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WO2009108175A1 - Structures de condensateur à nanotubes de carbone et procédés - Google Patents

Structures de condensateur à nanotubes de carbone et procédés Download PDF

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Publication number
WO2009108175A1
WO2009108175A1 PCT/US2008/013624 US2008013624W WO2009108175A1 WO 2009108175 A1 WO2009108175 A1 WO 2009108175A1 US 2008013624 W US2008013624 W US 2008013624W WO 2009108175 A1 WO2009108175 A1 WO 2009108175A1
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WO
WIPO (PCT)
Prior art keywords
cncap
cnts
cnt
vertical
carbon nanotube
Prior art date
Application number
PCT/US2008/013624
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English (en)
Inventor
Mark M. Budnik
Eric W. Johnson
Joshua D. Wood
Original Assignee
The Lutheran University Association, Inc. D/B/A Valparaiso University
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by The Lutheran University Association, Inc. D/B/A Valparaiso University filed Critical The Lutheran University Association, Inc. D/B/A Valparaiso University
Publication of WO2009108175A1 publication Critical patent/WO2009108175A1/fr

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
    • H01G4/00—Fixed capacitors; Processes of their manufacture
    • H01G4/002—Details
    • H01G4/005—Electrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
    • H01G4/00—Fixed capacitors; Processes of their manufacture
    • H01G4/002—Details
    • H01G4/228—Terminals
    • H01G4/232—Terminals electrically connecting two or more layers of a stacked or rolled capacitor
    • H01G4/2325—Terminals electrically connecting two or more layers of a stacked or rolled capacitor characterised by the material of the terminals

Definitions

  • the present disclosure relates generally to methods and apparatus associated with carbon nanotube capacitor structures and specifically to carbon nanotube capacitor structures providing high capacitance per unit area with respect to conventional metal-oxide-semiconductor and metal-insulator-metal capacitors.
  • Capacitors are important components in analog, digital, and mixed-signal circuits. They are used in a number of applications including decoupling circuits (the suppression of supply voltage variation due to transients in operating currents) and analog signal processing (in switched capacitor circuits, for example).
  • MOSC metal-oxide-semiconductor capacitor
  • MOSFET metal-oxide-semiconductor field effect transistor
  • the MOSFET' s gate functions as one electrode, its source and drain region function as the second electrode, and the gate dielectric serves as the capacitor dielectric.
  • MIM metal-insulator-metal capacitor
  • the MIM is fabricated in higher levels of metal with a thin dielectric material (often SiO 2 ).
  • CNTs carbon nanotubes
  • CNTs are cylinders of very small diameter typically formed by rolling very thin sheets of graphite. When rolled correctly, a CNT can exhibit metallic properties. When CNTs are rolled with a single wall, ballistic transport of electrons is possible in the presence of small and moderate electric fields. As such, bundles of single-walled CNTs are being used between traditional metal interconnects in integrated circuit technology at the nanoscale level. When CNT bundles, or vias, are connected to opposing polarities (operating voltage and ground, respectively), a carbon nanotube capacitor (CNCAP) is formed.
  • CNT bundles, or vias are connected to opposing polarities (operating voltage and ground, respectively).
  • a carbon nanotube capacitor (CNCAP) structure includes an anode, a cathode, a plurality of substrates, an array of carbon nanotubes (CNTs) aligned substantially perpendicular to and interconnected between the plurality of substrates, wherein each CNT or CNT bundle of the array is selectively coupled to parallel, yet alternately charged first and second electrodes.
  • CNTs carbon nanotubes
  • FIG. 1 illustrates a perspective view of a vertical carbon nanotube capacitor (CNCAP);
  • FIG. 2 is a top view of a cross-section of a vertical CNCAP structure
  • FIG. 3 illustrates a top cross-sectional view of a rotated version of the CNCAP structure of FIG. 2;
  • FIG. 4 is a partial perspective view of the CNCAP structure of FIG. 3;
  • FIG. 5 is a partial top view of a cross-section on its side of the vertical CNCAP of FIG. 1;
  • FIG. 6 is a top cross-sectional view of a dense, vertical CNCAP structure
  • FIG. 7 is a top cross-sectional view of a sparsely packed, vertical CNCAP structure
  • FIG. 8 is a schematic circuit diagram of an equivalent circuit of vertical, parallel, metallic, single-walled CNTs
  • FIG. 9 is a three-element model of a CNCAP
  • FIG. 10 is a graph illustrating the equivalent series resistance (ESR) of each of the CNCAP structures of FIGS. 2-4, 5-6 and 7 as a function of contact resistance;
  • FIG. 12 illustrates a top cross-sectional view of a pseudo-parallel plate CNCAP structure
  • FIG. 13 illustrates a top cross-sectional view of an interleaved CNCAP structure as shown in FIGS. 2-4, with electrical connections.
  • a vertical carbon nanotube capacitor (CNCAP) structure 20 is shown.
  • the CNCAP structure 20 includes two vertical interterconnects 22, via-like structures, which each include bundles of vertical CNTs 23.
  • the vertical interconnects 22 may include vertical CNTs 23 bundled in a variety of shapes and patterns, including but not limited to hexagonal, square, random, quasi-random, and sparsely packed bundles.
  • the CNTs 23 of one of the vertical interconnects 22 are connected at respective bases thereof to an electrode 24 and at respective top ends thereof to an electrode 25.
  • the CNTs 23 of the other interconnect 22 are also connected at respective bases thereof to an electrode 26 and at respective top ends thereof to an electrode 27.
  • the CNCAP structure 20 shown in FIG. 1 has its bundles of CNTs 23 formed in aligned arrays, extending substantially uniformly in a direction substantially perpendicular to the various substrates 24-27 to which one or more of the CNTs 23 may be connected.
  • the CNCAP structure 20 has a capacitance Cvi a that is achieved when the two bundles of CNTs 23 are alternately connected to opposing electrodes, forming a cathode and an anode, to achieve a relatively high value of capacitance per unit area.
  • FIG. 2 shows a cross-section of a vertical CNCAP structure 30, CNCAPl.
  • the electrostatic coupling capacitance C c is shown between one CNT (anode Al) and one CNT (cathode Cl). If the CNCAP structure 30 as shown in FIG. 2 is rotated about 45°, the anode CNTs, as designated by A1-A4, and the cathode CNTs, as designated by C and Cl, can be aligned longitudinally, as seen in FIG. 3.
  • the CNCAP structure 30 includes vertical CNTs in interconnects 32, similar to the vertical interconnects 22, where each CNT of the interconnects 32 is connected as a via between two substrates, capacitor electrodes 34 and 36, as shown in FIG. 4.
  • This alignment may allow the top and/or bottom of each vertical CNT to be connected to parallel, yet alternately connected capacitor electrodes 34 and 36.
  • This alternate connection of electrodes, forming a cathode and an anode with a capacitance C f can be seen in a top cross- sectional view in FIG. 13.
  • This area may also contain four of the electrostatic coupling capacitors Cc from FIG. 3 (where only one Cc is shown).
  • a typical value for the diameter of a single-walled CNT is about lnm.
  • the number of CNTs/ ⁇ m 2 can be calculated.
  • the CNCAP structure 30, CNCAPl utilizes about two CNTs/50nm 2 , and the total CNTs/ ⁇ m 2 will be about 40,000.
  • FIG. 5 A top view on its side of the vertical CNT interconnects 22 of FIG. 1 , is shown in FIG. 5. As shown, the diameter of a single-walled CNT is about lnm. The footprints of the vertical interconnects 22 are about lOnm by about lOnm. This footprint dimension can be expressed as the CNT bundle side length L SIDE - The number of CNTs per vertical CNT bundle is:
  • the vertical interconnects 22 are spaced a distance of about lOnm, which can be expressed as L SPACE , and there are approximately 100 CNTs per vertical CNT interconnect 22.
  • Such embodiments of vertical CNT interconnects 22 are relatively dense. For an inter-bundle distance of LS PACE (not always equal to L S I DE ), the number of CNCAP electrodes per unit area is given by
  • a CNCAP structure 40 includes a network of the relatively dense CNT bundles of FIG. 5, vertical CNT interconnects 42, similar to the vertical interconnects 32.
  • the CNT bundles are alternately connected to base electrodes 44 and/or top electrodes (not shown) to form anodes (A) and cathodes (C) of the CNCAP structure 40.
  • L SID E equaling about lOnm
  • L SPACE the same distance between interconnects
  • a unit cell of the vertical CNT interconnects is about 20nm by about 20nm and contains approximately 100 CNTs. This geometry results in about 2,500 electrodes/ ⁇ m 2 (about 1,250 anodes and about 1,250 cathodes).
  • a CNCAP structure 50 is shown in FIG. 7 and includes of a network of vertical CNT interconnects 52.
  • the CNT bundles are alternately connected to base electrodes 54 and/or top electrodes (not shown).
  • the CNCAP structure 50 is composed of sparse vertical CNT bundles, with only about four CNTs per approximately a lOOnm 2 bundle area.
  • the CNCAP structure 50, CNCAP3, has about 2,500 electrodes/ ⁇ m 2 , but may allow for greater inter-CNT distances.
  • FIG. 8 shows an equivalent circuit of two vertical, parallel, single-walled, metallic CNTs, such as those described in the CNCAP structure 20.
  • the quantum capacitance, C Q is approximately 40OaF per about l ⁇ m of CNT length (vertical height).
  • the inductance, L, of the CNTs is approximately 4nH/ ⁇ m.
  • Rc is the CNT-metal interconnect contact resistance at the top and the base of each CNT, where each CNT is connected to electrodes, such as capacitor electrodes 34 and 36 in the CNCAP structure 30, CNCAPl.
  • RQ is the quantum resistance (6.45k ⁇ )
  • ⁇ is the length of the CNT
  • ⁇ m fp,i O w is the CNT low-bias mean free path (approximately 1.6 ⁇ m)
  • V is the voltage drop across the CNT
  • Io is approximately 25 ⁇ A.
  • a typical value of the height of a CNCAP's vertical CNTs, ⁇ is about l ⁇ m.
  • the voltage across each CNT is about OV.
  • a CNCAP is used in integrated circuits near the end of the International Technology Roadmap for Semiconductors (ITRS), with operating voltages at about 0.5 V. If the maximum voltage drop across the CNTs is allowed to be about 10OmV, an illustrative CNT resistance can be approximated as:
  • the contact resistance, Rc, at the top and base of each CNT may be important to electrical modeling of the whole CNCAP structure.
  • the vertical CNT interconnects can be partially buried in their metallic electrode contacts, achieving relatively small contact resistances (much less than RQ). While in some instances Rc could be neglected, here the contact resistance is taken into account when calculating the equivalent series resistance of the CNCAP structures 30, 40, and 50 (CNCAPl, CNCAP2, and CNCAP3, respectively).
  • a variety of techniques to manufacture vertical CNTs are known to those skilled in the art, including, for example, chemical vapor deposition (CVD), as described in, for example, L. Zhu, Y. Sun, J. Xu, Z. Zhang, D. W. Hess, C. P. Wong, "Aligned carbon nanotubes for electrical interconnect and thermal management," Proc. Electronic Components and Technology, vol. 1, pp. 44-50, June 2005.
  • Other illustrative techniques to produce CNTs include, for example, arc discharge, laser ablation, high pressure carbon monoxide, and plasma enhanced CVD, some of which are described in, for example, U.S. Patent Nos. 7,132,714, 7,282,191, and 7,288,321.
  • Many manufacturing processes for growing CNTs onto a substrate layer take place in a vacuum and/or with process gases, as is understood by those skilled in the art.
  • a capacitance Cc is calculated between any two opposite polarity CNTs.
  • ⁇ of about l ⁇ m
  • Cc is about 15.6aF.
  • ⁇ the capacitance per unit area
  • C CNCAPI the capacitance per unit area
  • the total capacitance per unit area is about 4(14.5aF)/50nm 2 or about 58aF/50nm 2 .
  • the capacitance per unit area C c C CNCAPI of the CNCAP structure 30, CNCAPl, is about l,160fF/ ⁇ m 2 .
  • the capacitance per unit area of the CNCAP structure 30, CNCAPl can be approximated as: ⁇ m 3 ⁇ ⁇ m J
  • This very high capacitance per unit area of about 387fF/ ⁇ m 2 is more than an order of magnitude beyond the International Technology Roadmap for Semiconductors (ITRS) expectations for MOSC and MIM devices as forecast for the year 2018 (forecasts of l lfF// ⁇ m 2 and 10fF/ ⁇ m 2 , respectively).
  • ITRS International Technology Roadmap for Semiconductors
  • the CNCAP structure 40 may include about 1,250 anodes and about 1,250 cathodes per ⁇ m 2 .
  • the electrostatic coupling capacitance between electrodes (Cc 2 in FIG. 6) is about 35aF.
  • each anode has an electrostatic coupling capacitance between itself and its four nearest-neighbor cathode bundles. Again considering the fraction of metallic CNTs:
  • This parallel-plate approximation of the capacitance per unit area of CNCAP structure 40, CNCAP2 can be simulated for different dimensions of L SI D E and L SP A C E- AS L S IDE and L SPAC E are decreased below 0.5 ⁇ m, simulations performed on the CNCAP structure 40, CNCAP2, using FastCap, a 3-D capacitance extraction computer program, show an increase in C C N C AP2- These simulations can be seen in FIG. 11. Previous simulations by others, however, show that C C N C AP2, even at L S I DE and L SPACE dimensions of 10nm, remains consistent with the parallel-plate approximations.
  • the CNCAP may include about 1,250 anodes and about 1,250 cathodes per ⁇ m 2 .
  • the electrostatic coupling capacitance between electrodes is about 3OaF.
  • the capacitance per unit area of the CNCAP structure 50, CNCAP3, is calculated to be:
  • the ESL of the CNCAP structure 50, CNCAP3, is:
  • the footprint of the embodiments of CNCAPs of the present disclosure may take several different forms. While the CNCAP structures 30, 40 and 50 (CNCAPl, CNCAP2, and CNC AP3, respectively) may be directly implemented, a simpler, vertical pseudo-parallel plate version 60 of a CNCAP may be implemented with capacitance Cpp, as shown in FIG. 12.
  • the electrical models developed in the above illustrative example show that vertical CNCAPs only about l ⁇ m in height produce capacitances per unit area from about 50fF/ ⁇ m to about 387fF/ ⁇ m 2 , significantly higher than the 4fF/ ⁇ m 2 to 7fF/ ⁇ m 2 achievable today in conventional metal-oxide-semiconductor capacitors and metal-insulator-metal capacitors.
  • the electrical models as shown above illustrates that vertical CNCAP structures can become viable circuit components.

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  • Power Engineering (AREA)
  • Manufacturing & Machinery (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Semiconductor Integrated Circuits (AREA)

Abstract

L'invention concerne des structures et des procédés qui utilisent des nanotubes de carbone à croissance verticale (CNT) dans la formation de condensateurs à nanotubes de carbone (CNCAP). Dans différents modes de réalisation, les structures CNCAP contiennent des faisceaux ou parois CNT de densité variable pour remplacer les interconnexions classiques de couches intermétalliques, utilisant différents diamètres de CNT, différents écartements entre CNT et différentes longueurs de CNT.
PCT/US2008/013624 2007-12-12 2008-12-12 Structures de condensateur à nanotubes de carbone et procédés WO2009108175A1 (fr)

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US61/007,598 2007-12-12

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8350360B1 (en) 2009-08-28 2013-01-08 Lockheed Martin Corporation Four-terminal carbon nanotube capacitors
US8405189B1 (en) * 2010-02-08 2013-03-26 Lockheed Martin Corporation Carbon nanotube (CNT) capacitors and devices integrated with CNT capacitors

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20060214262A1 (en) * 2005-03-24 2006-09-28 Intel Corporation Capacitor with carbon nanotubes
US20070171594A1 (en) * 2005-12-16 2007-07-26 Budnik Mark M High density capacitor for integrated circuit technologies
US20070242417A1 (en) * 2005-10-06 2007-10-18 Mosley Larry E Forming carbon nanotube capacitors

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20060214262A1 (en) * 2005-03-24 2006-09-28 Intel Corporation Capacitor with carbon nanotubes
US20070242417A1 (en) * 2005-10-06 2007-10-18 Mosley Larry E Forming carbon nanotube capacitors
US20070171594A1 (en) * 2005-12-16 2007-07-26 Budnik Mark M High density capacitor for integrated circuit technologies

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8350360B1 (en) 2009-08-28 2013-01-08 Lockheed Martin Corporation Four-terminal carbon nanotube capacitors
US8405189B1 (en) * 2010-02-08 2013-03-26 Lockheed Martin Corporation Carbon nanotube (CNT) capacitors and devices integrated with CNT capacitors

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