Millimeter-wave Microscopy Research Articles

Sensitive Near-Field Slit Probe with High Spatial Resolution for Passive Millimeter-Wave Microscopy

A novel type of near-field slit probe with high sensitivity and high spatial resolution is proposed. We tested the implementation of this in passive millimeter-wave microscopy at frequencies around 50 GHz. The slit probe comprises a standard rectangular waveguide incorporating a triple-screw tuner penetrating into the waveguide, followed by a four-section quarter-wave transformer, and a metal-coated silicon chip with a micro-slit aperture fabricated at the probe tip using a bulk micromachining technique. The probe allows the transmission of the thermal radiation collected at the probe aperture to the radiometric receiver used in passive millimeter-wave microscopy to be maximized, resulting in highly sensitive measurements. The system noise temperature of the radiometric receiver including the slit probe used in the passive measurements was found to be 1800 K, meaning that a temperature resolution of 0.18 K with the integration time set to 1 s was achieved. This system noise temperature is four times better than that when a tapered slit probe with no tuning circuit was used. Image acquisition with a spatial resolution of better than 100 μm was demonstrated over the temperature range from 210 to 310 K.

Observation of Protein Thermodynamics in Ice by Passive Millimeter-Wave Microscopy

The study of protein functions attributed to the conformation and fluctuation that are ruled by both the amino acid sequence and thermodynamics, requires thermodynamic quantities given by calorimetry using thermometric techniques. The increased need for protein function in different applications requires improvements of measurement systems assessing protein thermodynamics to handle many kinds of samples quickly. We have developed a passive millimeter-wave microscope that allows near-field imaging of thermal radiation, even in the low temperature range under room temperature where passive infrared imaging systems are ineffective. This advantage of our microscope system in combination with low thermal emission property of water ice in the millimeter-wave region enables the characterization of the thermal radiation from the proteins themselves in aqueous solution at a temperature range low enough to freeze water and to trap conformation intermediates in the proteins. Experiments performed at a millimeter-wave frequency of 50 GHz in a temperature range from 130 K to 270 K for a 20 % bovine serum albumin (BSA) aqueous solution showed a displacement between two conformational states of BSA at a temperature of approximately 190 K as a boundary. Our microscope system using this freeze-trapping method is expected to provide noninvasive thermal images to enable novel high-throughput calorimetry useful for the analysis of protein functions.

W-Band Near-Field Microscope

A home-built scattering-type scanning near-field millimeter-wave microscope based on a 110-GHz continuous-wave solid-state source is demonstrated with a spatial resolution of 1 μm, approximately 1/3000 of the incident wavelength, and a signal-to-noise ratio of 23.8 dB. The relationship between the length of the tip (antenna) and the wavelength for resonant enhancement, and the near-field distribution around the tip apex at different tip-sample separations were explored using finite-difference time-domain electromagnetic simulations to facilitate the design of the microscope. The dependence of the spatial resolution on the tip-sample separation and the harmonic order of the modulation frequency at which the near-field signal was extracted has been investigated experimentally and discussed in terms of the signal-to-noise ratio and the standard deviation of the demodulated signal.

Note: Near-field imaging of thermal radiation at low temperatures by passive millimeter-wave microscopy

Imaging of thermal radiation with a spatial resolution below the diffraction limit is demonstrated with a passive millimeter-wave microscope. This technique utilizes a sensitive radiometric receiver in combination with a scanning near-field microscope. Experiments were performed at 50 GHz (λ = 6 mm) with sample temperatures ranging from room temperature down to 160 K, and the performance was shown to be superior to that achieved with passive imaging systems in the infrared region. The images are affected by non-uniformities in the transmission of thermal radiation from the sample to the receiver via the near-field probe and the reflection of thermal radiation back to the receiver from the probe. The effects of these non-uniformities were successfully removed using a sample image acquired by active measurements using a vector network analyzer.

60-GHz Near-Field Six-Port Microscope Using a Scanning Slit Probe for Subsurface Sensing

A new six-port based near-field millimeter-wave microscope using a scanning slit probe is proposed for subsurface sensing applications. The combination of a six-port reflectometer and a slit probe presents a viable and promising alternative to the costly heterodyne principle. The system presents advantages such as compactness, robustness, and low cost. To evaluate its performance, the spatial resolution is experimentally verified.

Near-field slit probe incorporating a micromachined silicon chip for millimeter-wave microscopy

A novel type of slit probe incorporating a micromachined silicon (Si) chip for millimeter-wave scanning near-field microscopy is proposed.To improve the spatial resolution and image contrast attainable in millimeter-wave microscopy, a metal-coated Si chip with a microslit aperture fabricated using a bulk micromachining technique was attached to the tip of an ordinary slit-type probe at the end of a tapered rectangular waveguide. The design and fabrication of the Si chip are described, and the results from experiments performed at U-band (40–60 GHz) frequencies to demonstrate the feasibility of this new probe configuration are presented. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:660–664, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25793

Passive Millimeter-Wave Microscopy

A new type of millimeter-wave imaging technique, passive millimeter-wave microscopy is proposed and demonstrated. Passive millimeter-wave imaging techniques when combined with scanning near-field microscopy enable direct observation of millimeter-wave signals thermally emitted from the viewed object with a spatial resolution below the diffraction limit. Details of our passive microscope system operating at Ka-band frequencies are explained. Millimeter-wave images obtained with the system are presented to demonstrate the feasibility of this new imaging technique.

Scanning Near-Field Millimeter-Wave Microscope: Application to a Vector-Coding Technique

The purpose of this paper is to propose an evanescent field-scanning millimeter-wave microscope to bridge the frequency gap that currently exists in probe microscopy. The method is supported by the use of a six-port-based reflectometer operating at 35 GHz in association with a microfabricated resonant micro stripline probe. The simplicity of the method makes it suitable for an industrial context and offers integration possibilities to gain in compacity, reliability, and time operation, in particular. This millimeter-wave microscope is well suited for the characterization of conductors and local electromagnetic properties of dielectrics. The resolution of the probe is experimentally verified by scanning gold lines deposited on a silicon substrate. In addition to the demonstration of the system, we propose to discuss various probe parameters that can be considered to design evanescent millimeter-wave probes (EMPs) for different applications. An original use of the system is suggested through a vector-coding technique of digital information that makes use of the real and imaginary parts of the reflection coefficient.

Properties of a dielectric probe for scanning near-field millimeter-wave microscopy

The characteristics of a dielectric probe for scanning near-field millimeter wave microscopy are presented in this paper. The dielectric probe was fabricated from Teflon and shaped like a cone. The beam profile of the millimeter-wave radiated from the tip of the Teflon probe was measured by three-dimensional scanning using a different Teflon probe. The 93.5 GHz millimeter wave was focused on the tip of the probe at the wavelength level, and the millimeter-wave power was found to decrease exponentially with distance from the tip, the same as a near-field wave.

Nondestructive characterization of various thin films using a near-field scanning millimeter-wave microscope

We demonstrate a nondestructive millimeter-wave surface imaging technique using a near-field scanning millimeter-wave microscope (NSMM) with a resonant standard waveguide probe at an operation frequency f = 30 – 39 GHz . A chemically etched metallic probe tip, was coupled to the resonant rectangular waveguide. By properly tuning the tunable resonator and the probe tip, we could improve sensitivity and spatial resolution of the NSMM. Measuring the change of the reflection coefficient S 11 in the near-field zone, sheet resistance changes of Ag, ITO, YBa 2Cu 3O y , organic copper(II) phthalocyanine (Cu–Pc) thin films, and MgO were obtained. We observed the NSMM images of Ag thin film on the glass substrate with a spatial resolution better than 2 μm.

Nondestructive high spatial resolution imaging with a 60 GHz near-field scanning millimeter-wave microscope

We demonstrate a nondestructive millimeter-wave surface imaging technique using a near-field scanning millimeter-wave microscope (NSMM) with a resonant standard waveguide probe at an operation frequency f=60 GHz. A chemically etched metallic probe tip was coupled to the resonant rectangular waveguide. By properly tuning the tunable resonator and the probe tip we could improve sensitivity and spatial resolution of the NSMM. By measuring the change of the quality factor in the near-field zone, near-field scanning millimeter-wave images of patterned metal films and YBa2Cu3Oy thin films were obtained with a spatial resolution better than 1 μm. We observed the dependence of the current density NSMM images of patterned indium tin oxide films on the bias currents.

Millimeter-wave scanning near-field microscope using a resonant waveguide probe

We demonstrate a millimeter-wave surface imaging technique using a near-field scanning millimeter-wave microscope with a resonant standard waveguide probe. The metallic probe tip in the resonant waveguide was designed to couple energy into and out of the resonant waveguide. By measuring the shift of the resonant frequency and the change of the quality factor in the near-field zone, we obtained millimeter-wave near-field images of YBa2Cu3Oy thin films on MgO substrates with a spatial resolution better than 2 μm.

Improvement in Image Reconstruction of Scanning Near-Field Millimeter-Wave Microscopy Using a Metal Slit-Type Probe

Improvements in image reconstruction of scanning near-field millimeter-wave microscopy using a metal slit-type probe have been demonstrated. A conjugate gradient method in combination with preconditioning and regularization has been used during the image reconstruction process to take into account the sensitivity distribution of the slit-type probe. The reconstructed images show that the image degradation that occurs due to the sensitivity distribution can be corrected.

Scanning near-field millimeter-wave microscopy using a metal slit as a scanning probe

In this paper, a novel type of scanning near-field millimeter-wave microscopy using a metal slit-type probe is proposed. A tapered reduced-height rectangular waveguide forms the slit aperture, which has a width much smaller than one wavelength /spl lambda/ and length of the order of /spl lambda/. The slit probe can be operated in the TE/sub 10/ mode and, thus, results in high transmission efficiency, even when the width is exceedingly small. An image reconstruction algorithm based on computerized tomographic imaging is used to obtain two-dimensional near-field images. Experiments performed at 60 GHz (/spl lambda/=5 mm) show that image resolution equal to the slit width (/spl sim/80 /spl mu/m) is achieved. As an application of this scanning slit microscopy, visualization of transition phenomena of photoexcited free carriers in silicon have been successfully demonstrated, yielding useful information on the dynamics of free carriers in semiconductor materials.

Interaction between a waveguide-fed narrow slot and a nearby conducting strip in millimeter-wave scanning microscopy

Millimeter-wave microscopy is investigated with the aid of a simplified model. The model consists of a parallel plate waveguide opening into a ground plane and radiating in the presence of a perfectly conducting strip. The method of moments is used together with a quasi-static approximation to solve for the reflection coefficient. Numerical results included indicate that high resolutions are feasible with this apparatus.

Visualization of photoexcited free carriers by scanning near-field millimeter-wave microscopy

Visualization of transition phenomena of photoexcited free carriers by scanning near-field millimeter-wave microscopy has been demonstrated. A scanning millimeter-wave microscope using a metal slit-type probe and an image reconstruction algorithm based on computerized tomographic imaging has been used in the experiment to achieve two-dimensional time-resolved imaging. Experiments performed at 60 GHz (λ=5 mm) under room temperature conditions show that generation, extinction, and diffusion processes of photoexcited free carriers generated in the silicon layer of a silicon on quartz substrate can be imaged with a time division of one nanosecond and a spatial resolution of 110 μm (∼λ/45).

ミリ波帯近接場顕微鏡による光励起キャリアの画像化

ミリ波帯近接場顕微鏡による光励起キャリアの画像化

Scanning Near-Field Millimeter-Wave Microscope.

A small aperture or antenna can confine electromagnetic radiation to dimensions far smaller than the wavelength. Scanning such a structure in close proximity to an object can yield microscopic images with correspondingly high resolution. The benefit of using microwaves and millimeter-waves in scanning near-field microscopy lies in the promise of new types of material contrast. A good example is the mapping of electronic transport properties. In this review an overview of scanning near-field microwave, millimeter-wave, and submillimeter-wave microscopy is presented, a millimeter-wave microscope system using a slit-type probe is described in detail, and the application of this microscope for the visualization of photo-excited free carriers in a silicon substrate is demonstrated.

High-spatial resolution resistivity mapping of large-area YBCO films by a near-field millimeter-wave microscope

We demonstrate a new millimeter-wave technique for the resistivity mapping of large-area conducting films, namely, a near-field resistivity microscope. The microscope is based on the idea that electromagnetic waves are transmitted through a narrow resonant slit with high efficiency. By scanning this slit at fixed height above an inhomogeneous conducting surface and measuring the intensity and phase of the reflected wave, the resistivity of this surface may be determined with a 10-100 /spl mu/m spatial resolution using 80-GHz radiation. Using this technique, we map normal-state resistivity of 1 in /spl times/1 in YBCO films at ambient temperature. In some films we find inhomogeneities of the normal-state sheet resistance of the order of 10%-20%.