Global shutter for transmission mode secondary electron multiplier with low voltage signal

Abstract

A night vision system is provided, along with a method for interrupting the continuous drawing of electrons from an image intensifier tube and an electron multiplier. The night vision system includes an electron multiplier, or possibly two electron multipliers, each including a silicon membrane. A shutter voltage is applied between a first surface and a second surface of the substantially parallel, opposing silicon membrane to interrupt the drawing of electrons through the electron multiplier and substantially interrupt the display of an image from the image intensifier tube under certain bright light conditions. Utilizing global shutter control for the electron multiplier and significantly reducing the voltage for such control reduces power consumption within the image intensifier, as well as electromagnetic interference and lag response time. A relatively low negative bias shutter voltage on only the electron multiplier selectively provides a global shutter for the image intensifier device.

Description

[Technical field]

[0001] Claiming priority This application claims priority to U.S. Patent Application No. 63 / 016,638, filed April 28, 2020, and No. 63 / 017,319, filed April 29, 2020, the disclosures of which are incorporated herein by reference in their entireties.

[0002] Example embodiments relate generally to night vision systems, and more specifically to image intensifier tubes and methods of manufacturing the same at wafer processing and photolithography scale. The image intensifier tube comprises a doped electron multiplier and an addressable electron emitter that produces multiplied secondary electrons and addressed electron emission from a rear surface of one or more transmission mode secondary electron (TMSE) image intensifiers that are shown on a display within the tube. Another exemplary embodiment relates to a night vision system that includes a power supply coupled to the image intensifier tube, and includes at least one TMSE within the image intensifier for receiving a low voltage signal that shuts off the output from the image intensifier. [Background technology]

[0003] Night vision systems, such as night vision goggles, typically include an image intensifier tube. The image intensifier tube, or "image intensifier," may include an electron multiplier disposed between a photocathode and a sensor anode. The photocathode detects infrared light in the form of photons from an object, and the image intensifier amplifies or multiplies the resulting photoelectrons, or "electrons," emitted from the photocathode. The multiplied electrons are drawn to the anode, where they can be converted back into photons displayed on a screen. Upon receiving an increased number of electrons, the anode or screen may include a sensor that senses the electrons and produces an enhanced representation of the image on the screen. The photocathode, electron multiplier, and anode are typically supported by a vacuum housing with a gap between the photocathode, electron multiplier, and sensor anode to provide gain and facilitate the flow of electrons between them.

[0004] Each of these devices within a vacuum tube can be classified as an analog image intensifier if the anode is an optical imaging device that converts electrons into photons that are displayed on a screen without converting them to digital electrical signals (binary 1s and 0s) before display. Thus, an analog image intensifier tube has an analog channel of nighttime image intensification of low intensity infrared or near infrared emissions reflected from a target or object and received by a vacuum sealed spaced apart photocathode, electron multiplier and phosphor coated anode screen, without any conversion to a binary digital electrical signal taking place during that time.

[0005] Night vision based on analog image intensifiers has been used for many years. In addition to the analog image intensifier, many night vision systems can also include a digital display to provide the user with situational awareness, symbology, and additional images of different wavelength modalities from a digital imager camera mounted on the night vision system. The additional data is provided from the digital imager camera as digital signal binary bits (binary 1 and 0 logic values) to an electronic digital display mounted on the night vision system. The electronic digital display generates an optical output image that is overlaid on the optical output image from the analog image intensifier by an optical beam combiner configured in the night vision system. The beam combiner and additional digital display consume power, increase the size / weight of the system, and add complexity to the manufacture of the night vision system.

[0006] The image from the analog image intensifier is generated normally, except that the output brightness is often increased to account for the transmission losses of the beam combiner. The beam combiner is used to combine the output optical image from the analog image intensifier with the output optical image from the digital display. The additional electronic digital display is generally fixed on one surface of the beam combiner in a manner that provides the same focal length as the output of the analog image intensifier on a separate channel of the beam combiner. If the secondary image from the electronic digital display is to be overlaid and coherently related to that displayed on the analog image intensifier screen, additional manufacturing complexity must be added to register the two images. The eyepiece of a typical night vision system must be designed to account for the additional distance of the beam combiner. The optical beam combiner adds size, weight, and manufacturing complexity to the system. The analog channel size of the analog image intensifier is large compared to the digital channel size of the digital imaging device camera, causing a mismatch and allowing only limited overlay of the image from the digital display onto the image from the analog image intensifier.

[0007] Users of night vision systems can often experience a wide range of incident light that is reflected as an optical image from a target or object. Under high (or bright) light conditions, the image intensifier can produce excessive gain that can damage the user's eyes. To mitigate this, the power supply of the night vision system may have circuitry designed to limit the maximum output brightness of the image intensifier. A common solution is to use large voltage shifts and high voltage gating to control the output light. However, these effects consume power, emit electromagnetic interference (EMI), and delay response timing.

[0008] Conventional analog image intensifiers use two voltage transformations to control the intensifier output brightness: automatic brightness control (ABC) and bright source protection (BSP). Under ABC, the control voltage of the image intensifier is reduced from its highest level (e.g., producing maximum gain) to its lowest level (e.g., producing a low level fixed gain). The lowest level cannot go to zero gain because the user must be able to see the image displayed on the analog image intensifier. The voltage swings from the highest level to the lowest level, which takes time to implement in the power supply circuitry, increasing the response timing of the image intensifier accordingly. Under BSP, the photocathode voltage, reduced to its lowest level, then begins gating between this low level and essentially off or reverse bias. This gating or switching of relatively high voltages (50-100V) is the primary source of emitted radiation or electromagnetic interference (EMI). The gating of these large voltages is the second major power drain of the image intensifier power supply. Summary of the Invention

[0009] The present disclosure provides a new and innovative night vision system that limits the gain of an image intensifier tube under relatively bright light conditions by applying a low voltage across a semiconductor gain layer, particularly a TMSE or electron multiplier semiconductor gain layer. The night vision system herein applies a small negative voltage across the semiconductor gain layer, or silicon film, in the electron multiplier. The small negative voltage substantially stops the flow of electrons reaching the electron emitting surface of the electron multiplier, effectively and efficiently providing a low voltage global shutter for the image intensifier device.

[0010] According to at least one embodiment of the present disclosure, the night vision system includes an electron multiplier having a silicon membrane. A shutter voltage between 1-2 volts, and preferably between 0.5-2.5 volts, is applied between a first surface and a substantially parallel opposing second surface of the silicon membrane. The night vision system may further include an image intensifier tube. The electron multiplier is preferably vacuum sealed within the image intensifier tube at a spaced distance between the photocathode and the anode. The electron multiplier includes a negatively biased silicon membrane.

[0011] According to another embodiment of the present disclosure, the silicon membrane includes a plurality of spaced apart doped regions extending partially between a first surface and an opposing second surface. The first surface of the silicon membrane, alternatively the electron multiplier, preferably faces towards the photocathode, and the second surface of the silicon membrane or the electron multiplier preferably faces towards the anode. The first and second surfaces comprise respective first and second metal layers dielectrically spaced apart from the first and second surfaces. The first and second metal layers are electrically coupled to terminals of a shutter voltage source to generate a positive shutter voltage value on the first metal layer and a negative shutter voltage value on the second metal layer. The second metal layer may comprise an electrically addressable electron emitter, such as a Spindt type emitter.

[0012] According to yet another embodiment of the present disclosure, an image intensifier tube is provided. The image intensifier tube, or "image intensifier", is preferably an analog image intensifier. The image intensifier includes at least one electron multiplier spaced in a vacuum between a photocathode and an anode. A positive bias first voltage is coupled between the photocathode and the electron multiplier to draw electrons from the photocathode into the electron multiplier. A negative bias shutter voltage is coupled across an opposing surface of the electron multiplier to block the continuous drawing of electrons from the electron multiplier. The shutter voltage can be selectively applied to substantially cease displaying an image from the image intensifier tube. A positive bias second voltage, preferably between 250 volts and 2000 volts (and optionally variable), is coupled between the electron multiplier and a grounded power supply.

[0013] The positive bias first voltage may comprise a negative terminal and a positive terminal of a variable first voltage source, the negative terminal of which is coupled to the photocathode. The positive terminal of the first voltage source may be coupled to the electron entrance surface of the electron multiplier. Thus, the negative bias shutter voltage comprises a positive terminal and a negative terminal of a shutter voltage source, the positive terminal of which is coupled to the electron entrance surface of the electron multiplier and the negative terminal of which is coupled to the multiplied electron emission surface of the electron multiplier.

[0014] According to yet another embodiment of the present disclosure, the positive bias third voltage may be in the range of 4150 to 4275 volts, and the third voltage source is fixed. The third voltage source is coupled between a ground power source and the anode. The positive bias first voltage may be in the range of 200 to 2000 volts. Also, the positive bias first voltage is variable. According to yet another embodiment of the present disclosure, a method of interrupting a continuous draw of electrons from an electron multiplier in an image intensifier tube is provided. The method may include applying a positive bias between a photocathode and an electron entrance surface of the electron multiplier to draw electrons into the electron multiplier. The method may also include applying a negative shutter bias between the electron entrance surface and a multiplied electron emission surface of the electron multiplier to substantially stop the draw of multiplied electrons through the electron multiplier. Applying the negative shutter bias is dependent on a change in magnitude of current in a phosphor-covered anode screen. [Brief description of the drawings]

[0015] Examples of the present disclosure are best understood from the following detailed description when read in conjunction with the accompanying drawings. According to common practice, the various features of the drawings are not drawn to scale or are shown only in partial perspective. Dimensions of the various embodiments have been arbitrarily expanded or reduced for clarity. Like numerals are used to represent like elements in the drawings. The drawings include the following features and elements, reference now being made to each of the drawings:

[0016] [Figure 1]FIG. 1 is a partial block diagram of a night vision system having a beam combiner that combines an output optical image of a digital display overlaid onto an output optical image of an analog image intensifier. [Diagram 2] 2 illustrates an example output image of a digital display overlaid on an output image of an analog image intensifier utilizing the night vision system of FIG. 1; [Diagram 3] Illustrates a digital display sensor device, or digital imaging device, and in particular an active pixel sensor device, within the back-end portion of a digital image capture device camera that produces a digital output signal to an electronic display so that the electronic display can produce an output optical image for optical overlay by the beam combiner of FIG. [Figure 4] 1 is a backside image of a microchannel plate (MCP) conventional electron multiplier, showing insufficient surface area for mounting electron emitters and control circuitry between the array of tube openings of the MCP. [Diagram 5] 1 is a backside image of a doped electron multiplier, or transmission mode secondary electron (TMSE) multiplier, before the electron emitters and control circuitry are placed between the multiplied electron emitting areas. [Figure 6] FIG. 1 is a partial block diagram of an improved night vision system that does not use a beam combiner, but instead incorporates one or more doped electron multipliers or addressable electron emitters on the rear surface of the TMSE within an analog image intensifier tube. [Figure 7] FIG. 7 is a side view of the analog image intensifier tube of FIG. [Figure 8] FIG. 1 is a diagram of the method steps used to produce an analog image intensifier tube and, if desired, a digital imaging device including electron multiplication and addressable emission. [Figure 9] FIG. 8 is a side view within region 9 of FIG. 7 showing an arrangement of electronically addressable electron emitters interlaced between multiplied electron emitting areas of the silicon membrane. [Figure 10]10 is a bottom or rear view within region 10 of FIG. 9 showing addressable pixelated electronically addressable electron emitters between the multiplied electron emission areas, and also showing an area reserved for control circuitry for receiving electrical signals from a digital imaging device to addressably activate the electron emitters. [Figure 11] FIG. 2 is a side view of an analog image intensifier tube showing the connections of the BSP, ABC, controller and variable first voltage source, variable second voltage source, fixed third voltage source, and power gate shutter voltage source. [Figure 12] 12A-12C illustrate different brightness control modes for the power supply of FIG. 11. [Figure 13] FIG. 13 is a side view of the semiconductor film of an electron multiplier having a negative bias shutter voltage source coupled through the electron multiplier. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] The following discussion is directed to various exemplary embodiments, however, those skilled in the art will appreciate that the examples disclosed herein have broad applicability, and that the discussion of any embodiment is meant to be merely an example of that embodiment, and is not intended to suggest that the scope of the disclosure, including the claims, is limited to that embodiment.

[0018] As mentioned above, the drawings are not necessarily to scale: certain features and components herein may be shown exaggerated in scale or in somewhat schematic form, and some details of conventional elements may not be shown for clarity and conciseness.

[0019] In the following discussion and claims, the terms "including" and "comprises" are used in an open-ended manner and should therefore be interpreted as meaning "including, but not limited to." Additionally, the terms "coupled" or "coupled" are 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. Furthermore, as used herein, the terms "axial" 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, outlet, or port), while the terms "radial" and "radially" generally mean perpendicular to a given axis. For example, an axial distance refers to a distance measured along or parallel to an axis, and a radial distance means a distance measured perpendicular to an axis.

[0020] 1, a partial block diagram of a night vision system 12 having a beam combiner 14 is shown. The night vision system 12 illustrates the present technique for performing optical overlay. The beam combiner 14 transmits both the output of an analog image intensifier 18 and the output from a digital electronic display 20 to a display 16. The night vision system 12 proves advantageous in that an image of an object 22 may thereby be captured by both the digital imager camera 24 and the analog image intensifier 18. Images from the object or target 22 may pass through lenses 28 and 30 and then through the respective digital imager camera 24 and analog image intensifier 18.

[0021] In some situations, digital images and analog images, which are typically associated with low-light night vision, must be captured to enhance the soldier's vision in finding and locating threats. Although the digital imaging device 24 cannot typically match the performance of the analog image intensifier tube 18 at very low light levels, the digital imaging device can be used to display to the soldier the scene in front of him, such as a direction or other symbology, scene or image object 22. In addition, the digital imaging device 24 can implement other imaging modalities, including sensitivity to different wavelengths, such as LWIR for thermal imaging of object 22, rather than the SWIR or NWIR imaging sensitivity that may occur with the analog image intensifier tube 18. The sensor in the digital imaging device 24 can pick up different wavelengths than the sensor in the analog image intensifier tube 18, or generate symbology on the overlaid scene of the combined optical image via controller 32. The image from the digital imaging device 24, or the symbology from controller 32, arrives on the digital display 20 as a digital electrical signal on bus 25. These electrical signals are converted by the beam combiner 14 into an optical signal or image that is combined with an optical image from an analog image intensifier 18 .

[0022] As shown in FIG. 1, the channel width or dimension of image capture that the digital imager 28 can accommodate is referred to as DCW. The DCW is typically smaller than the channel width or dimension of the analog channel ACW. This is evident in the output image of the composite display 16 of FIG. 1, as shown in FIG. 2. FIG. 2 illustrates the difference in DCW vs. ACW of the output image of the digital display overlaid on the output image of the analog image intensifier utilizing the night vision system of FIG. 1. For example, the digital imager camera 24 in FIG. 1 can overlay a thermal image output of a soldier 34 that cannot be detected by the low light detection of the analog image intensifier 18 output 35. Further, referring to the combination of FIG. 1 and FIG. 2, the controller 32 can transmit a plurality of electrical signals representing a symbol 36 on the digital electronic display 20. The digital display output 34, which can also include the symbol 36, can be overlaid on the analog image intensifier output 35 by the beam combiner 14.

[0023] Referring to FIG. 3, the digital imager camera or display sensor device 24 of FIG. 1 is shown. Digital sensor 24 is used in many night vision systems to allow display and viewing, recording, and other image processing, including fusion with other images, such as, for example, a forward looking infrared sensor in an analog image intensifier tube 18. Image sensing devices incorporating an array of image sensing pixels 40 are commonly used in electronic cameras. Each pixel generates an electrical output signal in response to incident light or photons. The electrical signals are often read out, typically row by row, to form an image. Digital imager camera 24 can use a charge coupled device (CCD) as a pixelated image sensor. For example, pixel array 40 can be controlled by timing and control circuitry 42, and the signals can be processed by processor 44, which can include an analog to digital converter located on each column as the signals are read out by column selection unit 46. Electrical signals corresponding to each pixel output can then be placed on bus 25.

[0024] The array of pixels 40 may be a photodiode type pixel structure. When reverse biased, incident light causes a current to flow through the photodiode, generating a photocurrent. Depending on the photodiode bias to the drain voltage, a photo-generated charge current is generated, and the charge may be amplified by a source follower transistor and a sensing unit in the analog processing portion of the analog-to-digital output structure 44. Depending on the magnitude of the sensed analog signal, a binary bit value of logic 1 or logic 0 may be created and placed on the bus 25. Digital sensor imagers 24 that incorporate an amplifier at each pixel for increased sensitivity are known as active pixel sensors. Furthermore, the digital imaging sensor 24 may be implemented either as a CCD or as a CMOS sensor with a combination of p-type and n-type transistors utilizing CMOS processing technology. Many modern digital imaging sensors use a CMOS sensor chip or die to perform photon or electron sensing. Regardless of whether a CCD or CMOS device is used by the digital sensor 24, a number of electrical signals are sent to the bus 25 representing an image or symbol to address the digital display 20 for subsequent emission of light from the corresponding pixel. When electrical signals on bus 25 forward bias the array of diodes in display 20, electrical energy is converted into light, or photons, which are then combined in beam combiner 14, causing the diodes to emit light on a pixel-by-pixel basis.

[0025] 1, analog image intensifier tubes 18 have the advantage over images produced by digital imaging devices 24 in that the tubes 18 are capable of producing high quality images over a wide range of light levels, including very low light levels such as those encountered under starlight. Night vision systems 12 utilizing analog image intensifiers 18 are fairly well known and are based on Generation III (GaAs photocathode) or Generation II (multi-alkali photocathode) image intensifying fibers, which can then be optically coupled to a CCD or CMOS sensor device to form an image intensified low light level camera.

[0026] However, the image intensifier 18 is an analog image intensifier. The analog image intensifier 18 produces an analog image on the beam combiner 14 and does not convert the image to a digital electrical signal representation. The analog image is produced directly on the eyepiece 16 without any photon-to-electrical signal conversion within the image intensifier tube itself. The image produced from the analog image intensifier 18 is not a plurality of binary 1's or 0's, as at the digital sensor 24 output. Instead, the analog image intensifier 18 produces multiplied and gained electrons that are converted to photons and displayed through a transparent fiber optic screen, for example.

[0027] The analog image intensifier 18 begins with a photocathode, such as a transmission photocathode 19. The photocathode 19 is made of glass with a faceplate coated with GaAs on the rear surface of the faceplate 19 facing the electron multiplier 21. Other type III-V materials such as GaP, GaIn, AsP, InAsP, InGaAs can be used. Alternatively, the photocathode 19 may be known as a Bi-alkali photocathode. The photoelectric effect semiconductor material of the photocathode 19 absorbs photons. The absorbed photons of the optical image that land on the faceplate of the photocathode 19 increase the carrier density of the semiconductor material, thereby generating a photocurrent of electrons 23 that are emitted from the rear surface of the photocathode 19. According to one embodiment, a semiconductor wafer may have GaAs epitaxially grown on the front surface of the wafer, and then the back surface may be thinned and bonded to a glass faceplate such that the surface on which the GaAs was epitaxially grown faces the electron multiplier 21. Alternatively, the semiconductor structure may be another type of semiconductor material other than silicon containing epitaxially grown GaAs. The alternative semiconductor structure may be GaAs itself.

[0028] The image intensifier tube 18 utilizes a photocathode 19 for the conversion of invisible light sources, such as near infrared or short wave infrared, to visible light, according to one example. In many image intensifiers, electrons emitted from the photocathode 19 are accelerated toward a phosphor-coated transparent anode, such as an electron-sensing anode 29. Electrons that strike the phosphor with high energy can generate photons in a phosphor coating 29a on the anode 29. The emitted photons are directed directly to the eyepiece by an optical device, such as a fiber optic bundle 29b. The combination of the phosphor coating and the fiber optic bundle is shown as 29a and 29b, respectively. The phosphor-coated fiber optic screen or sensor anode 29 is vacuum sealed within the analog image intensifier 18. A fiber optic taper or transfer lens within the fiber optic unit 29b transfers the amplified visual image through the beam combiner 14 to the eyepiece 16 for viewing by a user.

[0029] Existing analog image intensifiers 18 have numerous interfaces where the image is sampled, degrading the image, and adding noise to the incoming optical signal. This image degradation and reduced resolution is disadvantageous in night vision systems 12 that require high quality output. To counteract the image degradation resulting from the multiple optical interfaces in the image intensifier 18, a microchannel plate (MCP) electron multiplier 21 is often used. The MCP type electron multiplier receives the electrons 23 focused onto it by the photocathode 19, and enhances the electronic image by producing a secondary multiplication of those electrons at its output, as indicated by reference numeral 27. Although the MCP type electron multiplier 21 applies gain or amplification to the image intensifier 18, the MCP type electron multiplier maintains the geometric integrity of the incoming image, but the MCP is relatively noisy as an electronic amplifier. The added noise can degrade image quality at low light levels. Furthermore, due to the density with which each MCP channel opening must be placed close to its neighboring MCP channel openings, the rear surface of MCP 21 has very little room, as shown in FIG. 4, between openings 21a and 21b, for example, if there is no room to mount anything else on its rear surface.

[0030] Alternatively, a doped electron multiplier may be used in place of the MCP herein. The doped electron multiplier has an area on its rear surface sufficient to accommodate a Spindt-type electron emitter as well as produce the necessary multiplication and electron gain. The emission areas on the rear surface of the doped electron multiplier between those doped regions are activated to a negative electron affinity (NEA) state to promote the flow of electrons from the rear emission surface. Furthermore, in the regions between the multiplied electron emission areas of the doped electron multiplier, an array of electron emitters can be placed with the circuit actuators required to activate those emitters on a pixel basis, each of which is selected by a digital signal over bus 55 from an improved digital imaging device 54 shown in FIG. 6.

[0031] FIG. 5 shows a profile shot of the rear surface of the doped semiconductor electron multiplier 61. Since this is an example of the rear surface, the multiplied electrons are emitted from the rear surface between the doped regions 71 (shown as regions 71a, 71b, 71c, etc.), so that they may extend vertically upward from the page. FIG. 5 shows the rear surface of the doped semiconductor electron multiplier 61 before the addition of a Spindt-type electron emitter and gating circuitry, which are printed and diffused onto the rear surface, as described in more detail in FIG. 9. FIG. 5 is presented to show the sufficient area on the rear surface required to add electron emitters and control circuitry that is not available on the rear surface of the MCP-type electron multiplier 21. Thus, this embodiment utilizes a doped semiconductor electron multiplier rather than an MCP-type electron multiplier between the photocathode and the sensor anode of an image intensifier tube forming an analog image intensifier, and as described below, part of the digital imaging device 54.

[0032] Referring now to FIG. 6, an improved night vision system 52 is shown in block diagram form. The improved night vision system 52 according to the present disclosure does not utilize a beam combiner 14 or a digital electronic display 20 as described in the night vision system 12 of FIG. 1. The night vision system 52 still combines an addressable display in an analog image intensifier 58 onto an eyepiece 56. Instead of using a beam combiner to combine or overlay an image derived from a digital display with an image derived from an analog image intensifier 58, an electrical signal from a digital imager 54 is sent over an electrical bus 55 onto at least one, and preferably two, electron multipliers 61a and 61b. Any symbology from the controller 62 is also represented as binary bits and sent over the bus 55 as ones and zeros to the primary electron multiplier 61a and secondary electron multiplier 61b, respectively.

[0033] The image intensifier 58 of FIG. 6 includes a photocathode 59 with a GaAs semiconductor die, or epitaxially grown GaAs on a silicon die, bonded to a glass faceplate at its rear surface, shown as reference numeral 63. On the rear surface of the primary electron multiplier 61a is a semiconductor die with an array of electron emitters, shown as reference numeral 64a. On the rear surface of the secondary electron multiplier 61b is an array of electron emitters also formed on the semiconductor die, shown as reference numeral 64b. Conductive traces of the electrical bus 55 are connected to printed conductors that are routed through gating logic to the arrays of electron emitters 64a and 64b. The arrays of electron emitters in the primary electron multiplier 61a and secondary electron multiplier 61b are identical to each other, have the same spacing, and are aligned with each other.

[0034] On the front surface of the primary electron emitter 61a and the secondary electron emitter 61b are optically transparent glass plates 65a and 65b. As referred to herein, the front surface is the surface facing towards the photocathode 59, and the rear surface is the surface facing towards the sensor anode 69. The anode 69 may include a front surface of a transparent glass spacer die 69a and a rear region of a fiber optic bundle or lens 69b. The transparent glass spacer die 69a may be coated with phosphor to direct the phosphor-converted photons towards the eyepiece 56. The primary electron multiplier 61a multiplies electrons using doped semiconductor regions and transmits the multiplied electrons from a number of pixelated electron emitting regions to corresponding pixelated emitting regions in the secondary electron multiplier 61b, where the electrons are further multiplied to provide multiple electron gain and amplification on the phosphor screen of the sensor anode 69.

[0035] The electron emitters are also arranged on the rear surface of the primary electron multiplier 61a and the secondary electron multiplier 61b such that each electron emitter is adjacent to a corresponding electron emitting area. In this way, the electrons emitted from each emitter can be electrically addressed by the control circuitry corresponding to that emitter. The control circuitry is activated with a digital number corresponding to a set of binary 1's and 0's transmitted on the bus 55. The digital number can be converted to a corresponding analog value by a control circuitry having a digital-to-analog converter (DAC), and the analog voltage is applied to the pixel control gate. Within the digital imaging device 54, there is preferably another (second) analog image intensifier tube 58b. The image intensifier tube 58b is preferably identical to the image intensifier 58. Behind the image intensifier 58b is a digital sensor 56b, mounted on or separate from the rear surface of the image intensifier tube 58b. The digital sensor 56b comprises a plurality of active or passive pixel sensor devices arranged in an array that operate as optical pixels with CMOS circuitry that converts photons emitted from the image intensifier 58b into an electrical signal, similar to the pixel array 40 shown in Figure 3. The digital sensor 56b may be a CMOS imager used as an active pixel sensor device or a passive pixel device. The digital sensor 56b may be a CMOS imager chip or may be a die with an integrated amplifier as an active pixel sensor device incorporating both a photodiode and a readout amplifier.

[0036] Since the image intensifier tubes 58 and 58b are the same and have the same chip or die size, the improved night vision system 52 of FIG. 6 has a digital channel dimension or width DCW that matches the analog channel dimension or width ACW. Thus, the channel opening to the digital imaging device 54 is equal to the channel opening to the analog image intensifier 58. The observer will see the digitally derived image overlaid over the entire field of view of the analog derived image as the observer sees when looking at the object 53. Referring back to FIG. 2, the DCW may extend outward to be equal to the field of view of the ACW. However, the image seen by the DCW may be at a different wavelength or may include different image modalities and symbols that may not be visible by the ACW field of view seen by the user. Widening the field of view of the DCW corresponding to the ACW not only provides a more robust viewing experience, but also provides more information in different image modalities and symbology for a safer viewing experience. For example, the LWIR modality detectable by the digital imaging device 54 is displayed across the entire field of view (both height and width) of the analog image intensifier tube 58, not just a small portion of it.

[0037] The improved night vision system 52 of FIG. 6 thereby eliminates weight and enhances overall system transmission efficiency over conventional designs. The spatial and physical requirements of current MCP-type electron multipliers are also not suitable for incorporating data from external sources into conventional beam combiner-integrated displays. Current night vision system 52 uses wafer-scale photolithography and the physics of electron bombardment gain and negative electron affinity (NEA) in the emission areas between doped regions of the silicon surface. Night vision system 52 advances the performance of analog night vision with associated power reduction in both signal-to-noise ratio and modulation transfer function (MTF). The added functionality of incorporating external digital signals and binary 1 and 0 information can be achieved with not only one, but more than one electron multiplier. An advantage is the electrical signal transmitted to the electron emitter on the back surface of the electron multiplier. The digital electrical signal on bus 55 is preferably transmitted to the electron multiplier instead of, for example, the back surface of the photocathode. One advantage is that the emission from the electron emitter on the primary electron multiplier is further amplified or multiplied downstream on the secondary electron multiplier. The emission surface from the two rear surfaces is also identical across each array and positioned with both rear surfaces. The emission surface from the two rear surfaces is also identical across each array and positioned with both rear surfaces. When the emitter is placed on the rear surface of the photocathode, the GaAs or other III-V material of the photocathode rear side is not a semiconductor, photolithographically defined silicon surface. Silicon micromachining is more easily accomplished compared to any micromachining on a GaAs surface. Furthermore, the GaAs rear surface of the photocathode is too sensitive to residual gases in the vacuum than silicon. Therefore, it is desirable to minimize any current emitted from the GaAs photocathode rear side, since the emitted electrons tend to ionize the residual gases. The ionized gas has an opposite charge compared to the electrons, which results in the electrons being pulled back to the photocathode rear side by the internal electric field. Any back scattering of ions into the GaAs of the photocathode tends to poison the surface, thereby reducing its NEA capabilities.Therefore, for the reasons stated above, as well as others, it is much more desirable to incorporate an external digital signal on the electron multiplier rather than on the photocathode.

[0038] The improved night vision system 52 not only incorporates an external electrical digital signal to each electron emitter, but also allows the electron emitter at each pixel to utilize the existing phosphor 69a for integral light generation. The digitally injected image can be properly overlaid on the intensified scene within the vacuum envelope of the image intensifier tube 58. The improved night vision system 52 incorporates a second image intensifier tube 58b on the digital imaging device 54 to improve its performance. The digital imaging device 54 of the present invention can match the low illumination light level performance or time response of the image intensifier tube and display more information to the user than just the scene in front of the user. This information can include orientation (e.g., symbols) or other imaging modalities and image wavelengths on the analog image intensifier 58. The existing optically transparent screen 69b of the image intensifier tube 58 can be used to display digital data from other sensors, such as sensor 56b, or other digital symbols of binary 1's and 0's from the controller 62. The digital imaging device of improved night vision system 52 also incorporates a wider, larger display area to incorporate symbols and other information in the full field of view provided by analog image intensifier tube 58. The primary reason for the wider display is that digital imaging device 54 incorporates analog image intensifier tubes 58b similar to analog image intensifier tubes 58, each of the same chip or die size. Additionally, the photon-to-electron conversion to tube 58b matches that of tube 58, with each tube having one electron multiplier and preferably two electron multipliers for added low illumination performance.

[0039] Referring now to FIG. 7, there is shown a side view of the analog image intensifier tube 58 or 58b of FIG. 6. Because tube 58b is identical to tube 58, the reference numbers of tube 58 are also applicable to the reference numbers of tube 58b, and those reference numbers are taken from FIG. 6 illustrating tube 58. However, it is important to note that the same items in the analog image intensifier tube 58 are also in the analog image intensifier 58b in the digital imaging device 54 of FIG. 6. Referring again to FIG. 7, the photocathode in the analog image intensifier tube 58 / 58b comprises a faceplate 59 having one surface oriented toward the object being imaged and an opposing surface having GaAs material thereon. The GaAs material may be in the form of epitaxially grown GaAs material or may be a GaAs semiconductor body. As mentioned above, other III-V materials may be used for item 63 on the rear surface of faceplate 59. A sealing member 70a may be disposed between the GaAs material 63 and the glass spacer 65a. A getter material 72a may be disposed on the spacer 65a and adjacent to the sealing member 70a. The sealing member 70a may be deposited using various semiconductor processing techniques or via electroless plating, electrochemical deposition, or various combinations thereof. The sealing member 70a, as well as the sealing members 70b and 70c, may be made from one or more layers of a metallic material such as copper, gold, lead, tin, aluminum, platinum, or other suitable material or combination of materials that can provide a good wetting surface for solder, as shown in FIG.

[0040] Referring to another embodiment, the sealing members 70a, 70b, and 70c may be made of non-metallic materials such as glass, frit, ceramic, or other combinations of non-metallic substances. The sealing mechanism is implemented by compression, thermal compression, or other techniques to seal the vacuum gaps 74a, 74b, and 74c against the entry or exit of any substance or molecule. The vacuum gaps 74a, 74b, and 74c are created by hermetically sealing the spaced distance between the photocathode 59a and the sensor anode 69 through the sealing member compression electron multipliers 61a and 61b. The photocathode 59a includes a faceplate 59 and a rear coating material 63, while the sensor anode 69 includes a phosphor material 69a on the front surface of the fiber optic screen 69b.

[0041] The vacuum sealed cavities or gaps 74a, 74b and 74c can contain getter materials 72a, 72b and 72c within their internal cavities. The getter material 72 is used to maintain a target vacuum level within those cavities. Due to the use of sealing members to hermetically seal the electron multipliers 61a and 61b between the photocathode 59a and the anode 69 within the vacuum housing, a single vacuum pump structure may suffer from high leakage rates. The getter material 72 is applied as a coating to the surfaces adjacent the spacer members 65a, 65b and 69a. When activated through an evacuation process and / or combined with thermal energy, the getter material 72 can remove gas to maintain the vacuum level within the spaced gaps or cavities 74. The removal or maintenance of the vacuum is described herein as "getter pump or getter pumping." The getter material within the vacuum continually removes residual gas as it is produced, often achieving a higher vacuum than the pump alone could achieve during the sealing process.

[0042] The digital sensor 56b is spaced apart from or coupled to the rear side of the analog image intensifier tube 58b. The digital imaging device 54, and specifically the CMOS digital sensor 56a, transmits electrical signals corresponding to the optical readings on the pixel array to the rear surfaces 64a and 64b of the corresponding primary and secondary electron multipliers 61a and 61b. The electrical signals are transmitted to addressable electron spint emitters on the rear surfaces 64a and 64b. The electron emitters may be conductive protrusions 78 printed as an array of protrusions using conventional semiconductor photolithography and deposition techniques across the rear surface. Surrounded by and coupled to each protrusion 78 is an operating circuit coupled to the bus 25 to receive the corresponding electrical signal. Depending on whether the logic value is a binary 1 or a binary 0, the emitter protrusions 78 may emit electrons. Each electron emitter 78 emits electrons from a rear surface of the electron multiplier 61 a or 61 b ​​between a pair of spaced apart emitting surfaces where the multiplied electrons are emitted towards the sensor anode 69 .

[0043] The analog image intensifier tubes 58 and 58b may be formed simultaneously from a series of bonded and spaced apart sealing wafers. The wafers consist of a glass spacer wafer bonded to a suitable processed silicon wafer, with sealing and getter members spaced between the bonded wafers near the screed lines. A sealing member 70 is constructed around each individual die or chip, such that when sealed, the die or chip has a primary electron multiplier 61a and a secondary electron multiplier 61b between the photocathode 59a and anode 69, vacuum sealed to each other.

[0044] Since the primary electron multiplier 61a comprises a scribed semiconductor wafer die 64a that is identical to the scribed semiconductor wafer 64b of the secondary electron multiplier 61b, each electron emitter 78 of one electron multiplier 61b is aligned with a corresponding electron emitter 78 of the other electron multiplier 61a. More specifically, there are multiple emitter axes 82 extending through the central portion of each emitter protrusion 78, and the center of the emitter protrusion 78 in the primary electron emitter 61a is aligned along the same axis as the center of the emitter protrusion 78 in the secondary electron multiplier 61b. The emitter axes 82 are shown parallel to and spaced apart from the emission axis 84. The emission axis indicates the alignment between the multiplied electron emission areas of the primary electron multiplier 61a and the secondary electron multiplier 61b. Of course, the number of emitter axes 82 corresponds to the number of pairs of electron emitters in each of the primary electron multiplier 61a and the secondary electron multiplier 61b. The emitter tip of the emitter projection 78 extends through the axis and is centered about the axis 82 .

[0045] The emission axis 84 is parallel to and spaced apart from the corresponding emitter axis 82. The combination of the emitter axis 82 and the emission axis 84 comprises the path along which electrons are emitted as a single pixel for display. By forming the image intensifier through vacuum spaced bonding of the processed silicon wafer to the corresponding glass spacer wafer and then separating the vacuum sealed die or chip, the electron emission surfaces of the corresponding pixels are aligned along the axis 84 and the electron emitter projection surfaces are aligned along the axis 82, so that no resolution shift or blurring occurs at the pixel level. The DCW and ACW are limited to the same size and product only at the photolithography scale, which is much smaller than the format normally used in conventional beam combiners, and the ACW needs to be 18 mm or more in height and width. Furthermore, the present image intensifier 58 or 58b generates gain on the electron multipliers 61a and 61b, incorporating electronically addressed displays on these multipliers. Each electron multiplier 61a and 61b is identical and uses a negative electron affinity membrane instead of the conventional MCP used in most current image intensifiers. The electron multiplier devices are based on MEMS processing and wafer-scale technology, as further illustrated in FIG.

[0046] Referring now to FIG. 8, a total of eight wafers are used to fabricate the image intensifier tube. The eight wafers include a spacer wafer 65a bonded to a processed silicon wafer 64a to form a primary electron multiplier wafer 61a. A spacer wafer 65b is bonded to a processed silicon wafer 64b to form a secondary electron multiplier wafer 61b. A spacer wafer 69a is bonded to a fiber optic wafer 69b to form a sensor anode wafer 69, and a GaAs wafer 63 is bonded to a faceplate wafer 59 to form a photocathode wafer 59a. A phosphor 88 can be applied to either the spacer wafer 69a or the fiber optic wafer 69b of the sensor anode 69. A getter material 72 and a sealing member 70 are applied to the spacer wafers 65a, 65b and 69a.

[0047] According to a preferred embodiment, the overall thickness of the bonded spacer and processed silicon wafers, including the faceplate and fiber optic wafers of the photocathode and anode 59a and 69, is significantly thinner than conventional image intensifiers. Preferably, the faceplate 59 is 50-80 mils thick. The bonded primary electron multiplier wafer 61a is 3-4 mils thick, and the secondary electron multiplier wafer 61b is also 3-4 mils thick. The bonded fiber optic screen and spacer wafer 69a, including the phosphor coating 88 used to form the sensor anode 69, is preferably less than 80 mils thick. The faceplate can be thinned from a conventional faceplate, and the various spacers can also be thinned if sufficient structural integrity remains. Each of the semiconductor wafers can have its rear surface thinned before bonding to the corresponding spacer wafer. The spacer wafer is optically clear glass and provides a vacuum cavity that holds the getter and encapsulation materials. Once sealed, the gap between the photocathode and the primary electron multiplier, and the gap between the primary and secondary electron multipliers, is preferably less than 10 mils. The gap between the secondary electron multipliers is preferably less than 15 mils. The glass spacer wafer 69a is thermal expansion matched to the fiber optic wafer 59b, and as with all spacer wafers 65a and 65b, getters and sealing materials are then applied to the cavity. Atomic layer deposited (ALD) thin film phosphor 88 is applied to the spacer wafer 69a or fiber optic wafer 69b to provide the best imaging quality.

[0048] Once all the wafers are bonded with the sealing member surrounding each individual die, as shown in step 90, the sealed wafers are placed on vacuum posts and the full thickness of the vacuum sealed wafer combination is diced in step 92. After dicing, the individual dies are removed, as shown in step 94. The combination of the faceplate wafer, the primary and secondary electron multiplier wafers, and the sensor anode wafer are diced along the sealing member that is located along the lines sawed or scribed between the faceplate wafer, the primary and secondary electron multipliers, and the sensor anode wafer, forming a vacuum sealed cavity therebetween. Thus, the processed components on each of the sealed wafers are aligned with each other, and the emission and emitter axes of the primary and secondary electron multipliers are also photolithographically aligned. For example, one resulting die 94 can be sent to an analog imaging channel, specifically the image intensifier 58, and the other die 94 can be bonded into the digital imaging device 54 as a second image intensifier 58b. As shown, the bonded image intensifier tube 58b may further be molded into a packaging material having leads extending therefrom. The analog image intensifier tube 58 is coupled into the analog intensifier channel of the night vision system 52, while the packaged image intensifier 58b in the digital imaging device 54 is electrically coupled to these sockets with the printed bus 25 extending towards and coupled to the electron emitters 78 on both the primary electron multiplier 61a and the secondary electron multiplier 61b.

[0049] Referring now to FIG. 9, a detailed view along region 9 of FIG. 7 is shown. FIG. 9 shows an arrangement of electrically addressable electron emitters 78 extending from a rear surface of a processed silicon semiconductor die 64b. The processed silicon semiconductor die 64b multiplies electrons 93 entering an electron multiplier to present a plurality of electrons 95 obtained therefrom. The processed silicon semiconductor die 64b includes a doped region 97 that is doped from the rear surface toward the front surface, but the doped region does not extend all the way to the front surface. An additional doped region 99 is also formed. The doped region 99 is doped with boron or aluminum to constitute a p-type doped material. The doped region 99 is densely doped relative to the doped region 97, which is also doped with a p-type doping material. The multiplied electrons 95 are emitted from an emission region 102, which is activated to a negative electron affinity state to facilitate the flow of electrons from the emission region 102. Shown between the emission regions 102 are the emitters 78 and in particular the Spindt emitter tips extending as protrusions 78 from the rear surface. The protrusions are conductive and are coupled to a gating circuit 104. The gating circuit includes various actuators that receive electrical signals on bus 55 (FIG. 6) to turn corresponding emitters on or off.

[0050] The gating circuitry 104 may include printed conductors and may be deposited with multiple conductive regions disposed on a dielectric such as oxide 106 to separate the conductive members 104 from the doped regions 97. The conductive material may reduce electron backscattering and reduce any dark current by the percentage of the area blocked by the deposited metallic material. There are etched recesses on the front surface of the processed silicon substrate die 64b that may help channel the electron beam to the appropriate pixel area directly above the electron emitting surface 102. The texture of the front surface may help reduce halo and improve gain at low incident electron energies.

[0051] Each projection 78 at the emitter tip allows addressable electrons to be emitted next to the emitting area on a pixel basis, thereby forming an image independent of the intensified image. The processed silicon semiconductor die 64b, or silicon film, is lightly p-type doped in region 97 relative to region 99. The resulting product shows a 40-fold reduction in halo intensity and a 2-fold reduction in size, with the entire device having nearly zero halo. The electron receiving surface that receives the electrons 93 is more heavily p-type doped to push the electrons towards the emitting surface on the opposite (back) side of the device. When the electrons strike the front surface, they dissipate their energy by impact ionization, generating additional electrons. The noise factor of this amplification is about 1.12, much lower than the noise factor of the MCP, which ranges from 1.4 to 1.7. The result is an increase in the signal-to-noise ratio of 45, compared to 36 for the MCP-type intensifier. The resulting electrons diffuse towards the emitting surface. Without a fixed p-type doping profile in place, the electrons diffuse laterally as they move towards the emitting surface 102. This is to actively receive electrons 93 on one side, capture them, then diffuse them to the opposing surface 102 and re-emit them, giving the device the name Transmission Mode Secondary Electron (TMSE) intensifier. The doping profile directs the electrons to a smaller emitting surface. In MCP-based intensifiers, the input and output holes are about the same size, so the electrons are not focused. In TMSE devices, the receiving area is larger than the emitting area. This improves the modulation transfer function, or image fidelity. In MCP intensifiers, the largest loss in the modulation transfer function is the radial energy that the electrons retain as they leave the back of the MCP. This radial energy, or mean travel energy, allows the electrons to diffuse into the vacuum gap between the components. The negative electron-affinity surfaces of GaAs photocathode and silicon gain wafers have an MTE an order of magnitude smaller than MCPs.These features, small emission area, doping profile, low MTE, and front surface texture improve the MTF across all spatial frequencies, resulting in a device with a resolution of 90 (lp / mm) compared to MCP-based intensifiers with a resolution of 64-81 (lp / mm). The actual TMSE electron multiplier device has two silicon gain layers as both the primary and secondary electron multipliers to produce the same gain as the MCP-based intensifier. The improved MTF allows a 14mm die size electron multiplier to have the same range recognition as the current 18mm MCP-based image intensifier. Thus, the night vision system size can be reduced by reducing the image intensifier channels ACW and DCW, and the associated optics.

[0052] Screen resolution is important for both image intensifier channels and embedded screens. The radius that electrons travel from the initial emission spot of emission region 102 is determined by the average transverse energy of the emitted electrons. This is the amount of energy that is oriented parallel to the surface. The radius is given by:

number

[0053] As shown in Table 1 above, the spot radius of the electron emitter's electric field is on the order of the spots from negative electron affinity GaAs and silicon. The electronically addressable screen has approximately the same resolution as the image intensifier. With each intensifier pixel capable of containing an addressable field emission electron emitter array, the pixel count can also be the same. The intended pixel size of the intensifier is 6 microns, with a format of 14 mm horizontal and vertical. Thus, the array size is 5.4 megapixels. This exceeds most display requirements currently specified by military systems. Thus, the derived geometry is a monochrome display with the same colors as a normal image intensifier.

[0054] Referring now to FIG. 10, a bottom rear view within region 10 of FIG. 9 is shown. Specifically, FIG. 10 shows a multiplied electron emission area 102 spaced between a pair of electron emitters 78. The area around the emission area 102 is reserved for control circuitry 104 used to activate adjacent electron emitters 78 on a pixel-by-pixel basis. It will be appreciated that FIG. 10 shows only a portion of the rear surface of secondary electron multiplier 64b. It will also be appreciated that the rear surface of primary electron multiplier 64a is identical to the rear surface of secondary electron multiplier 64b. In this manner, a first plurality of spaced apart emission surfaces 102 on the rear surface of primary electron multiplier 64a are aligned with, and along the same emission axis as, a corresponding second plurality of spaced apart emission surfaces 102 on the rear surface of secondary electron multiplier 64b. The first plurality of spaced apart emission surfaces 102 are interlaced with the first plurality of spaced apart electron emitters 78. The second plurality of spaced apart emitting surfaces 102 are interlaced with the second plurality of spaced apart electron emitters 78. Each of the first plurality of spaced apart emitting surfaces are parallel to one another and aligned with a respective one of the second plurality of spaced apart emitting surfaces along a plurality of emission axes parallel to the inner wall of the vacuum housing. Additionally, the plurality of emitter axes are parallel to and interlaced with the plurality of emitter axes.

[0055] Creating a color display that includes red, green, and blue (RGB) pixels in a spatial arrangement reduces the resolution of both the image intensifier and the electronically addressable display built onto the rear surface of the electron multiplier. A color display can be created by dividing a fixed period in time, utilizing a white phosphor screen, and adding an external set of electronically adjustable color filters. For example, during a 1 / 30 second period, divided into unequal parts, any pixels that are red are addressed first, then those that are green are addressed and activated second, and finally, on the third time slice, the blue field emission points are activated and the blue filters are activated.

[0056] 11, an analog image intensifier 58 or 58b is provided depending on where the image intensifier is located. As mentioned above, the image intensifier includes a photocathode 59a spaced from the electron entrance surface 110a of the electron multiplier 61a. The anode 69 is spaced from the electron emission surface 110b of the electron multiplier 61a. The electron multiplier 61a includes a silicon membrane 64a, which may be referred to interchangeably. The silicon membrane 61a mentioned above is a doped semiconductor die. Although the terms are often interchanged, the electron multiplier 61a technically includes a silicon membrane 64a facing towards the anode 69, and a glass plate 65a bonded to the silicon membrane 64a. The electron entrance surface 110a for the glass plate 65 is as shown. However, the electron entrance surface of the silicon membrane or electron multiplier portion of the electron multiplier 61a is referred to as 110a'. Along with the electron multiplier 61 a , the image intensifier 58 , 58 b also shows a secondary electron multiplier 61 b ​​having a membrane 64 b , an electron incident surface 110 a ″, and an electron multiplier face facing the anode 69 .

[0057] FIG. 11 illustrates a power supply 120 coupled for use with the analog image intensifiers 58, 58b. The power supply 120 includes three primary voltage sources and a shutter voltage source. The three primary voltage sources are referred to as a first, second, and third voltage source (V1, V2, and V3, respectively). The first, second, and third voltage sources are coupled in series. According to one embodiment, the positive terminal of the third voltage source V3 is to a photoelectron detector, or current detector 122. The current detector 122 detects the intensity or amount of electrons flowing to the anode 69, and in particular the phosphor coating 69a of the screen 69b. The third voltage source V3 is fixed and applies a positive bias voltage between the phosphor coated anode 69 and a grounded power supply of 4150 to 4275 volts. The positive terminal of the second voltage source V2 is coupled to the ground supply, and the negative terminal of the second voltage source V2 is coupled to the positive terminal of the first voltage source V1 and to the positive terminal of the shutter voltage source VS. The shutter voltage source is switchably coupled to the metal layers of the first and second surfaces of the electron multiplier 61a and is negatively biased across the electron multiplier 61a. In particular, the shutter voltage VS is switchably coupled across the semiconductor film 64a of the electron multiplier 61a, the metal layer extending across the output surface, in particular a portion of the second surface of the semiconductor film of the electron multiplier 61a. The second surface is indicated as reference numeral 110b.

[0058] The negative terminal of the second voltage source V2 is coupled to a metal layer extending over at least a portion of the first surface 110a' of the membrane 64a. The surface 110a' is thus the first surface of the silicon membrane 64a, or an electron multiplier having a silicon membrane, and the second surface 110b faces the first surface 110a' and is substantially parallel to the first surface 110a'. The second surface 110b is an electron emission surface, in particular an emission surface for the electron multiplier from which the multiplied electrons are emitted towards the anode 69. The first surface 110a' is spaced apart by a dielectric over at least a portion of the first surface 110a' and comprises a first metal layer facing towards the photocathode 59a. The second surface 110b comprises a second metal layer spaced apart via the second surface 110b and faces the secondary electron multiplier 61b or, if the secondary electrons are removed, faces the anode 69. The first and second metal layers are spaced apart by a dielectric through respective portions of the first and second surfaces, which may be shown in FIG.

[0059] Referring again to the power supply 120, the voltage applied to the second voltage source V2, and the voltage between the entrance surface of the electron multiplier semiconductor membrane 64a and ground, is positively biased and is further variable between 250 and 2000 volts. The negative terminal of the first voltage source V1 is coupled to the photocathode 59a. The voltage across the first voltage source V1 can range from 200 volts to 2000 volts.

[0060] The power supply 120 may also include different modes for bright light source protection and automatic brightness control. A conventional BSP circuit may include passive components such as capacitors and resistors that are used to measure any voltage drop caused by the photocathode current flowing, for example, to reduce the voltage applied to the photocathode by V1. However, most current power supplies, including the power supply 120, combine both BSP and ABC into an operating mode, and call those modes output by the controller 124 the ABC controller 124, but the bright light source protection is included in the operating mode. However, the improved power supply 120 shown has an operating mode of voltage shutter control of the shutter voltage source VS. By reading the amount of photocurrent on the detector 122 coupled to the phosphor-coated anode 69, the controller 124 can read the amount of voltage from the first voltage source V1 and the second voltage source V2. According to the improved shutter voltage control, the controller 124 can also switch on the shutter voltage source VS.

[0061] Referring to FIG. 12, different operating modes of the controller 124 of the power supply 120 are shown. During normal operation, when no brightness control is required (mode 0), the first voltage source V1 and the second voltage source V2 operate at a maximum positive bias amount near 2000 volts. As I3 of the current detector 122 increases (mode 1), the amount of voltage from the second voltage source V2 decreases from 2000 volts. As I3 increases further (mode 2), the V2 bias decreases to approximately a minimum, i.e., 250 volts, and the V1 bias begins to decrease from 2000 volts. V1 can be gated off until I3 does not increase to a harmful level associated with an excessively bright light source from an object that reduces both V1 and V2 to a minimum. By reducing or eliminating the first and second voltage sources, and therefore their positive bias, electrons are substantially eliminated from being generated from the photocathode 59a and from reaching the anode 69.

[0062] Modes 0-3, shown above the dashed line in FIG. 12, do not gating the shutter voltage Vs at all. Gating occurs at a relatively large supply of V1, swinging from approximately 2000 volts to 250 volts. The relatively high voltage switching on V1 is a major source of emission radiation. Such radiation can extend into the photoelectron path and cause significant noise to the received and displayed images. Thus, FIG. 12 shows below the dashed line what happens when relatively small Vs switching, or gating, occurs instead of the larger V2 switching.

[0063] In mode 3, substantial brightness is detected via I3, and if VS is present, V1 and V2 can be minimized towards 200 volts without gating them off. More importantly, a relatively small shutter voltage VS between 0.5 and 2.5 volts can be gated across the electron multiplier 61a, and particularly across the membrane 64a of the electron multiplier (FIG. 11). Thus, in instances where brightness control is required, only switching occurs by applying a relatively small negative bias voltage of 0.5 to 2.5 volts, for example, rather than causing a much larger switching of the positive bias voltage of V1. Application of a relatively small negative bias mitigates the electronic gain in the electron multiplier 61a. Gating a fairly small VS output that is reverse biased compared to V1 or V2 is necessary to minimize the V1 and V2 outputs, but not gate them off, to avoid excessive output brightness from the phosphor screen of the anode 69 in some medium to high light conditions. V1 only needs to be gated off if I3 is in excess and large enough to harm the phosphor covered anode (mode 4). However, that situation rarely occurs, so all bright light source control and shutting it off can occur simply by turning on or off small voltage swings on VS. Of course, the switching across the electron multiplier 61a shown in the configuration of Figure 11 is just one example of one way to apply the shutter voltage VS.

[0064] The global shutter mechanism for electron multiplier 61a allows the amount of photoelectron current passing through electron multiplier 61a to be adjusted solely by a shutter voltage Vs of 0.5 to 2.5 volts. The applied Vs ranges from 0.5 to 2.5 volts when applied, and is reverse biased compared to V1 and V2. V1 and V2 can vary; however, V3 is fixed within the range of 4150 to 4275. The shutter voltage V S is a negative voltage. In other words, the shutter voltage is a negatively biased shutter voltage opposite to the first voltage V1, the second voltage V2, and the third voltage V3. By applying a negative bias voltage between the first and second surfaces, the flow of electrons can essentially stop from reaching the intensified emission surface 110b such that the image displayed on the image intensifier tube 58 / 58b is interrupted during moments when the night vision system experiences relatively high or bright light conditions.

[0065] According to a preferred example, the shutter voltage source VS applied during mode 3 may be used in place of the conventional BSP and ABC circuits. Thus, by eliminating the BSP and ABC, the relatively large voltage swings on the gating circuitry may be advantageously eliminated. If bright light conditions do not damage the photocathode 59a, the BSP protection is not required and all necessary protection may occur only in the electron multiplier utilizing the shutter voltage when restoring the amount of light. Furthermore, since the shutter voltage protection occurs before the electrons reach the anode 69, no further protection is required before the electrons impact the phosphor-coated anode 69. Thus, the conventional BSP and ABC controller mechanisms may be completely eliminated in favor of the global shutter control herein. Based on the detected photocurrent I3, the shutter voltage VS may be connected or disconnected. When normal light conditions occur, the high gain generated by the first voltage source V1 and the second voltage source V2 is utilized to achieve proper multiplied secondary electron emission. However, when high light conditions occur, the first positive bias voltage source V1 and the second positive bias voltage source V2 can be minimized and the negative bias shutter voltage VS is all that is applied across the first surface 110a' and the second surface 110b.

[0066] 13 shows the doped silicon membrane 64a of the electron multiplier 61a in more detail. FIG. 13 also shows various connections to the first surface 110a′ and corresponding first metal layer 112a, which extend partially across the first surface 110a′ and are dielectrically spaced from the silicon body by, for example, a silicon dioxide layer 114a. The first surface 110a′ may include a p-type dopant diffused into the first surface 110a′ at a concentration level higher than the p-type dopant concentration in region 97, as described above in FIG.

[0067] The second surface 110b also has a rear surface, or second metal layer 112b, dielectrically spaced above the second surface 110b. The oxide reference numerals associated with the oxide region between the second surface 110b and the second metal layer 112b are not shown in Figure 13, but are identified, for example, in Figure 9 as reference item 106.

[0068] The first metal layer 112a carries the electrons arriving on the entrance surface 110a' and helps to block backscattering or minimize halo problems. The same happens with the second metal layer 112b. The second metal layer 112b may also include emitters as part of its printed second metal layer 112b, such emitters being shown, for example, as reference numeral 78 in FIG. 9. The second metal layer 112b may also include gating circuits 104 for activating those emitters. Alternatively, emitters and gating circuits need not be used according to the embodiment of FIG. 13. Instead, the second metal layer 112b may simply be a printed metal layer dielectrically spaced from and adjacent to the doped regions 97 over a portion of the second surface between the multiplied emission regions.

[0069] According to one embodiment, the silicon membrane 64a of the electron multiplier 61a receives a shutter voltage VS between the first surface 110a' and the second surface 110b. The shutter voltage is a negative bias shutter voltage, whereby the positive terminal of the shutter voltage VS is coupled to the electron incident surface 110a' and the negative terminal of the shutter voltage VS is coupled to the multiplied electron emitting surface 110b via a switch or gate S1. The shutter voltage VS is applied when bright light mitigation is required. When the shutter voltage is applied, the negative bias of the shutter voltage can prevent the photoelectrons from moving to the emitting surface, as indicated by reference numeral 116. According to one embodiment, the gate S1 is coupled between the negative terminal of the VS and the multiplied electron emitting surface. Alternatively, the gate S1 can be coupled between the positive terminal of the VS and the electron incident surface. According to one example, the photocurrent detector used to control the controller 124 can be coupled to any other components of the electron multiplier 58, 58b, provided that the bright light source current state is read. For example, the photocurrent can be read from the photodiode 59a to control the switch S1, and also the amount of variable voltage control required for the positive bias first voltage V1 and the positive bias second voltage V2 can be read.

[0070] It is important to note that the configurations and arrangements of the various exemplary embodiments are illustrative only. While only a few embodiments are described in detail in this disclosure, those skilled in the art who review this disclosure will readily appreciate that many modifications (e.g., variations in size, dimensions, structure, shape and proportions of the various elements, parameter values, mounting arrangements, use of materials, colors, orientations, 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 constructed from multiple parts or elements, the positions of elements may be reversed or otherwise changed, and the nature or number of discrete elements or positions may be altered or changed. The order or sequence of any process or method steps may be altered or resequenced according to alternative embodiments. Additionally, features of certain embodiments may be combined with features of other embodiments as will be understood by those skilled in the art. Other substitutions, modifications, changes, and omissions may be made in the design, operating conditions, and arrangements of the various exemplary embodiments without departing from the scope of the invention.

[0071] As used herein, the terms "about," "approximately," "substantially," "generally," and the like mean plus or minus 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 indicates 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" used in the context of "X and / or Y" should be interpreted as "X" or "Y" or "X and Y."

[0072] The illustrated embodiments described in the detailed description, drawings, and claims are not intended 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 herein. Furthermore, certain aspects of each embodiment can be used in conjunction with other embodiments of the disclosure, and thus, embodiments of the disclosure may be combined as understood in the art. Aspects of the disclosure, as generally described herein and illustrated in the figures, can be arranged, substituted, combined, separated, and designed in a wide variety of different configurations, all of which are expressly contemplated herein.

[0073] Any use of the term "example" herein to describe various embodiments is intended to indicate that such embodiments are possible examples, representations, and / or illustrations of possible embodiments (and such terms are not intended to imply that such embodiments are necessarily exceptional or superlative examples). Furthermore, as used herein, the term "substantially" and similar terms are intended to have a broad meaning consistent with common and acceptable usage by those of ordinary skill in the art to which the subject matter of the present disclosure pertains. Those of ordinary skill in the art reviewing this disclosure should understand that these terms are intended to enable the description of the particular features described and claimed without limiting the scope of these features to the precise numerical ranges provided. Thus, these terms should be interpreted as indicating that insubstantial or consequential modifications or variations of the subject matter described and claimed (e.g., within plus or minus 5% of a given angle or other value) are considered to be within the scope of the invention as recited in the appended claims. The term "approximately" when used in reference to a value means plus or minus 5% of the associated value.

[0074] As used herein, the terms "coupled" and the like refer to the direct or indirect joining of two members to one another. Such joining can be fixed (e.g., permanent) or movable (e.g., removable or releasable). Such joining can be achieved by the two members or the two members and any additional intermediate members integrally formed with each other as a single, integral structure, or with the two members or the two members and any additional intermediate members attached to each other.

[0075] Although the figures herein may show a particular order and composition of method steps, it will be understood that the order of these steps may differ from that depicted. For example, two or more steps may be performed simultaneously or in 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 altered. The order or sequence of any elements or apparatus may be changed or substituted in accordance with alternative embodiments. Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the appended claims.

[0076] Without further elaboration, it is believed that those skilled in the art can use the preceding description to utilize the claimed invention to its fullest extent. The examples and embodiments disclosed herein are merely illustrative and should not be construed as limiting the scope of the present disclosure in any manner. It will be apparent to those skilled in the art that changes may be made to the details of the above-described embodiments without departing from the underlying principles discussed. 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 the features of the various embodiments described is contemplated.

Claims

1. 1. A night vision system comprising: an electron multiplier including a silicon membrane; A night vision system, wherein a shutter voltage between 0.5 volts and 2.5 volts is applied between a first surface of the silicon membrane and a substantially parallel, opposing second surface of the silicon membrane.

2. an image intensifier tube; 10. The night vision system of claim 1, wherein said electron multiplier is vacuum sealed within said image intensifier tube between a photocathode and an anode at a spaced distance.

3. The night vision system of claim 2 , wherein the silicon membrane comprises a plurality of spaced apart doped regions extending partially between the first and second surfaces.

4. 3. The night vision system of claim 2, wherein said first surface faces towards said photocathode and said second surface faces towards said anode.

5. 5. The night vision system of claim 4, wherein the first surface comprises a first metal layer dielectrically spaced apart across a portion of the first surface, and the second surface comprises a second metal layer dielectrically spaced apart across a portion of the second surface.

6. 6. The night vision system of claim 5, further comprising a power supply configured to cause the first metal layer to generate a positive shutter voltage value and to cause the second metal layer to generate a negative shutter voltage value.

7. 6. The night vision system of claim 5, wherein the second metal layer comprises an electrically addressable electron emitter.

8. 1. An image intensifier tube, comprising: a first electron multiplier spaced in a vacuum between the photocathode and the anode; a positive bias variable first voltage coupled between the photocathode and the first electron multiplier for drawing electrons from the photocathode to the first electron multiplier; a positive bias variable second voltage between 250 volts and 2000 volts coupled from an automatic brightness controller between the first electron multiplier and a ground power supply, the positive bias variable second voltage being coupled between the first electron multiplier and a second electron multiplier coupled to the ground power supply; a negative bias shutter voltage coupled across an opposing surface of the first electron multiplier to close off the continued drawing of electrons from the first electron multiplier to substantially cease displaying an image from the image intensifier tube.

9. 9. The image intensifier tube of claim 8, wherein the positively biased variable first voltage comprises a negative terminal and a positive terminal of a first voltage source, the negative terminal of the first voltage source being coupled to the photocathode and the positive terminal of the first voltage source being coupled to an electron entrance surface of the first electron multiplier.

10. 10. The image intensifier tube of claim 9, wherein the negative bias shutter voltage comprises a positive terminal and a negative terminal of a shutter voltage source, the positive terminal of the shutter voltage source being coupled to the electron entrance surface of the first electron multiplier and the negative terminal of the shutter voltage source being coupled to the multiplied electron emission surface of the first electron multiplier.

11. 9. The image intensifier tube of claim 8, further comprising a third voltage of positive bias between 4150 volts and 4275 volts coupled between the power supply ground and the anode.

12. 9. The image intensifier tube of claim 8, wherein said positive bias variable first voltage is between 200 volts and 2000 volts.

13. 9. The image intensifier tube of claim 8, wherein said positive bias variable first voltage is variable.

14. 1. A method for blocking continued electron draw from a first electron multiplier in an image intensifier tube, comprising: applying a positive bias between a photocathode and an electron incidence surface of the first electron multiplier to draw multiplied electrons into the first electron multiplier; applying a variable positive bias second voltage between 250 volts and 2000 volts coupled from an automatic brightness controller between the first electron multiplier and a power supply ground, the variable positive bias second voltage being coupled between the first electron multiplier and a second electron multiplier coupled to the power supply ground; applying a negative shutter bias between the electron entrance surface and the multiplied electron emission surface of the first electron multiplier to substantially discontinue drawing of multiplied electrons through the first electron multiplier.

15. 15. The method of claim 14, wherein applying the negative shutter bias varies in magnitude in response to readings of a current in a phosphor covered anode screen.

16. 16. The method of claim 15, further comprising applying a photocathode positive bias between the photocathode and the electron incident surface area that decreases when a photocurrent through the photocathode or a current through the phosphor covered anode screen exceeds a predetermined amount.

17. 15. The method of claim 14, further comprising varying the positive bias in response to an intensity reading obtained at a phosphor covered anode screen.

18. 15. The method of claim 14, further comprising switchably applying the negative shutter bias in response to an intensity reading obtained at a phosphor covered anode screen.

Images