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Search Publications by: Thomas Mitchell Wallis ()

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Displaying 51 - 75 of 79

Nanofibers for RF and Beyond

December 1, 2011
Author(s)
Thomas M. Wallis, Kichul Kim, Pavel Kabos, Dejan Filipovic
In order to realize new interconnect concepts based on nanofibers, reliable metrology is required. Given the clock-speeds of integrated circuits in the present as well as the foreseeable future, this metrology must be compatible with radio frequencies (RF)

High Frequency Characterization of Contact Resistance and Conductivity of Platinum Nanowires*

October 1, 2011
Author(s)
Kichul Kim, Paul Rice, Thomas M. Wallis, Dazhen Gu, SangHyun S. Lim, Atif A. Imtiaz, Pavel Kabos, Dejan Filipovic
Abstract— Individual platinum (Pt) nanowires (NWs) with 100 nm and 250 nm diameters, embedded in coplanar waveguide (CPW) structures are investigated. Three approaches for characterization of their contact resistance and conductivity at high frequencies

Electrical Characterization of Photoconductive GaN Nanowire Devices from 50 MHz to 33 GHz

July 1, 2011
Author(s)
Thomas M. Wallis, Dazhen Gu, Atif A. Imtiaz, Pavel Kabos, Paul T. Blanchard, Norman A. Sanford, Kristine A. Bertness, Christpher Smith
The electrical response of two-port., photoconductive GaN nanowire devices was measured from 50 MHz to 33 GHz. The admittance of individual contacted nanowires showed an increase on the order of 10% throughout the measured frequency range after exposure to

Deembedding parasitic elements of GaN nanowire MESFETs by use of microwave measurements

June 3, 2011
Author(s)
Dazhen Gu, Thomas M. Wallis, Paul T. Blanchard, SangHyun S. Lim, Atif A. Imtiaz, Kristine A. Bertness, Norman A. Sanford, Pavel Kabos
We present a deembedding roadmap for extracting parasitic elements of a nanowire (NW) MESFET device from full two-port scattering-parameter measurements in the frequency range from 0.1 GHz to 25 GHz. The NW MESFET is integrated in a microwave coplanar

Influence of Periodic Patterning on the Magnetization Response of Micromagnetic Structures

March 29, 2011
Author(s)
SangHyun S. Lim, Thomas M. Wallis, Atif A. Imtiaz, Dazhen Gu, Thomas Cecil, Pavel Kabos, Pavol Krivoski
The magnetization dynamics of a single, patterned, thin-film Permalloy (Ni80Fe20, Py) elements embedded in a coplanar waveguide (CPW) are investigated. The anisotropic magnetoresistance (AMR) effect serves as the detection mechanism in current-modulated

Broadband Measurements of Nanofiber Devices: Repeatability and Random Error Analysis

November 30, 2010
Author(s)
Thomas M. Wallis, Atif A. Imtiaz, SangHyun S. Lim, Pavel Kabos, Kichul Kim, Paul Rice, Dejan Filipovic
On-wafer, broadband measurements of two-port nanofiber devices were made in order to test the short-term repeatability of a widely used measurement approach that builds on established on-wafer calibration techniques. The test devices used in this study

Contactless Approaches for RF Characterization of Metallic Nanowires

September 28, 2010
Author(s)
Kichul Kim, Paul Rice, Thomas M. Wallis, SangHyun S. Lim, Dazhen Gu, Atif A. Imtiaz, Pavel Kabos, Dejan Filipovic
Two approaches for microwave characterization of nanowire (NW) conductivity are described in this paper. To remove the uncertainty associated with contacts, the NWs are either suspended above the center conductor of a coplanar waveguide (CPW) host or

Metrology of Microstructured Waveguides for Spintronic Applications

July 30, 2010
Author(s)
SangHyun S. Lim, Atif A. Imtiaz, Dazhen Gu, Pavel Kabos, Thomas Mitchell (Mitch) Wallis
Patterned permallay films as a part of a coplanar waveguide (CPW) were fabricated, and the magnetization dynamics of such structures was investigated as fundamental building blocks for magnetic spintronic devices. Anisotropic magneto-resistance (AMR)

Two modes behavior of vortex oscillations in spin-transfer nanocontacts subject to in-plane magnetic fields

June 25, 2010
Author(s)
Michaela Kuepferling, Claudio Serpico, Matthew Pufall, William Rippard, Thomas Mitchell (Mitch) Wallis, Atif A. Imtiaz, Pavel Kabos
The field dependence of vortex oscillations in a spin-transfer metallic nanocontact, subject to in-plane, spatially uniform, external fields, is studied by measuring the power spectral density of the voltage across the device. The measured spectra as a

Application of Microwave Scanning Probes to Photovoltaic Materials

June 20, 2010
Author(s)
Kristine A. Bertness, John B. Schlager, Norman A. Sanford, Atif A. Imtiaz, Thomas M. Wallis, Joel C. Weber, Pavel Kabos, Lorelle M. Mansfield
We demonstrate that near field scanning microwave microscopy (NSMM) can be used to detect photoresponse in photovoltaic materials with potential for submicrometer resolution. In this approach, a radio-frequency scanning tunneling microscopy (RF-STM) tip is

High frequency characterization of a Schottky contact to a GaN nanowire bundle

June 16, 2010
Author(s)
Chin J. Chiang, Thomas M. Wallis, Dazhen Gu, Atif A. Imtiaz, Pavel Kabos, Paul T. Blanchard, Kristine A. Bertness, Norman A. Sanford, Kichul Kim, Dejan Filipovic
A GaN nanowire (NW) Schottky contact was characterized up to 10 GHz. Using a calibration procedure and circuit model a capacitance-voltage (CV) curve was obtained, from which a carrier concentration was calculated for the first time. These results

Modeling and metrology of metallic nanowires with application to microwave interconnects

May 23, 2010
Author(s)
Kichul Kim, Thomas M. Wallis, Paul Rice, Chin J. Chiang, Atif A. Imtiaz, Pavel Kabos, Jintao Zhang
Abstract: Broadband characterization of individual metallic nanowires for microwave interconnect applications is discussed. Circuit and method of moments (MoM) modeling are benchmarked using a set of coplanar waveguide (CPW) test devices with microwire Au

Near-Field Antenna as a Scanning Microwave Probe for Characterization of Materials and Devices

April 12, 2010
Author(s)
Atif A. Imtiaz, Thomas M. Wallis, SangHyun S. Lim, Jonathan Chisum, Zoya Popovic, Pavel Kabos
The Scanning Microwave Probe (SMP) is emerging as an important broadband metrology tool for characterizing the materials and devices in the micron and sub-micron length scales in the frequency range of 10 MHz to 110 GHz. In this document we establish three

Broadband Characterization of Individual Platinum Nanowires

March 7, 2010
Author(s)
Kichul Kim, Thomas M. Wallis, Paul Rice, Chin J. Chiang, Atif A. Imtiaz, Pavel Kabos, Dejan Filipovic
Conductivity and contact resistance of 100 nm and 250 nm diameter platinum (Pt) nanowires (NWs) are investigated computationally and experimentally. Finite element method based full-wave modeling and circuit simulations are used in conjunction with

Micromachined resonators of high Q-factor based on atomic layer deposited alumina

September 24, 2009
Author(s)
Atif A. Imtiaz, Yuan-Jen Chang, Jason M. Gray, Dragon Seghete, Steven George, Thomas Mitchell (Mitch) Wallis, Pavel Kabos, Charles T. Rogers, Victor M. Bright
In this paper, atomic layer deposited (ALD) alumina (Al2O3) has been demonstrated as the structural material for a micro-resonator for the first time.  An electrostatically actuated micro-bridge made of chromium (Cr) coated ALD Al2O3 was used as a

Wideband measurement of extreme impedance with a multistate reflectometer

December 12, 2008
Author(s)
Arkadiusz C. Lewandowski, Denis X. LeGolvan, Ronald A. Ginley, Thomas M. Wallis, Atif A. Imtiaz, Pavel Kabos
Abstract: We present a technique for accurate wideband measurements of one-port devices with extreme impedances. Our technique uses a reflectometer with variable parameters (states) to obtain redundant measurements of the extreme impedance device. We

Calibrated Broadband Electrical Characterization of Nanowires

June 8, 2008
Author(s)
Thomas Mitchell (Mitch) Wallis, Atif A. Imtiaz, Hans Nembach, Kristine A. Bertness, Norman Sanford, Paul T. Blanchard, Pavel Kabos
A technique is presented for the broadband electrical characterization of nanowires. The technique relies on established on-wafer calibration methods as well as a direct measurement of the capacitive coupling that is in parallel with the nanowire

Near-field microwave microscope measurements to characterize bulk material properties

June 12, 2007
Author(s)
Atif A. Imtiaz, Thomas Baldwin, Hans T. Nembach, Thomas M. Wallis, Pavel Kabos
We measured bulk dielectric (Fused Silica), semiconductor (Silicon) and metal (Copper), with a Near-field Scanning Microwave Microscope (NSMM). We use three bulk materials to test the existing quasi-static theoretical approach to de-embed the materials

Metrology for High-Frequency Nanoelectronics

March 27, 2007
Author(s)
Thomas Mitchell (Mitch) Wallis, Atif A. Imtiaz, Hans Nembach, Paul Rice, Pavel Kabos
Two metrological tools for high frequency measurements of nanoscale systems are described: (i) tow/N-port analysis of nanoscale devices as well as (ii) near-field scanning microwave microscopy (NSMM) for materials characterization. Calibrated two/N-port

Broadband Electrical Characterization of Multiwalled Carbon Nanotubes and Contacts

March 22, 2007
Author(s)
Thomas M. Wallis, Stephen E. Russek, Pavel Kabos, Paul Rice
The electrical response of an individual multiwalled carbon nanotube (MWNT) and its contacts, welded to a coplanar waveguide (CPW), was measured up to 24 GHz using a technique that removes environment effects. This is the first time MWNT contact effects