Gold Electroplating Research Articles

Temperature Effects in Packaged RF MEMS Switches with Optimized Gold Electroplating Process.

Due to its excellent electrical performance, mechanical reliability, and thermal stability, electroplated gold is still the most commonly used material for movable beams in RF MEMS switches. This paper investigates the influence of process conditions on the quality and growth rate of gold electroplating, and the optimized process parameters for the gold electroplating process are obtained. The characterization of the optimized electroplated gold layer shows that it has small surface roughness and excellent thermal stability. With this optimized gold electroplating process, the RF MEMS switches are fabricated and hermetic packaged. In order to obtain the temperature environment adaptability of the packaged switch, the influence of working temperature is studied. The temperature effects on mechanical performance (includes pull-in voltage and lifetime) and RF performance (includes insertion loss and isolation) are revealed.

Enhancing the quality factor of aerosol jet printed RF spiral inductors through gold electroplating

Aerosol jet printing (AJP) outperforms inkjet printing by significantly reducing printed line width, effectively addressing issues such as bulging and surface irregularities. This technology allows for line widths as narrow as 10–100 μm with high aspect ratios, making it well-suited for radio frequency (RF) applications. Consequently, AJP emerges as a valuable tool for direct printing in RF applications. Among conductive inks, silver nanoparticle (Ag-NP) ink is preferred for its straightforward direct printing process and lower sintering temperature requirements. However, the conductivity of printed Ag NP traces falls markedly below that of bulk silver due to significant porosity, limiting its use in RF applications where a high-quality factor is essential. The quality factor of an inductor, indicative of its efficiency in energy storage and release, inversely correlates with its resistance. Our research combines AJP with selective electroplating to reduce the resistance of printed traces, thereby enhancing the inductor’s quality factor for RF applications. We fabricated spiral inductors on alumina substrates using silver NP ink and subsequently applied selective gold electroplating to these traces. This approach led to a significant increase in the inductors’ quality factor, improving it by a factor of 3–5 in the RF frequency range of 100–700 MHz.

Electrochemical detection of myeloperoxidase (MPO) in blood plasma with surface-modified electroless nickel immersion gold (ENIG) printed circuit board (PCB) electrodes

Printed circuit board (PCB) based biosensors have often utilized hard gold electroplating, that nullifies the cost advantages of this technology as compared to screen printed electrodes. Electroless nickel immersion gold (ENIG) is a popular gold deposition process widely used in PCB manufacturing, but vulnerable to pinhole defects and large surface roughness, which compromises biosensor performance. In this work, we present a method to address these challenges through electrodeposition of methylene blue (MB) to cover surface defects and improve electroactivity of ENIG PCB electrodes. We also demonstrate a process to realize in situ synthesis of gold nanoparticles (AuNPs) using acid-functionalized multi-walled carbon nanotubes (MWCNTs) as scaffold, that are used to immobilize antibody for the target molecule (myeloperoxidase: MPO, early warning biomarker for cardiovascular diseases) through a modified cysteamine/gluteraldehyde based process. The processing steps on the electrode surface are developed in a manner that do not compromise the integrity of the electrode, resulting in repeatable and reliable performance of the sensors. Further, we demonstrate a cost-effective microfluidic packaging process to integrate a capillary pump driven microfluidic channel on the PCB electrode for seamless introduction of samples for testing. We demonstrate the ability of the sensor to distinguish clinically abnormal concentrations of MPO from normal concentrations through extensive characterization using spiked serum and blood plasma samples, with a limit of detection of 15.79 ng/mL.

Highly Controllable Fabrication of Gold Composite Nanostructures by Multiple Electroplating for High‐Performance Electrochemical and Raman Scattering Measurements

Morphology‐controlled nanostructures are important functional materials in multidisciplinary research fields, such as sensing, imaging, catalysis, and energy harvesting. However, existing nanofabrication methods have limitations in terms of controllability, diversity, cost, and efficiency. Here, a novel nanofabrication approach is proposed to construct Au nanostructures with high controllability, cost‐efficiency, and high‐performance sensing and energy harvesting. The fabrication incorporates electric field‐assisted hydrothermal growth of zinc oxide nanorods (ZnO NRs) with two‐step gold electroplating. The ZnO NRs serve as a dissolvable template during the electroplating formation of gold nanostructures for eventually synthesizing pure gold nanostructures on electrodes. The synthesized gold nanostructures take unique composite shape of nanospheres (hundreds of nanometers) covered with tinier nanostructures (tens of nanometers) like floccules, grains, lamellas, or rods, which are highly controlled by regulating electroplating parameters. The gold composite nanostructures provide high‐performance sensing and energy harvesting, such as enhanced electrochemical sensing interface (electric double‐layer impedance decrease up to 97.1%), excellent surface‐enhanced Raman scattering (SERS enhancement factor up to ), and preferable visible–near‐infrared light harvesting (absorptivity near to 90%). For the first time, the application of tumor cell photothermal therapy with nanostructured electrodes and in situ bimodal monitoring of single‐cell impedance and SERS‐based molecular expression during therapy is demonstrated.

Electroplating on Unconventional Ultra-Compliant Substrates for Travelling Wave Tube Amplifiers

We report gold electroplating on ultra-compliant substrates comprising helical slow wave structures (SWSs) for traveling wave tube amplifiers (TWTAs) [1]. The novel ultra-compliant substrates are composed of edge-tethered tri-layer metal ribbons with a helical geometry of microscale diameter. After electroplating with gold, we obtain overall thicknesses of a few um. We discuss different controllable electroplating conditions that influence thickness, uniformity, roughness, and related properties of deposited gold films on helical ribbons. In addition to increasing conductance of the electroplated helical ribbons, electroplating stabilizes the helix at its equilibrium diameter, with the pitch predicted by Prakash et al.[1].Our method of fabrication of ultra-compliant helical ribbons starts with defining strips of width 5 µm to 10 µm by optical lithography, metal evaporation, and lift-off, deposited on Si substrates coated with a sacrificial layer of Ge or GeOx,. We use Cr/Au/Cr tri-layers to create an inherent stress gradient that causes the strip to self-assemble into a helix, after etching with XeF2 for selective removal of a sacrificial layer. Diameter and pitch of the released helices are controlled by varying the thickness, the elastic modulus, the residual stress, and the in-plane geometry of the deposited tri-layer metal strips. The gold electroplating process uses a sulphate-based gold solution in a two-electrode electrochemical setup with the helix as the cathode and a platinized mesh as the anode [2]. We deposit gold to a thickness of a few um, using a pulsed current source with variable parameters. Direct current can also be used with smaller deposition times. Our results demonstrate the application of electroplating to unconventional ultra-compliant helix of nanoscale dimensions. Reference [1] Divya J. Prakash,., Matthew M. Dwyer, Marcos Martinez Argudo, Mengistie L. Debasu, Hassan Dibaji, Max G. Lagally, Daniel W. van der Weide, and Francesca Cavallo. 2020. “Self-Winding Helices as Slow-Wave Structures for Sub-Millimeter Traveling-Wave Tubes.” ACS Nano, 2021, 15, 1229-1239. doi:10.1021/acsnano.0c08296.[2] Max G. Lagally, Anjali Chaudhary, Daniel van der Weide, Divya J. Prakash, and Francesca Cavallo, Improved Self-assembly of Helices via Electrodeposition on Freestanding Nanoribbons for TWT Application, provisional US patent application (P220249US01)Work supported by U.S. AFOSR-Award No FA9550-22-1-0086.

Mask design, fabrication, and experimental ghost imaging applications for patterned X-ray illumination.

A set of non-configurable transversely-displaced masks has been designed and fabricated to generate high-quality X-ray illumination patterns for use in imaging techniques such as ghost imaging (GI), ghost projection, and speckle tracking. The designs include a range of random binary and orthogonal patterns, fabricated through a combination of photolithography and gold electroplating techniques. We experimentally demonstrated that a single wafer can be used as an illumination mask for GI, employing individual illumination patterns and also a mixture of patterns, using a laboratory X-ray source. The quality of the reconstructed X-ray ghost images has been characterized and evaluated through a range of metrics.

Advanced Biomimetic Nanostructured Microelectrode Arrays for Enhanced Extracellular Recordings of Enteric Neurons

AbstractMicroelectrode surfaces covered with nanostructures derived from components of extracellular matrix, such as collagen fibers, have shown immense beneficial effects in promoting neuronal growth and cellular signaling. Synthetic nanostructures mimicking the features of biological nanostructures with durable conductive materials could promote the cell adhesion on microelectrode surfaces by providing topographical cues and simultaneously improve the charge transfer properties by reducing its global impedance. Therefore, an advanced nanostructuring method mimicking the structural and organizational features of natural collagen fibers onto metallic microelectrode surfaces has been presented here, which is adapted from previous technological achievements of the group and is based on nanoimprint lithography and gold electroplating. Surface characterization methods reveal an increase in surface area between 20% and 68% on the microelectrodes fabricated with two different nanostructure heights. Impedance spectroscopy measurements reveal reduction in impedance magnitude (at 1 kHz) between 22% and 41%, depending upon the nanostructure height and density on the microelectrode, which should subsequently modulate its charge transfer properties for biosensing application. Cell adhesion analysis performed with seal impedance measurements reveals a tighter coupling of enteric neurons on the nanostructured microelectrodes. Finally, extracellular recordings from enteric neurons exhibit a significant improvement in spike detection properties of the nanostructured microelectrodes.

Cleaning of fine tungsten wire before gold electroplating

This paper examines some issues related to the gold plating of fine tungsten wires. The key properties of tungsten are described that determined the choice of that material for manufacturing reflector curtains. Available information sources are considered which recommend cleaning of tungsten wires before electroplating. The paper gives a brief overview of electrolytes used in gold electroplating, as well as achievable gold plating rates. The authors offer a review of literature on existing electrochemical treatment machines for fine metal wires. It is shown that the high-rate cleaning (which only takes a few seconds) of tungsten wire can be more efficient when using alternating or reverse current. Thus, the best performance was achieved when a 50 Hz current was applied at the solution temperature of 60 oC (the solution contained 180 g/l NaOH) and the average current density of 180 A/dm2 for 3–4 sec. A similar cleaning performance was achieved when the same alkaline solution and the same solution temperature were used, but when reverse current was applied at the average density of 20 A/dm2 for 5 sec, with cathodic and anodic pulses having different lengths: 0.2 sec for the anodic one and 0.8 sec for the cathodic one. It was found that the above conditions for pre-treatment and alkaline cleaning of fine tungsten wires are associated with minimal alteration of the mechanical properties of such wires caused by hydrogen pick-up.

Ion trap with gold-plated alumina: Substrate and surface characterization

We describe a complete development process of a segmented-blade linear ion trap. An alumina substrate is characterized with an x-ray diffraction and loss-tangent measurement. The blade is laser-micromachined and polished, followed by sputtering and gold electroplating. Surface roughness is examined at each step of the fabrication via both electron and optical microscopies. On the gold-plated facet, we obtain a height deviation of tens of nanometers in the vicinity of the ion position. Trapping of laser-cooled 174Yb+ ions is demonstrated.

A tassel-type multilayer flexible probe for invasive neural recording

Invasive neural probes are one of the most critical components in the intracortical neural signal recording system. However, they can cause brain damage and tissue response during and after implantation. Thus, neural probes with high flexibility, biocompatibility, and simple implantation methods are required in brain research. Here we present a novel approach to fabricating a multilayer flexible tassel-type neural probe using low-cost maskless laser direct-write lithography, combined with straightforward release and assembly methods to prepare a whole implantation system. The probe has 32 recording electrodes with an area of 8 × 8 µm2, arranged into two rows of different depths and 16 separated shanks, aiming at the neural signal recording in an extensive range. Polyimide and gold are used as the insulating and conductive layers, respectively. With the help of a polyethylene glycol (PEG) coating, the tassel structure was mechanically enhanced for successful implantation, and our morphology characterization showed that the diameter of the coated probe was less than 50 µm. Mechanical property tests also proved that it had the necessary stiffness for brain implantation. Afterwards, electrochemical tests were carried out, which showed that the probe had a rather low impedance after a simple gold electroplating. Finally, in vivo experiments demonstrated our probe can be successfully used in neural recording.

Miniaturized Sulfite-Based Gold Bath for Controlled Electroplating of Zone Plate Nanostructures.

X-ray zone plates made from gold are common optical components used in X-ray imaging experiments. These nanostructures are normally fabricated using a combination of electron-beam lithography and gold electroplating with cyanide gold baths. In this study, we present a gold electroplating process in a miniaturized gold-suplphite bath. The miniaturization is enabled by on-chip reference plating areas with well defined sizes, offering a reliable way to control the height of the structures by carefully choosing the plating time at a given current density in accordance with a calibration curve. Fabricated gold zone plates were successfully used in X-ray imaging experiments with synchrotron radiation. Although gold electroplating of nanostructures is a well-established method, details about the actual process are often missing in the literature. Therefore, we think that our detailed descriptions and explanations will be helpful for other researchers that would like to fabricate similar structures.

A sandwich-type electrochemical immunosensor using trimetallic nanozyme as signal amplification for NT-proBNP sensitive detection

Heart failure (HF) is a major public health problem trigged by a heart circulation disorder. Early detection and diagnosis are conducive to the prevention and treatment of HF. N-terminal B-type natriuretic peptide precursor (NT-proBNP) is considered to be a sensitive diagnostic biomarker of HF. In this study, we constructed a NT-proBNP sandwich electrochemical immunosensor by using electroplated gold nanoparticles (Au NPs) as the substrate and utilizing rough-surfaced trimetallic Au@PdPt nanozymes (Au@PdPt RTNs) as current signal amplification. The Au NPs as substrate material modified glassy carbon electrode (GCE) have excellent conductivity and biocompatibility, which not only accelerate electron transfer rate, but also improve the loading capacity of primary antibody (Ab1). Moreover, the Au@PdPt RTNs were synthesized by a one-pot method and used as the labels to bound with secondary antibodies (Ab2) via the Pt-N. The large specific surface area and excellent catalytic properties for H2O2 of Au@PdPt RTNs can effectively enhance the stability and sensitivity of the immunosensor. With the favorable cooperation of Au NPs and Au@PdPt RTNs, the constructed immunosensor exhibited a wide concentration range from 0.1 pg mL−1 to 100 ng mL−1 and a low detection limit of 0.046 pg mL−1. Furthermore, the accuracy of the analysis of NT-proBNP in diluted human serum samples was satisfactory. The results revealed the electrochemical immunosensor has a prospective application in clinical detection.

Fabrication of X-ray Gratings for Interferometric Imaging by Conformal Seedless Gold Electroplating.

We present a method to produce small pitch gratings for X-ray interferometric imaging applications, allowing the phase sensitivity to be increased and/or the length of the laboratory setup to be minimized. The method is based on fabrication of high aspect ratio silicon microstructures using deep reactive ion etching (Bosch technique) of dense grating arrays and followed by conformal electroplating of Au. We demonstrated that low resistivity Si substrates (<0.01 Ohm·cm) enable the metal seeding layer deposition step to be avoided, which is normally required to initiate the electroplating process. Etching conditions were optimized to realize Si recess structures with a slight bottom tapering, which ensured the void-free Au filling of the trenches. Vapor HF was used to remove the native oxide layer from the Si grating surface prior to electroplating in the cyanide-based Au electrolyte. Fabrication of Au gratings with pitch in the range 1.2–3.0 µm was successfully realized. A substantial improved aspect ratio of 45:1 for a pitch size of 1.2 µm was achieved with respect to the prior art on 4-inch wafer-based technology. The fabricated Au gratings were tested with X-ray interferometers in Talbot–Laue configuration with measured visibility of 13% at an X-ray design energy of 26 keV.

Electrochemical Immunosensor Platform Using Low-Cost ENIG PCB Finish Electrodes: Application for SARS-CoV-2 Spike Protein Sensing

In recent years, lab-on-chip systems based on printed circuit board (PCB) substrates are gaining attraction primarily due to their low cost of manufacturing. Adapting inexpensive PCBs for development of immunosensors usually requires additional processing steps such as gold electroplating and electropolymerisation, that add to the manufacturing costs. In this work, we demonstrate methods to leverage electroless nickel immersion gold (ENIG) finish PCBs as electrodes for developing electrochemical immunosensors. We evaluated the performance of various parameters that impact sensor performance such as methods to clean impurities on PCB surface, optimization of redox probe concentration, and have successfully immobilized antibodies on the electrodes with cysteamine + glutaraldehyde aided process. Based on these methods, we demonstrate an application of ENIG finish PCB electrodes for detection of SARS-CoV-2 spike protein spiked in artificial saliva samples.

High‐Aspect‐Ratio Grating Microfabrication by Platinum‐Assisted Chemical Etching and Gold Electroplating

Diffractive optics play a key role in hard X‐rays imaging for which many scientific, technological, and biomedical applications exist. Herein, high‐aspect‐ratio microfabrication of gratings for X‐ray interferometry is demonstrated using Pt as a catalyst for the metal assisted chemical etching of Si in a solution of HF and H2O2. The Pt layer is thermally treated to realize a porous catalyst layer that stabilizes the etching of a pattern with a pitch size from 4.8 to 20 μm in the direction perpendicular to the &lt;100&gt; Si substrate and an aspect ratio up to 60:1. The superior etching performance of Pt as a catalyst and its stability in a solution with high HF content are reported in direct comparison with the Au catalyst for the same grating parameters. The Si structure is then used as a template for filling with Au, as a high absorbing X‐ray material. The Pt catalyst layer is used as a conductive seed for Au electroplating. The quality of the overall process is assessed by obtaining a visibility map using 30 μm‐thick Au grating in an X‐ray interferometric setup at 20 keV.

Cyanide Degradation from Mining Effluent Using Two Reagents: Sodium Metabisulphite and the Metabisulphite Mixture with Hydrogen Peroxide

Cyanide ion (CN-) is widely used in different industrial operations, such as jewelry, steel manufacture, gold and silver extraction and electroplating. However, industrial emissions containing the CN- ion have to be treated to comply with environmental regulations. This research aimed to degrade free cyanide (CNL) present in the tailing of a metallurgical plant that processes gold-bearing ores and uses sodium cyanide (NaCN) as a leaching reagent. Sodium metabisulfite (Na2S2O5) and sodium metabisulfite with hydrogen peroxide (Na2S2O5 + H2O2) were used as oxidizing agents. To evaluate the effect of the factors, we used a factorial design with three independent variables: stirring time, reagent excess percentage, type of reagent and a dependent variable: CNL degradation (mg/L). According to the analysis of variance (ANOVA), the variables influenced significantly CNL degradation, being the most relevant the reagent excess percentage and according to the results, the maximum CNL degradation was 97.67% when 400% of Na2S2O5excess was added with 4 hours of stirring.

Using Impedance Measurement to Characterize Cell-Electrode Adhesion with Customized 3D-Nanostructured Multielectrode Arrays

Multielectrode array (MEA) technology is used as an extracellular recording method to investigate the electrical activity of complex excitable cell networks and tissue slices. In this context, an array of single-contactable, sensing electrodes record the electrical field potentials induced by the ion flux across the cell membranes. Therefore, MEAs are an ideal tool to investigate network activities for prolonged periods. Still, MEA technology suffers from low-signal-to-noise ratios caused by a dissatisfied cell-electrode contact, thus revealing only limited measurements. To improve cell recording, a tight cell-electrode contact is inalienable. This can be achieved by three-dimensional micro- or nanostructures on top of the sensing electrodes. Beside the fact of increasing the electrochemically active surface area, thus leading to a decrease in the overall chip impedance, the nano-sized structures can also trigger an engulfment process of the cells. By minimizing the gap between cell and electrode, a high seal resistance can be achieved which in return results in recording of higher signal amplitudes. In this work, electrochemical concepts are used for fabrication as well as for characterizing the chips and to investigate the cell-electrode interaction.The developed process allows the fabrication of half-structured MEAs with different three-dimensional nanostructure shapes, geometries and pitch lengths and is mainly based on thermal nanoimprint lithography (NIL), gold electroplating and microstructuring techniques. During thermal NIL a customized, nanostructured master mold is pressed into a polymer resist of a wafer substrate, thus creating a negative copy of the master´s nanostructures. The subsequent electroplating step can be adjusted in a way, that it fills or overgrows the NIL templates, thereby creating different shapes. Photolithography, chemical vapor deposition and etching steps are used to fabricate the overall MEA geometry.Cyclic voltammetry as well as electrochemical impedance spectroscopy have been applied to characterize the effect of different nanostructure geometries on charge transfer, double-layer capacitance and impedance of the MEA electrodes. Compared to unstructured electrodes, charge transfer and double-layer capacitance of the nanostructured electrodes are increased, whereas the impedance of the nanostructured electrodes are decreased. These results can directly be related to an increase of the electrochemically active surface area and vary with the investigated nanostructure layout.To examine the effect of the nanostructures on cell-electrode coupling in detail and to quantify cell adhesion, impedance sensing at a fixed frequency of 1 kHz has been performed using the impedance-stable human embryonic kidney cell line HEK 293. Impedance values have been measured with and without cells. Due to the chip layout where non- and nanostructured electrodes have been included on the chip, the relative change of the impedance values could directly be correlated with cell-electrode adhesion. By this, a significant increase or decrease of cell-electrode coupling depending on the nanostructure layout could be demonstrated. For verification, action potential recordings with neural stem cells of the subventricular zone of postnatal mice have been performed, showing a distinct increase of the recorded signal amplitudes of the nanostructured electrodes compared to unstructured electrodes of the same chip. The latter might be correlated to an engulfment process of the cells. Figure: Left: Impedance measurement to quantify cell-electrode adhesion. Right: SEM picture of attached SVZ cells on top of overgrown pillar structures (Inset: Magnification, scale bar: 2 µm). Figure 1

(Invited) MEMS Accelerometer Fabricated by Gold Multi-Layer Metal Technology

MEMS(microelectromechanical systems) accelerometers are key devices for IoT (Internet of Things) technology. Throughout the technical progress, the resolution of detecting acceleration has been required to be the level of micro-G (1 G = 9.8 m/s2) in spite of small sensor size. In order to solve the problem, we proposed capacitive MEMS accelerometers with gold proof mass and have been developing MEMS accelerometers [1-4] using the multi-layer metal technology [5]. Figure 1 shows the relationship between the Brownian noise (BN ) and the proof mass size of MEMS accelerometers. BN is a crucial factor to determine the resolution of MEMS accelerometer [6]. In this Fig. 1, we compare our developed MEMS accelerometers with the other reported ones. These results suggest that we can obtain the low value of 22 nG/(Hz)1/2 by utilizing gold as a high density material of the proof mass, despite the same size of gold proof mass as that of silicon proof mass [7-11]. We have proved the feasibility of the MEMS accelerometer with the gold proof mass. This paper reviews the feature of our proposed MEMS accelerometer and the issue of its reliability. Figure 2 shows a schematic illustration of the proposed MEMS accelerometer. The MEMS accelerometer consists of suspensions, stoppers, a proof mass as upper electrode, and a fixed electrode. When the upper electrode is moving to the vertical direction by the input of acceleration, the capacitance is detected by the fixed electrode. The stoppers are built to prevent mechanical destruction caused by over-swinging of the upper electrode. Figure 3 shows an SEM photograph of the MEMS accelerometer. The result shows that MEMS accelerometer fabrication process is established by the multi-layer metal technology, which consists of the gold electroplating and the photo-sensitive polyimide film [5]. On the basis of the design concept and the fabrication process, we have developed the MEMS accelerometers described above. From the viewpoint of the usage of gold material for MEMS structures, we have investigated the reliability by conducting the heat cycle and the vibration cycle tests [12, 13]. These tests were carried out on MEMS accelerometers and cantilevers for evaluating the material characteristics. Figure 4 shows the results of applying the continuous vibration to the MEMS accelerometer. It is revealed that the MEMS accelerometer is immune to the vibration. In conclusion, we confirm that our proposed MEMS accelerometer can make a contribution to a new technical development. Reference [1] T. Konishi et al., Jpn. J. Appl. Phys., 52, p. 06GL04, (2013). [2] D. Yamane et al., Appl. Phys. Lett., 104, p. 074102, (2014). [3] D. Yamane et al., APCOT 2016, pp299, (2016). [4] D. Yamane et al., Sensors and Materials, (2019). [5] K. Machida et al., IEEE Trans. On ED, 48, 2273, (2001). [6] B. E. Boser and R. T. Howe, IEEE JSC, 31, p. 366, (1996). [7] J. Chae et al., JMEMS, vol.13, pp.628-635, (2004). [8] H. Qu et al., IEEE Sensors Journal, vol.8, pp.1511(2008). [9] R. G. Walmsley et al., in Proc. IEEE SENSORS2009, (2009). [10] R. A. Dias et al., Sensors and Actuators A: pp. 47 (2011). [11] X. Zou et al., in Proc. Transducers 2015, (2015). [12] T. Konishi et al., MNC 2017, (2017). [13] D. Yamane et al., Transducers 2017,2187, (2017). Figure 1

A Study on Corrosion Resistance of Electroplated Gold over Nanocrystalline Ni-W for Contact Applications

Highly conductive metal with least corrosion resistance is the most prominent requirement of contact industries. Although deposition of gold over Ni sulfamate is a standard interface for contact and connector applications, the performance of gold over Ni sulfamate has faced several problems such as wear durability, porosity of gold layers and biased corrosion resistance. The deposition of nanocrystalline Ni-W (nc Ni-W) between gold and Ni sulfamate improves the mechanical and surface properties of interfaces. In this work two different types of samples were processed and compared in terms of corrosion. The first sample (Au/NiSO4) was prepared using electroplating of gold, Ni sulfamate and Ni strike over base material of copper alloy with thicknesses of 0.9 µm, 1.9 µm and 0.5 µm respectively. In the second sample (Au/nc Ni-W/NiSO4), all layers of electroplating were same except the addition of 1.8 µm of nanocrystalline Ni-W before deposition of gold. Both samples were passed through the environments of (a) 85% relative humidity at 85oC for 24 hours, (b) 85% relative humidity at 85oC for 96 hours and (c) nitric acid vapors for 60 minutes. The effect on electrical, mechanical and materials properties of samples were investigated before and after passing through these environments using Force Deflection Resistance (FDR), Life-cycle test (LCT), Scanning electron microscopy (SEM), Energy dispersive spectroscopy (EDS) and X-Ray CT scanning. Although Au/NiSO4 is a well-known interface for connector applications [1], the deposition of nc Ni-W between gold and NiSO4 reduces the rate of corrosion because nc Ni-W has a weak tendency for grain boundary segregation and building broader range of accessible grain sizes [2]. There is formation of grain colonies in Ni-W deposit which controls crack propagation and corrosion [3]. The performance of two different interfaces of Au/NiSO4 and Au/nc Ni-W/ NiSO4 against corrosion was tested after electroplating on spring probes. Spring probe is one of the product of Smiths Interconnect which is used for different applications like defense, medical, rail, semiconductor, space etc. [4]. In FDR, the spring force, coefficient of friction and contact resistance was measured under a hysteresis of compression and extension for a travel distance of 0.14 inch. In the case of Au/NiSO4, the difference in compression and extension force at 0.14 inch was 6.1 oz. In the case of Au/nc Ni-W/ NiSO4, this difference was 4.6 oz which means that there is less friction with the deposition of nanocrystalline Ni-W underneath gold. Moreover, the difference in contact resistances was lower in second sample which means that the addition of nc Ni-W enhances the interface of gold and NiSO4. After treatment in humidity from 24 hrs to 96 hrs the difference in compression and extension force at 0.14 inch was increased by 7 oz in first sample but in second sample this difference was only increased by 3.6 oz which means that there is less increase in friction due to the presence of nc Ni-W. In LCT the resistance was measured at a test current of 0.025 amps under a stroke length of 0.09 inch for 10,000 life cycles with a cycle rate of 4 cycles/sec. The rate of increase in resistance with number of cycles was higher in the case of Au/NiSO4 than Au/nc Ni-W/ NiSO4. In first sample, the sticky coefficient was increased from 0 to 25 % after treatment in humidity for 24 hrs and it further increased to 37.5% after keeping in humidity for 96 hrs. The wear off rate and friction reduction of Au/nc Ni-W/ NiSO4 helped in maintaining the sticky coefficient to be constant even after kept in humidity for 96 hrs. The failure of the probes were tested from front and cross section SEM, point and line scan EDS and X-Ray CT scanning. SEM was used to observe mechanical marks and microstructure analysis which explained the reasoning of low wear rate in the case of Au/NiSO4. The failure of the probes was also confirmed from X-Ray CT Scanning in the probes during compression of spring. The complete set of experimental results will be added in the full version of the paper.

3D Nanostructured Multielectrode Arrays: Fabrication, Electrochemical Characterization, and Evaluation of Cell–Electrode Adhesion

Abstract3D nanostructures on top of planar multielectrode array (MEA) electrodes increase the surface area and can offer a tight and stable cell–electrode interface, thus leading to a crucial increase of the signal‐to‐noise ratio during measurement. However, each individual cell type might need specific dimensions and an arrangement of nanostructures that fits ideally to a specific cell type. Therefore, a fabrication method of 3D nanostructured MEA chips based on nanoimprint lithography, gold electroplating, and microstructuring techniques is presented which allows the fabrication of a whole set of MEA chips with different nanostructure layouts in one single approach. The chips are characterized using electrochemical methods, atomic force, and scanning electron microscopy. Furthermore, an impedance measurement method is presented to quantify cell–electrode adhesion of nanostructured and unstructured electrodes using the human embryonic kidney cell line (HEK 293). Double‐layer capacitance, transferred charge, and impedance values of different nanostructure layouts revealed a significant improvement compared to unstructured electrodes. The improvement strongly correlates with the increase of the electrochemical active surface area. Impedance measurement with impedance‐stable HEK 293 cells allows discriminating differences of cell adhesion between the individual nanostructure layouts. A significant increase or decrease of cell–electrode coupling depending on the nanostructure layout is demonstrated.