The variation of their crystallinity, in other words, the order of atom arrangement of grain boundaries in electroplated gold thin films was investigated by changing their manufacturing conditions. Then, the effect of the crystallinity on both their mechanical and electrical properties was measured by using nano-indentation test and electromigration test. The crystallinity of the gold thin films was varied by changing the under-layer material used for electroplating. Also, the micro texture of gold thin films was evaluated by EBSD (Electron Back-Scatter Diffraction) and XRD (X-Ray Diffraction). It was clarified that the crystallinity of the electroplated gold thin films changed drastically depending on the crystallinity of the under-layer materials and electroplating conditions such as current density and temperature. This variation of the crystallinity should have caused wide variation of mechanical properties of the films. In addition, their mechanical properties such as Young’s modulus and hardness showed wide variation by about 3 times comparing with those of bulk gold. Similarly, the EM resistance of the electroplated gold bumps varied drastically depending on the ratio of porous grain boundaries and their crystallinity. Both the ratio and crystallinity also varied depending on the crystallinity of the under layer and electroplating conditions. The effective lifetime of the gold bumps was successfully predicted by considering both the crystallinity and residual stress of fine gold bumps. The lifetime varied more than 10 times as a strong function of the crystallinity of grain boundaries in the fine bumps. Therefore, it is very important to control the crystallinity of the under-layer for electroplating in order to control the distribution of the mechanical properties and reliability of the electroplated gold thin films.

Graphene shows unique super-conductive properties and graphene nanoribbons (GNRs) with band gaps are the candidates for a sensing component of highly sensitive strain sensors. Usually, there is a large energy barrier between electrodes and semiconductors which is not suitable for electron transfer. Therefore, ohmic contact between them is indispensable for fabricating electronic applications. In order to achieve the ohmic contact between external electrodes and detective elements in the devices, the dumbbell-shaped structure of GNRs was proposed for the basic structure of the GNR-based strain sensors, dubbed as dumbbell-shape GNR (DS-GNR). It consists of a long narrow GNR at the center of the structure as the sensing element coalesced with two wider GNRs at both ends of the narrow GNR as the contact components to external electrodes. Both narrow and wide segments of DS-GNR consist of only carbon atoms. The effect of the interaction in the vicinity of the junction area between wide metallic and narrow semiconductive GNRs, however, has not been clearly demonstrated. In this study, first-principles calculations were implemented to the analysis of the electronic band structure of the DS-GNR. It was found that the localized distribution of the energy states of electrons exists in the wide segment of DS-GNR. The changes varied from wide to narrow segment is smooth and observable as strong functions of the length and the width of DS-GNRs. The current-voltage characteristics showed curved semiconductive-like electronic properties with a smooth-electron flow in DS-GNR. Therefore, the DS-GNR has great potential for the use of next-generation highly sensitive and deformable strain sensors.

Electroplated copper thin films often contain porous grain boundaries and the volume ratio of porous grain boundaries in the copper thin films is much larger than that in bulk copper. Thus, the lifetime of the interconnection components fabricated by electroplating is strongly dominated by the strength of grain boundaries because final fracture caused by the acceleration of atomic diffusion during electromigration (EM) occurs at grain boundaries in polycrystalline interconnections. It is important, therefore, to quantitatively evaluate the grain boundary strength of electroplated copper films for estimating the lifetime of the interconnection in order to assure the product reliability. In this study, relationship between the strength and crystallinity of electroplated copper thin films was investigated experimentally and theoretically. In order to investigate the relationship between the strength and grain boundary quality, molecular dynamics (MD) simulations were applied to analyze the deformation behavior of a bicrystal sample and its strength. The variation of the strength and deformation property were attributed to the higher defect density around grain boundaries.

This paper presents a radio frequency (RF) energy harvesting (RFEH) system with a multiband antenna configuration that can simultaneously harvest energy from the sub-6 GHz and 5G millimeter-wave (mm-Wave) frequency bands. The performance of the RFEH system is studied from −25 dBm to 5 dBm input power levels underlying the maximization of the overall efficiency and possible optimization strategies. The maximum achievable power conversion efficiency (PCE) is formulated as a mathematical programming problem and solved by optimizing the design factors including antenna geometry, operational frequencies, rectifier topologies, and rectifier parameters. An array of broadband high gain patch antennas with reconfigurable rectifiers, an impedance matching network, and a voltage-multiplier circuit are employed in the system to maximize the PCE. The voltage standing wave ratio (VSWR) and reflection coefficient (S 11 ) of the antenna are estimated and optimized by numerical method. Simulations are conducted to evaluate the performances of the rectenna and the voltage-multiplier circuit. Results for radiation pattern, wave absorption, input impedance, voltage, and power across the load resistance as a function of frequency are obtained for the optimized configuration. The overall efficiency of the optimized RFEH system is measured at various power inputs and load resistances.

Deep Neural Networks (DNNs) have transformed various fields, yet their application in design of microsystem has been limited. Here, we demonstrate a framework for application of adversarial generative networks in design of microresonators targeting for operation in MHz frequencies. The topology of the microresonators are constrained based on the critical dimension common in the photolithography process. The design-space includes a free standing window of Si film on an SOI wafer that is supported on its four sides. The film is etched through a mask with an arbitrary 2D layout. We employ DNNs in finding 2D layouts that result in a membrane with desirable natural frequencies. For this purpose, deep generative networks (generators) and deep neural networks (discriminators) are employed. Two datasets representing desirable and undesirable layouts are created using finite element analysis. Subsequently, the discriminator is trained to classify desirable and undesirable layouts as well as those generated by the generator. Simultaneously, the generator is trained to sample layouts that are more likely to be classified as desirable by the discriminator. The results show that this framework is capable of producing designs with desirable vibrational features, encouraging further research in this topic.

This paper presents an innovative system to monitor the physical soil conditions needed for modern agriculture. The current technique to measure soil properties relies on taking samples from place to place and takes them for laboratory testing. To build up and monitor a data-based system for a large area, such a method is costly and time-consuming. This paper reported our recent work on the development of a passive impedance-loaded surface acoustic wave (SAW) sensor for a low-cost soil condition monitoring system. The SAW sensor will eventually be connected to an antenna and a impedance-based sensor for autonomous soil nutrient sensing. In this research, first, the coupling-of-modes (COM) analysis was performed to simulate the SAW device. The sensors were fabricated with E-beam lithography techniques and tested with different external load resistances. We investigated how the sensor signal changed with the external resistance loading. The experimental results were verified by comparing them with simulation results.

Magnetic assembly of micro/nano materials are of great interest due to their unique properties. These nano-scale materials can be ensemble with other matrixes to prepare for new functional micro/nano composites with enhanced specific properties such as, thermal conductivity. In this study, we demonstrated the distribution and magnetic alignment of nickel (Ni) nanoparticle/nanowires inside of a non-magnetic matrix, (e.g., water or a molten wax), experimentally and computationally. A two-dimensional Monte Carlo simulation model is employed to investigate the aggregate structures of Ni nanoparticle/nanowires subjected to a one-directional static magnetic field. It is anticipated that the applied magnetic strength will influence the attractive forces between nanoparticle/nanowires that will produce chain-like cluster structures parallel to magnetic direction where the aligned chains will be separated by a range of distances that are also function of magnetic field strength.

In dielectrophoresis, a neutral particle experiences a partial charge separation, i.e. induced net dipole moment, when exposed to a non-uniform electric field, and this leads translational movement of the particle. This induced attractive or repulsive motion of the particle suspended in a fluid is known as dielectrophoresis (DEP). In this paper, we have characterized the strength of DEP traps depending on geometry. Three different micro-trap geometries, i.e. triangle, square and circle, were tested to characterize the effect of trap shape on trap stiffness experimentally and numerically using single particle immobilized in the trap. The maximum DEP force generated in triangular μ-trap was found largest among tested geometries. The maximum DEP force of square and circular trap was found around 68.4% and 79.1% of triangular μ-trap, respectively. The trajectory analysis using trapped single particle revealed that the stiffness of circular μ-trap is 1.23 and 1.34 times stronger than the triangular and square μ-trap, respectively. These results will provide useful information in DEP trap geometry designing to enhance trapping efficiency.

Chinese hamster ovary (CHO) cell is the most widely used mammalian cell line for commercial production of therapeutic protein. Any presence of non-viable cells in culture medium may adversely affect subsequent functionality of these proteins. Therefore, separation of non-viable cells from suspending medium is critical in biopharmaceutical and biomedical sectors. One such method termed Deterministic Lateral Displacement has already shown promising capabilities in separating cells based on the cell size difference by taking advantage of the predictable flow laminae. However, in cases where size overlaps between viable and non-viable cells are present, separation based solely on size suffers and high-resolution separation techniques are required. Dielectrophoresis, one of the most widely used nonlinear electro-kinetic mechanism, has the potential to manipulate the same size cells depending on the dielectric properties of individual cells. In this work, we demonstrated that a DLD device can be combined with a frequency-based AC electric field to perform high resolution continuous separation of non-viable CHO cells from the viable or productive cells. The behavior of the coupled DLD-DEP device is further investigated by employing numerical simulation to check the effect of geometrical parameters of the DLD arrays, velocities of the flow field and required applied voltages. A moderate row shift fraction with velocity 700μm/s provided a good separation behavior without any trapping. The cell viability was also ensured by maintaining proper electric field which otherwise may cause cell loss due to ion leakage. Our developed numerical model and presented results lay the groundwork for design and fabrication of high resolution DLD-DEP microchips for enhanced separation of viable and nonviable cells.

To increase the production of crops, chemical fertilizers are used in crop fields. However, underuse or overuse cannot increase crop yields but even decrease them and cause severe environmental problems. Thus, the detection and monitoring of chemical concentration are increasingly important. To build up and monitor a data-based system for a large area, such a method is costly and time-consuming. In this research, we developed a conductive polymer-based sensor to detect nitrate concentrations in soil water. Conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) was used as our sensing material. To increase its conductivity, we used the vacuum phase polymerization method to achieve a high conductive and stable polymer film. The conductivity of the polymer film is 500 S/cm. Our results have demonstrated that the conductive polymer-based sensors have high sensitivity to nitrate solution. The response to 1000 ppm nitrate solution is 47.2% (Response = (I nitrate - I DIwate ) / I DIwater ). The sensors can detect nitrate range from 1ppm to 1000 ppm. The response time is less than 1 minute. This impedance-based sensor will eventually be integrated with the surface acoustic wave sensors, combined with an antenna and a GPR unit for low maintenance, autonomous, and in-situ soil nutrient sensing.

Circulating Tumor Cells (CTCs), which migrate from original sites in a body to distant organs through blood, are a key factor in cancer detection. Emerging Label-free techniques owing to their inherent advantage to preserve characteristics of sorted cells and low consumption of samples can be promising to the prediction of cancer progression and metastasis research. Deterministic Lateral Displacement (DLD) is one of the label-free separation techniques employing a specific arrangement of micro-posts for continuous separation of suspended cells in a buffer based on the size of cells. Separation based solely on size is challenging since the size distributions of CTCs might overlap with those of normal blood cells. To address this problem, DLD can be combined with dielectrophoresis (DEP) technique which is the phenomenon of particle movement in a non-uniform electric field owing to the polarization effect. Although, DLD devices employ the laminar flow in low Reynolds number (Re) fluid flow due to predictability of such flow regimes, they should be improved to work in higher Re flow regime so as to attain high throughput devices. In this paper, a particle tracing simulation is developed to study the effects of different post shapes, shift fraction of micropost arrays, and dielectrophoresis forces on separation of CTCs from peripheral blood cells. Our numerical model and results provide a groundwork for design and fabrication of high-throughput DLD-DEP devices for improvement of CTC separation.

Adhesives, medical devices, and many cleaning products depend on the wetting of liquids on solid surfaces. The liquid/solid interaction depends on chemistry, surface topology, and external energy input. For instance, surfactants are commonly used in cleaning solutions to improve their effectiveness, and electrical fields are frequently used to control the contact angle of liquid droplets. Low frequency vibration has been used to spread, move, and manipulate droplets using the mode shape oscillations of the droplet to displace the contact line. Ultrasonic vibration (above 20 kHz) can also cause a liquid droplet to wet or spread out on a solid surface under the right circumstances. We have previously demonstrated that ultrasonic vibration can be used to control the wetting/spreading of liquid droplets on smooth hydrophobic surfaces and that the response is relatively insensitive to excitation frequency or fluid properties [1]. This paper reports on the use of ultrasonic vibration to initiate spreading on surfaces with etched pillars. Ultrasonic vibration successfully initiated a transition from Cassie to Wenzel states in all geometries with no apparent need to tune excitation frequencies to the geometry. However, the magnitude of the acceleration required to initiate the transition decreased with increased pillar spacing. For small pillar spacing, some smooth spreading in the Cassie wetting mode was observed before transition.

It is highly desired to develop an inexpensive, wireless embedded sensor system that can provide high-bandwidth measurements of temperature and pressure inside a pipeline for rocket propulsion test applications. The fuel is generally liquid hydrogen and liquid oxygen, which must be kept at cryogenic temperatures. The environment places additional requirements on the design of sensors that is beyond the scope of most available products. Surface acoustic wave (SAW) technology has received considerable attention for harsh environment applications. The ultimate goal of our research is to develop a SAW sensor system for temperature and pressure sensing in the cryogenic environment. In this paper, the temperature testing of the SAW sensor was finished from 30 to 80°C. The strain testing was performed at room temperature. The results have shown that the temperature coefficient of the delay (TCD) at the room temperature is around 74.4 ppm/°C. The Strain coefficient of delay (SCD) of the testing result is 0.38 ppm/με at room temperature.

Deterministic Lateral Displacement (DLD) is an inertial size-based particle separation technique with great possibilities for use with biological sample preparation. Recently it has been shown that particle shift of a DLD is highly dependent on the Reynolds number. Additionally, particle trajectory has been characterized in a high throughput airfoil array DLD with varying Angle of Attack (AoA) in Deionized water. The AoA can be shifted negatively assisting in particle trajectory increases at low Reynolds numbers. With variations in fluid viscosity, particle trajectories compared to Reynolds value should theoretically have a constant and similar slope. In this work, various viscosities are tested in a DLD with a neutral and negative AoA to eventually characterize non-Newtonian fluids within a DLD. Due to higher viscosities increasing the internal pressure of the device, the negative AoA DLD shows promising results at higher range viscosities due to its ability to shift particles at lower Reynolds numbers.

Microfluidics has shown great promise for the sorting or separation of biological cells such as circulating tumor cells since the first studies came out a few decades ago. With recent advances in high-throughput microfluidics, analysis of massive amounts of data needs to be completed in an iterative, timely manner. However, the majority of analysis is either performed manually or through the use of superimposing multiple images to define the flow of the particles, taking a significant amount of time to complete. The objective of the work is to increase the efficiency and repeatability of particle detection in a high-throughput deterministic lateral displacement (DLD) device. The program proposed is in the early stages of development, but shows promise. The average time it takes to analyze over a gigabyte of video is 24.21 seconds. The average percent error of the total particle detection was 21.42%. The assumptions made for the initial version of the program affect the accuracy of the particle in wall detection, so new techniques that do not follow the assumptions will need to be investigated. More work will be completed to implement machine learning or deep learning to assist in the development of DLD devices.

High Q-Factor vibrational energy harvesters are ideal as they maximize power generation, but a narrow bandwidth limits the potential use in most commercial applications, and it is a major challenge that has not been resolved. Numerous designs have been investigated to solve this challenge but most of the attempts are based on frequency sweeping mechanism or require complex design/fabrication which are not practical especially for MEMS devices. This paper reports for the first time a transverse vertical moving mass inside the proof mass as a method to widen the bandwidth which is independent of frequency sweeping. The out-of-plane movable mass is achieved by fabricating a vertical cavity in the proof mass and partially filling the cavity with metallic spheres. Ultra-wide bandwidth was achieved for low (0.5g) and high (1g) accelerations with an increase in bandwidth from 3.9 Hz (control) to 56 Hz (movable mass). This transverse method of widening the bandwidth is potentially scalable to MEMS devices.

The above referenced paper has been removed from publication. (March 11, 2020) Copyright © 2020 by ASME

This paper presents the innovative integration of both frontier submillimeter magnetic microrobot and integrated ultrasound and photoacoustic (USPA) imaging. The integrative technique will allow for potential real non-invasive microrobot operation in deep biological tissue for biomedical applications. In this study, the magnetic microrobot prototypes are fabricated in series of different sizes through patterning SU-8 photoresist mixed with nickel particles. In order for proof-of-concept, the magnetic microrobot is actuated by a static magnetic field, which is produced by a multiple magnet cone array. As mimicking the opaque biological environment, the magnetic microrobot is placed in a fluid environment bounded by a non-transparent phantom. The USPA imaging system consists of a laser system to illuminate working space and an ultrasound system to receive the acoustic signal generated by imaging object due to photonic signal absorption. The experimental tests prove that the USPA imaging protocol can detect single microrobot smaller than 100 μm through the 15 mm thick opaque phantom. The imaging test has been accomplished both statically and in a motion of approximately 2.0 mm/s. Further investigation of this concept will focus on the collaboration of photoacoustic imaging and magnetic manipulation of microrobot under real biological fluid media.

Surface acoustic wave (SAW) devices have been applied as telecommunication filter for decades. Due to its simple interdigitated transducer (IDT) layout and geometry-dependent frequency, the SAW filter operates at the designed frequency and its working bandwidth could be designed to fulfill specific applications. Researchers also use SAW devices for sensing the mass or pressure in air. Furthermore, SAW device can be employed in liquid environments. The main focus of this paper is to present a Love mode device for liquid sensing. The Love mode device included a shear-horizontal surface acoustic wave (SH-SAW) delay-line configuration with a photoresist waveguide, which was deposited on split-electrode IDT and reflectors. The substrate was ST-cut quartz, and the SH-SAW propagated between the waveguide and the piezoelectric substrate. Using the Love mode device, we monitored the frequency shift corresponding to a water drop. We demonstrate that the insertion loss level is not critical for S-parameter transmission signal readout. The signal quality within the resonant narrowband is very important for water sensing. In this study, two types of SH-SAW devices were fabricated and tested; SH-SAW resonator and SH-SAW delay-line. We also demonstrate single and split electrodes electrode configurations to generate acoustic waves. Four different waveguide thickness values were tested to prove the benefit of thick polymer waveguide. This research also offers a standard method to fabricate SAW on ST-quartz for liquid application. In the future, we plan to integrate the Love mode device with a cell-culturing chamber to obtain a biosensor.

Power semiconductors and modules are basic components of electrical infrastructure and are currently widely used in applications such as power conversion devices, industrial equipment, railways, and automobiles. Power modules are being developed with the aim of downsizing and increasing power output. With the larger current densities and higher operating temperatures associated with downsizing and increasing power output, degradation of power modules can occur as a result of electromigration. Electromigration is a phenomenon where atoms move due to the momentum transfer between conducting electrons and metal atoms. In addition, atoms are also moved by mechanical stress gradients and temperature gradients, so it is necessary to take into consideration the combined effects of electrical, thermal, and mechanical stress. In this report, we describe an electrical-thermal-mechanical coupled analysis of electromigration in a bonding wire of a power module. First, the analysis is validated under the condition that the displacement of the wire surface is fixed. The distributions of vacancy concentrations and hydrostatic stress are almost equal to those in previous studies. Next, we present the influences of current density, temperature, and the displacement constraint on electromigration in a wire with a simplified shape. The analysis results confirm that the plasticity and creep should be taken into consideration in a bonding wire. This also confirm that vacancy concentration increase more rapidly by changing the displacement of the wire surface from the fixed condition to the free condition. Finally, we present analysis results for a bonding wire with the actual shape found in power modules. In this wire, a local concentration peak appear in the electrode terminal. The analysis results reveal that electromigration may affect not only void formation but also other failure phenomena in the bonding wire of power modules.