T. Mitch Wallis

Establishing traceability of an electronic calibration unit using the NIST Microwave Uncertainty Framework

We present a method for establishing traceability of a commercial electronic calibration unit for vector network analyzers by characterizing the scattering parameters of its internal states with repeated multiline thru-reflect-line (TRL) calibrations and utilizing the NIST Microwave Uncertainty Framework to propagate uncertainties. With the electronic calibration unit characterized, we use it to calibrate a network analyzer, and characterize a number of verification devices with corresponding uncertainties. We also characterize the same verification devices using one of the previous multiline TRL calibrations, and compare results.

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

A two-port GaN nanowire (NW) device with one Schottky contact and one Ohmic contact was characterized up to 10 GHz using on-wafer microwave measurements. In addition to the measurement of the broadband response, two additional applications of microwave measurements are introduced: (1) the capability to distinguish a Schottky-type contact from an Ohmic contact based on the reflected broadband signals (S11 and S22) and (2) the measurement of a capacitance voltage (CV) curve for a Schottky contact to a bundle of a few NWs. The junction capacitance of the Schottky contact is determined at various bias voltages by fitting the broadband response with a microwave circuit model. The carrier concentration is estimated from the resulting CV curve to be 5.3×1018/cm3 and the Schottky barrier height is estimated to be 0.89 eV.

Magneto-mechanical investigation of spin dynamics in magnetic multilayers

The Einstein-de Haas effect is used to study experimentally the interfacial spin transport in a bilayer metallic system. Specifically, mechanical torque on a permalloy film interfaced with a non-magnetic metallic film (platinum or copper), deposited on a microcantilever, is measured. The torque is generated by the transfer of the spin angular momentum from the permalloy film to the mechanical angular momentum of the cantilever. Measurement of the cantilever deflection shows that the presence of a thin non-magnetic metallic layer with strong spin-orbit interaction (platinum) changes the interfacial spin transport and causes a dramatic reduction of the mechanical torque. The observed behavior of the cantilever is attributed to the increased effective damping of the domain wall motion in the permalloy layer.

Modeling and metrology of metallic nanowires with application to microwave interconnects

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 Au microwire (MW) interconnect and air gaps in the middle of the CPW. Comparison with measurements reveals significantly larger errors from circuit models though all dimensions are much smaller than wavelength. Similar CPW devices hosting 100 nm and 250 nm diameter Pt nanowires (NWs) are then investigated to determine the ranges of conductivity and contact resistance for each Pt NW. An algorithm that utilizes the transmission line theory and different nanowire lengths to determine the actual conductivity and contact resistance is proposed and validated.

Broadband measurements of nanofiber devices: Repeatability and random error analysis

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 consist of Pt nanowire and Au microbridge structures incorporated into two-port coplanar waveguides. Based on repeated measurements of these test structures, we computed statistical (Type A) uncertainties. The standard deviation (k=1) of five repeated measurements of a Pt nanowire device was less than 50 μS. The analysis suggests refinements to the measurement process depending on the desired output of the measurements, e.g. the broadband response itself or the extraction of circuit model parameters.

Metrology For High‐Frequency Nanoelectronics

Two metrological tools for high‐frequency measurements of nanoscale systems are described: (i) two/N‐port analysis of nanoscale devices as well as (ii) near‐field scanning microwave microscopy (NSMM) for materials characterization. Calibrated two/N‐port measurements were made on multiwalled carbon nanotubes (MWNT) welded to a coplanar waveguide. Significant changes in the extracted high‐frequency electrical response of the welded MWNT were measured when the contacts to the MWNT were modified. Additionally, NSMM was used to characterize films of nanotube soot deposited on copper and sapphire substrates. The material properties of the films showed a strong dependence on the substrate material.

Near-field microwave microscopy of one-dimensional nanostructures

With the ability to measure sample conductivity with nanometer spatial resolution, scanning microwave microscopy (SMM) is a powerful tool to study nanoscale electronic systems and devices. Here we demonstrate the general capability to image electronic variations within nanomaterials using nanowires of VO2 and Si as model systems. For VO2 we image the temperature-dependent metal-insulator domain coexistence that arises due to the built-in strain in substrate-clamped wires. In Si NWs integrated into a transistor device architecture we observe large increases in the source-drain current with the tip passing over the wire, correlated with variations in the SMM signal. We attribute this effect to local rectification of the microwave signal by the local tip-sample Schottky junction.

A genetic algorithm for generating RF circuit models from calibrated broadband measurements

A genetic algorithm has been developed to generate circuit models from calibrated broadband measurements of coaxial and on-wafer devices under test (DUTs). The algorithm randomly builds a population of circuit models from lumped as well as distributed elements and compares the simulated scattering parameters for those models with calibrated measurements. The genetic approach iteratively culls the circuit models that agree most closely with calibrated measurements. In order to “test-drive” this approach, the genetic algorithm was applied to calibrated measurements of several two-port 1.85 mm coaxial DUTs. The resulting circuit models are reasonable and their simulated response agrees closely with the measurements. Subsequently, the algorithm was applied to calibrated measurements of a two-port, on-wafer nanowire device. This algorithm automates exploration of potential circuit models for yet-to-be-modeled devices, including those that incorporate nanowires.

An overview of measurement techniques for radio frequency nanotechnology (Invited paper)

We present an overview of the historical development and current state-of-the-art in measurement techniques for radio frequency (RF) nanotechnology. The field of RF nanotechnology focuses on the study and engineering of RF and microwave devices that are enabled by nanomaterials and other advances in nanoscience. Measurements play a critical role in this emerging field, enabling the transition from discoveries of new phenomena and new materials to practical engineering and eventual commercial application of RF nanotechnology. One critical challenge is to overcome the inherent impedance mismatch between nanoscale systems and commercial test equipment. Early work focused on the extension of existing guided-wave and on-wafer microwave measurement techniques to nanoelectronic devices. The objective of most of these early techniques was measurement of the complex, two-port scattering parameters of passive devices that incorporated a small number of individual nanoscale building blocks. More recently, local measurement techniques such as near-field scanning microwave microscopy have been developed for broadband characterization of nanomaterials and intradevice measurement of defects, contacts, and interfaces.

Measurement techniques for radio frequency nanoelectronics

Abbe limit, see diffraction limit ABCD matrices, 78, 80, 86 acoustic waves, 226 actin, 303 adapter, 47 adaptive weight smoothing, 301 admittance, 11, 22, 62, 63, 95, 97, 98, 99, 101, 137, 143, 174, 175, 180, 195, 196, 198, 301, 303 matrices, 78, 197 ambient conditions, 150, 206, 207 angular frequency, 83 anisotropic dielectrics, 126 anisotropic magnetoresistance, 263 ANSYS Designer, 71 antenna, 5, 67, 123, 129, 145, 173, 227, 228, 233, 241, 246, 271, 283, 284, 285 free space resistance, 130 nanoscale, 68 nearield, 163 approach curve, 137 atomic force microscope, 5, 6, 33, 107 conductive, 218 contact mode, 107, 110, 131, 135, 153, 166, 293 noncontact mode, 107, 247 attenuator, 54, 139, 140 AWR Microwave Ofice, 71