Dielectric Resonator Technique Research Articles

Radio-Frequency Conductivity Characteristics and Corresponding Mechanism of Graphene/Copper Multilayer Structures.

High-radio-frequency (RF) conductivity is required in advanced electronic materials to reduce the electromagnetic loss and power dissipation of electronic devices. Graphene/copper (Gr/Cu) multilayers possess higher conductivity than silver under direct current conditions. However, their RF conductivity and detailed mechanisms have rarely been evaluated at the micro scale. In this work, the RF conductivity of copper-copper (P-Cu), monolayer-graphene/copper (S-Gr/Cu), and multilayer-graphene/copper (M-Gr/Cu) multilayer structures were evaluated using scanning microwave impedance microscopy (SMIM) and dielectric resonator technique. The results indicated that the order of RF conductivity was M-Gr/Cu < P-Cu < S-Gr/Cu at 3 GHz, contrasting with P-Cu < M-Gr/Cu < S-Gr/Cu at DC condition. Meanwhile, the same trend of M-Gr/Cu < P-Cu < S-Gr/Cu was also observed using the dielectric resonator technique. Based on the conductivity-related Drude model and scattering theory, we believe that the microwave radiation can induce a thermal effect at S-Gr/Cu interfaces, leading to an increasing carrier concentration in S-Gr. In contrast, the intrinsic defects in M-Gr introduce additional carrier scattering, thereby reducing the RF conductivity in M-Gr/Cu. Our research offers a practical foundation for investigating conductive materials under RF conditions.

Highly sensitive DS-CSRR based microwave sensor for permittivity measurement of liquids

In this work, a low-cost double split complementary split ring resonator (CSRR) microwave sensor has been designed and fabricated on an FR4 substrate for permittivity characterization of liquids. This modified CSRR structure is proposed to make use of the benefits of the dielectric resonator technique compared to other types of microwave methods. The resonator structure comprises two slits in each of the rings normal to each other while maintaining one slit in each ring along the feed line for maximum excitation of the resonator. The resonator with substrate dimensions of acts like an inductance-capacitance-resistance (LCR) circuit and operates at of the industrial scientific and medical band. Eleven different liquid samples (each with of volume) covering a wide permittivity range of have been used to measure the transmission coefficient using vector network analyzer. In comparison with many recently reported works, the sensitivity of the sensor is found to be higher with average and normalized sensitivity of permittivity and respectively. Fit equations are developed for both real and imaginary parts of permittivity, and using the fit equations the permittivity of three unknown samples are determined with less than error. The sensor adopts a unique orientation of the slits to enhance the E-field intensity for better interaction of the samples with the sensor. A compact form factor, low production cost, future integration possibilities, and high sensitivity are the distinct highlights of the sensor. The sensor promises to be a potential candidate for situations that demands low-cost and highly accurate measurements and may be a good alternative to commercial sensors for dielectric characterization, concentration analysis, and impurity measurement of liquids.

Characterisation of copper and stainless steel surfaces treated with laser ablation surface engineering

In the past few years, it has been established that Laser Ablation Surface Engineering (LASE) is a very effective way of producing surfaces which have Secondary Electron Yields (SEY) < 1. This can be achieved with a variety of laser pulse durations from nano-to picoseconds. However, the features (i.e. moderately deep grooves and nano-particulates) that help to reduce the SEY can produce undesirable effects such as an increase in the RF surface resistance. In this paper we discuss the methods employed utilising the dielectric resonator technique to quantify the surface resistance of laser treated copper and stainless steel samples. The quantification is based on a non-destructive measurement of high-frequency losses on the conducting surface. It has been demonstrated that the LASE surface can be produced with SEY<1 and an RF surface resistance of only ~6% higher than that on untreated surfaces. Furthermore, a comparative study of electron stimulated desorption (ESD) between the LASE treated and untreated samples of copper and stainless steel is reported for H2, CH4, CO and CO2. It has been shown that there are negligible differences in ESD between LASE treated and untreated stainless steel. It has been demonstrated that LASE-treated copper samples have a considerable reduction in ESD as compared with untreated sample.

Enhanced symmetrical split ring resonator for metallic surface crack detection

An enhanced sensor based on symmetrical split ring resonator (SSRR) functioning at microwave frequencies has been proposed in order to detect and characterize the metal crack of the materials. This sensor is based on perturbation theory, in which the dielectric properties of the material affect the quality factor and resonance frequency of the microwave resonator. Conventionally, coaxial cavity, waveguide, dielectric resonator techniques have been used for characterizing materials. However, these techniques are often large, and expensive to build, which restricts their use in many important applications. Thus, the enhanced bio-sensing technique presents advantages such as high measurement sensitivity with the capability of suppressing undesired harmonic spurious and permits potentially metal crack material detection. Hence, using a High Frequency Structure Simulator (HFSS) software, the enhanced sensor is modeled and the reflection S11 is performed for testing the aluminum metal with crack and without crack at the frequency range of 100 MHz to 3GHz. Variation of crack width and depth has been investigated and the most obvious finding emerged from this study is that the ability of detecting a minimum of sub-millimeter crack width and depth which is a round 10 𝛍m width or depth where the minimum shift of reflected frequency is recorded at 6.2 MHz and 3 MHz for crack width and depth respectively. The enhanced SSRR provides high capability of detecting small crack defection by utilizing the interaction between coupled gap resonators and it is useful for various applications such as aircraft fuselages, nuclear power plant steam generator tubing, and steel bridges and for others that can be compromised by metal fatigue.

Enhanced room-temperature microwave dielectric properties in bismuth zinc niobate thin films

Synthesis temperature is always playing a crucial role on the determination of dielectric properties of materials. In this letter, (Bi1.5Zn0.5)(Zn0.5Nb1.5)O7 (BZN) thin film was deposited onto quartz glass substrate by RF magnetron sputtering at room temperature and then post-annealed using rapid thermal processing. Film has been characterized with respect to crystalline phase and surface morphology, by means of X-ray diffraction and atomic force microscopy, suggesting no crystalline structure exists in annealed BZN film after post-annealing. Microwave dielectric properties were measured by split post dielectric resonator technique. After annealing at 150 °C, film showed excellent dielectric permittivity and low loss in microwave frequency range. This result indicates that the annealed BZN thin film has a great potential to be alternative of microwave materials fabricated at low temperature.

Spin–Spin and Spin–Phonon Interaction as a Nature of Microwave Absorption in He II

Experimentally observed with dielectric disk resonator technique, microwave absorption–amplification in liquid He II below $$\lambda $$ -point has been interpreted theoretically as a phenomenon in electrically active dielectric medium with low-energy excitations which exist near the ground state of the four-electron He–He interatomic bond due to spin–spin and spin–phonon coupling. The experimentally registered microwave absorption line is $$f_0=180.3\,\hbox {GHz}$$ at $$T=1.4\,\hbox {K}$$ and $$f_0=150.0\,\hbox {GHz}$$ at $$T=2.1\hbox {K}$$ which strongly corresponds to the values of roton gap known from neutron diffractometry. Our theoretical estimation gives only an upper limit $$>250\,\hbox {GHz}$$ for resonant response of the system. We interpret the dielectric $$^4\hbox {He}$$ superfluid as a working substance for low-temperature MASER and clarify the atomic mechanism of microwave absorption–amplification in the condensed helium phases.

Microwave spectroscopy of superfluid He II

Experimentally observed with dielectric disc resonator technique the resonant microwave absorption- amplification in superfluid He II below λ-point has been interpreted theoretically as a phenomenon in electrically active dielectric medium with low-energy excitations which exist near the ground state of the He–He interatomic bond due to fine structure of spin subsystem in condensed helium phase. The experimentally registered microwave resonant absorption line with fres = 180.3 GHz at T = 1.4 K and fres = 150.0 GHz at T = 2.1 K is closely related to the standard value of roton gap Δ/kB = 8.64 K (179.36 GHz). The measured temperature dependence of the resonant absorption demonstrates an excellent agreement with the corresponding neutron diffraction data for Δ(T) known from different literature sources. From the common point of view the obtained resonant absorption provides a typical example of the microwave spectroscopy which occurs widely among molecular systems with rotational and vibrational degrees of f...

Ultra-low dielectric loss BiSmMoO6 flexible tapes for hybrid integrated circuits

A low temperature co-fireable ceramic tape based on BiSmMoO6 (BSMO)-2 wt.% BBSZ (40Bi2O3:49B2O3:6SiO2:5ZnO) sinterable at 875 °C was successfully developed. The glass added ceramic was formulated into a well dispersed and homogenised slurry using xylene-ethanol binary mixture as solvent and fish oil as dispersant. The structural as well as microstructural properties of the casted tapes were analysed using XRD and SEM. The average surface roughness estimated using AFM was found to be 229 nm. The microwave dielectric properties of the green tapes, isostatically formed ones as well as sintered tapes were measured at 5 GHz and 10 GHz using split post dielectric resonator (SPDR) technique and found that resultant tape has ultra-low dielectric loss, of the order of 10−4. The BSMO-2 wt.% BBSZ tapes have shown a thermal expansivity of 12.3 ppm/˚C which is marginally higher than commercial tapes, but advantageous since closer to that of silver electrode.

Effect of thickness on optical and microwave dielectric properties of Hydroxyapatite films deposited by RF magnetron sputtering

This study present findings on the structural, optical and dielectric properties of polycrystalline Hydroxyapatite [HAp, Ca10(PO4)6(OH)2] films, deposited using radio-frequency (RF) magnetron sputtering. The X ray diffraction (XRD) studies revealed that the unit cell volume and crystallite size of the films deposited on quartz substrates enhanced with an increase in film thickness. The Young's modulus (Ehkl) and the Poisson ratio (νhkl) of the thin films along different crystallographic directions have been calculated using the X-ray elastic constants. The Young's modulus of the films exhibited crystallographic direction dependence which suggests that the sputtered films are anisotropic. The dielectric constant εr and the loss tangent tanδ of the sputtered films were in the range 29–85 and 0.0028–0.0014 respectively at a frequency of 1 MHz. These values are by far the best for films deposited under a pure argon environment. The improvement in crystallinity and uniform grain size of the films are used as parameters to understand the variation in dielectric properties of the sputtered films. The best microwave dielectric properties were in the range εr = 75 - 65 and tanδ = 0.014–0.032 when measured at 5 and 10 GHz, employing split post dielectric resonator (SPDR) technique. The obtained results suggest that HAp sputtered films can be promising for optical limiting and applications in tunable microwave devices.

Origin of dielectric loss in Ba(Co1/3Nb2/3)O3 microwave ceramics

AbstractThe microwave dielectric loss of stoichiometric and non‐stoichiometric Ba(Co1/3Nb2/3)O3 ceramics have been measured from 2 to 300 K in magnetic fields ranging from 0 to 5 T using a dielectric resonator (DR) technique. The microwave absorption from spin excitations of unpaired d‐electrons in exchange coupled Co2+ ions dominate the loss of the Ba(Co1/3Nb2/3)O3 ceramics at cryogenic temperatures. Two peaks in the loss tangent (tan δ) vs temperature relation from a distinctly different origin occur at 25‐30 K and 90 K, which increase in magnitude with increasing Co content in the bulk dielectric samples. Evidence that these peaks result from polaron conduction from hopping between Co2+ and Co3+ ions includes (i) the peak's observed temperature range; (ii) the decrease in peak intensity of approximately a factor of two in a large applied magnetic fields (5 T); and (iii) a strong correlation between the peak's magnitude and both the fraction of the minority Co3+ in the dominant Co2+ matrix and D.C. conductivity at elevated temperatures. A magnetic‐field independent high temperature peak with a maximum at 250 K dominates the room temperature microwave loss whose magnitude correlates with those of the low temperature peaks. This suggests that the defects responsible for carrier conduction play an important role in establishing the loss tangent at room temperature.

Microwave characterization of normal and superconducting states of MOCVD made YBCO tapes

We have used a microwave, non-contact, non-destructive, dielectric resonator (DR) technique to characterize complex conductivity of different quality YBCO/Hastelloy tapes for the purpose of exploring such a technique as a potential quality control method for fabrication of YBCO tapes. The tapes were deposited at different temperatures on Hastelloy-supported oxide buffer layers using the MOCVD technique. The buffer stack consisted of aluminum oxide (Al2O3), yttrium oxide (Y2O3), and textured ion beam assisted deposition-MgO and LaMnO3 layers. Two dielectric resonators (DRs), the single post DR, consisting of high-permittivity barium zirconium titanate ceramic operating at 13 GHz in quasi-TE01δ mode, and the rod DR, consisting of rutile single crystal disk operating at 9.4 GHz in-TE011 mode, were designed to meet sensitivity requirements for characterization of conductivity of the superconductor at normal and superconducting states, respectively. For calculations of complex conductivity from experimental data of Q-factor and resonant frequency shift, a commercial electromagnetic simulator HFSS, based on finite elements analysis, was used. The theoretical Q-factor and resonant frequency on conductivity functions obtained from full wave numerical simulations of microwave fields were matched with the experimental data to determine conductivity of the YBCO tapes in both normal and superconducting states. In addition, for comparison purposes, 280 nm thick high-quality YBCO epitaxial film deposited on a dielectric substrate was also characterized, including frequency dependence of the complex conductivity. Discussion about feasibility of using DR microwave techniques as a quality control tool via measurements of conductivity versus temperature slope of the YBCO/Hastelloy tape in normal state is included. Also, microwave conductivity values of Hastelloy substrate as a function of temperature are reported.

A NOVEL MICROWAVE SENSOR WITH HIGH-Q SYMMETRICAL SPLIT RING RESONATOR FOR MATERIAL PROPERTIES MEASUREMENT

A new sensor based on symmetrical split ring resonator (SSRR) functioning at microwave frequencies has been proposed in order to detect and characterize the properties of the materials. This sensor is based on perturbation theory, in which the dielectric properties of the material affect the quality factor and resonance frequency of the microwave resonator. Conventionally, coaxial cavity, waveguide, dielectric resonator techniques have been used for characterizing materials. However, these techniques are often large, and expensive to build, which restricts their use in many important applications. Thus, the proposed bio-sensing technique presents advantages such as high measurement sensitivity (around 400 Q-factor) with the capability of suppressing undesired harmonic spurious and permits potentially material characterization and determination. Hence, using a specific experimental methodology, tests performed have demonstrated the biosensor ability to characterize at least four references materials with known permittivity (Air, Roger Duriod RT 5880, Roger Duriod RT 4530, FR4) and one material with unknown permittivity (Beef). Accordingly, the numerically established relations are experimentally verified for these reference materials and the results indicated that the average estimation error of measuring the permittivity was 2.56 % at resonant of around 2.2 GHz. The proposed design is useful for various applications such as food industry, medicine, pharmacy, bio-sensing and quality control

Measurement of Vortex Pinning in YBCO and YBCO/BZO Coated Conductors Using a Microwave Technique

In order to study the effect of pinning in coated conductors, we have used pulsed laser ablation to grow $\text{YBa}_{2}\text{Cu}_{3}\text{O}_{7-x}$ (YBCO) and $\text{YBa}_{2}\text{Cu}_{3}\text{O}_{7-x}/\text{BaZrO}_{3}$ (YBCO/BZO) films on metallic templates. Despite the complexity of the structure, after the optimization of the deposition procedure, the YBCO/BZO showed only a moderate reduction of $T_{c}$ with respect to the pure YBCO sample. We use a very high frequency (∼47.7 GHz) dielectric resonator technique in order to induce very short distance vortex shaking, thus probing the steepness of the potential well. We report on measurements of the microwave response of the superconducting structures in terms of the quality factor $Q$ and the frequency resonance $\nu_{0}$ as a function of a moderate dc magnetic field $H$ , at different temperatures $T$ . To keep as much contact as possible to the raw data ( $Q$ and $\nu_{0}$ ), in agreement with a generalized model for vortex dynamics, we determine the pinning parameter $r$ and the upper limit for the creep factor $\chi_{M}$ . Based on the field dependence of the pinning parameters, the vortex pinning regimes were discussed. We find that the improvement of pinning by BZO is much reduced with respect to the effect observed in films grown on single crystals. In particular, the reduction of the critical temperature must be taken into account in order to appreciate the results.

Dielectric properties of highly resistive GaN crystals grown by ammonothermal method at microwave frequencies

Permittivity, the dielectric loss tangent and conductivity of semi-insulating Gallium Nitride crystals have been measured as functions of frequency from 10 GHz to 50 GHz and temperature from 295 to 560 K employing quasi TE0np mode dielectric resonator technique. Crystals were grown using ammonothermal method. Two kinds of doping were used to obtain high resistivity crystals; one with deep acceptors in form of transition metal ions, and the other with shallow Mg acceptors. The sample compensated with transition metal ions exhibited semi-insulating behavior in the whole temperature range. The sample doped with Mg acceptors remained semi-insulating up to 390 K. At temperatures exceeding 390 K the conductivity term in the total dielectric loss tangent of Mg compensated sample becomes dominant and it increases exponentially with activation energy of 1.14 eV. It has been proved that ammonothermal method with appropriate doping allows growth of high quality, temperature stable semi-insulating GaN crystals.

A Broadband Absorber With a Resistive Pattern Made of Ink With Graphene Nano-Platelets

A novel type of a broadband flexible electromagnetic absorbing panel made of a resistive pattern printed on a dielectric spacer backed by a conducting surface is investigated in this paper. It is shown that an appropriate choice of the shape and sheet resistance of the pattern allows extending an absorption spectrum up to an octave and beyond, which is very competitive over alternative solutions. The pattern is made of ink with graphene nano-platelets, which allows achieving expected sheet resistance with decent repeatability, what is confirmed with measurements undertaken with the DC point probe and microwave dielectric resonator techniques. An exemplary sample of the proposed absorber is manufactured and characterized, indicating a very good agreement between theoretical study and experiments.

Structure, composition and microwave dielectric properties of bismuth zinc niobate pyrochlore thin films

(Bi1.5Zn0.5)(Zn0.5Nb1.5)O7 (BZN) pyrochlore thin films were deposited onto both Pt/TiO2/SiO2/Si and polycrystalline alumina substrates using pulsed laser deposition technique and then post-annealed using rapid thermal processing. The deposition temperature varies from 300 °C to 600 °C, and all the BZN films showed cubic pyrochlore structure after annealing at 650 °C for 30 min in air. The influence of the substrate associated with crystal structure is significant in the as-deposited films and disappears after post-annealing. The dielectric properties as a function of frequency up to the microwave frequency in both films were measured by LCR meter and split-post dielectric resonator technique. It is found that the BZN film deposited at 400 °C and post-annealed at 650 °C shows excellent dielectric properties with low loss in the microwave frequency range. This result indicates that the BZN thin film is a potential microwave material.

Measurement of sheet resistance of GaN films on a dielectric substrate

The sheet resistance of gallium nitride films deposited with metal organic chemical vapor deposition on sapphire is investigated in this paper. Two types of contactless measurement techniques are used for that purpose. The first one is a microwave dielectric resonator technique, widely applicable to the precise electrical characterization of resistive films. Due to a small exposure area, the profile of sheet resistance can be acquired across the whole semiconductor film. Another technique is based on a frequency domain capacitive approach, where the film under test functions as a resistive electrode. The method is supplemented with full-wave electromagnetic simulations as well as equivalent circuit representation. The capacitive method is sensitive mostly to the out-of-plane resistance of the layer. Consequently, the combination of both methods provides the tools for the comprehensive and quantitative evaluation of the quality of the semiconductor film.

Electrical properties of deuteron irradiated high resistivity silicon

We have investigated resistivity changes introduced on the high-resistivity p-type silicon wafer by the irradiation with deuteron beam with an energy of 4.4GeV performed in the NUCLOTRON superconducting accelerator. Two contactless techniques were used for the measurements of resistivity changes: namely the microwave split post dielectric resonator (SPDR) technique and capacitance measurements in the frequency domain. The first technique allows resistivity measurements in the plane of the wafer, while the second one in the direction perpendicular to the wafer. The resistivity map obtained with the SPDR technique enabled us to obtain a permanent fingerprint of the accelerator beam intensity profile. It has been shown that after the irradiation, the material resistivity increased to ∼3.9×105Ωcm in the wafer region exposed to the maximum beam intensity. Complementary studies of the properties and concentrations of radiation deep-level defects were performed by the high-resolution photo-induced current transient spectroscopy (HRPITS). These studies have shown that the irradiation of the high resistivity silicon with 4.4-GeV deuterons results in the formation of several types of deep-level defects responsible for the charge compensation.

Nanomechanical and microwave dielectric properties of SrBi4Ti4O15 thin films sputtered on amorphous substrates by rf sputtering

SBTi (SrBi4Ti4O15) thin films were prepared on amorphous fused silica substrates by rf magnetron sputtering technique and crystallized in a microwave oven and conventional furnace. The difference in crystalline perfection was observed for both conventional and microwave annealed films. Nanoindentation and nanoscratch test were preformed to extract the mechanical properties of the films. Microwave annealed films exhibited higher hardness (6.2 GPa), Young’s modulus (103 GPa) and low friction coefficient than conventional annealed films. Microwave dielectric properties are measured at 10 and 20 GHz using spilt post dielectric resonator technique. Microwave annealed films have shown good microwave dielectric properties even at high temperatures by controlling the Bi volatization.

Dielectric properties of highly anisotropic nematic liquid crystals for tunable microwave components

In this Letter, we report on measurements of the complex permittivity of highly anisotropic nematic liquid crystals at microwave frequencies as a function of the AC bias voltage. Permittivity measurements have been performed by the split post dielectric resonator technique. The experiments have shown that when the AC bias voltage increases from 0 to 8 V, the real part of the permittivity of these liquid crystals changes by up to 28%. The tunability and the relatively low dielectric losses observed in these liquid crystal mixtures mean that they are ideal materials for the design of tunable microwave components.