Design for reliability of field emitter x-ray sources.

Abstract

An X-ray source design for improving reliability by mitigating the effects of vacuum arcing, ion back-bombardment, and ion sputtering includes an X-ray source including one or more field emitter arrays and a circuit configured to control the one or more field emitter arrays. The one or more field emitter arrays include a gate and an emitter. The circuit is configured to apply a voltage between the gate and the emitter.

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application claims the benefit of and priority to U.S. Provisional Patent Application No. 63 / 396,689, filed August 10, 2022, the entire contents of which are incorporated herein by reference.

[0002] The present disclosure relates to system designs for radiography equipment, including digital radiography, fluoroscopy, tomosynthesis, and computed tomography (CT). [Background technology]

[0003] Field emission has been proposed as a cathode for X-ray sources, and arrays of nanostructures have been used to obtain current levels suitable for practical applications. Field emission-based X-ray sources allow for normally off, room-temperature operation with the close cathode spacing required for distributed and multi-source X-ray imaging applications such as tomosynthesis and computed tomography. Reliability has been a significant issue for field emission-based sources compared to conventional thermionic electron sources, which are typically tungsten-based filaments. Field emission cathodes are made using a variety of solid materials, including silicon, molybdenum, and carbon nanotubes, and emit light from their sharp, tip-like surfaces, meaning tip movement and damage can lead to changes in device performance. Due to their physical operating mechanism, field emitter devices are more susceptible to reliability issues related to high voltages. Summary of the Invention

[0004] One aspect of the present disclosure provides a system including an x-ray source including one or more field emitter arrays and a circuit configured to control the one or more field emitter arrays, the one or more field emitter arrays including gates and emitters, the circuit configured to apply a voltage between the gates and the emitters.

[0005] In one aspect of the present disclosure, the x-ray source can further include an anode, and the voltage includes a waveform having a duty cycle greater than about 5% and a pulse width less than the transit time of ions between the anode and one or more field emitter arrays.

[0006] In one embodiment of the present disclosure, the x-ray source may further include an anode. A voltage is applied between the gate and emitter of each of the one or more field emitter arrays. The circuitry is configured to vary the voltage to alternate which of the one or more field emitter arrays is configured to emit electrons while maintaining a duty cycle of greater than 5% for each of the one or more field emitter arrays. The voltage has a pulse width shorter than the transit time of ions between the anode and the one or more field emitter arrays.

[0007] In one aspect of the present disclosure, the x-ray source may further include an anode and field emitter array protection configured to shield the field emitter array from back-impinging ions originating from the anode and to deflect the electron beam so as not to impinge on a location within a line of sight from the anode to the field emitter array.

[0008] In another aspect of the present disclosure, the field emitter array protection may include a conductor.

[0009] In one aspect of the present disclosure, the x-ray source may further include an anode and one or more conductor pairs configured to deflect the electron beam by applying an electrostatic force to the one or more conductor pairs, the one or more conductor pairs having opposite voltage polarities configured to cause electrons to strike the anode outside the line of sight of the field emitter array.

[0010] In one aspect of the present disclosure, the x-ray source can further include an anode, an x-ray tube, and one or more magnets disposed inside or outside the x-ray tube and configured to apply a magnetic force to deflect the electron beam so that the electrons strike the anode outside the line of sight of the field emitter array.

[0011] In another aspect of the disclosure, the one or more magnets are permanent magnets or electromagnets.

[0012] In one aspect of the present disclosure, the x-ray source may further include an anode, a plurality of electrostatic electrodes configured to apply an electrostatic force, and an electromagnet configured to apply a magnetic force, the electrostatic electrodes and the electromagnet configured to deflect the electron beam by a combination of the electrostatic and magnetic forces so that the electrons strike the anode outside the line of sight of the field emitter array.

[0013] In one aspect of the present disclosure, one or more field emitter arrays can be configured to achieve a desired electron focal spot size after manipulation from electrostatic or magnetic forces outside the line of sight of the field emitter array.

[0014] In one embodiment of the present disclosure, the x-ray source may further include an anode, and a voltage is applied between the gate and emitter of each of the one or more field emitter arrays. The circuitry is configured to vary the voltage to alternate which of the one or more field emitter arrays is configured to emit electrons while maintaining a duty cycle of greater than about 5% for each of the one or more field emitter arrays. The voltage has a pulse width longer than the transit time of ions between the anode and the one or more field emitter arrays.

[0015] In one aspect of the present disclosure, one or more field emitter arrays, multiple of which may be simultaneously operational, provide one or more distinct focal spot sizes configured to emit x-rays.

[0016] In another aspect of the present disclosure, the system may further include a transient voltage suppressor in parallel with the gate and emitter contacts of the x-ray source.

[0017] Further details and aspects of the present disclosure are described in more detail below with reference to the accompanying drawings.

[0018] A better understanding of the features and advantages of the present disclosure will be obtained by reference to the following detailed description that sets forth illustrative embodiments in which the principles of the disclosure are utilized, and the accompanying drawings of which: [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a block diagram of an X-ray tube connected to a control circuit and a power supply, according to an aspect of the present disclosure. [Figure 2] 1 is a graph illustrating exemplary waveforms of gate-emitter voltage and anode current as a function of time, according to an embodiment of the present disclosure. [Figure 3] 1 is a graph illustrating exemplary waveforms of gate-emitter voltage and anode current measured at the output of an exemplary x-ray source including two field emitter arrays, according to an embodiment of the present disclosure. [Figure 4] FIG. 1 is a side cutaway view of an X-ray tube including the electron beam and returning ion path without beam deflection, according to an embodiment of the present disclosure. [Figure 5] FIG. 1 illustrates a side cutaway view of an X-ray tube with beam deflection, including the path of the electron beam and returning ions, according to an aspect of the present disclosure. [Figure 6] 1 is a side cutaway view of an X-ray tube including electrostatic beam deflection positioned before and after field emitter array protection after electrons leave the field emitter array, according to an aspect of the present disclosure. [Figure 7] FIG. 1 is a side cutaway view of an exemplary X-ray tube with internal and external electromagnets for applying magnetic fields that affect the paths of electrons and ions, according to an embodiment of the present disclosure. [Figure 8] FIG. 1 is a side cutaway view of an exemplary X-ray tube with electrostatic beam deflection using electromagnets, according to an aspect of the present disclosure. [Figure 9] FIG. 2 is a diagram of a field emitter array of the X-ray tube of FIG. 1 in accordance with an embodiment of the present disclosure. [Figure 10] FIG. 10 is a diagram of a field emitter array of the X-ray tube of FIG. 9 in accordance with an embodiment of the present disclosure. [Figure 11] FIG. 1 is a diagram of multiple field emitter arrays from multiple individual X-ray sources, according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0020] This disclosure relates to systems that use field emission X-ray sources used in conventional 2D, tomosynthesis, and computed tomography (CT). Previous field emission X-ray sources have not employed methods to address reliability challenges associated with ionizing X-ray environments.

[0021] Vacuum arcing is a major reliability challenge for both field-emission and thermionic cathodes in X-ray sources. Vacuum arcing is caused by a positive feedback loop of ion formation, which shorts the anode, gate, and cathode together. In thermionic X-ray sources, X-ray output is temporarily disabled until the arcing event passes, resulting in loss of X-ray images during computed tomography scans. In field-emission-based X-ray sources, arcing can cause catastrophic failure by exposing the field-emitting material and gate to high voltages. Field emitters often experience reduced or increased current between the gate and emitter terminals, potentially requiring replacement to meet performance requirements. This can be mitigated by carefully degassing all components, but this is not sufficient to improve field emitter reliability.

[0022] 1, a block diagram of a system 100 including an X-ray source 102 is shown. The X-ray source 102 (e.g., an X-ray tube) includes one or more field emitter arrays 120, a control circuit 150 configured to control the one or more field emitter arrays 120, and a power supply 160. The one or more field emitter arrays 120 include a gate 130, an anode 110, and an emitter 140. The control circuit 150 is configured to apply a voltage between the gate 130 and the emitter 140. In some embodiments, the X-ray source 102 can further include a transient voltage suppressor 190.

[0023] Arcing in vacuum tubes is inevitable, and even if it does not directly affect the field emitter array, proper design of the X-ray tube and circuitry is necessary to prevent the effects of arcing events. The transient voltage suppressor 190 may include electrostatic discharge (ESD) devices, such as diodes, thyristors, and circuitry. The transient voltage suppressor 190 may be integrated in parallel with the cathode gate and emitter contacts to mitigate failure of the X-ray source 102 due to either excessive current surges or overvoltages. Another way to mitigate the overall impact of vacuum arcing on the silicon electroluminescent element array is to provide a power supply isolated from other components and implement a structure that shields the silicon electroluminescent element array from electromagnetic fields resulting from arcing: a metal “cage” that is grounded in one or more dimensions. In some embodiments, metal can be used as a Faraday cage to shield the field emitter array 120 from certain electric fields (FIG. 9).

[0024] The system 100 includes a field emitter operating design designed to mitigate the possibility of vacuum arcing in the field emitter. The field emitter may operate at a high frequency (less than approximately 10 ns), at a current higher than the required current level, and at a low voltage (less than approximately 100 V). These features enable the design to operate the field emission X-ray source by turning the X-ray source 102 on and off, controlled by the controller 150 and / or circuitry designed to operate at a high duty cycle (greater than approximately 5%) with a pulse width shorter than the time required for ions to accumulate and cause a vacuum arc. A vacuum arc can occur when ions from the anode 110 or field emitter array 120 cascade to reach the opposite terminal and cause catastrophic failure of the field emitter array 120. The controller 150 may include a processor and memory, or circuitry.

[0025] In some embodiments, the controller 150 can apply a voltage between the gate and emitter of each of the one or more field emitter arrays. The controller 150 can be further configured to vary the voltage to alternate which of the one or more field emitter arrays emits electrons while maintaining a duty cycle of greater than about 5% for each of the one or more field emitter arrays. The voltage has a pulse width that is longer than the transit time of ions between the anode and the one or more field emitter arrays. This has the advantage of giving the emitters a "rest" time, reducing the impact of ion back-bombardment on the device.

[0026] In some embodiments, one or more field emitter arrays are operated simultaneously to provide one or more distinct focal spot sizes from which x-rays can be emitted.

[0027] Referring to FIG. 2, a diagram showing the pulsed gate 130 voltage versus the emitter 140 voltage and the expected anode 110 current is shown. To obtain the desired continuous on-current required for the application, the voltage is driven at a duty cycle greater than approximately 5%. However, the x-ray source 102 is turned on and off quickly enough so that no continuous stream of ions forms, preventing vacuum arcing. This can also be applied to multiple field emitter arrays 120 to maintain continuous anode 110 current with lower current drive, as shown in FIG. 3. In addition to reducing the likelihood of vacuum arcing, focal spot movement can also be used for anti-aliasing.

[0028] An additional reliability mechanism for field emitter arrays is ion back-bombardment and sputtering, which results from the ionization of gas molecules in the high electric field between the anode and cathode. Ions formed in the high electric field are accelerated toward the field emitter array, causing bulk crystal damage and sputtering of material from the field emitter array. While ion back-bombardment is significant in conventional thermionic x-ray sources, it is more detrimental in field emission sources due to the crystal surface structure. This disclosure includes several structures that can reduce both ion back-bombardment and sputtering of the cathode.

[0029] The disclosed approach uses a high aspect ratio conductor or field emitter array shield 170 to shield the cathode from the line of sight of the electron focus on the anode 110 using electrostatic or magnetic forces.

[0030] Figure 4 shows a field emission X-ray source configuration in which the cathode is in the direct line of sight of the ions. Back-bombarded and sputtered ions impinge on the cathode, degrading the field emission material over time. Figure 5 is an example diagram of the X-ray source 102 configuration showing the direction of the applied force from the electrostatic or magnetic field and the trajectory of the electron beam. In this configuration, most of the electron beam path is blocked from the line of sight to the field emitter array 120, resulting in a significant reduction in net ion flux and limiting the energy of ions impinging on the field emitter array, greatly improving the overall reliability of the structure.

[0031] As seen in Figure 7, a magnetic field can be applied to achieve a similar result by incorporating a permanent magnet or electromagnet 200 either inside or outside the X-ray source 102. The magnetic field bends the electron beam relative to the anode, positioning the electrons to strike the desired location. The magnetic field can also be integrated with an electrostatic field to obtain the desired beam path (Figure 8). For example, the X-ray source 102 can include an electrostatic electrode 180.

[0032] Referring to FIG. 10, there are several possible configurations for implementing electrostatic and magnetic fields to steer the beam to follow a specific direction. Electrostatic steering requires applying potentials to both sides of the electron beam, for example, using electrostatic electrodes 180 (FIG. 8). Off-center deflection is achieved by applying positive and negative potentials to opposite sides of the electron beam, and multiple layers of electrostatic potentials can be applied to steer the beam in multiple directions. These electrostatic potentials and gates can be integrated before or after the ion collector to prevent ions from impacting the cathode, or they can be integrated within the packaging of the X-ray source 102 (e.g., X-ray tube).

[0033] As the electron beam is deflected by different forces, the shape and size of the focal spot may also change. To account for the changes in shape and size, the geometry of the field emitter array can be altered to compensate for the expected change in size of the spot on the anode. This is accomplished in one of two ways: by changing the lithographically patterned size and shape of the field emitters to the desired shape, or by turning on multiple tiles to achieve a given cathode emission shape.

[0034] 11, one or more redundant and similar field emitter arrays 120 (e.g., silicon field emitter arrays) can be integrated in case one or more field emitter arrays 120 are destroyed, resulting in loss of functionality of a given array. This can be part of an existing array of tiles or a separate, explicit set of field emitter arrays 120, but they do not operate simultaneously. In some embodiments, this section only becomes active and continues imaging if the primary cathode is destroyed.

[0035] The embodiments disclosed herein are examples of the claimed subject matter and may be embodied in various forms. For example, although certain embodiments herein are described individually, it should be understood that each embodiment herein can be combined with one or more of the other embodiments described herein. The specific structural and functional details disclosed herein are not to be construed as limiting, but rather as a basis for the claims and as a representative basis for teaching those skilled in the art how to variously use the present disclosure in substantially any suitable detailed configuration. Like reference numerals may refer to similar or identical elements throughout the description of the figures.

[0036] Particular embodiments of the present disclosure may include some, all, or none of the above advantages and / or one or more other advantages that will be readily apparent to one of ordinary skill in the art from the drawings, descriptions, and claims contained herein. Additionally, while certain advantages have been enumerated above, various embodiments of the present disclosure may include all, some, or none of the enumerated advantages and / or other advantages not specifically enumerated above.

[0037] The embodiments disclosed herein are examples of the present disclosure and may be embodied in various forms. For example, although certain embodiments herein are described as separate embodiments, each embodiment herein can be combined with one or more of the other embodiments herein. The specific structural and functional details disclosed herein should not be construed as limiting, but rather as a basis for the claims and as a representative basis for teaching those skilled in the art how to variously use the present disclosure in substantially any suitable detailed structure. Like reference numerals may refer to similar or identical elements throughout the description of the figures.

[0038] The phrases "in one embodiment," "in an embodiment," "various embodiments," "in some embodiments," or "in other embodiments" may each refer to one or more of the same or different exemplary embodiments provided in this disclosure. A phrase in the form "A or B" means "(A), (B), or (A and B)." A phrase in the form "at least one of A, B, and / or C" means "(A)," "(B)," "(C)," "(A and B)," "(A and C)," "(B and C)," or "(A, B, and C)."

[0039] It should be understood that the foregoing description is merely illustrative of the present disclosure. Those skilled in the art may devise various alternatives and modifications without departing from the present disclosure. Accordingly, the present disclosure is intended to embrace all such alternatives, modifications, and variations. The embodiments described with reference to the accompanying drawings are presented only to illustrate particular examples of the present disclosure. Other elements, steps, methods, and techniques that differ substantially from those described above and / or in the appended claims are also intended to be within the scope of the present disclosure.

Claims

1. Gate and Emitter and one or more field emitter arrays including: a circuit configured to control the one or more field emitter arrays to apply a voltage between the gate and the emitter; an X-ray source including A system including:

2. 10. The system of claim 1, wherein the x-ray source further comprises an anode, and wherein the voltage comprises a waveform having a duty cycle greater than about 5% and a pulse width less than a transit time of ions between the anode and the one or more field emitter arrays.

3. the X-ray source further comprises an anode; the voltage is applied between the gate and emitter of each of the one or more field emitter arrays; the circuitry is configured to vary a voltage to alternate which of the one or more field emitter arrays are configured to emit electrons while maintaining a duty cycle of greater than 5% for each of the one or more field emitter arrays; the voltage has a pulse width that is shorter than the transit time of ions between the anode and the one or more field emitter arrays; The system of claim 1 .

4. the X-ray source an anode; shielding the field emitter array from back-impinging ions originating from the anode; Deflecting the electron beam so as not to impinge on a location within a line of sight from the anode to the field emitter array. Field emitter array protection and The system of claim 1 further comprising:

5. The system of claim 4 , wherein the field emitter array protection is a conductor.

6. the X-ray source an anode; one or more conductor pairs configured to deflect the electron beam, wherein the electron beam is deflected by applying an electrostatic force to the one or more conductor pairs; the one or more pairs of conductors are of opposite voltage polarity and configured to cause electrons to strike the anode outside the line of sight of the field emitter array; The system of claim 1 .

7. the X-ray source an anode; An X-ray tube; one or more magnets disposed inside or outside the x-ray tube and configured to apply a magnetic force, the one or more magnets configured to deflect the electron beam with the magnetic force so that electrons strike the anode outside the line of sight of the field emitter array; The system of claim 1 further comprising:

8. The system of claim 7 , wherein the one or more magnets are permanent magnets or electromagnets.

9. the X-ray source an anode; a plurality of electrostatic electrodes configured to apply an electrostatic force; an electromagnet configured to apply a magnetic force; The electrostatic electrode and the electromagnet are configured to deflect the electron beam by a combination of the electrostatic force and the magnetic force, causing the electrons to strike the anode outside the line of sight of the field emitter array. The system of claim 1 .

10. 10. The system of claim 1, wherein the one or more field emitter arrays are configured to achieve a desired electron focal spot size after manipulation from electrostatic or magnetic forces outside the line of sight of the field emitter array.

11. the x-ray source further includes an anode, and the voltage is applied between the gate and emitter of each of the one or more field emitter arrays; the circuitry is configured to vary a voltage to alternate which of the one or more field emitter arrays are configured to emit electrons while maintaining a duty cycle of greater than about 5% for each of the one or more field emitter arrays; the voltage has a pulse width greater than the transit time of ions between the anode and the one or more field emitter arrays; The system of claim 1 .

12. The system of claim 1 , wherein the one or more field emitter arrays provide one or more distinct focal spot sizes configured to emit x-rays, multiple of which are operative simultaneously.

13. The system of claim 1 further comprising a transient voltage suppressor in parallel with the gate and emitter contacts of the x-ray source.

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