Patent Publication Number: US-2021193372-A1

Title: Electronic Package for an Electrically Small Device with Integrated Magnetic Field Bias

Description:
FEDERALLY-SPONSORED RESEARCH AND DEVELOPMENT 
     The United States Government has ownership rights in this invention. Licensing and technical inquiries may be directed to the Office of Research and Technical Applications, Naval Information Warfare Center Pacific, Code 72120, San Diego, Calif., 92152; voice (619) 553-5118; ssc_pac_t2@navy.mil. Reference Navy Case Number 109259. 
    
    
     BACKGROUND OF THE INVENTION 
     Electrically small devices include quantum devices and topological devices. Such electrically small devices can be adversely affected by an external magnetic field, such as a geomagnetic field of the Earth. 
     SUMMARY 
     An electronic package includes a mounting platform for mounting an electrically small device, at least one coil, and an insulator. The coil regulates a magnetic field through the electrically small device at the mounting platform. The coil is adapted to conduct a current for nullifying the magnetic field through the electrically small device at the mounting platform. The insulator is between the mounting platform and the coil for isolating the electrically small device from the coil. An electronic circuit includes this electronic package and the electrically small device mounted at the mounting platform of the electronic package. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Throughout the several views, like elements are referenced using like references. The elements in the figures are not drawn to scale and some dimensions are exaggerated for clarity. 
         FIGS. 1 and 2  are each a cross-sectional diagram of an electronic package for an electrically small device in accordance with an embodiment of the invention.  FIG. 1  is a cross-sectional diagram through section  1 - 1  of  FIG. 2 .  FIG. 2  is a cross-sectional diagram through section  2 - 2  of  FIG. 1 . 
         FIG. 3  is a cross-sectional diagram of an electronic package for an electrically small device in accordance with an embodiment of the invention having a central coil and six peripheral coils.  FIG. 3  is a cross-sectional diagram through section  3 - 3  of  FIG. 4  and  FIG. 5 . 
         FIG. 4  is a cross-sectional diagram of the electronic package of  FIG. 3  through section  4 - 4  of  FIG. 3  showing the induced magnetic field when only the central coil is conducting current. 
         FIG. 5  is a cross-sectional diagram similar to  FIG. 4  except that only the left and right coils of  FIG. 3  are conducting currents, and these currents are in opposite directions. 
         FIGS. 6, 7, 8, 9, and 10  are cross-sectional diagrams of various embodiments of coils of an electronic package for an electrically small device. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     The disclosed packages and circuits below may be described generally, as well as in terms of specific examples and/or specific embodiments. For instances where references are made to detailed examples and/or embodiments, it should be appreciated that any of the underlying principles described are not to be limited to a single embodiment, but may be expanded for use with any of the other methods and systems described herein as will be understood by one of ordinary skill in the art unless otherwise stated specifically. 
       FIGS. 1 and 2  are each a cross-sectional diagram of an electronic package  100  for an electrically small device  101  in accordance with an embodiment of the invention.  FIG. 1  is a cross-sectional diagram through section  1 - 1  of  FIG. 2 .  FIG. 2  is a cross-sectional diagram through section  2 - 2  of  FIG. 1 . 
     The electronic package  100  can be manufactured without and therefore not include the electrically small device  101  to enable production of a single type of electronic package  100  for a variety of different types of the electrically small device  101 . The electronic package  100  has a mounting platform for mounting the electrically small device  101 . The mounting platform is a surface  112  of an insulator  110  or a surface  122  of a conductive plate  120 . The electrically small device  101  can be mounted on surface  122  of a conductive plate  120  via insulator  110 . The conductive plate  120  is optional, and when conductive plate  120  is omitted, the insulator  130  is also omitted or is combined with insulator  110 . When conductive plate  120  is included, the insulator  110  can be omitted with the electrically small device  101  directly mounted on surface  122  of conductive plate  120 . 
       FIG. 1  shows a coil  140  for regulating a magnetic field through the electrically small device  101  at the mounting platform. For simplicity,  FIG. 1  shows only one coil  140 ; however, it will be appreciated that this embodiment encompasses multiple coils as shown in  FIG. 3-10 , and that the multiple coils of  FIG. 3-10  can have structural features as shown for coil  140  in  FIGS. 1 and 2 . The coil  140  is adapted to conduct a current for nullifying the magnetic field through the electrically small device  101  at the mounting platform, which is a surface  112  or  122  opposite coil  140 . The coil  140  is layered, alternating patterned conductive layers  141 ,  143 ,  145 , and  147  and insulation layers  142 ,  144 ,  146 , and  148 . Each of the conductive layers  141 ,  143 ,  145 , and  147  is patterned to form a conductive loop for conducting the current through the coil  140 .  FIG. 2  shows a cross-section through the conductive loop of patterned conductive layer  141 . 
     A controller  150  is adapted to control the current through the coil  140  to nullify the magnetic field through the electrically small device  101  at the mounting platform. The controller  150  supplies the current via an exterior conductive connector  160  into the conductive loop of patterned conductive layer  141  and this current spirals around three times as shown in  FIG. 2  until reaching interior via  162  connecting the conductive loops of patterned conductive layers  141  and  143 . Patterned conductive layer  143  is similar to patterned conductive layer  141  shown in  FIG. 2 , except that the conductive loop of patterned conductive layer  143  is a mirror image, and instead of exterior conductive connector  160 , the conductive loop of patterned conductive layer  143  has an exterior via  164 , which connects the conductive loops of patterned conductive layers  143  and  145 . Patterned conductive layers  145  and  147  are connected by interior via  166 , and eventually the current returns to controller  150  via exterior conductive connector  168 . 
     Thus, the conductive loops of patterned conductive layers  141 ,  143 ,  145 , and  147  form a solenoid in which each conductive loop induces a magnetic field that reinforces the magnetic field induced by the other conductive loops. The maximum strength of the induced magnetic field of coil  140  depends upon factors including the maximum amperage of current driven through the conductive loops, the number of patterned conductive layers  141 ,  143 ,  145 , and  147 , and the number of times the current spirals around in each conductive loop of the patterned conductive layers  141 ,  143 ,  145 , and  147 . It will be appreciated that the conductive layers  141 ,  143 ,  145 , and  147  can be patterned using photolithography and each include a conductive loop that spirals around many more times than the three times schematically shown in  FIG. 2 . To avoid stacked vias, such as interior vias  162  and  166  shown stacked in  FIG. 1 , each conductive loop can spiral around a non-integer number of times. It will also be appreciated that the number of patterned conductive layers  141 ,  143 ,  145 , and  147  can be more or less than the four layers shown in  FIG. 1 , and can include a single patterned conductive layer with exterior and interior connectors to controller  150 . 
     A drawback of coil  140  is that coil  140  tends to act as an antenna that collects electromagnetic interference  170 , especially electromagnetic interference  170  having a wavelength approximately corresponding to the dimensions of coil  140 . This collected electromagnetic interference  170  can generate an oscillating current in coil  140  and this current induces a corresponding oscillating magnetic field from coil  140 . This oscillating magnetic field interferes with the operation of the electrically small device  101  for certain types of the electrically small device  101 . 
     When the conductive plate  120  is included between the mounting platform and the coil  140 , any oscillating magnetic field from coil  140  reaches the electrically small device  101  predominantly after passing through the conductive plate  120 . However, any oscillating magnetic field passing through the conductive plate  120  induces eddy currents within conductive plate  120 , and these eddy currents oppose and attenuate the oscillating magnetic field. The degree of attenuation of the oscillating magnetic field depends upon dimensions and other characteristics of the conductive plate  120 , such as the thickness of the conductive plate  120  as compared to the skin depth for each frequency of the oscillating magnetic field. The conductive plate  120  is optionally grounded at ground connection  172 . When not grounded, floating conductive plate  120  still opposes and attenuates any oscillating magnetic field from coil  140  that induces eddy currents within conductive plate  120 . When grounded, the conductive plate  120  is a ground plane that generally opposes and attenuates a wider range of oscillating magnetic fields than a floating conductive plate  120  because the ground connection  172  increases the effective size of the conductive plate  120 . Thus, whether grounded or not, the conductive plate  120  shields the electrically small device  101  from electromagnetic interference  170  collected in the coil  140 . 
     When the conductive plate  120  is included, the internal magnetic field that controller  150  intentionally induces from the current through coil  140  also predominantly passes through the conductive plate  120 . However, a substantially static portion of the internal magnetic field passes unimpeded through the conductive plate  120  toward the electrically small device  101 . In addition, controller  150  can provide a time-varying current that induces a time-varying internal magnetic field from coil  140 , and to a certain extent limited by the dynamic range given by the maximum achievable current through coil  140 , the controller  150  can amplify the time-varying current to compensate for the conductive plate  120 ′s attenuation of the time-varying internal magnetic field. This can be useful for more completely nullifying the lower-frequency components of electromagnetic interference  170  collected in coil  140  when the conductive plate  120  does not fully attenuate these lower-frequency components. 
     The insulators  110 ,  130  between the mounting platform and the coil  140  isolate the electrically small device  101  from the coil  140 . The insulators  110 ,  130  are an electrical insulator for electrically isolating the electrically small device  101  from the coil  140 . The internal magnetic field induced from the current in the coil  140  passes unimpeded through the insulators  110 ,  130  toward the electrically small device  101 . 
     In one embodiment, the insulators  110 ,  130  and the insulation layers  142 ,  144 ,  146 , and  148  are each aluminum oxide having an extremely high resistivity, such that the necessary electrical isolation is achieved with a very thin layer of nanometers of the aluminum oxide. Such a thin layer of aluminum oxide presents a small amount of thermal insulation, such that the insulators  110 ,  130  and the insulation layers  142 ,  144 ,  146 , and  148  do not significantly impair cryogenic cooling of the electrically small device  101  by cold finger  180 . In this embodiment, the conductive loop of each of the patterned conductive layers  141 ,  143 ,  145 , and  147  is composed of a superconductive material for conducting the current from controller  150  when cooled to a cryogenic temperature. This eliminates heat generated in coil  140 , such that the cold finger  180  more readily cools the electrically small device  101  to a cryogenic temperature. 
     In one embodiment, an electronic circuit includes both the electronic package  100  and the electrically small device  101  mounted on the electronic package  100  at the mounting platform. In this embodiment, the electrically small device  101  is a quantum device and/or a topological device when cooled to a cryogenic temperature by cold finger  180 . An example of such a quantum or topological device is a radio frequency (RF) receiver or transmitter vulnerable to decreased sensitivity or other decreased performance unless the coil  140  nullifies the magnetic field through the electrically small device  101 . Thus, to prevent decreased performance of the RF receiver or transmitter, the controller  150  is adapted to control the current through the coil  140  for nullifying the magnetic field through the electrically small device  101 . In one embodiment, the controller  150  is included within the electrically small device  101 . 
       FIG. 3  is a cross-sectional diagram of an electronic package  300  for an electrically small device  101  in accordance with an embodiment of the invention having a central coil  310  and six peripheral coils  321 ,  322 ,  323 ,  234 ,  325 , and  326 .  FIG. 3  is a cross-sectional diagram through section  3 - 3  of  FIG. 4  and  FIG. 5 . 
       FIG. 4  is a cross-sectional diagram of the electronic package of  FIG. 3  through section  4 - 4  of  FIG. 3  showing the induced magnetic field  301  when only the central coil  310  is conducting current. The induced magnetic field  301  through the electrically small device  101  is approximately upwardly vertical. The induced magnetic field  301  is also rotationally symmetric about a central vertical axis of the magnetic field line  302 . Not shown is the portion of the induced magnetic field  301  below the central coil  310 ; however, because magnetic field lines form closed loops, the portion of the induced magnetic field  301  below the central coil  310  has a similar shape to the shown portion of the induced magnetic field  301 . 
       FIG. 5  is a cross-sectional diagram similar to  FIG. 4  except that only the left coil  321  and the right coil  322  of  FIG. 3  are conducting current. The left and right coils  321  and  322  are shown conducting the same amperage of current in opposite directions. This can be alternatively achieved with coils  321  and  322  wound in opposite directions. The induced magnetic field from coil  321  tends to be captured by coil  322 , and vice versa, so that the induced magnetic field  301  through the electrically small device  101  is approximately horizontal from left to right. 
     In general, the central coil  310  and the peripheral coils  321 ,  322 ,  323 ,  234 ,  325 , and  326  are adapted to conduct respective currents that collectively nullify the magnetic field through the electrically small device  101  at the mounting platform. The magnetic field through the electrically small device  101  at the mounting platform is a superposition of an external magnetic field  330  (see dashed line of  FIG. 5 ) including a geomagnetic field of the Earth and the internal magnetic field  301  induced from the currents in the central coil  310  and the peripheral coils  321 ,  322 ,  323 ,  234 ,  325 , and  326 . To nullify the magnetic field through the electrically small device  101 , these central and peripheral coils are adapted to conduct respective currents for inducing the internal magnetic field  301  that has a same magnitude as the external magnetic field  330  but in an opposing direction. 
     For example, when the external magnetic field  330  lies in the plane of  FIG. 5  directed at a 45 degree angle through the electrically small device  101  as shown with the dashed line of  FIG. 5 , the induced magnetic field  301  nullifies the external magnetic field  330  when the central coil  310  conducts current of appropriate amperage as shown in  FIG. 4  concurrently with the left and right coils  321  and  322  conducting respective currents of appropriate amperage in opposite directions as shown if  FIG. 5 . With appropriate currents in coils  310 ,  321 , and  322 , the superposition of the external magnetic field  330 , the induced magnetic field  301  of  FIG. 4 , and the induced magnetic field  301  of  FIG. 5  is a nullified magnetic field through the electrically small device  101 . 
     An advantage of the central coil  310  and the peripheral coils  321 ,  322 ,  323 ,  234 ,  325 , and  326  as shown in  FIG. 3  is fairly good decoupling of the nullification of the vertical and horizontal components of the magnetic field through the electrically small device  101 . In one embodiment, the electrically small device  101  includes a magnetic field sensor adapted to measure the magnitude of the vertical component of the magnetic field perpendicular to a plane of the mounting platform and adapted to measure the magnitude and in-plane direction of the horizontal component of the magnetic field parallel to the plane of the mounting platform. 
     In this embodiment, the electrically small device  101  also includes a controller  150  adapted to control the current supplied to central coil  310  and to adjust the amperage of this current until the magnetic field sensor measures no vertical component of the magnetic field through the electrically small device  101 . Relying on the arrangement of the peripheral coils  321 ,  322 ,  323 ,  234 ,  325 , and  326  that enables inducing an induced magnetic field  301  oriented in any in-plane direction through the electrically small device  101  with three respective amperages through opposing peripheral coils  321  and  322 , opposing peripheral coils  323  and  325 , and opposing peripheral coils  324  and  326 , controller  150  is adapted to control the three currents supplied to peripheral coils  321 ,  322 ,  323 ,  234 ,  325 , and  326  and to adjust the amperages of these three currents until the magnetic field sensor measures no horizontal component of the magnetic field through the electrically small device  101 . This induces the total internal magnetic field  301  having a same magnitude as the external magnetic field  330  but in an opposing direction, and this nullifies the magnetic field through the electrically small device  101  as measured by its magnetic field sensor. 
     Upon changes in three-dimensional orientation of the electronic circuit and its electrically small device  101  relative to the external magnetic field  330  or the geomagnetic field, the magnetic field sensor is adapted to measure corresponding changes in the horizontal and vertical components of the magnetic field through the electrically small device  101 . In response, the controller is adapted to continue to control the current through the central coil  310  and the respective currents through each of the peripheral coils  321 ,  322 ,  323 ,  234 ,  325 , and  326  to induce the internal magnetic field  301  having a same magnitude as the external magnetic field  330  but in an opposing direction to nullify the magnetic field through the electrically small device  101 . 
     Although the central coil  310  and the peripheral coils  321 ,  322 ,  323 ,  234 ,  325 , and  326  as shown in  FIG. 3  have fairly good decoupling for nullification of the vertical and horizontal components of the magnetic field through the electrically small device  101 , the controller  150  is not required to independently control the vertical and horizontal components of the magnetic field. For example, the induced horizontal magnetic field  301  shown in  FIG. 5  has a slight outward bowing at the electrically small device  101 , and this slight outward bowing can be flattened with a small current through central coil  310  that induces a weak vertical magnetic field in a direction opposite to that shown in  FIG. 4 . 
     Generally, for arrangements of coils having less decoupling than the arrangement of central coil  310  and the peripheral coils  321 ,  322 ,  323 ,  234 ,  325 , and  326  as shown in  FIG. 3 , such as the arrangements of coils shown in  FIG. 6-10 , electromagnetic simulations and careful measurement of actual performance can produce the appropriate amperages needed to induce an internal magnetic field that best nullifies any amplitude and three-dimensional direction of the external magnetic field. The controller  150  can include tables or formulae for incrementally updating the respective current through each of the coils given a measurement of an amplitude and a three-dimensional direction of the residual magnetic field currently passing through the electrically small device  101 . This produces time-varying currents, and controller  150  can include a transfer function that amplifies certain frequency ranges of the time-varying currents to compensate for expected attenuation produced when conductive plate  102  is included. 
     The electronic package  300  includes conductive connectors, such as the conductive connector  340  shown in  FIG. 3-5  for supplying the respective current to coil  321 . The other coils  310 ,  322 ,  323 ,  234 ,  325 , and  326  have similar conductive connectors that are not shown. Because the conductive connector  340  supplying current induces a stray magnetic field that could adversely affect the electrically small device  101 , the supply conductive connector  340  and the corresponding return conductive connector  342  are arranged as close as possible to each other so that their stray magnetic fields tend to cancel each other. Returning to  FIG. 1 , if supply conductive connector  160  is routed immediately to a portion of patterned conductive layer  145  adjacent return conductive connector  168  in patterned conductive layer  147 , then supply conductive connector  160  and return conductive connector  168  can be extended to reach controller  150  in patterned conductive layers  145  and  147  while separated only by the thin insulation layer  146 , such that the stray magnetic fields of the supply and return currents cancel each other at a short distance from patterned conductive layers  145  and  147 . 
     Other conductive connectors include conductive connector  344  shown in  FIGS. 4 and 5  for communicating with the electrically small device  101 . For example, when the electrically small device  101  is an RF receiver, the conductive connector  344  carries information specifying the RF signal received by the RF receiver. When the electrically small device  101  is an RF transmitter, the conductive connector  344  carries information specifying the RF signal to be transmitted from the RF transmitter. 
     In one embodiment, a coaxial cable connects the conductive connector  344  to an external system. Due to the temperature differential between the external system at room temperature and the electrically small device  101  when the electrically small device  101  is cooled to a cryogenic temperature by cold finger  180 , the connecting coaxial cable encounters a range of temperatures that affect many properties of the coaxial cable including varying its impedance from the nominal impedance along its length. This varying impedance produces reflections of the RF signal that can corrupt the received RF signal. 
     However, the external system can compensate when the varying impedance is known. Conductive connectors  350 ,  352 , and  354  help characterize the varying impedance of coaxial cables connected thereto. In one embodiment, conductive connectors  350 ,  352 , and  354  are RP-SMA (reverse polarity surface mount adaptors) respectively connected to an electrical short  351 , a nominal impedance  353  of  50  ohms in this example, and an electrical open  355 . The external system having a representative coaxial cable connected to each of the conductive connectors  350 ,  352 , and  354  can calibrate properties of the coaxial cable including its varying impedance. The calibration circuit of electrical short  351 , nominal impedance  353 , and electrical open  355  is provided in electronic package  300  or in electrically small device  101 . 
       FIGS. 6, 7, 8, 9, and 10  are cross-sectional diagrams of various embodiments of coils of an electronic package for an electrically small device. It will be appreciated that a particular electronic package has layers similar to patterned conductive layers  141 ,  143 ,  145 , and  147  of  FIG. 1 , with each patterned conductive layer having the same or different arrangement of coils. For example, the particular electronic package has two patterned conductive layers with one having coils as shown in  FIG. 7  and the other having coils as shown in  FIG. 8 , with each coil on each layer independently driven or with overlapping coils on different patterned conductive layers forming a single coil. 
       FIG. 6  is a cross-sectional diagram of an electronic package  600  for an electrically small device in accordance with an embodiment of the invention having a central coil  601  and a single peripheral coil  602 . One particular type of electrically small device is adversely affected by a component of an external magnetic field lying in a plane, but is not affected by a component of the external magnetic field perpendicular to this plane. For example, the electrically small device is adversely affected by the component of an external magnetic field in the x-z plane of  FIG. 6 , but not by the component of the external magnetic field along the y axis. A central coil  601  underneath the electrically small device induces a z component of the internal magnetic field at the electrically small device and an adjacent peripheral coil  602  induces an x (and z) component of the internal magnetic field at the electrically small device, such that appropriate currents in coils  601  and  602  induce an internal magnetic field at the electrically small device that nullifies the component in the x-z plane of any external magnetic field. This prevents the external magnetic field from adversely affecting this particular type of electrically small device. 
       FIG. 6  has the advantage of a simple construction having only two coils  601  and  602 , but with the tradeoff of somewhat greater complexity in determining the appropriate currents in coils  601  and  602  for nullifying a measured external magnetic field, and limitation to certain types of electrically small devices. This simple construction outweighs the somewhat greater complexity in certain embodiments where manufacturing cost increases with an increased number of coils and/or manufacturing yield decreases with an increased number of coils. 
       FIG. 7  is a cross-sectional diagram of an electronic package  610  for an electrically small device in accordance with an embodiment of the invention having sixteen coils  612 . The large number of coils increases the flexibility for inducing an internal magnetic field for nullifying an external magnetic field. This flexibility can include that smaller coils  612  induce nearby magnetic fields with more non-linearity, and such a non-linear induced magnetic field can help nullify the external magnetic field at the electrically small device. 
       FIG. 8  is a cross-sectional diagram of an electronic package  620  for an electrically small device in accordance with an embodiment of the invention having a central coil  622  and twelve peripheral coils  624 . 
       FIG. 9  is a cross-sectional diagram of an electronic package  630  for an electrically small device in accordance with an embodiment of the invention having four coils  632 . 
       FIG. 10  is a cross-sectional diagram of an electronic package  640  for an electrically small device in accordance with an embodiment of the invention having ten coils  642 . 
     From the above description of the Electronic Package for an Electrically Small Device with Integrated Magnetic Field Bias, it is manifest that various techniques may be used for implementing the concepts of electronic package without departing from the scope of the claims. The described embodiments are to be considered in all respects as illustrative and not restrictive. The method/apparatus disclosed herein may be practiced in the absence of any element that is not specifically claimed and/or disclosed herein. It should also be understood that electronic package is not limited to the particular embodiments described herein, but is capable of many embodiments without departing from the scope of the claims.