HK1138101B - Nanotube-based switching elements and logic circuits - Google Patents

Description

Nanotube-based switching element with multiple controls and circuits made therefrom

The present invention patent application is an international invention patent application entitled "Nanotube-based Switching Elements with multiple controls and Circuits from the Same" having application number PCT/US2004/027455, and a divisional application of chinese invention patent application entitled "Nanotube-based Switching element with multiple controls and circuit Made therefrom" having application number 2004800298015.

RELATED APPLICATIONS

This application claims priority to U.S. provisional patent application 60/494,889, filed on 13/8/2003 under 35U.S. C. § 119(e), entitled "Nanotube-Based nanoelectromechanical Logic (nanoelectromechanical Logic"), the entire contents of which are incorporated herein by reference. This application also claims priority to U.S. provisional patent application 60/561,330, filed 4/12/2004 under 35U.S. C. § 119(e), entitled "Non-volatile Carbon Nanotube (CNT) Dual-rail differential Logic," which is incorporated herein by reference in its entirety.

Technical Field

The present invention relates generally to nanotube switching circuits, and more particularly to nanotube switching circuits that use nanotubes to form the conductive pathways of the switch, which can be interconnected into larger circuits, such as Boolean logic circuits.

Background

Digital logic circuits are used in personal computers, portable electronic devices such as personal organizers and calculators, electronic entertainment devices, and in control circuits in certain equipment, telephone switching systems, automobiles, aircraft, and other articles of manufacture. Early digital logic was built with discrete switching elements consisting of individual bipolar transistors. With the invention of bipolar integrated circuits, a large number of individual switching elements can be combined on a single silicon substrate (substrate) to produce fully digital logic circuits such as inverters, NAND gates, NOR gates, flip-flops, adders, and the like. However, the density of bipolar digital integrated circuits is limited by the high power consumption of the circuits during operation and the heat dissipation capability of the packaging technology. Metal oxide semiconductor ("MOS") devices using field effect transistors ("FETs") greatly reduce the power consumption of digital logic and allow the construction of high density, complex digital circuits in use today. The density and speed of MOS digital circuits are still limited by the need for heat dissipation during device operation.

Digital logic integrated circuits built from bipolar or MOS devices currently cannot operate in high thermal conditions or extreme environments. Current digital integrated circuits are typically designed to operate below 100 degrees celsius, and very few operate above 200 degrees celsius. In conventional integrated circuits, the leakage current of a single switching element in the off ("off") state may increase rapidly with temperature. As leakage current increases, the operating temperature of the device increases, the power consumed by the device increases, and the difficulty in distinguishing between closed ("on") and open states reduces the reliability of the circuit. Conventional digital logic circuits also suffer from internal short circuits when subjected to certain extreme environments due to the current generated within the semiconductor material. Although it is possible to fabricate integrated circuits with special devices and isolation techniques such that they remain operational when exposed to such environments, the high cost of these devices limits their availability and usefulness. Furthermore, such digital circuits exhibit time differences from their normal counterparts, requiring additional design verification to add protection to existing designs.

Integrated circuits built from bipolar or FET switching elements are volatile. Its internal logic state is maintained only when power is applied to the device. The internal state is lost when power is removed unless a non-volatile memory such as an EEPROM (electrically erasable and read only memory) is added internally or externally to maintain the logic state. Even if non-volatile memory is used to maintain the logic state, additional circuitry is required to transfer the digital logic state to memory before power is removed and to restore the state of the individual logic circuits before the device is powered on. Other solutions to avoid loss of information in volatile digital circuits, such as battery backup, also increase the cost and complexity of digital designs.

Important features of logic circuits in electronic devices are low cost, high density, low power, and high speed. Conventional logic solutions are limited to silicon substrates, but logic circuits built on other substrates can enable logic devices to be integrated directly with many manufactured products in a single step, thereby reducing cost.

Devices such as nanoscale (nanoscopic) lines of single-walled carbon nanotubes have been proposed for forming crossbar (crossbar) junctions for use as memory cells. (see WO 01/03208 "Nanoscopic Wire-Based devices, Array, and Methods of the same" (nanoscale Wire-Based devices, arrays, and Methods of Their Manufacture), and Thomas Rueckes et al, Science 289, Vol.289, pp.94-97, 2000, 7.7.7.2000, "Carbon Nanotube-Based Nonvolatile Random Access memory for Molecular Computing"). These devices are hereinafter referred to as nanowire crossbar memories (NTWCMs). Under these proposals, each single-walled nanotube wire suspended (suspend) on other wires defines a memory cell. Electrical signals are written to one or both lines causing them to be physically attracted or repelled with respect to each other. Each physical state (i.e., attracted or repelled wires) corresponds to an electrical state. The repelling line is an open junction. The attraction line is in a closed state forming a rectifying junction. When power is removed from the junction, the lines retain their physical (and thus electrical) state, thereby forming a non-volatile memory cell.

U.S. patent publication No. 2003-0021966 discloses electromechanical circuits, such as memory cells, wherein the circuits include structures having conductive traces and supports extending from the surface of the substrate. An electromechanically deformable (Deform) or switchable nanotube ribbon (ribbon) is suspended by supports across the conductive traces. Each strip includes one or more nanotubes. These ribbons are generally formed by selectively removing material from a layer or entangled structure of nanotubes.

For example, as disclosed in U.S. patent publication No. 2003-0021966, nanostructures can be patterned into strips, which can be used as a means of creating non-volatile electromechanical memory cells. The ribbon may be electromechanically deflected in response to control traces and/or electrical stimulation of the ribbon. The deflected physical state of the tape can be used to represent the corresponding information state. The deflected physical state has a non-volatile nature, meaning that the tape retains its physical (and thus information) state even if the memory cell is powered down. As explained in U.S. patent publication No. 2003-0124325, a three-trace architecture can be used for the electromechanical memory cell, where two traces are the electrodes that control the band deflection.

Electromechanical bistable devices for digital information storage have also been proposed (compare US 4979149: Non-volatile memory device comprising a micromechanical storage element).

Fabrication and operation of bistable nanomechanical switches based on carbon nanotubes (including monolayers constructed therefrom) and metal electrodes are described in detail in prior patent applications to nantro inc (U.S. patent applications nos. 6574130, 6643165, 6706402, serial nos. 09/915093, 10/033323, 10/033032, 10/128117, 10/341005, 10/341054, 10/341130, 10/776059, and 10/776572, which are incorporated herein by reference in their entirety).

Disclosure of Invention

The invention provides nanotube-based switching elements with multiple controls and circuits made therefrom.

According to one aspect of the invention, a switching element includes an input node, an output node, and a nanotube channel element having at least one conductive nanotube. A control structure is configured in relation to the nanotube channel to controllably form and release a conductive path between the input node and the output node. The output node is constructed and arranged such that the formation of the channel is substantially unaffected by the electrical state of the output node.

According to another aspect of the invention, the control structure includes a control electrode and a release electrode disposed on opposite sides of the nanotube channel element.

According to yet another aspect of the invention, the channel is formed in a non-volatile state.

According to yet another aspect of the invention, the control and release electrodes are configured in relation to a nanotube channel element, and the conductive channel is formed and released by electromechanically deflecting the nanotube channel element.

According to another aspect of the invention, a nanotube channel element includes a spacer structure having two sets of electrodes disposed on opposite sides of a control structure, each set of electrodes including electrodes disposed on opposite sides of the nanotube channel element.

According to a further aspect of the invention, the two sets of electrodes are symmetrically placed with respect to the control structure.

In accordance with yet another aspect of the present invention, a nanotube channel element is electrically connected to an input node and is spaced apart and interdigitated with respect to a control electrode and a release node, wherein deflection of the nanotube channel element is responsive to electrostatic forces generated by signals on the input node, the control electrode, and the release electrode.

According to another aspect of the invention, deflection of the nanotube channel element is responsive to a differential signal relationship applied to the control electrode.

According to yet another aspect of the present invention, a Boolean logic circuit includes at least one set of differential inputs and an output, and a network of nanotube switching elements electrically disposed between the at least one set of differential inputs and the output. The nanotube switching element network performs Boolean function conversion of Boolean signals on at least one set of differential inputs.

According to yet another aspect of the invention, a network of nanotube switching elements implements a Boolean NOT (NOT) function of a signal on at least one set of differential inputs.

According to another aspect of the invention, a network of nanotube switching elements performs a Boolean NOR (NOR) function of signals on at least first and second sets of differential inputs.

According to yet another aspect of the present invention, a Boolean logic circuit includes at least one differential input and one output, and a network of nanotube switching elements electrically disposed between the at least one differential input and the output. The nanotube switching element network performs Boolean function switching of Boolean signals on at least one differential input and on at least one nanotube switching element capable of non-volatile retention of an information state.

According to yet another aspect of the invention, at least one nanotube switching element capable of non-volatilely retaining an informational state includes a nanotube channel element having at least one electrically conductive nanotube and a control structure positioned relative to the nanotube channel element to controllably form and release an electrically conductive channel between an input node of the at least one switching element and an output node of the at least one switching element.

According to another aspect of the present invention, a latch circuit includes at least one input terminal and one output terminal, and first and second inverter circuits. Each inverter circuit includes a nanotube switching element having an input node, an output node, a nanotube channel element having at least one conductive nanotube, a control electrode positioned relative to the nanotube channel element to controllably form a conductive path to the output node, and a release electrode positioned relative to the nanotube channel element to controllably release the conductive path to the output node. An output node of the first inverter circuit is coupled to a control electrode of the second inverter circuit, and an output node of the second inverter circuit is coupled to a control electrode of the first inverter circuit.

According to yet another aspect of the invention, each nanotube channel element remains in the absence of signals from the nanotube element, the control electrode, and the release electrode.

Drawings

FIGS. 1A-1D illustrate cross-sectional views of a nanotube switching element of some embodiments in two different states, including plan views of the element;

FIGS. 2A-3C illustrate schematic diagrams of nanotube switching elements;

FIG. 4 shows a schematic diagram of an exemplary dual rail input, dual rail output inverter circuit constructed from nanotube switching elements;

FIG. 5 shows a schematic diagram of an exemplary dual rail flip-flop circuit constructed from nanotube switching elements;

FIGS. 6A-6B show schematic diagrams of a nonvolatile ram cell constructed using an exemplary nanotube steady-state ram cell and a dual-rail flip-flop circuit;

FIG. 7 shows a schematic diagram of a dual rail nanotube-based NOR circuit;

FIGS. 8A and 8B illustrate exemplary schematic diagrams of a volatile 4-terminal nanotube switching device operating as a 3-terminal device in a latch circuit.

Detailed Description

Preferred embodiments of the present invention provide switching elements in which nanotube-based channels are controllably formed and de-formed so that signals can be transmitted from a signal node to an output node. The switching element includes a plurality of control electrodes for controlling the shaping and release of the channels, providing dual rail capability, and being used in a novel manner. Depending on the manner in which the switching elements are used and arranged, the transmitted signal may be a varying signal or a reference signal. The preferred embodiment provides an isolation structure such that the operation of the signal transfer and switching elements is substantially invariant to the output state. For example, the output node may be floating and/or connected to other electrical components, and the circuit will operate in a switch-like manner as contemplated. Therefore, the switching element can form a larger circuit such as a boolean logic circuit. In some embodiments, these switching elements are used as complementary circuits. In some embodiments, these switches retain their state in the absence of a power supply providing non-volatile logic. In some embodiments, these switching elements are used to form differential (dual rail) logic.

FIG. 1A is a cross-sectional view of a preferred nanotube switching device 100. The nanotube switching element includes a lower portion having an insulating layer 117, a control electrode 111, and output electrodes 113c and 113 d. The nanotube switching element also includes an upper portion having a discharge electrode 112, output electrodes 113a and 113b, and signal electrodes 114a and 114 b. The nanotube channel element 115 is located between and secured by the upper and lower portions.

The discharge electrode 112 is made of an electrically conductive material and is isolated from the nanotube channel element 115 by an insulating material 119. The nanotube channel element 115 is separated from the opposing surface of the insulator 119 by a gap height G102.

The output electrodes 113a and 113b are made of an electrically conductive material and are isolated from the nanotube channel element 115 by an insulating material 119.

Output electrodes 113c and 113d are similarly made of a conductive material and are separated from nanotube channel element 115 by a gap height G103. Note that the output electrodes 113c and 113d are not covered with an insulator.

Control electrode 111 is made of a conductive material and is isolated from nanotube channel element 115 by an insulating layer (or membrane) 118. The nanotube channel element 115 is separated from the opposing surface of insulator 118 by a gap height G104.

Each of the signal electrodes 114a and 114b is in contact with nanotube channel element 115, and thus any signal whatsoever on the signal electrode can be provided to the nanotube channel element 115. This signal may be a fixed reference signal (e.g., Vdd or ground) or a variable (e.g., a variable boolean discrete signal). Only one of the signal electrodes 114a and 114b need be connected, but both are used to reduce the effective resistance.

Nanotube channel element 115 is a planar print-defined object of an article made of porous nanotube fabric (described in more detail below). Which is electrically connected to the signal electrodes 114a and 114 b. The electrodes 114a and 114b and the support 116 sandwich or fix the channel member 115 at both ends thereof, and are suspended in the middle spaced apart from the output electrodes 113c and 113d, the control electrode 111 and the discharge electrode 112. This spaced relationship is defined by the gap heights G102-G104 described above. For certain embodiments, the suspended portion of channeled member 115 may have a length of approximately 300 to 350 nanometers (nm).

In a particular embodiment, the gap heights G103, G104, G102 range from 5 to 30 nm. For example, the dielectric range on terminals 112, 111, 113a and 113b is 5 to 30 nm. The carbon nanotube construction density is about, for example, 10 nanotubes per 0.2 x 0.2 micrometer (um) area. The nanotube channel element has a suspended length in the range of, for example, 300 to 350 nm. The ratio of the flying length to the gap is, for example, about 5 to 15 for non-volatile devices and less than 5 for volatile operations.

Fig. 1B is a plan view or layout of nanotube switching device 100. As shown in this figure, electrodes 113b and 113d are electrically connected, as indicated by the label 'X' with item 102. Similarly, electrodes 113a and 113c are connected, as indicated by the reference 'X'. In the preferred embodiment, these electrodes are further connected by a connection 120. All these output electrodes together form the output node 113 of the switching element 100.

In a preferred embodiment, the nanotube switching device 100 of FIGS. 1A and 1B operates as shown in FIGS. 1C and 1D. Specifically, when the nanotube channel element is in position 122 of FIG. 1C, nanotube switching element 100 is in an open (off) state. In this state, channel element 115 is in mechanical contact with dielectric layer 119 by electrostatic forces generated by a potential difference between electrode 112 and channel element 115. Output electrodes 113a and 113b are in mechanical (and not electrical) contact with channel element 115. When channel element 115 is extended to position 124 as shown in fig. 1D, nanotube switching element 100 is in a closed (conducting) state. In this state, channel element 115 is in mechanical contact with dielectric layer 118 by electrostatic forces generated by a potential difference between electrode 111 and channel element 115. Output electrodes 113c and 113d are in mechanical and electrical contact with channel element 115 at region 126. Thus, when channel element 115 is in position 124, signal electrodes 114a and 114b are electrically connected to output terminals 113c and 113d through channel element 115, and signals on electrodes 114a and 114b can be transmitted to output electrodes 113c and 113d via the channel (including channel element 115).

By appropriately adjusting the geometry of nanotube switching element 100, nanotube switching element 100 can be used as a non-volatile or volatile switching element. As an example, the device state of fig. 1D may be made non-volatile by appropriate selection of the length of the channel element relative to gap G104. (Length and gap are two parameters that extend the restoring force of deflection channel element 115.) for non-volatile devices, the ratio of length to gap is preferably greater than 5 and less than 15; for volatile devices, the ratio of length to gap is preferably less than 5.

The nanotube switching element 100 operates in the following manner. If signal electrode 114 and control electrode 111 (or 112) (via corresponding signals on the electrodes) have a sufficiently large potential difference, the signal relationship will produce an electrostatic force that is large enough to deflect suspended nanotube channel element 115 into mechanical contact with electrode 111 (or 112). (this aspect of operation is described in the incorporated reference patents.) this deflection is depicted in FIG. 1D (and 1C). The attractive force stretches and deflects the nanotube fabric of channel element 115 until it contacts insulating region 118 of electrode 111. The nanotube channel element is thus tensioned and has a restoring tension depending on the geometry of the circuit etc.

By utilizing the appropriate geometry of the components, switching element 100 can achieve the closed conductive state of fig. 1D, in which nanotube channel 115 is in mechanical contact with control electrode 111 and output electrodes 113c and 113D. Since the control electrode 111 is covered by insulation 118, any signal on the electrode 114 is transmitted from the electrode 114 to the output electrode 113 via the nanotube channel element 115. The signal on the electrode 114 may be a varying signal, a fixed signal, a reference signal, a power supply line, or a ground line. The formation of the channel is controlled via a signal applied to the electrode 111 (or 112). In particular, the signal applied to the control electrode 111 needs to be sufficiently different with respect to the signal on the electrode 114 to generate an electrostatic force that deflects the nanotube channel element to deflect the channel element 115 and form a channel between the electrode 114 and the output electrode 113, so that the switching element 100 is in a closed (conducting) state.

Conversely, if the signals on electrode 114 and control electrode 111 are not sufficiently different, the nanotube channel element 115 is not deflected and no conductive path is formed to the output electrode 113. Instead, the channel element 115 is attracted to and physically contacts the insulating layer on the release electrode 112. The off state is shown in fig. 1C. Nanotube channel element 115 has a signal from electrode 114, but the signal is not transmitted to output node 113. Instead, the state of the output node 113 depends on which circuit it is connected to and the state of that circuit. In this regard, the state of output node 113 is independent of the channel element voltage from signal electrode 114 and nanotube channel element 115 when switching element 100 is in the off (off) state.

If switching element 100 is designed to operate in a volatile mode and the electrical connection or path between electrode 115 to output node 113 is open, then channel element 115 returns to a non-extended state if the voltage difference between control electrode 111 (or 112) and channel element 115 is removed (see FIG. 1A).

Preferably, if the switching element 100 is designed to operate in a non-volatile mode, the channel element will not operate in a manner that achieves the state of FIG. 1A. Instead, it is contemplated that electrodes 111 and 112 would operate to place channel element 115 in the state of FIG. 1C or 1D.

Output node 113 is constructed to include an isolated structure in which the operation of channel element 115, and thus the formation of a channel, is invariant to the state of output node 113. Since the pass element is electromechanically deflected in response to an attractive electrostatic force in the preferred embodiment, the floating output node 113 may have any potential in principle. Thus, the potential on the output node may be sufficiently different relative to the state of pass element 115 such that pass element 115 deflects and interferes with the operation of switching element 100 and its passage formation; that is, the channel formation will depend on the state of the unknown floating node. In the preferred embodiment, this problem is solved by the output node comprising an isolation structure to prevent such interference.

Specifically, nanotube channel element 115 is disposed between two oppositely disposed electrodes 113b and 113d (and 113a and 113c) of equal potential. Thus, there are equal but opposite electrostatic forces generated by the voltages on the output nodes. Because of the equal but opposite electrostatic force, the state of output node 113 cannot deflect nanotube channel element 115 regardless of the voltage on output node 113 and nanotube channel element 115. Thus, the operation and formation of the channel becomes invariant to the output node state.

In certain embodiments of the present invention, the nanotube switching element 100 of fig. 1A may be used as a pull-up and pull-down device to form an active power circuit. Unlike MOS and other forms of circuitry, the pull-up and pull-down devices may be identical devices and need not have different sizes or materials. To facilitate the description of such a circuit and to avoid the complexity of the layout and the actual design of fig. 1A to 1D, a schematic diagram has been generated to describe the switching element.

Fig. 2A is a schematic diagram of the nanotube switching device 100 of fig. 1A. The nodes thereof use the same reference numerals. Fig. 2A illustrates a non-volatile device in which the restoring mechanical force generated by nanotube extension is insufficient to overcome van der Waal forces, such that nanotube element 115 remains in either the first or second non-volatile state even after a power outage. In a first non-volatile state, nanotube switch 100 remains in a closed (on) state in contact with control electrode 111 (shown in FIG. 1D) and output electrode 113 (shown in FIG. 1D), such that output electrode 113 is in contact with nanotube element 115, which in turn is in contact with signal electrode 114. In the second non-volatile state, nanotube element 115 remains in an open (off) state in contact with release electrode 112, such that nanotube element 115 does not contact output electrode 113 as shown in FIG. 1C when power is off. Fig. 2A is a schematic diagram of nanotube switching element 100 of fig. 1A. Its nodes are labeled the same but with a prime' sign added to distinguish them from fig. 2A. Fig. 2A 'shows a volatile device in which the restorative mechanical force generated by nanotube extension is sufficient to separate the nanotube element 115' from physical contact with the control electrode 111 'and physical and electrical contact with the output electrode 113', thereby disconnecting the signal electrode 114 'from the output electrode 113'. Arrow 202 shows the direction of mechanical restoring force of nanotube channel element 115'. For example, as shown, the channel element has a force away from the control electrode 111 ', i.e., if the channel element 115 ' is deflected into contact with the electrode 111 ', the mechanical restoring force would be in the direction of arrow 202. The arrows indicating the direction of the mechanical restoring force are only used in devices designed to operate in a volatile mode.

Fig. 2B-2C depict nanotube channel element 100 for a pull-up configuration and its operating state. For example, FIG. 2B is a schematic diagram illustrating the nanotube switching element of FIG. 1C in the open (off) state, where node 114 and nanotube channel element 115 are at V_DDThe control electrode 111 is at a voltage of generally V_DDWhile the discharge electrode 112 is at zero volts. The nanotube channel element is not in electrical contact with output node 113. Fig. 2C is a schematic diagram illustrating the nanotube switching element of fig. 1D in a closed (on) state. In this case, signal node 114 and nanotube channel element 115 are at V_DDNext, the control electrode 111 is at zero volts, while the release electrode 112 is at a voltage of generally V_DDAt a positive voltage. The nanotube channel element is deflected into mechanical and electrical contact with output node 113. Furthermore, if the geometry is chosen appropriately as described above, the contact will be non-volatile due to van der Waals forces between the channel element and the control electrode. The state of electrical contact is depicted by the short black line 204, which indicates that the nanotube channel element is in contact with output terminal 113. This results in the output node 113 assuming the same signal (i.e., V) as nanotube channel element 115 and signal node 114_DD)。

Fig. 3A-C are similar to fig. 2A-C except that they are used to illustrate nanotube channel element 100 and its operating state as a pull-down device.

In fig. 2 and 3, the nanotube switching element always (at least when power is applied) operates in such a way that the control electrode 111 and the release electrode 112 are always at opposite voltage values. For example, if the control electrode 111 is at zero volts, the release electrode 112 is at a voltage of generally V_DDAt a positive voltage. However, if the control electrode 111 is at a general V_DDAt zero volts, the discharge electrode 112 is at zero volts. If a positive voltage is associated with a logic "1" state and zero volts is associated with a logic "0" state, then the logic states applied to the input and release electrodesTrue and complement, respectively (or complement and true, respectively).

In this manner, nanotube switching element 100 operates as a dual-rail differential logic element. The dual-rail differential logic design (or just differential logic design) techniques applied to the non-volatile 4-terminal nanotube switch device 100 of FIG. 1 can produce non-volatile dual-rail differential logic family columns by forming the basic building blocks of the logic family (e.g., NOT and NOR circuits) using the device 100. The non-volatile dual rail differential logic family performs logic operations when active and retains logic states in a non-volatile mode when powered down (or not). The family of logic resumes logic operation when power is applied, with each logic circuit in the same state as before the power outage (or power outage). An example of a circuit is as follows.

Fig. 4A illustrates a dual-rail inverter 420 according to a specific embodiment of the present invention. The inverter circuit 420 includes an upper portion 410T and a lower portion 410C.

The upper portion 410T includes a nanotube switching element 412 arranged with a connection to V_DDThe pull-up device of the signal node of (1); and a nanotube switching element 414 arranged as a pull-down device having a signal node connected to ground. Both of these switching elements receive a true version A of the logic signal A of the control node (111 of FIG. 1A) via input link 411T, respectively_TAnd both have their output nodes (113 of FIG. 1A) connected together to an output node 413T, the output node 413T providing a complementary version A of the logic signal A_C。

Lower portion 410C includes a nanotube switching element 416 arranged with a connection to V_DDThe pull-up device of the signal node of (1); and a nanotube switching element 418 arranged as a pull-down device having a signal node connected to ground. Both of these switching elements receive a complementary version A of the logic signal A of the control node (111 of FIG. 1A), respectively, via input link 411C_CAnd both have their output nodes (113 of FIG. 1A) connected together to output node 413C, the output node 413C providing the true version A of the logic signal A_T。

The input 411T of the upper portion 410T is coupled to the release nodes of the two switching elements of the lower portion 410C. Similarly, input 411C of lower portion 410C is coupled to the release nodes of both switching elements of upper portion 410T.

Thus, in operation as described above, inverter circuit 420 receives a dual-rail differential input A of logic signal A_TAnd A_CAnd provides corresponding input versions on links 411 and 413, respectively. In addition, the logic is non-volatile, i.e., the gate maintains its state even if power is interrupted from the circuit. Furthermore, since the circuit is arranged as a complementary circuit with pull-up and pull-down devices, current (and power consumption) flows only during switching, so that there will be no V_DDDirect Current (DC) current to ground.

Fig. 5 illustrates a particular embodiment of a non-volatile state device 520, using the same schematic labels as above. Latch 520 is formed by bridging inverters 510 and 511. The output node 512 of inverter 510 is connected to the control electrode input of inverter 511 and the release electrode input of inverter 510. Output node 513 is connected to the control electrode input of inverter 510 and the release electrode input of inverter 511. The state device 520 is a non-volatile storage element; that is, the state device 520 retains its logic state if powered down and assumes the same state when powered up. The state device 520 may be combined with logic gates (not shown) to produce the non-volatile NRAM memory cell shown in figure 6A, various flip-flops and latches for, e.g., S-R, J-K, and other flip-flop structures. Fig. 6B shows a state device 520 for a latching configuration. The current flows only during switching, so there is no V_DDAnd ground.

FIG. 6A shows a state device 620 for use as a non-volatile nanotube static RAM cell (NRAM cell) 630, according to another embodiment of the invention. In this embodiment, the control electrode of the upper inverter 510A, and the release electrode of the lower inverter 511A, are connected to a logic Bit Line (BL) via a select transistor 632 controlled by a signal WL_T) The signal is input and connected to state device 620 at node 621. Lower inverter 511A, and the release electrode of the upper inverter 510A, are connected to a complementary version of a logic Bit Line (BL) input signal (BL) via select transistor 634, which is controlled by signal WL_C) And is connected to state device 620 at node 622. In this manner, the state device may form a non-volatile NRAM memory cell 630. Inverters 510A and 511A are designed to be electrically identical so that the NRAM cell is balanced (not preferring one of the states). Select devices 632 and 634 are designed to be large enough in order to provide a drive current large enough to overcome the stored state of state device 620, as is well known in the art of static RAM cell design.

NRAM cell 630 has the advantage of non-volatile storage. The nanotube latch portion 620 may also be formed using a separation layer. Select transistors 632 and 634 are the only semiconductors needed in the cell region. NRAM cells can be smaller than SRAM cells because no transistor latch is required. Removing the transistor flip-flops also removes the need for PMOS and NMOS in the cell, and P-well and N-well regions to accommodate the source and drain diffusions of the NMOS and PMOS transistors, respectively. Because only NMOS select transistors 632 and 634, and contact to the nanotube-based latch 620 layer are required, the non-volatile NRAM cell 630 may be smaller than a volatile (transistor-based) SRAM cell. The current flows only during the switching (cell writing) or cell reading, so that there is no V_DDAnd ground. NRAM cells 630 are non-volatile; that is, if power is turned off (or powered down), the memory state is maintained and restored to the same memory state as the memory state before power was turned off (or powered down).

Fig. 6B shows a state machine 660 for use as a non-volatile nanotube latch 650, according to yet another embodiment of the invention. In this embodiment, the control electrode of the upper inverter 510B, and the release electrode of the lower inverter 511B, are connected to a logic input signal A via a select transistor 662 controlled by a clock signal CLK_T(which is applied to IN1) and is connected to the state device 660 at node 671. Control electrode of lower inverter, and release of upper inverterDischarge electrodes connected to a complementary version A of an input signal via a select transistor 664 controlled by a clock signal CLK_C(which is applied to IN2) and is connected to the state device 660 at node 672. In this manner, a state machine can form nanotube latch 650. Inverter 511B is designed as a master inverter (comprised of nanotube devices including more nanotubes) and 510B is designed as a feedback inverter (comprised of nanotube devices including fewer nanotubes) that passes the charge required to compensate for the discharge of state device nodes in noisy situations, for example, as described in reference to "Circuits, Interconnections, and Packaging" for VLSI "(circuit, interconnect and package for very large scale integrated Circuits), pages 349 and 351, published by addison-Wesley press, h.b. Inverters 511B, 510B and pass transistors 662 and 664 are proportioned to ensure that latch 660 switches to a desired state when data is written to latch 660. In the Bakolu reference, feedback inverter 510B must be weak enough to enable circuitry (not shown) of state device 660 driven via clock devices 662 and 664 to supply very high power to feedback inverter 510B and overcome the latch 650 state stored in state device 660. The complementary logic latch outputs are labeled OUT1 and OUT 2. The latch 650 is non-volatile; that is, if the power is turned off (or powered down), the logic state is maintained and restored to the same logic state as the logic state before the power was turned off (or powered down).

Fig. 7 illustrates a non-volatile, nanotube-based, gate-Cathode Voltage Switch Logic (CVSL) circuit 700, in accordance with certain embodiments. The circuit 700 is made up of two complementary logic portions 740 and 742. The output of the logic circuit 700 needs to produce true 720T and complementary 720C logic outputs. The logic circuit 700 is non-volatile; that is, if the power is turned off (or powered down), the logic state is maintained and restored to the same logic state as the logic state before the power was turned off (or powered down). Logic circuit 740 is a non-volatile, nanotube-based NOR circuit whose inputs are activated by true and complementary forms A and B, and whose corresponding output is (A)_T+B_T)_CAs shown in fig. 7. The logic circuit 742 is a nonvolatile NANDCircuit when it is powered from input A_CAnd B_CWhen activated, its output is A_T+B_TAnd releases a and B as shown in fig. 7. The current flows only during switching, so there is no V_DDAnd ground.

As already discussed, the 4-terminal device of fig. 1 can also be constructed with a nanotube length having a ratio of nanotube length to gap size of less than 5 to create a volatile device. The 4-terminal volatile device can also operate as dual rail differential logic, but does not retain a logic state when the circuit is powered down. A schematic diagram of a volatile 4-terminal device is shown in fig. 2A'. If the release electrode is connected to the nanotube channel element through a low resistance path, such as a metallization layer, the 4-terminal volatile device can operate as a 3-terminal volatile device. For example, referring to FIG. 2A ', the release electrode 112 ' is electrically connected to the nanotube signal electrode 114 '. This allows for the mixing of single rail volatile logic, dual rail volatile logic, and dual rail non-volatile logic on a single substrate using nanotube switch devices designed for non-volatile operation, as well as nanotube switch devices designed for volatile operation. Fig. 8A-8B illustrate an example of a 4-terminal device being used as a 3-terminal device in a configuration of a four-device volatile state device.

Nanotube-based logic may be used in conjunction with and in the absence of diodes, resistors, and transistors, or may be part of or replace CMOS, biCMOS, bipolar, and other transistor-level technologies. In addition, nonvolatile flip-flops may also replace SRAM flip-flops to create NRAM cells. The interconnect lines used to interconnect the nanotube device terminals may be conventional wires such as aluminum copper (AlCu), tungsten (W), or copper with an appropriate insulating layer such as silicon dioxide, polyimide, etc., or may be single-walled or multi-walled nanotubes used as wires.

The inventors envision other volatile and non-volatile or hybrid nano-electromechanical designs depending on the particular application, speed, power requirements, and density desired. Furthermore, the inventors foresee the use of multi-walled carbon nanotubes, nano-sized, as switching elements at the contact points in the switch. As technology evolves, node sizes decrease from 90nm to 65nm, and down to the size of individual nanotubes or nanowires, the present inventors foresee that the basic electromechanical switching elements and their operation will change with this size decrease to a new generation of nanoscale devices with tunable performance characteristics.

The nanotube switching element of the preferred embodiment uses multiple controls for forming and deactivating the channels. In some embodiments, the device is sized to create a non-volatile device and one of the electrodes is used to form a channel, while the other is used to release the channel. The electrodes may be used as differential dual rail inputs. Alternatively, they may be set and used at different times. For example, the control electrode may be used in the form of a clock signal, or the release electrode may be used in the form of a clock signal. The control electrode and the release electrode may also be placed at, for example, the same voltage so that the state of the nanotube is not disturbed by noise sources such as voltage spikes (spikes) on adjacent wire nodes.

The device of fig. 1 may be designed to operate as a volatile or non-volatile device. In the case of volatile devices, the mechanical recovery force due to nanotube extension is stronger than the van der waals holding force, and when the electric field is removed, the mechanical contact of the nanotube with the control or release electrode insulator is broken. In general, nanotube geometries, such as a ratio of suspended length to gap of less than 5-1, are used in volatile devices. In the case of non-volatile devices, the mechanical recovery force due to nanotube extension is weaker than the van der waals holding force, and the mechanical contact of the nanotubes with the control or release electrode insulation remains uninterrupted when the electric field is removed. In general, nanotube geometries, such as a ratio of suspended length to gap of greater than 5-1, are used in non-volatile devices. An electric field that generates an electrostatic force needs to be applied to change the state of the nanotube device. The van der waals force between the nanotube and the metal and insulator is a function of the material used to fabricate the nanotube switch. By way of example, this includes insulators such as silicon dioxide and silicon nitride, metals such as tungsten, aluminum, copper, nickel, palladium, and semiconductors such as silicon. For the same surface area, the force may vary by less than 5% for some material combinations, or may vary by more than a factor of 2 for other material combinations, so that volatile and non-volatile operation is determined based on, for example, the float length and gap size and the materials selected. However, it is also possible to design the device by selecting geometries and materials that exhibit stronger or weaker van der waals forces. By way of example, nanotube suspension length and gap height and build-up layer density, control electrode length, width, and dielectric layer thickness may vary. The output electrode size and spacing from the nanotubes may also vary. In addition, layers specifically designed to increase Vanderwatt forces (not shown) may also be added during the fabrication of nanotube switching element 100 as shown in FIG. 1. For example, a thin (e.g., 5 to 10nm) layer (not shown) of metal (non-electrically connected), semiconductor (non-electrically connected), or insulating material may be added on the insulator layer associated with the control electrode 111 or the release electrode 112, which may increase the van der Waals holding power without substantial change to the device for preferred non-volatile operation. In this way, the geometry and material selection is used to optimize device operation, in this example to optimize non-volatile operation.

In a complementary circuit, such as an inverter using two nanotube switching elements 100 with connected output terminals, there may be a transient current between the power supply and ground in the inverter circuit when the inverter changes from one logic state to the other. In CMOS, this occurs when both the PFET and NFET are momentarily closed at the time of the logic state transition, and is sometimes referred to as a "breakdown" current. In the case of a mechatronic inverter, if the nanotube fabric of the first nanotube switch makes conductive contact with the first output structure before the nanotube fabric of the second nanotube switch releases conductive contact with the second output structure, a transient current occurs when the logic state changes. However, if the first nanotube switch breaks contact between the first nanotube fabric and the first output electrode before the second nanotube switch causes contact between the second nanotube fabric and the second output structure, then break-before-make (break-before-make) inverter operation occurs and the "shoot through" current is minimized or eliminated. Electromechanical devices that prefer break-before-contact operation may, for example, be designed with different gap heights above and below the nanotube switching element, such that the forces exerted on the nanotube switching element by the control and release electrodes are different; and/or the travel distance of the nanotube switch element in one direction is different from that in the other direction; and/or materials are selected (and/or added) to increase the van der waals force in one switching direction and decrease the van der waals force in the opposite direction.

By way of example, the nanotube switching device 100 shown in FIG. 1 is designed such that the gap G102 is substantially smaller (e.g., 50% smaller) than the gap G104. Gap G103 can also be made larger so that contact of nanotube element 115 during switching is delayed. Further, the dielectric thickness and the dielectric constant may be different such that, for example, for the same applied voltage difference, the electric field between the release electrode 112 and the nanotube element 115 is stronger than the electric field between the control electrode 111 and the nanotube element 115 to more quickly cut the nanotube element 115 off from the output terminals 113c and 113 d. Output electrodes 113c and 113d may be designed to have a smaller radius and thus have a smaller contact area with nanotube element 115 than the contact size (area) between nanotube element 115 and the insulation on control terminal 111 in order to release the contact between nanotube element 115 and output electrodes 113c and 113 d. The material for electrodes 113c and 113d may be selected to be weaker relative to the van der waals force exhibited by nanotube element 115, as compared to, for example, the van der waals force between nanotube element 115 and the insulation on release electrode 112. These and other approaches may be used to design nanotube switching elements that prefer a contact-before-open operation, thus minimizing or eliminating "shoot-through" current when a circuit, such as an inverter, switches from one logic state to another.

The materials used to make the electrodes and the contacts for the nanotube switches depend on the particular application, i.e., no particular metal is required for operation of the present invention.

The nanotubes may be functionalized with planar conjugated hydrocarbons such as pyrene (pyrene), which may contribute to the internal adhesion between the nanotubes in the ribbon. The surface of the nanotubes can be derivatized to create a more hydrophobic or hydrophilic environment to promote better adhesion of the nanotube fabric to the underlying electrode surface. In particular, the functionalization of the wafer/substrate surface involves "derivatizing" the surface of the substrate. For example, a hydrophilic state may be chemically switched to a hydrophobic state, or a functional group such as an amine, carboxylic acid, thiol, or sulfonate may be provided to transform the surface characteristics of the substrate. Functionalization may include an optional primary step of oxidizing or ashing the substrate in an oxygen plasma to remove carbon or other impurities from the substrate surface and provide a uniformly reactive oxidized surface that is then reacted with silane. One possible polymer to use is 3-Aminopropyltriethoxysilane (APTS). The substrate surface may be derivatized prior to application of the nanotube fabric.

Although single-walled carbon nanotubes are preferred, multi-walled carbon nanotubes may be used. Nanotubes may also be used in conjunction with nanowires. Reference herein to nanowires is intended to refer to single nanowires, collections of unbraided nanowires, nanoclusters (nanocrusters), nanowires entangled with nanotubes comprising nanostructures, clusters of nanowires, and the like. The present invention relates to the creation of nanoscale conductive elements for any electronic application.

The following patent references relate to various techniques for fabricating nanotube-structured articles and switches, and are assigned to the assignee of the present application. The entire contents of each are hereby incorporated by reference.

U.S. patent application Ser. No. 10/341,005, filed on 13/1/2003, entitled "Methods of Making Carbon Nanotube Films, Layers, constructions, tapes, components, and articles";

U.S. patent application Ser. No. 09/915,093, filed 25.7.2001, entitled "Electrical mechanical Memory Array Using nanotubes ribs and Method for making same" (Electromechanical Memory arrays Using Nanotube Ribbons and methods of making same);

U.S. patent application Ser. No. 10/033,032, filed on 28/12/2001, entitled "Methods of Making Electromechanical Three-Trace Junction Devices";

U.S. patent application serial No. 10/033,323, filed on 28.12.2001, entitled "Electromechanical Three-Trace Junction Devices";

U.S. patent application serial No. 10/128,117, filed on 23/4/2002, entitled "methods of NT Films and Articles" (method of NT Films and Articles);

U.S. patent application Ser. No. 10/341,055, filed on 13/1/2003, entitled "methods of Using Thin Metal layer to Make Carbon Nanotube Films, Layers, constructions, Ribbons, Elements and Articles", and methods of making Carbon Nanotube Films, Layers, constructions, Ribbons, Elements and Articles Using Thin Metal Layers;

U.S. patent application Ser. No. 10/341,054, filed on 13/1/2003, entitled "methods of Using Pre-formed Nanotubes to Make Carbon Nanotube Films, Layers, constructions, tapes, components and Articles" (methods of Using Pre-formed Nanotubes to Make Carbon Nanotube Films, Layers, constructions, tapes, components and Articles);

U.S. patent application Ser. No. 10/341,130, filed on 13/1/2003, entitled "carbon nanotube Films, Layers, Fabrics, Ribbons, Elements and Articles" (methods for carbon nanotube Films, Layers, constructions, tapes, components and Articles);

U.S. patent application Ser. No. 10/776,059, filed on 11/2/2004, entitled "devices for horizontal-Disposed Nano-textile Articles and Methods of Making The Same" (apparatus with Horizontally Disposed nanostructured Articles and method of Making The Same); and

U.S. patent application Ser. No. 10/776,572, filed on 11/2/2004, entitled "devices with Vertically-positioned nanostructured Articles and Methods of Making The Same".

The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Claims (12)

1. A boolean logic circuit comprising:

at least one set of differential input terminals and one output terminal;

a network of nanotube switching elements electrically disposed between the at least one set of differential input terminals and the output terminals, the network of nanotube switching elements being a network of nanotube switching elements;

the nanotube switching element network performs boolean function conversion on boolean signals of the at least one set of differential input terminals;

wherein the network of nanotube switching elements comprises first and second nanotube switching elements, each nanotube switching element comprising:

an output node;

a nanotube channel element having at least one electrically conductive nanotube; and

a control electrode controllably formed into an electrically conductive pathway to the output node relative to the nanotube channel element placement;

a discharge electrode controllably released from an electrically conductive pathway to the output node relative to the nanotube channel element placement;

wherein a first differential input terminal of the Boolean logic circuit is electrically connected to control electrodes of the first and second nanotube switching elements;

wherein a second differential input terminal of the Boolean logic circuit is electrically connected to the release electrodes of the first and second nanotube switching elements;

wherein the output nodes of the first and second nanotube switching elements are electrically coupled with the output terminal of the Boolean logic circuit;

wherein the nanotube channel element of the first nanotube switch element is electrically connected to a logic true value and the nanotube channel element of the second nanotube switch element is electrically connected to a logic false value.

2. The boolean logic circuit according to claim 1, wherein the network of nanotube switching elements implements a boolean NOT function of signals on the at least one set of differential input terminals.

3. The boolean logic circuit according to claim 1, wherein the network of nanotube switching elements implements a boolean NOR function of signals on the at least first and second sets of differential input terminals.

4. The boolean logic circuit according to claim 1, wherein the network of nanotube switching elements implements a boolean NAND function of signals on the at least first and second sets of differential input terminals.

5. The boolean logic circuit according to claim 3, wherein the circuit is a cascode voltage switch logic circuit, and wherein the network of nanotube switch elements further implements a boolean NAND function of signals on the at least first and second sets of differential input terminals.

6. A boolean logic circuit, comprising:

at least one input terminal and one output terminal;

a network of nanotube switching elements electrically disposed between the at least one input terminal and the output terminal, the network of nanotube switching elements being a network of nanotube switching elements;

said network of nanotube switching elements performing a Boolean function transformation on said at least one input terminal and on a Boolean signal on at least one of said nanotube switching elements capable of non-volatilely retaining an informational state;

wherein the network of nanotube switching elements comprises first and second nanotube switching elements, each nanotube switching element comprising:

an output node;

a nanotube channel element having at least one electrically conductive nanotube; and

a control electrode controllably formed into an electrically conductive pathway to the output node relative to the nanotube channel element placement;

a discharge electrode controllably released from an electrically conductive pathway to the output node relative to the nanotube channel element placement;

wherein a first differential input terminal of the Boolean logic circuit is electrically connected to control electrodes of the first and second nanotube switching elements;

wherein a second differential input terminal of the Boolean logic circuit is electrically connected to the release electrodes of the first and second nanotube switching elements;

wherein the output nodes of the first and second nanotube switching elements are electrically coupled with the output terminal of the Boolean logic circuit;

wherein the nanotube channel element of the first nanotube switch element is electrically connected to a logic true value and the nanotube channel element of the second nanotube switch element is electrically connected to a logic false value.

7. The boolean logic circuit according to claim 6, wherein the at least one nanotube switching element capable of non-volatilely retaining an informational state includes a nanotube channel element having at least one conductive nanotube and a control structure positioned relative to the nanotube channel element to controllably form and release a conductive path between an input node of the at least one switching element and an output node of the at least one switching element.

8. The boolean logic circuit according to claim 7, wherein the control structure includes a control electrode and a release electrode disposed on opposite sides of the nanochannel element.

9. The boolean logic circuit according to claim 6, wherein the formation of either channel of the first and second nanotube switching elements is caused by an electromechanical deflection of the nanotube channel elements to bring the nanotube channel elements into contact with the output node.

10. The Boolean logic circuit of claim 6 wherein said nanotube channel element is deflectable in response to electrostatic forces resulting from signal relationships on said nanotube channel element, said control electrode and said release electrode, and wherein each of said first and second nanotube switching elements includes an isolation structure positioned relative to said nanotube channel such that the formation of said channel is substantially invariant to said output node state.

11. The boolean logic circuit according to claim 10, wherein each nanotube channel element is positionable into one of at least two positional states in response to a signal relationship on the nanotube channel element, the control electrode, and the release electrode, and wherein one of the at least two positional states is defined by the nanotube channel element being in a floating state and not electrically connected to the output node.

12. The boolean logic circuit according to claim 11, characterized in that the positional state of each nanotube channel element is maintained in the absence of signals of the nanotube element, the control electrode and the release electrode.