WO2016102575A1

WO2016102575A1 - High-energy electron source made from cnt with offset electromagnetic wave control element

Info

Publication number: WO2016102575A1
Application number: PCT/EP2015/080990
Authority: WO
Inventors: Jean-Paul Mazellier; Pierre Legagneux; Laurent Gangloff; Florian ANDRIANIAZY; Pascal Ponard
Original assignee: Thales
Priority date: 2014-12-23
Filing date: 2015-12-22
Publication date: 2016-06-30
Also published as: EP3238225B1; EP3238225A1; FR3030873A1; ES2721017T3; FR3030873B1

Abstract

A high-energy switchable electron source controlled by a current source (SCCO) in which: • the switchable cathode comprises at least one field-effect transmitter (105) and one screening electrode (111) located in or under a plane P comprising the conductive surface located under the foot of the transmitter (105), • an input terminal (132) of the SCCO (120) disposed outside the vacuum chamber is linked to the HV power supply and to the screening electrode (111), • an output terminal (131) of the SCCO is linked to the base electrode between the transmitter (105) and the substrate. • The high voltage power supply (103) delivers a potential for creating an anode field for inducing the transmission from the transmitter (105), • the output potential (131) being greater than or equal to the input potential (132), the screening electrode (111) is capable of reducing the electric field induced by the anode (106) on the transmitter (105) such that the current transmitted by the transmitter is equal to the current delivered by the SCCO.

Description

HIGH ENERGY ELECTRON SOURCE BASED ON CNT WITH ELECTROMAGNETIC WAVE CONTROL ELEMENT DEPORTEE

The invention relates to a high energy electron source, between 20 and 500 kV, for example, comprising at least one switchable or modulatable cathode or electron source and an electromagnetic wave control element external to the cathode structure. switchable.

It is used in the field of electron tubes incorporating an electron gun, and more particularly in the field of X-ray tubes. It relates to switchable or modulatable cathodes comprising one or more field effect emitters, or based on nanotubes. carbon nanofibers or CNT, associated with an electromagnetic wave (SCCO) controlled current source that can be physically deported out of the X-ray tube. It relates to an X-ray source, RX, delivering a wave-controlled RX flux. electromagnetic, for example an optical illumination source, and can be switched between an ON state and an OFF state or be regulated between these two states.

Switchable cathodes with an electromagnetic wave proposed today are optically controlled cathodes (photocathodes). One of the problems in CNT photocathodes is that photoelements physically associated with CNTs are subject to X-rays and ionizing bombardment within the tube enclosure. Their integration therefore requires a hardening technology. In addition, their integration in the form of a network homologous to the network of CNTs constrains the possible dimensions of these photoelements, which can limit their breakdown voltage, for example typically 40V, while the use of larger photoelements allows voltages of breakdown up to several hundred volts. The document US 2006/0002514 discloses a device comprising a network of electronic emitters associated with an extraction grid, a photosensitive component connected on the one hand to a voltage source and on the other hand to the extraction grid, and a resistance connected to the mass. In this configuration, the gate is positively polarized with respect to the tip so as to allow the emission of electrons from this tip. The emission of electronic transmitters depends on the difference in voltage between the gate voltage and the tip voltage. This voltage difference depends on the on or off state of the photosensitive device. The emission current then follows the Fowler-Nordheim law known to those skilled in the art which is, as a first approximation, an exponential of the gate voltage. As a result, the emission current can not be finely controlled.

US Patent 5,804,833 discloses a structure comprising a photocathode and an anode. The photocathode comprises an emitter structure made on a detector structure. The bias voltage is typically 10 kV. Such a configuration does not make it possible to manufacture an RX source (operating voltage of 50 to 500 kV) having a low RX flux in the OFF state corresponding to the unlit detector structure. This patent discloses a second configuration that involves the use of a voltage source to bias the gate relative to the contact to activate the sensing structure. In the ideal configuration, anode to the ground to facilitate its cooling and high-voltage photocathode, the addition of a source of voltage at the photocathode complicates the high voltage supply of the photocathode, by adding a photocathode transformer. isolation, for example. The detector and emitter structures are made in a continuous piece of semiconductor with the photoconductive element located under the emitter. It is therefore exposed to X-rays generated in the tube. The photoelements always having a leakage current, there is an electron emission current that generates on the target X-rays. These X-rays in turn generate a current in the photoconductor. This loop induces the appearance of a residual flow of X-rays. It is therefore not possible in this configuration to obtain an extremely low residual X-ray flux in the OFF state, Le., Without illumination of the photoelement.

In the following description, in the state "ON" the photoelement is illuminated, while in the state "OFF" the photo element is not illuminated. The same element will be referred to as "a current source controlled by an electromagnetic wave" or "a current control element".

The subject of the invention relates to a new high energy electron source structure controllable by an electromagnetic wave based on field effect transmitters, for example carbon nanotubes / nanofibers (CNT) where the configuration of the electrodes of the switchable cathode allows a dynamic reconfiguration of the potential in the vicinity of the CNTs. The nanotube or nanotubes are electrically connected to a base, all placed on a surface. The reconfiguration of the potential is in particular ensured by the coupling of the CNTs with a current source controlled by an electromagnetic wave (SCCO) which is externalised from the substrate and which, in fact, can be physically removed from a tube incorporating the switchable cathode (or modular) as an electronic source. This integration makes it possible in particular to avoid the direct exposure of the photoelement to the X-rays generated in the tube and the effect of the high-energy ion flux on the cathode which may lead to erosion or a modification of the electrical properties of the substrate, for example , the hydrogenation of silicon.

The invention relates to a high-energy electron source controlled by an electromagnetic wave comprising a vacuum chamber, a switchable or modulatable cathode based on field effect transmitters comprising at least one screening electrode, at least one transmitter field effect connected to a base electrode disposed on a substrate, an anode grounded, a high voltage power supply, at least one control circuit of a current source controlled by a electromagnetic wave or SCCO connected to said switchable cathode characterized in that:

• The SCCO is placed outside the vacuum chamber,

• An input terminal of the SCCO is connected to the high-voltage power supply and the switchable cathode shield electrode,

• An output terminal of the SCCO is connected to the base electrode between the field effect transmitter and the substrate,

• The high voltage supply delivering a potential to create an anode field sufficient to induce emission from the field effect transmitter,

The potential of the output terminal being greater than or equal to the potential of the input terminal, the screening electrode is adapted to reduce the electric field induced by the anode on the transmitter,

• Since the screening electrode is located in a plane P comprising the conductive surface located under the foot of the emitter or located in the same plane, an electrically insulating zone exists between the screening electrode and this conductive surface.

According to an alternative embodiment, the SCCO is disposed in a high voltage connector associated with the vacuum chamber, said connector comprising a window transparent to the electromagnetic wave, at least one source of electromagnetic waves controlled by the control circuit.

According to one embodiment, the source of electromagnetic waves is an optical source such as a laser source, a laser diode, a light emitting diode, and the window is transparent to the wavelength of the optical source.

According to another variant, the source of electromagnetic waves is a radiofrequency source comprising a transmission module and an RF radiofrequency transmission antenna, and the SCCO comprises an RF reception antenna connected to an RF reception module, and a source current controlled by this receiving module. The SCCO includes, for example, an RF receiving antenna connected to an RF receiving module, two cathodes and a microprocessor adapted to drive the current generation.

According to one embodiment, a switchable or modulatable cathode based on field effect transmitters comprises at least two zones, each of these zones is connected to an output of a corresponding current source and one or more connected laser sources. to a control circuit.

The transport of the optical wave can be carried out using an insulating optical fiber inserted into a solid material.

According to one embodiment, the substrate comprises a screening electrode having on one part an opening Oi, on which an encapsulation insulator is deposited, the base electrode and the emitter being arranged opposite the the opening made in the screening electrode.

According to a variant, a base electrode having a radius R, the distance between the base electrode and the screening electrode is of the order of R.

The electron source may comprise a substrate covered with an insulating layer comprising a via allowing contact of the base electrode of the field effect transistor, a screening electrode positioned around a transmitter effect of field, a layer of encapsulation insulator deposited to cover the screening electrode and at least partially the base electrode of the nanotube.

The source may also include an array of field effect transmitters connected to the substrate through the presence of through contacts.

According to one embodiment, the substrate comprises a continuous screening electrode, an encapsulation insulator on which are positioned the base electrode and the associated field effect transmitter.

According to one embodiment, a field effect transmitter is a carbon nanotube or a carbon nanofiber. The invention also relates to a source of electrons where the electrons strike an anode for the production of X-rays.

Other features and advantages of the present invention will emerge more clearly on reading exemplary embodiments given by way of illustration and in no way limitative, appended to the figures which represent:

FIG. 1, an exemplary structure according to the invention,

FIG. 2, an example of a structure according to the invention with the CNT,

FIG. 3, an exemplary embodiment with a network of CNTs,

• Figure 4, an illustration of the operation of the switchable cathode,

FIG. 5, the difference in voltage between the nanotube and the screening electrode, which allows a cancellation of the field at the top of a nanotube,

FIG. 6, a first variant embodiment of the system with optical fiber control,

FIGS. 7 and 8, two exemplary embodiments with radio frequency control,

FIG. 9, a second variant comprising several sources,

• Figure 10, a variant to remove current leakage on the surface of the insulation,

FIG. 11, an alternative of networks of CNTs connected to the substrate and various surface control electrodes,

FIG. 12, a variant in which the CNTs are individually polarized and have a common control surface electrode,

• Figure 13, an example of integration at a surface level,

FIG. 14, an exemplary embodiment of different emission zones with individual control of the emitted current,

FIG. 15A and FIG. 15B show two examples of buried shield electrode structure, FIG. 1 6 is a schematic of another variant of a buried screening electrode structure,

FIG. 17 represents an electronic control circuit, and

• Figure 18, an example of a network with three connections.

The following examples are given for the use of

CNTs, but could be implemented for any type of micrometric field effect transmitter, for example, silicon or metal micropoints, diamond, zinc oxide ZnO, etc.

FIG. 1 depicts a first exemplary embodiment of a switchable or modulable electromagnetic wave high energy electron source 100 which comprises a grounded vacuum enclosure 101 comprising an X-ray transparent window 102, a high voltage power supply 103, (-30 to -500 kV), a switchable cathode 104 based on field effect emitters, for example CNT carbon nanotubes / nanofibers, 105, incorporating one or more screening electrodes 1 1 1, the conductive layers on either side or around the nanotube are connected. The electromagnetic wave current control element (SCCO) is arranged outside the vacuum chamber, the switchable cathode and the SCCO being polarized at the high negative voltage, an anode 106 to ground, a source of electromagnetic waves 1 07, for example an optical source such as a laser, a laser diode or a light-emitting diode, a window transparent to the electromagnetic wave 108 and a control circuit 109 of this source of electromagnetic waves, for example a optical source. The power supply of the source is galvanically decoupled from the high voltage supply 103. The high voltage supply 103 delivers a potential having a value chosen to create an anode field sufficient to induce transmission from the transmitter 105.

The current control element (SCCO) remote from the enclosure, in this example, is a phototransistor or photodiode illuminated by an optical source through an optically transparent window and a gas optically transparent dielectric. The SCCO 120 is located in a high voltage connector 121, comprising a ground-tight envelope 122 and composed of electrical insulators 123 and pressurized gas with high dielectric strength and optically transparent 124.

The switchable cathode 104 (FIG. 2, FIG. 3) comprises at least one multi-walled carbon nanotube / nanofiber 105 (CNT), comprising a conductive surface 105s situated under the foot of the emitter, the CNT is oriented vertically with respect to the plane of the cathode, a shielding electrode 1 1 1 of the field induced by the anode 106 located on either side or around the nanotube, these elements being arranged on a substrate 1 12. The electrical insulator 1 15 has of openings at the base electrodes 1 10 so as to electrically connect the CNTs 105 to the substrate 1 12.

A CNT has an important aspect ratio, for example, in the range [100-200], between its length one hundred nanometers to several microns, and its diameter taken at the apex or equivalent for apex surfaces of Non spherical CNTs, one nanometer to several tens of nanometers. The distance between the screening electrode 11 1 and the nanotube 105 is close to the height h _C NT of the nanotube. The screening electrode 11 1 is preferably disposed in a plane P comprising the foot conductive surface 105p of the transmitter or located below this plane.

The insulating zone 1 15 supports the potential difference between the disk at the base of the nanotube and the screening electrode. The reduction of this voltage makes it possible to limit the induced electrical stress.

The conductive electrode between the nanotube 105 and the substrate 1 12 is connected to the output terminal 131 of the SCCO. The screening electrode 1 1 1 on the surface of the substrate is connected to the input terminal 1 32 of the SCCO. The input terminal 132 of the SCCO is connected to the high voltage HT. The optical source 107 illuminates the current source SCCO with a power controlled by the electronic control circuit 1 09. The potential of the output terminal 131 is in this example greater than or equal to the potential of the terminal 132. The screening electrode 1 1 1 only reduces or eliminates the electric field induced by the anode 106 on the transmitter 105, in normal operation.

The model in this example is defined for the following assumptions:

CNT 105 has an aspect ratio of 100 to 200 between its length I and its diameter at the top,

V represents the voltage between the nanotube 105 and its base electrode 1 10 relative to the screening electrode 11 1,

· R is the radius of the opening in the screening electrode.

When the tube RX is energized, a negative voltage is applied to the switchable cathode 104 and SCCO 1 relative to the anode 106. This potential difference induces an electric field at the cathode 104. An electric field is then applied to CNT 105 which can induce the emission of electrons. The current I _C NT delivered by the carbon nanotube is equal to the current Iscco delivered by the current source SCCO, it adjusts to the current. This operating point results in a self-polarization phenomenon of the CNT 105: when the current I _S cco delivered by the current source SCCO decreases, this increases the positive voltage on the nanotube 105 relative to the screening electrode 1 1 1 . The screening electrode then screens the anode field applied locally to the nanotube, which automatically reduces the CNT emission current I _C NT, until the I _C NT current delivered by the CNT is equal to the Iscco current delivered by the current source SCCO. The current I _C NT delivered by the nanotube (s) automatically adjusts to the Iscco current delivered by the SCCO. This operating mode makes it possible to control the emission current of the nanotube according to a quasi-linear law of the optical power, in this exemplary embodiment (the SCCO being a photodiode or a phototransistor).

The position of the SCCO 1 20 outside the vacuum chamber prevents its exposure to X-rays generated. The residual flow of X-rays emitted when the power source is not illuminated, OFF state, is then very weak. This configuration does not require an active voltage source to handle the voltage of the shielding electrode or to activate the SCCO. As a result, the high voltage power supply generates only one signal to bias the switchable cathode and the SCCO relative to the anode. It is thus possible to design a very compact high voltage power supply that does not require an isolation transformer in normal operation.

Due to the provision of the SCCO outside the enclosure, it is possible to obtain a dark current equal to the intrinsic dark current (<1 nA) of the SCCO and thus a current of emission of extremely low nanotubes (<1 nA), which is essential for medical applications, for example.

The anode 106 is grounded which facilitates its cooling. According to one embodiment, the anode 106 may include an opening for the passage of electrons, the anode 106 being connected to a vacuum chamber according to a scheme known to those skilled in the art. The source according to the invention is a source of high energy electrons, for example from 20 to 500 kV.

FIG. 3 illustrates an exemplary embodiment of the invention with a CNT network, 105i. The elements referenced in this figure have been described previously.

Figure 4 schematically illustrates the operation of the cathode controlled by the SCCO. It includes the emission current I _C NT of a CNT as a function of the potential difference between the nanotube 105 and the screening electrode 11 1, and this for a constant anode field. It also includes the current Iscco supplied by the SCCO as a function of the polarization voltage of this SCCO and as a function of the optical power Popt received by the SCCO.

In the configuration shown, the difference in voltage between the nanotube and the screening electrode, which is equal to the voltage difference between the output terminal and the input terminal of the SCCO source.

As the current supplied by I _C NT nanotubes is equal to the current delivered by Iscco the SCCO, the current value is the intersection, the _s, the curve 200 between the current delivered by the SCCO and curve 201 current of emission of the nanotube. For an optical power P _opt i of illumination of the SCCO corresponding to a current delivered by this source SCCO of 10 μΑ, the emission current of the CNT is equal to this current of 1 0 μΑ.

When the transmission power of the source SCCO decreases, curve P _op t2, the current l _SC co issued by the SCCO decreases, in the example, 5 μΑ. The electrons initially accumulated at the top of the CNT will partly be emitted by field effect, thereby reducing the extraction field at its peak. The emission current I _C NT will be reduced. This process stops when the emission current becomes equal to 5 μΑ. It is possible to temporally modulate the illumination power of the source SCCO and thus the emission current I _C NT of the nanotubes and thus the RX flux emitted on the object to be examined.

When the SCCO is no longer illuminated, OFF state, the current Iscco delivered by the source is equal to the current value corresponding to the intersection of the curve describing the dark current se and the emission curve of the nanotube. . In order to obtain an extremely low OFF state current, the dark current of the SCCO source must be extremely low and a voltage across the SCCO current source must be lower than the avalanche voltage of the SCCO source. SCCO.

Figure 5 shows the voltage difference between a CNT and a shielding electrode for canceling the field at the top of the CNT. For a CNT of height 5 μηι and an opening radius in the shielding electrode of 1 μιη, this voltage is 1 10 V. In this configuration, an SCCO with an avalanche voltage higher than 1 is chosen. 10V and has an extremely low dark current. There are photodiodes with avalanche voltages of 200 V with a dark current of less than 1 nA. It is therefore possible with this configuration to make an RX tube with an electron current in the OFF state less than 1 nA. The current source SCCO can also feed a network of nanotubes, as will be schematized later. The current in the ON state, illuminated current source, can reach for example 1 mA. An ON / OFF ratio of 1 0 ^{6 is} then obtained. It is particularly advantageous to use short and thin CNTs, for example 2 μηπ high and 20 nm in diameter at the top. For the same electrode radius of 1 μηη, the voltage that makes it possible to cancel the field at the top of the nanotube is of the order of 50 V. It is then possible to use SCCOs having a lower avalanche voltage.

For a buried screening electrode, the insulation thickness will be adjusted according to the voltages to be held and the insulating material. For example, 1 μm of thermal silica can hold a voltage of 200V and theoretically 1000V. The operating principle of the switchable cathode described above remains the same for this variant embodiment.

FIG. 6 represents an alternative embodiment using an electrical insulating optical fiber for the propagation of the control signal. The elements of this variant identical to those described in Figure 1 bear the same references. An insulating optical fiber 140 allows the propagation of the signal from the source 107. This fiber passes through a dielectric solid 141, such as a polymer, a ceramic, an epoxide, in order to excite the SCCO 120. The assembly is disposed in An electrical insulator 142. As in the example of FIG. 1, there is a direct optical link between the optical source and the remote SCCO source.

Figure 7 illustrates a radiofrequency electromagnetic wave source 180 for controlling the SCCO. The radiofrequency source comprises a transmission module 181 and an RF emission antenna 182. The SCCO comprises an RF reception antenna 183 connected to a module RF receiver 184, and a current source controlled by this receiving module. The SCCO is therefore a source of current controlled by the source of electromagnetic waves 180. Such a device does not require any direct link between the RF source and the SCCO. This device is particularly well suited for controlling many switchable cathodes carried at high voltage by an electromagnetic wave having different modulations and thus allowing transmission multiplexing and demultiplexing at the reception of each channel, CNT cathode. The control can be in all or nothing (On / Off) or allow a precise control of the current intensity of the CNTs by pulse width modulation or PWM in Anglo-Saxon Pulse Width Modulation.

FIG. 8 schematizes a variant for controlling two cathodes Ci, C ₂ by multiplexing Mix. This device allows, for example, the RF control and the generation of PWM signals to control the current from a second microprocessor 185. The communication between the two RF microprocessors can be done using the SPI protocol for example.

FIG. 9 represents a variant for which the switchable cathode comprises at least two zones 81, 82, or even more than two zones. Each zone comprises one or more CNTs 105 and each zone is connected to an output 83s, 84s, of a current source 83, 84 corresponding thereto. Each CNT 105 is associated with a screening electrode positioned on either side or around the nanotube as described above. One or more laser sources 85, 86 are connected to a control circuit. The operation of this variant is similar to that described for the preceding figures with a greater possibility in the modulation.

FIG. 10 is a sectional view of an example of a solution making it possible to eliminate current leaks that may exist on the surface of the insulator 1001. In this example, the substrate 1000 is covered with an insulating layer 1001 comprising a via 1002 allowing the contact of the nanotube base electrode, a screening electrode 1 1 1 positioned around the nanotube 105 (Figure 2). An encapsulation insulator layer 1004 is deposited to cover the shielding electrode and at least partially the base electrode of the nanotube. This arrangement advantageously makes it possible to reduce or even cancel the leakage currents.

FIG. 11 represents a network of nanotubes 105 connected to the substrate thanks to the presence of traversing contacts 1100, known by the abbreviation TSV (through silicon vias). The presence of these TSV makes it possible to transfer contacts from the rear face January 01 to the front face January 1 02. In addition, being themselves isolated from the substrate, they can control electrically different areas chip surface. Thus, all the CNTs 105 are connected to the substrate 91. Electrically isolated shielding electrodes can be added to different zones of CNTs, thus independently controlling their emission currents.

FIG. 12 schematizes an example of nanotubes 105 individually polarized thanks to the presence of through-contacts TSV 1100 and the presence of a surface control electrode 1200 common to the various CNT nanotubes.

Figure 13 shows an example of integration at a surface level. On the substrate 1300 an insulating layer 1301 is deposited. Then a conductive layer is cut into two disjoint conductive areas, 1303, 1304, but interlaced so as to obtain an interdigitated structure. One of the electrodes serves as a base electrode 1 1 0 CNT 105 (Figure 2), the other electrode acts as a screening electrode 1 1 1. Here the substrate no longer has an electric role, only a role of mechanical support.

FIG. 14 gives an exemplary embodiment of different transmission zones 1401, 1402, 1403, 1404, 1405 with individual control of the emitted current. Each zone has a structure such as that described in Figure 12. The different areas are positioned next to each other according to the specifications of the intended application. It is possible carry out a transfer of contacts on the rear face without changing the operating principle.

FIGS. 15A and 15B show two examples of insulating multilayer structures. FIG. 15A represents a first variant embodiment that makes it possible in particular to avoid the risk of current leakage on the surface of the insulator. Is deposited on an insulating substrate a screening electrode 151 having on one part an opening O, on which is deposited an encapsulation insulator 1 52. The base electrode and the nanotube are arranged vis-à-vis the opening made in the screening electrode. FIG. 15B schematizes a second variant in which is provided on the insulating substrate, a continuous screening electrode, an encapsulation insulator 1 54 on which the base electrode 1 10 and the associated nanotube 1 05 will be positioned.

In these two configurations, the conductor network at the potential of the nanotubes is separated from the control screening electrode by an insulating dielectric layer. The galvanic isolation between the two conductive elements is no longer surface but intrinsic. This device is interesting with regard to arcing phenomena, partially conductive deposits may appear in the vacuum electronic tubes and more particularly the RX tubes. The control screening electrode preferably operates in self-polarization thus ensuring electrostatic shielding of the main field created by the anode which is carried at high voltage.

FIG. 16 schematizes an example of buried buried electrode structure optimized to reduce to the maximum the coupling capacitors between the base electrode 1 connecting the CNTs 105 and the buried screening electrode 1 1 1 represented in FIG. dashed lines, it may take the form of a flat ring and has a certain surface extending outside the surface of the base electrode. This structure makes it possible to envisage operating frequencies greater than frequencies used at a continuous buried screening electrode which exhibits a stronger capacitive coupling with the base electrodes.

FIG. 17 shows an example of an electronic circuit for controlling current of the nanotubes by an optically controlled current source. The screening electrode 1 1 1 is voltage controlled using a phototransistor, illuminated it is passing. The screening electrode 1 1 1, in dotted lines, is polarized at the high voltage HT (potential reference system). If the phototransistor 171 is unlit, it becomes blocking: the screening electrode 1 1 1 finds itself negatively polarized with respect to the high voltage HT thanks to a battery 172 (typical polarization 40V). This makes it possible to control the voltage level of the screening electrode with respect to the potential reference. The base electrode 1 10 is connected to the high voltage HT through a phototransistor 1 75 which acts as an optically controlled switch. Illuminated under strong flux, the phototransistor 175 is fully conducting, thereby providing a direct connection of the base electrode 1 1 0 to the high voltage HT. In the absence of light flux, the phototransistor 175 is blocking and the current emitted by the nanotubes 105 equals the dark current of the phototransistor (typically <1 nA). With intermediate illumination, the current level of the phototransistor can be regulated precisely: the current emitted by the CNTs 105 then equals this current per operating point (see FIG. 2). The level of illumination of the phototransistor makes it possible to control the electronic emission level of the CNTs. A Zener diode 176 placed in parallel with the phototransistor 175 makes it possible to avoid overvoltages on the phototransistor 175 and avoids its destruction during uncontrolled events such as breakdowns in the X-ray tube.

FIG. 18 schematizes an example of a three-connection network allowing the use of individual emitters and requiring electrostatic symmetry around the emission axis of a nanotube to minimize electron optical aberrations. Indeed the generated electric field has the symmetry of the electrodes which forms it (near the CNT). Thus a high symmetry is obtained by making a shielding electrode connection and base electrode connected by three channels 191, 192, 1 93 distributed at 120 °.

The offset of the SCCO out of the tube offers a greater margin of maneuver on the choice of the SCCO (photo element for example), dimensions, electrical characteristics, resistance in tension, etc. The SCCO is no longer subject to the direct environment of the tube, X-rays, bombardment and ion implantation, etc. The configuration of the electrodes notably allows a dynamic reconfiguration of the potential in the vicinity of the nanotubes.

Claims

claims

1 - High energy electron source controlled by an electromagnetic wave comprising a vacuum chamber (1 01), a switchable or modulatable cathode (104) based on field effect transmitters (1 05) comprising at least one electrode 1 (1 1), at least one field effect transmitter (105) connected to a base electrode (1 10) disposed on a substrate (1 12), an anode (106) grounded, a high voltage power supply (103), at least one control circuit (1 09) of a current source controlled by an electromagnetic wave or SCCO (120) connected to said switchable cathode characterized in that:

• The SCCO (120) is disposed outside the vacuum chamber,

• An input terminal (132) of the SCCO is connected to the high-voltage power supply and the switchable cathode (1 1 1) of the switchable cathode

(104)

An output terminal (131) of the SCCO is connected to the base electrode (1 1 0) between the field effect transmitter and the substrate (1 1 2),

• The high voltage power supply (103) provides a potential to create an anode field sufficient to induce emission from the field effect transmitter (105),

• Since the potential of the output terminal (1 31) is greater than or equal to the potential of the input terminal (1 32), the screening electrode (1 1 1) is adapted to reduce the electric field induced by the anode (106) on the transmitter (105),

• The screening electrode (1 1 1) being located in a plane P comprising the conductive surface (105p) located under the foot of the field effect transmitter (105) or located in this same plane, an insulating zone electrically (1 15) exists between the screening electrode and this conductive surface. 2 - electron source according to claim 1 characterized in that the SCCO (120) is disposed in a high voltage connector (121) associated with the vacuum chamber, said connector (1 21) comprising a transparent window to the electromagnetic wave, at least one wave source

Electromagnetic circuit (107) controlled by the control circuit (1 09).

3 - electron source according to claim 2 characterized in that the source of electromagnetic waves is an optical source such as a laser source, a laser diode, a light emitting diode, (107) and the window (108) is transparent to the wavelength of the optical source.

4 - electron source according to claim 1 characterized in that the source of electromagnetic waves is a radiofrequency source comprising a transmission module (1 81) and an emission antenna RF5 (182), and in that the SCCO (1 20) comprises an RF receiving antenna (183) connected to an RF receiving module (184), and a current source controlled by this receiving module.

5 - Electron source according to claim 4, characterized in that the SCCO (120) comprises an RF receiving antenna (183) connected to an RF receiver module (1 84), two Ci, C ₂ cathodes, a microprocessor ( 185) adapted to drive the current generation.

6 - Electron source according to claim 1, characterized in that a switchable or modulatable cathode (104) based on field effect emitters (105) comprises at least two zones (81, 82), each of which zones is connected to an output (83s, 84s) of a current source (83, 84) corresponding thereto and in that one or more laser sources (85, 86) are connected to a control circuit (1 09) .

0 7 - Electron source according to claim 1 characterized in that the transport of the optical wave is done using an insulating optical fiber (140) inserted into a solid material (141). 8 - Electron source according to one of the preceding claims characterized in that the substrate comprises a screening electrode (1 51) having on one part an opening Oi, on which is deposited an encapsulation insulator (152), the base electrode and the emitter being arranged opposite the opening made in the screening electrode.

9 - electron source according to one of the preceding claims characterized in that a base electrode (1 10) having a radius R, the distance between the base electrode (1 1 0) and the electrode of screening (1 1 1) is of the order of radius R.

10 - electron source according to one of the preceding claims characterized in that it comprises a substrate (1000) covered with an insulating layer (1001) comprising a via (1 002) for contacting the electrode base of the field effect transistor, a screening electrode (11) positioned around a field effect transmitter (105), an encapsulation insulator layer (1004) deposited to cover the field screening electrode (1 1 1) and at least partially the base electrode (1 10) of the nanotube. 1 - Electron source according to one of the preceding claims characterized in that it comprises an array of field effect transmitters connected to the substrate through the presence of through-contacts (1 1 00).

12 - Electron source according to one of the preceding claims characterized in that the substrate comprises a screening electrode continuous, an encapsulation insulator (1 54) on which are positioned the base electrode (1 10) and the associated field effect emitter (105).

13 - Electron source according to one of the preceding claims characterized in that a field effect transmitter is a nanotube or a carbon nanofiber (105).

14 - Electron source according to one of the preceding claims characterized in that the electrons strike an anode for the production of X-rays.