Microchannel plate and method for manufacturing microchannel plate selectively formed on one side of channel opening and having metal contact

Abstract

To provide an improved micro channel plate.SOLUTION: A method for selectively vapor-depositing electrode contact metal on one side of a MCP channel opening is prepared. One or more MCPs are removably fixed on the surface of a platter rotating around the central platter axis, inclined on a rotary ring fixture surrounding the vapor deposition source of contact metal and further rotating so as to go around the vapor deposition source of the contact metal. A mask having a mask opening having a variable size is arranged between the rotating platter and the vapor deposition source, and the mask goes around the vapor deposition source with the rotating platter without rotating along the own axis like the rotating platter.SELECTED DRAWING: Figure 10

Description

[Technical Field]

[0001] Exemplary embodiments relate generally to night vision systems, and more particularly to image intensifier tubes and a method for manufacturing an improved microchannel plate (MCP) for an image intensifier tube using a masked planetary evaporative deposition system. The MCP includes a channel opening with metal contacts extending a predetermined distance into the channel opening on only one side of the channel opening to enhance the open area ratio (OAR), first strike efficiency (FSE), secondary electron amplification, and overall signal-to-noise ratio (SNR) of the MCP. [Background technology]

[0002] Night vision systems, such as night vision goggles, typically include an image intensifier. The image intensifier or "image intensifier" may include an electron multiplier disposed between a photocathode and a sensor anode. The photocathode detects light in the form of photons transmitted from an object through a lens. The image intensifier includes an electron multiplier, such as an MCP, which amplifies or boosts the photoelectrons or "electrons" emitted from the photocathode. The boosted electrons are attracted to an anode, where they are converted into photons that are displayed on a screen. Upon receiving the boosted number of electrons, the anode or screen may include a sensor that senses the electrons and generates an enhanced representation of the image on the screen. The photocathode, electron multiplier, and anode are typically supported in a vacuum housing with a gap between the photocathode, electron multiplier, and sensor anode to provide gain and facilitate the flow of electrons therebetween. The night vision system may further include goggles disposed on the night vision system between one or more eyepieces or screens and the user's eyes.

[0003] An MCP is a type of electron multiplier. It is positioned between a photocathode and a phosphor-coated sensor anode. The photocathode generates a pattern of electrons corresponding to the pattern of photons generated from a low-light image. Through the use of an electrostatic field, the pattern of photoelectrons emitted from the photocathode is directed toward the face of the MCP. The MCP input face is substantially planar and has apertures distributed across it, each extending as a microchannel or "channel" from the input face to an opposite output face substantially parallel to the input face. Secondary electrons are generated when input electrons impinge on the inner surface of the channel aperture. Thus, the MCP emits a proportional number of secondary electrons from its microchannels depending on the number of primary electrons transmitted from the photocathode. The secondary electrons thereby form an electron shower, amplifying the electrons generated by the photocathode in response to the initial low-light image. This electron shower, much more intense than that generated by the photocathode, is then directed toward a phosphorescent screen on the phosphor-coated anode. A phosphor layer on the screen produces a visible light image that replicates the low light level image that would appear in the eyepiece of a night vision system.

[0004] An MCP can be formed from a bundle of very small cylindrical tubes or glass fibers fused together in a parallel orientation. The bundle can then be sliced ​​to form the MCP. The glass fiber bundle is thus arranged with its length generally along the thickness of the MCP. Thus, the MCP can contain a large number of hollow tubes or microchannels between the input and output faces of the MCP. Each channel can form an electron pathway between the input and output faces of the MCP.

[0005] In many cases, each channel is at a slight angle relative to the normal to the MCP's flat input and output faces. For example, the central axis of each channel can be biased relative to the normal to the MCP's flat input and output faces at a channel bias angle (CBA), which is typically 5° to 16° from the normal. The CBA is determined by the fact that electrons entering a channel perpendicular to the MCP input face are deflected by the channel walls. This ensures that the electrons strike the photocathode (or arcuate sidewalls) and helps prevent positive ions generated during operation of the image intensifier from migrating to the photocathode, where they could cause damage. The physical properties of the channel walls or arcuate sidewalls surrounding the central axis of the channel are generally such that multiple electrons are emitted for each high-energy electron contacting the sidewall. The material of the channel sidewalls that curve around the central axis of the channel has a high secondary electron emission coefficient to produce an electron emission rate greater than one.

[0006] The input and output faces of the MCP have continuous metal contacts. The input metal contacts on the input face of the MCP are preferably biased to a different voltage than the output metal contacts on the output face of the MCP. The contact metal applied to the input face is often called the input electrode, while the contact metal applied across the output face is often called the output electrode. The input and output electrodes are voltage-biased to generate an electric field through each channel. The electric field attracts secondary electrons generated at the input channel openings through the MCP toward the anode. The electrostatic field across each channel continues to multiply, or cascade, the secondary electrons along the length of each channel, and the cascaded electrons exit individual channels of the MCP under the influence of other electrostatic fields, further accelerating the multiplied electrons onto the phosphor-covered screen anode. The number of electrons emitted from a channel is averaged with the number of electrons emitted from other channels, producing an overall amplification or boost for the MCP.

[0007] One inherent problem with MCPs is that photoelectrons emitted from the photocathode may not enter one of the slightly angular channels but instead impact the input surface area between the channel openings. Because the area between the channel openings contains contact metal on the input surface of the MCP, some electrons may strike that area, resulting in unwanted electron scattering or bouncing. This can cause a loss of image fidelity, but more seriously, many of these electrons are absorbed and cannot participate in the amplification process, reducing the overall SNR of the MCP. Electrons that strike the MCP from the photocathode are called "primary electrons." Primary electrons are the first electrons or photoelectrons to strike the MCP. When primary electrons strike the MCP—more specifically, the wall or side of a channel opening near the input surface of the MCP—they generate a group of secondary electrons called "first strike electrons." Thus, primary electrons that enter a channel and strike the channel wall emit secondary electrons from their impact. The number of secondary electrons produced by the impact of a primary electron is called the "first strike efficiency."

[0008] In the above example, primary electrons scattered from the region between the channel apertures may enter another channel that is not properly aligned with the photocathode's origin. First-impact electrons originating from the region between the apertures may bounce or scatter under bias into another nearby channel, causing a halo effect at the MCP's output. Scattered first-impact electrons sent to nearby channel apertures also reduce overall image fidelity by visually distorting the image produced by the image intensifier. In another example, errant electrons may simply be absorbed by the contact metal on the input surface of the MCP between the apertures and not be amplified to produce part of the image or signal produced by the detector anode, resulting in a reduced SNR.

[0009] One solution to this challenge is to increase the channel diameter. By using an etch barrier around each channel, the diameter of each channel can be increased, thereby improving the ratio of the total channel opening area to the area between the channel openings. This technique can produce MCPs with a theoretical OAR of over 65%. However, while increasing the OAR increases the probability that electrons will enter the channel and improve SNR image doubling, the relatively thin residual cladding between the channel openings reduces the overall structural integrity of the MCP.

[0010] In addition to conventional MCPs having theoretical limits on OAR and SNR, contact metal on the input surface of the MCP can also adversely affect SNR and gain. When primary electrons strike contact metal, which typically extends into the input-side opening of the channel, secondary electrons are suppressed and no first impact electrons are generated. A typical side of a channel opening that does not contain contact metal on that side has an electron emission coefficient greater than 1. However, because contact metal on the input surface of the MCP may also extend into the input-side channel opening, primary electrons may strike contact metal with an electron emission coefficient much smaller than 1. Because the electron emission coefficient of contact metal is typically about 0.8, approximately 20% of electrons striking the contact metal on the inner wall of the input-side channel opening are immediately lost to the much higher electron emission coefficient in a channel that does not contain a contact metal coating. Summary of the Invention [Means for solving the problem]

[0011] Most of the problems outlined above are resolved by an improved night vision system including an image intensifier tube and an MCP, and a method for fabricating the same. Channel aperture formation can be improved to increase OAR beyond 80% without adversely affecting the structural integrity and manufacturing yield of the MCP. The MCP channel aperture is improved by selectively forming contact metal on each aperture to increase the first-impact electrons generated from the primary electron impact while maintaining an appropriate electrostatic field across each channel. Each channel can be biased with a CBA relative to the input and output faces of the MCP. Each channel aperture can also be tapered. The tapered sidewall surfaces of each channel aperture define an entrance that receives the majority of the primary electrons, with an enlarged tapered aperture having the smallest area between the apertures at the input face. The output face of the MCP opposite the channel aperture also includes a contact metal coating coupled to a voltage source to generate an electrostatic field from the tapered channel aperture on the input side through the channel to the output side. Thus, the contact metal is selectively applied to only one side of the input channel aperture, typically extending partially into the channel by no more than three-quarters of the channel diameter (D). D can be measured at the surface of the MCP or, if tapered, across the tapered portion of the channel.

[0012] By biasing each channel with a CBA relative to the plane normal of the MCP input surface and tapering the channel aperture at the input surface, a larger surface area is available to receive primary electrons. Therefore, increased OAR is available, increasing the SNR and gain of the MCP. Placing contact metal on the primary electron impact side of the channel aperture at the input surface or on the "shaded" side of the channel aperture, opposite the "showered" side, can generate more first-impact electrons. This is because, because the channel aperture is biased, the primary electrons essentially contact the shower side rather than the shaded side of the channel aperture. Tapering the channel aperture to form a funnel-shaped channel aperture at the input surface of the MCP and placing contact metal only on the shaded region of each channel aperture can prevent primary and first-impact electrons from being absorbed. The improved performance of MCPs leads to improved image intensifiers in night vision systems.

[0013] An important feature of combining a funnel-shaped channel opening with contact metal disposed only on a selected shielded side of the opening is that, when the contact metal is deposited, more surface area is available on one side of the channel opening due to the tapered opening and the deposition angle from the opposite side. The combination of the improved funnel shape, selecting a metallization depth into the channel, and selecting metallization circumferentially only around the arcuate shielded side provides a key advantage: the ability to optimize contact metal placement for improved MCP performance. Thus, the metallization used to create contact metal on the input face of an MCP can be selectively placed at different depths within each of a plurality of channel openings, at different circumferential distances around each of the channel openings, and only on the shielded side of each of the channel openings.

[0014] According to at least one example of the present disclosure, a night vision system is provided. The night vision system may include an image intensifier disposed between a lens and an eyepiece. The image intensifier may include a photocathode and a phosphor-coated anode. An MCP is disposed between the photocathode and the anode. The MCP includes a plurality of spaced apart channel openings disposed at a distance between the photocathode and the phosphor-coated anode. The channel openings are funnel-shaped and face the photocathode at an MCP input surface to receive incident electrons from the photocathode. Contact metal is applied to a first side of the channel openings, specifically, only the shielding side of each of the plurality of parallel spaced apart channel openings, via a planetary evaporation system.

[0015] The first side (or shield side) of the channel openings at the surface of the MCP is less than half the circumferential distance around each of the plurality of channel openings. The second side of each channel opening is preferably radially opposite the first side and is less than half the circumferential distance around each opening. The contact metal preferably attracts first impinging electrons generated from the second side (or shower side) of the channel opening. The first side can include contact metal selectively disposed circumferentially less than half the circumferential distance around the inner surface of the input side of the channel opening. Thus, the first and second sides extend around the inner wall in an arcuate pattern, each opposite each other and equidistant from the central axis of each channel. The first side including the contact metal can extend a selectable distance into each channel opening, depending on the configuration of the planetary deposition system.

[0016] According to another example of the present disclosure, a system for depositing contact metal on an MCP is provided. The system includes a contact metal deposition source and a platter spaced from the deposition source. The platter has a central axis extending vertically through the center of the platter and substantially flat opposing surfaces of the platter. The platter holds multiple MCPs and is configured to rotate about its central axis while being held in an inclined position that orbits (or revolves around) the deposition source. A mask is disposed between the platter and the deposition source. The mask includes an adjustable mask opening that exposes an adjustable, variable area of ​​the platter, including the MCP, to the deposition source. Importantly, because the mask is fixed relative to the rotating platter, the mask opening is also fixed relative to the rotating platter and the MCP mounted thereon.

[0017] The MCPs, specifically the channel openings of each MCP, are attached to the platter in a biased orientation. The channel openings of each MCP are arranged such that a vector along the CBA, specifically the CBA, extends from each channel opening along its respective channel central axis toward the platter central axis. The plane of the platter on which the MCPs are held is tilted from a vertical axis. The platter can be tilted at a first angle φ1 relative to a first axis. In one example, the first axis can be a vertical axis. The rotatable platter is held in the tilted position and further configured to rotate around the deposition source at a second angle φ2 relative to a second axis. In one example, the second axis can be a horizontal axis.

[0018] According to another example, the channel opening can be a funnel-shaped channel opening. Tapered first and second sides of the funnel-shaped channel opening extend a first distance from the input face into the channel. The contact metal is configured to be electrically biased and extends a first distance that is less than ¾ of the diameter (D) along only the tapered first side. The diameter (D) of the channel is measured further down the channel beyond the tapering or funnel distance.

[0019] According to yet another example of the present disclosure, a method for selectively depositing contact metal in channels of an MCP is provided. The method includes fixing an MCP on a platter. The platter can then be rotated about its central axis while tilting the platter relative to a contact metal deposition source. The rotating and tilted platter, including at least one MCP, is rotated (or orbited) around the deposition source while the MCP is fixed and a mask is maintained between the rotating and orbiting platter. The platter rotating around its central axis and rotating or orbiting around the deposition source implements a planetary deposition methodology. The mask is fixed relative to the rotating platter, and specifically, an opening in the mask is fixed relative to the rotating platter to selectively expose the channel openings of each MCP on the platter to the deposition source.

[0020] According to another example, when the corresponding MCP is mounted on the platter, the channel central axis of each channel is aligned at a channel bias angle along a vector pointing toward the platter central axis. By aligning each MCP so that the CBA of each channel opening faces toward the center of the platter, contact metal can be deposited only on the first side of the channel opening through the mask opening when the evaporation source is activated. By tilting and rotating the platter relative to the evaporation source at different first and second angles, the planetary evaporation system and method can deposit contact metal at different distances within the channel sidewall. By varying the mask opening from a wedge shape to a semicircular shape, the planetary evaporation system and method can deposit contact metal at different circumferential distances around the channel sidewall, specifically around the first or shielded side.

[0021] According to another example, the method further provides forming a funnel-shaped channel opening for each of the channel openings before securing the MCP to the platter. Each glass core is formed by surrounding it with glass cladding. Next, the glass cladding is etched a first distance into the plate at the boundary between the glass core and the surrounding glass cladding. The glass core is then etched away completely from the remaining glass cladding to form a plurality of funnel-shaped, separated channels. Next, contact metal is formed radially only along a first side of each of the plurality of separated funnel-shaped channels, extending no more than halfway along each of the plurality of separated channels. The contact metal on the first side is formed in an arcuate pattern around the central axis of each channel, along a tapered funnel-shaped opening, and downward into each channel, preferably less than halfway along the central axis of each of the separated channels. Each of the separated channels is parallel to each other in a CBA relative to the normal along which primary electrons reach the MCP input surface from the photocathode. Importantly, because of the CBA and the ability to funnel the opening, tapering with larger sized contact metal on the shielding or first side of the channel opening, the second or shower side of the tapered channel opening produces larger first impact electrons to enhance overall MCP performance. [Brief explanation of the drawings]

[0022] Examples of the present disclosure are best understood when the following detailed description is read in conjunction with the accompanying drawings. According to common practice, various features of the drawings are not drawn to scale or are shown only in partial perspective view. Dimensions of the various embodiments are shown arbitrarily expanded or reduced for clarity. Like reference numerals are used to represent like elements in the drawings. The drawings include the following features and elements, and reference is made to each of the following drawings: [Figure 1] FIG. 1 is a partial block diagram of a night vision system utilizing an image intensifier tube with an MCP. [Figure 2] FIG. 2 is a partial top view of the MCP taken along section 2-2 of FIG. [Figure 3]FIG. 3 is a partial cross-sectional view along section 3-3 of FIG. 2, showing the central axis of each channel aligned with the CBA and the first impact angle at which primary electrons impinge on the first shower impact side of each channel wall near each channel opening. [Figure 4] FIG. 4 is a partial cross-sectional view of contact metal advantageously formed only on a first side, or shielding side, of an exemplary funnel-shaped channel opening that is radially opposite a second side, or shower side, of the funnel-shaped channel opening where no contact metal is present. [Figure 5] FIG. 5 is a front view showing the contact metal and the depth and circumferential dimension of the contact metal selectively and adjustably formed on a first side of the channel opening. [Figure 6] FIG. 6 is a partial cross-sectional view of the glass core and cladding during the initial fabrication of the funnel-shaped opening of the MCP channel. [Figure 7] FIG. 7 is a partial cross-sectional view of the section of FIG. 6 after selective etching of the glass cladding at the core-cladding boundary. [Figure 8] FIG. 8 is a partial cross-sectional view of the section of FIG. 7 after etching the glass core to completely remove the core from the cladding. [Figure 9] FIG. 9 is a partial cross-sectional view of the section of FIG. 8 after forming contact metal along the first side, which is the shielding side, of the funnel-shaped opening. [Figure 10] FIG. 10 is a top view of a planetary deposition system for selectively depositing contact metal on an input surface of an MCP mounted on multiple platters surrounding a contact metal deposition source, specifically, a deposition system for selectively depositing contact metal on a first side, which is the shielded side, of a channel opening. [Figure 11a] FIG. 11a is a top view of adjustable mask apertures, specifically a semicircular mask aperture, a wedge-shaped mask aperture and an opposing wedge-shaped mask aperture. [Figure 11b] FIG. 11b is a top view of adjustable mask apertures, specifically a semicircular mask aperture, a wedge-shaped mask aperture and an opposing wedge-shaped mask aperture. [Figure 11c]FIG. 11c is a top view of adjustable mask apertures, specifically a semicircular mask aperture, a wedge-shaped mask aperture and an opposing wedge-shaped mask aperture. [Figure 12] FIG. 12 is a top view of multiple MCPs attached to the surface of a platter and their vectors CBA oriented toward the central axis of the platter. [Figure 13] FIG. 13 is a partial cross-sectional view of the MCP taken along section 13-13 of FIG. 12, showing the CBA of each channel oriented toward the central axis of the platter. [Figure 14] FIG. 14 is a side view of a planetary deposition system showing a mask with openings positioned between tilted, rotating, orbiting MCP-carrying platters, which provides contact metal to channel openings on a first side, which is an oblique or shielded side facing the deposition source or in the line of sight of the deposition source. [Figure 15] Figure 15 is a top view from the deposition source with a platter mounted with an MCP that rotates under the mask opening to expose only the first side, the shielded side, of each of the multiple channel openings to the deposition source according to the adjustable size of the mask opening and the adjustable tilt and orbit angles. DETAILED DESCRIPTION OF THE INVENTION

[0023] The following description refers to various exemplary embodiments. However, those skilled in the art will understand that the examples disclosed herein are broadly applicable, and the description of any embodiment is intended only to illustrate that embodiment and is not intended to suggest that the scope of the disclosure, including the claims, is limited to that embodiment.

[0024] As noted above, the drawings are not necessarily to scale. Certain features and components of the present application may be shown in exaggerated or somewhat schematic form, and some details of conventional elements may not be shown for the sake of clarity and conciseness.

[0025] In the following description and claims, the terms "including" and "comprising" are used in an open-ended sense and should be interpreted to mean "including, but not limited to." The term "coupled" is also intended to mean either an indirect or direct connection. Thus, when a first device is coupled to a second device, the connection may be through a direct connection between the two devices or through an indirect connection established through other devices, components, nodes, and connections. Additionally, as used herein, the terms "axis" and "axially" generally mean along or parallel to a given axis (e.g., the x-, y-, or z-direction or central axis of a body, opening, channel, outlet, or port), while "radial" and "radially" generally mean perpendicular to a given axis. For example, an axial distance means a distance measured along the central axis, and a radial distance means a distance measured perpendicular to the central axis. Radially opposite means on opposite sides of the central axis and in a spaced apart arcuate pattern partially around an axial distance from the central axis.

[0026] 1, a partial block diagram of a night vision system 12 is shown. The night vision system 12 includes an image intensifier tube 14 disposed between a pair of lenses 16 and 18. The lens 16 may be a focusing lens that focuses photons from an object 15 onto the image intensifier tube 14. The lens 18 may be an eyepiece that directs the emitted photons generated from the image intensifier tube 14 toward a user's eye. The night vision system 12 may include two eyepieces, for example, where the eyepiece 18 may be a pair of goggles.

[0027] The image intensifier 14 is a vacuum tube based on either third-generation (GaAs photocathode) or second-generation (bialkali photocathode) image intensifier fibers, which are fairly well known. Within the image intensifier 14 is a photocathode 20. The photocathode 20 includes a glass faceplate with a GaAs coating on the rear surface of the faceplate. Other III-V materials, such as GaP, GaIn, AsP, InAsP, and InGaAs, can also be used. Alternatively, the photocathode 20 may be known as a bialkali photocathode. The light-emitting semiconductor material of the photocathode 20 absorbs photons that arrive at the photon-receiving surface of the image intensifier 14. Photons absorbed by the photocathode 20 increase the carrier density of the semiconductor material, thereby generating a photocurrent of electrons 21 that are emitted from the rear electron-emitting surface of the photocathode 20.

[0028] According to one example, the photocathode 20 converts a low-level light source into an invisible or visible light. The invisible light source can be near-infrared or short-wave infrared to become visible. The electron multiplier 22 receives the electrons 21 and multiplies them to produce multiplied electrons 23. A typical electron multiplier includes a microchannel plate (MCP). The MCP 22 is typically formed from multiple glass fibers, each having a core surrounded by an outer glass cladding. Each of the multiple cores can be removed, leaving multiple spaced microchannels or "channels" from the input face to the output face of the MCP. The inner walls or sides of each channel opening have a high electron emissivity coefficient to generate a shower of secondary electrons. The channels are spaced apart and extend from the input plane or face to the output plane or face, from which the multiplied electrons are emitted. The secondary emitted electrons amplify the electrons generated by the photocathode in response to the initial low-level image. The shower of electrons is produced at a greater intensity than that produced by the photocathode, so the MCP 22 has amplification and gain.

[0029] A voltage source can be applied between various elements of the image intensifier 14 to attract electrons from the photocathode 20 to the MCP 22 through the MCP 22 and from the rear emitting surface of the MCP 22 to the anode 24. The voltage source creates an electrostatic field that attracts both primary and secondary electrons through the image intensifier 14 and imparts a desired energy to the multiplied electrons, which are applied to a phosphor-coated screen or anode 24. The phosphor-coated screen converts the multiplied electron pattern originating from the photocathode 20 into a visible light representation of the low-level image originally received from the target 15. Emitted photons are directed from the image intensifier 14 to the eyepiece 18 by an optical system, such as a fiber optic bundle. When viewed through the eyepiece 18, a user can discern low-level visible or invisible photons reflected from or generated by the target image 15 through the use of the increased gain and electron multiplication of the MCP 22.

[0030] Next, FIG. 2 shows a top view of the MCP 22 as viewed from the photocathode 20. Specifically, the top view is taken along section 2-2 of FIG. 1. Multiple channels penetrate completely through the MCP 22. Each channel 26 includes adjacent openings on the input and output sides of the MCP 22. Because the MCP 22 is shown in FIG. 2 from the photocathode side, the input side or input face is the electron receiving side that receives primary electrons 21 from the photocathode 20, as shown in FIG. 1. Each channel 26 preferably has the same diameter across its input and output side openings, as well as across the channel and opening. Therefore, the dimensions of the channels 26 are preferably consistent across the MCP 22. The pitch or spacing between the channels 26 should also be consistent. Due to defects in the composition, manufacturing, etching, and cleaning of the sides of the channels, some channels 26 may be larger in diameter than others, resulting in non-uniform emission of multiplied electrons at the output face of the MCP 22. Furthermore, such defects can cause the sides or walls of the channels to etch through, resulting in emission points on the glass surface. It is desirable to have as high an open area ratio (OAR) as possible, i.e., the ratio of the open area to the space between the openings. Conventional non-funnel-shaped channels have an OAR of less than 70% because they must retain enough channel wall material between the openings to maintain the overall structural strength required for MCPs.

[0031] 3, which shows a cross-sectional view of plane 3-3 of FIG. 2. FIG. 3 shows in more detail the multiple channels 26 within the honeycomb structure of MCP 22. If the channels 26 are properly tilted or biased with an optimal CBA, the channels provide a fairly reliable electron multiplier. A voltage source V is supplied to contact metal 30 applied across the input surface. s An electric field is formed between the input and output faces of the MCP 22 and contact metal 32, which is continuously applied across the input and output faces. Thus, channels 26 are openings between the input and output faces of the MCP 22 that can be cleaned to suppress secondary emission or remove residual impurities that may cause positive ion bombardment of the photocathode. An accelerating electrostatic field through each channel 26 applies contact metal to the input and output faces and couples the contact metal to a voltage supply V sThe contact metals 30 and 32 may extend partially into the channels. The tilt angle, or CBA, is taken along the central axis of the channels 26 and is substantially the same across each channel 26 because the channels are parallel to one another. The CBA may be between 5° and 16° relative to the normal to the MCP planar input face.

[0032] Electrons 21 transmitted from the photocathode 20 (FIG. 1) strike the side of each channel 26 at a first angle of incidence (FSA). Herein, electrons transmitted from the photocathode 20 are referred to as primary electrons 21. Because secondary electrons result from the first strike of a primary electron 21, these secondary electrons are referred to herein as first strike electrons. First strike electrons are only those electrons resulting from the first strike of a primary electron. First strike electrons 36 likely include primary electrons in addition to secondary electrons. Subsequent strikes from secondary electrons further down each channel are secondary electron strikes, but are not referred to as first strike electrons because first strike electrons are reserved for electrons generated by the first strike of a primary electron from the photocathode. Secondary electrons from the first impinging electron or subsequently generated secondary impinging electrons are biased downstream of each channel 26, where tertiary and other impinging electrons occur on opposing arcuate surfaces surrounding the axial center of the channel, further enhancing the multiplication effect. While multiple collisions can occur from the input face to the output face of each channel, resulting in multiplied electrons with gain, the initial collision of only the primary electron 21 generates the first impinging electron 36. It will be appreciated that each channel 26 generates the first impinging electron 36 from the first collision of the primary electron 21 at a first impingement angle FSA relative to the channel bias angle. FSA is perpendicular to the input face of the MCP 22. The first impingement angle is perpendicular to the input face of the MCP 22 but is an acute angle relative to the CBA. Therefore, the CBA is preferably 5 to 16 degrees, more preferably 5 to 8 degrees, relative to the normal to the MCP input face.

[0033] The overall electron multiplication, amplification, and gain of an MCP depend largely on the average number of electrons generated in response to an input event. These electrons, or primary electrons 21, generated in response to an input event (first impact electrons 36), significantly impact the overall performance of the MCP 22. As discussed below, with reference to Figure 4, one way to increase the generation of first impact electrons 36 is to selectively apply contact metal to areas where first impact electrons are not normally generated, thereby increasing the surface area over which first impact electrons are generated. Currently commercially available MCPs 22 are typically 20 mils thick or less. The cross-sectional diameter of the channel 26 is typically 3-8 microns.

[0034] Mismatches in either core pitch or diameter can result in a proportion of channels being larger than others, resulting in the formation of excessively large electron emission points in these enlarged channels. Consequently, electron emission intensity values ​​are higher in larger diameter channels where there is a greater opportunity for first-impact electrons to form. However, this greater intensity is localized to a very small number of pixels read by the phosphor-coated optical fiber. Another cause of increased, localized intensity when channel diameters are inconsistent is a greater opportunity for first-impact electrons striking the input contact metal 30 to reflect or bounce off the contact metal and enter larger channels or channels caused by etch-through of adjacent channels. Nonuniform, periodically sharp electron emission points form from enlarged channels due to adjacent channels being joined together through cladding etch-through. One technique for increasing the OAR, SNR, and MTF of the MCP 22 is to form the channel openings 26 into funnel-shaped or tapered openings.

[0035] The difference in first impact angle (FSA) can depend on whether the channel opening is funnel-shaped (tapered) or non-tapered. The first impact angle is relative to the channel bias angle, which is typically perpendicular to the input face of the MCP, while the CBA is the angle along the central axis along which each parallel, spaced channel extends. Because each channel is biased by the CBA, the CBA can also be considered relative to the normal to the input face. The increase in the number of first impact electrons is due to the increased number of primary electrons impinging on the shower side of the channel when the channel opening side is tapered rather than non-tapered. Tapering the shower side of the channel toward the normal generates more first impact electrons, thereby increasing the efficiency of the MCP. Increasing the surface area of ​​the shower-side surface improves MCP performance, but the placement of contact metal on that surface can have a negative effect. Therefore, it is beneficial to combine a funnel-shaped channel opening with selectively placed contact metal on the shield side of the channel opening rather than the shower side, as shown in Figure 4.

[0036] FIG. 4 shows contact metal 30 formed only on the input or electron-receiving surface of MCP 22 and on the first, or shielded, side of channel opening 26. The shielded side of the channel opening is not in a perpendicular line-of-sight relationship with the funnel-shaped opening of channel 26. In the region of initial electron impact (i.e., primary electron 21 impact), the interior surface of channel 26 has a high secondary electron emissivity coefficient that is intentionally not coated with the low electron emissivity conductive material of contact metal 30. Electron amplification in channel 26 begins immediately upon impact on the second, or shower side, of channel 26, rather than being delayed until the second or third impact of secondary electrons. When primary electrons contact the shower-side metallization material, the metal absorbs the primary electrons, resulting in less amplification within channel 26 because not enough first impact electrons are generated. Contact metal is intentionally placed only on the shielded or first side of each channel 26. According to one example, the contact metal 30 is intentionally positioned along the side of the channel a distance of less than 3 / 4D from the channel opening, regardless of whether the channel opening is tapered, where distance D is the diameter of the channel after the taper or funnel no longer exists if the channel opening is tapered.

[0037] Forming contact metal 30 on the input face of the MCP only on the first, shielded side of the aperture (whether tapered or not) allows for sufficient generation of electrostatic field 42 that essentially efficiently pushes or electrostatically biases the first impacting electrons 36 generated from the second, showered side further down into channel 26. Thus, careful and selective placement of contact metal 30 only on the first, shielded side maximizes the efficiency of the first impact and generates a significant electrostatic field 42, generating more effective secondary impacting electrons further down each channel.

[0038] As depicted in Figure 5, the surface area along plane 5-5 of Figure 4 shows the contact metal on the first side of channels 26. The contact metal 30 on the first side, or shielded side, of the channel extends into each channel a distance of ¾D or less downward from the input face of the MCP (measured across the funnel-shaped opening, if the opening is funnel-shaped).

[0039] Referring now to FIGS. 6-8, a method for fabricating an MCP is illustrated. For ease of illustration, the illustrated channels to be formed are not biased along a channel bias angle. However, it will be understood that the channels can be biased at an appropriate channel bias angle to maximize electron amplification and gain. FIG. 6 illustrates multiple glass cores surrounded by respective glass claddings positioned at a first angle relative to both sides of the future MCP. For simplicity, only two glass cores 52 are shown, each surrounded by its own glass cladding 54. The cores 52 can be made of an alkali-resistant, acid-soluble glass, while the claddings 54 can be made of an alkali-soluble, acid-resistant glass.

[0040] Referring to FIG. 7, an alkaline etchant composition can preferentially etch portions of the cladding 54, particularly the core / cladding interface, to create grooves on the input plate surface of the MCP input face. Each groove 60 extends a distance D within the interface. Because the core / cladding interface experiences significant mechanical stress when the glass fiber is formed, certain types of etchant compositions, such as sodium hydroxide, can attack the exposed interface due to the high chemical and mechanical stress in that region. To form a funnel-shaped opening in each channel, the interface region is exposed only at the input and output ends of the channel, with the core 52 still present. For simplicity, only the input faces of the channel openings are shown for only two channels.

[0041] Next, as shown in Figure 8, the glass core 52 is preferably etched, for example, by an acid de-coring process using an acid-based etching composition. After the core 52 is removed, the openings of the hollow channels 26 extend completely through the MCP from the input face to the output face, with each channel 26 having a funnel-shaped opening at least on the input face, as shown in Figure 8. The funnel-shaped openings thus have tapered sides that extend a distance D into each channel. D is substantially the same as the diameter of the channel 26 measured from the funnel-shaped opening to a point further into the channel.

[0042] Referring now to FIG. 9 , contact metal 30 is shown along only the first, shielded side of a plurality of spaced-apart channel openings 26. According to one example, the channel openings 26 can be funnel-shaped, as shown in FIG. 9 . Contact metal 30 is formed on each of the first sides of the channel openings, down the sides of the openings a distance of 3 / 4D or less within the opening. While FIG. 9 illustrates the channels vertically for ease of illustration, it will be understood that the channels 26 are nevertheless biased with CBA. Primary electrons 21 impinge only on the second, or shower, side 31 a of the channel openings. The primary electrons 21 impinge along the shower side 31 a, which extends a first distance from the opening into the opening. If the channel openings are funnel-shaped, the first distance may correspond to the tapered portion of the funnel. The primary electrons 21 impinge on the second side 31 a of each opening, e.g., only at the tapered portion of the opening, specifically radially opposite the first side on which contact metal 30 is formed. Therefore, the first impinging electrons 36 are beneficially obtained at the most efficient geometric position of the aperture, with a taper angle closer to the normal of the microchannel plate input surface facing the photocathode.

[0043] A deposition window appears so that deposition of the contact metal occurs along a line of sight 62 between the deposition source and the exposed first side 31b onto which the contact metal 30 is deposited. The contact metal 30 is deposited using a planetary deposition system and method further described with reference to Figures 10-15.

[0044] Referring now to FIG. 10 , a top view of a planetary evaporation system 70 is shown. The evaporation system 70 utilizes a series of platters 72 surrounding an electron beam evaporation source 74. The evaporation source 74 (or other line-of-sight thin-film evaporation source) directs contact metal vapor particles toward a target object for vacuum deposition of the contact metal source material, such as Inconel or Nichrome. The target objects are multiple MCPs 22 attached to the face of each platter 72. Upon contact with the MCPs 22, the applied contact metal subsequently condenses back into a solid state. The MCPs 22 are attached to a corresponding platter 72, and each platter 72 is configured to rotate 76 about its central axis 78. Each platter 72 is configured to rotate about its platter central axis 76 while attached to a ring fixture 80. The ring fixture 80 preferably rotates 82 about its central axis, along which the evaporation source 74 resides. Deposition system 70 includes a rotating platter 72 that rotates about its central axis 78 and further rotates around a deposition source 74 located at the axis of a ring fixture 80. The deposition source 74, located at the axis of the ring fixture 80, can be aligned above or below the plane of the ring fixture along the central axis of the fixture 80. Thus, planetary deposition system 70 includes a system for depositing contact metal uniformly on MCP 22 and selectively on the MCP input surface and partially within each channel opening at the input surface. For simplicity and clarity, FIG. 10 does not show a mask configured between deposition source 74 and each platter 72. However, FIG. 11 shows such a mask.

[0045] FIG. 11a shows a top view of a platter 72 partially covered by a mask 82a. The mask 82a may comprise any material that blocks evaporation or deposition of source material onto the target material. The mask 82a may be any shape that covers the platter 72, except for the openings 84a in the mask 82a. The mask 82a is positioned between the evaporation source 74 and the platter 72, and the openings 84a are fixed while the platter 72 rotates 76 about its central axis 78. The mask 82a is preferably positioned as close as possible to the platter 72 to maximize deposition placement control. To achieve this goal, the mask openings 84a are preferably less than a few inches in front of the platter 72. In FIG. 11a, the mask openings 84a are shown as semicircular. The semicircular shape forms contact metal 30 at a semicircular, arcuate, circumferential distance on the first, shielded side 31b of each channel opening, as described further below.

[0046] FIG. 11b also shows a top view of the platter 72 covered with a mask 82b. The mask 82b includes a wedge-shaped opening 84b. The wedge shape correspondingly forms the contact metal 30 in a semicircular, arc-shaped, circumferential distance around the first side 31b, or the shielded side. The circumferential distance around the first side 31b depends on the size of the wedge, particularly the length of the triangular side 88a of the opening 84b. FIG. 11c shows a smaller wedge-shaped opening 84c and a correspondingly shorter length of the triangular side 88b of the opening 84c. Thus, the mask 82c with the opening 84c forms a smaller circumferential distance around the first side 31b than the mask 82b with the opening 84b, and that circumferential distance is certainly smaller than the circumferential distance around the first side 31b than the mask 82a with the semicircular opening 84a. Also, as shown in FIG. 11c, two openings 84c may be provided to illustrate that the contact metal can be deposited in a number of different ways, possibly on other than the shielding side, possibly twice per rotation of the platter 72 about its central axis 78.

[0047] 12 is a top view of multiple MCPs 22 mounted on the surface of each platter 72. In part, to achieve deposition only on the first side 31b, which is the shielded side, the CBA of each channel, and in particular the vector of the CBA, must be oriented 90° (or biased) toward the platter central axis 78. Because the core and cladding of each channel forming the MCP 22 are simultaneously generated with the same CBA vector extending in the same direction, the MCPs on each platter can be positioned such that the CBA of each channel, looking downward, is positioned within each channel so that the CBA of each channel of each MCP mounted on the platter 72 is oriented as shown by arrow 90.

[0048] FIG. 13 is a partial cross-sectional view of the MCP taken along section 13-13 of FIG. 12, showing the CBA of each channel 26 oriented toward the platter central axis 78. Specifically, the channel openings of each MCP are positioned on the platter 72 so that they are biased by the CBA. The CBA extends from the channel opening along each channel central axis toward the platter central axis 78, and when the deposition source 74 is activated, it receives contact metal 30 only on the first side 31b, which is the shielded side of the shower, but not on the second side 31a, through mask openings 84a, 84b, or 84c. For simplicity and clarity, FIG. 13 shows only two channels 26 and the corresponding first and second sides 31b, 31a of their channel openings. However, it will be understood that each MCP includes more than 1,000 channels.

[0049] FIG. 14 is a partial side view of a planetary deposition system 70 in which a mask 82 having openings 84 is positioned between tilting, rotating, orbiting platters 72 on which an MCP is mounted, resulting in contact metal 30 being deposited on the oblique or obscured first side 31b of the channel openings facing and in line of sight with the deposition source 74. Note that as the platters 72 rotate, the position of the mask openings 84 changes relative to the MCP channels, specifically the channel openings. By varying the amount or angle of the mask openings 84, the circumferential distance around the channel openings over which contact metal 30 is deposited on the first side 31b changes accordingly. FIG. 14 further illustrates variations in the depth to which contact metal can be deposited at each channel opening. For example, the depth of deposition can be varied by changing the first tilt angle φ1 relative to the first axis 94. By decreasing the first angle φ1, the depth of deposition can be increased. Additionally, for example, the depth of deposition can be changed by changing the rotation angle around the deposition source 74 to a second angle φ2 relative to the second axis 96. The depth of deposition can be reduced by reducing the second angle φ2. The first axis 94 and the second axis 96 can be perpendicular to each other. For example, the first axis 94 can be a vertical axis, and the second axis 96 can be a horizontal axis. The first tilt angle φ1 relative to the first axis 94 is preferably 0 to 15°, and the second rotation or orbital angle φ2 relative to the second axis 96 is preferably 65 to 80°.

[0050] FIG. 15 shows a top view from the deposition source 74. The platter 72 with the attached MCP is shown in dashed lines and rotates behind the mask 82, more specifically, the openings 84 in the mask 82. The amount of openings 84 can be adjusted by correspondingly varying the circumferential distance 98 along the first side 31b exposed to the deposition source 74. Using a planetary motion in which both the ring fixture and the platter rotate allows for more uniform deposition of the contact metal 30 only on the first side 31b. Importantly, the mask 82, which is fixed to and rotates with the ring fixture and remains in front of the platter but does not rotate with the platter about its own axis or the platter's central axis, selectively deposits the contact metal circumferentially around the first side 31b. Thus, the MCP electrodes are deposited on the channel walls on the first side as determined by the mask design and opening configuration. The mask openings provide fully configurable circumferential coverage and location of the contact metal to the channel openings, providing deposition uniformity since each MCP is exposed to the same deposition, and providing improved electrode contact metal conductivity compared to any non-rotating method. Thus, the planetary deposition system and method combines enhanced MCP SNR performance with the high yield offered by rotating contact metal deposition through a tunable mask.

[0051] It is important to note that the construction and arrangement of the various illustrative embodiments are for illustrative purposes only. While only a few embodiments have been described in detail in this disclosure, those skilled in the art, having access to this disclosure, will readily appreciate that many changes (e.g., changes in the size, dimensions, structure, shape, and proportions of various elements, parameter values, mounting arrangements, use of materials, color, orientation, etc.) are possible without substantially departing from the novel teachings and advantages of the subject matter described herein. For example, elements shown as integrally formed may be composed of multiple parts or elements, the positions of elements may be reversed or otherwise changed, and the nature or number of individual elements or positions may be modified or changed. The order or sequence of any process or method steps may be changed or re-arranged according to alternative embodiments. Additionally, features from particular embodiments may be combined with features from other embodiments, as will be understood by those skilled in the art. Other substitutions, modifications, changes, and omissions may also be made in the design, operating conditions, and arrangement of the various illustrative embodiments without departing from the scope of the present invention.

[0052] As used herein, terms such as "about," "approximately," "substantially," and "generally" refer to ±10% of the stated value or range. Additionally, as used herein, the singular forms "a," "an," and "the" are intended to include the plural forms unless the context clearly dictates otherwise. The term "and / or" includes any and all combinations of one or more of the associated listed items. For example, reference to a "feature" includes a plurality of such "features." The term "and / or" when used in the context of "X and / or Y" should be interpreted as "X," "Y," or "X and Y."

[0053] The illustrative embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented herein. Additionally, certain aspects of each embodiment may be utilized in conjunction with other embodiments of the present disclosure, and thus, disclosed embodiments may be combined, as understood in the art. It will be readily understood that the aspects of the present disclosure, as generally described and illustrated herein, can be arranged, substituted, combined, separated, and designed in a wide variety of different configurations, all of which are expressly contemplated herein.

[0054] It should be noted that the use of the term "exemplary" herein to describe various embodiments is intended to indicate possible examples, representations, and / or descriptions of possible embodiments (such terminology does not necessarily imply that such embodiments are particularly or exclusively exemplary). Additionally, the terms "substantially" and similar terms, as used herein, are intended to have a broad meaning consistent with common usage accepted by those skilled in the art to which the subject matter of this disclosure pertains. Those skilled in the art, exposed to this disclosure, should understand that these terms are intended to allow the description of the scope of the particular features described and claimed without limiting them to the precise numerical ranges provided. Accordingly, these terms should be interpreted to indicate that insubstantial or insignificant modifications or variations of the described and claimed subject matter (e.g., within ±5% of a given angle or other value) are considered to be within the scope of the invention as set forth in the appended claims. The term "about" used in connection with a value means ±5% of the associated value.

[0055] As used herein, the term "coupled" or the like means that two members are directly or indirectly connected to one another. Such a connection may be fixed (e.g., permanent) or movable (e.g., removable or releasable). Such a connection may be achieved by the two members or the two members and an additional intermediate member being integrally formed as a single body, or by the two members or the two members and an additional intermediate member being attached to one another.

[0056] It should be understood that while the diagrams herein may show a particular order and arrangement of method steps, the order of these steps may differ from that depicted. For example, two or more steps may occur simultaneously or with partial concurrence. Also, some method steps performed as separate steps may be combined, steps performed as combined steps may be separated into separate steps, the sequence of certain processes may be reversed or otherwise changed, and the nature or number of separate processes may be modified or changed. The order or sequence of any elements or devices may be changed or substituted in accordance with alternative embodiments. Accordingly, all such variations are intended to be included within the scope of the present disclosure, as defined by the appended claims.

[0057] Without further elaboration, it is believed that those skilled in the art can utilize the present invention to its fullest extent using the above description. The examples and embodiments disclosed herein are merely illustrative and should not be construed as limiting the scope of the present disclosure in any way. Those skilled in the art will appreciate that changes can be made to the details of the above-described embodiments without departing from the underlying principles described. In other words, various modifications and improvements of the embodiments specifically disclosed in the above description are within the scope of the appended claims. For example, any suitable combination of features of the various embodiments described is contemplated.

Claims

1. 1. A deposition system for depositing contact metal on a microchannel plate, comprising: a contact metal deposition source; a platter having a central axis, the platter holding the microchannel plate, the platter configured to rotate about the central axis while tilting toward the deposition source relative to the central axis, and also rotate about the deposition source; a mask disposed between the platter and the deposition source, the mask including a mask opening having a shape that exposes only a first side of each of a plurality of channel openings in the microchannel plate to the deposition source; Including, The deposition system, wherein the first side corresponds to the plurality of channel openings in the microchannel plate positioned in front of the mask openings.

2. 2. The deposition system of claim 1, wherein the platter is tilted at a first angle φ1 relative to a first axis, and the platter central axis is further configured to rotate around the deposition source at a second angle φ2 relative to a second axis, the second axis being perpendicular to the first axis.

3. 3. The deposition system of claim 2, wherein the first angle and the second angle are adjustable to correspondingly adjust the amount of the contact metal deposited within the channel opening.

4. 2. The deposition system of claim 1, wherein the channel openings extend along respective channel central axes, each of the channel central axes being biased at a channel bias angle extending from the channel opening along its respective channel central axis toward the platter central axis to receive contact metal through the mask opening and only on a first side of the channel opening during operation of the deposition source.

5. 5. The deposition system of claim 4, wherein the channel bias angle is between 5° and 16° relative to a normal to an input face of the microchannel plate.

6. 2. The deposition system of claim 1, wherein a first side of each of the plurality of channel openings is less than half a circumferential distance around each of the plurality of channel openings, and a second side of each of the plurality of channel openings radially opposite the first side is less than half a circumferential distance around each of the plurality of channel openings.

7. 5. The deposition system of claim 4, wherein the mask openings are adjustable from wedge-shaped openings to semicircular openings to correspondingly adjust radial exposure sizes about the channel central axis on each first side of each of the channel openings relative to the deposition source.

8. 8. The deposition system of claim 7, wherein the wedge-shaped openings generate contact metal less than half a circumferential distance around each of the plurality of channel openings, and the semicircular openings generate contact metal approximately half a circumferential distance around each of the plurality of channel openings.

9. 10. The deposition system of claim 1, wherein the channel opening is a funnel-shaped channel opening that decreases in diameter from an input face of the microchannel plate to a first distance from the input face.

10. 1. A deposition method for selectively depositing contact metal into channels of a microchannel plate, comprising: securing the microchannel plate on a platter; rotating the platter about its central axis; tilting the platter relative to the platter central axis toward a contact metal deposition source; rotating the platter around the deposition source while maintaining a mask opening in a fixed position relative to the rotating platter and between the rotating platter and the deposition source; activating the deposition source to selectively deposit a contact metal within the channel; Including, The vapor deposition method, wherein the mask opening has a shape that exposes only the channel in front of the mask opening to the vapor deposition source.

11. The fixing step comprises: positioning the channels such that central channel axes extend from a plurality of channel openings along each channel and toward a central axis of a platter, such that contact metal is received through the mask openings and only on first sides of the plurality of channel openings during operation of the deposition source; The deposition method of claim 10 , comprising:

12. 12. The deposition method of claim 11, further comprising forming the plurality of channel openings in the shape of a funnel that decreases in diameter from an input face of the microchannel plate to a first distance from the input face.

13. Prior to the fixing, forming a glass core surrounded by a respective glass cladding at the channel central axis on each side of the microchannel plate; etching the glass cladding a first distance into the microchannel plate at an interface between the glass core and the surrounding glass cladding; etching the glass core to completely remove it from the remaining glass cladding so as to leave a plurality of spaced apart funnel-shaped channels; The deposition method of claim 11 further comprising:

14. The tilting and rotating may include: tilting the platter at a first angle φ1 relative to a first axis; rotating the platter at a second angle φ2 relative to a second axis, the second axis being perpendicular to the first axis; The deposition method of claim 11 , comprising:

15. 15. The deposition method of claim 14, wherein adjusting the first angle and the second angle results in a corresponding adjustment of the amount of the contact metal deposited in the plurality of channel openings.

16. 12. The deposition method of claim 11, further comprising adjusting the mask openings from wedge-shaped openings to semicircular openings to correspondingly adjust radial exposure sizes about the channel central axis of each of the first sides of each of the plurality of channel openings relative to the deposition source.

17. 17. The deposition method of claim 16, wherein the wedge-shaped openings create contact metal less than half the circumferential distance around each of the plurality of channel openings, and the semicircular openings create contact metal about half the circumferential distance around each of the plurality of channel openings.

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