of the surface such as the work function of the cathode surface and the effective electron emission area changes. The rate at which the surface is contaminated is a function of the number of molecules in the gas phase, or pressure. Therefore, the pressure can be obtained 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 is mainly reduced by gas molecule adsorption. I (t) = a (t) cV (t) ² exp (−bφ ^3/2 / V (t)) (1) where a (t) is an effective radiation area, and c and b are The constant, φ, is the work function of the cathode, and V (t) is the high voltage. The effective radiation area is given by a (t) = a _o exp (−t / τ) (2) from the experiment, where the time constant τ is inversely proportional to the pressure P. = Σ / τ (3) Here, σ is a constant, and the condition that the radiation current does not depend on time is
Equation (1) is given from the condition that the equation is differentiated with time and becomes zero. Since V (t) ^{2 in the} exponential term has a small effect on current fluctuation, if a constant V (o) ² is set,

(Equation 1) The work function is a constant that is a value specific to the cathode material.

(Equation 2) It is represented by However, m = bφ ^{3 /} 2σ. DV / dt in the equation (5) is obtained by the differentiating circuit 4, and V ² is obtained by the squaring circuit 5. These outputs are output from the division circuit 6
To calculate the pressure P, multiplied by an appropriate coefficient m, and displayed by the display unit 7.

[0006]

FIG. 1 is a block diagram showing the construction of a first embodiment of a vacuum gauge according to the present invention. In FIG. 1, a positive high voltage is applied to an anode 1 to extract a field emission current drawn by a high electric field generated on the surface of a field emission cathode 2. An example of a detection method on the cathode side will be described. FIG. 2 is a sectional view showing an example of mounting the anode and the field emission cathode in the first embodiment. A positive high voltage (several kv depending on the radius of the tip of the cathode, several kilovolts) is applied to the anode 1 to obtain a radiation current. An example of mounting both electrodes when used for connection is shown. In FIG. 1 and FIG. 2, reference numeral 1 denotes an anode, which may be a normal conductor or a phosphor coated thereon to enable observation of a field emission image. Reference numeral 2 denotes a field emission cathode, which is a heat-resistant conductor wire whose tip is sharply polished to about 0.1 μm. Reference numeral 9 denotes a cathode support wire, which also serves as an electric heating electrode for heating and cleaning the cathode 2 before pressure measurement. Reference numeral 12 denotes a vacuum flange used for mounting on a vacuum device to be measured. A current introduction terminal 10 supporting the field emission cathode 2 through a cathode support 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. 12 attached.

[0007] A constant current power supply 3 for automatically applying a required high voltage V according to a set field emission current I is connected between the anode 1 and the field emission cathode 2. The electric field emission current I can be set arbitrarily. However, in consideration of the response of the current detection circuit, the influence of noise, and the effect of gas emission from the anode due to the emission current, a value of about 0.1 nA to about 100 uA is selected. Seems appropriate. A differentiating circuit 4 for differentiating the high voltage V and a squaring circuit 5 for squaring are connected to the constant current power supply 3, and a dividing circuit 6 for inputting their outputs to the differentiating circuit 4 and the squaring circuit 5 to obtain a pressure P is provided. The display unit 7 for displaying the pressure is connected to the dividing circuit 6.

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

FIG. 3 is a block diagram showing the configuration of a second embodiment of the vacuum gauge according to the present invention, in which a negative high voltage is applied to the field emission cathode 2 and current is detected in the constant current power supply 3. Others are the same as the first embodiment shown in FIG. FIG. 4 is a cross-sectional view showing an example of mounting the anode and the field emission cathode in the second embodiment. The anode 1 may be a normal conductor or a phosphor coated on the conductor so that the field emission image can be observed. The field emission cathode 2 uses a conductor wire whose tip is sharply polished to about 0.1 μm. In the second embodiment, the anode terminal 8 of the anode 1
Is attached directly to the vacuum flange 12 and the field emission cathode 2 for applying a negative high voltage to the anode 1 is connected to the cathode support electrode 9.
The operation is the same as that of the first embodiment, except that the current introduction terminal 10 supported through the fin 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.

[0010]

As described above, according to the present invention, since the field emission type vacuum gauge is in the constant current operation mode, (1) a heat source is not used at the time of operation, so that 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) The sensitivity can be reduced arbitrarily with little dependence on the shape. (4) The anode and cathode are extremely simple with a two-pole structure. In addition to the features such as (5) partial selectivity can be measured based on the selectivity of adsorption and the characteristics of each field type of the field emission image, etc. Compared to the constant voltage mode in which the pressure is measured from the current change, (6) In the case where the cathode surface state changes abruptly due to sputtering or the like, the local electric field on the cathode surface increases, and the emission current increases significantly. (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 change, there is no need to change the measurement conditions, and no special knowledge is required for use. (8) A more preferable feature can be obtained when used as a practical vacuum gauge, such as a simple control circuit without the need for a protection circuit.

[Brief description of the 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 sectional view showing an example of mounting an anode and a field emission cathode in the first embodiment.

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

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

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 anode 2 field emission cathode 3 constant current power supply 4 differentiating circuit 5 squaring 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)

(57) [Claims] 1. A high voltage (V) required between an anode (1) and a field emission cathode (2) according to a set field emission current (I).
Is connected, 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 supply (3). A dividing circuit (6) for inputting their outputs to the differentiating circuit (4) and the squaring circuit (5) to obtain a pressure (P) is connected, and a display unit (7) for displaying the pressure on the dividing circuit (6). ) Is a constant current operation field emission vacuum gauge connected to 2. A current introduction terminal (10) supporting a field emission cathode (2) via a cathode support electrode (9) and an anode (1) for applying a positive high voltage to the cathode (2). Anode terminal (8) with insulator (11) flange for vacuum (12)
2. A constant current operation field emission type vacuum gauge according to claim 1, wherein said vacuum gauge is mounted on said vacuum chamber. 3. The anode terminal (8) of the anode (1) is connected to a vacuum flange (12) at a ground potential, and the anode (1) is
Current introduction terminal (10) supporting, via a cathode support electrode (9), a field emission cathode (2) for applying a negative high voltage to
2. A constant current operation field emission vacuum gauge according to claim 1, wherein the vacuum gauge is attached to the vacuum flange by an insulator.