Title: Molecular-wire-based restorative multiplexer, and method for constructing a multiplexer based on a configurable, molecular-junction-nanowire crossbar
Abstract: A method for configuring any m-to-n multiplexer from a molecular-junction-nanowire crossbar, and m-to-n multiplexers configured according to the disclosed method. In the described embodiments, a complementary/symmetry molecular-junction-nanowire crossbar is employed, with input nanowire signal lines intersecting certain relatively high-voltage narrow nanowires via nFET devices and intersecting grounded nanowires via pFET devices. The relatively high-voltage and grounded nanowires are, in turn, selectively coupled to one or more output nanowire signal lines.
Patent Number: 6,880,146 Issued on 04/12/2005 to Snider
| Inventors:
|
Snider; Greg (Mountain View, CA)
|
| Assignee:
|
Hewlett-Packard Development Company, L.P. (Houston, TX)
|
| Appl. No.:
|
355465 |
| Filed:
|
January 31, 2003 |
| Current U.S. Class: |
716/17; 716/1; 716/16 |
| Intern'l Class: |
G06F 017//50 |
| Field of Search: |
716/17,16,1,9,8,10
|
References Cited [Referenced By]
U.S. Patent Documents
Primary Examiner: Siek; Vuthe
Assistant Examiner: Lin; Sun James
Claims
What is claimed is:
1. An m-to-n nanoscale multiplexer comprising:
m input nanowire signal lines;
n output nanowire signal lines;
a number of input nanowire address lines; and
a nanoscale circuit that selects a particular input nanowire signal line
for output to each output nanowire signal line based on an address input
on the number of input naowire address lines.
2. The m-to-n nanoscale multiplexer of claim 1 implemented in a
complementary/symmetry lattice additionally including other nanoscale
components that, together with the nanoscale multiplexer, compose an
electrical subsystem.
3. The electrical subsystem of claim 2 wherein the nanoscale components are
configured together at densities within the electrical subsystem at
densities greater than 1.0 giga-transistors/cm.sup.2.
4. The m-to-n nanoscale multiplexer of claim 1 wherein the nanoscale
circuit comprises pFET, nFET, and interconnection junction components
programmed within a molecular-junction-nanowire crossbar.
5. The m-to-n nanoscale multiplexer of claim 4 wherein each input address
selects, for each output nanowire signal line
a first nanowire, interconnected with an input nanowire signal line by an
nFET, interconnected with a high voltage source, and interconnected with
the output nanowire signal line; and
a second nanowire, interconnected with the input nanowire signal line by a
pFET, interconnected with ground, and interconnected with the output
nanowire signal line.
6. The m-to-n nanoscale multiplexer of claim 4 wherein the
molecular-junction-nanowire crossbar is configured to select a number of
input nanowire address lines and output nanowire address lines and produce
output signals for each possible input signal according to a truth table.
7. The m-to-n nanoscale multiplexer of claim 1 wherein each input address
uniquely selects a single input nanowire signal line, and unused addresses
result in undriven output.
8. The m-to-n nanoscale multiplexer of claim 1 wherein microscale
non-semiconductive signal lines are used in place of nanoscale
non-semiconductive signal lines.
9. A method for configuring an m-to-n nanoscale multiplexer, the method
comprising:
providing a complementary/symmetry lattice;
selecting m input nanowire signal lines within the complementary/symmetry
lattice;
selecting n output nanowire signal lines within the complementary/symmetry
lattice;
selecting a number of input nanowire address lines; and
programming junction components within the complementary/symmetry lattice
to implement a nanoscale circuit that selects a particular input nanowire
signal line for output to each output nanowire signal line based on an
address input on the number of input nanowire address lines.
10. The method of claim 9 wherein programming junction components within
the complementary/symmetry lattice further comprises:
selectively configuring pFET, NFET, and interconnection electrical
components at molecular junction within a molecular-junction-nanowire
crossbar.
11. The method of claim 10 further including:
selectively configuring pFETs and nFETs so that each input address selects,
for each output nanowire signal line, a first nanowire and a second
nanowire.
12. The method of claim 10 further including:
selectively configuring nFETs and pFETs to interconnect, by an NFET, the
first nanowire with an input nanowire signal line, with a high voltage
source, and with an output nanowire signal line, and to interconnect, by a
pFET, the second nanowire with the input nanowire signal line, with
ground, and with the output nanowire signal line.
13. An m-to-n nanoscale multiplexer comprising:
m input nanowire signal lines;
n output nanowire signal lines;
a number of input nanowire address lines; and
a means for selecting a particular input nanowire signal line for output to
each output nanowire signal line based on an address input on the number
of input nanowire address lines.
Description
TECHNICAL FIELD
The present invention relates to electronic multiplexers and, in
particular, programmable, nanoscale-sized electronic multiplexers
configured from molecular-junction-nanowire crossbars that may be
integrated with additional components in extremely dense electrical
subsystems.
BACKGROUND OF THE INVENTION
During the past fifty years, the electronics and computing industries have
been relentlessly propelled forward by the ever decreasing sizes of basic
electronic components, such as transistors and signal lines, and by the
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. Not only must expensive semiconductor fabrication facilities
be rebuilt in order to use the new techniques, many new obstacles are
expected to be encountered. For example, it is necessary to construct
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 services 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 construction in semiconductors.
In view of these problems, researchers and developers have expended
considerable research effort in fabricating microscale and nanoscale
electronic devices using alternative technologies, where nanoscale
electronic devices generally employ nanoscale signal lines having widths,
and nanoscale components having dimensions, of less than 100 nanometers.
More densely fabricated nanoscale electronic devices may employ nanoscale
signal lines having widths, and nanoscale components having dimensions, of
less than 50 nanometers.
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. Even were such straightforwardly
miniaturized circuits able to 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.
One type of useful circuit that would be desirable to produce at nanoscale
dimensions is a signal multiplexer. One type of signal multiplexer is used
to output a selected one of many input signals under the control of
address lines. FIGS. 1A-B illustrate a 4-input-line-to-1-output-line, or
4-to-1, multiplexer. As shown in FIG. 1A, the 4-to-1 multiplexer 101
receives four molecular input-signal lines "in.sub.1," "in.sub.2,"
"in.sub.3," and "in.sub.4 " 602-605, each of which can be in a high
voltage, or ON, state, or a low-voltage, or OFF, state. In general, an ON
state is designated as "1," while an OFF state is designated as "0." The
4-to-1 multiplexer 601 outputs a single molecular output-signal line 106.
The 4-to-1 multiplexer, in addition, receives four input address lines
"a.sub.1," "ā.sub.1," "a.sub.2," and "ā.sub.2 " 108-111 which
correspond to two address bits "a.sub.1 " and "a.sub.2." Thus, in other
words, the 4-to-1 multiplexer receives two address bits, each address bit
redundantly encoded in an address-bit signal line and its complement
signal line. FIG. 1B shows a truth table indicating how the values of the
two address inputs "a.sub.1 " and "a.sub.2 " determine the state of the
molecular output-signal line by the 4-to-1 multiplexer shown in FIG. 1A.
The two address inputs "a.sub.1 " and "a.sub.2," each comprising a pair of
signal lines, as discussed above, serve as a 2-bit, 4-value address, each
address selecting one of the four input lines "in.sub.1," "in.sub.2,"
"in.sub.3," and "in.sub.4 ". As shown in FIG. 1B, the a.sub.1 /a.sub.2
input value "00" selects output by the 4-to-1 multiplexer of the value
currently input on input line "in.sub.1." Similarly, the address values
"01," "10," and "11," select output of the current value of inputs
"in.sub.1," "in.sub.2," "in.sub.3," and "in.sub.4," respectively. Thus,
the 4-to-1 multiplexer outputs the state of one of four input lines
selected by a two-bit, four-value input address.
Multiplexers find frequent use in electronic circuits. Designers and
manufacturers of nanoscale electronic devices, including molecular-wire
lattices, have recognized the need for implementing multiplexers at the
nanoscale level. Unfortunately, the current methods by which multiplexers
are fabricated are not amenable to simple miniaturization using
nanowire-based structures similar to those currently employed at larger
dimensions. Instead, designers, manufacturers, and users of devices that
include multiplexers have recognized the need for new methods for
implementing multiplexers that are useable at nanoscale dimensions.
Moreover, to facilitate reuse and flexibility of multiplexer components,
designers, manufacturers, and users of devices that include multiplexers
have recognized the need for reprogrammable multiplexers that can be
reconfigured for alternative uses or to enhance the devices in which they
are included.
SUMMARY OF THE INVENTION
Four n-to-1 multiplexers, where n=2, 3, 4, and 5, are provided as four
exemplary embodiments of the present invention. More generally, the
present invention provides an approach to configuring an arbitrary m-to-n
multiplexer from a molecular-junction-nanowire crossbar. In the described
embodiments, a complementary/symmetry lattice is employed, with input
nanoscale signal lines intersecting certain relatively high-voltage
nanowires via nFET devices and intersecting grounded nanowires via pFET
devices. The relatively high-voltage nanowires and grounded nanowires are,
in turn, selectively coupled to one or more molecular output-signal lines.
Thus, any general m-to-n multiplexer can be configured from a sufficiently
large complementary/symmetry lattice.
Molecular-junction-nanowire crossbar implementations of multiplexers
consume very little power, and have extremely high densities. These
extremely dense multiplexers can then be combined into extremely dense
subsystems that include many additional electrical components, implemented
within a set of complementary/symmetry ("CS") lattices. Thus, rather than
simply representing a miniaturization of existing multiplexer circuits, in
isolation, the present invention provides for building multiplexers into
complex subsystems having transistor densities equal to, or greater than,
1 billion transistors/cm.sup.2, or, in other words, having 1.0
giga-transistor/cm.sup.2 densities and greater transistor densities.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A-B illustrate a 4-input-line-to-1-output-line multiplexer.
FIG. 2 illustrates a basic molecular-junction-nanowire crossbar.
FIG. 3 illustrates a junction, or intersection, between two nanowires.
FIG. 4 illustrates one possible approach for configuring a network of
nanoscale electrical components from a two-dimensional
molecular-junction-nanowire crossbar.
FIG. 5 schematically illustrates a number of simple electrical components
that can be programmed at the junctions of nanowires in
molecular-junction-nanowire crossbars.
FIG. 6 illustrates an exemplary CS lattice.
FIGS. 7A-B illustrate implementation of a 2-to-1 multiplexer using a CS
lattice similar to the CS lattice described above with reference to FIG.
5.
FIGS. 8A and 8B illustrate a 3-to-1 multiplexer implemented using a CS
lattice.
FIGS. 9A and 9B illustrate implementation of a 4-to-1 multiplexer.
FIGS. 10A-B illustrate implementation of a 4-to-2 multiplexer.
FIGS. 11A-B illustrate a 5-to-1 multiplexer.
DETAILED DESCRIPTION OF THE INVENTION
As discussed below, molecular-junction-nanowire crossbars represent one of
a number of emerging nanoscale electronic-circuit media that can be used
to construct nanoscale electronic circuits. Various techniques have been
developed to selectively configure different types of simple electronic
components, such as transistors, resistors, diodes, and connections, at
the junctions between conductive paths of two different layers of a
molecular-junction-nanowire crossbar. The present invention provides a
method for configuring m-to-n input-to-output multiplexers from
molecular-junction-nanowire crossbars and, in particular, from
complementary/symmetry lattices ("CS lattices"). In a first subsection,
below, molecular-junction-nanowire crossbars are described. In a second
subsection, a number of embodiments of the present invention that employ
molecular-junction-nanowire-crossbar technology are described.
Molecular-Junction-Nanowire Crossbars
A relatively new and promising alternative technology involves
molecular-junction-nanowire crossbars. FIG. 2 illustrates a
molecular-junction-nanowire crossbar. In FIG. 2, a first layer of
approximately parallel nanowires 202 is overlain by a second layer of
approximately parallel nanowires 204 roughly perpendicular, in
orientation, to the nanowires of the first layer 202, 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 204
overlying all of the nanowires of the first layer 202 and coming into
close contact with each nanowire of the first layer 202 at intersection
points, or junctions that represent the closest contact between two
nanowires.
Nanowires can be fabricated using mechanical nanoprinting 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-dimensional molecular-junction-nanowire crossbar comprising
first and second layers, as shown in FIG. 2, can be manufactured via a
relatively straightforward process. 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 molecular-junction-nanowire crossbar
may be connected to microscale signal-line leads or other electronic leads
through a variety of different methods to incorporate the nanowires into
electrical circuits.
Molecular-junction-nanowire crossbars are not only layers of parallel
conductive elements but may also be used to create arrays of nanoscale
electronic components, such as transistors, diodes, resistors, and other
familiar basic electronic components. FIG. 3 illustrates a junction
between nanowires of two contiguous layers within a
molecular-junction-nanowire crossbar. In FIG. 3, the junction between a
first nanowire 302 of a first nanowire layer intersects a second nanowire
304 of a second nanowire layer. Note that the junction may or may not
involve physical contact between the two nanowires 302 and 304. As shown
in FIG. 3, the two nanowires are not in physical contact at their closest
point of approach, but the gap between them is spanned by a small number
of molecules 306-309. Various different types of molecules may be
introduced at junctions for a variety of different purposes. In many
cases, the molecules of a junction may be accessed, for various purposes,
through different voltage levels or current levels placed on the nanowires
forming the junction. The molecules spanning the junction in FIG. 3 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 intersecting at a junction may
be a nonlinear function of the voltage across the 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.
In general, a molecular 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
molecular-junction-nanowire crossbar, may arise from asymmetries of
junction molecules combined with junction molecules being uniformly
oriented with respect to the nanowire layers, and may arise both from
differences in the properties of the nanowires as well as
junction-molecule asymmetries. The fact the molecular junctions may have
polarities allows for controlling junction properties by applying positive
and negative voltages to molecular junctions, eliciting forward and
reverse currents within the molecular junctions.
As shown in FIG. 3, the nanowires may include outer coatings, such as outer
coatings 310 and 312. The outer coatings may serve to insulate nanowires
from one another, may constitute the molecules that serve to span
junctions when the nanowires are placed in contact with one another, 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 junctions between crossing nanowires may be introduced as a
separate layer formed between layers of nanowires. In some cases, the
state changes of junction molecules may not be reversible. For example,
the junction molecules may initially be resistive, and may be made
conductive through application of relatively high voltages. In other
cases, the junction molecules may be conductive, but the molecules may be
irreversibly damaged, along with portions of the nanowires proximal to the
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 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.
FIG. 4 illustrates one possible approach to configuring a network of
reconfigurable nanoscale electrical components from a two-dimensional
molecular-junction-nanowire crossbar. In FIGS. 4A-E, a small 3.times.3
molecular-junction-nanowire crossbar is shown, with circles at all nine
junctions to indicate the state of the junction molecules. In one state,
labeled "1" in FIGS. 4A-E, the junction molecules may have certain
semiconductor, or conductive properties, while in a second state, labeled
"2" in FIGS. 4A-E, junction molecules may have different properties.
Initially, as shown in FIG. 4A, the states of the junctions of the
molecular-junction-nanowire crossbar 400 are indeterminate. In other
words, as shown in FIG. 4A, the states of the junctions, such as junction
402, are randomly distributed between state "1" and state "2." Next, as
shown in FIG. 4B, a reset voltage "v.sub.reset, " often either a
relatively large positive or negative voltage, is applied to all junctions
in order to uniformly set the states of all junctions to a particular
state, in the case shown in FIG. 4B, state "2." Next, as shown in FIG. 4C,
each junction may be uniquely accessed by applying a write voltage, or
configuring voltage, to the nanowires that form the junction in order to
configure, or program, the junction to have the state "1." For example, in
FIG. 4C, a first write voltage v.sub.w ' is applied to horizontal nanowire
404 and a second write voltage v.sub.w " is applied to vertical nanowire
406 to change the state of the junction from "2" to "1." Individual
junctions may be configured through steps similar to the steps shown in
FIG. 4C to finally result in a fully configured nanoscale component
network as shown in FIG. 4D. Note that, in FIG. 4D, the states of
junctions 402, 408, and 410 that form a downward-slanted diagonal through
the molecular-junction-nanowire crossbar have been configured by selective
application of write voltages. Finally, as shown in FIG. 4E, the nanoscale
electrical component network can be used as a portion of an integrated
circuit. Input voltages v.sub.i ', v.sub.i ", and v.sub.i '" may be
applied to the nanoscale electrical component lattice as inputs 412 and
output voltages v.sub.0 ", v.sub.0 ", and v.sub.0 '" 414 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.sub.i ', v.sub.i ", and v.sub.i '" and v.sub.o ',
v.sub.o ", and v.sub.o '" have relatively low magnitudes compared with the
write voltages v.sub.w and the reset voltages v.sub.reset. Should the
integrated circuit need to be reconfigured, the reset voltage v.sub.reset
may be again applied to the molecular-junction-nanowire crossbar, as in
FIG. 4B, and the device reconfigured, or reprogrammed, as shown in steps
in FIGS. 4C-D. Depending on the types of nanowires, types of dopants
employed in the case of semiconductor nanowires, and the types of junction
molecules employed in the molecular-junction-nanowire crossbar, many
different, but similar configuring processes may be used to configure
molecular-junction-nanowire crossbars into nanowire-based electrical
components networks. The example of FIG. 4 is meant to illustrate a
general process by which molecular-junction-nanowire crossbars may be
configured as useful portions of electronic circuits.
Junctions of nanowires in molecular-junction-nanowire crossbars may be
configured, in various techniques depending on the chemical nature of the
nanowires and junction-spanning molecules, to form a wide variety of
different, simple electronic devices. FIG. 5 schematically illustrates a
number of simple electrical components that can be configured at the
junctions of nanowires in molecular-junction-nanowire crossbars. A
junction may represent (1) a simple conductive connection between the two
nanowires, as shown in FIG. 5A; (2) a diode that conducts current in only
one direction between the two nanowires, as shown in FIG. 5B; (3) a
resistor, with the magnitude of resistance configurable by application of
different configuring voltages, as shown in FIG. 5C; (4) a negatively
doped field-effect transistor ("nFET"), as shown in FIG. 5D; (5) a
positively doped field-effect transistor ("pFET"), as shown in FIG. 5E;
and (6) the crossing of two conductive nanowires, with the voltage and
current associated with each nanowire completely independent from one
another, as shown in FIG. 5F. In the case of the nFET, shown in FIG. 5D, a
relatively low voltage state on the gate wire 502 results in current
passing through the source/drain wire 504, while a relatively high voltage
on the gate wire 502 prevents conduction of current on the source/drain
nanowire 504. The pFET of FIG. 5E exhibits opposite behavior, with high
voltage on the gate wire 506 facilitating flow of current through the
source/drain wire 508, and low voltage on the gate wire 506 preventing
flow of current on the source/drain wire 508. Note also that a junction
may also be configured as an insulator, essentially interrupting
conduction at the junction with respect to both nanowires. Thus, as
discussed above with reference to FIGS. 2-5, a two-dimensional
molecular-junction-nanowire crossbar may be constructed and then
configured as a network of electrical components. Note also that a
junction, although shown in FIGS. 5A-F to comprise the junction of two
single nanowires, may also comprise a number of junctions between a number
of wires in a first layer of a molecular-junction-nanowire crossbar that
together comprise a single conductive element and the nanowires in a
second nanowire layer that together comprise a second conductive element.
The configurable electrical resistance of molecular junctions is an
important and special property of molecular junctions. When certain types
of molecules are used for molecular junctions, the initially relatively
high resistance of the molecular junction may be lowered by applying a
relatively large positive voltage to the molecular junction. The
resistance of the molecular junction is generally a function of the
magnitude of the highest voltage applied to the junction. By applying
higher and higher positive voltages to a junction, the resistance of the
junction can be made lower and lower. A relatively low resistance 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 molecular junction configurable, the electrical resistance
may also be reconfigurable, depending on the type of molecules forming the
molecular junction.
A particularly useful type of nanoscale electronic component array based on
molecular-junction-nanowire-crossbar technology is referred to as a
"complementary/symmetry lattice" ("CS lattice"). FIG. 6 illustrates an
exemplary CS lattice. Note that, although CS lattices are generally
configured to represent logical and useful circuits, the CS lattice in
FIG. 6 is rather arbitrarily configured, and is shown not as a
representation of a particular subcircuit implemented by the CS lattice,
and may not even be useful or functional, but rather is included to show
the basic features of the CS lattice itself. In general, because of the
small scales of the molecular-junction-nanowire-crossbar grids, it is
difficult to chemically alter individual junctions. Techniques do exist
for applying a very small number of molecules to a particular junction,
but the techniques are painstakingly time consuming, and unsuitable for
mass production. However, it is currently relatively straightforward to
chemically alter subregions or microregions, comprising a number of
junctions using currently available semiconductor manufacturing
technologies. The term "microregion" is meant to indicate a scale larger
than an individual molecular junction, but not necessarily a particular
range of dimensions. It is current technically feasible to fabricate
sub-mircon-sized microregions, for example. In the exemplary CS lattice
shown in FIG. 6, four distinct, square microregions, demarcated by dashed
lines 601-604, are shown within the molecular-junction-nanowire crossbar
600. Microregion 601 is chemically altered so that junctions within
microregion 601 may be selectively configured as nFET components.
Conversely, microregion 602 has been chemically altered so that junctions
within subregion 602 may be selectively configured as pFET components. The
microregions 603 and 604 have been chemically configured so that junctions
within microregions 603 and 604 can be selectively configured as
conductive links that electrically connect the nanowires forming the
junctions. In certain embodiments, one set of parallel wires, the
horizontal, conductive nanowires in FIG. 6, may be of nanoscale dimensions
or of greater, sub-mircoscale or microscale dimensions, while the other
set of parallel wires, the vertical semiconductive nanowires in FIG. 6,
need to be of nanoscale dimensions in order for a CS-lattice-based circuit
to properly function.
In a CS lattice, some number of nanowires is considered as a set of
molecular input-signal lines. For example, in the CS lattice shown in FIG.
6, horizontal nanowires 606-613 are considered as inputs, and labeled
"in.sub.1 "-"in.sub.8 ". Similarly, a distinct set of wires is normally
considered as a set of molecular output-signal lines. For example, in the
CS lattice shown in FIG. 6, horizontal nanowires 614-618 are considered as
molecular output-signal lines, and designated in FIG. 6 as "out.sub.1
"-"out.sub.5." Consider, for example, molecular output-signal line, or
horizontal nanowire, "out.sub.5 " 618. Proceeding along nanowire
"out.sub.5 " 618 from left to right, it can be seen that molecular
output-signal line "out.sub.5 " is connected via junction connections 620
and 622, denoted by small circles in the junctions, to vertical nanowires
624 and 626, respectively. Traversing these vertical nanowires 624 and
626, it can be seen that vertical wire 624 is connected with molecular
input-signal line "in.sub.3 " 608 via an nFET 628 and connected with
molecular input-signal line "ins" 613 via an nFET 629. Thus, when
molecular input-signal lines "in.sub.3 " 608 and "in.sub.5 " 613 are low,
the nFETs 628 and 629 are activated to connect molecular output-signal
line "out.sub.5 " with a high voltage source 630, potentially driving
molecular output-signal line "out.sup.5 " to a high-voltage state.
However, following vertical nanowire 626 upwards from the connection 622
to molecular output-signal line "out.sub.5 " 618, it can be seen that the
vertical nanowire 626 interconnects with molecular input-signal line
"in.sub.8 " 613 via a pFET 632 and interconnects with molecular
input-signal line "in.sub.1 " 606 via pFET 634. Whenever molecular
input-signal lines "in.sub.1 " and "in.sub.8 " are both in a high-voltage,
or ON, state, then the pFETs 632 and 634 are activated to interconnect the
vertical nanowire 626 with ground 636, essentially shorting vertical
nanowire 626 and molecular output-signal line "out.sub.5 " 618 to ground.
When molecular input-signal lines "in.sub.1 " and "in.sub.8 " are high, or
ON, molecular output-signal line "out.sub.5 " 618 is low, or OFF. When
both of molecular input-signal lines "in.sub.1 " and "in.sub.8 " are not
high, or ON, and both molecular input-signal lines "in.sub.3 " and
"in.sub.5 " are not low, or OFF, then molecular output-signal line
"out.sub.5 " is undriven, and in a high impedance state. Thus, the state
of molecular output-signal line "out.sub.5 " 618 depends only on the
states of molecular input-signal lines "in.sub.1," "in.sub.3," and
"in.sub.8," and a truth table summarizing the response of molecular
output-signal line to all possible input-signal-line-states can be
provided as follows:
in.sub.1 in.sub.3 in.sub.8 out.sub.5
0 0 0 1
0 0 1 1
0 1 0 high Z
0 1 1 high Z
1 0 0 1
1 0 1 0
1 1 0 high Z
1 1 1 0
Various different types and sizes of CS lattices are possible. The
configuration of CS lattices is constrained only by the fact that there is
a minimum area of a molecular-junction-nanowire crossbar to which discrete
types of chemically modifying agents can be applied, by direct deposit, by
photolithographic methods, or by other methods. Thus, CS lattices comprise
blocks of sublattices, or microregions, within which one or a small number
of different types of nanoscale electrical components can be selectively
created at nanowire junctions.
While a brief introduction to nanowire lattices has been provided, above,
more detailed information is available in a number of patent applications
and issued patents. Additional information may be obtained from: Kuekes,
et al., U.S. Pat. No. 6,314,019B1; Kuekes, et al., U.S. Pat. No.
6,256,767B1; Kuekes, et al., U.S. Pat. No. 6,128,214; and Snider, et al.,
U.S. patent application Ser. No. 10/233,232.
A Number of Embodiments of the Present Invention
FIGS. 7A-B illustrate implementation of a 2-to-1 multiplexer using a CS
lattice similar to the CS lattice described above with reference to FIG.
5. In FIG. 7A, two input lines, or input nanowires, "in.sub.1," and
"in.sub.2 " 701 and 702 are selected by a single-bit, 2-value address
input, through an address line "a" 703 and its complement "a" 704, for
output to a single molecular output-signal line, or output nanowire 706.
FIG. 7B is a truth table indicating the output value based on each of the
two possible addresses "0" and "1." When the address line "a" is low, and
the complement address line "a" is high, corresponding to the address "0,"
then the state of input line "in.sub.1 " 701 is inverted and output to
output line 706. Conversely, when the address line "a" is high, and the
complement address line "a" is low, corresponding to the address "1," then
the state of input line "in.sub.2 " 702 is inverted and output to output
line 706. Thus, FIG. 7A illustrates implementation of a 2-to-1 inverting
multiplexer.
Consider, with reference to FIG. 7A, operation of the 2-to-1 multiplexer
when the input address is "0." In that case, the state of the input
address line "a" 703 is low, or OFF, and the state of the complement
address line "a" 704 is high, or ON. In this case, nFET 708 is switched
on, interconnecting the output line 706 with a vertical nanowire 707 that
serves to interconnect a high voltage source 710 with the output line 706.
Conversely, nFET 712 is not active, since complement address line "a" is
in a high state, or "1." Note that, although vertical nanowire 707 may
potentially interconnect the output line 706 with the high voltage source
710, an additional nFET 714 must be switched on in order to complete the
connection. Continuing to the right-hand microregion of the CS lattice, in
the case that address "0" is input, pFET 716 is not switched on, since
address line "a" 703 is low, while pFET 718 is switched on, since
complement address line "a" is high. In this case, vertical nanowire 720
may potentially interconnect output line 706 with ground 722, depending on
the state of pFET 724.
When input line "in.sub.1 " 701 is high, nFET 714 is not activated, and the
molecular output-signal line 706 is not connected with the high voltage
710. However, when molecular input-signal line "in.sub.1 " 701 is high,
pFET 724 is activated, shorting the molecular output-signal line 706 to
ground 722. Conversely, when molecular input-signal line "in.sub.1 " 701
is low, nFET 714 is activated and PFET 724 is not activated, resulting in
molecular output-signal line 706 being in an ON state. Thus, when the
address input is "0," resulting in activation of nFET 708 and pFET 718,
the molecular output-signal line has the inverse state of molecular
input-signal line "in.sub.1 " 701. This corresponds to the first row of
the truth table shown in FIG. 7B. A similar analysis, when the states of
the input address lines "a" and "a" are reversed, results in output, on
output nanoscale signal line 706, of the inverse of the state of molecular
input-signal line "in.sub.2," corresponding to the second row in the truth
table shown in FIG. 7B.
Another way to look at the configuration of the electrical components
selectively placed in the CS lattice is as follows. The nFETs activated by
address lines set to a particular address serve to select a single
vertical nanowire that may potentially interconnect the output line with
high voltage. Similarly, the pFETs activated by address lines in the state
corresponding to the single address serve to select a single, vertical
nanowire that may potentially interconnect the molecular output-signal
line with ground. The two selected vertical nanowires must then intersect
the input line corresponding to the address with an nFET and pFET,
respectively. When the selected input line is high, or "1," the pFET is
activated and the molecular output-signal line is shorted, or produces a
low or "0" output state. Conversely, when the selected molecular
input-signal line is low, or "0," then the nFET is activated and the
molecular output-signal line is interconnected with a high-voltage source
to produce a high output-signal line state. The output-signal represents
inversion of the molecular input-signal line selected by the input
address.
FIGS. 8A and 8B illustrate a 3-to-1 multiplexer implemented using a CS
lattice. In this case, two address bits are needed in order to encode
three different addresses corresponding to the three different input
lines. By using two bits, four address values are available. In the
implementation shown, one of these addresses is discarded so that, when
the discarded address is input through the address lines, the state of the
molecular output-signal line is that of high impedance, or high-Z. FIG. 8A
shows the nanoscale electrical components, pFETs, nFETs, and connections,
selectively formed within the CS lattice, to implement the 3-to-1
multiplexer. FIG. 8B shows a truth table that indicates outputs output by
the multiplexer in response to each possible address. The two address bits
are encoded in four address lines, with each address bit encoded by the
states of a pair of address lines representing an address line and its
complement. Thus, the address "00" shown in the first row of the truth
table in FIG. 8B corresponds to the address lines "a.sub.1 " and "a.sub.2
" being in a low-voltage state, and the complement address lines
"ā.sub.1 " and "ā.sub.2 " being in high-voltage states.
Operation of the 3-to-1 multiplexer illustrated in FIGS. 8A-B is similar
to that of the 2-to-1 multiplexer, described above with reference to FIGS.
7A-B. Each address, input via address lines 802-805, selects a single
vertical nanowire that may potentially interconnect the molecular
output-signal line 806 with a high voltage source 808 and a single
vertical nanowire that may potentially interconnect the molecular
output-signal line 806 with ground 810. The two selected vertical
nanowires are interconnected to a single input line through pFET and nFET
junction components. As in the 2-to-1 multiplexer, when the selected
molecular input-signal line is in a high state, the molecular
output-signal line is shorted to ground, and when the selected molecular
output-signal line is in a low state, the molecular output-signal line is
interconnected with the high voltage source 808. Thus, the 3-to-1
multiplexer inverts the signal of an input line selected by the states of
the address lines.
Note that the high-Z state, in addition to the high-voltage state and
ground state, provide three distinct, detectable values, allowing the
output of the multiplexer to distinguish valid input addresses from
invalid addresses. In the 3-to-1 multiplexer, discussed above with
reference to FIGS. 8A-B, the addresses "00," "01," and "10" select, for
output, the inverse of each of the three input signals "in.sub.1,"
"in.sub.2," and "in.sub.3." When the invalid input address "11" is input
to the 3-to-1 multiplexer, the high-Z state is output, indicating an
invalid input address. In many current multiplexers, an invalid input
address produces one of two output signals indistinguishable from that
produced by a valid input address, namely "0" or "1."
FIGS. 9A and 9B illustrate a 4-to-1 multiplexer in the same fashion as the
3-to-1 multiplexer and 2-to-1 multiplexer were illustrated in FIGS. 8A-B
and 7A-B, respectively. Because all four addresses are needed for
selecting the four molecular input-signal lines, there is no discarded
address in the implementation of the 4-to-1 multiplexer shown in FIGS.
9A-B.
It is also possible to construct the general m-to-n multiplexers by the
technique discussed with respect to FIGS. 7-9. FIGS. 10A-B illustrate a
4-to-2 multiplexer in which each address input to the multiplexers select
two different signal lines for output to two molecular output-signal
lines. Again, analysis of the network of selectively configured electronic
components within the CS lattice shown in FIG. 10A reveals the identical
pattern discussed above, with reference to FIGS. 7-9. Each address, in
this case, selects two vertical nanowires that potentially corresponding
to arbitrarily selected truth tables. Additional Boolean logic may be
included in a multiplexer, by configuring additional junction components,
in order to produce desired output signals from input signals. While the
above embodiments use a CS lattice with pFET, nFET, and direct
interconnection components, with the direct junction components residing
in the bottom two quadrants of the CS lattice, nFET components residing in
the top, left-hand quadrant of the CS lattice, and pFET components
residing in the top, right-hand quadrant of the CS lattice, many different
alternative configurations may produce identical output response to the
molecular input-signal lines and input address lines. Electrical
components other than nFETs and pFETs may be employed, in which case
different topologies and configurations may be required to effect each
different type of multiplexer. It is possible to invert the sense of the
electrical components, to produce inverted outputs. Essentially, a
multiplexer defined by any arbitrary truth table describing operation of
the multiplexer can be implemented at nanoscale sizes using the method
described above.
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 purpose of illustration and description. They are not
intended to be exhaustive 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.
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