Micro/Nano Electronics

Project Goals

The next generation of high-frequency electromagnetic applications will require higher operating frequencies, wider bandwidths, increased dynamic range, and a substantial reduction in device dimensions. To meet these challenges, the Micro/Nano Electronics Project develops new measurement techniques, standards, and instrumentation to satisfy the growing metrology needs of the high-speed telecommunications, microelectronics, magnetic storage, and computing industries.

Customer Needs

The full impact of nanotechnology research may be decades away, but one current critical need, according to the National Nanotechnology Initiative (NNI), is the creation and development of the fundamental metrology necessary to characterize nanoscale electrical and magnetic devices. An additional complexity is that future applications of both microwave and nanotechnology will involve the transmission and detection of broad-bandwidth signals having complicated modulation schemes at frequencies ranging from the microwave region to the terahertz region. Therefore, development of nanotechnology metrology will require synergy between research areas as diverse as nanoelectronics, telecommunications, microwave metrology, and materials science.

Technical Strategy

To support the future needs of the microelectronics and emerging nanoelectronics industries, both the International Technology Roadmap for Semiconductors (ITRS) and the NNI outline many of the metrology needs that must be addressed for the next generation of microelectronic and nanoelectronic devices. In both of these industries, metrology must be developed for characterization of smaller devices that carry complicated, modulated signals at frequencies that extend into and beyond the microwave range. This project’s expertise in microwave and terahertz metrology, high-speed waveform metrology, measurements for telecommunication systems, and high-frequency nanodevice characterization allows it to tackle some of the major metrology issues facing the microelectronics and nanoelectronics industries.

This project has played an important role in developing the fundamental tools for performing onwafer microwave measurements. Building on this expertise, we are extending traditional on-wafer techniques to develop the necessary metrology for supporting the telecommunications and emerging nanoelectronics industry. One such extension is in the area of high-speed waveform metrology. As data rates of optical links exceed 40 gigabits per second, and emerging digital circuits operate with clock rates over 100 gigahertz, electrical measurements with conventional techniques no longer work; they are invasive and limited in frequency. To meet this need, we have developed a fully calibrated electro-optic sampling system for characterizing photodetectors and calibrating oscilloscopes for microwave signal characterization. This has enabled us to develop new tools, such as electro-optic on-wafer scattering and waveform measurements up to 200 gigahertz and modulated microwave signal and coaxial signal-source characterization to 400 gigahertz. With these tools, we are providing the fundamental metrology that will enable development of the next generation of highfrequency oscilloscopes, microwave transition analyzers (MTAs), and related instruments.

High-frequency characterization of nanodevices is another focus of research in this project. Development of atomic force microscopes (AFMs), scanning tunneling microscopes (STMs), and high-impedance and near-fi eld evanescent probing systems that operate at high frequencies allows for characterization of the electromagnetic fields, materials, and nanodevice electrical properties at frequencies in the microwave and millimeter-wave range with submicrometer resolution.

Another extension of the on-wafer microwave metrology work is in the area of on-wafer noise characterization. Here, we are developing new measurement techniques that can be used to characterize the on-wafer noise properties of complementary metal oxide semiconductor (CMOS) devices, which can be used not only to improve device performance but to assist in physical model development. In addition to the measurements performed on-wafer, we are also developing new techniques for noise characterization at terahertz frequencies, which will provide traceability to a critical parameter of active terahertz devices.

In addition to the on-wafer activities, the project also develops measurement methods and calibrations for coaxial instrumentation capable of accurately characterizing RF-based systems that transmit complex modulated signals. These include Electrical Engineering Laboratory next-generation and broadband wireless system technologies, as well as broadband systems utilized by first responders to emergencies. The project is also involved in development of test signals that will provide easier calibrations for wireless system measurements.

Besides the characterization of noise at terahertz frequencies, we are also focusing on applications of passive terahertz imaging. Terahertz radiation can penetrate clothing and, to some extent, can also penetrate biological materials. Because of their shorter wavelengths they offer higher spatial resolution than microwaves or millimeter-waves. This project focuses on developing the critical metrology necessary to characterize newly developed terahertz devices and systems that are coming to market.

High-Frequency Nanodevice Metrology — The primary focus is the development of metrology for high-frequency scanned-probe microscopy and micro-electromechanical systems (MEMS) with submicrometer resolution. Specifically, this includes the areas of quantitative high-frequency imaging, measurement of electromagnetic field components, and characterization of materials that are incorporated into nanoscale electrical and magnetic devices.

In order to investigate the high-frequency response of nanoscale structures such as carbon nanotubes and Si-based nanowires, we constructed a universal scanning probe station that can operate as a RF-STM probe, near-field scanning probe, AFM probe, or a high-impedance, noncontacting probe with nanometer spatial positioning at frequencies up to 50 gigahertz.

For more accurate measurements of electromagnetic field components, we designed a three-layer SiN/SiO/SiN cantilever probe for high-frequency calorimetric field imaging and showed a demonstrable improvement in performance and yield over traditional two-layer micro-electromechanical system (MEMS) calorimetric probes.

Investigating the Einstein–de Hass effect, we developed a MEMS-based approach to measuring the magneto-mechanical ratio g ' , a critical parameter for the development of materials for spin electronics and magnetic data storage.

We demonstrated that calibrated on-wafer techniques can be employed to characterize the broadband frequency response of high-impedance devices such as multiwalled carbon nanotubes as well as quantify the effect of contact resistances.

A multi-wall carbon nanotube welded across a gap in the center conductor or a coplanar waveguide.

A multi-wall carbon nanotube welded across a gap in the
center conductor of a coplanar waveguide.

Admittance (which includes conductance) in millisiemens
as a function of frequency in gigahertz at the left contact
of the carbon nanotube. Data were taken with illumination
of the nanotube on and off. The admittance is calculated
from scattering parameters measured with a network analyzer.

High-Speed Waveform Metrology — Sales in the high-speed telecommunications market are based on the ability to deliver high-speed, reliable, and interoperable communication systems with greater information-carrying capacity and at a lower cost. Integrated digital and microwave electronics now require bandwidths in excess of 110 gigahertz, larger than can be supported by current coaxial connectors. To meet these demanding needs, we are developing both 110 gigahertz coaxial waveform metrology, as well as on-wafer metrology to even higher frequencies. Our current focus includes design of a 400 gigahertz opto-electronic source, integration of this source into a microwave probe, and construction of an electro-optic measurement system to characterize the bandwidth of this source.

We developed a coaxial waveform measurement service that is traceable to our electro-optic sampling system. It includes point-by-point uncertainties and correction for mismatches, and is traceable to 110 gigahertz. We demonstrated the ability to generate and accurately characterize pulses onwafer with the NIST electro-optic sampling system up to 200 gigahertz, important for characterizing 40 gigabit and higher communications systems. We developed new measurements for characterizing microwave mixers and modulated signal sources. We also developed a new 110 gigahertz, 1.0 millimeter coaxial scattering-parameter calibration and covariance-based uncertainty analysis.

Thermal Noise Characterization at Terahertz Frequencies — Applications of electromagnetic measurements at terahertz frequencies are poised for explosive growth, but lack of fundamental standards is a serious impediment. Traceability to NIST noise standards at terahertz frequencies would allow comparison of different measurements and meaningful comparison of performance of components and systems.

For characterization of cryogenic amplifiers, we developed a method for accurate noise figure measurements. We measured effective input noise temperatures in the 1 to 12 gigahertz range, with results as low as 2.3 kelvins with a standard uncertainty of 0.3 kelvin, corresponding to a noise figure of 0.034 decibels ± 0.004 decibels. We developed and demonstrated a terahertz receiver with a quasioptical adapter for coupling incident radiation into a receiver. The receiver is based on heterodyne detection with a hot-electron-bolometer (HEB) mixer. To house the receiver portion of the radiometer, we purchased and instrumented a cryocooler.

Passive Spectral Terahertz Imaging — Much interest exists in applications for imaging and spectroscopy at terahertz frequencies. We developed a two-dimensional scanning passive terahertz imaging system based on a phonon-cooled quasioptically coupled HEB mixer that is integrated with an InP monolithic microwave integrated circuit (MMIC) intermediate frequency (IF) low-noise amplifi er. We demonstrated the ability of a scanning passive terahertz imaging system to obtain full two-dimensional images of various objects by scanning the target with a fl at mirror mounted on a computer-controlled elevation/azimuth translator. The overall sensitivity, defined in terms of noise equivalent delta temperature (NET), is better than 0.5 kelvin.

Metrology for Wireless Systems — We are developing test methods to characterize signal degradation, including attenuation and phase distortion, in complex environments including large buildings and basements. In particular, we are focusing on development of wideband measurement methods in the new 4.9 gigahertz public safety radio band for transmission of voice, data, images, and video.

To improve measurements of wideband, modulated signals, we developed a method to extend the measurement bandwidth of narrowband vector receivers. We developed impedance mismatch correction techniques for vector signal generators in their large-signal operating state. In one recent application, we investigated the viability of using RF modulated-signal measurements order to identify nodes in a wireless local-area network. We performed measurements of wideband, modulated signals in typical first-responder environments.

On-Wafer Noise Measurements $#8212; As transistor technology evolves to smaller, lower-noise devices used at higher frequencies, measuring their noise characteristics becomes increasingly difficult. The difficulties increase due to the very low noise levels that must be measured and to the very high reflections exhibited by such devices. We are developing accurate measurement techniques that can be used to evaluate and improve physical models, as well as design and predict the performance of systems that employ transistors.

In order to characterize poorly matched transistors, we extended and improved a Monte Carlo program used for amplifier noise parameter uncertainty analysis and used it to perform simulations comparing different measurement strategies. We developed the capability to measure noise parameter of on-wafer transistors or low-noise amplifiers. We performed a measurement comparison with two companies of on-wafer noise parameters of CMOS transistors with 0.13 micrometer gate lengths.

To better determine the optimal input source reflection coefficient, we developed an improved on-wafer noise-parameter measurement method.

Photograph (left) and 0.850 terahertz image (right) of two objects at room
temperature suspended over an absorber immersed in liquid nitrogen.
The terahertz image covers a temperature range of 200 kelvins.

Workshops

To disseminate newly developed on-wafer noise measurements, we organized a joint International Microwave Symposium (IMS)/IEEE Radio Frequency Integrated Circuits (RFIC) full-day workshop on “Noise Measurement and Modeling for CMOS” in San Francisco, CA, in June 2006.

New measurement techniques useful to wireless engineers were presented in two full-day workshops at the IMS conference organized by project members. One was on the topic “Memory Effects in Power Amplifiers,” while the other was on “Techniques and Applications of Wireless Sensor Networks.”

Software