Near-field Scanning Microwave Microscope Research Articles

Nondestructive characterization of surface resistance for copper(II) phthalocyanine thin films using a near-field scanning microwave microscope

We observed the surface resistance of copper(II) phthalocyanine (Cu-Pc) thin films dependence on substrate heat-treatment conditions by a nondestructive characterization method using a near-field scanning microwave microscope (NSMM) at an operating frequency f=5.2–5.3 GHz. The changes in surface resistance were investigated by NSMM by measuring the reflection coefficient S 11. The surface resistance of Cu-Pc thin films depends on the grain alignment. When the Cu-Pc thin films were annealed at 150 °C for 3 h, the films are aligned with the b-axis normal to the substrate and have a lower surface resistance.

Imaging of oxide dielectrics by near-field microwave microscopy

Scanning near-field microwave microscopy was used to image LaAlO 3 and TiO 2 single crystals and bulk yttria-stabilized zirconia (YSZ) polycrystalline ceramic microstructures. The effect of microstructural features including grain boundaries, twins, surface roughness, and oxygen content variations on the local dielectric constant, and the resulting microscope image quality are discussed.

Studies of surface resistance of copper(II) phthalocyanine thin films by using a near-field scanning microwave microscope

We observed the surface resistance of copper(II) phthalocyanine (Cu–Pc) thin films dependence on substrate heating temperature by using a near-field scanning microwave microscope (NSMM). The NSMM system was coupled to a dielectric resonator with a distance regulation system at an operating frequency f=4.5–5.5 GHz. The crystal structures and surface resistance of Cu–Pc thin films due to different heating temperatures were observed by using X-ray diffraction including the 2 θ and φ-scan and the near-field scanning microwave microscope. As the temperatures increased from room temperature to 200 °C, the crystal structure of Cu–Pc thin films was transformed from monoclinic α-Phase to thermally stable monoclinic β-Phase. The changes in surface resistance of Cu–Pc thin films due to different substrate heating temperatures were investigated by NSMM by measuring the reflection coefficient S 11. The surface resistance of Cu–Pc thin films depends on the morphology and crystal alignment of these films. When the substrate temperature for deposition was 150 °C, the minimum surface resistance of Cu–Pc thin films was obtained.

Measurement of electric-field intensities using scanning near-field microwave microscopy

In this paper, we propose methods for the measurement of electric intensities of a microwave field above the surface of microwave circuits. Using miniaturized coaxial antennas, we measure all spatial components of the induced field above device-under-test. A special position/signal difference method is used to better localize the measured field and increase the spatial resolution of the field mapping. During the scanning process, the antenna is driven at the defined distance above the sample surface according to previously acquired topographic data. For measurement of the tangential-field components parallel to the sample surface, the antenna is tilted by approximately 45/spl deg/ relative to the sample surface. By its rotation about the vertical axis, various components of the field are measured, and vertical and horizontal electric-field intensities are recalculated. The probes are calibrated in a well-defined field standard and allow good quantitative characterization of the measured field.

Near-field scanning microwave microscope using a dielectric resonator

We describe a near-field scanning microwave microscope which uses a high-quality dielectric resonator with a tunable screw. The operating frequency is f=4.5 GHz. The probe tip is mounted in a cylindrical resonant cavity coupled to a dielectric resonator for the TE011 mode. We tuned the resonance cavity to match the impedance of 50 Ω by using a tunable screw and could improve sensitivity and spatial resolution to better than 1 μm. To demonstrate the ability of local microwave characterization, the surface resistance dependence of the metallic thin films on film thickness has been mapped.

Improving images from a near-field scanning microwave microscope using a hybrid probe

We fabricated a near-field scanning microwave microscope (NSMM) using a hybrid tip combining a reduced length of the tapered part with a small apex. In order to understand the function of the probe, we fabricated three different tips using a conventional chemical etching technique and observed three different NSMM images for patterned Cr films on glass substrates. These probe tips were coupled to a high-quality dielectric resonator at an operating frequency f=4.46 GHz. By using the hybrid tip, we demonstrated an improved, high-contrast NSMM image of lambda phage DNA on a glass substrate.

Tip–sample distance control for near-field scanning microwave microscopes

We demonstrate a near-field scanning microwave microscope (NSMM) which uses a tuning fork shear-force feedback method to control the distance between tip and sample. This distance control method is independent of local microwave characteristics. The probe tip for the NSMM is attached to one prong of a quartz tuning fork and directly coupled to a high-quality microstrip resonator with a dielectric resonator at an operating frequency of f=4.5–5.5 GHz. The amplitude of the tuning fork was used as a distance control parameter in the feedback system. To demonstrate the ability of the distance regulation system, we present topographic images of an uneven conducting metal sample and compare the height response and the NSMM image.

Near-field microwave microscope with improved sensitivity and spatial resolution

The near-field scanning microwave microscope has become a popular instrument to quantitatively image high-frequency properties of metals and dielectrics on length scales far shorter than the wavelength of the radiation. We have developed several new ways to operate this microscope to dramatically improve its spatial resolution and material property sensitivity. These include a novel distance-following method that takes advantage of the stability of a synthesized microwave source to improve the signal-to-noise ratio of our earlier frequency-following imaging technique. We also discuss novel height-modulated imaging techniques, culminating in a new tapping-mode method, which makes a 14 dB improvement in sensitivity, a 17.5 dB improvement in signal-to-noise ratio, and a factor of 2.3 improvement in spatial resolution compared to distance-following imaging.

Method of increasing spatial resolution of the scanning near-field microwave microscopy

In this article we propose methods for the measurement of electric intensity of a microwave field above the surface of microwave circuits. Using miniaturized coaxial antennas and a special probe positioning system, we measure both the amplitude and the phase of the induced field above the device under test. We introduce a position/signal difference method to further increase the spatial resolution down to about 30 μm—about one order better than contemporary microwave scanning devices utilizing coaxial antennas. The effect is theoretically analyzed and experimentally verified. The probes are calibrated in a well-defined field standard to allow quantitative characterization of the measured field. Performance of our scanning system utilizing these methods is demonstrated using a PCB finger capacitor.

Theoretical and experimental characterization of a near-field scanning microwave microscope (NSMM)

An important aspect to understanding near-field optics and imaging involves the electromagnetic scattering characteristics of objects illuminated by the near field of a sub-wavelength-sized aperture. This paper addresses one particular application of near-field optics: a transmission-mode near-field scanning microscope (NSM). Specifically, some peculiar phenomena are investigated including a near-field focusing effect, as well as an impedance-based image-shape effect. To this end, we first describe the physical attributes of an NSM and then present two computational models we use to characterize this instrument. Both moment-method and finite-difference time-domain models are discussed. These two models are applied to the analysis of the NSM for various configurations and compared to other theoretical and experimental results. Finally, the construction of an X-band NSM is described - which we label a near-field scanning microwave microscope (NSMM) - and the experimental near-field imaging measurements are compared with our numerical predictions.

Probing the local microwave properties of superconducting thin films by a scanning microwave near-field microscope

In this paper, we present our approach to probe the local microwave properties of superconducting thin films by using the microwave near-field scanning technique. We have employed a coaxial cavity together with a niobium tip as the probe and established a scanning sample stage cooled by liquid nitrogen to study thin film devices at low temperature in our scanning microwave near-field microscope. Nondestructive images have been obtained on the inhomogeneity of the YBaCuO superconducting thin films at microwave frequency. We believe that these results would be helpful in evaluating the microwave performance of the devices.

Development of a near-field scanning microwave microscope using a tunableresonance cavity for high resolution

We report on the operational principles and the practical implementation of anear-field scanning microwave microscope system consisting of a λ/4coaxial resonator with a tunable resonance cavity coupled to a sharp probe tip.The changes of sensitivity and spatial resolution as a function of cavity length areclearly modulated by tuning the resonance cavity. By tuning the resonance cavity,we demonstrate improved sensitivity and spatial resolution better than 4 µm of thenear-field images of a YBa2Cu3Oy thin film on a MgO substrate at an operating frequency of f = 1–1.5 GHz. We modelledthe λ/4coaxial resonator by a LCR circuit and the principles of operation can beexplained by using perturbation theory, considering the radius of the probe tip,the quality factor, impedance matching, and the sample–tip distance.

Microfabricated silicon coaxial field sensors for near-field scanning optical and microwave microscopy

We report a comprehensive process for fabricating silicon-based near-field electromagnetic antennas that are used with scanning force microscopy (SFM), and we also present initial results from measurements made with these tips. We present processes to make coaxial and diode tips. In both processes, anisotropic reactive ion etching (RIE) is used to define the tip and special resist spinning protocols are used to create sub-micrometer openings. One process results in a shielded coaxial tip structure used for electric field imaging in the microwave regime. By varying a few steps, Schottky diode junctions are formed at the tips and can act as optical sensors. The resulting tip opening is in the range of 100 nm for photodiode tips and 500 nm for open-ended coaxial tips. We have integrated such tips with the appropriate cantilevers, chip bodies, electrical interfaces and probe station necessary for routine experimental application. We show experimental data using both types of tips.

Nondestructive evaluation of the dielectric properties of the substrate materials for high-Tc superconducting microwave devices

In this paper, microwave near-field scanning technique has been employed to study the local dielectric properties of the substrate materials for superconducting microwave devices. A coaxial cavity together with a niobium tip has been used as a probe in our scanning microwave near-field microscope (SMNFM). Using the SMNFM, quantitative measurement of both the relative permittivity and the loss tangent of various substrate materials for the high-temperature superconducting thin films have been obtained, which coincide with the data reported in the literature quite well. Nondestructive imaging of the dielectric properties of the substrate is also given with a spatial resolution of several micrometres. We believe that the SMNFM is a reliable method for nondestructively evaluating the dielectric properties of the substrates in the microwave circuit devices. It will be helpful to better understand the influences of the variations and defects in the substrates on the designing and performance of the superconducting microwave devices.

Improved surface imaging with a near-field scanning microwave microscope using a tunable resonator

We report a microwave surface imaging technique using a near-field scanning microwave microscope with a tunable resonance cavity. By tuning the resonance cavity, we could demonstrate improved sensitivity and spatial resolution of the topographic image of YBa2Cu3Oy thin films on MgO substrates. By measuring the shift of resonant frequency and the change of quality factor, we obtained near-field scanning microwave images with a spatial resolution better than 4 μm at an operating frequency of f=1–1.5 GHz. The principal of operation could be explained by the perturbation theory of a coaxial resonant cavity, considering the radius of the probe tip, the sample–tip distance, and the impedance matching.

Local microwave characterization of metal films using a scanning microwave near-field microscope

In microwave integrated circuits, the performance of devices is often influenced by the homogeneity of microwave properties of metal thin films in the circuits. In this paper, a scanning microwave near-field microscope (SMNFM) has been designed using a coaxial resonator as the probe, to study the local microwave properties of the electronic devices. Several typical samples of metal films have been measured and the results have shown that we can image the local microwave properties by recording the changes of the resonant frequency and quality factor of the coaxial resonator probe. The spatial resolution of the SMNFM has been improved to be better than 5 μm by utilizing a probe with a structure similar to that used in a scanning tunnelling microscope. To demonstrate the ability of local microwave characterization, the surface resistances of Cr thin film and Ag/Cr multilayer have been imaged by the SMNFM.

Microwave frequency ferroelectric domain imaging of deuterated triglycine sulfate crystals

We have used a near-field scanning microwave microscope to image domain structure and quantitatively measure dielectric permittivity and nonlinearity in ferroelectric crystals at 8.1 GHz with a spatial resolution of 1 μm. We imaged ferroelectric domains in periodically poled LiNbO3, BaTiO3, and deuterated triglycine sulfate (DTGS) with a signal-to-noise ratio of 7. Measurement of the permittivity and nonlinearity of DTGS in the temperature range 300–400 K shows a peak at the Curie temperature, TC≈340 K, as well as reasonable agreement with thermodynamic theory. In addition, the domain growth relaxation time shows a minimum near TC. We observe coarsening of ferroelectric domains in DTGS after a temperature quench from 360 to 330 K and evaluate the structure factor.

Magnetic permeability imaging of metals with a scanning near-field microwave microscope

We describe a scanning near-field microwave microscope which uses a loop probe to measure local magnetic properties of metallic samples on a length scale of 200 μm. We demonstrate imaging at 6 GHz through spatiallyresolved ferromagnetic resonance experiments on a single crystal of the colossal magneto-resistive material La0.8Sr0.2MnO3. We find the experimental results are qualitatively and quantitatively well described by a simple model of the system.

Nondestructive imaging of the microwave properties of superconducting thin film devices with a scanning microwave near-field microscope

In this paper, nondestructive microwave scanning techniques have been used to image the local microwave properties of planar microwave devices. A coaxial cavity, together with a niobium tip, has been used as a probe in the scanning microwave near-field microscope. Quantitative images of the dielectric constant of the substrates as well as the variations of the surface resistance of the line patterns in the metal multilayers have been obtained. Local surface resistances at 3GHz have been measured on microwave devices prepared with laser ablated YBaCuO thin films, which helps in evaluating the performance of the devices.

In-Situ Monitoring of Thin-Film Quality Using Evanescent Microwave Local Imaging Probes with Near-Atomic Resolution

Local probes, such as scanning tunneling (STM), atomic force (AFM), near-field scanning (NSOM), and evanescent microwave (EMM) microscopes are important material characterization tools with very high spatial resolutions capable of operating in many different environments. All these probes are currently laboratory tools with limited real-time manufacturing applications because of their low speed. Of all these probes. EMM has the greatest potential of acquiring higher scanning speed because it does not require an intimate contact with the material surface. Moreover, EMM is capable of characterizing a variety of organic and inorganic materials including metals, semiconductors, and insulators over a wide range of frequencies and length scales. Here we discuss the application of parallel EMMs (PEMM) in monitoring thin-film quality in real-time and in-situ.