Abstract:
The present invention relates to non-volatile memory chips having graphene drums. In some embodiments, the non-volatile memory chips have one or more layers that each includes a plurality of graphene-drum memory chip cells.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This patent application is a §371 national stage patent application based on International Patent Application No. PCT/US11/55167 filed Oct. 6, 2011, entitled “NON-VOLATILE GRAPHENE-DRUM MEMORY CHIP,” which claims priority to U.S. Provisional Patent Application No. 61/391,727, filed on Oct. 11, 2010, which are both incorporated herein by reference in their entirety. 
     TECHNICAL FIELD 
     The present invention relates to non-volatile memory chips having graphene drums. 
     SUMMARY OF THE INVENTION 
     Graphene membranes (also otherwise referred to as “graphene drums”) have been manufactured using process such as disclosed in Lee et al. Science, 2008, 321, 385-388. PCT Patent Appl. No. PCT/US09/59266 (Pinkerton) (the “PCT US09/59366 Application”) described tunneling current switch assemblies having graphene drums (which graphene drums generally having a diameter between about 500 nm and about 1500 nm). As described in the PCT US09/59366 Application, which is attached hereto at Appendix A, the graphene drum is capable of completely sealing the chamber formed by the graphene drum (i.e., the graphene drum provides a complete seal to fluids inside and outside the chamber). U.S. Patent Appl. No. 61/301,209 (Pinkerton) (“the &#39;209 Application) described pump and engine systems having graphene drum. The &#39;209 Application is attached hereto at Attachment B. 
     In embodiments of the present invention, graphene drums are employed in a non-volatile memory chip, i.e. a graphene-drum memory chip (“GDMC”). 
     Advantages of utilizing graphene drums in a memory chip include:
         a. The GDMC can have many active layers. This is because the GDMC does not require the pure silicon at the bottom of the chip like current flash devices.   b. Many memory elements can share the same input/output wiring. This is because each graphene drum within a cell has a unique mechanical resonant frequency that can be addressed by driving the entire cell with an electrical frequency that matches this mechanical frequency.   c. Each cell (which might contain 1000 graphene drums) can be addressed with just four input/output pins per layer. This can be done by selecting a unique row and column by matching the electrical input to the mechanical resonant frequency of a graphene drum that connects to a given row/column.   d. The graphene drum memory chip requires less power to read/write than flash memory because it takes less voltage (typically less than 1 volt) to read/write an array of graphene drums.   e. The power demand of the memory chip is reduced because many graphene drums within a given array can be read simultaneously by applying a DC voltage and making use of the thermal vibrations of each graphene drum (instead of driving each graphene drum with an AC signal).   f. The device will have a high read speed because many graphene drums within a cell can be read simultaneously.   g. The state of each graphene drum within an array can be rapidly changed by scrolling through a range of resonant frequencies with a voltage signal on a nearby trace.       

     These advantages yield a very high memory density of at least one terabyte per square centimeter (using a relatively conservative 90 nanometer feature size) and low cost per gigabyte (since the device can use lower cost “old” foundries and the gigabyte per mass of material is low). 
     As used herein, a “graphene-drum memory chip” (or “GDMC”) is a memory chip that utilizes one or more graphene drums (such as a memory chip that utilizes an array of graphene drums). A “graphene-drum memory chip cell” is a cell of a memory chip that utilizes one or more graphene drums. A “graphene-drum memory chip layer” is a layer of a memory chip that utilizes one or more graphene drums. 
     Alternatively, other types of electrically conductive membranes (also referred to as “electrically conductive drums”) may be utilized in lieu of graphene membranes in embodiments of the present invention, such as, for example, graphene oxide membranes. 
     In general, in one aspect, the invention features a memory chip that includes an array of electrically conductive drums that have a range of mechanical resonant frequencies that can be individually addressed with an electrical signal between said electrically conductive drums and a nearby electrically conductive member. 
     Implementations of the invention can include one or more of the following features: 
     The array of electrically conductive drums can be an array of graphene drums. 
     The memory chip can include a layer. The layer can include the array of graphene drums. 
     The layer can include a plurality of graphene drum memory chip cells. Each of the graphene drum memory chip cells can include at least one graphene drum. 
     The memory chip can further include a selection trace system. The selection trace system can include a plurality of selection traces. Each of the graphene memory chip cells can be operably connected to a corresponding pair of selection traces in the selection traces such that each of the graphene memory chip cells can be individually selected by selecting the corresponding pair of selection traces for the graphene-drum memory chip cell. 
     Each of the graphene drums in the plurality of graphene-drum memory chip cells can be operable to be in an “on” position and an “off” position. 
     The memory chip can further include a contact trace system. The contact trace system can include at least one contact trace. A graphene drum in the plurality of graphene-drum memory chip cells is in a first position when the graphene drum is contacting at least one of the contact traces in the contact trace system. The graphene drum in the plurality of graphene-drum memory chip cells is in a second position when the graphene drum is not contacting at least one of the contact traces in the contact trace system. The first position and the second position are either (a) the “on” position and the “off” position, respectively, or (b) the “off” position and the “on” position; respectively. 
     The memory chip further includes a voltage source and an external circuitry. The voltage source can be operable to apply a voltage such that the external circuitry can determine whether the graphene drum memory chip cell of the plurality of graphene-drum memory chip cells is in the “on” or “off” position. 
     The memory chip can further include a high voltage source. The high voltage source that can be operable to apply a pulse individually to the graphene drum in the graphene memory chip cells to switch the graphene drum from the “on” position to the “off” position. 
     The memory chip can further include a trace system. The trace system can include at least a first trace and a second trace. A graphene drum in the plurality of graphene-drum memory chip cells can be in the “on” position when the graphene drum is in a stable equilibrium between the van der Waals forces caused by the first trace and a mechanical restoration force. The graphene drum in the plurality of graphene-drum memory chip cells can be in the “off” position when the graphene drum is in a stable equilibrium between the van der Waals forces caused by the second trace and the mechanical restoration force. 
     The graphene drum does not need to contact the first trace when in the first position. The graphene drum does not need to contact the second trace when in the second position. 
     The graphene drum can be operable to receive a voltage such that a thermal amplitude of the graphene drum can cause an AC tunneling current that can be detected to determine whether the graphene drum is in the “on” position or the “off” position. 
     The memory chip can further include a trace system having at least a first trace and a second trace. The first trace can be in contact with a first layer of oxide positioned between the first trace and the graphene drum. The first layer of oxide can be in contact with a first layer of metal positioned between the first layer of oxide and the graphene drum. 
     A graphene drum in the plurality of graphene-drum memory chip cells can be in a first position when the graphene drum is contacting the first layer of metal. The graphene drum in the plurality of graphene-drum memory chip cells can be in a second position when the graphene drum is not contacting the first layer of metal. The first position and second position can be (a) the “on” position and the “off” position, respectively, or (b) the “off” position and the “on” position, respectively. 
     The second trace can be contacted with a second layer of oxide positioned between the second trace and the graphene drum. The second layer of oxide can be contacted with a second layer of metal positioned between the second layer of oxide and the graphene drum. 
     The memory chip can have a plurality of layers. Each layer of the plurality layers can include an array of graphene drums. Each layer of the plurality layers can include a plurality of graphene-drum memory chip cells. Each of the graphene-drum memory chip cells can include at least one graphene drum of the plurality of graphene drums. 
     Some of the electrically conductive drums of the memory chip can have particles of material on one side. The electrically conductive drums that have particles can have an altered resonant frequency due to the particles there upon. 
     The particles of material can be balls of materials. 
     The electrically conductive drums can be graphene drums. 
     The material of the particles can be a metal. 
     The particles can be particles of sputtered metal. 
     The amount of alteration of the resonant frequency of the electrically conductive drums can depend on the number, size, and location of the particles upon the electrically drums. 
     The memory chip can further include a trace system having at least a first trace and a second trace. The first trace can be in contact of at least one non-conductive feature positioned between the first trace and the graphene drum. 
     The non-conductive feature can be an oxide feature. 
     A graphene drum in the plurality of graphene-drum memory chip cells can be in a first position in which the graphene drum is contacting the non-conductive feature when the graphene drum is in the first position. The graphene drum in the plurality of graphene-drum memory chip cells can be in a second position in which the graphene drum is not contacting the non-conductive feature when the graphene drum is in the second position. The first position and second position can be (a) the “on” position and the “off” position, respectively, or (b) the “off” position and the “on” position, respectively. 
     The particles are operable for enabling a field emission current to flow between the graphene drum and the second trace. 
     In general, in another aspect, the invention features a method of reading a memory state of an electrically conductive drum in an electrically conductive memory chip cell. The electrically conductive drum is operable for moving between a first position and a second position. The method includes applying a voltage between the electrically conductive drum and a nearby electrically conductive member that can cause a tunneling current due to the thermal amplitude of the graphene drum. The method further includes sensing the frequency of the tunneling current. The method further includes determining whether the electrically conductive drum is in the first position or the second position. The first position and second position are (a) the “on” position and the “off” position, respectively, or (b) the “off” position and the “on” position, respectively. 
     Implementations of the invention can include one or more of the following feature 
     The electrically conductive drum can be a graphene drum. 
     The electrically conductive drum can be in a first position in which the electrically conductive drum is contacting the electrically conductive member when the electrically conductive drum is in the first position. The electrically conductive drum can be in a second position in which the electrically conductive drum is not contacting the electrically conductive member when the electrically conductive drum is in the second position. 
     The second position can be a stable equilibrium position where van der Waals forces are balanced with mechanical restoration forces upon the electrically conductive drum when positioned at the second position. 
     The electrically conductive drum can be in a first position in which the electrically conductive drum is not contacting the electrically conductive member when the electrically conductive drum is in the first position. The electrically conductive drum can be in a second position in which the electrically conductive drum is not contacting the electrically conductive member when the electrically conductive drum is in the second position. 
     The first position can be a first stable equilibrium position where van der Waals forces are balanced with mechanical restoration forces upon the electrically conductive drum when positioned at the first position. The second position can be another stable equilibrium position where the van der Waals forces are balanced with the mechanical restoration forces upon the electrically conductive drum when positioned at the second position. 
     The electrically conductive member can be in contact with a first layer of oxide positioned between the electrically conductive member and the electrically conductive drum. The first layer of oxide can be in contact with a first layer of metal positioned between the first layer of oxide and the electrically conductive drum. 
     The electrically conductive drum can be in a first position when the electrically conductive drum is contacting the first layer of metal when the electrically conductive drum is in the first position. The electrically conductive drum can be in the second position when the electrically conductive drum is not contacting the first layer of metal when the electrically conductive drum is in the second position. 
     A second electrically conductive member nearby the electrically conductive drum can be contacted with a second layer of oxide positioned between the second electrically conductive member and the electrically conductive drum. The second layer of oxide can be contacted with a second layer of metal positioned between the second layer of oxide and the electrically conductive drum. 
     The method can further include selecting the electrically conductive drum using a selection trace system operatively connected to the electrically conductive drum memory chip cell. The selection trace system can include a plurality of selection traces. The electrically conductive drum memory chip cell can be operably connected to a corresponding pair of selection traces in the selection traces such that the electrically conductive memory chip cell can be individually selected by selecting the corresponding pair of selection traces for the electrically conductive drum memory chip cell. 
     There has thus been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof may be better understood, and in order that the present contribution to the art may be better appreciated. There are additional features of the invention that will be described hereinafter. 
     In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of the description and should not be regarded as limiting. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  depicts a cutaway view of a single graphene-drum memory chip layer of a graphene-drum memory chip. 
         FIG. 2  depicts a detailed view illustrating how three graphene-drum layers can be stacked in a graphene-drum memory chip. 
         FIG. 3  depicts the stacked graphene-drum memory chip of  FIG. 2 . 
         FIG. 4  depicts an embodiment of the present invention in which the graphene-drum memory chip has graphene drums whose resonant frequency has been altered by the addition of small balls of material on a side of the graphene drums. 
         FIGS. 5A-5D  depict several graphene-drum memory chip cells of the present invention. 
         FIG. 6  depicts an embodiment of the present invention in which the graphene-drum memory chip has a voltage placed between the graphene and a trace. 
     
    
    
     DETAILED DESCRIPTION 
     In an embodiment of the present invention, one or more graphene drums can be utilized in a graphene-drum memory chip.  FIG. 1  depicts a cutaway view of a single graphene-drum memory chip layer  101  of a graphene-drum memory chip. 
     The small drum traces on the left and top of the chip (selection traces  102  and  103 ) are used to select a given row or column of the device. For example, to access the center cell (cell  104 , which contains four graphene drums), one would apply an AC signal with a DC component (via two pins, one of which (pin  105 ) is visible in first figure) to the upper and lower layers of the left selection trace (selection trace  102 ) that matches the mechanical resonant frequency of the middle graphene drum pair  106  (pair is for redundancy). These two redundant graphene drums would then vibrate up/down until they contacted a middle trace which is electrically connected to the middle row in figure. The DC component would help the graphene drums to pull down toward the conductive trace and also help the graphene drum stay engaged with the conductive trace once contact is made. 
     Applying another AC (with a DC component) signal between the upper and lower layers of the top selection trace (selection trace  103 ) that matches the mechanical resonant frequency of the middle graphene drum pair  1 - 7  vibrates these drums up/down until they contacted a middle trace (which is electrically connected to the middle column) in figure. At this point, the upper left selection trace  102  is electrically connected to the middle row and the upper top selection trace  103  is electrically connected to the middle column. The four larger graphene drums (in cell  104 ) that have the active row and column are the “graphene-drum memory chip cell.” 
     To read the memory state (on or off) of each graphene drum within a cell, an AC voltage is applied to the two selection traces at a frequency that matches a given graphene drum within a cell. If the graphene drum is free (not stuck down to a column trace), it will resonate and create an AC tunneling current that can be sensed as “off” by external circuitry (not shown); if the drum is stuck down to the column trace (which is a metallic trace with a thin layer of oxide on its surface to prevent large currents) via attractive van der Waals surface forces it will not generate an AC tunneling current and will be considered “on.” A range of frequencies are applied to the cell until each graphene drum within the cell is found to be on or off. Once finished, the DC component applied to each selection trace is turned off and the graphene drums of the selection traces disengage. The process can then be repeated to read the stated of other graphene drums within other cells using the same process. 
     A resonating graphene drum will have a significant variation in capacitance over its range of travel that will also create a unique current response at the resonant frequency that can be used to sense the state of a graphene drum, even if tunneling current does not occur. 
     Another method to read the memory state of all the graphene drums within a cell simultaneously is to apply a voltage signal that contains a superposition of all of the resonant frequencies of the graphene drums. The resulting current signal can be then be parsed for individual drum responses using a set of bandpass filters, or any other suitable method of time domain or frequency domain signal processing, either with analog or digital electronics. 
     To change the state of graphene drums within a give cell, a relatively high voltage pulse of the same polarity is applied to a given column and row trace, resulting in an electrostatic repulsion that frees any graphene drum that was adhered to the column trace. At this point, an AC signal can be applied to the row and column traces (via the selection traces) that has a frequency that matches the mechanical frequency of a given graphene drum, forcing the graphene drum to resonate until it contacts and adheres to the column trace. A different AC frequency can be used to make a different graphene drum within a cell adhere to the column trace. 
       FIG. 2  depicts a detailed view illustrating how three graphene-drum layers can be stacked in a graphene-drum memory chip, and  FIG. 3  depicts this stacked graphene-drum memory chip. As can be seen in  FIGS. 2-3 , it is possible to stack many layers (three layers  202 ,  203 , and  204  are shown) together to achieve very high storage per unit area. Layer  204  is shown in detail illustrating the graphene sheet  210  (having the graphene drums), the metal sheets  209  and  207 , and oxide sheet  208 . Each of layers  202 ,  203 , and  204  has four via pins that make their way to the bottom of the chip  206  for easy access to a circuit board. For example, Layer  202  has pins  205   a ,  205   b ,  205   c , and  205   d.    
       FIG. 4  depicts a graphene-drum memory chip  401  that has graphene drums  402  whose resonant frequency has been altered by the addition of small balls  403  of material on a side of the graphene drums. Such balls of material can be made of metal. Such balls can be added by a sputtering process, which can be designed to control the number, size, and location of the balls. The number, size, and location of the balls on the graphene drum will alter the resonant frequency of the graphene drum. 
       FIG. 5A  depicts a graphene-drum memory chip cell  501  that does not require the graphene drum to physically contact with the metal traces. As shown in the graphene-drum memory chip cell  501  of  FIG. 5A , a small graphene drum  502  (such as a 5-100 nanometer diameter graphene drum) can move up toward trace  503  (as illustrated in the first position “a” of graphene drum  502  shown by the solid line) or down toward trace  504  (as illustrated in the second position “b” of graphene drum  502  shown by the dashed line). When the graphene drums are this small, there can be a stable equilibrium between (shown as the first position “a and the second position “b” in  FIG. 5A ) the van der Waals force and mechanical restoration force that does not require physical contact between the graphene membrane and metal trace  503  or metal trace  504 . For example, first position “a” could be the “off” state for this particular graphene drum and second position “b” could be the “on” state. 
     To read the memory state, a DC voltage can be applied between the graphene  505  (which is between the oxide  506 ) and trace  503 . The thermal amplitude of the graphene drum  502  (such as in on the order of 1 angstrom) will cause an AC tunneling current at a certain frequency that can be sensed to determine that a particular graphene drum within a cell is in a given state (“off” in the instance illustrated in  FIG. 5A ). To change the state of the pictured graphene drum from “off” (i.e., position “a”) to “on” (i.e., position “b”), a DC voltage with an AC voltage component (with a frequency near the mechanical resonant frequency of the target graphene-drum) is applied between trace  504  and the graphene  505 . After a short time, the graphene drum  502  will move from “off” (i.e., position “a”) to “on” (i.e., position “b”) (wherein position “b” is another non-contact stable equilibrium position where van der Waals forces are balanced with mechanical restoration forces). 
     An advantage of the embodiment illustrated in  FIG. 5A  is that no physical contact is required for any state (thus no mechanical wear). Another advantage is that both the “on” and “off” states can be rapidly read with a DC voltage and that all the graphene drums within a cell can be read at the same time. Each graphene drum within a cell will give off an AC tunneling current at a particular frequency that can be sensed/differentiated by an external circuit just as radio waves of different frequencies can be sensed by a single radio receiver. 
       FIG. 5B  depicts another graphene-drum memory chip cell  507 . As shown in  FIG. 5B , graphene-drum memory chip cell  507  is arranged similar to the graphene-drum memory chip cell  501  shown in  FIG. 5A , in which a thin layer of oxide  508  (such as an oxide disk) is added to metal trace  504  on the side facing graphene drum  502 . The thickness of this thin layer of oxide  508  can be around a few angstroms (i.e., around 1 to 3 angstroms). On the side of the thin layer of oxide  508  facing the graphene drum  502  is a layer of metal  509  (such as a metal disk). The thickness of the layer of metal  509  can be a few nanometers (i.e., around 1 to 3 nm). 
     When graphene-drum memory chip cell  507  is read, the graphene membrane  502  comes within field emission (FE) or tunneling current range of the metal layer  509  and current flows into the metal layer  509 , through the oxide layer  508  and into metal trace  504 . Because the effective resistance of the oxide layer  508  is high, there will be a large voltage drop between the metal layer  509  and metal trace  504  when current is flowing, which in turn lowers the electrostatic attraction between the graphene membrane  502  and the metal layer  509 . Again, due to a balance between van der Waals forces, electrostatic forces, and mechanical restoration forces, the graphene drum  502  will be at a stable equilibrium position near the metal layer that is within FE or tunneling current range. 
     A thermal oscillation (or an induced oscillation) of the graphene membrane will cause an AC FE/tunneling current that has an electrical frequency equal to the mechanical resonant frequency of graphene drum  502 . In this position, the graphene drum  502  is considered to be in an “on” state. In cells that have multiple graphene drums, even though the array of graphene drums within that memory chip cell may have different mechanical properties (such as stiffness), the graphene drums will each establish a precise FE/tunneling distance between themselves and the metal layer due the voltage drop effect described above. 
     To write the memory element shown in  FIG. 5B , an AC voltage (with an electrical frequency equal to the mechanical resonant frequency of graphene drum  502 ) between V 2  and V 3  is used to force graphene drum  502  to mechanically oscillate much more than the other graphene drums connected to trace  503  and metal trace  504 . Eventually, graphene drum  502  will come so close to the metal layer  509  that van der Waals forces will pull graphene drum  502  into the metal layer  509  and graphene drum  502  will “stick” on the metal layer  509 . At this point, graphene drum  502  cannot mechanically oscillate and will thus be in an “off” state. To switch graphene drum  502  back into an “on” state, a voltage V 1  on upper gate  503  can be used to pull graphene drum  502  off of the metal layer  509  with an electrostatic force and allow it to remain in a free state (where it can be read as described above). 
       FIG. 5C  depicts another graphene-drum memory chip cell  510 . As shown in  FIG. 5C , graphene-drum memory chip cell  510  is arranged similar to the graphene-drum memory chip cell  501  shown in  FIG. 5B , in which a thin layer of oxide  511  (such as an oxide disk) is added to trace  503  on the side facing graphene drum  502 . Like oxide  508 , the thickness of this thin layer of oxide  511  can also be around a few angstroms (i.e., around 1 to 3 angstroms). On the side of the thin layer of oxide  511  facing the graphene drum  502  is a layer of metal  512  (such as a metal disk). Like metal layer  509 , the thickness of the layer of metal  512  can be a few nanometers (i.e., around 1 to 3 nm). 
     Graphene-drum memory chip cell  510  can be used just like graphene-drum memory chip cells  501  and  507 , with the benefit that the metal/oxide layers on traces  503  and  504  allow graphene drum  502  to be read over a much wider range of voltages and constructed with relaxed tolerances (because the voltage drop across the oxide layers  508  and  511  allows a precise FE/tunneling gap to be established between graphene drum  502  and the metal layers  509  and  512 , respectively, even if each graphene drum in the cell has significantly different mechanical properties). 
       FIG. 5D  depicts another graphene-drum memory chip cell  513 . As shown in  FIG. 5D , graphene-drum memory chip cell  513  is arranged similar to the graphene-drum memory chip cell  501  shown in  FIG. 5A , in which the graphene drum  502  includes small metallic particles  514  (such as metallic dots) and trace  504  has an array of oxide features  516  on the side facing the graphene drum. 
     The metallic particles  514  will change the mechanical resonant frequency of the graphene drum (as discussed above). Furthermore, the metallic particles will also create an electric field “enhancement factor” that enables a field emission current (I FE )  515  to flow between graphene drum  502  and trace  503 . 
     This field emission current can be used to read the memory state of graphene drum  502  even when the graphene drum  502  is several nm away from trace  503 . This would render the device easier to manufacture than a device that requires 3-10 angstrom tunneling current gaps. 
     To position the graphene drum  502  in an “off” position, an AC voltage between graphene  505  and trace  504  at an electrical frequency close to the mechanical resonant frequency of graphene drum  502  will put the graphene drum  502  in contact with an oxide feature  516 . Once in contact with the oxide feature  515 , graphene drum  502  will remain in this position (i.e., the graphene drum  502  will remain in the “off position”) due to van der Waals forces. 
     To position the graphene drum  502  in an “on,” a voltage can be applied between trace  503  and graphene drum  502 . Once free from the oxide feature  516 , graphene drum  502  will remain in an unstuck position (i.e., the “on” position). To read a graphene drum in an on position, an AC voltage between graphene  505  and trace  503  at an electrical frequency close to the mechanical resonant frequency of graphene drum  502  will put the metallic particles  514  on the graphene drum near enough to trace  503  to produce a time-varying FE current  515  that can be read/measured. When a given graphene drum cannot be read through a FE current at a certain AC voltage excitation frequency it can be assumed to be in the off position (stock on oxide feature  516 ). 
     As oriented above for  FIG. 5D , first position “a” could be the “on” state for this particular graphene drum  513  and second position “b” could be the “off” state (which is opposite the orientation of “on” and “off” as defined above for  FIG. 5A ). The “on” and “off” states are positions relative to one another. A person of skill in the art would understand that one position can be designated as the “on” position for the graphene drum in the graphene-drum memory chip cell, and the other position as the “off” position (and vice versa). 
       FIG. 6  depicts how a given graphene drum cell  602  of an assembly  601  can be chosen by placing a voltage between the graphene of the graphene-drum cell  602  and either trace  604  or trace  605 . As with the other embodiments, the graphene drums  603  within a given graphene-drum cell  602  can be individually addressed by exploiting the differences in the mechanical resonant frequency of each graphene drum  603  within the target graphene-drum cell  602 . A purpose for the cross bar assembly as shown in  FIG. 6  (graphene oxide assembly  601 ) is that it allows for the isolation of one graphene-drum cell from the other cells of the assembly  601  to limit the number of graphene drums within a given graphene cell. By such isolation, each graphene drum within a given cell can have a distinct resonant frequency without varying the size of each graphene drum (or the number and/or placement of the metallic balls) too much. 
     A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims. 
     While embodiments of the invention have been shown and described, modifications thereof can be made by one skilled in the art without departing from the spirit and teachings of the invention. The embodiments described and the examples provided herein are exemplary only, and are not intended to be limiting. Many variations and modifications of the invention disclosed herein are possible and are within the scope of the invention. For example, the selection traces could be replaced with an array of conventional silicon switches to address individual cells. Accordingly, other embodiments are within the scope of the following claims. The scope of protection is not limited by the description set out above, but is only limited by the claims which follow, that scope including all equivalents of the subject matter of the claims. 
     The disclosures of all patents, patent applications, and publications cited herein are hereby incorporated herein by reference in their entirety, to the extent that they provide exemplary, procedural, or other details supplementary to those set forth herein.