Field-effect miter microstructure with reduced gate current

Abstract

The invention relates to a field-effect emitter microstructure, an electron emitter device, an X-ray tube and a method for generating X-rays using an X-ray tube. The field-effects miter microstructure according to the invention for an X-ray tube has - an emitter needle, wherein the emitter needle has a field-effect emission section at a first end, - a gate electrode with a gate opening, wherein the gate opening connects a bottom side of the gate electrode facing the emitter needle with a top side of the gate electrode facing away from the bottom side, wherein the longitudinal center axis of the emitter needle is oriented perpendicular to the gate electrode towards the gate opening in the emission direction, and - a first insulating layer which borders at least partially on the emitter needle below the field-effect emission section and on the underside of the gate electrode, - wherein free electrons can be generated in the field-effect emission section by means of an emission voltage that can be applied between the gate electrode and the field-effect emission section, and is characterized in that - that the first end of the emitter needle has a protrusion greater than or equal to zero relative to the top of the gate electrode, and / or - that the first insulation layer borders the inner wall of the gate opening.

Description

[0001] The invention relates to a field-effect emitter microstructure, an electron emitter device, an X-ray tube and a method for generating X-rays using an X-ray tube.

[0002] Field-effect core microstructures as electron sources in a vacuum are generally known. Particularly when used as electron emitters in evacuated X-ray tubes, field-effect core microstructures are advantageous due to their fast switching capability, the possibility of pixelating the emission surface, and / or the comparatively high electron emission current density, depending on the design. For example, Guerrera et al. disclose silicon field-effect core microstructures with an electron emission density exceeding 100 A / cm² in "Silicon Field Emitter Arrays With Current Densities Exceeding 100 A / cm² at Gate Voltages Below 75 V" (IEEE ELECTRON DEVICE LETTERS, VOL. 37, NO. 1, JANUARY 2016).

[0003] A typical problem in the operation of field-effect microstructures is the current flowing across the gate electrode, generated by some of the electrons passing through the emitter needles. This gate current can be caused, for example, by an electrically conductive contact between a gate electrode and an emitter needle of the field-effect microstructure due to a faulty manufacturing process and / or mechanical damage. Alternatively or additionally, impurities can connect the emitter needles to the gate electrode. Excessive currents through individual emitter needles can lead to damage in the form of a conductive connection to the gate electrode. Such conductive connections can also be caused by high-voltage flashovers onto the field-effect microstructure.Another example concerns the fact that a gate current can arise without a direct, conductive connection between the gate electrode and the emitter needle, namely through scattering of the emitted electrons, whereby some of the scattered electrons flow away via the gate electrode.

[0004] A high-voltage flashover typically has one of the following effects: - The gate electrode can evaporate, preventing the generation of an emission voltage to the underlying emitter needles. In this case, an undamaged portion of the field-effect emitter microstructure can advantageously continue to generate free electrons. - the gate electrode can melt and close the gate openings, so that electrons generated at the underlying emitter needles hit the melted gate electrode, which can ultimately evaporate as a result. - the gate electrode can melt and create an electrically conductive connection to an emitter needle, so that no emission voltage can be built up between the gate electrode and typically all emitter needles due to the electrical short circuit, which is why the entire field-effect miter microstructure typically can no longer generate electrons.

[0005] RF Asadi, T. Zheng, J. Da Silva, G. Rughoobur, AI Akinwande and B. Gnade, in “Failure Mode of Si Field Emission Arrays based on Emission Pattern Analysis”, 2021 34th International Vacuum Nanoelectronics Conference (IVNC), Lyon, France, 2021, pp. 1-2, doi: 10.1109 / IVNC52431.2021.9600740, describe that, in principle, individual defects, especially previously described damage, regularly have negative effects on the entire field-effect medial microstructure, as the emission voltage is usually affected.

[0006] WO 2016 / 134 701 A1 relates to an X-ray source for the ionization of gases with a field emission peak array in a vacuum chamber. This is intended to create a device for the ionization of gases that combines the simple, compact, and cost-effective design and arrangement of beam-shaped high-voltage ionizers with the advantages of low-energy X-ray ionizers. This is achieved by arranging a field emission peak array within a vacuum chamber enclosed by a hood and part of a support plate. The field emission peak array is electrically insulated from the support plate and connected to a high-voltage source as the cathode. A transmission window transparent to X-rays is arranged centrally above the field emission peak array in the hood, and the hood is configured as the anode.

[0007] From US 2023 / 0298847A1, it is known that an electron gun for an electron microscope or similar device comprises a field-emitter cathode with a field-emitter protrusion extending from the output surface of a monocrystalline silicon substrate, and electrodes configured to enhance the emission of electrons from a tip section of the field-emitter protrusion to generate a primary electron beam. A continuous TiN layer is deposited directly onto at least the tip section of the field-emitter protrusion using a process that minimizes oxidation and defects in the TiN layer.

[0008] The invention is based on the objective of providing a field-effect emitter microstructure, an electron emitter device, an X-ray tube and a method for generating X-rays using an X-ray tube with a reduced gate current.

[0009] The problem is solved by the features of the independent claims. Advantageous embodiments are described in the dependent claims.

[0010] The field-effects miter microstructure according to the invention for an X-ray tube has - an emitter needle, wherein the emitter needle has a field-effect emission section at a first end, - a gate electrode with a gate opening, wherein the gate opening connects a bottom side of the gate electrode facing the emitter needle with a top side of the gate electrode facing away from the bottom side, wherein the longitudinal center axis of the emitter needle is oriented perpendicular to the gate electrode towards the gate opening in the emission direction, and - a first insulating layer which borders at least partially on the emitter needle below the field-effect emission section and on the underside of the gate electrode, - wherein free electrons can be generated in the field-effect emission section by means of an emission voltage that can be applied between the gate electrode and the field-effect emission section, and is characterized in that - that the first end of the emitter needle has a protrusion greater than or equal to zero relative to the top of the gate electrode, and / or - that the first insulation layer borders the inner wall of the gate opening.

[0011] The electron emitter device according to the invention has - a field-effect medial microstructure and - a voltage source connected to the field-effect miter microstructure to provide an emission voltage and / or a focusing voltage.

[0012] The X-ray tube according to the invention has - a housing with an evacuable interior, - an electron emitter device in the interior and - an anode in the interior for generating X-rays depending on free electrons that can be generated by means of the electron emitter device.

[0013] The inventive method for generating X-rays using an X-ray tube comprises the following steps: - Applying an emission voltage between the gate electrode and the emitter needle to generate free electrons, - Applying a focusing voltage between the focusing layer and the gate electrode to focus the free electrons, - Generating X-rays using the anode of the X-ray tube by interacting with the focused free electrons.

[0014] An advantage of the invention is that if the overhang is greater than or equal to zero and / or the first insulating layer borders the inner wall of the gate opening, the gate current can be reduced. In particular, the gate current is reduced more significantly the greater the overhang. This advantageously reduces or completely prevents melting of the gate electrode. Advantageously, despite the overhang, free electrons can be generated in the field-effect emission section when the emission voltage is applied. The invention thus advantageously enables a reduction of the gate current flowing across the gate electrode due to the increased distance of the free electrons from the gate electrode, thereby increasing the probability that the free electrons are drawn away or accelerated towards the anode.

[0015] The fact that the first insulating layer abuts the inner wall of the gate opening further advantageously reduces or even completely prevents short circuits between the emitter needle and the gate electrode. Thus, a field-effect semiconductor microstructure designed in this way is more robust against flashovers and / or manufacturing inaccuracies.

[0016] The field-effect miter microstructure is suitable for an X-ray tube in such a way that the electrons generated by the field-effect miter microstructure produce tube currents in a vacuum sufficient for imaging and / or therapeutic applications using the X-rays generated at the anode. Depending on the application, a current density of up to approximately 10 A / cm² is required in the focal spot on the anode. Conventional thermionic emitters have current densities of approximately 3 A / cm², which is why a conventional thermionic emitter cannot be directly imaged onto the focal spot. In contrast, the field-effect miter microstructures according to the invention can have emission surfaces that achieve current densities of, for example, up to 100 A / cm². Direct imaging would therefore be possible, for example, by means of suitable focusing.Imaging procedures can include, in particular, computed tomography, angiography, mammography, conventional radiography, image-guided materials testing, and / or image-guided customs inspection. The therapeutic application of X-rays can include, in particular, radiation therapy.

[0017] The field-effect microstructure essentially concerns an arrangement of microstructure components, in particular the emitter needle, the gate electrode, and the first insulating layer, relative to each other. The field-effect microstructure exhibits structures in the micrometer or nanometer range. The field-effect microstructure is, in particular, a microstructure component. The field-effect microstructure can be a semiconductor component. The field-effect microstructure can, in particular, be manufactured by a semiconductor manufacturer.

[0018] A field-effect thermionic microstructure with only a single emitter needle is typically at least an order of magnitude smaller in its dimensions compared to a conventional thermionic electron emitter. A field-effect thermionic microstructure with multiple emitter needles, especially with a multitude of emitter needles, can have essentially the same dimensions as a conventional thermionic electron emitter.

[0019] The field-effect microstructure has, in particular, connections for tapping the emission voltage and / or the focusing voltage. For example, the gate electrode may have a connection for tapping a first emission potential. Similarly, the emitter needle and / or an electrical feed to the emitter needle may have a connection for tapping a second emission potential. If the field-effect microstructure includes a focusing layer, the first focusing layer typically has a connection for tapping a first focusing potential. Depending on the reference point of the focusing voltage, the emitter needle connection or the gate electrode connection may tap a second focusing potential. By definition, the focusing voltage is applied between the focusing layer and the gate electrode.

[0020] The voltage source of the electron emitter device can preferably generate the emission voltage and / or the focusing voltage and provide it at the terminals of the field-effect emitter microstructure. For this purpose, the voltage source can have leads, in particular leads and / or conductors. The generated voltage is applied by providing the generated voltage at the terminals.

[0021] The housing of the X-ray tube typically comprises metal and / or glass. The housing can typically be temperature-controlled, preferably cooled, and / or electrically insulated during operation by means of a medium that interacts with the outside of the housing. The housing is particularly high-voltage resistant. The interior of the housing can be evacuated. The housing may include a device, for example, a housing opening and / or a valve, for evacuating the interior. The vacuum in the interior is typically a high vacuum. The electron emitter device and the anode are typically arranged opposite each other within the interior.

[0022] A high voltage is typically applied between the anode and the electron emitter device, which usually forms the cathode, to accelerate the free electrons. This high voltage can be up to 200 kV, for example, but is typically between 20 and 150 kV. The high voltage is typically generated by a high-voltage source and / or provided at the anode or cathode. After acceleration, the electrons interact with the anode to generate the X-rays. The anode can be a rotating anode or a stationary anode. Alternatively, the anode and the housing can be rotatably mounted. In this case, the anode and the housing are typically fixed against rotation. Advantageously, a series resistor can be connected upstream of the anode to limit a short-circuit current through the focusing layer.

[0023] The emitter needle is, in particular, a field-effect emitter. The emitter needle is typically a nano- or microstructural component. The emitter needle can alternatively be referred to as a nanotube. For example, the term carbon nanotube is also known for emitter needles made of carbon. The emitter needle is typically electrically conductive and / or a semiconductor. The emitter needle can be made of carbon, silicon, or another material. Preferably, the emitter needle is designed as a silicon emitter needle, as described by Guerrera et al.

[0024] The emitter needle is an elongated and narrow column. It can typically be divided into two functional sections. At the first end is the field-effect emission section, from which electrons can exit the emitter needle via the field effect and be propelled away from the needle as free electrons. At the second end is, for example, a connecting section, which serves to conduct electrons from a power source to the field-effect emission section and typically contributes little or nothing to electron emission. The connecting section can be configured, in particular, to supply an electrical potential corresponding to the emission voltage to the field-effect emission section.The emitter needle can additionally include a current-limiting unit, which is arranged, in particular, upstream of the field-effect emission section, for example, between the field-effect emission section and the connecting section, in order to limit current flow through the emitter needle. In particular, the current-limiting unit can be a transistor or another type of switch. The current-limiting unit can be arranged at the second end of the emitter needle.

[0025] The emitter needle can be, in particular, pin-shaped. The emitter needle can typically be divided into two geometric sections, in particular a section with a constant, especially round or polygonal, cross-section and a tapered section. The connecting section is typically part of the cylindrical section. The field-effect emission section is typically part of the tapered section. Typically, most electrons are emitted at the outermost tip or the region adjacent to the outermost tip of the tapered section of the emitter needle. The angle formed by the tapered section with the longitudinal center axis can, for example, be 30°.

[0026] The emission direction of the emitter needle typically lies along its longitudinal center axis. The emission direction is typically away from the field-effect emission section and towards the focusing layer. The emission direction is particularly indicated by the tapered section of the emitter needle.

[0027] The gate electrode is, in particular, a gate electrode layer. The gate electrode is electrically conductive, especially made of a metal or a doped material, onto which a metallic cover layer may be applied.

[0028] The gate electrode has, in particular, the gate opening, the underside facing the emitter needle, and the upper side facing away from the underside. The gate opening is a cavity that connects, in particular, the underside of the gate electrode with its upper side and / or is bounded by an inner wall of the gate electrode. The gate opening is preferably enclosed by the inner wall of the gate electrode.

[0029] In the following, the term diameter is used with the proviso that the diameter is fundamentally defined in the plane of the respective layer and that, for non-circular units, especially apertures, the maximum diameter is considered. Insofar as units, for example apertures, have varying diameters perpendicular to the respective layer, for example in the emission direction and / or along the longitudinal center axis of the emitter needle, the diameter, unless otherwise specified, refers to a mean diameter calculated from the (maximum) location-dependent, varying diameters. The mean diameter is, in particular, an arithmetic mean.

[0030] The gate opening is preferably rotationally symmetrical. The gate opening preferably comprises a cylindrical volume. The gate opening particularly has a circular cross-section. Typically, the diameter of the gate opening is larger than the diameter perpendicular to the longitudinal center axis of the emitter needle. The gate opening is particularly designed to allow the passage of free electrons.

[0031] The gate electrode is oriented perpendicular to the emitter needle such that the longitudinal center axis of the emitter needle preferably intersects the cross-section of the gate opening at its center. The gate electrode and the emitter needle are arranged in an approximately T-shape. The longer leg is formed, in particular, by the emitter needle, which divides the gate electrode centrally within the gate opening into approximately two shorter legs. The gate electrode and the emitter needles are not electrically connected to each other. The emitter needle, or rather its longitudinal center axis, intersects the gate electrode at its gate opening, preferably without an electrically conductive connection. Preferably, the center axis of the gate opening and the longitudinal center axis of the emitter needle coincide.

[0032] In the present application, "adjacent" means that a unit, in particular a layer, which adjoins another unit, in particular another layer, is in full-surface and physical contact with that other unit. Adjacent units or layers typically have no cavities between them, but, if any, minimal gaps in the nanometer or micrometer range due to manufacturing processes.

[0033] The fact that one unit, in particular a layer, is at least partially adjacent to another unit, in particular another layer, specifically implies that the other unit is at least partially adjacent to the first unit and can mean that the other unit is fully adjacent to the first unit. In other words, whether one unit is only partially adjacent to the other and the other is fully adjacent to the first depends on the dimensions and / or the respective arrangement of the units or layers relative to each other, depending on the perspective. In assessing whether there is a partial or full adjoining relationship, the present application considers in particular the areas around the gate opening or the respective passage opening. The degree of adjoining relationship describes, in particular, a proportion of the coverage and not, in particular, a quality of the connection between them.

[0034] The first insulating layer is particularly suitable for electrically isolating the emitter needle from the gate electrode and vice versa. The first insulating layer typically couples the emitter needle and the gate electrode non-conductively, primarily through mechanical coupling.

[0035] The first insulating layer consists, for example, of silicon dioxide. The first insulating layer is specifically composed of an electrically non-conductive and / or dielectric material. The first insulating layer is, in particular, a body through which the emitter needle can be aligned relative to the gate electrode without establishing an electrical connection between them. The first insulating layer can be referred to as the insulating matrix.

[0036] With regard to the T-shaped arrangement of the gate electrode and the emitter needle, the first insulating layer fills, in particular, the half-spaces below the short legs of the gate electrode up to the emitter needle. Conventionally, the cylindrical section of the emitter needle is typically completely surrounded by the first insulating layer. However, it is conceivable that the tapered section of the emitter needle could at least partially abut the first insulating layer.

[0037] The first insulating layer may extend beyond the gate electrode, or vice versa. The first insulating layer has a top side facing the gate electrode and a bottom side facing away from it. The fact that the first insulating layer is at least partially adjacent to the bottom of the gate electrode means, in particular, that the top side of the first insulating layer does not, to a certain extent, abut the bottom of the gate electrode. The bottom of the gate electrode may be completely adjacent to the top side of the first insulating layer. It is conceivable that a closed area adjoining the gate opening on the underside of the gate electrode is not covered by the first insulating layer and therefore does not abut it. In other words, a border around the gate opening may remain uncovered on the underside.Alternatively, depending on the design, it is conceivable that the first insulating layer adjoins the underside of the gate electrode up to the gate opening.

[0038] The emitter needle is embedded in the first insulating layer, at least below the field-effect emission section. Embedded means that it is fully adjacent to each other.

[0039] The emission voltage can be, in particular, between greater than zero and less than or equal to 1000 V, especially between 1 V and 100 V, preferably 50 V. The electrical potential of the field-effect emission section is typically more negative than the electrical potential of the gate electrode during electron emission. It is conceivable that the electrical potential of the gate electrode is 0 V or negative. By applying the emission voltage, electrons are regularly emitted from the emitter needle in the field-effect emission section.

[0040] The protrusion at the first end refers specifically to the highest position of the emitter needle in the emission direction. Typically, the outermost end of the emitter needle has the highest position relative to the emission direction, specifically the end of the tapered section. This protrusion is, for example, between 0.001 µm and 1 µm, and more specifically between 0.01 µm and 0.4 µm.

[0041] With a protrusion of zero relative to the top surface, the first end of the emitter needle is flush with the top surface of the gate electrode. In this case, the first end of the emitter needle extends into the gate opening but not beyond it. With a protrusion of zero, there is no protrusion at all. With a protrusion of zero, the top surface of the gate electrode has no protrusion relative to the first end of the emitter needle. With a protrusion of zero, the top surface of the gate electrode and the first end of the emitter needle are at the same height.

[0042] With a greater than zero protrusion relative to the top surface, the first end of the emitter needle is positioned above the top surface of the gate electrode. In this case, the first end of the emitter needle extends into and beyond the gate opening. Fabrication of the field-effect miter microstructure is particularly challenging with this variant due to the positive protrusion.

[0043] The inventors recognized that, despite the protrusion, free electrons can be generated in the field-effect emission section when the emission voltage is applied. This variant advantageously allows for a reduction in the gate current flowing across the gate electrode due to the increased distance of the free electrons from the gate electrode, thereby increasing the probability that the free electrons are drawn away or accelerated towards the anode.

[0044] One embodiment of the invention provides that the first insulating layer adjoins an inner wall of the gate opening. The first insulating layer extends, in particular, into the gate opening. It is advantageous if the first insulating layer adjoins the inner wall of the gate opening in an annular form and has a passage opening for the free electrons and / or the emitter needle. Typically, the first insulating layer extends continuously from the underside of the gate electrode to the inner wall of the gate opening. It is conceivable that the first insulating layer covers only a portion of the thickness, i.e., the extent of the gate opening in the emission direction, particularly starting from the underside of the gate electrode. Alternatively, the first insulating layer can cover the inner wall of the gate opening along its entire thickness and / or only starting from the top side of the gate electrode and / or only in the center.

[0045] One embodiment provides that the first insulating layer abuts the sides of the field-effect emission section. The first insulating layer abuts the field-effect emission section, particularly in the circumferential direction. This embodiment is especially advantageous because it allows the gate current to be further reduced. It is conceivable that the field-effect emission section abuts the first insulating layer only partially or completely. In particular, the field-effect emission section can be completely embedded in the first insulating layer. In this case, it is advantageous that a portion of the field-effect emission section can be burned off by applying a voltage. The voltage can, in principle, be equal to or different in magnitude from the emission voltage. It is conceivable that, for the purpose of burning off the interference, the voltage, for example the emission voltage, is applied for a longer period than would occur without the burning-off process.Burn-off, in particular, means increasing the electrical charge in the region of the first insulating layer adjacent to the field-effect emission section, such that thermal effects resulting from the electrical charge cause the material of the first insulating layer to be eroded. This further development of this embodiment is particularly advantageous for maximizing the electrical insulation of the emitter needle to reduce the gate current. Specifically, the method according to the invention can include the following process step: applying a voltage between the gate electrode and the emitter needle before the emission voltage to burn off at least a portion of the field-effect emission section.

[0046] One embodiment provides that the first insulating layer has a recess with a sectionally constant cross-section in which the emitter needle is arranged. The cross-section can, in particular, be round or polygonal. The recess can, in particular, be sectionally cylindrical. In particular, the recess can be geometrically shaped according to the emitter needle.

[0047] One embodiment provides that the first insulating layer, at the level of the field-effect emission section, has a recess with a section having a larger diameter than a section below the field-effect emission section. In this case, the first insulating layer is designed to widen, particularly in the emission direction. This embodiment can be advantageous in order to reduce the number of free electrons that charge the first insulating layer.

[0048] One embodiment provides that the emitter needle has a tapered section, wherein the field-effect emission section is part of the tapered section, the pointed end of the tapered section being located above the top surface of the gate electrode and the broad end of the tapered section, opposite the pointed end, being located below the bottom surface of the gate electrode. In other words, the gate opening and the field-effect emission section are oriented centrally with respect to the emission direction.

[0049] One embodiment provides that the field-effect miter microstructure further comprises: - a second insulating layer with a bottom side facing the emitter needle and a top side facing away from the bottom side, - an electrically conductive focusing layer with a bottom surface facing the emitter needle and a top surface facing away from the bottom surface, - wherein the underside of the second insulating layer at least partially abuts the top side of the gate electrode, - wherein the upper side of the second insulating layer at least partially borders the lower side of the focusing layer, - wherein the second insulating layer and the focusing layer each have a pass-through opening for the free electrons that can be generated in the field-effect emission section.

[0050] An advantage of this embodiment is that the free electrons can be focused by means of the focusing layer. In this case, the conventional deflection unit for electrostatic or electromagnetic focusing of the electrons can preferably be omitted.

[0051] The focusing layer is particularly advantageous due to its spatial proximity to the field-effect emission section compared to a conventional deflection unit, and is therefore especially suitable for focusing. Near the field-effect emission section, electrons can be focused using a small electric field component in the focusing direction compared to a conventional focusing voltage, particularly since they still have a low velocity. Preferably, sufficient focusing can be achieved with moderate focusing voltages, while the main component of the field accelerates the electrons.

[0052] Another advantage is that focusing deflects some of the free electrons that would normally be directed towards the gate electrode, thereby reducing the gate current. This is particularly beneficial for designs where the free electron current is maximized up to 100 A / cm². This advantage is especially true for field-effect microstructures with silicon emitter needles compared to field-effect microstructures with carbon emitter needles, the latter typically having an external grid electrode located at a greater distance from the emitter needles.

[0053] A further advantage of this embodiment is that the focusing layer, rather than the gate electrode, is exposed to the anode compared to a conventional field-effect microstructure. Consequently, in the event of a voltage flashover from the anode to the field-effect microstructure, the focusing layer is primarily damaged. At the very least, the probability that the voltage flashover will affect the focusing layer and not the gate electrode or the emitter needle is significantly increased. Ideally, such a voltage flashover will therefore have no effect on the gate electrode, or only a comparatively strong flashover will affect it. If the focusing layer is damaged, typically only the focusing of the electrons is impaired or prevented.In contrast to damage to the gate electrode of a conventional field-effect miter microstructure, which can lead to the failure of the entire field-effect miter microstructure, for example, a molten focusing layer would still have to bridge the insulating gap along the second insulating layer before the flashover could have an indirect, negative impact on the gate electrode and / or the emitter needle.

[0054] A further advantage of the invention is that the focusing layer can be made virtually arbitrarily thick in order to exhibit high thermal resistance, as may be necessary in the case of voltage flashovers. Advantageously, the currents occurring during a voltage flashover can be dissipated without damaging the field-effect median microstructure.

[0055] The second insulating layer has a bottom surface facing the emitter needle and a top surface facing away from the bottom surface, as well as a through-hole connecting the top and bottom surfaces of the second insulating layer. The second insulating layer preferably covers at least part of the gate electrode. It is conceivable that a closed area adjoining the gate opening on the top surface of the gate electrode is not covered by the second insulating layer and thus does not abut it. In other words, a border around the gate opening on the top surface can remain uncovered. Alternatively, depending on the embodiment, it is conceivable that the second insulating layer abuts the top surface of the gate electrode in such a way that the through-hole of the second insulating layer and the gate opening have the same diameter and their centers coincide.

[0056] The pass-through opening of the second insulating layer is bounded by an inner wall of the second insulating layer. The pass-through opening of the second insulating layer is preferably enclosed by the inner wall of the second insulating layer. The pass-through opening of the second insulating layer is specifically designed to allow the passage of free electrons.

[0057] The second insulating layer can, in particular, consist of silicon dioxide. The second insulating layer can, in particular, consist of an electrically non-conductive and / or a dielectric material. The first insulating layer and the second insulating layer can consist of the same material. Typically, the first insulating layer is more voluminous than the second insulating layer. The second insulating layer typically has a thickness that is less than the thickness of the first insulating layer. The second insulating layer, in particular, has a dielectric strength of at least 100 V / µm, preferably at least 400 V / µm.

[0058] The focusing layer is, in particular, a focusing electrode. The focusing layer has a bottom surface facing the emitter needle and a top surface facing away from the bottom surface, as well as a transmission aperture connecting the top and bottom surfaces of the focusing layer. Advantageously, the focusing layer completely covers the top surface of the second insulating layer. The transmission aperture of the focusing layer is bounded by an inner wall of the focusing layer. The transmission aperture of the focusing layer is preferably enclosed by the inner wall of the focusing layer. The transmission aperture of the focusing layer is specifically designed to allow the passage of free electrons. A focusing voltage can be applied to the focusing layer to focus the free electrons generated in the field-effect emission section.

[0059] In the present application, focusing means, in particular, influencing the trajectories of the free electrons such that the spatial distribution of the emitted electrons perpendicular to the emission direction is changed, in particular increased and / or decreased. The change can include an increase in the spatial distribution, also called defocusing, and a decrease in the spatial distribution, also called focusing. In other words, the focusing layer is configured for focusing and defocusing the free electrons.

[0060] The focusing voltage can be between -5000 V and +5000 V, particularly between -1000 V and +1000 V, preferably 200 V or 50 V. The electrical potential of the gate electrode is preferably more negative than the electrical potential of the focusing layer during electron emission. The inventors have recognized that, advantageously, a reduction in the spatial distribution of the electrons, i.e., focusing, can be achieved in certain voltage ranges regardless of the sign of the focusing voltage.

[0061] The diameter of the gate opening and / or the diameter of the through-hole of the second insulating layer and / or the diameter of the through-hole of the focusing layer is particularly less than 100 µm, preferably less than 25 µm. In particular, the diameter of the gate opening can be less than 10 µm.

[0062] The focusing layer is made of an electrically conductive material. The electrical conductivity can be achieved by doping the material of the focusing layer and / or be inherent to the material. For example, the electrically conductive material can be a metal. According to an advantageous embodiment, the focusing layer is made of tungsten to be more thermally resistant.

[0063] In the present application, the thickness of a layer refers in particular to the extent in the emission direction and / or along the longitudinal center axis of the emitter needle.

[0064] The thickness of the first insulating layer is, in particular, greater than the thickness of the gate electrode and / or the second insulating layer and / or the focusing layer. The thickness of the first insulating layer and / or the gate electrode and / or the second insulating layer and / or the focusing layer is typically constant.

[0065] The thickness of the first insulating layer is typically determined by the length of the emitter needle, which is regularly mechanically stabilized by the first insulating layer. The first insulating layer is typically thick enough to isolate the voltage between the field-effect emission section and the gate electrode. Such a thickness is particularly important when the first insulating layer borders the inner wall of the gate opening.

[0066] The thickness of the gate electrode is particularly between 0.01 µm and 25 µm, preferably between 0.1 µm and 2.5 µm, and / or is, for example, 0.24 µm. In particular, the thickness of the doped material can be 0.2 µm and the thickness of the cover layer 0.04 µm.

[0067] The thickness of the second insulating layer is particularly between 0.01 µm and 10 µm, preferably between 0.1 µm and 1 µm. The thickness of the second insulating layer is particularly limited at the lower end by the dielectric strength of the second insulating layer, which depends in particular on the material and its thickness, and / or on the maximum focusing voltage. The second insulating layer should preferably be at least thick enough to isolate the potential difference between the gate electrode and the focusing layer.

[0068] The thickness of the focusing layer is preferably between 0.1 µm and 100 µm, and preferably between 1 µm and 15 µm. The focusing layer is advantageously as thick as possible to withstand thermal flashovers while still allowing free electrons to pass through. The thickness of the second insulating layer is preferably greater than the thickness of the gate electrode. The thickness of the focusing layer is preferably less than the thickness of the gate electrode.

[0069] The emitter needle's extension transverse to the longitudinal center axis is, for example, between 0.02 µm and 20 µm, particularly between 0.05 µm and 1 µm, advantageously 0.2 µm. The first end of the emitter needle can, for example, extend into the gate opening to the midpoint of the gate electrode's thickness.

[0070] The diameter of the gate opening can be, for example, between 0.05 µm and 2 µm, in particular between 0.1 µm and 1 µm, advantageously 0.34 µm.

[0071] The gate opening and / or the through-hole of the second insulating layer and / or the through-hole of the focusing layer are, in particular, rotationally symmetrical. Alternatively, the cross-section of the gate opening and / or the through-hole of the second insulating layer and / or the through-hole of the focusing layer can be polygonal, in particular quadrilateral, preferably square.

[0072] The center axis of the gate opening and / or the aperture of the second insulating layer and / or the aperture of the focusing layer can, in particular, coincide with the longitudinal center axis of the emitter needle. In this case, the longitudinal center axis can, in particular, intersect the gate opening and / or the aperture of the second insulating layer and / or the aperture of the focusing layer at its center. Alternatively, it is conceivable that the longitudinal center axis is at a greater than zero distance and / or forms an angle greater than zero with the center axis of the gate opening and / or the aperture of the second insulating layer and / or the aperture of the focusing layer.

[0073] One embodiment provides that the diameter of the gate opening is smaller than the diameter of the focusing layer's aperture. This embodiment is particularly advantageous because it reduces the number of free electrons that strike the focusing layer and are then conducted away from it. This preferably reduces the gate current. In other words, it advantageously increases the proportion of free electrons that can strike the anode.

[0074] One embodiment provides that the diameter of the gate opening is smaller than the diameter of the through-hole of the second insulating layer. This embodiment is particularly advantageous because it reduces the charging of the second insulating layer by electrons striking it. This results in a smaller or even no electric field in the second insulating layer that could disrupt the trajectories of the free electrons.

[0075] One embodiment provides that the pass-through opening of the second insulating layer is designed to widen in the emission direction of the emitter needle. In this case, the diameter of the pass-through opening of the second insulating layer increases with increasing distance from the gate electrode. This embodiment is particularly advantageous because the spatial distribution of free electrons perpendicular to the emission direction increases in the immediate vicinity of the field-effect emission section. The widening pass-through opening can advantageously compensate for this effect and, at the same time, advantageously provide optimal coverage of the gate electrode and reduce the input of electrons into the second insulating layer.

[0076] A further development of the previous embodiment provides that the opening of the second insulating layer is formed with a frustoconical inner wall and that the inner wall of the opening of the second insulating layer forms an angle greater than 0° and less than 60° with the longitudinal center axis. This embodiment is particularly advantageous because the frustoconical inner wall is easy to manufacture and still offers the aforementioned advantages. In this embodiment, the opening of the focusing layer and the gate opening are typically cylindrical. The center axes of the openings of the focusing layer, the second insulating layer, and the gate opening coincide, in particular, with the longitudinal center axis of the emitter needle.The frustoconical inner wall of the second insulating layer is typically bounded in the emission direction by the underside of the focusing layer and / or against the emission direction, in particular by the top of the gate electrode.

[0077] One embodiment provides that the smallest diameter of the pass-through opening of the second insulating layer is larger than the largest diameter of the gate opening. This embodiment is particularly advantageous because the second insulating layer cannot interact with electrons propagating parallel to the emission direction. This embodiment is especially advantageous in combination with one of the two previous embodiments in which the pass-through opening of the second insulating layer is designed to widen in the emission direction.

[0078] One embodiment provides that the transition from the top surface of the gate electrode to an inner wall of the gate opening is arc-shaped. An advantage of this embodiment is the resulting reduction in electric field strength at this transition. The transition is, in particular, the ring-shaped edge from the top surface to the inner wall. In other words, in cross-section parallel to the emission direction, a corner between the inner wall of the gate opening and the top surface of the gate electrode is arc-shaped. Arc-shaped means that the gate electrode is processed in such a way that the radius of the transition is intentionally increased. In other words, the sharpness of the transition is reduced, for example, by rounding. Arc-shaped design means, in particular, that it is manufactured and / or post-processed in an arc-shaped manner.

[0079] One embodiment of the invention provides that the first insulating layer and the second insulating layer abut each other through the gate opening. In particular, the first insulating layer can abut the second insulating layer and / or the second insulating layer can abut the first insulating layer. The first insulating layer and the second insulating layer are preferably connected to each other without gaps, especially through the gate opening. The first insulating layer and the second insulating layer are connected to each other, in particular, by a closed intermediate piece, which has a central through-hole for the emitter needle and / or the free electrons. The intermediate piece can, in particular, be annular in shape. "Without gaps" means that at every level of the gate opening in the circumferential direction, material of the first insulating layer or the second insulating layer is present between the gate opening and the gate electrode.The intermediate layer, depending on the perspective, the first insulating layer and / or the second insulating layer, preferably abuts the inner wall of the gate opening. In this case, the first insulating layer advantageously consists of the same material as the second insulating layer. This embodiment advantageously improves the insulating properties of both the first and second insulating layers. Furthermore, this embodiment advantageously reduces the gate current flowing across the gate electrode.

[0080] One embodiment provides that the field-effect emitter microstructure has at least one further emitter needle and at least one further gate opening, wherein the longitudinal center axis of the at least one further emitter needle is aligned with the at least one further gate opening parallel to the emission direction of the emitter needle. Such a field-effect emitter microstructure particularly forms an array of field-effect emitters. The number of emitter needles of the field-effect emitter microstructure can be greater than two, particularly greater than 100, preferably greater than 10,000 or 100,000, for example approximately 1,000,000. The emitter needle and the at least one further emitter needle preferably form an emission surface for generating a current density of at least 1 A / cm², advantageously at least 3 A / cm², and particularly advantageously at least 10 A / cm².

[0081] Typically, each emitter needle is associated with a gate opening. The arrangement of the emitter needles relative to their respective gate openings is typically the same. Multiple emitter needles can be arranged in a plane perpendicular to the emission direction. For example, the emitter needles can form a matrix with at least 2 x 2 in each spatial direction. Typically, groups of emitter needles can be switched on and off together. It is conceivable that each emitter needle can be switched on and off independently of the other emitter needles. If specific regions of the field-effect miter microstructure can be switched on and off, the field-effect miter microstructure is, in particular, a segmented or pixelated emitter. The gate electrode can have the gate opening and at least one other gate opening. In this case, the gate electrode is continuous, i.e., not segmented.Alternatively, the gate electrode can have the gate opening, and at least one other gate electrode can have at least one further gate opening. In this case, an emission voltage and / or different emission voltages can advantageously be applied to the two gate electrodes independently of each other. It is conceivable to subdivide the first insulating layer and / or second insulating layer and / or the focusing layer analogously to the gate electrode. It is advantageous for fabrication if, in particular, the first insulating layer and / or the second insulating layer are formed as a continuous unit. For applying different focusing voltages, it can be advantageous to form the focusing layer in segments, i.e., not as a continuous unit.Depending on the embodiment of the field-effect miter microstructure, the gate electrode and / or the first insulating layer and / or the second insulating layer and / or the focusing layer can be designed as a continuous or segmented structure.

[0082] The computer program product can be a computer program or comprise a computer program. The computer program product particularly includes the program code means that implement the process steps according to the invention. This allows the process according to the invention to be defined and executed repeatably, and enables control over the transfer of the process according to the invention. The computer program product is preferably configured such that the computing unit can execute the process steps according to the invention by means of the computer program product. The program code means can, in particular, be loaded into a memory of the computing unit and typically executed by means of a processor of the computing unit with access to the memory.When the computer program product, in particular the program code, is executed in the processing unit, all embodiments of the described method according to the invention can typically be carried out. The computer program product is, for example, stored on a physical, computer-readable medium and / or digitally stored as a data packet in a computer network. The computer program product can represent the physical, computer-readable medium and / or the data packet in the computer network. Thus, the invention can also start from the physical, computer-readable medium and / or the data packet in the computer network. The physical, computer-readable medium is usually directly connectable to the processing unit, for example, by inserting the physical, computer-readable medium into a DVD drive or plugging it into a USB port, thereby allowing the processing unit to access the physical, computer-readable medium, particularly for reading.The data packet can preferably be retrieved from the computer network. The computer network can contain the computing unit itself or be indirectly connected to the computing unit via a wide-area network (WAN) or a (wireless) local area network (WLAN or LAN) connection. For example, the computer program product can be stored digitally on a cloud server at a storage location within the computer network and transferred to the computing unit via the WAN over the internet and / or via WLAN or LAN, particularly by accessing a download link that points to the storage location of the computer program product.

[0083] Features, advantages, or alternative embodiments mentioned in the description of the device are also transferable to the method, and vice versa. In other words, claims relating to the method can be further developed with features of the device, and vice versa. In particular, the device according to the invention can be used in the method.

[0084] Regardless of the grammatical gender of a particular term, persons with male, female or other gender identities are included.

[0085] The invention will now be described and explained in more detail with reference to the embodiments illustrated in the figures. In principle, structures and units that remain essentially the same in the following figure descriptions will be named with the same reference numeral as when the respective structure or unit first appeared.

[0086] They show: Fig. 1 a first variant of the field-effect miter microstructure according to the invention, Fig. 2 a second variant of the field-effects miter microstructure according to the invention, Fig. 3 a third variant of the field-effect miter microstructure according to the invention, Fig. 4 a first embodiment of the field-effect miter microstructure, Fig. 5 a second embodiment of the field-effect medial microstructure, Fig. 6 a third embodiment of the field-effect medial microstructure, Fig. 7 an electron emitter device according to the invention, Fig. 8 an X-ray tube according to the invention, Fig. 9 a method according to the invention for generating X-rays using an X-ray tube and Fig. 10 a first embodiment of the method. Detailed description of the exemplary implementations

[0087] Fig. Figure 1 shows a first variant of the field-effect miter microstructure 10 according to the invention in a longitudinal section in the emission direction R.

[0088] The field-effect miter microstructure 10 has an emitter needle 11. The emitter needle 11 has a field-effect emission section 12 at one end.

[0089] The field-effect emitter microstructure 10 further comprises a gate electrode 13 with a gate opening 14. The gate opening 14 connects a lower side of the gate electrode 13 facing the emitter needle 11 with a higher side of the gate electrode 13 facing away from the lower side. The longitudinal center axis A of the emitter needle 11 is oriented perpendicular to the gate electrode 13 and directed towards the gate opening 14 in the emission direction R.

[0090] The field-effect emitter microstructure 10 further comprises a first insulating layer 15. The first insulating layer 15 borders the emitter needle 11 at least below the field-effect emission section 12 and at least partially the underside of the gate electrode 13. Free electrons can be generated in the field-effect emission section 12 by means of an emission voltage that can be applied between the gate electrode 13 and the field-effect emission section 12.

[0091] The first end of the emitter needle 11 has a protrusion D greater than zero relative to the top surface of the gate electrode 13. The protrusion D is between 0.001 µm and 1 µm, particularly between 0.01 µm and 0.4 µm.

[0092] The emitter needle 11 has a tapered section. The field-effect emission section 12 is part of this tapered section. The pointed end of the tapered section is located above the top surface of the gate electrode 13. The broad end of the tapered section, opposite the pointed end, is located below the bottom surface of the gate electrode 13.

[0093] In Fig. 1 is a diameter of the emitter needle 11 smaller than a diameter of the gate opening 14. The gate opening 14 is arranged centered around the longitudinal center axis A and has a constant diameter.

[0094] The first insulating layer 15 does not abut the inner wall of the gate opening 14 or the sides of the field-effect emission section 12. The first insulating layer 15 has a recess with a sectionally constant cross-section in which the emitter needle 11 is arranged. At the level of the field-effect emission section 12, the first insulating layer 15 has a recess with a section having a larger diameter than a section below the field-effect emission section 12.

[0095] Fig. Figure 2 shows a second variant of the field-effect miter microstructure 10 according to the invention in a longitudinal section in the emission direction R.

[0096] The first end of the emitter needle 11 has a protrusion D of zero relative to the top surface of the gate electrode 13. Therefore, the first end of the emitter needle 11 is flush with the top surface of the gate electrode 13.

[0097] In Fig. For illustrative reasons, in figure 2 the emitter needle 11 is shown shortened by the part which is in Fig. 1 protrudes beyond the top surface of the gate electrode 13. Alternatively, instead of removing the protruding part, the emitter needle 11 can be positioned deeper and flush with the top surface of the gate electrode 13.

[0098] Fig. Figure 3 shows a third variant of the field-effect miter microstructure 10 according to the invention in a longitudinal section in the emission direction R.

[0099] The first insulation layer 15 abuts an inner wall of the gate opening 14. The first insulation layer 15 also abuts the sides of the field-effect emission section 12. Thus, the entire gate opening 14 is filled with the first insulation layer 15. The field-effect emission section 12 is completely embedded in the first insulation layer 15.

[0100] The first end of the emitter needle 11 has a protrusion D of zero relative to the top surface of the gate electrode 13. Therefore, the first end of the emitter needle 11 is flush with the top surface of the gate electrode 13.

[0101] Fig. Figure 4 shows a first embodiment of the field-effect miter microstructure 10 in a longitudinal section along the emission direction R.

[0102] The first end of the emitter needle 11 has no protrusion D greater than or equal to zero relative to the top of the gate electrode 13. The top of the gate electrode 13 has a protrusion greater than zero relative to the first end of the emitter needle 11. Not in Fig. Figure 4 shows that the first insulation layer 15 adjoins an inner wall of the gate opening 14.

[0103] The field-effect emitter microstructure 10 further comprises a second insulating layer 16. The second insulating layer 16 has a bottom side facing the emitter needle 11 and a top side facing away from the bottom side.

[0104] The field-effect emitter microstructure 10 further comprises an electrically conductive focusing layer 17. The electrically conductive focusing layer 17 has a bottom surface facing the emitter needle 11 and a top surface facing away from the bottom surface.

[0105] The underside of the second insulating layer 16 borders at least partially on the top side of the gate electrode 13. The top side of the second insulating layer 16 borders at least partially on the underside of the focusing layer 17. The second insulating layer 16 and the focusing layer 17 each have a transmission aperture 18, 19 for the free electrons generated in the field-effect emission section 12.

[0106] In Fig. The diameter of the emitter needle 11 is smaller than the diameter of the gate opening 14 and the diameter of the passage openings 18 and 19. The gate opening 14 and the passage openings 18 and 19 are centered around the longitudinal center axis A. The diameter of the gate opening 14 is smaller than the diameter of the passage opening 19 of the focusing layer 17. The diameter of the gate opening 14 is smaller than the diameter of the passage opening 18 of the second insulating layer 16. The smallest diameter of the passage opening 18 of the second insulating layer 16 is larger than the largest diameter of the gate opening 14.

[0107] The passage opening 18 of the second insulating layer 16 widens in the emission direction R of the emitter needle 11. The passage opening 18 of the second insulating layer 16 has a frustoconical inner wall. The inner wall of the passage opening 18 of the second insulating layer 16 forms an angle α greater than 0° and less than 60° with the longitudinal center axis A. The transition from the top surface of the gate electrode 13 to the inner wall of the gate opening 14 is arc-shaped.

[0108] Advantageously, the second insulating layer 16 has a dielectric strength of at least 100 V / µm, preferably at least 400 V / µm. The focusing layer 18 can be made of tungsten.

[0109] Fig. Figure 5 shows a second embodiment of the field-effect miter microstructure 10 in a longitudinal section along the emission direction R.

[0110] The first insulating layer 15 and the second insulating layer 16 abut each other through the gate opening 14. As in Fig. As shown in Figure 5, the entire gate opening 14 can be completely filled with the first insulating layer 15 and / or the second insulating layer 16, as well as with the emitter needle 11. Alternatively, it is conceivable that the gate opening 14 is not completely filled with the first insulating layer 15 and / or the second insulating layer 16.

[0111] In Fig. 5 The first end of the emitter needle 11 has a protrusion D greater than zero relative to the top surface of the gate electrode 13. In particular, the field-effect emission section 12 has a protrusion greater than zero relative to the top surface of the gate electrode 13. In other words, the emitter needle 11 protrudes from and / or through the gate opening 14.

[0112] Fig. Figure 6 shows a third embodiment of the field-effect miter microstructure 10 in a longitudinal section along the emission direction R. The representation of the Fig. Figure 6 is not to scale.

[0113] The field-effect emitter microstructure 10 has at least one further emitter needle 11.1, ... 11.N and at least one further gate opening 14.1, ... 14.N. The longitudinal center axis A.1, ... AN of the at least one further emitter needle 11.1, ... 11.N is aligned with the at least one further gate opening 14.1, ... 14.N parallel to the emission direction R of the emitter needle 11.

[0114] Fig. Figure 7 shows an electron emitter device 20 according to the invention in a block diagram.

[0115] The electron emitter device 20 comprises a field-effect transmitter microstructure 10 and a voltage source 21. The voltage source 21 is connected to the field-effect transmitter microstructure 10 to provide an emission voltage and / or a focusing voltage.

[0116] Fig. Figure 8 shows an X-ray tube 30 according to the invention in a block diagram.

[0117] The X-ray tube 30 has a housing 31. The housing 31 has an evacuable interior 32.

[0118] The X-ray tube 30 also includes an electron emitter device 20. The electron emitter device 20 is arranged in the interior space 32.

[0119] The X-ray tube 30 also has an anode 33. The anode 33 is arranged in the interior 32 and is designed to generate X-rays depending on free electrons that can be generated by means of the electron emitter device 20.

[0120] Fig. Figure 9 shows a method according to the invention for generating X-rays using an X-ray tube in a flowchart.

[0121] Process step S100 characterizes the application of an emission voltage between the gate electrode 13 and the emitter needle 11 to generate free electrons.

[0122] Process step S101 characterizes the application of a focusing voltage between the focusing layer 17 and the gate electrode 13 to focus the free electrons.

[0123] Process step S102 characterizes the generation of X-rays by means of the anode 33 of the X-ray tube 30 by interaction with the focused free electrons.

[0124] Fig.Figure 10 shows a first embodiment of the method for generating X-rays using an X-ray tube in a flowchart with the additional process step S103, wherein a voltage is applied between the gate electrode and the emitter needle before the emission voltage for burning off at least part of the field-effect emission section.

[0125] Although the invention has been illustrated and described in detail by the preferred embodiments, the invention is nevertheless not limited by the disclosed examples and other variations can be derived by the person skilled in the art without leaving the scope of protection of the invention.

Claims

[1] Field-effect miter microstructure (10) for an X-ray tube (30), comprising - an emitter needle (11) wherein the emitter needle (11) has a field-effect emission section (12) at a first end, - a gate electrode (13) with a gate opening (14), wherein the gate opening (14) connects a bottom side of the gate electrode (13) facing the emitter needle (11) with a top side of the gate electrode (13) facing away from the bottom side, wherein the longitudinal center axis (A) of the emitter needle (11) is oriented perpendicular to the gate electrode (13) towards the gate opening (14) in the emission direction (R), - a first insulating layer (15) which borders at least partially on the emitter needle (11) below the field-effect emission section (12) and on the underside of the gate electrode (13), - wherein free electrons can be generated in the field effect emission section (12) by means of an emission voltage that can be applied between the gate electrode (13) and the field effect emission section (12), characterized by , - that the first end of the emitter needle (11) has a protrusion (D) greater than or equal to zero relative to the top of the gate electrode (13), and / or - that the first insulating layer (15) borders an inner wall of the gate opening (14). [2] Field effect miter microstructure (10) according to claim 1, wherein the first insulation layer (15) adjoins the sides of the field effect emission section (12). [3] Field-effect emitter microstructure (10) according to one of the preceding claims, wherein the first insulating layer (15) has a recess with a sectionally constant cross-section in which the emitter needle (11) is arranged. [4] Field effect miter microstructure (10) according to one of the preceding claims, wherein the first insulation layer (15) at the level of the field effect emission section (12) has a recess with a section having a larger diameter than a section below the field effect emission section (12). [5] Field-effect miter microstructure (10) according to one of the preceding claims, wherein the field-effect emission section (12) is completely embedded in the first insulation layer (15). [6] Field-effect miter microstructure (10) according to one of the preceding claims, wherein the supernatant (D) is between 0.001 µm and 1 µm. [7] Field-effect emitter microstructure (10) according to one of the preceding claims, wherein the emitter needle (11) has a tapered section, wherein the field-effect emission section (12) is part of the tapered section, wherein the pointed end of the tapered section is located above the top of the gate electrode (13) and wherein the wide end of the tapered section, which is opposite the pointed end, is located below the bottom of the gate electrode (13). [8] Field-effect miter microstructure (10) according to any of the preceding claims, wherein the field-effect miter microstructure (10) further comprises: - a second insulating layer (16) with a bottom side facing the emitter needle (11) and a top side facing away from the bottom side, - an electrically conductive focusing layer (17) with a bottom surface facing the emitter needle and a top surface facing away from the bottom surface, - wherein the underside of the second insulating layer (16) at least partially abuts the top side of the gate electrode (13), - wherein the upper side of the second insulating layer (16) is at least partially adjacent to the lower side of the focusing layer (17), - wherein the second insulating layer (16) and the focusing layer (17) each have a pass-through aperture (18, 19) for the free electrons that can be generated in the field-effect emission section (12). [9] Field-effect miter microstructure (10) according to claim 8, wherein the first insulating layer (15) and the second insulating layer (16) are adjacent to each other through the gate opening (14). [10] Field-effect emitter microstructure (10) according to one of claims 8 or 9, wherein the passage opening (18) of the second insulating layer (16) is designed to widen in the emission direction (R) of the emitter needle (11). [11] Field-effect emitter microstructure (10) according to one of the preceding claims, wherein the field-effect emitter microstructure has at least one further emitter needle and at least one further gate opening, wherein the longitudinal center axis of the at least one further emitter needle is aligned with the at least one further gate opening parallel to the emission direction of the emitter needle. [12] Electron emitter device (20), comprising - a field-effect medial microstructure (10) according to one of the preceding claims and - a voltage source (21) connected to the field-effect miter microstructure (10) to provide an emission voltage and / or a focusing voltage. [13] X-ray tube (30), comprising - a housing (31) with an evacuable interior (32), - an electron emitter device (20) according to claim 12 in the interior space (32), - an anode (33) in the interior (32) for generating X-rays depending on free electrons that can be generated by means of the electron emitter device (20). [14] Method for generating X-rays using an X-ray tube (30) according to claim 13, comprising the steps: - Applying an emission voltage between the gate electrode (13) and the emitter needle (11) to generate free electrons, - Applying a focusing voltage between the focusing layer (17) and the gate electrode (13) to focus the free electrons, - Generating X-rays by means of the anode (33) of the X-ray tube (30) by interacting with the focused free electrons. [15] Method according to claim 14, wherein a voltage is applied between the gate electrode (13) and the emitter needle (11) prior to the emission voltage for the purpose of clearing at least part of the field effect emission section (12).

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