JPS5832737B2 - Denkai Hoshiya Sochi - Google Patents

Description

[Detailed description of the invention] The present invention relates to a field emission device.

In particular, it relates to preventing damage to field emission electron sources.

When a voltage is applied to a field emission electron source with a very sharp tip,
Electrons are emitted from its tip.

It is well known that an electron gun made based on this principle is called a field emission electron gun.

The electron beam emitted from a field emission electron gun has a higher brightness than that from a conventional thermionic electron gun, and has a very small spot diameter.

However, whereas the radiation current in a conventional thermionic electron gun is almost constant over time, it exhibits a peculiar change over time as shown in waveform a in FIG.

That is, time T.

The radiated electron flow I from the start of field emission to time T is I.

It changes rapidly from 1 to 11 (initial unstable region).

From time T1, the radiation electron flow I hardly decreases and becomes almost constant, and then gradually increases, and reaches the radiation electron flow I2 at time T2.

(Stable region) It is in this stable region that the electron gun can be used stably.

After time T2, the electron flow (2) increases with fluctuations.

(Late unstable region) Particularly after time T3, even larger fluctuations occur, and if field emission is continued further, the field emission electron source will be damaged by overcurrent.

Therefore, it is necessary to once stop the field emission after time T2 and regenerate the field emission electron source by heating or the like.

If the field emission electron source is cleaned, the emitted electron current will change over time in approximately the same way again.

Conventionally, this operation for stopping electric field emission has been performed manually by an operator while monitoring the radiation electron flow.

However, there is a risk that the field emission electron source may be damaged due to lack of operator caution.

In order to solve the above drawbacks, the minimum value of radiant electron flow ■8
Detect and store.

Alternatively, the radiated electron flow I,) is detected and stored after a predetermined time (Tt) has elapsed after the start of field emission.

There is a means of stopping the operation of the high voltage power supply when the radiated electron current becomes larger than the stored level of the radiated electron current.

According to the above means, damage to the field emission electron source can be prevented, but
Since functions such as detecting and storing the minimum value of the radiation electron flow are required, the device becomes complicated and expensive.

As is clear from Fig. 1, the radiated electron current increases with fluctuations in the late unstable region.

Therefore, it is possible to prevent damage to the field emission electron source by detecting fluctuations in the radiation electron flow and turning off the high-voltage power supply when the fluctuations exceed a predetermined magnitude.

However, even in the stable region (period T□ to T2 in FIG. 1), the emitted electron flow often fluctuates for a relatively short period of several seconds to several tens of seconds.

For this reason, the method of controlling the voltage power supply by detecting the variation has the disadvantage that the stable period of the emitted electron flow is substantially shortened.

As mentioned above, the field emission electron source can be used any number of times if it is regenerated by heating or the like.

However, the voltage required to radiate the necessary radiated electron flow each time the regeneration is performed becomes higher.

As the voltage increases, the field emission source will eventually discharge and be damaged.

Therefore, it is desirable to reduce the number of playback processes as much as possible.

In other words, it is necessary to detect the late unstable region of the field emission electron flow more reliably.

Therefore, the object of the present invention is to eliminate the above-mentioned drawbacks,
An object of the present invention is to provide a field emission device that can reliably prevent damage to a field emission electron source.

In order to achieve the above object, first of all, a value of the emitted electron current at which field emission should be stopped is set.

Then, when the radiation electron flow reaches the above value, the high voltage applied to the field emission electron source is reduced to zero.

Hereinafter, the present invention will be explained in detail with reference to Examples.

The cause of damage to field emission electron sources is that overcurrent flows through the electron source, so the allowable current level is
As shown by level b in the figure, the emitted electron flow must not exceed the above-mentioned allowable current level during any period from the start to the end of field emission.

Accordingly, the present invention can improve the T of the radiated electron flow shown by waveform a in FIG.

- Any level C that is higher than the period up to T2, that is, from the start of field emission to the end of the stability region, and lower than the above-mentioned permissible current level shown as level b in Figure 1. stipulate.

When the radiation electron flow (waveform a) reaches the set level C (time Tn in FIG. 1), the field emission can be stopped to prevent damage to the field emission electron source.

Note that the time until time Tn varies depending on the degree of vacuum of the vacuum chamber in which the field emission electron source is placed, the residual gas components, the size of the emitted electron flow, etc., and may take several minutes or several tens of hours. be.

FIG. 2 shows one implementation sequence for embodying the above operation.

That is, a high voltage power supply 3 is connected to the field emission source 2 of the field emission electron gun 1, and a field emission electron current detector 4 is connected between the high voltage power supply 3 and the field emission electron gun 1.

The output of this detector 4 is applied to a comparator 6 having a reference power supply 5 at one end.

The high voltage power supply 3 includes a power switch 12 and a switch controller 9.
The high voltage controller 8 is connected via a switch 9' controlled by a switch 9'.

The switch controller 9 is normally in a closed state.

Further, an electron source cleaning power supply 10 is connected to the field emission electron source 2 via a switch 11.

In the above configuration, when performing electric field radiation, first switch 1
Cleaning of the field emission electron source 2 is performed by closing switch 1 and then opening switch 11.

Next, when the power switch 12 is closed and a high voltage from the high voltage power supply 3 is applied to the field emission electron source 2, a field emission electron flow is emitted.

This radiation electron flow changes over time as shown in FIG. 1-a.

The electric field emission continues further and the reference power source 5 corresponds to the arbitrarily set level of the radiated electron flow (Level C in Figure 1).
When the output of the radiation electron current detector 4 becomes larger than the voltage value of , the output of the comparator 5 becomes "Hi".

As a result, the switch controller 9 operates, the switching is opened, and the voltage generation of the high voltage power supply 3 is stopped.

That is, damage to the field emission electron source can be prevented.

Thereafter, when the switch 11 is closed and the field emission electron source 2 is cleaned by the electron source cleaning power supply 10, the switching is closed, and stable field emission is performed again.

Of course, after the switching is automatically opened, it is necessary to reset the switch controller 9 before making the electric field radiate again.

Preferably, this reset is performed by closing switch 11.

This is because if the switching is opened automatically, it is dangerous to continue field emission any further, and if the field emission electron source 2 is not cleaned and the switch is turned on again. Then, the field emission electron source 2 may be damaged.

Therefore, as shown by the dotted line in FIG. 3, the switch controller 9 is configured to be reset by the switch 11.

In this way, the high voltage power supply 3 cannot be operated unless the field emission electron source 2 is cleaned.
The dangers mentioned above can be solved.

The radiation electron flow is not necessarily used continuously until the late unstable region (time T3 in FIG. 1) is reached.

Electric field emission may be stopped midway through.

In such a case, there is no need to clean the field emission electron source by heating or the like since the field emission has not yet come to an end.

It is sufficient to apply a constant high pressure from the beginning.

In this case, since the switching is closed, it is only necessary to open and close the power switch 12.

As detailed above, the present invention provides a set level for the flow of emitted electrons.

When the actual radiation electron flow reaches the set level, the high voltage applied to the field emission electron source is reduced to zero, thereby preventing damage to the field emission electron source.

Here, it is safer to set the setting level as low as possible.

For example, when the radiation electron current is 50 μA, the setting level is increased by 10 to 55 μA, and the radiation electron current is 1 μA.
In the case of A, it is desirable to set the current to 1.1 μA.

Therefore, it is sufficient to determine the setting level in conjunction with the radiation electron flow value.

However, if the radiation electron flow and the set level are close to each other in this way, as is clear from Fig. 1 (waveform a), a very large radiation electron flow will flow immediately after the electric field emission starts, so that the set level will be lowered. exceeds the voltage, and the high-voltage power supply turns off.

After a high voltage is applied to the field emission electron source, the radiation electron flow is controlled by providing constant current characteristics to the high voltage power supply until the radiation electron flow reaches a stable region where it hardly changes over time. keep constant.

Then, when the emitted electron flow hardly changes, the above-mentioned problem can be solved by switching the high voltage power supply to constant voltage characteristics.

FIG. 3 shows this concrete implementation sequence. 13 is a timer that is triggered by closing the power switch 12 and connects the switches 13' and 13'' to the @1711 side for a certain period of time.

Reference numeral 12 denotes a memory device having a function of holding the output voltage of the comparator 6.

The other blocks have already been explained.

The operation of the above components will be explained below. First, the field emission electron source 2 is cleaned by closing the switch 11, and then the switch 11 is opened.

Next, when the switch 12 is closed, the timer 13 is triggered, and the operation of the timer 13 is controlled by the switches 13' and 1.
3" are in contact with the a1/11 side, respectively.

Switching is because the switch controller 9 is not operating.
By closing switch 12, high voltage power supply 3 is also activated.

As a result, the field emission electron source 2 emits a field emission electron stream.

This emitted electron flow is converted into a voltage by the detector 4, and the difference from the reference power source 5 appears in the output of the comparator 6.

Therefore, if the closed circuit loop consisting of the comparator 6, high voltage controller 8, and high voltage power supply 3 is configured to provide negative feedback, the radiation electron flow emitted from the field emission electron source 2, that is, the detector 4, the output of the high voltage power supply 3 changes so that it is always equal to the reference power supply 5.

That is, it exhibits constant current characteristics.

Therefore, if the reference power source 5 is set to a voltage corresponding to, for example, 50 μA, the emitted electron current will always flow at 50 μA.

When time passes and the timer 13, which is set to a time corresponding to the expected initial instability period, returns to its original state, the contacts of the switches 13' and 13'' touch the tt 2F'' side, but the memory Since the output of the comparator 6 immediately before the power supply 12 continues to be held, there is no change in the state of the high voltage controller 8, and therefore the output voltage of the high voltage power supply 3 remains unchanged regardless of changes in the magnitude of the radiation current. , becomes a constant value.

Shows constant voltage characteristics. Here, ri is a reference power source set to a voltage higher than the reference power source 5 by, for example, 10φ.

Immediately after the high voltage power source 3 is switched to a constant voltage source, the voltage of the reference voltage G is higher than the voltage of the detector 4.

As a result, the output of the comparator 6 becomes, for example, "low", and if the switch controller 9 is made inoperative in this state, the switching is closed as a result.

As time progresses in this manner, and the radiation electron flow reaches the late unstable region (after time T3 in FIG. 1), the radiation electron flow increases.

Finally, the output voltage of the radiation electron flow detector 4 becomes larger than the voltage of the reference power source.

Comparator 6 then flips to "high" and triggers switch controller 9.

As a result, the switching is opened and the output voltage of the high voltage power supply 3 becomes zero.

That is, damage to the field emission electron source can be prevented.

Figure 4 shows the temporal change in field emission electron flow based on the above results.

In the figure, To-T is the period of constant current operation, and the emitted electron current is the set value.

controlled so that

As time elapses and time T1 comes, the high voltage power supply becomes constant voltage characteristic, so the emitted electron current follows the characteristics of the field emission electron source.

That is, in some cases, as in waveform A, there is almost no change until the end of the stable region T2, and in other cases, as in waveform B, an initial unstable region remains immediately after switching to a constant voltage source. obtain.

However, as is clear from FIG. 1, the change in the emitted electron flow is greatest immediately after applying a high voltage to the field emission electron source.

Therefore, if the period during which the high voltage power supply exhibits constant current characteristics, that is, the operating time of the timer 13, is set to approximately 3 to 5 minutes, there will be almost no change in the emitted electron flow after switching to constant voltage customization. Who?

According to the configuration described above, the radiation electron current hardly changes from immediately after the start of field emission until it reaches the late unstable region, so the setting level at which field emission is stopped is a value close to the radiation current. Since it can be set to , the field emission electron source can be reliably protected.

As detailed above, the set level of the radiation electron flow of the present invention is set, and when the radiation electron flow becomes larger than the set level, the high voltage applied to the field emission electron source is automatically brought to zero. Alternatively, damage to the field emission electron source can be prevented by lowering the high voltage to such an extent that no field emission occurs.

Furthermore, if the configuration is as shown in Fig. 3, there will be no large fluctuations in the radiation electron flow due to the initial unstable region of field emission, so the setting level at which field emission is stopped should be brought closer to the radiation electron flow value. This allows for more reliable protection of the field emission electron source.

Furthermore, by interlocking the reference power source 5, it is possible to stop the electric field emission when the emitted electron flow value increases by a certain percentage.

Mochi theory standard power supply 5. ! It goes without saying that instead of /, the reference power source may be kept constant and the detection sensitivity of the current detector 4 may be changed.

[Brief explanation of drawings]

FIG. 1 is a diagram showing changes over time in the emitted electron flow of a field emission electron source, FIGS. 2 and 3 are diagrams showing an embodiment of the present invention, and FIG. 4 is a diagram showing emitted electrons as a result of the embodiment shown in FIG. FIG. 3 is a diagram showing changes in flow over time.

Claims (1)

[Claims] 1 Consisting of a field emission electron source, a high voltage power supply for applying a high voltage to the field emission electron source, and a detector for detecting the emitted electron flow from the field emission electron source, means for controlling the output voltage of the high voltage power supply so that the radiation electron current value is smaller than a predetermined magnitude for a predetermined period from 1. A field emission device characterized in that the field emission device is configured to stop the operation of a high voltage power supply if the magnitude exceeds .