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Monolithic Integrated Antennas and Nanoantennas for Wireless Sensors and for

Wireless Intrachip and Interchip Communication

Peter Russer1, Nikolaus Fichtner1, Paolo Lugli1, Wolfgang Porod2 and Hristomir Yordanov1

1Institute for Nanoelectronics, Technische Universität München, Germany2Center for Nano Science and Technology, University of Notre Dame, USA

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Contents

1. Introduction2. CMOS Integrated Antennas3. Nanoantennas with MOM Tunnel Diodes4. Nanoantennas Based on Carbon Nanotubes and

Graphene5. Alternative Materials and Fabrication Techniques6. Outlook

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On-Chip Nanoantennas for Sensing and Communication

• As the structure size of circuit devices and components is continuously decreasing the same will hold for antennas and radiation elements used in integrated circuits for on-chip and chip-to-chip communication.

• Following the general scaling trend on-chip antennas will soon enter the micrometer- and even the nanometer regime.

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Introduction

• The rate of signal transmission on or between monolithic integrated circuits is limited by the cross-talk and the dispersion due to the wired interconnects.

• An interesting option to overcome the bandwidth limitations is wireless chip-to-chip and on-chip interconnects via integrated antennas.

• The electromagnetic coupling of antennas may occur via waves radiated into space and scattered by objects or via surface waves.

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Inter-Chip and Intra-Chip MIMO Communication

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The Wireless MIMO Channel Model

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Contents

1. Introduction2. CMOS Integrated Antennas3. Nanoantennas with MOM Tunnel Diodes4. Nanoantennas Based on Carbon Nanotubes and

Graphene5. Alternative Materials and Fabrication Techniques6. Outlook

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On-chip meander antenna

An intrachip wireless interconnect system using meander monopole on-chip antennas and operating at 22 GHz to 29 GHz is described inM. Sun, et al., “Performance of Intra-Chip wireless interconnect using On-Chip antennas and UWB radios,’’ IEEE Trans. on Ant. & Prop., vol. 57, no. 9, pp. 2756-2762, 2009. On-chip UWB radios in that frequency band are discussed there. The on-chip antennas arevmeander monopoles with 1 mm axial length.

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CMOS Integrated Antennas

Schematic drawing of a chip with an integrated antenna

• Instead of dedicating chip area for the antenna the antenna can make use of the available on-chip metallization.

• This can be obtained by dividing the top metallization layer into patches and impressing an RF signal across the gap between the patches.

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Differential Lines, Connecting the Digital Circuits Under the Separate Antenna Patches

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Chip with Integrated Antenna

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CMOS Integrated Antennas

2 mm 50 mm

1.1

mm

Simulated current distribution of a two-patch antenna operated at 66 GHz

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CMOS Integrated Antennas

Photograph of the open slot antenna

H. Yordanov and P. Russer, “Area-efficient integrated antennas for inter-chip communication,” Proc. of the 40th European Microwave Conference, EuMC 2010, Paris, France, Sep 2010.

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Antenna Characteristics

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Antenna Impedance vs. Gap Width

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CMOS Integrated Antennas

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CMOS Integrated Antennas

Main Direction

Minimum Direction

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Contents

1. Introduction2. CMOS Integrated Antennas3. Nanoantennas with MOM Tunnel Diodes4. Nanoantennas Based on Carbon Nanotubes and

Graphene5. Alternative Materials and Fabrication Techniques6. Outlook

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Integration of Antennas with MOM Diodes

• A promising novel concept for infrared (IR) detectors is the combination of a nanoantenna with a rectifying element.

• The rectifying element extracts a DC component from the rapidly-varying current delivered from the nanoantenna. Semiconductor diodes are widely used, but they encounter frequency limitations for the mm-wave and long-wave IR regime.

• It has been demonstrated that MOM tunnel diodes can provide rectification for IR and even optical radiation

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Antenna with Integrated MOM Diode

P. Esfandiari, G. Bernstein, P. Fay, W. Porod et al., “Tunable antennacoupledmetal-oxide-metal (MOM) uncooled IR detector,” in Proc. ofSPIE, vol. 5783, 2005, pp. 471 – 482.

The MOM dieode is naturaly formed at the overlaparea between the antenna arms

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Al

MOM diodeAl-AlOx-Pt

Electrical leads

diode formed antennaantenna

PtAl

Design 1Shadow evaporation

Design 2Two step lithography

Pt

MOM diodeAl-AlOx-Pt

ACMOMD Design

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linearly polarized IR

radiation

Al-AlOx-Al nanoantenna

Metal Oxide Metal Metal Oxide Metal

Metal X Oxide Metal X

Electrode 1 Electrode 2

QMTunneling

Net e-transfer for one half cycle

Electrode 1 Electrode 2

Net e-transfer for other half cycle

Electrode 1 Electrode 2

For symmetrical barrier MOM

No net e-transfer over complete cycle of IR

radiationNo net QM Tunneling

current

Symmetric MOM - Unbiased

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Symmetric MOM - Biased

linearly polarized

IR radiation

Al-AlOx-Al nanoantenna

Electrode 1 Electrode 2

Metal X Metal XElectrode 1 Electrode 2

+applied biased

Biased symmetric MOM diode

Electrode 1 Electrode 2

For BIASED symmetrical barrier MOMNet e-transfer over complete cycle of IR radiation

Symmetric MOM - Biased

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Asymmetric MOM

linearly polarized IR radiation

Al-AlOx-Pt nanoante

nna

Metal X Metal YElectrode 1 Electrode 2

Metal X Metal YElectrode 1 Electrode 2

Equilibrium conditionΔ = 1 2=W1-W2

21

Δ

Metal X Oxide Metal Y

Vacuum level

W1

For unbiased asymmetrical barrier MOM

Net e-transfer over complete cycle of IR radiation

Asymmetric MOM - Unbiased

Metal X Metal YElectrode 1 Electrode 2

W2

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20 finished devices through 2 step lithography process

Corresponding SEM image 2-step lithography dipole antenna

AlPt

Al-AlOx-Pt Overlap50x80 nm

Gold bonding

pads

Two Step Lithography DevicesOptical Microscope Images

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J. A. Bean, B. Tiwari, G. H. Bernstein, P. Fay, and W. Porod, “Thermal infrared detection using dipole antenna-coupled metal-oxide-metal diodes,” Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, vol. 27, p. 11, 2009.

SEM Image of a Shadow Evaporation Device

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MOM overlap area of a Shadow evaporation device

One Step Lithography Devices

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Polarization Dependent Response

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Contents

1. Introduction2. CMOS Integrated Antennas3. Nanoantennas with MOM Tunnel Diodes4. Nanoantennas Based on Carbon Nanotubes and

Graphene5. Alternative Materials and Fabrication Techniques6. Outlook

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Carbon Nanotube Antennas

• A further considerable size reduction of integrated antenna structures may be achieved using CNTs.

• CNTs exhibit exceptional electron transport properties, yielding ballistic carrier transport at room temperature with a mean free path of around 0.7 mm and a carrier mobility of 10,000 cm2/Vs.

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Carbon Nanotube Antennas

• Quantum transport effects in the CNT yield a quantum capacitance CQ and a kinetic inductance LK in addition to the geometric capacitance CG and inductance LG.

• The phase velocity for the modified equivalent circuit is around 0.02 c0 which is in accordance with the reduced wavelength of the surface plasmons.

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Carbon Nanotube Antennas

• Due to the extremely high aspect ratio (length to cross sectional area), CNTs have AC resistances per unit length in the order of several kW/μm.

• This causes high conduction losses and thus seriously decreases the efficiency and the achievable gain ofnanoantennas.

• This problem could be bypassed using of arrays of nanoantennas or a bundle of parallel nanowires.

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Graphene Antennas• Like CNTs, graphene also exhibits excellent conductivity and slow

wave properties. The achievable slow-wave effect in plasmon modes is in the order of c0/100.

• At THz frequencies a population inversion in the graphene layer can be realized by optical pumping or forward bias which yields an amplification of the surface plasmon.

• Graphene allows the realization of planar structures and also the realization of active circuits.

J. Moon et al., “Development toward Wafer-Scale graphene RF electronics,” in Topical Meeting on Silicon Monolithic Integrated Circuits in RF Systems, January 11–13, 2010, New Orleans, LA, Jan 2010, pp. 1-3.

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Graphene Antennas

Theoretical investigations have shown that antennas with sizes in the order of several hundred nanometers are suitable to radiate electromagnetic waves in the terahertz band, i. e. from 0.1 THz to 1 THz.

J. M. Jornet and I. F. Akyildiz, “Graphene-based nano-antennas for electromagnetic nanocommunications in the terahertz band,” in Proc. of 4th European Conference on Antennas and Propagation, EUCAP, 2010.

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Contents

1. Introduction2. CMOS Integrated Antennas3. Nanoantennas with MOM Tunnel Diodes4. Nanoantennas Based on Carbon Nanotubes and

Graphene5. Alternative Materials and Fabrication Techniques6. Outlook

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Alternative Materials and Fabrication Techniques

• The antennas described previously are generally fabricated with conventional technologies, namely evaporation of the metallic films followed by patterning via photo or electron-lithography.

• In the CNT or graphene case, the conductive layers have to be grown epitaxially on the given substrate.

• Especially when small dimensions are required, as for the nanometer gaps required in plasmonic structures or in nanometer scale MOM diodes, a very interesting alternative could be offered by nanotransfer techniques.

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Schematic of Direct Metal-Transfer

A metal coated high resolution heterostructure is pressed onto a substrate, thereby creating nanometer separated electrodes.

S. Harrer, S. Strobel, G. Scarpa, G. Abstreiter, M. Tornow, and P. Lugli, “Room temperature nanoimprint lithography using molds fabricated by molecular beam epitaxy,” IEEE Trans. Nanotechnology, vol. 7, no. 3, pp. 363–370, 2008.

S. Harrer, S. Strobel, G. Penso Blanco, G. Scarpa, G. Abstreiter, M. Tornow, and P. Lugli, “Technology assessment of a novel highyield lithographic technique for sub-15-nm direct nanotransfer printing of nanogap electrodes,” IEEE Trans. Nanotechnology, vol. 8, no. 6, pp. 662 –670, 2009.

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Transfer Metal Pads with a Gap of a Few Nanometers.

• Transferred metal pads, exhibiting a gap featuring line separations down to approximately 9 nm.

• The structures could be transferred along the complete length of the mold (approximately 4 mm) with an efficiency of about 80%.

• Structures containing several lines separated by nanometer gaps have also been realized.

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Contents

1. Introduction2. CMOS Integrated Antennas3. Nanoantennas with MOM Tunnel Diodes4. Nanoantennas Based on Carbon Nanotubes and

Graphene5. Alternative Materials and Fabrication Techniques6. Outlook

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Conclusion and Outlook

• As the structure size of circuit devices and components is continuously decreasing the same will hold for antennas and radiation elements used in integrated circuits for on-chip and chip-to-chip communication.

• Following the general scaling trend,on-chip antennas will soon enter the m- and even the nanometer regime.

• Integrated antennas based on nanoelectronics provide a tremendous potential for the realization of novel devices and systems from DC up to the optical range.

• The applications will cover wireless intra-chip and interchip transmission at Gbit/s rates, field sensors and photon harvesting systems.

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Conclusion and Outlook

• Intrachip and interchip wireless broadband communication at millimeterwave carrier frequencies can be realized in CMOS technology and will allow the transfer of Gbit/s data rates.

• A further size reduction of antenna structures will be possible by integration of CNT and graphene antenna structures.

• When small dimensions are required, as for the nanometer gaps required in plasmonic structures or in nanometer scale MOM diodes, a very interesting alternative could be offered by nanotransfer techniques.