RF Nanoscale and Molecular Probing Metrology
Goals
Project supports the microwave, semiconductor, computing, magnetic and electric storage industries through research and development of high-frequency scanned-probe microscopy based metrology and micro-electromechanical systems (MEMS) with sub micrometer resolution. The goal of the project is to develop metrology for quantitative imaging and measurement of electromagnetic field components and material characterization of nanoscale electrical and magnetic devices by establishing accurate spatially resolved waveform and frequency-domain metrology.
Customer Needs
The National Nanotechnology Initiative calls for the creation of a new research and development infrastructure to tackle the challenges and opportunities of nanotechnology. Full exploitation of the potential of nanotechnology requires long-term interdisciplinary research across such fields as chemistry, physics, materials science, electronics, biotechnology, medicine, and engineering. Research will be conducted to provide fundamental measurements needed for future generations of hardware needed to replace semiconductor and magnetic technology in a decade or so. Our expertise in microwave metrology, optics, materials characterization, clean room microfabrication — as well as collaboration with other projects — helps us develop new tools and materials characterization techniques for nanotechnology in the frequency range up to 100 gigahertz and beyond.
Technical Strategy
Based on an understanding of the physics of the interaction between materials and electromagnetic waves, we are focusing on the development of new experimental tools and techniques that address future needs of industry that require noninvasive probing and characterization of submicrometer and nanoscale structures at radio frequencies (RF). We are working with the Magnetics Group, the Optoelectronics Division, and the Materials Science and Engineering Laboratory to apply on-wafer measurement methods to nanoscale devices and interconnects such as carbon nanotubes or Si nanowires. We are developing techniques for performing noninvasive on-wafer waveform measurements for signal-integrity characterization in digital silicon integrated circuits and in magnetic recording media, and calibration procedures for nanoscale electrical and magnetic probing systems. In order to characterize nanostructures, it is important to extend the high spatial and temporal resolution of existing nanoprobes. The objective is to observe and control the dynamical evolution of physical phenomena in nanostructures. The development of nanometer-scale RF pump-probe techniques, nanometer-scale feedback and control, and other probes of local behavior are sought to provide new insight into nanoscale phenomena.
Radio-Frequency Atomic-Force Microscope (RF-AFM) Development — Several projects require high-frequency, near-field imaging capabilities. We are developing experimental techniques in collaboration with the Magnetics Group and the Materials Science and Engineering Laboratory for measuring the high-frequency response and noise of small magnetic structures. The focus is on the contribution of the edges on the measured characteristics of small samples. The results from different experimental techniques will be compared and evaluated to get a better understanding of the behavior of small magnetic elements.
The possibility of chip-to-chip wireless communication requires the design of novel micrometerscale antennas with special radiation patterns to ensure the errorless transfer of data from chip to chip at high data-transfer rates. The imaging of the near-field radiation patterns of such structures is of crucial importance for such applications.
Electromagnetic compatibility (EMC) applications require noncontact measurements of the electromagnetic fields in the vicinity of the chip-to-wafer wiring structures. Similar requirements apply to tracing the spurious coupling channels in high-frequency devices.
To achieve the necessary sensitivity and spatial resolution for above mentioned and similar applications, some modifications to the control hardware and software of our RF-AFM microscope will be necessary. We will enhance the capabilities of our microscope to achieve the necessary performance through digital signal processor (DSP) control with development of the supporting software. The available scanning capabilities are well within the requirements. The control system will be designed to allow flexibility for simple future modifications that will be necessary for new applications.
This year, we plan to design the DSP hardware for RF-AFM control and develop the necessary software. In following years, we will collaborate on the design of antennas and measure the antenna patterns for chip-to chip communication applications, characterize the eigenmodes of small magnetic structures, and relate the measured mode structure to the noise response of the devices.
Radio-Frequency Probe Development — In order to improve on the spatial resolution and spectral bandwidth of the probes for high-frequency near-field metrology applications we are also focusing on development of special probes. These probes will be designed and tailored to particular applications. This tailoring includes the spatial resolution, bandwidth, and adjustment of the design. We may implement small particles or more complex nanoscale structures on the tip area of cantilevers based on micro-electromechanical systems (MEMS). Depending on the application, these structures can be magnetic, dielectric, or more complicated composite structures that would allow either high-frequency or optical detection of the near electric and magnetic fields. We plan to characterize new MEMS-based sensors for the developed near-field imaging applications.
Evanescent Microwave Probe — We are participating in a collaboration with the Electromagnetic Properties of Materials project on the development of metrology for micrometer and submicrometer characterization of materials for electronic and packaging applications. We have developed new theory and software to characterize the microscopic fields in evanescent probe metrology. We will extend new software and theory for the evanescent microscope methods and do on-wafer measurements of substrate materials.
Nanomaterials and Metamaterials Characterization — Carbon nanotubes and Si-based nanowires are considered as possible option for the next generations of interconnects and high-integration-density structures. Although extensive research is ongoing on the structural, mechanical, and optical properties and applications of these materials, very little is known about their behavior in another important frequency range, from a few megahertz to 100 gigahertz and beyond. This could be due to difficulties in separating the characteristics of the investigated nanostructures from environmental influence at these frequencies. We are developing non-invasive metrology based on well developed on-wafer techniques that allow separating the behavior of the nanostructures of interest from that of their environment.
In recent years there has been increased interest in the development of composite and artificially structured materials with properties that differ significantly from the properties of standard materials. Among those are the band-gap materials for different frequency ranges and the so-called "negative index" materials that support the propagation of electromagnetic waves with opposite phase and group velocities. Due to their special properties, several challenges in the theory, tailored material design, and metrology will have to be mastered. We are working on all aspects of this challenge. In the area of metrology, we are developing techniques to measure the group and phase velocities. In the area of theory, we work on understanding the electromagnetic boundary conditions and the scattering problems that are relevant for the optimal design of these materials for particular applications. These applications may include the design of novel reference materials for broadband, high-frequency calibrations. We will characterize and measure metamaterials in collaboration with the Electromagnetic Properties of Materials project and the Complex Fields project.
Accomplishments
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- RF-AFM Development — In collaboration with the Nanoprobe Imaging Project in the Magnetics Group we developed a microwave AFM probe station designed to test the frequency response of high-frequency sensors. This year the RFAFM head was redesigned (see figure). The head is attached to a standard microwave probe station furnished with a piezoelectric positioner. The head can work both as an AFM system and as a highimpedance noncontact probe with nanometer spatial positioning. The design allows positioning the probe between standard microwave on-wafer probes at a 500 micrometer separation. This requirement was necessary to be able to access standard on-wafer thru-reflect-line (TRL) calibration test structures. A commercial 50 gigahertz probe is attached to the x-y-z positioner to be able to attach the microwave probe to the MEMS waveguide structure (at the position of the cantilever in the figure). We developed calibration procedures to characterize the properties of the attached microwave MEMS structures up to 50 gigahertz. A knowledge of the MEMS sensor characteristics provides the opportunity to measure the true signals at the tip of the noncontact MEMS probe and also to assess the invasiveness of the probes used to measure the voltage and current at the given node or position on a wafer.
- RF Probe Development — In collaboration with the Nanoprobe Imaging Project, we are developing several types of micromachined standard or bi-material cantilever probes with either thinfilm FMR or thin-film metallic sensors to probe microwave fields near active devices. The first picture shows a loop probe for direct magnetic field detection and the second figure shows the probe for calorimetric detection of microwave magnetic fields. Similar sensors are available for electric field detection. These sensors are designed for use with the above-described RF-AFM system. The sensors can be of broad bandwidth or can be designed to be frequency selective. Absorption of the microwave energy in a Ni-Fe sensor, for example, is maximized when the microwave frequency matches the ferromagnetic resonance condition. This condition can be adjusted by changing the DC magnetic bias field, making the sensor frequency selective. On the other hand the nonmagnetic metal ring eddy-current sensor in the figure is broadband. The choice depends on the application.
- Evanescent Microwave Probe — A new theoretical model has been developed for wire evanescent microwave probes suspended over a multiple-dielectric (thin-film on dielectric substrate) test structure for performing on-chip permittivity measurements. The theory represents a significant advance in the near-field probing of materials because it can be easily extended to thin-film and multilayer structures.
- Local and Macroscopic Fields in Materials — In collaboration with Electromagnetic Properties of Materials project we have developed, from basic statistical-mechanics principles, the microscopic and macroscopic relationships for the local and macroscopic fields in materials, and then related these to exact expressions for the constitutive parameters.
- Nanomaterial and Metamaterial Characterization — With the Electromagnetic Properties of Materials project, the Complex Fields project, and the Magnetics Group, we developed and performed measurements on a novel metamaterial. The material consists of yttrium garnet spheres in Styrofoam. The permeability of the spheres is tuned using a DC bias magnetic field until "left-handed" behavior is observed. We plan to further develop and measure left-handed meta-, magnetoelectric, and photonic band-gap materials.
Award
- NIST Bronze Medal for development of Pulsed Inductive Microwave Magnetometer, 2004 (Tom Silva, Tony Kos, and Pavel Kabos).
Recent Publications
P. Kabos, U. Arz, and D. F. Williams, "Multiport Investigation of Coupling of High Impedance Probes," IEEE Microwave Wireless Comp. Lett., in press.
T. M. Wallis, J. Moreland, B. F. Riddle, and P. Kabos, "Microwave Power Imaging with Ferromagnetic Calorimeter Probes on Bimaterial Cantilevers," J. Magn. Magn. Mater., in press.
J. Baker-Jarvis, P. Kabos, and C. L. Holloway, "Nonequilibrium Electromagnetics: Local and Macroscopic Fields and Constitutive Relationships," Phys Rev E 70, 036615/1-13 (September 2004).
J. Baker-Jarvis and P. Kabos, "Modified de Broglie Approach Applied to the Schrödinger and Klien-Gordon Equations," Phys. Rev. A 68, 042110/1-8 (October 2003).
C. L. Holloway, E. F. Kuester, J. Baker-Jarvis, and P. Kabos, "A Double Negative (DNG) Composite Medium Composed of Magnetodielectric Spherical Particles Embedded in Matrix," IEEE Trans. Ant. Prop. 51, 2596-2602 (October 2003).
P. Kabos, H. C. Reader, U. Arz, and D. F. Williams, "Calibrated Waveform Measurement with High-Impedance Probes," IEEE Trans. Microwave Theory Tech. 51, 530-535 (February 2003).
A. B. Kos, T. J. Silva, and P. Kabos, "Pulsed Inductive Microwave Magnetometer," Rev. Sci. Instrum. 73, 3563-3569 (October 2002).
R. G. Geyer, P. Kabos, and J. R. Baker-Jarvis, "Dielectric Sleeve Resonator Techniques for Variable-Temperature Microwave Characterization of Ferroelectric Materials," IEEE MTT-S Int. Microwave Symp., Seattle, WA, pp. 1657-1660 (June 2002).