Abstract:
An anode array system includes a number of electrically conductive strips arranged in an array to form an anode, each of the plurality of electrically conductive strips having a first end and a second end, electrical connectors at the first end and at the second end of each of the electrically conductive strips, and a substrate at least partially supporting the electrically conductive strips, wherein the substrate is porous.

Description:
BACKGROUND 
       [0001]    A microstrip anode is an anode structure having an array of electrically conductive strips or lines. A corresponding cathode can be positioned next to the microstrip anode, with a substrate between the microstrip anode and the cathode. Connectors such as coaxial connectors can be connected to the ends of the anode strips and to the cathode. As such devices are used for increasingly high speed applications, the signal propagation speed along the anode strips and the bandwidth transmission become limiting characteristics of increasing importance. A lower speed of a wave traveling through the anode strips results in a shorter wavelength for the same frequency range and increases electrical length. This increases coupling among strips and loss of transmission, all of which will be translated to a rapid transmission drop when frequency increases. 
       BRIEF SUMMARY 
       [0002]    Some embodiments of the present invention provide a microstrip anode device with a substrate having a lower overall dielectric constant, by selectively removing or omitting material from the substrate. In some embodiments, some substrate material is removed from an underside, opposite the microstrip anode. In some embodiments, slits, grooves or channels are cut in the substrate. Such grooves or channels can be under or between the strips or placed in another arrangement. In some embodiments, a honeycomb pattern of tubes or other structures is formed in the substrate. In some embodiments, material is removed from the substrate, leaving supportive posts or pillars to support the cathode. In some embodiments, material is selectively added via an additive process to create, for example, posts and/or pillars, etc. 
         [0003]    Notably, the substrate formation to result in a lower overall dielectric constant is not limited to any particular process or operation, and the use of the term “removed” does not specify or imply that a solid substrate is first provided then modified. Rather, the non-solid substrate can be formed in any suitable manner, such as a formation process that selectively places or deposits material where desired in the substrate, or in a combination of additive and subtractive operations. 
         [0004]    This summary provides only a general outline of some embodiments according to the present invention. Many other embodiments of the present invention will become more fully apparent from the following detailed description, the appended claims and the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]    A further understanding of the various embodiments of the present invention may be realized by reference to the figures which are described in remaining portions of the specification. In the figures, like reference numerals are used throughout several figures to refer to similar components. 
           [0006]      FIG. 1  depicts a top view of a microstrip anode in accordance with some embodiments of the present invention; 
           [0007]      FIG. 2  depicts a side view of a microstrip anode, substrate and cathode along a cross-section through an anode strip and showing only solid substrate in accordance with some embodiments of the present invention; 
           [0008]      FIG. 3  depicts a side view of a microstrip anode, substrate and cathode along a cross-section through an anode strip and showing cavities in the substrate in accordance with some embodiments of the present invention; 
           [0009]      FIG. 4  depicts an end view of a microstrip anode, substrate and cathode showing cavities in the substrate under anode strips in accordance with some embodiments of the present invention; 
           [0010]      FIG. 5  depicts an end view of a microstrip anode, substrate and cathode showing cavities in the substrate between anode strips in accordance with some embodiments of the present invention; 
           [0011]      FIG. 6  depicts an end view of a microstrip anode, substrate and cathode showing cavities in the substrate under anode strips and extending into spaces between the anode strips in accordance with some embodiments of the present invention; and 
           [0012]      FIG. 7  depicts an end view of a microstrip anode, substrate and cathode showing cavities in the substrate between anode strips and extending into spaces under the anode strips in accordance with some embodiments of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0013]    Embodiments of the present invention are related to a microstrip anode device with a substrate between the microstrip anode and a cathode having a reduced (effective) dielectric constant when compared with a solid substrate of the same material, by selectively removing or omitting material from the substrate. In some embodiments, substrate material is removed from an underside, opposite the microstrip anode. In other embodiments the substrate is removed from the topside/upper side, etc. In some embodiments, grooves, slits, spacers, tubes or channels, etc. are cut in the substrate. Such grooves or channels can be under or between the strips or placed in another arrangement. In some embodiments, a honeycomb pattern or honeycomb-like pattern is formed in the substrate. In some embodiments, material is removed from the substrate, leaving supportive posts or pillars to support the cathode. The substrate is thus porous, where the term “porous” indicates that the substrate is not a homogenous solid material, but contains voids or regions which are not formed from the same material as the substrate frame. These voids or regions can be filled with any material in any state, including, but not limited to, air or other materials in gaseous, liquid or solid state, and can also be evacuated to form a vacuum. 
         [0014]    Notably, the substrate formation to result in a lower overall dielectric constant is not limited to any particular process or operation, and the use of the term “removed” does not specify or imply that a solid substrate is first provided then modified. Rather, the non-solid substrate can be formed in any suitable manner, such as a formation process that selectively places or deposits material where desired in the substrate, or in a combination of additive and subtractive operations. 
         [0015]    The microstrip anode device disclosed herein is not limited to use with any particular application. In some embodiments, the microstrip anode device is used in a very fast large-area photodetector with picosecond-level resolution for providing better time, energy, position, etc. 
         [0016]    resolutions. Radio frequency or RF-strip-line anodes for large-area microchannel plate (MCP)-based photodetectors provide for the foundation of fast photodetectors. MCP-based photodetectors offer the small intrinsic spatial scale necessary for small fluctuations in timing due to path length variations, but, at the same time, are scalable to large areas. Microstrip anodes as disclosed herein, also referred to as RF transmission line anodes or large-area picosecond photo-detectors (LAPPD) anode arrays in some embodiments, can cover large areas inexpensively while preserving the time resolution method of digitizing the signal. Microstrip anodes can be daisy chained in series to cover more area with the same electronics channel count. The microstrip anode disclosed herein can achieve picosecond and sub-picosecond time resolution, and can be used in MCP-based detectors with analog bandwidths in the multi-GHz, while maintaining the large area of the photodetector for better signal-to-noise performance. In some embodiments, the substrate is a sealable glass substrate. 
         [0017]    Other applications for some embodiments of the microstrip anode include less expensive, lower cost, and more precise Positron Emission Tomography (PET) cameras in medical imaging, scanners for transportation security, and particle detectors in high-energy neutrino and collider physics, astrophysics, and nuclear physics. Photodetection anodes can be optimized for neutron or photon detection. Large area panels would allow economical scanners for containers and trucks in nuclear non-proliferation and transportation security, respectively. 
         [0018]    Turning to  FIG. 1 , a top view of a microstrip anode  100  is shown in accordance with some embodiments of the present invention. The microstrip anode  100  is not limited to any particular number of anode strips, or to any particular width, length, or spacing of the anode strips. Although the anode strips are shown as straight conductors in parallel configuration with uniform widths, the microstrip anode is not limited to this configuration, and anode strips can be positioned at angles to each other, can have varying widths, can change directions, curve, etc. An array of anode strips  102  is positioned on a substrate  104 , running between sets of connectors  106 ,  110 . In this view, a cathode (not shown) lies beneath the substrate  104 . The anode strips  102  can be formed directly on the substrate  104 , or be provided in another manner and placed against substrate  104 . For example, in some embodiments, the anode strips are formed directly on the substrate between the anode strips and cathode, such as by deposition of a metal layer on a glass substrate  104 , followed by patterning including, for example, but not limited to, photolithography and etching to remove undesired metal material to leave the anode strips  102 . Any method may be used to pattern, form, create, remove, cut, add, subtract, etc. to produce the anode strips and associated structures. In some other embodiments, the anode strips  102  are formed on another substrate and then positioned against a separate dielectric substrate  104  between the anode strips  102  and a cathode below, such that the substrate on which the anode strips  102  are formed is not between the anode strips  102  and cathode. The anode plate can also be free standing, formed on a thin dielectric as mentioned above, deposited on another material, etc. 
         [0019]    The anode strips  102 , substrate  104  and cathode can be formed using any suitable materials giving the desired behavioral characteristics, such as a copper material, a copper alloy, silver, silver paste, and in certain cases, gold, platinum, aluminum, etc. or, in general, other electrically conductive material for the anode strips  102 , and a glass or other material with a suitable dielectric constant for the substrate  104 . In some embodiments, the substrate  104  is a borofloat glass with removed or omitted sections. Although the microstrip anode is not limited to any particular layout or configuration of slits, grooves, tubes, channels, cavities, etc. in the substrate, in one example embodiment with a honeycomb substrate structure containing a 65% open air ratio, the signal transit time across the anode strips is reduced by about 35% as compared with a solid substrate structure. 
         [0020]    Methods such as sputtering, thermal evaporation, electron beam evaporation, plasma evaporation, plasma assisted evaporation, molecular beam epitaxy or evaporation, and other physical vapor deposition, chemical vapor deposition, etc, electroplating, electroless plating, etc, 
         [0021]    Embodiments of the present invention can also use mechanical and machining approaches to realize implementations, of the present invention including molding, punching, forming, 3-D (three dimensional) printing, cutting, pressing, lathing, sawing, water jetting, etc. 
         [0022]    Electrical signals can be connected to the anode strips  102  and cathode in any suitable manner, such as, but not limited to, using a coaxial SMA connector, or Sub-Miniature version A coaxial RF connectors, with the center conductors connected to the anode strips  102  and the outer sleeve conductors connected to the cathode. 
         [0023]    Turning to  FIG. 2 , a side view of a microstrip device  200  depicts a microstrip anode  202 , substrate  204  and cathode  206  along a cross-section through an anode strip  210  and showing only a solid cross-section of the substrate  204  in accordance with some embodiments of the present invention. The substrate  204  includes cavities (not shown), missing material, or openings of any configuration, causing the substrate  204  to have an overall dielectric constant such that the microstrip device  200  has the desired signal transmission frequency, bandwidth and other characteristics. The microstrip device  200  is not limited to any particular configuration, including the relative thicknesses of the microstrip anode  202 , substrate  204  and cathode  206 . The drawing in  FIG. 2  is merely a non-limiting example. The details and measurements of the elements of the microstrip device  200  can be configured in any manner to provide the desired operating characteristics. 
         [0024]    Turning to  FIG. 3 , a side view of a microstrip device  300  depicts a microstrip anode  302 , substrate  304  and cathode  306  along a cross-section through an anode strip  310  and showing cavities  312 ,  314 ,  316 ,  320  in the substrate  304  in accordance with some embodiments of the present invention. The microstrip device  300  may extend to the left and right beyond the edges of drawing in  FIG. 3 , with connectors at the left and right end of the anodes  302 . The microstrip device  300  is not limited to any particular number of cavities  312 ,  314 ,  316 ,  320 . The cavities  312 ,  314 ,  316 ,  320  may be interconnected to form one large cavity, or may be independent and separate from each other. In some embodiments, the cavities  312 ,  314 ,  316 ,  320  are filled with air. In some other embodiments, the cavities  312 ,  314 ,  316 ,  320  are filled with another gas. In some other embodiments, the cavities  312 ,  314 ,  316 ,  320  are pumped down to a vacuum, including a high vacuum or ultra-high vacuum, or partial vacuum. 
         [0025]    Turning to  FIG. 4 , an end view of a microstrip device  400  depicts a microstrip anode  402 , substrate  404  and cathode  406  showing cavities  422 ,  424 ,  426 ,  430  in the substrate  404  under the anode strips  432 ,  434 ,  436 ,  440  in accordance with some embodiments of the present invention. In this embodiment, the cavities  422 ,  424 ,  426 ,  430  are substantially the same width as the anode strips  432 ,  434 ,  436 ,  440  and lie under the anode strips  432 ,  434 ,  436 ,  440 . The cavities  422 ,  424 ,  426 ,  430  may run the entire length of the anode strips  432 ,  434 ,  436 ,  440  or may comprise a number of separate cavities  422 ,  424 ,  426 ,  430 . 
         [0026]    Turning to  FIG. 5 , an end view of a microstrip device  500  depicts a microstrip anode  502 , substrate  504  and cathode  506  showing cavities  552 ,  554 ,  556 ,  560  in the substrate  504  between the anode strips  542 ,  544 ,  546 ,  548 ,  550  in accordance with some embodiments of the present invention. In this embodiment, the cavities  552 ,  554 ,  556 ,  560  are substantially the same width as the gaps between anode strips  542 ,  544 ,  546 ,  548 ,  550  and lie between the anode strips  542 ,  544 ,  546 ,  548 ,  550 . The cavities  552 ,  554 ,  556 ,  560  may run the entire length of the anode strips  542 ,  544 ,  546 ,  548 ,  550  or may comprise a number of separate cavities  552 ,  554 ,  556 ,  560 . 
         [0027]    Turning to  FIG. 6 , an end view of a microstrip device  600  depicts a microstrip anode  602 , substrate  604  and cathode  606  showing cavities  662 ,  664 ,  668 ,  670  in the substrate  604  under anode strips  632 ,  634 ,  636 ,  640  and extending into spaces between the anode strips  632 ,  634 ,  636 ,  640  in accordance with some embodiments of the present invention. The amount by which the cavities  662 ,  664 ,  668 ,  670  in the substrate  604  extend beyond the anode strips  632 ,  634 ,  636 ,  640  is not limited to the distance shown in the example of  FIG. 6 . The depth of the cavities  662 ,  664 ,  668 ,  670  in the substrate  604  is also not limited to that shown. The size and shape of the cavities  662 ,  664 ,  668 ,  670  can be adapted to balance the stability and rigidity of the substrate  604  to provide the desired support to microstrip anode  602  and cathode  606 , versus the desired dielectric constant of the substrate  604 . The size and shape of the cavities  662 ,  664 ,  668 ,  670  can also be adapted to achieve the desired electrical and/or magnetic field effects during operation of the microstrip device  600 . 
         [0028]    Turning to  FIG. 7 , an end view of a microstrip device  700  depicts microstrip anode  702 , substrate  704  and cathode  706  showing cavities  772 ,  774 ,  776 ,  780  in the substrate  704  between anode strips  742 ,  744 ,  746 ,  748 ,  750  and extending into spaces under the anode strips  742 ,  744 ,  746 ,  748 ,  750  in accordance with some embodiments of the present invention. The amount by which the cavities  772 ,  774 ,  776 ,  780  in the substrate  704  undercut the anode strips  742 ,  744 ,  746 ,  748 ,  750  is not limited to the distance shown in the example of  FIG. 7 . The depth of the cavities  762 ,  764 ,  768 ,  770  in the substrate  704  is also not limited to that shown. The size and shape of the cavities  762 ,  764 ,  768 ,  770  can be adapted to balance the stability and rigidity of the substrate  704  to provide the desired support to microstrip anode  702  and cathode  706 , versus the desired dielectric constant of the substrate  704 . The size and shape of the cavities  762 ,  764 ,  768 ,  770  can also be adapted to achieve the desired electrical and/or magnetic field effects during operation of the microstrip device  700 . 
         [0029]    Although  FIGS. 2 through 7  generally show the cavities as being below the anode with solid material directly below the anode, this is merely for illustrative purposes and the cavities could also be directly below or in any other configuration including both directly below and partially below the anode etc. It is understood that words indicating vertical relative positions such as below, directly below, above, etc. are merely intended to be illustrative for the particular drawings of the present invention and not limiting in any way or form. 
         [0030]    Again, material can be removed or omitted from the substrate between the microstrip anode and the cathode in any manner and pattern. In some embodiments, the substrate includes cavities on the side opposite the microstrip anode and adjacent the cathode, although the microstrip anode device is not limited to this configuration. The cavities may have any height in the substrate and any suitable layout. In some embodiments, the cavities comprise circular cutouts, as in a honeycomb patterned cavity pattern. In some embodiments, the cavities comprise slits, grooves, tubular openings/channels, square openings/channels, rectangular openings/channels, oblong openings/channels, etc. or slots in any width, depth, orientation, spacing, etc. In some embodiments, the cavities comprise a single large cavity with supportive posts or pillars throughout the cavity to provide support to the anode and/or cathode. In some embodiments the cavities may, but are not limited to, have one or more of the following shapes: square, circular, elliptical, round, hexagonal, octagonal, star, triangular, rectangular, N-sided where N is typically greater than 3, oblong, elongated, tubes, cylinders, parallel-piped, spheres, semi-circles, semi-spheres, arbitrary, etc. 
         [0031]    Although the figures have in general illustrated a vertical type of cavity structure, horizontal and lateral cavity structures that, for example, run parallel or perpendicular to the plane of the anodes may also be used. In general any type of vertical, horizontal, lateral cavities and cavity structures, types, forms, geometries, construction, design, fabrication, assembly, manufacturing, etc. or combinations of these may be used to realize and implement the present invention. 
         [0032]    The substrate for the microstrip anode device can be manufactured or fabricated in any suitable manner. In some embodiments, the substrate is manufactured by providing a solid substrate and fabricating walls on the solid substrate to result in a substrate with cavities defined by the walls. Such walls may be formed by a combination of additive and subtractive operations. For example, pattern material such as photoresist can be deposited in the locations of the walls, followed by deposition of sacrificial material to fill in the cavity locations between the wall locations. The pattern material in the locations can then be removed or etched away. A wall material can then be deposited in the wall locations where the pattern material was removed, followed by removal or etching of the sacrificial material filling the cavity locations, resulting in walls with cavities between them. Thus, pillars and/or posts could use (i.e., be formed by) additive or subtractive methods, including, but not limited to, etching (chemical, dry or plasma, etc, or combinations), molds, photoresist including SU-8 and other photoresists including, but not limited to screen printable photoresists and other materials and such materials, blanket photomaterials and photoresists, fusing, bonding, heat treatment, water jetting, sawing, dicing, molding, 3-D printing, precision machining, conventional machining, casting, micromachining, microfabrication, nanofabrication, fixtures, fixturing, melting, ablation including laser ablation, plasma jetting, plasma deposition, PVD, CVD, ALE, ALD, stamping, printing, pressing, frit, frit molding, heat treatment, light sensitive materials, etc. 
         [0033]    Materials including hollow or otherwise tubes, balls, cylinders, squares, rectangles, most any geometrical shapes and individual components etc. to realize and implement a reduced material volume, surface area and/or area structure with an effective lower dielectric constant. 
         [0034]    Most any periodic/symmetric cavity and support structure can be used, to provide the desired overall or averaged effective dielectric constant without substantially affecting the field and mode distribution of the microstrip anodes. Cross members, four squares, ‘open air’ structures, diamonds, squares, circles, frames with cut-outs, arrays of pillars and/or posts, cut-outs, bottom openings, etc. can be used. 
         [0035]    In conclusion, embodiments of the present invention provide novel systems, devices, methods and arrangements for a high speed microstrip anode. While detailed descriptions of one or more embodiments of the invention have been given above, various alternatives, modifications, and equivalents will be apparent to those skilled in the art without varying from the spirit of the invention. Therefore, the above description should not be taken as limiting the scope of embodiments of the invention which are encompassed by the appended claims.