Scanning Microwave Microscopy Research Articles

Imaging Nanomechanical Vibrations and Manipulating Parametric Mode Coupling via Scanning Microwave Microscopy.

In this study, we present a novel platform based on scanning microwave microscopy for manipulating and detecting tiny vibrations of nanoelectromechanical resonators using a single metallic tip. The tip is placed on the top of a grounded silicon nitride membrane, acting as a movable top gate of the coupled resonator. We demonstrate its ability to map mechanical modes and investigate mechanical damping effects in a capacitive coupling scheme, based on its spatial resolution. We also manipulate the energy transfer coherently between the mode of the scanning tip and the underlying silicon nitride membrane, via parametric coupling. Typical features of optomechanics, such as anti-damping and electromechanically induced transparency, have been observed. Since the microwave optomechanical technology is fully compatible with quantum electronics and very low temperature conditions, it should provide a powerful tool for studying phonon tunnelling between two spatially separated vibrating elements, which could potentially be applied to quantum sensing.

Coaxial tips for a scanning microwave microscope and its calibration with dielectric references

Scanning microwave microscopy (SMM) is a combination of an atomic force microscope with a vector network analyzer (VNA) to measure locally resolved impedances. The technique finds application in the realms of semiconductor industries, material sciences, or biology. To determine quantitative material properties from the measured impedances, the system must be calibrated. Transferring the calibration from the calibration substrate onto the material under test is strongly limited when using unshielded probes, as the electromagnetic coupling to the surroundings can reach several centimeters. This work reports the fabrication of coaxially shielded probes for a scanning microwave microscope and their integration into such an instrument. We discuss a calibration method with dielectric references, using a simulation-assisted 1-port VNA calibration algorithm. Uncertainty considerations of the measurement process are included and propagation throughout the algorithm is performed. The calibration is verified with an additional dielectric reference. As an application example, the results for a static-random-access memory sample are presented. We identified system-related drift and trace noise as the dominant contributors to the uncertainties of the calibrated results. The here presented shielded tips can broaden the application scope of SMM, as they are door-openers for measurements in liquids.

Submicronic-Scale Mechanochemical Characterization of Oxygen-Enriched Materials.

Conventional techniques that measure the concentration of light elements in metallic materials lack high-resolution performance due to their intrinsic limitation of sensitivity. In that context, scanning microwave microscopy has the potential to significantly enhance the quantification of element distribution due to its ability to perform a tomographic investigation of the sample. Scanning microwave microscopy associates the local electromagnetic measurement and the nanoscale resolution of an atomic force microscope. This technique allows the simultaneous characterization of oxygen concentration as well as local mechanical properties by microwave phase shift and amplitude signal, respectively. The technique was calibrated by comparison with nuclear reaction analysis and nanoindentation measurement. We demonstrated the reliability of the scanning microwave technique by studying thin oxygen-enriched layers on a Ti-6Al-4V alloy. This innovative approach opens novel possibilities for the indirect quantification of light chemical element diffusion in metallic materials. This technique is applicable to the control and optimization of industrial processes.

Fabrication of oscillating metal probe for dynamic scanning microwave microscopy

Abstract A microwave probe plays a critical role in near-field imaging, and there is a continuous effort to develop them through straightforward methods. This study designed and fabricated an oscillating metal probe and used it for scanning microwave imaging of micro-nano structures. The surface smoothness of the cantilever is approximately 19.3 nm after polishing with diamond abrasive paper, and the tip radius is less than 20 nm using electrochemical etching. The impact of metal electrode materials on microwave signals was assessed in the frequency range of 1–20 GHz. The microwave imaging capability of the devised probe was explored through the imaging of a micro-nano structure. The spatial resolution of microwave imaging reached 0.5 μm over a scanning area of 50 μm × 50 μm. This study has far-reaching significance for developing higher-performance microwave probes and advancing scanning microwave microscopy.

Comparison of Impedance Matching Networks for Scanning Microwave Microscopy

Comparison of Impedance Matching Networks for Scanning Microwave Microscopy

Coplanar waveguide ground potential imbalance as a source of useful signal in near-field scanning microwave microscopy

Various techniques are available in order to obtain information on samples of a different nature in near-field scanning microwave microscopy (NSMM), with transmission-line resonator (TLR) techniques considered the most advanced in terms of sensitivity and resolution. In this paper, we focus on the development of TLR-based NSMM supplied by a new source of useful signal: coplanar waveguide ground potential imbalance. Electromagnetic modeling of the device and experimental scanning of two planar structures are conducted to examine the performance of the proposed technique. Both modeling and experimental results demonstrate the ability to distinguish symmetric inhomogeneity positions with respect to the central conductor of the coplanar waveguide by the phase of the imbalance signal. The thin-film structure scanning procedure displays the possibility of the proposed approach to resolve low-contrast structures with an accuracy of up to 98.7%.

Microwave characterization of two Ba 0.6Sr 0.4TiO 3 dielectric thin films with out-of-plane and in-plane electrode structures

Ferroelectric thin films have recently attracted renewed interest in research due to their great potential for designing novel tunable electromagnetic devices such as large intelligent surfaces (LIS). However, the mechanism of how the polar structure in the ferroelectric thin films contributes to the desired tunable performance, especially at the microwave frequency range which is the most widely used frequency range of electromagnetics, has not been illustrated clearly. In this paper, we described several straightforward and cost-effective methods to fabricate and characterize Ba_0.6Sr_0.4TiO₃ (BST) thin films at microwave frequencies. The prepared BST thin films here exhibit homogenous structures and great tunability in a wide frequency and temperature range when the applied field is in the out-of-plane direction. The high tunability can be attributed to the high concentration of polar nanoclusters. Their response to the applied DC field was directly visualized using a novel non-destructive near field scanning microwave microscope (NSMM) technique. Our results have provided some intriguing insight into the application of ferroelectric thin films for future programmable high-frequency devices and systems.

Magneto-electric effects in coaxial nanofibers of hexagonal ferrites and ferroelectrics

We report on magneto-electric (ME) effects in core-shell nanofibers of hexagonal ferrites and ferroelectrics synthesized by electrospinning. The core-shell structure in annealed fibers of M, Y, and W-type hexagonal ferrites and PZT was confirmed by electron and scanning microwave microscopy. Fibers showed ferroelectric polarization and magnetization smaller than for bulk samples. The ME coupling strength was measured by magnetic field H induced polarization and ME voltage coefficient (MEVC). In SrM-PZT fibers the remnant polarization decreased by as much as 20% with the application of H. The highest MEVC was measured for magnetic field assembled films of SrM–PZT fibers.

An approach of flow velocity measurement on microfluidic chip by near-field scanning microwave microscopy

A novel approach for flow velocity measurements on a microfluidic chip using near-field scanning microwave microscopy (NSMM) is proposed. It does not require the tested sample to contain visible particles, as the intrinsic electromagnetic properties of the fluid can be detected. Compared with conventional flowmetry, NSMM can measure flow velocity of the tested specimen without any invasive detectors inside or in contact with the specimen, and it can preserve original characteristics of the sample. The flow velocity of different types of solutions is obtained in point scanning, and flow velocity distribution in a microfluidic channel is illustrated in line scanning of NSMM measurement. The flow velocity distribution in microfluidic channel demonstrates distinctive differences between flow velocities of adjacent points, and the microfluidic channel is recognized with a lateral resolution of 10 μm. This approach can help optimize localized flow velocity measurement in drug screening and chemical reaction, and it can be developed for 2D/3D flow velocity imaging in chemical industry and biomedical field.

Physics-Assisted Learning Scheme for Quantitative Imaging via Near-Field Scanning Microwave Microscopy

Quantitative determination of the dielectric property is important to the analysis and evaluation of the investigated samples’ performance. This article proposes a physics-assisted learning scheme (PALS) for the quantitative imaging via the near-field scanning microwave microscopy (NFSMM) in a nondestructive way. To avoid using the machine learning in a black-box way, an efficient input generation is realized by utilizing the Rayleigh approximation method. Numerical and experimental examples demonstrate that the PALS recovers the dielectric parameters of the subsurface perturbation more accurately and shows a better generalization ability. The proposed learning scheme provides a reasonable way to combine the machine learning with underlying physics in the NFSMM, rather than utilizing machine learning in a black-box way. The same principle is also potential to be applied in other types of scanning microscopies, such as optical and thermal ones.

Near-Field Microwave Microscopy for 3D Surface Assessment of Manufactured Structures

Using near-field scanning microwave microscopy as a contact and non-contacting investigative tool for 3D surface metrology with three differing measurement modes, it has been possible to analyse structures that may be difficult for existing metrology systems. The system utilizes the small change in capacitance between a coaxial resonant probe (at around 2 GHz) ending in an open circuit tip, and the sample surface. This is measured in the frequency domain by the shift in the resonance frequency of the voltage transmission coefficient |S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sub> |. It is also possible to investigate various materials (metallics, plastics etc.) owing to their differing dielectric properties. The probe has been tested on a computer-controlled 3D stage but is suitable for incorporation into a commercial co-ordinate measurement machine (CMM) to enhance its capability to inspect the inside surfaces of structures, e.g., threads in small bores.

Imaging microwave field of chip surfaces based on scanning microwave microscopy

With the rapid development of semiconductor chip circuit integration and miniaturization, especially the high integration of microwave chips, it has become critical to realize the surface microwave field imaging for such chips. In this paper, a new method of microwave field imaging for chip surface is proposed based on scanning probe microscopy. We analyse the echo signal and extract the peak-to-peak values to characterize the microwave field intensity on the chip surface by building a theoretical model of the microwave signal coupling. Using a high-precision scanning stage based on a piezoelectric ceramic tube, we realize the imaging of microwave field. The experimental results show that the imaging method can complete the chip surface microwave field imaging, which is important to support the optimization of semiconductor chip manufacturing process, fault analysis and new material research, and promote the development and progress of the semiconductor industry.

Design of low loss at high frequency and integrated scanning microwave probe gripper

We have designed a gripper for scanning microwave microscopy (SMM) based on atomic force microscopy, which is optimized for impedance-matching structures and high-frequency microwave loss. The gripper is simple in construction and highly integrated. The return loss near the target operating frequency of 20 GHz is less than −30 dB. The minimum detected power reach −40 dBm with the order of nW. The microwave scanning image of the sample surface structure was experimentally tested, showing that the gripper can be applied to microwave scanning imaging. The research results have contributed to the development of SMM.

High-Resolution Detection of Microwave Fields on Chip Surfaces Based on Scanning Microwave Microscopy

With the development of microwave chips toward high integration, new challenges have been posed to high-precision microwave field test techniques. In this article, we propose a chip surface microwave field characterization method and design a corresponding microwave power measurement system based on a scanning probe imaging system and microwave test technology. The minimum detected microwave power of the system is better than 1 nW by experimental verification. The proposed method can be applied to image the distribution of the microwave field of the chip and it is helpful to optimize chip design and performance in the future.

Analytical expressions for spreading resistance in lossy media and their application to the calibration of scanning microwave microscopy.

This paper presents the analytical derivation of spreading resistance expressions for diverse geometries of a conducting probe submerged in a lossy medium. Resulting equations can be used to calibrate scanning impedance/scanning microwave microscopes operating in liquid. The expressions are systematically validated through numerical and experimental methods for the calibration of an inverted Scanning Microwave Microscope (iSMM) when operating in a lossy saline medium, such as Dulbecco's Modified Eagle Medium (DMEM), a widely used medium for supporting the growth of biological cells. The calibration process within DMEM plays an important role in the quantitative local evaluation of electromagnetic properties of biological samples under physiological conditions. Additionally, measurements are performed in distilled water for comparative analysis.

Nanoscale electrochemical charge transfer kinetics investigated by electrochemical scanning microwave microscopy.

We show how microwave microscopy can be used to probe local charge transfer reactions with unprecedented sensitivity, visualizing surface reactions with only a few hundred molecules involved. While microwaves are too fast under classical conditions to interact and sense electrochemical processes, this is different at the nanoscale, where our heterodyne microwave sensing method allows for highly sensitive local cyclic voltammetry (LCV) and local electrochemical impedance spectroscopy (LEIS). LCV and LEIS allow for precise measurement of the localized charge transfer kinetics, as illustrated in this study for a ferrocene self-assembled monolayer immersed in an electrolyte. The theoretical analysis presented here enables a consistent mapping of the faradaic kinetics and the parasitic contributions (nonfaradaic) to be spectrally resolved and subtracted. In particular, this methodology reveals an undistorted assessment of accessible redox site density of states associated with faradaic capacitance, fractional surface coverage and electron transfer kinetics at the nanoscale. The developed methodology opens a new perspective on comprehending electrochemical reactivity at the nanoscale.

Nanoscale Characterization of Graphene Oxide-Based Epoxy Nanocomposite Using Inverted Scanning Microwave Microscopy.

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.

Learning-Based Subsurface Quantitative Imaging via Near-Field Scanning Microwave Microscopy

Accurate characterization of sample dielectric property is essential for scientists and engineers to analyze and evaluate the performance of the invested sample. This article proposes a learning-based (LB) method for quantitative subsurface imaging via coaxial-resonator-based near-field scanning microwave microscopy (CR-NFSMM) in a nondestructive way. To efficiently generate the database, a well-designed forward solver is critical since many samples will be included in the database, each sample needs a scanning procedure, and each scanning point involves solving the forward problem once. A fast forward problem solver is used to evaluate the tip–sample interaction in CR-NFSMM that avoids repeated meshing during the scanning process and it can apply to an arbitrary tip shape. Once the neural network is trained, it generates the reconstructed image within 1 s. Numerical and experimental results show that the proposed LB method could improve the resolution of the image and recover the dielectric properties of the subsurface perturbation pixel-by-pixel. Moreover, the proposed method outperforms the traditional objective function approach in terms of image resolution and time cost. The proposed method is promising to realize a nondestructive and real-time local dielectric evaluation of the subsurface object.

Advanced Investigation of the Electrolyte-Mg Anode Interphase for the Development of Mg-Ion Batteries

Magnesium-ion batteries (MIBs) represent a promising chemistry to potentially substitute lithium-ion technologies in the e-mobility and stationary energy storage applications. This is due to the favourable properties of metallic Mg, such as: abundancy, non-toxic nature, high recycling rate1, low redox potential (-2.37 vs SHE), safety (smooth Mg2+ electrodeposition), as well as divalent character of Mg2+ cations which leads to higher theoretical volumetric capacity (3833 mAh/cm3) than Li (2046 mAh/cm3) and commercial graphite (760 mAh/cm3).2 However, the major obstacle in the further development of MIBs is the incompatibility of Mg metal anode with conventional electrolyte solutions, which are formed by mixing simple Mg-based salts (e.g Mg(TFSI)2, Mg(ClO4)2, etc.) and polar aprotic solvents (e.g. acetonitrile, carbonates, etc.). These solutions decompose at the surface of metallic Mg forming an electronic and ionic insulating layer, leading to the passivation of the Mg anode and poor performance of the overall cell. Conversely, organoborate (Mg-tetrakis(hexafluorosisopropyloxy)borate in monoglyme, MgBOR)3 or organoaluminate (1:2 AlCl3:PhMgCl in THF, APC)4 ethereal solutions are known to prevent the passivation of the Mg metal anode, allowing the reversible electrochemical Mg2+ electrodeposition onto its surface.Despite a great effort has been done in the development of MIB,5 very little is known about the formation, evolution and degradation of the solid electrolyte interphase (SEI) formed at the interface between metallic Mg and electrolyte. This work, therefore, aims to investigate the interactions between Mg metal and passivating (Mg(TFSI)2 in monoglyme:diglyme) and non-passivating (MgBOR and APC) electrolytes combining ex-situ and in-situ spectroscopic and microscopic techniques with electrochemical testing. The properties of the SEIs will be evaluated at different states of charge (ex-situ) and during cell cycling (in-situ).Raman, Fourier transformed infrared (FTIR) and X-ray photoelectron (XPS) spectroscopies are used to identify the composition of the electrolyte interphases, as well as monitor their changes upon cell discharge-charge cycles. Scanning electron microscopy (SEM) is performed to analyse the interphase morphologies, whereas scanning microwave microscopy (SMM)6,7 locally probes the impedance of the SEI layer. Atomic force microscopy (AFM) is also employed to evaluate the roughness of the Mg metal electrodes. Cyclic voltammetry (CV) and galvanostatic cycling with potential limitation (GCPL) are carried out in order to determine the electrochemical performance of bare Mg metal or covered with SEI layers. Furthermore, electrochemical impedance spectroscopy (EIS) is employed to probe the Mg2+ diffusion coefficients through the SEI layers at different state of charge (e.g. open circuit voltage, etc.) and determine charge transfer evolution with cycling time of the Mg metal anode.As the first step, a successful polishing method was developed to remove the native oxide layer form the surface of Mg discs allowing to expose a bare Mg metal to the electrolyte solutions and to evaluate their interactions. The polishing method also enabled to perform SMM imaging of the Mg metal since a roughness between 1-2.5 µm was achieved. The Mg discs were then immersed in the electrolyte solutions and an initial deposition of interfacial species (few nanometre thickness) was observed by SEM when Mg(TFSI)2 in monoglyme:diglyme was used, whereas a smooth surface was detected with MgBOR and APC electrolytes. This resulted in different electrochemical behaviours. In fact, symmetric cells (Mg||Mg) with MgBOR electrolyte showed a significantly higher cycling stability (> 250 h) than those with Mg(TFSI)2 in monoglyme:diglyme solution. In addition, when the latter electrolyte was used, fluorinated by-products were identified by XPS. In order to study the SEI formation and growth further, in-situ spectroscopic techniques (e.g. Raman and SMM) were employed to establish a correlation between the chemical composition of the electrolyte, the voltage range of the electrochemical tests and cycling time. In particular, the SMM method was applied to MIB technologies for the first time in this work. References I. R. P. United Nations Environment Programme, (available at https://wedocs.unep.org/20.500.11822/8702);J. Niu, Z. Zhang, D. Aurbach, Adv. Energy Mater., 2020, 10, 2000697;Z. Zhao-Karger, M. E. Gil Bardaji, O. Fuhr, M. Fichtner, J. Mater. Chem. A, 2017, 5, 10815–10820;D. Aurbach, Z. Lu, A. Schechter, Y. Gofer, H. Gizbar, R. Turgeman, Y. Cohen, M. Moshkovich, E. Levi, Nature, 2000, 407, 724;R. Dominko, J. Bitenc, R. Berthelot, M. Gauthier, G. Pagot, V. Di Noto, J. Power Sources, 2020, 478, 229027;A. Buchter, J. Hoffmann, A. Delvallée, E. Brinciotti, D. Hapiuk, C. Licitra, K. Louarn, A. Arnoult, G. Almuneau, F. Piquemal, M. Zeier, F. Kienberger, Rev. Sci. Instrum., 2018, 89, 23704;J. Hoffmann, M. Wollensack, M. Zeier, J. Niegemann, H. Huber, F. Kienberger, in 2012 12th IEEE International Conference on Nanotechnology (IEEE-NANO), pp. 1–4.

(Invited) Towards the Physical Reliability of 3D-Integrated Systems: Broadband Dielectric Spectroscopic (BDS) Studies of Material Evolution and Reliability in Integrated Systems

In this talk, we present an overview of our current research focus in developing non-destructive metrology for monitoring reliability issues in 3D-integrated electronic systems. Working closely with the semiconductor industry, we have been looking at various performance limiting phenomena in 3D-interconnects, the associated dielectrics, and advanced packaging for integrated circuits.The talk will identify some common reliability concerns, and identify some metrology gaps, for 3-D integrated systems. We will introduce a suite of microwave-based Broadband Dielectric Spectroscopic (BDS) techniques and show how these non-destructive metrologies can serve as early warning monitors for reliability issues. These techniques are based on the application of high frequency microwaves, to probe impedance changes due to material and structural changes in integrated circuits under various external stress. For example, we will also discuss the combination of BDS with scanning probe infrastructure to create the Scanning Microwave Microscopy (SMM) technique, which has been used to detect buried artifacts and characterize metallic contacts. We further illustrate the capabilities of the BDS-based techniques with case studies of three potential reliability issues in 3D IC.We conclude with a forward look at the future metrology and standards needs 3-D interconnects and the associated advanced packaging.