We present a general-purpose, fast and computationally efficient numerical method to predict the ... more We present a general-purpose, fast and computationally efficient numerical method to predict the performance of filters based on electric-LC (ELC) resonators or split-ring resonators (SRR) in a very large frequency range (i.e., 8-40 GHz). In particular, we tackle the problem arising from the design of arrays of ELC/SRR-based resonators developed in a multi-layer dielectric stack under a coplanar waveguide excitation. The intrinsic complexity of the analyzed structure (open, multi-layer, and with resonators) makes it unpractical to rely exclusively on full-wave electromagnetic simulations. Furthermore, the presence of multiple modes in propagation can lead to a quite difficult assessment of the optimal simulation conditions. For all these reasons, we propose a method based on the cascade of scattering matrices for all the submodules of the considered filters. We demonstrate the efficacy of the proposed numerical technique for a good prediction of the high-frequency performance of the filters. The fabrication on silicon substrate of structures integrating electric-LC resonators (for X band applications) or split-ring resonators (for Ka band applications) serves the purpose of validating the presented method, with a very good agreement between simulations and measurements. INDEX TERMS Electromagnetic modeling, planar resonators, microwave filters, numerical analysis, numerical modeling.
We present a method for assessing the spreading resistance of electrodes immersed in a lossy medi... more We present a method for assessing the spreading resistance of electrodes immersed in a lossy medium, useful for the calibration of scanning microwave microscopy and also in other fields such as fluidic sensors.
In this paper, we propose a comparative method to analyze a complex microwave structure consistin... more In this paper, we propose a comparative method to analyze a complex microwave structure consisting of a silicon-based coplanar waveguide line and four electric-LC resonators, thus forming a wideband microwave band-stop filter that can be easily integrated at the wafer level together with other devices and sub-systems for large-scale production of high-frequency electronics. A rigorous and careful approach is needed when choosing the proper simulation settings and, as a good rule of thumb, both time and frequency domains should provide the same results. Furthermore, the experimental validation requires supplementary components (like connectors), often ignored when designing an electromagnetic structure highly impacting on the overall performance. In this work, we go in depth into all these issues and show how the right choices in terms of computational parameters can lead to a good agreement with the measurements of the proposed CMOS-compatible band-stop filter in the band 2–18 GHz, ...
This work details an effective dynamic chemical etching technique to fabricate ultra-sharp tips f... more This work details an effective dynamic chemical etching technique to fabricate ultra-sharp tips for Scanning Near-Field Microwave Microscopy (SNMM). The protruded cylindrical part of the inner conductor in a commercial SMA (Sub Miniature A) coaxial connector is tapered by a dynamic chemical etching process using ferric chloride. The technique is optimized to fabricate ultra-sharp probe tips with controllable shapes and tapered down to have a radius of tip apex around ∼1 μm. The detailed optimization facilitated the fabrication of reproducible high-quality probes suitable for non-contact SNMM operation. A simple analytical model is also presented to better describe the dynamics of the tip formation. The near-field characteristics of the tips are evaluated by finite element method (FEM) based electromagnetic simulations and the performance of the probes has been validated experimentally by means of imaging a metal-dielectric sample using the in-house scanning near-field microwave micr...
A MM-loaded sub-THz on-chip antenna with a narrow beamwidth, 9 dB gain and a simulated peak effic... more A MM-loaded sub-THz on-chip antenna with a narrow beamwidth, 9 dB gain and a simulated peak efficiency of 76% at the center frequency of 300 GHz is presented. By surrounding the antenna with a single MM-cell ring defined solely on the top metal of the back-end of line, an efficient suppression of the surface waves is obtained. The on-chip antenna has been designed using IHPs 130 nm SiGe BiCMOS technology with a 7-layer metallization stack, combined with the local backside etching process aimed to creating an air cavity which is then terminated by a reflective plane. By comparing the measured MM-loaded antenna performances to its non-MM-loaded counterpart, an enhanced integrity of the main lobe due to the MM-cells shielding effect can be observed. An excellent agreement between the simulated and measured performances has been found, which makes the MM-loaded antennas a valid alternative for the upcoming next-generation sub-THz transceivers.
Scanning microwave microscopy (SMM) is a novel metrological tool that advances the quantitative, ... more Scanning microwave microscopy (SMM) is a novel metrological tool that advances the quantitative, nanometric, high-frequency, electrical characterization of a broad range of materials of technological importance. In this work, we report an inverted near-field scanning microwave microscopy (iSMM) investigation of a graphene oxide-based epoxy nanocomposite material at a nanoscopic level. The high-resolution spatial mapping of local conductance provides a quantitative analysis of the sample’s electrical properties. In particular, the electrical conductivity in the order of ∼10−1 S/m as well as the mapping of the dielectric constant with a value of ∼4.7 ± 0.2 are reported and validated by the full-wave electromagnetic modeling of the tip–sample interaction.
Millimeter-Wave Meta Cells Loaded Coplanar Transmission Line for Component Applications
2020 Fourteenth International Congress on Artificial Materials for Novel Wave Phenomena (Metamaterials)
In this work, a planar transmission line loaded with square shaped split ring resonator (SRR) met... more In this work, a planar transmission line loaded with square shaped split ring resonator (SRR) metamaterials works around 150 GHz is modeled and validated by means of full-wave electromagnetic simulations. The transmission characteristics of such a transmission line is reported. The SRR loaded coplanar waveguide (CPW) structure exhibits stop band characteristics in response to the resonance of the inductively coupled SRR rings excited by the magnetic fluxes through the rings. A parametric analysis of the rings and arrays of SRRs carried out to predict the behavior of the meta cells loaded transmission line. Since these metamaterials are much smaller than the feeding signal wavelength, these metamaterials loaded transmission lines are potentially useful to optimize size and quality factor of millimeter-wave circuit components and radiating elements.
Reversing the Humidity Response of MoS2- and WS2-Based Sensors Using Transition-Metal Salts
ACS Applied Materials & Interfaces, 2021
Two-dimensional materials, such as transition-metal dichalcogenides (TMDs), are attractive candid... more Two-dimensional materials, such as transition-metal dichalcogenides (TMDs), are attractive candidates for sensing applications due to their high surface-to-volume ratio, chemically active edges, and good electrical properties. However, their electrical response to humidity is still under debate and experimental reports remain inconclusive. For instance, in different studies, the impedance of MoS2-based sensors has been found to either decrease or increase with increasing humidity, compromising the use of MoS2 for humidity sensing. In this work, we focus on understanding the interaction between water and TMDs. We fabricated and studied humidity sensors based on MoS2 and WS2 coated with copper chloride and silver nitrate. The devices exhibited high chemical stability and excellent humidity sensing performance in relative humidity between 4 and 80%, with response and recovery times of 2 and 40 s, respectively. We have systematically investigated the humidity response of the materials as a function of the type and amount of induced metal salt and observed the reverse action of sensing mechanisms. This phenomenon is explained based on a detailed structural analysis of the samples considering the Grotthuss mechanism in the presence of charge trapping, which was represented by an appropriate lumped-element model. Our findings open up a possibility to tune the electrical response in a facile manner and without compromising the high performance of the sensor. They offer an insight into the time-dependent performance and aging of the TMD-based sensing devices.
Scanning microwave microscopy technique for nanoscale characterization of magnetic materials
Journal of Magnetism and Magnetic Materials, 2016
Abstract In this work, microwave characterization of magnetic materials using the scanning microw... more Abstract In this work, microwave characterization of magnetic materials using the scanning microwave microscopy (SMM) technique is presented. The capabilities of the SMM are employed for analyzing and imaging local magnetic properties of the materials under test at the nanoscale. The analyses are performed by acquiring both amplitude and phase of the reflected microwave signal. The changes in the reflection coefficient S 11 are related to the local properties of the material under investigation, and the changes in its magnetic properties have been studied as a function of an external DC magnetic bias. Yttrium iron garnet (YIG) films deposited by RF sputtering and grown by liquid phase epitaxial (LPE) on gadolinium gallium garnet (GGG) substrates and permalloy samples have been characterized. An equivalent electromagnetic transmission line model is discussed for the quantitative analysis of the local magnetic properties. We also observed the hysteretic behavior of the reflection coefficient S 11 with an external bias field. The imaging and spectroscopy analysis on the experimental results are evidently indicating the possibilities of measuring local changes in the intrinsic magnetic properties on the surface of the material.
The paper presents a methodology for de-embedding scanning microwave microscopy (SMM) measurement... more The paper presents a methodology for de-embedding scanning microwave microscopy (SMM) measurements, mainly for semiconductor characterization. Analytical modeling, a parametric study and experimental verification are presented. The proposed methodology is based on the analysis of system response in the linear scale, instead of the dB scale commonly utilized in RF measurements, and on expressing the standard calibration capacitances per unit area. In this way the total measured capacitance is determined by the tip area which is then obtained as a result of the model fitting on the experimental data. Additional evaluation is performed by a straightforward experimental comparison with the usually adopted technique that is based on the electrostatic force microscopy approach curve method. The results obtained by the application of both techniques on the same tip during the same experiment were found to be in good agreement and moreover allowed a detailed discussion on the features of each one of the two methodologies. The paper provides also in this way useful knowledge for the potential users in order to choose the most appropriate technique according to the corresponding SMM application.
Scanning microwave microscopy for nanoscale characterization of semiconductors: De-embedding reflection contact mode measurements
2015 European Microwave Conference (EuMC), 2015
A methodology towards de-embedding contact mode scanning microwave microscopy (SMM) reflection me... more A methodology towards de-embedding contact mode scanning microwave microscopy (SMM) reflection measurements is presented. A calibration standard that consists of differently doped stripes is required, while the reflection coefficient amplitude |S11|, is modeled and analyzed in the linear scale, instead of the commonly adopted dB scale. This allows the straightforward experimental determination of important parameters such as the effective tip radius and the magnitude of stray capacitances. Values of 145 nm and 22 fF have been obtained respectively. The proposed methodology can be easily and repeatedly performed during the experimental procedure, offering in this way the necessary de-embedding to get an enhanced accuracy on SMM measurements for semiconductors characterization.
Nanoscale characterization of MOS systems by microwaves: Dopant profiling calibration
EUROSOI-ULIS 2015: 2015 Joint International EUROSOI Workshop and International Conference on Ultimate Integration on Silicon, 2015
ABSTRACT The paper presents a calibration of scanning microwave microscopy signals for doping pro... more ABSTRACT The paper presents a calibration of scanning microwave microscopy signals for doping profiling in MOS systems. The experimentally obtained S-parameters are matched through a linear relation to the calculated MOS system capacitance and then to doping. The proposed approach is verified by simulations with the equivalent LCR circuit as well as by experimental results obtained on a calibration sample with differently doped areas.
In this work, a simple and efficient circuit modelling of metamaterial structures, providing a co... more In this work, a simple and efficient circuit modelling of metamaterial structures, providing a compact circuit able to describe accurately the device over a large bandwidth of operation is proposed. The equivalent circuit model is obtained by the identification process of the load in terms of shunt branches constituted by reactive elements that can be both positive and negative. The circuit model is validated by analysing the Split Ring Resonator (SRR) structure. The presence of negative elements in the non-Foster load are transformed to positive reactive elements by converting the load from shunt to series. Unlike the T or Π circuit models, using this approach a circuit model can be constructed directly from the scattering parameters and valid for any circuit topologies.
Inverted Scanning Microwave Microscopy for Nanometer-scale Imaging and Characterization of Platinum Diselenide
Near-field scanning microwave microscopy (SMM) is a technique gaining popularity for the study of... more Near-field scanning microwave microscopy (SMM) is a technique gaining popularity for the study of the electrical properties of both soft and hard matter on the nanometer scale. Despite the current focus on semiconductors, the applications of SMM on new two-dimensional materials such as platinum diselenide (PtSe2) are still in an initial stage. In this work, the imaging capabilities of an innovative SMM and the analysis of the electrical properties of PtSe2 are demonstrated.
Electrical properties of Jurkat cells: an inverted scanning microwave microscope study
2020 IEEE/MTT-S International Microwave Symposium (IMS), 2020
Near-field Scanning Microwave Microscopy (SMM) makes use of a high frequency signal to image and ... more Near-field Scanning Microwave Microscopy (SMM) makes use of a high frequency signal to image and characterize electrical properties of samples. Recently, a new SMM setup was developed, the so called inverted-SMM (iSMM), whose biocompatibility allows its application to sample of biological interest. The experimental arrangement of the iSMM combines an Atomic Force Microscope (AFM), a Vector Network Analyser (VNA) and a slot line as a sample holder. In this work, a calibration protocol for reflection mode measurements is applied to the imaging of biological samples, in particular Jurkat cells. The complex local admittance of a single cell is extracted and the dielectric constant is estimated to be around 2.6 ± 0.3. Thus, the first quantitative characterization of iSMM operating in reflection mode is reported, as well as the first electrical characterization of Jurkat cells by this tool.
Quantitative Characterization of Platinum Diselenide Electrical Conductivity With an Inverted Scanning Microwave Microscope
IEEE Transactions on Microwave Theory and Techniques, 2021
Near-field scanning microwave microscopy is a technique with increasing popularity for the study ... more Near-field scanning microwave microscopy is a technique with increasing popularity for the study of nanometer-scale electrical properties of samples. Here, we present an approach to quantify sample properties in images obtained with an inverted scanning microwave microscope (iSMM), recently introduced by our group. In particular, this study reports the analysis of the local electrical conductivity of a platinum diselenide sample and proves its semimetal behavior. The approach is validated by a full-wave numerical model, reproducing the complete iSMM operation as well as all steps of the calibration algorithms. To extract local sample properties, this article provides two calibration procedures, respectively, for transmission and reflection mode measurements, based on a two-port equivalent circuit of the iSMM. This enables the high-frequency quantitative characterization of a wide variety of samples and surfaces.
Real-Time Removal of Topographic Artifacts in Scanning Microwave Microscopy
Near-field scanning microwave microscopy (SMM) employs microwave radiation to image and character... more Near-field scanning microwave microscopy (SMM) employs microwave radiation to image and characterize samples down to the atomic scale, including soft biological structures or inorganic materials, such as ferroelectric films. However, SMM generally also senses sample topography; hypersensitivity to topography becomes problematic with additional parasitic contributions and may partially or completely mask nontopographic sample features in the data, such as contrast in electrical conductivity or permittivity. This work proposes a simple and effective procedure to remove unwanted parasitic effects from SMM images. Differently from existing procedures, the method is applicable either in postprocessing or in real time, i.e., during the scanning operation. This allows the immediate visualization of nontopographic sample features in the instrument screen. As a proof of concept, hafnium zirconium oxide (HfZrO) ferroelectric film with high surface roughness is studied; unwanted contributions ...
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Papers by C. H. Joseph