JP4389625B2 - Driving method of electron source - Google Patents

Description

  In the present invention, a voltage is applied so that the surface electrode is on the high potential side between the surface electrode provided on the main surface of the electron passing layer that is solid and the lower electrode facing the surface electrode through the electron passing layer. The present invention relates to a driving method of a field emission type electron source that emits electrons when applied.

  Various types of field emission type electron sources have been proposed. For example, as shown in FIG. 6, a lower electrode 2 is formed on a support substrate 1 made of an insulating substrate such as a glass substrate or a ceramic substrate. And a structure in which an electron passage layer 4 made of a semiconductor is interposed between the lower electrode 2 and the surface electrode 3 is known. Various structures are known for the electron passage layer 4. For example, an electron source having an MIM structure in which the electron passage layer 4 is formed of an insulator layer such as silicon oxide, silicon nitride, or aluminum oxide, An electron source in which a strong electric field drift layer having a fine structure such as porous polycrystalline silicon is formed is known. In any electron source, a voltage at which the surface electrode 3 is at a high potential is applied between the lower electrode 2 and the surface electrode 3, and an electric field is applied to the electron passage layer 4, so that the surface electrode The electrons tunneling 3 are emitted.

  The example shown in FIG. 6 is an electron source provided with an electron passage layer 4 having a fine structure, and the electron passage layer 4 performs nanocrystallization processing such as anodic oxidation on non-doped polycrystalline silicon. Thus, a structure having a strong electric field drift layer as shown in FIG. 7 is formed. As shown in FIG. 7, the strong electric field drift layer formed in the electron passage layer 4 has a large number of columnar grains 41 made of polycrystalline silicon extending in the thickness direction of the electron passage layer 4 as an internal structure. Between the grains 41 there are a large number of silicon microcrystals 42 in the order of nanometers. Further, on the surfaces of the grains 41 and the microcrystals 42, silicon oxide films having a film thickness smaller than the grain size of the microcrystals 42 are formed as insulating films 43 and 44 (see, for example, Patent Document 1).

  As shown in FIG. 6, the electron source having this structure is used with the collector electrode 6 facing the surface electrode 3, and the surface electrode 3 has a higher potential than the lower electrode 2 between the lower electrode 2 and the surface electrode 3. A DC voltage is applied from the power supply circuit 5 so that the collector electrode 6 is at a higher potential than the surface electrode 3 between the collector electrode 6 and the surface electrode 3. . When a voltage is applied in the relationship of FIG. 6, electrons are injected from the lower electrode 2 into the electron passage layer 4. Inside the electron passage layer 4, an electric field is intensively generated in the insulating films 43 and 44 and the insulating films 43 and 44 are very thin, so that the electric field strength of the electric field generated in the insulating film 43 becomes extremely large. Therefore, the electrons injected into the electron passage layer 4 are accelerated by a strong electric field generated in the insulating films 43 and 44, drift in the region between the grains 41 toward the surface electrode 3, and tunnel through the surface electrode 3 in the air. To be emitted. That is, inside the electron passage layer 4, electrons move along the insulating films 43 and 44, so that they are hardly scattered by the microcrystal 42, move toward the surface electrode 3 at a high speed, and move the surface electrode 3. Tunnel easily.

By the way, in Patent Document 1, in order to emit electrons captured in traps due to defects, impurities, dangling bonds, etc. existing in the electron passage layer 4, the surface electrode 3 is provided. In addition to the forward voltage period in which the lower electrode 2 has a high potential (in Patent Document 1, the period in which the forward bias is applied), the reverse voltage period in which the surface electrode 3 has a lower potential with respect to the lower electrode 2 (Patent Document). 1 describes a technique for providing a period during which a reverse bias voltage is applied. In the technique described in Patent Document 1, the voltage applied between the lower electrode 2 and the surface electrode 3 is managed, and the magnitude relationship between the voltage applied in the forward voltage period and the voltage applied in the reverse voltage period. And provisions on the application time.
Japanese Patent Laying-Open No. 2003-203589 (paragraph 0003-0012, FIGS. 16-18)

  By the way, in the technique described in Patent Document 1, since the voltage applied between the lower electrode 2 and the surface electrode 3 is managed, it seems that dielectric breakdown has occurred in a part of the insulating films 43 and 44. In such a case, an excessive current flows through the electron passage layer 4 and a large Joule heat may be generated to promote deterioration of the electron passage layer 4. The dielectric breakdown of the insulating films 43 and 44 may be caused by, for example, trapping electrons in traps formed inside the electron passage layer 4 or deterioration of the electron passage layer 4 over time. This is considered to be caused by the local concentration of the electric field in FIG. In short, since the technique described in Patent Document 1 is configured to control the voltage applied to the electron passage layer 4, a region where current easily flows locally in the electron passage layer 43 is generated, and the resistance value is reduced. In such a case, the current passing through the electron passage layer 4 is increased in order to maintain the applied voltage, and the deterioration of the electron passage layer 4 may be promoted by Joule heat.

  The present invention has been made in view of the above reasons, and its purpose is to prevent overcurrent from passing through the electron passage layer regardless of the forward voltage period and the reverse voltage period, and to suppress deterioration of the electron passage layer. It is to provide a driving method of an electron source.

  According to the first aspect of the present invention, a voltage is applied between the surface electrode provided on the main surface of the electron passage layer and the lower electrode facing the surface electrode so that the surface electrode has a higher potential than the lower electrode, and the electron passage layer A method of driving an electron source that emits electrons that tunnel through the surface electrode from the electron passage layer by applying an electric field to the surface, and the voltage between the surface electrode and the lower electrode is higher than the lower electrode. And a reverse voltage period for applying a voltage at which the surface electrode has a lower potential than the lower electrode is provided between the surface electrode and the lower electrode, and the electron passage layer is provided in the forward voltage period and the reverse voltage period. Current flowing through the electron passage layer so that the current density of the current flowing through the electron passage layer during the reverse voltage period is equal to or lower than the current density of the current flowing through the electron passage layer during the forward voltage period. Swing Characterized in that it sets the.

  According to this method, since the current passing through the electron passage layer is maintained at a set value, overcurrent does not pass through the electron passage layer regardless of the forward voltage period and the reverse voltage period, and Deterioration can be suppressed. That is, even if dielectric breakdown occurs in part of the electron passage layer, the progress of dielectric breakdown during the reverse voltage period can be suppressed.

  According to a second aspect of the present invention, a voltage is applied between the surface electrode provided on the main surface of the electron passage layer and the lower electrode facing the surface electrode so that the surface electrode has a higher potential than the lower electrode, and the electron passage layer. A method of driving an electron source that emits electrons that tunnel through the surface electrode from the electron passage layer by applying an electric field to the surface, and the voltage between the surface electrode and the lower electrode is higher than the lower electrode. And a reverse voltage period for applying a voltage at which the surface electrode has a lower potential than the lower electrode is provided between the surface electrode and the lower electrode, and the electron passage layer is provided in the forward voltage period and the reverse voltage period. The amplitude of the current flowing through the electron passage layer so that the amount of charge moving through the electron passage layer during the reverse voltage period is equal to or less than the amount of charge moving through the electron passage layer during the forward voltage period. And current flow Characterized in that it sets the time and.

  According to this method, since the current passing through the electron passage layer is maintained at a set value, overcurrent does not pass through the electron passage layer regardless of the forward voltage period and the reverse voltage period, and Deterioration can be suppressed. That is, even if dielectric breakdown occurs in part of the electron passage layer, the progress of dielectric breakdown during the reverse voltage period can be suppressed. In addition, by defining the amount of charge between the forward voltage period and the reverse voltage period, the reverse voltage period prevents the electrons trapped in the trap inside the electron passage layer from being excessive or insufficient during the forward voltage period. By adjusting the charge amount at, electrons trapped in the trap can be released without damaging the electron source during the reverse voltage period. In addition, since the amount of charge moving through the electron passage layer is a function of the amplitude of the current passing through the electron passage layer and time, the amplitude can be reduced by increasing the time, resulting in the electron passage layer. The voltage applied to the voltage decreases, and the stress on the electron passage layer during the reverse voltage period can be reduced.

  According to a third aspect of the present invention, in the second aspect of the present invention, the current that flows through the electron passage layer during the forward voltage period and the reverse voltage period is a rectangular wave pulse current.

  According to this method, since a rectangular wave pulse current flows in the forward voltage period and the reverse voltage period, the charge amount can be determined by the product of the current value and the pulse width, and the charge amount can be easily managed.

  According to a fourth aspect of the present invention, in the third aspect of the present invention, a plurality of pulse currents are intermittently passed through the electron passage layer during the reverse voltage period.

  According to this method, since current is intermittently passed through the electron passage layer during the reverse voltage period, the temperature increase of the electron passage layer is suppressed, and deterioration due to the temperature increase is suppressed.

  According to a fifth aspect of the present invention, in the third or fourth aspect of the invention, the ON period of one pulse current in the reverse voltage period is set to be less than or equal to the ON period of one pulse current in the forward voltage period. It is characterized by.

  According to this method, even when the amplitude of the pulse current in the reverse voltage period is equal to the amplitude of the pulse current in the forward voltage period, the charge amount in the reverse voltage period is made smaller than that in the forward voltage period. The amount of heat generated can be suppressed.

  According to a sixth aspect of the present invention, in the first to fifth aspects of the present invention, an output current of a power supply circuit that applies a voltage between the lower electrode and the surface electrode during the forward voltage period and the reverse voltage period. Monitoring is performed by a current sensor, and feedback control is performed on the output of the power supply circuit so as to maintain a preset current value for the forward voltage period and the reverse voltage period.

  According to this method, the current flowing through the electron passage layer can be accurately controlled by feedback control of the current flowing through the electron passage layer.

  According to a seventh aspect of the present invention, in the first to fifth aspects of the present invention, the lower electrode passes through one of a pair of constant current diodes connected in reverse parallel to each other from a power supply circuit in the forward voltage period and the reverse voltage period. Each of the constant current diodes is selected such that a voltage is applied between the electrode and the surface electrode, and a preset current value flows in the forward voltage period and the reverse voltage period.

  According to this method, open control is performed while the current flowing through the electron passage layer is maintained at a set value, so that the configuration for flowing current through the electron passage layer becomes simpler than when feedback control is performed.

  In the invention of claim 8, in the invention of claims 1 to 7, after repeating the forward voltage period and the reverse voltage period a plurality of times, a value of a current flowing through the electron passage layer in the forward voltage period is obtained, A voltage determined so as to obtain the current value is applied between the lower electrode and the surface electrode in a forward voltage period, and a current value that is a specified ratio with respect to the current value is a current in a reverse voltage period. It is characterized by being used for a value.

  According to this method, so-called aging is performed on the electron source, so that the forward voltage period is maintained while the electron emission surface is cleaned by detaching impurities, adsorbed gas, etc. adhering to the electron source from the electron emission surface. In addition, the current value in the reverse voltage period can be determined.

  According to the method of the invention of claim 1, since the current passing through the electron passage layer is maintained at the set value, overcurrent can pass through the electron passage layer regardless of the forward voltage period and the reverse voltage period. And deterioration of the electron passage layer can be suppressed. That is, even if dielectric breakdown occurs in a part of the electron passage layer, there is an advantage that the progress of dielectric breakdown during the reverse voltage period can be suppressed.

  According to the method of the invention of claim 2, since the current passing through the electron passage layer is maintained at the set value, overcurrent may pass through the electron passage layer regardless of the forward voltage period and the reverse voltage period. There is an advantage that deterioration of the electron passage layer can be suppressed. That is, even if dielectric breakdown occurs in part of the electron passage layer, the progress of dielectric breakdown during the reverse voltage period can be suppressed. In addition, by defining the amount of charge between the forward voltage period and the reverse voltage period, the reverse voltage period prevents the electrons trapped in the trap inside the electron passage layer from being excessive or insufficient during the forward voltage period. By adjusting the charge amount at, electrons trapped in the trap can be released without damaging the electron source during the reverse voltage period. In addition, since the amount of charge moving through the electron passage layer is a function of the amplitude of the current passing through the electron passage layer and time, the amplitude can be reduced by increasing the time, resulting in the electron passage layer. This has the advantage that the voltage applied to the voltage drops and the stress on the electron passage layer during the reverse voltage period can be reduced.

  In the embodiments described below, the explanation will be made on the assumption that a field emission type electron source similar to the conventional configuration shown in FIGS. 6 and 7 is used. An electron having a structure in which an electron passing layer 4 is provided between the electrode 3 and electrons are emitted from the electron passing layer 4 through the surface electrode 3 by applying a voltage between the lower electrode 2 and the surface electrode 3. Any structure can be used as long as a current passes between the lower electrode 2 and the surface electrode 3 in the direction along the electron passage layer 4.

  The electron passage layer 4 in the electron source having the structure shown in FIGS. 6 and 7 can flow a current bidirectionally between the lower electrode 2 and the surface electrode 3. Therefore, when a voltage is applied between the lower electrode 2 and the surface electrode 3 so as to make the surface electrode 3 have a high potential with respect to the lower electrode 2 in order to emit electrons, the electron passage layer is formed from the surface electrode 3. 4, a current flows toward the lower electrode 2, and when a voltage is applied so that the surface electrode 3 has a low potential with respect to the lower electrode 2, a current flows from the lower electrode 2 through the electron passage layer 4 toward the surface electrode 3. Flowing. In the following, the forward voltage period T1 is a period from the start of voltage application so that electrons are emitted until the voltage is applied with reverse polarity, and the reverse voltage period T2 is a voltage having a polarity opposite to that of the forward voltage period T1. A period from the start of application to the start of the forward voltage period T1 (see FIG. 1B). The forward voltage period T1 and the reverse voltage period T2 may each have a period in which no voltage is applied. As shown in FIG. 1A, a voltage is applied between the lower electrode 2 and the surface electrode 3 by a power supply circuit 5 having a current source. As will be described later, the power supply circuit 5 of the present embodiment has a function of keeping the current density of the passing current of the electron passing layer 4 at a preset target value and limiting the upper limit of the current density.

  Hereinafter, the current flowing through the electron passage layer 4 between the lower electrode 2 and the surface electrode 3 is referred to as a diode current. The diode current can be detected as a current flowing in a path passing through the power supply circuit 5 between the lower electrode 2 and the surface electrode 3. Since the diode current can flow in both directions as described above, when it is necessary to distinguish the direction, the diode current when the voltage having the polarity for emitting electrons from the surface electrode 3 is applied is the forward diode. This is called current Id, and the diode current when a reverse polarity voltage is applied is called reverse diode current -Id.

  In the illustrated example, a collector electrode 6 is provided opposite to the surface electrode 3, and a DC power supply 7 is provided between the surface electrode 3 and the collector electrode 6 so that the collector electrode 6 has a higher potential than the surface electrode 3. Voltage is applied. Hereinafter, a current flowing between the surface electrode 3 and the collector electrode 6 by electrons emitted from the surface electrode 3 is referred to as an emission current Ie. The emission current Ie can be detected as a current flowing in a path passing through the DC power source 7 between the surface electrode 3 and the collector electrode 6.

  FIG. 2 shows the relationship of the forward diode current Id, the reverse diode current −Id, and the emission current Ie with the potential of the surface electrode 3 when the potential of the lower electrode 2 is set as a reference potential. That is, in the illustrated example, when the potential is 0 V, it indicates that the potential of the surface electrode 3 is equal to the potential of the lower electrode 2, and in the region where the potential is positive, electrons are emitted from the surface electrode 3 and the emission current Ie is As the current flows, a forward diode current Id flows, and in a region where the potential is negative, electrons are not emitted and only the reverse diode current -Id flows. Further, all of the forward diode current Id, the reverse diode current −Id, and the emission current Ie increase as the potential difference between the surface electrode 3 and the lower electrode 2 increases.

  In order to measure the characteristic indicating the relationship between the potential and the current shown in FIG. 2, the potential of the surface electrode 3 is higher than the potential of the lower electrode 2 so that the difference between the potential of the lower electrode 2 and the potential of the lower electrode 2 increases with time. Then, a series of operations of changing the potential of the surface electrode 3 on the low potential side with respect to the potential of the lower electrode 2 so that the difference from the potential of the lower electrode 2 spreads over time is repeated three times. During the second operation, the forward diode current Id, the reverse diode current -Id, and the emission current Ie are measured. The reason for measuring during the third operation is to age the electron source. Note that the number of times of repeating the forward voltage period T1 and the reverse voltage period T2 for aging is not limited to two times, and may be repeated three or more times.

As described above, when the relationship between the forward diode current Id, the reverse diode current −Id, and the emission current Ie with respect to the potential difference between the lower electrode 2 and the surface electrode 3 is obtained, the relationship between the lower electrode 2 and the surface electrode 3 A reference value for the voltage applied between them can be determined. For example, the current density of the emission current Ie is 1 mA / cm ² , the current density of the forward diode current Id is 100 mA / cm ^2, and the current density of the reverse diode current −Id is 10% of the forward diode current Id. It can be determined as 10 mA / cm ² or the like. The reverse diode current −Id may be 5 to 30% of the forward diode current Id. In order to satisfy the above-described conditions, the potential difference between the lower electrode 2 and the surface electrode 3 may be obtained with reference to FIG. 2, for example, 18 V from the request for the forward diode current Id, and the reverse diode current −Id. It is set to -16V from the request. Note that the current density of the reverse diode current −Id may be selected within a range of 5 to 30% of the current density of the forward diode current Id.

  By the way, in the present embodiment, as shown in FIG. 1B, the waveform of the current flowing between the lower electrode 2 and the surface electrode 3 in the electron passage layer 4 is a rectangular wave, and the electron passage layer 4 has a rectangular wave. The pulse currents P1 and P2 are supplied. The pulse currents P1 and P2 are generated by the power supply circuit 5. The power supply circuit 5 monitors the current flowing through the electron source A by the current sensor 8, and the current value detected by the current sensor 8 is supplied to the power supply circuit 5. The output voltage is feedback controlled so that the value is maintained. Here, since the areas of the lower electrode 2 and the surface electrode 3 do not change, the current value of the forward diode current Id or the reverse diode current −Id detected by the current sensor 8 is proportional to the current density. That is, the power supply circuit 5 performs feedback control so as to keep the current densities of the forward diode current Id and the reverse diode current −Id flowing in the electron passage layer 4 at target values.

  Note that the magnitude of the forward diode current Id and the reverse diode current −Id is defined by the current density of the current passing through the electron passage layer 4 from the power supply circuit 5 to the plurality of electron sources A. This is because when the number of electron sources A to be supplied is collectively changed and the number of electron sources A to be driven changes with time, the output value of the current sensor 8 varies depending on the number of electron sources A being driven. is there. Therefore, in such a case, the output value of the current sensor 8 is substituted for the current density by dividing by the number of the electron sources A to be driven.

  As described above, the current density of the reverse diode current −Id is selected in the range of 5 to 30% of the current density of the forward diode current Id, and the current density of the reverse diode current −Id is the forward direction. It is set smaller than the current density of the diode current Id. Therefore, when a reverse diode current -Id is passed, particles with a small mass such as electrons trapped in the trap move, but a large current that affects the fine structure inside the electron passage layer 4 is As a result, the generation of Joule heat can be suppressed.

  The power supply circuit 5 includes a protection circuit that reduces the output current (including when the output is stopped) when the output current exceeds a threshold value defined for the target value. That is, the upper limit values of the forward diode current Id and the reverse diode current −Id are defined by the protection circuit, and an extremely large current may flow in the electron passage layer 4 with respect to the target value set in the power supply circuit 5. However, the Joule heat generated in the electron passage layer 4 can be suppressed to prevent the electron passage layer 4 from being damaged. As described above, the forward diode current Id and the reverse diode current −Id are both pulse currents P1 and P2, the pulse width is set to 1 ms, for example, and the duty for the forward voltage period T1 and the reverse voltage period T2 is For example, it is set to 10%. That is, the forward diode current Id and the reverse diode current −Id are allowed to flow for 1 ms for each of the forward voltage period T1 and the reverse voltage period T2 of 10 ms. This condition is, of course, an example, and the pulse width and duty of the pulse currents P1 and P2 can be set as appropriate.

  By the way, it is considered that the amount of electrons released from the trap by the reverse diode current −Id and released to the outside of the electron passage layer 4 is proportional to the amount of charge moved by the reverse diode current −Id. According to this finding, in order to release electrons from the trap and emit them from the electron passage layer 4, it can be said that it is desirable to manage the amount of charge that is moved by the reverse diode current −Id. Since the charge amount can be obtained as a product of current and time, the pulse current P1 of the forward diode current Id and the pulse current P2 of the reverse diode current −Id are controlled as shown in FIG. 1B. , The amplitude of the pulse current P2 for flowing the reverse diode current −Id is made smaller than that of the example of FIG. 1, as shown in FIG. In addition, the pulse width of the pulse current P2 can be increased. Thus, reducing the amplitude of the pulse current P2 means that the voltage applied between the lower electrode 2 and the surface electrode 3 is smaller than in the example shown in FIG. The acting electric field is also reduced. As a result, it is possible to reduce the influence on the fine structure of the electron passage layer 4 while releasing lightweight electrons from the trap and moving them. The amount of charge obtained by the product of the amplitude and pulse width of the pulse current P2 flowing the reverse diode current -Id is the charge obtained by the product of the amplitude and pulse width of the pulse current P1 flowing the forward diode current Id. Set below the amount. With this setting, it is possible to prevent an excessive charge amount from the charge amount required to cause the electrons trapped in the trap to be emitted from the electron passage layer 4, and to prevent the generation of Joule heat due to the reverse diode current -Id. Can be suppressed.

  In order to further suppress the temperature rise of the electron passage layer 4 due to Joule heat generated by the reverse diode current -Id, as shown in FIG. 4, a plurality of pulse currents P21 to P23 are allowed to flow in one reverse voltage period T2. What should I do? That is, the reverse diode current -Id is intermittently supplied. In this manner, by intermittently passing a plurality of pulse currents P21 to P23, heat is radiated from the electron passage layer 4 during the pause period of the pulse currents P21 to P23, so that the pulse currents have the same amplitude as the pulse currents P21 to P23. Compared with the case where one pulse current P2 having the total pulse width of P21 to P23 is passed, the temperature rise of the electron passage layer 4 can be suppressed. That is, it is possible to suppress the deterioration of the electron passage layer 4 due to the temperature rise. Here, the pulse widths of the pulse currents P21 to P23 are preferably equal to or less than the pulse width of the pulse current P1 when the forward diode current Id is passed. Under this condition, the heat generation amount of the electron passage layer 4 due to the reverse diode current −Id does not exceed the heat generation amount of the electron passage layer 4 due to the forward diode current Id. That is, in the reverse voltage period T2, the temperature of the electron passage layer 4 does not rise more than the forward voltage period T1.

  By the way, in each of the above-described examples, a voltage is applied between the lower electrode 2 and the surface electrode 3 using the power supply circuit 5 provided with a current source, and a current is passed through the electron passage layer 4. As described above, the power supply circuit 9 that generates the bidirectional pulse current at an appropriate timing is used, and two constant current diodes Di1 and Di2 are connected in reverse parallel between the power supply circuit 9 and the electron source A. A circuit may be inserted. Since the constant current diode Di1 determines the forward diode current Id and the constant current diode Di2 determines the reverse diode current -Id, the specifications of the constant current diodes Di1 and Di2 are selected so as to satisfy the above-described conditions. . In this configuration, it is not necessary to perform feedback control, and the power supply circuit 9 only determines the pulse widths of the pulse currents P1 and P2, and the amplitude of the pulse currents P1 and P2 is determined by the specifications of the constant current diodes Di1 and Di2. Therefore, the configuration is simple because it becomes open control.

(A) is a schematic circuit diagram which shows embodiment of this invention, (b) is operation | movement explanatory drawing same as the above. It is operation | movement explanatory drawing of the electron source used for the same as the above. It is operation | movement explanatory drawing which shows the other operation example same as the above. It is operation | movement explanatory drawing which shows another operation example same as the above. It is a schematic circuit diagram which shows other embodiment of this invention. It is a schematic circuit diagram which shows the usage example of an electron source. It is a principal part enlarged view which shows an example of an electron source.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Support substrate 2 Lower electrode 3 Surface electrode 4 Electron passage layer 5 Power supply circuit 6 Collector electrode 7 DC power supply 8 Current sensor A Electron source P1, P2 Pulse current

Claims (8)

  By applying a voltage between the surface electrode provided on the main surface of the electron passing layer and the lower electrode facing the surface electrode so that the surface electrode has a higher potential than the lower electrode, and applying an electric field to the electron passing layer. A driving method of an electron source that emits electrons that tunnel through a surface electrode from an electron passage layer, and a forward voltage period in which a voltage with a surface electrode having a higher potential than the lower electrode is applied between the surface electrode and the lower electrode; A reverse voltage period is applied between the surface electrode and the lower electrode to apply a voltage at which the surface electrode has a lower potential than the lower electrode, and the current passing through the electron passage layer in the forward voltage period and the reverse voltage period is a set value. And the amplitude of the current flowing in the electron passage layer is set so that the current density of the current flowing in the electron passage layer in the reverse voltage period is equal to or less than the current density of the current flowing in the electron passage layer in the forward voltage period. This The driving method of an electron source characterized by.   By applying a voltage between the surface electrode provided on the main surface of the electron passing layer and the lower electrode facing the surface electrode so that the surface electrode has a higher potential than the lower electrode, and applying an electric field to the electron passing layer. A driving method of an electron source that emits electrons that tunnel through a surface electrode from an electron passage layer, and a forward voltage period in which a voltage with a surface electrode having a higher potential than the lower electrode is applied between the surface electrode and the lower electrode; A reverse voltage period is applied between the surface electrode and the lower electrode to apply a voltage at which the surface electrode has a lower potential than the lower electrode, and the current passing through the electron passage layer in the forward voltage period and the reverse voltage period is a set value. And the amplitude of the current flowing through the electron passage layer and the time during which the current flows are set such that the amount of charge moving through the electron passage layer during the reverse voltage period is equal to or less than the amount of charge moving through the electron passage layer during the forward voltage period. Set The driving method of an electron source characterized by Rukoto.   3. The method of driving an electron source according to claim 2, wherein the current flowing through the electron passage layer during the forward voltage period and the reverse voltage period is a rectangular wave pulse current.   4. The method of driving an electron source according to claim 3, wherein a plurality of pulse currents are intermittently passed through the electron passage layer during the reverse voltage period.   5. The electron source according to claim 3, wherein an ON period of one pulse current in the reverse voltage period is set to be equal to or less than an ON period of one pulse current in the forward voltage period. Driving method.   In the forward voltage period and the reverse voltage period, the output current of the power supply circuit that applies a voltage between the lower electrode and the surface electrode is monitored by a current sensor, and the forward voltage period and the reverse voltage period are set in advance. 6. The method of driving an electron source according to claim 1, wherein the output of the power supply circuit is feedback-controlled so that the current value is maintained.   In the forward voltage period and the reverse voltage period, a voltage is applied between the lower electrode and the surface electrode through one of a pair of constant current diodes connected in reverse parallel to each other from the power supply circuit, and reverse to the forward voltage period. 6. The method of driving an electron source according to claim 1, wherein each constant current diode is selected so that a preset current value flows with respect to the voltage period.   After repeating the forward voltage period and the reverse voltage period a plurality of times, a current value flowing through the electron passage layer in the forward voltage period is obtained, and the voltage determined so as to obtain the current value is determined in the forward voltage period. 8. The method according to claim 1, wherein a current value applied between a lower electrode and the surface electrode and having a ratio defined with respect to the current value is used as a current value in a reverse voltage period. 2. A method for driving an electron source according to item 1.

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