Abstract:
Various embodiments of the present invention are directed to a binary signal converter that facilitates distinguishing an original direct signal on a nanowire by superimposing an alternating signal on the original direct signal. The binary signal converter includes an alternating signal source connected to the nanowire that superimposes an alternating signal with an initial amplitude on the nanowire. The binary signal converter may also include a selective alternating signal filter that selectively passes the alternating signal from the nanowire to a signal sink.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates to electronic devices, and, in particular, to electronic device designs that can reliably output well separated, distinguishable high and low signal levels carried by nanowires.  
       BACKGROUND OF THE INVENTION  
       [0002]     During the past fifty years, the electronics and computing industries have been relentlessly propelled forward by ever decreasing sizes of basic electrical components, such as transistors and signal lines, and by correspondingly ever increasing component densities of integrated circuits, including processors and electronic memory chips. Eventually, however, it is expected that fundamental component-size limits will be reached in semiconductor-circuit-fabrication technologies based on photolithographic methods. As the size of components decreases below the resolution limit of ultraviolet light, for example, far more technically demanding and expensive higher-energy-radiation-based technologies need to be employed to create smaller components using photolithographic techniques. Expensive semiconductor fabrication facilities are being rebuilt in order to use the new techniques. Many new obstacles are also expected to be encountered. For example, it is necessary to fabricate semiconductor devices through a series of photolithographic steps, with precise alignment of the masks used in each step with respect to the components already fabricated on the surface of a nascent semiconductor. As the component sizes decrease, precise alignment becomes more and more difficult and expensive. As another example, the probabilities that certain types of randomly distributed defects in semiconductor surfaces result in defective semiconductor devices may increase as the sizes of components manufactured on the semiconductor surfaces decrease, resulting in an increasing proportion of defective devices during manufacture, and a correspondingly lower yield of useful product. Ultimately, various quantum effects that arise only at molecular-scale distances may altogether overwhelm current approaches to component fabrication in semiconductors.  
         [0003]     In view of these problems, researchers and developers have expended considerable research effort in fabricating submicroscale and nanoscale electronic devices using alternative technologies. Nanoscale electronic devices generally employ nanoscale signal wires having widths, and nanoscale components having dimensions, of less than 100 nanometers. More densely fabricated nanoscale electronic devices may employ nanoscale signal wires having widths, and nanoscale components having dimensions, of less than 50 nanometers, or, in certain types of devices, less than 10 nanometers.  
         [0004]     Although general nanowire technologies have been developed, it is not necessarily straightforward to employ nanowire technologies to miniaturize existing types of circuits and structures. While it may be possible to tediously construct miniaturized, nanowire circuits similar to the much larger, current circuits, it is impractical, and often impossible, to manufacture such miniaturized circuits using current technologies. Even were such straightforwardly miniaturized circuits able to be feasibly manufactured, the much higher component densities that ensue from combining together nanoscale components necessitate much different strategies related to removing waste heat produced by the circuits. In addition, the electronic properties of substances may change dramatically at nanoscale dimensions, so that different types of approaches and substances may need to be employed for fabricating even relatively simple, well-known circuits and subsystems at nanoscale dimensions. Thus, new implementation strategies and techniques need to be employed to develop and manufacture useful circuits and structures at nanoscale dimensions using nanowires.  
         [0005]     Nanowire technologies have been developed to fabricate nanoscale electronic devices, such as multiplexer/demultiplexers, by selectively fabricating simple electrical components, such as conductors, transistors, resistors, diodes, and other components, in the gaps between nanowires and overlapping address wires. In general, computational electronic devices that employ nanoscale technologies rely heavily on binary state operations. Electronic devices typically realize binary state operations by generating and transmitting distinguishable high and low voltage and/or current levels. However, at nanoscale dimensions, the electrical components often fail to reliably operate. As a result, nanowire-based nanoscale devices may output voltage and/or current levels that cannot be distinguished as high or low. Electronic devices that depend on receiving distinguishable high or low voltage and/or current levels output by nanoscale devices are, as a result, unable themselves to provide reliable output signals. Designers, manufacturers, and users of these systems have recognized the need for nanoscale-multiplexer/demultiplexer designs that can reliably output well separated, distinguishable low and high voltage and/or current levels.  
       SUMMARY OF THE INVENTION  
       [0006]     Various embodiments of the present invention are directed to a binary signal converter that facilitates distinguishing an original direct signal on a nanowire by superimposing an alternating signal on the original direct signal. The binary signal converter includes an alternating signal source connected to the nanowire that superimposes an alternating signal with an initial amplitude on the nanowire. The binary signal converter may also include a selective alternating signal filter that selectively passes the alternating signal from the nanowire to a signal sink.  
         [0007]     Various embodiments of the present invention are directed to a method for determining whether a high original direct signal or a low original direct signal is being carried on a nanowire. The method comprises providing an alternating signal source connected to the nanowire that superimposes an alternating signal with an initial amplitude on the nanowire, and providing a selective alternating signal filter that selectively passes the alternating signal from the nanowire to a signal sink. The method of the present invention may also include determining whether a high or low direct signal is carried by the nanowire based on detecting an oscillation in the superimposed signal carried by the nanowire.  
         [0008]     Various embodiments of the present invention are directed to a multiplexer/demultiplexer nanowire that tolerates gray scale signal levels. In one embodiment of the present invention, the multiplexer/demultiplexer nanowire comprises a nanowire that carries an original signal, an alternating signal source connected to the nanowire that superimposes an alternating signal with an initial amplitude on the original signal carried by the nanowire. The multiplexer/demultiplexer nanowire may also include a diode having an anode end connected to the nanowire and a cathode end connected to a voltage sink, and a reverse-bias source connected at the cathode end of the diode that supplies a signal to set a forward bias threshold for the diode that selectively passes the alternating signal from the nanowire to the voltage sink. 
     
    
     DETAILED DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  illustrates a nanowire crossbar.  
         [0010]      FIG. 2  illustrates a nanowire junction between two roughly orthogonal nanowires.  
         [0011]      FIGS. 3A-3D  illustrate one of many possible approaches for configuring a network of nanoscale electrical components from a two-layer nanowire crossbar.  
         [0012]      FIGS. 4A-4F  schematically illustrate a number of simple electrical components that can be programmed at the nanowire junctions of nanowires in nanowire crossbars.  
         [0013]      FIG. 5A  illustrates an exemplary nanowire-crossbar multiplexer/demultiplexer.  
         [0014]      FIG. 5B  illustrates a summary of 3-bit binary-code nanowire addresses for the multiplexer/demultiplexer shown in  FIG. 5 .  
         [0015]      FIG. 6A  illustrates a two-way AND logic gate.  
         [0016]      FIG. 6B  illustrates a truth table summarizing input signal combinations and corresponding output signals for the two-way AND logic gate shown in  FIG. 6A .  
         [0017]      FIG. 6C  illustrates an exemplary two-way AND logic-gate that employs pFETs to realize the two-way AND logic gate shown in  FIG. 6A .  
         [0018]      FIG. 7  shows an exemplary voltage axis that can be used to determine binary values of multiplexer/demultiplexer nanowires.  
         [0019]      FIG. 8  illustrates binary signal converters appended the end of each multiplexer/demultiplexer nanowire, that represents one or many possible embodiments of the present invention.  
         [0020]      FIG. 9  illustrates an enlargement of a binary signal converter shown in  FIG. 8 , that represents one of many possible embodiments of the present invention.  
         [0021]      FIG. 10  conceptually illustrates operation of a diode, shown in  FIG. 9 .  
         [0022]      FIG. 11  conceptually illustrates operation of a diode, shown in  FIG. 9 , under a reverse bias.  
         [0023]      FIG. 12  illustrates a modified gray-scale signal range, that represents one of many possible embodiments of the present invention.  
         [0024]      FIGS. 13A-13D  are voltage versus time plots for example oscillating voltages on a nanowire, each representing an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0025]     As discussed below, nanowire crossbars represent one of a number of emerging nanoscale technologies that can be used to construct nanoscale electronic devices, such as multiplexer/demultiplexers. Multiplexer/demultiplexer nanowires often carry voltage signals comprising relatively high-voltage and low-voltage states corresponding to the binary values “1” and “0,” respectively. The relatively high voltage is generally readily distinguishable from the relatively low voltage. However, if the voltage in a wire falls between the high voltage and the low voltage, the binary value represented by the voltage may be indeterminate, leading to subsequent, indeterminate logic output values.  
         [0026]     Various embodiments of the present invention are directed to multiplexer/demultiplexer designs that produce readily distinguishable, binary signals. The present invention is described below in two subsections: (1) an overview of nanowire crossbars, and (2) a discussion of several embodiments of the present invention.  
       Overview of Nanowire Crossbars  
       [0027]     A relatively new and promising technology for manufacturing electronic devices involves nanowire crossbars.  FIG. 1  illustrates a nanowire crossbar. In  FIG. 1 , a first layer of approximately parallel nanowires  102  is overlain by a second layer of approximately parallel nanowires  104  roughly perpendicular, in orientation, to the nanowires of the first layer  102 , although the orientation angle between the layers may vary. The two layers of nanowires form a lattice, or crossbar, each nanowire of the second layer  104  overlying all of the nanowires of the first layer  102  and coming into close contact with each nanowire of the first layer  102  at nanowire intersections that represent the closest contact between two nanowires. Note that the term “nanowire crossbar” may refer to crossbars having one or more layers of sub-microscale, microscale, or larger wires in addition to nanowires.  
         [0028]     Nanowires can be fabricated using mechanical nanoscale imprinting techniques. Alternatively, nanowires can be chemically synthesized and can be deposited as layers of nanowires in one or a few process steps. Other alternative techniques for fabricating nanowires may also be employed. Thus, a two-layer nanowire crossbar comprising first and second layers, as shown in  FIG. 1 , can be manufactured by any of numerous relatively straightforward processes. Many different types of conductive and semi-conductive nanowires can be chemically synthesized from metallic and semiconductor substances, from combinations of these types of substances, and from other types of substances. A nanowire crossbar may be connected to microscale signal-wire leads or other electronic leads through a variety of different methods to incorporate the nanowires into electrical circuits.  
         [0029]     Nanowire crossbars may be used to create arrays of nanoscale electrical components, such as transistors, diodes, resistors, and other familiar basic electrical components.  FIG. 2  illustrates a nanowire junction that interconnects nanowires  202  and  204  of two contiguous layers within a nanowire crossbar. Note that the nanowire junction may or may not involve physical contact between the two nanowires  202  and  204 . As shown in  FIG. 2 , the two nanowires are not in physical contact at their overlap point, but the gap between them is spanned by a small number of molecules  206 - 209 . Various different types of molecules may be introduced at nanowire junctions for a variety of different purposes. In many cases, the molecules of a nanowire junction may be accessed, for various purposes, through different voltage levels or current levels placed on the nanowires forming the nanowire junction. The molecules spanning the nanowire junction in  FIG. 2  may have various different quantum states in which the molecules exhibit resistive, semiconductor-like, or conductive electrical properties. The current passing between the two nanowires interconnected by a nanowire junction may be a nonlinear function of the voltage across the nanowire junction as a result of quantum-mechanical tunneling of electrons through relatively low-energy, unoccupied quantum states of the molecules. The quantum states, and relative energies of quantum states, of the molecules may be controlled by applying differential currents or voltages to the nanowires forming the interaction. For example, molecules may be conductive in a reduced state, but may act as insulators in an oxidized state, with redox reactions controlled by voltage levels determining which of the quantum states the molecules inhabit.  
         [0030]     In general, a nanowire junction is anisotropic, having a polarity or direction with respect to physical properties, including electrical properties. This anisotropy may arise from different chemical and/or physical properties of nanowires in the two layers of a nanowire crossbar, may arise from asymmetries of nanowire-junction molecules, and uniform orientation of the nanowire-junction molecule with respect to the nanowire layers, and may arise both from differences in the properties of the nanowires as well as nanowire-junction-molecule asymmetries. The fact that nanowire junctions may have polarities allows for controlling nanowire junction properties by applying positive and negative voltages to nanowire junctions, eliciting forward and reverse currents within the nanowire junctions.  
         [0031]     As shown in  FIG. 2 , the nanowires may include outer coatings, such as outer coatings  210  and  212 . The outer coatings may serve to insulate nanowires from one another, may constitute the molecules that serve to span nanowire junctions when the nanowires are placed in contact with one another, and/or may serve as modulation-dopant-layers, which can be selectively activated to dope semiconductor nanowires. Both p-type and n-type modulation dopant coatings have been developed. In other applications, the molecules spanning nanowire junctions between overlapping nanowires may be introduced as a separate layer, referred to as “intermediate layer,” formed between layers of nanowires. In some cases, the state changes of nanowire-junction molecules may not be reversible. For example, the nanowire-junction molecules may initially be resistive, and may be made conductive through application of relatively high voltages. In other cases, the nanowire-junction molecules may be conductive, but the molecules may be irreversibly damaged, along with portions of the nanowires proximal to the nanowire junctions, through application of very high voltage levels, resulting in disrupting conductivity between the two nanowires and breaking electrical connection between them. In yet other cases, the nanowire-junction molecules may transition reversibly from one state to another and back, so that the nanoscale electrical components configured at nanowire junctions may be reconfigured, or programmed, by application of differential voltages to selected nanowire junctions.  
         [0032]     One type of nanowire junction that can be configured behaves as if it were a resistor in series with a switch that may be opened or closed. When the switch is closed, the nanowire-junction molecule connects the overlapping nanowires at the nanowire junction. When the switch is open, the nanowire junction molecule spanning the nanowire junction has no effect on the current.  
         [0033]     Nanowire junctions can be configured electrically, optically, mechanically or by other means.  FIG. 3  illustrates one possible approach to configuring a network of reconfigurable nanoscale electrical components from a two-layer nanowire crossbar. In  FIGS. 3A-3D , a small 3×3 nanowire crossbar is shown, with circles at all nine nanowire junctions that indicate the state of the nanowire-junction molecules. In one state, labeled “ 1 ” in  FIGS. 3A-3D , the nanowire-junction molecules may have certain semiconductor, or conductive properties, while in a second state, labeled “ 2 ” in  FIGS. 3A-3D , nanowire-junction molecules may have different properties. Initially, as shown in  FIG. 3A , the states of the nanowire junctions of the nanowire crossbar  300  are in the state labeled “ 2 .” Next, as shown in  FIG. 3B , each nanowire junction may be uniquely accessed by applying a WRITE voltage, or configuring voltage, to the nanowires that form the nanowire junction in order to configure, or program, the nanowire junction to have the state “ 1 .” For example, in  FIG. 3B , a first WRITE voltage v w ′ is applied to horizontal nanowire  302  and a second WRITE voltage v w ″ is applied to vertical nanowire  304  to change the state of the nanowire junction  306  from “ 2 ” to “ 1 .” Individual nanowire junctions may be configured through steps similar to the steps shown in  FIG. 3B , resulting finally in a fully configured nanoscale component network as shown in  FIG. 3C . Note that, in  FIG. 3C , the states of nanowire junctions  306 ,  308 , and  310 , forming a downward-slanted diagonal through the nanowire crossbar have been configured by selective application of WRITE voltages. Finally, as shown in  FIG. 3D , the nanoscale electrical component network can be used as a portion of an integrated circuit. Input voltages v i ′, v i ″, and v i ′″ may be applied to the nanoscale electrical component lattice as inputs  312  and output voltages v o ′, v o ″, and v o ′″  314  may be accessed as the result of operation of the nanoscale electrical component network that represents a portion of an integrated circuit. In general, the input and output voltages v i ′, v i ″, and v i ′″ and v o ′, v o ″, and v o ′″ have relatively low magnitudes compared with the WRITE voltages v w . Depending on the types of nanowires, types of dopants employed in the case of semiconductor nanowires, and the types of nanowire-junction molecules employed in the nanowire crossbar, many different, but similar configuring processes may be used to configure nanowire crossbars into nanowire-based electrical components networks. The example of  FIG. 3  is meant to illustrate a general process by which nanowire crossbars may be configured as useful portions of electronic circuits.  
         [0034]     Nanowire junctions in nanowire crossbars may be configured, in various techniques depending on the chemical nature of the nanowires and nanowire-junction-spanning molecules, to form a wide variety of different, simple electrical components.  FIG. 4  schematically illustrates a number of simple electrical components that can be configured at nanowire junctions in nanowire crossbars. A nanowire junction may represent (1) a simple conductive connection between two nanowires, as shown in  FIG. 4A ; (2) a diode that conducts current in only one direction between two nanowires, as shown in  FIG. 4B ; (3) a resistor, with the magnitude of resistance configurable by application of different configuring voltages, as shown in  FIG. 4C ; (4) a negatively doped field-effect transistor (“nFET”), as shown in  FIG. 4D ; (5) a positively doped field-effect transistor (“pFET”), as shown in  FIG. 4E ; and (6) the overlapping of two conductive nanowires, with the voltage and current associated with each nanowire completely independent from one another, as shown in  FIG. 4F .  
         [0035]     The nFET and pFET electrical components perform switch operations, controlled by the signal level placed on gate wires, that can either enable or disable source/drain wires. An enabled source/drain wire allows current to flow beyond the nFET or pFET electrical component, and the flow of current beyond the nFET or pFET electrical component is not allowed in a disabled source/drain wire. However, nFETs and pFETs exhibit opposite behavior based on the signal level applied to the gate wires. In the case of the nFET, shown in  FIG. 4D , a relatively low signal on the gate nanowire  402  causes the nFET to disable source/drain nanowire  404 , while a relatively high signal on gate nanowire  402  causes nFET to enable source/drain nanowire  404 . By contrast, in the case of the pFET, shown in  FIG. 4E , a relatively low signal on gate nanowire  406  causes the pFET to enable source/drain nanowire  408 , and a relatively high signal on gate nanowire  406  causes the pFET to disable source/drain nanowire  408 . Note that a electrical component may also be configured as an insulator, essentially interrupting conduction at the electrical component with respect to both overlapping nanowires.  
         [0036]     Thus, as discussed above with reference to  FIGS. 1-4 , a two-dimensional nanowire crossbar may be fabricated and then configured as a network of electrical components. Note also that a nanowire junction, although shown in  FIGS. 4A-4F  to comprise the nanowire junction of two single nanowires, may also comprise a number of nanowire junctions between a number of nanowires in a first layer of a nanowire crossbar that together comprise a single conductive element and the nanowires in a second nanowire layer that together comprise a second conductive element.  
         [0037]     The configurable electrical resistances of nanowire junctions are important and special properties of certain types of nanowire junctions. When certain types of molecules are used for nanowire junctions, the initially relatively high resistances of the nanowire junctions may be lowered by applying relatively large positive voltages to the nanowire junctions. The resistances of the nanowire junctions may be a function of the magnitude of the highest voltages applied to the nanowire junction. By applying higher and higher positive voltages to a nanowire junction, the resistance of the nanowire junction may be made lower and lower. A relatively low resistive state achieved by application of a positive voltage may be reversed by applying a sufficiently high, negative voltage. Thus, not only is the electrical resistance of a nanowire junction configurable, the electrical resistance may also be reconfigurable, depending on the type of molecules forming the nanowire junction.  
         [0038]     Note that the term “signal” refers to a detectable low or high physical quantity, such as voltage or current, transmitted by nanowire-crossbar wires. The terms “low” and “high” generally refer to a range of values associated with a signal. For example, a signal that ranges between no signal and a signal threshold may be called a “low signal,” and any signal above the signal threshold is called a “high signal.” A low signal is represented by the bit value “0,” and a high signal is represented by the bit value “1.” 
         [0039]     A particularly useful type of nanowire crossbar is a multiplexer/demultiplexer. Multiplexer/demultiplexers can be used to address nanowires.  FIG. 5A  illustrates an exemplary nanowire-crossbar multiplexer/demultiplexer. In  FIG. 5A , vertical lines  501 - 508  represent a first layer of approximately parallel nanowires, while horizontal bars  509 - 514  represent a second overlapping layer of approximately parallel horizontal address wires. Note that the address wires in  FIG. 5A  can be of nanoscale, sub-microscale, microscale, or greater dimensions and can be composed of conductor material or semiconductor material. The shaded rectangles, such as shaded rectangle  515  represent electrical components that interconnect address wires with nanowires. The electrical components can be resistors, conductive links, diodes, or FETs, as described above with reference to  FIGS. 4A-4F .  
         [0040]     In  FIG. 5A , a pattern of electrical components is fabricated at selected nanowire junctions. The electrical-component pattern ensures that each nanowire is uniquely interconnected with three of the six address wires. For example, electrical components  515 - 517  interconnect nanowire  507  with address wires  510 ,  512 , and  513 , respectively, and no other nanowire is interconnected to all three address wires  510 ,  512 , and  513 . A nanowire that receives three high signals via three address wires is said to be “addressed,” and carries a resulting signal that represents the bit value “1.” The remaining nanowires that are not addressed, or selected, are assigned the bit value “0.” For example, if address wires  510 ,  512 , and  513  carry high signals, then nanowire  507  is the only nanowire receiving three separate high signals, and, therefore, nanowire  507  is selected to carry a high voltage representing the bit value “1,” while the remaining nanowires carry a low voltage representing the bit value “0.” 
         [0041]     Nanowires  501 - 508  each have a unique 3-bit binary-code address represented by A 1 A 2 A 3 , where A 1 , A 2 , and A 3  each represents an independent high or low input signal. Input lines  518 - 520  carry input signals A 1 , A 2 , and A 3  to address wires  509 - 514 . Note that input lines  518 - 520  each branch to one pair of address wires. For example, input line  518  branches to the pair of address wires  509  and  510 . One address wire of each pair is inverted with respect to the other address wire of the pair. For example, NOT gate  521  inverts input signal A 1  to {overscore (A)} 1 , carried on address wire  509 , while signal A 1  is carried on address wire  510 . The pair of address wires  509  and  510  is referred to as a “complementary pair of address wires.” 
         [0042]     In  FIG. 5A , each nanowire is addressed according to a unique pattern of high and low input signals A 1 , A 2 , and A 3 . The electrical-component pattern ensures that no two nanowires have identical addresses by interconnecting each nanowire with a unique set of three address wires. For example, if the input signals A 1 , A 2 , and A 3  supply high, high, and low signals, respectively, then address wires  510 ,  512 , and  513  carry high signals to nanowire  507  via electrical components  515 - 517 . Nanowire  507  is the only nanowire interconnected with address wires  510 ,  512 , and  513 , and, thus, the only nanowire receiving three high signals. The 3-bit binary-code address for nanowire  507  is “110.”  FIG. 5B  shows a table summarizing the 3-bit addresses associated with nanowires  501 - 508 .  
         [0043]     In general, a binary-code multiplexer/demultiplexer, such as the binary-code multiplexer/demultiplexer shown in  FIG. 5A , employs n input lines to uniquely address 2 n  nanowires. For example, the multiplexer/demultiplexer described above with reference to  FIG. 5A  uses only three external communication wires to address 2 3 , or eight nanowires.  
         [0044]     Typically, multiplexer/demultiplexer-nanowire junctions are composed of two-way AND logic gates.  FIG. 6A  illustrates a two-way AND logic gate. In  FIG. 6A , two-way AND logic gate  601  accepts input signals A and B and produces output signal AB. The output signal is represented by the product AB, because a two-way AND gate performs the Boolean algebra equivalent operation of multiplication on the input signals. Thus, if both input signals A and B are high, or have the binary value “1,” then the output signal AB is high, and if either or both input signals A or B are low, or have the binary value “0,” then the output signal AB is low.  FIG. 6B  illustrates a truth table summarizing input signal combinations and corresponding output signals for the two-way AND logic gate shown in  FIG. 6A .  
         [0045]      FIG. 6C  illustrates an exemplary two-way AND logic gate that employs pFETs to realize the two-way AND logic gate described above with reference to  FIGS. 6A-6B . In  FIG. 6C , a high signal, denoted by V in , passes through resistor  602  to wire  603 . Signal V in  can be passed from wire  603  to either or both grounds  604  and  605 , depending on whether input signals A and B enable or disable the signal paths controlled by pFETs  606  and  607 . For example, if input signal A is low, then pFET  606  enables signal to pass to ground  604  pulling V in  down to a low output signal V out . On the other hand, if both input signals A and B are high, then pFETs  606  and  607  are disabled, and V in  is not able to pass to either ground  604  or  605 , providing a high output signal V out . Note that two-way AND logic gates can also be fabricated using nFETs or diodes.  
       Embodiments of the Present Invention  
       [0046]     Voltage signals within electronic devices are generally binary, with a high voltage representing binary value “1,” and a low voltage representing binary value “0,” although alternative conventions can be used. In general, binary value “0” corresponds to a range of voltages between a low voltage minimum and a low voltage maximum, and binary value “1” corresponds to a range of voltages between a high voltage minimum and a high voltage maximum. However, nanoscale electrical components, such as transistors and diodes, fabricated at nanowire junctions may fail to provide output signals that fall within the ranges of voltages corresponding to binary values “0” and “1.” As a result, certain multiplexer/demultiplexer nanowires may have voltages that fall into an intermediate-voltage range, called the “gray-scale-voltage range,” located between the low voltage maximum and the high voltage minimum.  
         [0047]      FIG. 7  shows an exemplary voltage axis that can be used to determine binary values of multiplexer/demultiplexer nanowires. In  FIG. 7 , line  701  represents a positive-voltage axis that displays a range of voltages. Low-voltage range  702  ranges from a low voltage minimum, denoted by V min , to a low voltage maximum, denoted by V ml , while high-voltage range  703  ranges from a high voltage minimum, denoted by V mh , to a high voltage maximum, denoted by V max . If a nanowire voltage is within low-voltage range  702 , the nanowire has the binary value “0,” and if a nanowire voltage is within high-voltage range  703 , the nanowire has the binary value “1.” Low-voltage-range maximum, V ml , and high-voltage-range minimum, V mh , define lower and upper limits, respectively, of a gray-scale-voltage range  704 . Nanowires having voltages in gray-scale-voltage range  704  may be indeterminate.  
         [0048]     In one embodiment of the present invention, a binary signal converter is attached to the end of a multiplexer/demultiplexer nanowire to assign an appropriate bit value to the nanowire.  FIG. 8  illustrates binary signal converters appended to the ends of multiplexer/demultiplexer nanowires, that represents one of many possible embodiments of the present invention. In  FIG. 8 , binary signal converters  801 - 808  are each composed of a diode, a reverse-bias source, an alternating-voltage-source wire, and a connection to ground. For example, binary signal converter  807  is composed of diode  817 , reverse-bias source  818 , alternating-voltage-source wire  819 , and connection to ground  820 . The alternating-voltage-source wires, such as alternating-voltage-source wire  819 , are connected to an alternating-voltage source, not shown, that places an alternating voltage on each nanowire. Note that each diode contains a cathode end that emits current and an anode end that receives current. In  FIG. 8 , the diode-anode ends are connected to the nanowire ends and the diode-cathode ends are connected to the reverse-bias sources.  
         [0049]      FIG. 9  illustrates an enlargement of binary signal converter  807  appended to nanowire  815  shown in  FIG. 8 , that represents one of many possible embodiments of the present invention. An alternating voltage, denoted by V AC , is applied to nanowire  815  on alternating-voltage-source wire  819 . Diode  817  allows current to flow in a forward direction but not in the opposite reverse direction. In general, current flows through a diode from the anode end to the cathode end. For example, diode  817  allows current to flow from the anode end attached to nanowire  815  to the cathode end leading to reverse-bias source  818 , as indicated by current arrow  901 . When a diode allows current to flow from the anode end to the cathode end, the diode is in a low resistance state and said to be “forward biased.” For example, diode  817  is forward biased in the direction indicated by current arrow  901 . Note that the term “forward bias” refers to a voltage applied in the direction a diode allows current to flow. Reverse-bias source  818  applies a voltage, denoted by V rev , in the direction indicated by current arrow  902  that reverse-biases diode  817 . The reverse bias is a voltage applied across a diode that increases the resistance in the forward direction. A diode in a high resistance state due to a reverse bias is said to be “reversed biased.” 
         [0050]     Typically, in the absence of a reverse bias, a diode does not allow current to flow in the forward direction unless the voltage applied in the forward direction is greater than a forward-bias threshold, denoted by V t . If the voltage applied to the diode is less than the forward-bias threshold, the diode resistance is high and little current flows through the diode in the forward direction, but if the voltage applied to the diode is greater than the forward threshold, the diode resistance is lowered and significant current flows through the diode in the forward direction, the amount of current dependent on the forward voltage applied to the diode.  
         [0051]      FIG. 10  illustrates operation of diode  817 , shown in  FIG. 9 . In  FIGS. 10 and 11 , horizontal lines, such as horizontal line  1001 , represents the voltage axis, while vertical lines, such as vertical line  1002 , represent the current axis. Curve  1003  represents the amount of current flowing through diode  817  in the forward direction. If a voltage applied to diode  817  is less than forward-bias threshold  1005 , the resistance of diode  817  is high and a very small amount of current passes, as indicated by the nearly zero current in region  1004 . However, if a voltage applied to diode  817  is greater than forward-bias threshold  1005 , the resistance of diode  817  is lowered and significant current passes, as indicated by the steep increase in curve  1003  for voltage levels greater than forward-bias threshold  1005 .  
         [0052]     Note that the forward-bias threshold can be increased by applying a reverse bias to the diode. For example, in  FIG. 9 , reverse-bias source  818  places a reverse bias on diode  817 . As a result, the forward-bias threshold of diode  817  is increased.  
         [0053]      FIG. 11  illustrates operation of diode  817 , shown in  FIG. 9 , under a reverse bias. In  FIG. 11 , curve  1101  represents the amount of current flowing through diode  817  in the forward direction. Note that forward-bias threshold  1005  is increased by the magnitude of the reverse bias, V rev , supplied by reverse-bias source  818 . In other words, the voltage applied to diode  817  in the reverse-bias direction by reverse-bias source  818  shifts forward-bias threshold  1005  in the forward direction to modified-forward-bias threshold  1102 . In order for current to freely flow through diode  817 , the forward bias applied to nanowire  815  needs to be greater than modified-forward-bias threshold  1102 . For example, if a voltage applied to diode  817  in the forward direction is less than modified-forward-bias threshold  1102 , the resistance of diode  817  remains high and very little current is allowed to flow through diode  817 , as indicated by nearly zero current in region  1103 . However, if the voltage applied to diode  817  is greater than modified-forward-bias threshold  1102 , the resistance of diode  817  is lowered and significant current passes, as indicated by the steep increase in curve  1103  for voltages greater than modified-forward-bias threshold  1102 .  
         [0054]     Modified-forward-bias thresholds are set, in the multiplexer/demultiplexer representing one embodiment of the present invention, by applying a reverse bias, V rev , according to the following condition: 
 
 V   ml   &lt;V   rev   +V   t   &lt;V   mh   Condition 1: 
 
 Next, an alternating current is applied to the nanowires. The alternating current corresponds to an alternating voltage that oscillates between ±V AC  and satisfies the following condition: 
 
 V   ml   &lt;V   rev   +V   t   ±V   AC   &lt;V   mh   Condition 2: 
 
 Note that applying an alternating voltage to a nanowire already carrying a constant voltage V DC  results in a superimposed oscillating voltage that oscillates in a voltage interval given by: 
 
V DC ±V AC  
 
 The binary value of the nanowire is determined by detecting the presence of an oscillation in the nanowire voltage. If an oscillating voltage is detected on a nanowire, the nanowire has the binary value “0,” and if no oscillating voltage is detected on a nanowire, the nanowire has the binary value “1.” Note that, in general, detecting an oscillating voltage on a nanowire can be accomplished more quickly than measuring a constant-voltage. 
 
         [0055]     The device that detects oscillating voltages on a nanowire, such as voltmeter, ammeter, or potentiometer, may have a threshold amplitude, denoted by A th , for detecting oscillations in the voltages carried by the nanowires. For example, if a nanowire carries an oscillating voltage with an amplitude less than A th , then an oscillation in the voltage carried by the nanowire cannot be detected, and if a nanowire carries an oscillating voltage with an amplitude greater than A th , then an oscillation in the voltage carried by the nanowire can be detected. Selecting V AC  equal to or less than the threshold amplitude reduces the size of the gray-scale signal range.  
         [0056]      FIG. 12  illustrates a modified gray-scale signal range, that represents one of many possible embodiments of the present invention. In  FIG. 12 , axis  701  and gray-scale signal range  704  are reproduced, as described above with reference to  FIG. 7 . Note that interval  1201  represents a voltage interval given by Condition 2 as follows: 
 (V rev +V t −V AC , V rev +V t +V AC )  
 Setting V AC  equals the threshold amplitude, A th , for the voltage detection device, reduces gray-scale signal range  704  to modified gray-scale signal range  1202  on voltage axis  1203 . Note that V AC  can be set to values greater than or less than threshold amplitude A th . 
 
         [0057]      FIGS. 13A-13D  are voltage versus time plots for example oscillating voltages on a nanowire, each representing an embodiment of the present invention. In  FIGS. 13A-13D , horizontal lines, such as horizontal line  1301  in  FIG. 13A , represent time axes, while vertical lines, such as vertical line  1302  in  FIG. 13A , represent voltage axes  1201 , as described above with reference to  FIG. 12 . Dashed lines, such as dashed line  1303  in  FIG. 13A , identifies the modified-forward-bias threshold provided by Condition 1. Sinusoidal curves, such as sinusoidal curve  1304  in  FIG. 13A , represent oscillating voltages, where the amplitude V AC  equals the threshold amplitude A th . The constant-voltage component, V DC , determines the equilibrium of the three oscillating voltages, each with an amplitude V AC . For example, in  FIG. 13A , dashed line  1305  represents the constant voltage component, V DC , that determines the equilibrium of oscillating voltage  1304  with amplitude V AC . Square-bracketed region  1306  identifies a voltage range, such as voltage range  1201  described above with reference to  FIG. 12 .  
         [0058]      FIG. 13A  illustrates a hypothetical oscillating voltage having a constant-voltage component  1305  that is less than modified-forward-bias threshold  1303 . As a result, the full oscillating-superimposed signal  1304  is less than modified-forward-bias threshold  1303  and the resistance of the diode remains high. The oscillating votlage does not pass to ground through the binary signal converter and is detectable on the nanowire. A nanowire with a detectable oscillating voltage therefore has the binary value “0.” 
         [0059]      FIG. 13B  illustrates a hypothetical oscillating voltage having a constant-voltage component  1307  that is greater than the high-signal range. As a result, the full oscillating voltage  1308  is greater than modified-forward-bias threshold  1303 . The resistance of the diode is lowered and the oscillating voltage leaks to ground. A nanowire without a detectable oscillating voltage has the binary value “1.” 
         [0060]      FIGS. 13C-13D  illustrates a hypothetical oscillating voltage having a constant-voltage component  1309  that falls within voltage range  1306 . The dashed-line portion of oscillating voltage  1310  identifies time durations where the oscillating voltage is greater than modified-forward-bias threshold  1303 . As a result, the diode resistance is lowered for portions of oscillating voltage  1310  that are greater than modified-forward-bias threshold  1303  and the portions leak to ground, while the diode resistance remains high for portions of oscillating voltage  1310  that are less than diode threshold  1303  and the voltage remains on the nanowire. For example, during time duration  1311 , the diode resistance is lowered allowing the corresponding dashed-line portion of oscillating voltage  1310  to leak to ground. By contrast, during time duration  1312  the corresponding portion of oscillating voltage  1310  remains on the nanowire. As a result, the amplitude of oscillating voltage  1310  is reduced.  FIG. 13D  illustrates the hypothetical reduced amplitude oscillating voltage described above with reference to  FIG. 13C . Dashed-line  1313  identifies the equilibrium of reduced amplitude oscillating voltage  1314  that remains on the nanowire. Interval  1315  identifies the reduced amplitude, denoted by A chop , of oscillating voltage  1314 . Note that because the amplitude A chop  is less than threshold amplitude  1316  the nanowire has a binary value “0.” 
         [0061]     Although the present invention has been described in terms of an embodiment, it is not intended that the invention be limited to the above described embodiment. Modifications within the spirit of the invention will be apparent to those skilled in the art.  
         [0062]     For example, in an alternate embodiment, a single binary signal converter may be employed to distinguish the signals carried by the nanowires. In an alternate embodiment, other electrical components or combinations of electrical components can be employed other than diodes to filter signals carried by the nanowires.  
         [0063]     The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the invention. However, it will be apparent to one skilled in the art that the specific details are not required in order to practice the invention. The foregoing descriptions of specific embodiments of the present invention are presented for purposes of illustration and description. They are not intended to be exhaustive of or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations are possible in view of the above teachings. The embodiments are shown and described in order to best explain the principles of the invention and its practical applications, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents: