Method for manufacturing a microchannel plate having metal contacts selectively formed on one side of the microchannel plate and channel openings

Abstract

To provide an improved microchannel plate.SOLUTION: The invention provides a night vision system, a microchannel plate (MCP), and a planetary deposition system and methodology for selectively depositing an electrode contact metal on one side of MCP channel openings. One or more MCPs can be releasably secured to a face of a platter that rotates about its central platter axis. The rotating platter can be tilted on a rotating ring fixture surrounding an evaporative source of the contact metal. Therefore, the rotating platter further rotates such that it orbits around the evaporative source of the contact metal. A mask with a variable size mask opening is arranged between the rotating platter and the evaporative source. Although the mask orbits around the evaporative source together with the rotating platter, the mask does not rotate along its own axis as does 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 of the inherent problems of MCPs is that the photoelectrons emitted from the photocathode may not enter one of the slightly flared channels, but instead can affect the input surface area between the channel openings. Since the area between the channel openings contains contact metal on the input surface of the MCP, some electrons strike that area, resulting in unwanted electron scattering or reflection from there. This can cause a loss of image fidelity, but more seriously, since many of these electrons are absorbed and cannot participate in the amplification process, the overall SNR of the MCP decreases. The electrons that strike the MCP from the photocathode are called "primary electrons". Primary electrons are the electrons or photoelectrons that first strike the MCP. When primary electrons strike the MCP, more specifically, the walls or sides of the channel openings near the input surface of the MCP, they generate a group of secondary electrons called "first strike electrons". Thus, primary electrons that enter the channel and strike the channel walls emit secondary electrons from that impact. The number of secondary electrons generated by the impact of primary electrons is called the "first strike efficiency".

[0008] In the above example, primary electrons scattered from the area between the channel openings can enter another channel that is not aligned with the proper position of the origin of the photocathode. A halo effect can be caused at the output of the MCP when first strike electrons originating from the area between the openings bounce back or scatter under bias and enter a nearby different channel. The scattered first strike electrons sent to a nearby channel opening also degrade the overall image fidelity by visually distorting the image generated by the image intensifier. In other examples, the wrong electrons are simply absorbed by the contact metal on the input surface of the MCP between the openings and are not amplified to contribute to the image or signal generated by the detector anode, resulting in a decrease in 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 can include an image intensifier disposed between a lens and an eyepiece. The image intensifier tube can include a photocathode and a phosphor-coated anode. There is an MCP between the photocathode and the anode. The MCP is disposed spaced apart between the photocathode and the phosphor-coated anode and includes a plurality of spaced channel openings. The channel openings are funnel-shaped, face the photocathode at the MCP input surface, and receive incident electrons from the photocathode. The contact metal is applied via a planetary deposition system only to the first side of the channel opening, particularly to the shielding side of each of the plurality of parallel spaced channel openings.

[0015] The first side (or shielding side) of the channel opening in the plane of the MCP is less than or equal to 1 / 2 of 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 less than or equal to 1 / 2 of the circumferential distance around each opening. The contact metal preferably attracts the first impact electrons generated from the second side (or shower side) of the channel opening. The first side can include a contact metal selectively disposed circumferentially within 1 / 2 of the inner surface around the input side of the channel opening. Thus, the first side and the second side extend around the inner wall in an arcuate pattern, each being on the opposite side of the 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 arrangement 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 deposition source of contact metal and a platter spaced from the deposition source. The platter has a platter central axis that extends vertically through a substantially flat opposing surface of the platter at the center of the platter. The platter holds a plurality of MCPs and is configured to rotate about its platter central axis while being held in an inclined position that orbits (or goes 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 MCPs to the deposition source. Importantly, since the mask is fixed relative to the rotating platter, the mask opening is also fixed relative to the rotating platter and the MCPs mounted thereon.

[0017] The MCPs, and in particular the channel openings of each MCP, are attached to the platter in a bias direction. The channel openings of each MCP are arranged such that, for example in a CBA, vectors along the CBA extend from each channel opening along their respective channel central axes towards the platter central axis. The plane of the platter on which the MCPs are held is inclined from a vertical axis. The platter can be inclined at a first angle φ1 with respect to a first axis. According to one example, the first axis can be a vertical axis. The rotatable platter is held in an inclined position and is further configured to rotate around the deposition source at a second angle φ2 with respect to a second axis. According to 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. The tapered first and second sides of the funnel-shaped channel opening extend a first distance into the channel from the input surface. The contact metal is configured to be electrically biased and extends a first distance that is less than 3 / 4 of the diameter (D) only along the tapered first side surface. The diameter (D) of the channel is measured further down the channel beyond the taper or funnel distance.

[0019] According to yet another example of the present disclosure, a method for selectively depositing contact metal on channels of an MCP is provided. The method includes fixing the MCP on a platter. Next, while tilting the platter with respect to the deposition source of the contact metal, the platter can be rotated about its own platter central axis. The rotating and tilted platter including at least one MCP is rotated (or orbited) around the deposition source while maintaining a mask between the fixed, rotating, and orbiting platter. The platter that rotates about its own platter central axis and rotates or orbits around the deposition source implements a planetary deposition methodology. The mask is fixed to the rotating platter. Specifically, the openings in the mask are fixed 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, the channel central axis of each channel is arranged to extend at a channel bias angle along a vector pointing towards the platter central axis when the corresponding MCP is mounted on the platter. By arranging each MCP such that the CBA of each channel opening faces towards the center of the platter, when the deposition source is activated, contact metal can be deposited only on the first side of the channel opening through the mask opening. By tilting and rotating the platter with respect to the deposition source at different first and second angles, the planetary deposition system and method can deposit contact metal at different distances within the channel sidewall. By changing the mask opening from a wedge shape to a semi-circular shape, the planetary deposition system and method can deposit contact metal at different circumferential distances around the channel sidewall, specifically at different circumferential distances around the first or shielded side.

[0021] According to another example, the method further provides for forming a funnel-shaped channel opening for each of the channel openings before fixing the MCP to the plate. The glass cores are formed by surrounding each with a glass cladding. Next, at the boundary between the glass core and the surrounding glass cladding, the glass cladding is etched in the plate to a first distance. Next, the glass core is etched and completely removed from the remaining glass cladding to form a plurality of separated funnel-shaped channels. Next, a contact metal is formed radially within a range not exceeding half of each of the plurality of separated channels, only along the first side of the plurality of separated funnel-shaped channels. The contact metal on the first side is preferably formed in an arcuate pattern around the central axis of each channel, along the tapered funnel-shaped opening, and downwardly into each channel at a distance less than half of the distance around the central axis of each of the separated channels. Each of the separated channels is parallel to each other in CBA with respect to the normal at which the primary electrons reach the MCP input surface from the photocathode. Importantly, for CBA and for being able to make the opening funnel-shaped, and for tapering with a larger-sized contact metal on the shielding side or the first side of the channel opening, the second side or the shower side of the tapered channel opening generates a larger first impact electron to enhance the overall MCP performance.

Brief Description 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. In accordance with common practice, various features of the drawings are not drawn to scale or are shown only in partial perspective views. Dimensions of various embodiments are arbitrarily enlarged or reduced for clarity. Like reference numerals are used to represent like elements within the drawings. The drawings include the following features and elements, with reference to each of the following drawings.

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[0023] The following description relates to various exemplary embodiments. However, those skilled in the art will understand that the examples disclosed herein are widely 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 described above, the drawings are not necessarily to scale. Certain features and components of the present application may be shown with exaggerated scale or in a somewhat schematic form, and some details of conventional elements may not be shown for clarity and brevity.

[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 "connected" is also intended to mean either an indirect or direct connection. Thus, when a first device is connected to a second device, that connection can 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 the central axis of a body, opening, channel, outlet, or port), while "radius" 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 the opposite side of the central axis, partially surrounding and spaced from the axial distance from the central axis in an arcuate pattern.

[0026] Next, referring to FIG. 1, a partial block diagram of the 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 can be a focusing lens that focuses photons from the object 15 onto the image intensifier tube 14. The lens 18 can be an eyepiece that directs the output photons generated from the image intensifier tube 14 towards the user's eye. The night vision system 12, for example, the eyepiece 18 can be goggles, and the eyepiece 18 can include two eyepieces.

[0027] The image intensifier 14 is a vacuum tube based on third-generation (GaAs photocathode) or second-generation (multi-alkali photocathode) image intensifier fibers and is fairly well known. Inside the image intensifier tube 14 is a photocathode 20. The photocathode 20 includes a glass faceplate, and the rear surface of the faceplate is coated with GaAs. Other III-V materials such as GaP, GaIn, AsP, InAsP, InGaAs, etc. can be used. Alternatively, the photocathode 20 can be known as a multi-alkali photocathode. The photoemissive semiconductor material of the photocathode 20 absorbs photons arriving at the photon-receiving surface of the image intensifier tube 14. The photons absorbed by the photocathode 20 increase the carrier density of the semiconductor material, thereby generating a photocurrent of electrons 21 emitted from the electron-emitting surface on the rear side of the photocathode 20 in the material.

[0028] According to one example, the photocathode 20 converts a non-visible or visible low light source. The non-visible light source can make near-infrared or short-wave infrared visible. The electron multiplier tube 22 receives the electrons 21 and multiplies them to generate multiplied electrons 23. A common electron multiplier tube includes a microchannel plate (MCP). The MCP 22 is usually formed through a plurality of glass fibers each having a core covered with an outer glass cladding. Since each of the plurality of cores can be removed, a plurality of microchannels or "channels" with a space between the input surface and the output surface of the MCP remain. The inner wall or side surface of each channel opening has a high electron emissivity coefficient to generate a shower of secondary electrons. The channels are spaced apart from each other and extend from the input plane or input surface to the output plane or output surface from which the multiplied electrons are emitted. The secondary emission electrons amplify the electrons generated by the photocathode in response to the initial low-level image. Since the shower of electrons is generated with a greater intensity than that generated by the photocathode, the MCP 22 has amplification and gain.

[0029] The voltage source can be applied between various elements of the image intensifier 14 to draw electrons from the photocathode 20 to the MCP22 via the MCP22 and also from the emission surface behind the MCP22 to the anode 24. The voltage source draws both primary and secondary electrons through the image intensifier 14 to generate an electrostatic field that gives the multiplied electrons applied to the screen covered with a phosphor or the anode 24 the desired energy. The screen covered with a phosphor converts the multiplied electron pattern starting from the photocathode 20 into a visible light image of the low-level image first received from the target 15. The emitted photons are directed from the image intensifier 14 to the eyepiece 18 by an optical system such as a bundle of optical fibers. When viewed through the eyepiece 18, the user can identify the low-level visible or invisible photons reflected or generated from the target image 15 through the use of the amplified gain and electron multiplication of the MCP22.

[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 sIt is caused by biasing. The contact metal can include a good electrical conductivity material such as Inconel or Nichrome. The contact metals 30 and 32 can extend partially into the channel. The tilt angle or CBA is taken along the central axis of the channel 26 and is substantially the same across each channel 26 since the channels are parallel to each other. The CBA can be between 5° and 16° with respect to the normal of the MCP plane input surface.

[0032] The electrons 21 sent from the photocathode 20 (FIG. 1) collide with the side surfaces of each channel 26 at the first incident angle (FSA). In the present application, the electrons sent from the photocathode 20 are referred to as primary electrons 21. Since the secondary electrons are generated from the first collision of the primary electrons 21, in the present application, the secondary electrons generated from the first collision of the primary electrons 21 are referred to as the first collision electrons. The first collision electrons are only the electrons generated from the first collision of the primary electrons. The first collision electrons 36 probably include primary electrons in addition to secondary electrons. Subsequent collisions generated from secondary electrons further down each channel are secondary electron collisions but are not called the first collision electrons. This is because the first collision electrons are reserved only for the electrons generated by the first collision of the primary electrons from the photocathode. The secondary electrons from the first collision electrons or from the secondary collision electrons generated thereafter are biased downstream of each channel 26. Downstream of each channel 26, collision electrons such as tertiary electrons occur on the opposing arcuate surfaces surrounding the axial center of those channels, further enhancing the multiplication effect. Multiple collisions occur from the input surface to the output surface of each channel, and multiplied electrons with gain can be generated, but only the first collision of the primary electrons 21 generates the first collision electrons 36. It will be understood that each channel 26 generates the first collision electrons 36 from the first collision of the primary electrons 21 at the first collision angle FSA with respect to the channel bias angle. The FSA is perpendicular to the input surface of the MCP 22. The first collision angle is perpendicular to the input surface of the MCP 22 but is an acute angle with respect to the CBA. Therefore, the CBA is preferably 5 to 16° with respect to the normal of the MCP input surface, and more preferably 5 to 8°.

[0033] Most of the overall electron multiplication, amplification, and gain of the MCP depend 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 have a significant impact on the overall performance of the MCP 22. As will be described later, referring to FIG. 4, one way to increase the generation of the first collision electrons 36 is to selectively apply a contact metal to the region where the first collision electrons are not normally generated, thereby increasing the surface area where the first collision electrons are generated. The thickness of currently commercially available MCP 22 is usually 20 mils or less. The cross-sectional diameter of the channel 26 is usually 3 to 8 microns.

[0034] If there is any mismatch in either the core pitch or diameter, a higher percentage of channels larger than other channels can occur, and overly large electron emission spots can be formed in these enlarged channels. Therefore, the electron emission intensity value increases where there is a greater chance of the first collision electrons being formed in the larger diameter channels. However, the higher intensity is localized in a very small number of pixels read by the phosphor-coated optical fiber. Another cause of the increased and localized intensity when the channel diameter is inconsistent is that the first collision electrons colliding with the input-side contact metal 30 have a greater chance of being reflected from or bouncing off the contact metal and entering larger channels or channels caused by the etch-through of adjacent channels. Non-uniform and periodically sharp electron emission spots are formed from the enlarged channels by adjacent channels joined together through the etch-through of the cladding. One technique to increase the OAR, SNR, and MTF of the MCP 22 is to form the channel aperture 26 into a funnel-shaped or tapered aperture.

[0035] The difference in the first collision angle (FSA) can depend on whether the channel opening is funnel-shaped (tapered) or not. The first collision angle is relative to the channel bias angle, where the first collision angle is typically perpendicular to the input surface of the MCP, while the CBA is the angle along the central axis along which each parallelly spaced channel extends. Since each channel is biased by the CBA, the CBA is also considered to be relative to the normal of the input surface. The increase in the number of first collision electrons is because when the side of the channel opening is tapered rather than non-tapered, the number of primary electrons colliding on the shower side of the channel increases. By tapering the shower side of the channel towards the normal direction, more first collision electrons are generated, thereby increasing the efficiency of the MCP. Increasing the surface area of the shower side surface improves the performance of the MCP, but the arrangement of the contact metal on that surface can have an adverse effect. Therefore, it is beneficial to combine a funnel-shaped channel opening with selectively arranged contact metals located on the shielding surface rather than on the shower surface of the channel opening, as shown in FIG. 4.

[0036] FIG. 4 shows contact metal 30 formed only on the input surface or electron receiving surface of MCP22 and on the first side which is the shielding side of channel opening 26. The shielding side of the channel opening is not in the relationship of the sight line perpendicular to the funnel-shaped opening of channel 26. In the region of the initial electron impact (i.e., the impact of primary electrons 21), the inner surface of channel 26 has a high secondary electron emission coefficient which is not intentionally coated with the low electron emissivity conductive material of contact metal 30. The electron amplification in channel 26 does not start being delayed until the second or third collision of secondary electrons occurs, but starts immediately upon impact on the second side which is the shower side of channel 26. When the primary electrons contact the metallized material on the shower side, the metal absorbs the primary electrons and insufficient first collision electrons are generated, so the amplification in channel 26 is reduced. The contact metal is intentionally arranged only on the shielding side or the first side of each channel 26. According to one example, contact metal 30 is intentionally arranged at a distance less than 3 / 4D along the side of the channel to the channel opening regardless of whether the channel opening is tapered, and the distance D is the diameter of the channel after the taper or funnel no longer exists when the channel opening is tapered.

[0037] (Regardless of whether it is tapered or not) By forming contact metal 30 only on the first side which is the shielding side of the opening on the input surface of the MCP, a sufficient electrostatic field 42 can be generated, and the electrostatic field 42 essentially efficiently pushes or electrostatically biases the first collision electrons 36 generated from the second side which is the shower side further downward into channel 26. Therefore, by carefully and selectively arranging contact metal 30 only on the first side which is the shielding side, the first collision efficiency is maximized, a significant electrostatic field 42 is generated, and more effective secondary collision electrons are generated further downward in each channel.

[0038] As described in FIG. 5, the surface area along plane 5-5 of FIG. 4 shows the contact metal on the first side of channel 26. The contact metal 30 on the first side which is the shielding side of the channel extends downward from the input surface of the MCP by a distance of 3 / 4D or less into each channel (measured beyond the funnel-shaped opening if the opening is funnel-shaped).

[0039] Next, referring to FIGS. 6 to 8, a method of manufacturing an MCP is shown. For ease of illustration, the channels shown to be formed are not biased along the 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 shows a plurality of glass cores surrounded by respective glass clads arranged at a first angle with respect to both sides of the future MCP. For simplicity of the drawing, only two glass cores 52 each surrounded by its own glass clad 54 are shown. The core 52 can be made of an alkali-resistant acid-soluble glass, while the clad 54 can be made of an alkali-soluble acid-resistant glass.

[0040] Referring to FIG. 7, an etched composition of an alkali material can preferentially etch a part of the clad 54, particularly the core / clad interface, to generate grooves on the input plate surface of the MCP input surface. Each groove 60 extends a distance D within the interface. Since the core / clad interface is subject to significant mechanical stress when the glass fibers are formed, certain types of etching 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 of the drawing, only the input surface of the channel opening is shown for only two channels.

[0041] Next, as shown in FIG. 8, the glass core 52 is preferably etched by an acid decoring process using, for example, an acid-based etching composition. After the core 52 is removed, as shown in FIG. 8, the openings of the hollow channels 26 completely penetrate the MCP from the input surface to the output surface, and each channel 26 has at least a funnel-shaped opening at the input surface. Thus, the funnel-shaped opening has a tapered side extending a distance D within each channel. D is substantially the same as the diameter of the channel 26 measured at a point further inside the channel from the funnel-shaped opening.

[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] Figure 11a is a top view of the platter 72 partially covered by the mask 82a. The mask 82a includes any material that blocks the deposition or accumulation of the raw material on the target material. The mask 82a can have any shape as long as it covers the platter 72, except when there is an opening 84a in the mask 82a. The mask 82a is disposed between the evaporation source 74 and the platter 72. The opening 84a is fixed, while the platter 72 rotates 76 about its platter central axis 78. The mask 82a is preferably disposed as close as possible to the platter 72 to maximize the evaporation arrangement control. To achieve this goal, it is preferably in front of the platter 72 by less than a few inches. In Figure 11a, the mask opening 84a is shown as semi-circular. The semi-circular shape forms the contact metal 30 at a semi-circular, arc-shaped, circumferential distance on the first side 31b, which is the shielding side of each channel opening, as further described below.

[0046] Figure 11b is also a top view of the platter 72 covered by the mask 82b. The mask 82b includes a wedge-shaped opening 84b. The wedge shape correspondingly forms the contact metal 30 at a semi-circular, arc-shaped, circumferential distance around the first side 31b, which is the shielding side. The circumferential distance around the first side 31b depends on the size of the wedge, and in particular, the length of the triangular side 88a of the opening 84b. Figure 11c shows a smaller wedge-shaped opening 84c and the correspondingly shorter length of the triangular side 88b of the opening 84c. Therefore, 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 surely smaller than the circumferential distance around the first side 31b of the mask 82a with the semi-circular opening 84a. Also, as described in Figure 11c, two openings 84c can be provided to show that the contact metal can be deposited in a number of different ways, in some cases outside the shielding side and in some cases twice per rotation of the platter 72 about its central axis 78.

[0047] FIG. 12 is a top view of a plurality of MCP22s attached to the surface of each platter 72. In part, in order to achieve deposition only on the first side 31b which is the shielding side, the CBA of each channel, particularly the vector of the CBA, must be directed (or biased) at 90 degrees towards the platter central axis 78. Since the core and cladding of each channel forming the MCP22 are simultaneously generated with the same CBA vector extending in the same direction, the MCPs on each platter can be arranged such that the CBA of each channel of each MCP attached to the platter 72 is arranged to be directed as indicated by arrow 90, and the CBA of each channel looking downwards within each channel is arranged accordingly.

[0048] FIG. 13 is a partial cross-sectional view of the MCP along section 13-13 of FIG. 12, showing the CBA of each channel 26 directed towards the platter central axis 78. In particular, the channel openings of each MCP are arranged on the platter 72 such that they are biased by the CBA. The CBA extends from the channel opening along the central axis of each channel towards the platter central axis 78, and when the deposition source 74 is activated, the contact metal 30 is received only on the first side 31b which is the shielding side rather than on the second side 31a of the shower through the mask openings 84a, 84b or 84c. For the sake of brevity and clarity, FIG. 13 shows only two channels 26 and the corresponding first side 31b and second side 31a of their channel openings. However, it will be understood that each MCP includes more than 1000 channels.

[0049] FIG. 14 is a partial side view of a planetary deposition system 70 in which a mask 82 having an aperture 84 is disposed between an inclined, rotating, and orbiting platter 72 to which an MCP is attached, such that contact metal 30 is deposited on a first side 31b that is the slanted or shielded side of the channel aperture facing and on the line of sight of the evaporation source 74. Note that as the platter 72 rotates, the position of the mask aperture 84 changes relative to the MCP channels, particularly the channel apertures. By varying the amount or angle of the mask aperture 84, the circumferential distance around the channel aperture on which the contact metal 30 is deposited on the first side 31b changes accordingly. FIG. 14 shows a further variation in the depth to which the contact metal can be deposited on each channel aperture. For example, by changing the first tilt angle φ1 with respect to the first axis 94, the depth of deposition can be changed. By decreasing the first angle φ1, the depth of deposition can be increased. Also, for example, by changing the angle of rotation around the evaporation source 74 to a second angle φ2 with respect to the second axis 96, the depth of deposition can be changed. By decreasing the second angle φ2, the depth of deposition can be decreased. 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 with respect to the first axis 94 is preferably from 0 to 15°, and the second rotation or orbital angle φ2 with respect to the second axis 96 is preferably from 65 to 80°.

[0050] FIG. 15 is a top view as seen from the evaporation source 74. The platter 72 with the MCP attached is shown by the dashed line and rotates behind the mask 82, more specifically behind the opening 84 in the mask 82. The amount of the opening 84 can be adjusted by correspondingly varying the circumferential distance 98 along the first side 31b exposed to the evaporation source 74. By using a planetary motion in which both the ring fixture and the platter rotate, the contact metal 30 can be more uniformly deposited only on the first side 31b. Also, importantly, by using a mask 82 that is fixed to the ring fixture and rotates with the ring fixture, stays in front of the platter, but does not rotate about its own axis or the central axis of the platter together with the platter, the contact metal is selectively arranged circumferentially around the first side 31b. Thus, the MCP electrode is deposited on the channel wall of the first side as determined by the mask design and the opening configuration. The mask opening provides a fully configurable circumferential coverage and position of the contact metal to the channel opening, provides deposition uniformity since each MCP is exposed to the same deposition, and provides an improvement in the electrode contact metal conductivity compared to any non-rotating method. Thus, the planetary evaporation system and method combine the high yield resulting from the deposition of the rotating contact metal through an adjustable mask with the enhanced MCP SNR performance.

[0051] It is important to note that the configurations and arrangements of the various exemplary embodiments are merely illustrative. Although only some embodiments have been described in detail in this disclosure, those skilled in the art who have touched upon this disclosure will readily understand that many changes (e.g., changes in the sizes, dimensions, structures, shapes and ratios of various elements, values of parameters, mounting arrangements, use of materials, colors, orientations, etc.) can be made without substantially departing from the novel teachings and advantages of the subject matter described in this application. For example, elements shown as integrally formed may be composed of a plurality of parts or elements, the positions of the 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 rearranged according to alternative embodiments. In addition, as will be understood by those skilled in the art, features from specific embodiments may be combined with features from other embodiments. Without departing from the scope of the present invention, other substitutions, modifications, changes and omissions may also be made to the designs, operating conditions and arrangements of the various exemplary embodiments.

[0052] Terms such as "about", "substantially", "generally", etc. used in this application mean ±10% of the recited value or range. In addition, the singular forms "a", "an" and "the" used in this application are intended to include the plural forms as well, unless the context clearly dictates otherwise. The term "and / or" includes any and all combinations of one or more of the recited related items. For example, a reference to a "feature" includes such a plurality of "features". The term "and / or" used in the context of "X and / or Y" should be construed as "X", "Y" or "X and Y".

[0053] The exemplary embodiments described in the detailed description, the drawings, and the claims are not meant to be limiting. Other embodiments may be used and other changes may be made without departing from the spirit or scope of the subject matter presented in this application. Additionally, specific aspects of each embodiment may be used in combination with other embodiments of this disclosure, and thus, as understood in the art, the disclosed embodiments may be combined. The aspects of the disclosure generally described and illustrated in this application can be arranged, substituted, combined, separated, and designed in a wide variety of configurations, and it will be readily understood that all of these are explicitly intended in this application.

[0054] Note that the use of the term "exemplary" in this application to describe various embodiments is intended to indicate possible examples, representations, and / or explanations of possible embodiments (such terms do not mean that such embodiments are necessarily special or the best examples). Also, the term "substantially" and similar terms used in this application are intended to have a broad meaning consistent with the general usage accepted by those skilled in the art relevant to the subject matter of this disclosure. Those skilled in the art to which this disclosure pertains should understand that these terms are intended to enable the description of the scope of the specific features described and claimed without limiting them to the exact numerical ranges provided. Therefore, these terms should be interpreted as indicating that modifications or variations that are not substantial or negligible (e.g., within ±5% of a given angle or other value) of the described and claimed subject matter are considered to be within the scope of the invention described in the appended claims. The term "about" used with respect to a value means ±5% of the relevant value.

[0055] Terms such as "connected" used in this application mean that two members are directly or indirectly connected to each other. Such connections can be fixed (e.g., permanent) or movable (e.g., removable or detachable). Such connections can be realized in a state where two members or two members and an additional intermediate member are formed integrally as a single body with each other or where two members or two members and an additional intermediate member are attached to each other.

[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

Claim 1 A night vision system comprising an image intensifier tube disposed between a lens and an eyepiece, said image intensifier tube comprising a photocathode, a phosphor-coated anode, a microchannel plate disposed at a distance between said photocathode and said phosphor-coated anode, said microchannel plate comprising a plurality of spaced-apart channel openings having a circular cross-section extending from an input side of said microchannel plate facing said photocathode to an output side of said microchannel plate, and said plurality of channel openings being funnel-shaped channel openings, said plurality of channel openings having a channel bias angle along a central axis of said plurality of channel openings, the central axis of said plurality of channel openings being inclined with respect to a normal to a plane of said microchannel plate, said microchannel plate having an unshielded side corresponding to an inner surface of said plurality of channel openings visible from a line of sight perpendicular to a surface of said microchannel plate on said input side and a shielded side corresponding to an inner surface of said channel openings not visible from a line of sight perpendicular to a surface of said microchannel plate on said input side, a first side of said shielded side including a contact metal for extracting first impact electrons generated from a second side of said channel openings diametrically opposite to said first side, said contact metal on said first side of said shielded side extending downwardly a distance of 3 / 4D or less from a surface of said microchannel plate on said input side into each of said plurality of channel openings, where D is a diameter of each of said plurality of channel openings, the night vision system. Claim 2 The night vision system according to claim 1, wherein said contact metal is connected to a voltage source to generate an electric field for extracting first impact electrons from each of said channel openings through respective corresponding channels. Claim 3 The night vision system according to claim 1, wherein said funnel-shaped channel openings have a diameter that decreases between a first distance away from said input side and an output side of said microchannel plate, and the diameter is constant from said first distance to a second distance up to an output side of said microchannel plate. Claim 4 The night vision system according to claim 1, wherein said channel bias angle is 5 to 16° with respect to a normal to a plane of said microchannel plate. Claim 5 The dark vision system according to claim 1, wherein the photocathode is configured to generate primary electrons that mainly collide with a second side of the channel opening and generate the first collision electrons only from the second side.

6. The dark vision system according to claim 1, wherein there is substantially no contact metal on a second side of each of the plurality of channel openings.

7. The dark vision system according to claim 1, wherein a first side of each of the plurality of channel openings is less than 1 / 2 of a circumferential distance around each of the plurality of channel openings, and a second side of each of the plurality of channel openings that is radially opposite to the first side is less than 1 / 2 of a circumferential distance around each of the plurality of channel openings.

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