Patent Publication Number: US-9431100-B1

Title: Device and method for storing or switching

Description:
FIELD OF THE INVENTION 
     The invention relates to a device and a method for storing data or for switching an electrical resistance. Furthermore, the device and the method relate to security or encryption applications. 
     BACKGROUND 
     The field of electromechanical memory and switching devices, in particular the field of micro- and nano-electromechanical devices, has become a field of high research activity and technological interest. The capability of storing multi-bit information is one of the challenges in memory technologies. It provides a way to increase the memory density per volume and may pave the way for an improved design on the system level with higher memory density at lower cost. Efforts have been made to develop non-volatile memory devices with reliable data storage at low cost. Among many kinds of memory devices, flash memories which employ a floating gate structure with two programmable charge states are used, wherein their basic operation is based on charge trapping in a floating gate. Nevertheless, flash technology seems to be limited in scaling as charge leakage increases and charge separation becomes increasingly difficult upon scaling down the device dimensions. 
     US 2013/0321064 A1 discloses a single-molecule switching device. A tunneling current is applied across a tunneling junction, wherein the tunneling junction includes an endohedral fullerene that includes a fullerene cage and a trapped cluster. One or more internal motions of the trapped cluster are excited because of the tunneling current. The conductance of the endohedral fullerene is based on the one or more excited internal motions. One or more electronic processes are controlled based on the changed conductance of the endohedral fullerene. 
     The current modulation is based on a rotational change of the trapped cluster inside the fullerene cage. In order to induce this rotational change a higher bias potential must be applied. The rotational change is caused by a larger tunneling current through the endohedral fullerene. Therefore, a bias-based switching is disclosed. 
     BRIEF SUMMARY OF THE INVENTION 
     According to a first aspect, the invention can be embodied as a device, comprising: a first layer including a first molecular network having a first 2-dimensional (2D) lattice structure, a second layer including a second molecular network having a second 2D lattice structure, wherein the first layer and the second layer are arranged at a distance from each other such that the first and the second molecular network interact electronically via molecular orbital interactions, and a rotation device implemented to rotate the first layer relative to the second layer by a rotation angle, wherein an electrical resistance between the first molecular network and the second molecular network changes as a function of the rotation angle. 
     According to a second aspect, the invention can be embodied as a method for storing or switching, comprising: arranging a first layer including a first molecular network having a first 2D lattice structure and a second layer including a second molecular network having a second 2D lattice structure at a distance from each other such that the first and the second molecular network interact electronically via molecular orbital interactions, and rotating the first layer relative to the second layer by a rotation angle with a rotation device, wherein an electrical resistance between the first molecular network and the second molecular network changes as a function of the rotation angle, thereby storing information by switching the electrical resistance. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a perspective view of a first embodiment of a device; 
         FIG. 2A  shows molecular building blocks of the first 2D and the second 2D layer of the device of  FIG. 1  when the molecular networks are aligned, hence interaction by molecular orbitals taking place; 
         FIG. 2B  shows molecular building blocks of the first 2D and the second 2D layer of the device of  FIG. 1  when the molecular networks are misaligned, hence no molecular orbital interaction taking place; 
         FIG. 2C  shows a top view of  FIG. 2B ; 
         FIG. 2D  shows the resistance as a function of the rotation angle for the device having a first layer and a second layer as shown in  FIG. 2A ; 
         FIG. 3A to 3D  show different 2D lattice structures for the first and second molecular network as shown in  FIG. 2A ; 
         FIG. 4  shows alternative heterogeneous molecular building blocks of the first and second 2D layers of  FIG. 1  for the case of aligned 2D lattice structures; 
         FIGS. 5A and 5B  show different 2D lattice structures for the first and second molecular network as shown in  FIG. 4 ; 
         FIG. 6  shows the resistance as a function of the rotation angle for a device having a first layer and a second layer comprising molecular building blocks as shown in  FIG. 4 ; 
         FIG. 7  shows an arrangement of the first and second layer at preferred rotation angles; 
         FIG. 8  shows a sequence of the preferred rotation angles shown in  FIG. 7  with the time; 
         FIG. 9  shows the current corresponding to the sequence as depicted in  FIG. 8 ; 
         FIG. 10  shows an alternative position of the rotation axis; 
         FIG. 11  shows a top view of a second embodiment of a device; and 
         FIG. 12  shows a cross section of the device of  FIG. 11 . 
     
    
    
     Similar or functionally similar elements in the figures have been allocated the same reference signs if not otherwise indicated. 
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       FIG. 1  shows a perspective view of a first embodiment of a device  1 . The device  1  comprises a first layer  2 , a second layer  3  and a rotation device  4 . The first layer  2  includes a first molecular network  5  having a first 2D lattice structure. Further, the second layer  3  includes a second molecular network  6  having a second 2D lattice structure. 
     First and second layer  2 ,  3  are arranged at a distance  7  from each other. The distance  7  is chosen such that the first and second molecular network  5 ,  6  interact electronically via molecular orbital interactions. The rotation device  4  can rotate the first layer  2  relative to the second layer  3  by a rotation angle Θ. That means the first layer  2  defines a plane with two orthogonal directions x and y. A rotation axis  8  which can be orthogonal to the first and second layer  2 ,  3  and to the directions x, y is located somewhere in the first layer  2 , preferably in the center of the first layer  2 . The first layer  2  can be rotated by the rotation device  4  around the rotation axis  8  by the rotation angle Θ. In an alternative, the second layer  3  is rotated. 
     An electrical resistance R is measured between the first molecular network  5  and the second molecular network  6 . The electrical resistance R changes as a function of the rotation angle Θ. 
     Therefore, the resistance response pattern upon rotational changes of device  1  is functionally independent from an additional bias voltage. This is in particular the case when operating the device as a memory or resistance switching device. The change in resistance is predominantly induced by the mechanical rotation. 
     The first layer  2  including the first molecular network  5  and/or the second layer  3  including the second molecular network  6  comprise a first dimension d 1  and a second dimension d 2 . As can be seen in  FIG. 1  the first dimension d 1  can be smaller than the second dimension d 2 . In this case the first dimension d 1  can be in the range 1 to 100 nm and preferably in the range 5 to 50 nm. However, the first layer  2  including the first molecular network  5  and/or the second layer  3  including the second molecular network  6  can also have a square or circular shape. In this case there is only one dimension d, wherein the parameter d can be in the range 1 to 100 nm and preferably in the range 5 to 50 nm. 
       FIG. 2A  shows a first molecular building block  9  of the first layer  2  and a second molecular building block  10  of the second layer  3  of the device  1  of  FIG. 1 . As depicted in  FIG. 2A  the first molecular network  5  and the second molecular network  6  are aligned. Therefore, also the first molecular building block  9  and the second molecular building block  10  are aligned. 
     The first layer  2  including the first molecular network  5  and/or the second layer  3  including the second molecular network  6  can comprise between 1 and 500000 molecular building blocks  9 ,  10 , preferably between 1 and 1000 molecular building blocks  9 ,  10  and more preferably between 1 and 500 molecular building blocks  9 ,  10 . That means a layer  2 ,  3  can comprise a molecular network  5 ,  6  and the molecular network  5 ,  6  can comprise one or more molecular building blocks  9 ,  10 . 
     For example, the first or second molecular network  5 ,  6  can be implemented as graphene-like systems having a cross-sectional extension in-plane of about 100 nanometers. Then, roughly 100.0000-200.00 benzene-like molecular building blocks  9 ,  10  are involved. 
     The molecular building block  9 ,  10  can comprise molecular orbitals  13  which can be hybridized orbitals, especially sp 2  and/or sp a  orbitals. That means also the first molecular network  5  and/or the second molecular network  6  can comprise hybridized orbitals, especially sp 2  and/or sp a  orbitals. 
     The first molecular network  5  has a first 2D lattice structure  11  and the second molecular network  6  has a second 2D lattice structure  12 . As can be seen in  FIG. 2A  the first 2D lattice structure  11  and the second 2D lattice structure  12  can be identical. The 2D lattice structure  11 ,  12  is given by the number and arrangement of the molecular orbitals  13  of the corresponding molecular building block  9 ,  10  and the distance between the molecular orbitals  13  of the corresponding molecular building block  9 ,  10 . 
     As can be seen in  FIG. 2A  the molecular orbitals  13  of the first molecular network  5  are of the same kind and the molecular orbitals  13  of the second molecular network  6  are of the same kind. Also, the molecular orbitals  13  of the first and second molecular networks  5 ,  6  can be of the same kind. 
     The first layer  2  and the second layer  3  can be arranged such that the molecular orbitals  13  of the first molecular network  5  and the molecular orbitals  13  of the second molecular network  6  provide an electronic interaction mechanism  14 . Furthermore, the electronic interaction mechanism  14  can be implemented to change the electronic overlap as a function of the rotation angle Θ. When the molecular orbitals  13  of the first molecular building block  9  are arranged above the molecular orbitals  13  of the second molecular building block  10  then a molecular orbital  13  of the first molecular building block  9  strongly electronically interacts forming a hybridized joint molecular orbital  14  to the second molecular building block  10 . 
       FIG. 2B  shows the first molecular building block  9  of the first layer  2  and the second molecular building block  10  of the second layer  3  of the device  1  of  FIG. 1 . As depicted in  FIG. 2B  the first molecular network  5  and the second molecular network  6  are misaligned. 
     In contrast to the situation of  FIG. 2A  in  FIG. 2B  the first layer  2  has been rotated with rotation angle Θ. As a result the molecular orbitals  13  of the first molecular network  5  and the second molecular network  6  do not provide an electrical interaction  14  any more. Therefore, in the arrangement of the layers  2 ,  3  as depicted in  FIG. 2B  the resistance R will be high. 
       FIG. 2C  shows a top view of  FIG. 2B . The solid line corresponds to the first layer  2 , the first molecular network  5  and the first molecular building block  9 . The dotted line corresponds to the second layer  3 , the second molecular network  6  and the second molecular building block  10 . 
     As can be seen when the first molecular building block  9  is arranged to the second molecular building block  10  as depicted in  FIG. 2C  there is no molecular orbital interaction leading to current suppression between the molecular orbitals  13  of the different molecular building blocks  9 ,  10 . 
       FIG. 2D  shows the electrical resistance R as a function of the rotation angle Θ (solid line) for the device  1  having a first layer  2  and a second layer  3  as shown in  FIG. 2A . 
     When the molecular orbitals  13  of the different molecular building blocks  9 ,  10  are perfectly aligned above each other (situation as shown in  FIG. 2A ) then the electrical resistance R has a local minimum. That means the device  1  is in the on state  15  and a current can flow between the first and second layer  2 ,  3 . When the molecular orbitals  13  of the different molecular building blocks  9 ,  10  are perfectly misaligned (a situation shown in  FIGS. 2B and 2C ) then the electrical resistance R has a local maximum. That means the device  1  is in the off state  16  and no current will flow between the first and second layer  2 ,  3 . 
     As can be seen in  FIG. 2D  the on state  15  is only realized at certain rotation angles Θ. In contrast thereto, the device is in the off state for certain ranges of rotation angles Θ. That is because the electrical interaction  14  is very sensitive to the rotation angle Θ. For the hexagonal 2D lattice structure  11 ,  12  as shown in  FIG. 2A  the on state  15  is repeated at an rotation angle Θ of 60°. 
       FIG. 3A to 3D  show different 2D lattice structures  11 ,  12  for a first and second molecular network  5 ,  6  as shown in  FIG. 2A . As described before, the 2D lattice structure  11 ,  12  is given by the number of the molecular orbitals  13 , by the arrangement of the molecular orbitals  13  and by the distance between the molecular orbitals  13 . 
     In  FIG. 3A to 3D  is always only one molecular building block  9 ,  10  depicted. The first 2D lattice structure  11  and/or the second 2D lattice structure  12  can have an arbitrary shape. Especially, the first 2D lattice structure  11  and/or the second 2D lattice structure  12  can have a hexagonal shape (see  FIG. 3A ), a pentagonal shape (see  FIG. 3B ), a square shape (see  FIG. 3C ) and a triangular shape (see  FIG. 3D ). 
       FIG. 4  shows alternative molecular building blocks  9 ,  10  of the first and second layer  2 ,  3  of  FIG. 1  when the molecular networks  5 ,  6  are aligned. As can be seen from  FIG. 4  there are two kinds of interacting molecular orbital situations. There are first molecular orbitals  13   a  and second molecular orbitals  13   b . Further, there are first electrical interactions by hybridized orbitals  14   a  between first molecular orbitals  13   a  of two different molecular building blocks  9 ,  10  and there are second electrical interactions by hybridized orbitals  14   b  between second molecular orbitals  13   b  of two different molecular building blocks  9 ,  10 . 
     In principal, the first molecular network  5  and the second molecular network  6  can comprise molecular orbital interactions of several kinds  13   a ,  13   b , especially two, three or four kinds of molecular orbital interactions  13 . 
       FIGS. 5A and 5B  show different 2D lattice structures  11 ,  12  for a first and second molecular network  5 ,  6  as shown in  FIG. 4 . As can be seen in these 2D lattice structures  11 ,  12  first molecular orbitals  13   a  alternate with second molecular orbitals  13   b .  FIG. 5A  shows a hexagonal 2D lattice structure  11 ,  12  and  FIG. 5B  shows a square 2D lattice structure  11 ,  12 . 
       FIG. 6  shows the electrical resistance R as a function of the rotation angle Θ for a device  1  having a first layer  2  and a second layer  3  as shown in  FIG. 4 . The electrical resistance R reaches a local maximum, i.e. an off state  16 , when the first molecular network  5  and the second molecular network  6  are perfectly misaligned. However, there are two local minima  15   a ,  15   b  of the electrical resistance R. The first local minima, i.e. the first on state  15   a , is reached when the molecular orbitals  13   a  and the molecular orbitals  13   b  of the two different layers  2 ,  3  are aligned. The second local minima, i.e. the second on state  15   a , is reached when the molecular orbitals  13   a  of one layer  2 ,  3  are aligned with molecular orbitals  13   b  of the other layer  3 ,  2 . 
     The first molecular network  5  and/or the second molecular network  6  is one of the group of: benzene, graphene, phenyl, oligophenyl, pyridine or tetrathiafulvalene. A preferred material can be phenyl with distinct sp 2  orbitals. More complicated are oligophenyles which possess conjugated π-systems and the pitch between them is defined by C—C single, double or triple bonds (C: carbon). Substitution of the C can lead in artificial structures, namely pyridines, tetrathiafulvalene (TTF), etc. The molecular building blocks  9 ,  10  can be self-linking to each other due to the attractive forces in the orbital landscape, e.g. the p-p stacking in phenyl. 
       FIG. 7  shows an arrangement of the first and second layer  2 ,  3  at preferred rotation angles Θ. The example of  FIG. 7  shows a first and a second layer  2 ,  3  comprising graphene.  FIG. 7  shows four different figures for four different rotation angles Θ. In a first figure the first layer  2  is rotated by a rotation angle Θ of 0°. That means the first layer  2  is not rotated with respect to the second layer  3 . In a second figure the first layer  2  is rotated by a rotation angle Θ of 10°. In a third figure the first layer  2  is rotated by a rotation angle Θ of 21.8°. And in a fourth figure the first layer  2  is rotated by a rotation angle Θ of 38.2°. 
     There are locations  17  where a first molecular building block  9  and a second molecular building block  10  are aligned. The more of these locations  17  are present at a rotation angle Θ the lower the electrical resistance R between the first and the second layer  2 ,  3  is. As can be seen in  FIG. 7  the most of these locations  17  can be found by a rotation angle Θ of 0° and no of these locations  17  can be found for a rotation angle Θ of 10°. For a rotation angle Θ of 21.8° more of these locations  17  can be found than for a rotation angle Θ of 38.2°. 
     The first layer  2  and the second layer  3  can be arranged such that the electrical resistance R has a local minimum at preferred rotation angles. For a first layer  2  and a second layer  3  comprising graphene, such preferred rotation angles Θ are 0°, 21.8° and 38.2°. 
       FIG. 8  shows a sequence of the preferred rotation angles Θ shown in  FIG. 7  with the time t. 
       FIG. 9  shows the current A corresponding to the sequence as depicted in  FIG. 8 . As can be seen the highest current A will flow between first layer  2  and second layer  3  for an rotation angle Θ of 0°. There will flow some current A for a rotation angle Θ of 21.8° and there will flow no current A for a rotation angle Θ of 10°. 
       FIG. 10  shows an alternative position of the rotation axis  8 . The rotation device  4  is implemented to rotate the first layer  2  relative to the second layer  3  about the rotation axis  8 , wherein the rotation axis  8  is located outside the first and second layer  2 ,  3 . 
       FIG. 11  shows a top view of a second embodiment of the device  1 . The rotation device  4  comprises at least one actuator  18  coupled to the first or second layer  2 ,  3 . Especially, the rotation device  4  can comprise one, two, three, four or five actuators  18 . The device  1  shown in  FIG. 11  comprises two actuators  18 . 
     The device  1  can comprise a housing  19 . Further, the rotation device  4  can comprise guide arms  20 , wherein the actuators  18  are arranged in the guide arms  20 . The guide arms are connected with the first or second layer  2 ,  3  and the housing  19 . Therefore, the guide arms  20  can guide the rotation of the first layer  2  with respect to the second layer  3  or vice versa. 
     In an alternative the guidance and the actuation can be separated. The guidance can be realized by a bearing. Further, the actuation can be realized with an electro motor, by using a magnetic effect or by using a piezo effect. 
     Each of the first and the second layer  2 ,  3  can be in electrical contact with a metal layer  21 . Each of the metal layers  21  are contacted by electrical contacts  22 . 
       FIG. 12  shows a cross section of the device of  FIG. 11  along the XI-XI line. As can be seen the device  1  can further comprise a device  23  for injecting a current across the first and second layer  2 ,  3 . The device  1  can also comprise a device  24  for measuring the current flowing from the first to the second layer  2 ,  3 . Especially, the device  24  for measuring the current measures the current injected by the device  23  for injecting a current. The device  24  for measuring the current and the device  23  for injecting a current can be one single device. 
     The device  24  for measuring the current further comprises a first and a second metal layer  21   a ,  21   b , wherein the first layer  2  is in contact with the first metal layer  21   a  and the second layer  3  is in contact with the second metal layer  21   b . Further, a first electrical contact  22   a  can establish an electrical connection between the first metal layer  21   a  and the device  24  for measuring the current. Also, a second electrical contact  22   b  can establish an electrical connection between the second metal layer  21   b  and the device  24  for measuring the current. 
     As shown in  FIG. 12  the second layer  3  and the second metal layer  21   b  can be arranged on a carrier  25 . The first layer  2  and the first metal layer  21   a  can rotate with respect to the second layer  3  and the second metal layer  21   b.    
     The first layer  2  can include several first molecular networks  5  layered in a stack and/or the second layer  3  can include several second molecular networks  6  layered in a stack. Handling of the device  1  becomes easier when each of the first and second layer  2 ,  3  comprises several molecular networks  5 ,  6  layered in a stack. 
     Further a method for storing data or for switching an electrical resistance R is described. The method comprises arranging a first layer  2  including a first molecular network  5  having a first 2D lattice structure  11  and a second layer  3  including a second molecular network  6  having a second 2D lattice structure  12  at a distance  7  from each other such that the first and the second molecular network  5 ,  6  interact electrically. The method further comprises rotating the first layer  2  relative to the second layer  3  by a rotation angle Θ with a rotation device  4 . Thereby, an electrical resistance R between the first molecular network  5  and the second molecular network  6  changes as a function of the rotation angle Θ. 
     Therefore, by manipulating the rotation angle Θ an electrical resistance R can be stored. Further, by manipulating the rotation angle Θ an electrical resistance R can be switched. For security, a series of current signals can be associated with a series of rotation angles Θ. The device and method therefore allow for a non-volatile resistance or information storage. In particular, the resulting relative electrical resistance with respect to different rotational angles is generally defined by the respective angle and not by an additional bias voltage across the layer system. Multilevel memory elements are also feasible. 
     The electrical resistance R can be stored or switched by a rotation angle Θ in the range of 0.001° and 0.1°, preferably in the range of 0.005° and 0.015°. A sensitivity of 0.01° for rotational changes can be realized. 
     More generally, while the present invention has been described with reference to certain embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the present invention. In addition, many modifications may be made to adapt a particular situation to the teachings of the present invention without departing from its scope. Therefore, it is intended that the present invention not be limited to the particular embodiments disclosed, but that the present invention will include all embodiments falling within the scope of the appended claims. 
     REFERENCE SIGNS 
     
         
           1  device 
           2  first layer 
           3  second layer 
           4  rotation device 
           5  first molecular network 
           6  second molecular network 
           7  distance 
           8  rotation axis 
           9  first molecular building block 
           10  second molecular building block 
           11  first 2D lattice structure 
           12  second 2D lattice structure 
           13  molecular orbital 
           13   a  first molecular orbital 
           13   b  second molecular orbital 
           14  electrical interaction 
           14   a  first electrical interaction 
           14   b  second electrical interaction 
           15  on state 
           15   a  first on state 
           15   b  second on state 
           16  off state 
           17  location 
           18  actuator 
           19  housing 
           20  guide arm 
           21  metal layer 
           21   a  first metal layer 
           21   b  second metal layer 
           22  electrical contact 
           22   a  first electrical contact 
           22   b  second electrical contact 
           23  device for injecting a current 
           24  device for measuring the current 
           25  carrier 
         x direction 
         y direction 
         Θ rotation angle 
         R electrical resistance 
         d dimension 
         d 1  first dimension 
         d 2  second dimension 
         t time 
         A current