Table of contents

Automatic wire bonding is a highly mature, cost-efficient and broadly available back-end process, intended to create electrical interconnections in semiconductor chip packaging. Modern production wire-bonding tools can bond wires with speeds of up to 30 bonds per second with placement accuracies of better than $\mathrm{2\;\unicode{xb5}\mathrm{m}}$, and the ability to form each wire individually into a desired shape. These features render wire bonding a versatile tool also for integrating wires in applications other than electrical interconnections. Wire bonding has been adapted and used to implement a variety of innovative microstructures. This paper reviews unconventional uses and applications of wire bonding that have been reported in the literature. The used wire-bonding techniques and materials are discussed, and the implemented applications are presented. They include the realization and integration of coils, transformers, inductors, antennas, electrodes, through silicon vias, plugs, liquid and vacuum seals, plastic fibers, shape memory alloy actuators, energy harvesters and sensors.

Among the electrophysiology techniques, the voltage clamp and its subsequent scaling to smaller mammalian cells, the so-called patch clamp, led to fundamental discoveries in the last century, revealing the ionic mechanisms and the role of single-ion channels in the generation and propagation of action potentials through excitable membranes (e.g. nerves and muscles). Since then, these techniques have gained a reputation as the gold standard of studying cellular ion channels owing to their high accuracy and rich information content via direct measurements under a controlled membrane potential. However, their delicate and skill-laden procedure has put a serious constrain on the throughput and their immediate utilization in the discovery of new cures targeting ion channels until researchers discovered 'lab-on-a-chip' as a viable platform for the automation of these techniques into a reliable high-throughput screening functional assay on ion channels. This review examines the innovative 'lab-on-a-chip' microtechnologies demonstrated towards this target over a period of slightly more than a decade. The technologies are categorically reviewed according to their considerations for design, fabrication, as well as microfluidic integration from a performance perspective with reference to their ability to secure G Ω seals (gigaseals) on cells, the norm broadly accepted among electrophysiologists for quality recordings that reflect ion-channel activity with high fidelity.

We have designed, fabricated, calibrated and tested actuators for shear characterization to assess microscale shear properties of soft substrates. Here, we demonstrate characterization of dry silicone and hydrated polyethylene glycol. Microscale tools, including atomic force microscopes and nanoindenters, often have limited functionality in hydrated environments. While electrostatic comb-drive actuators are particularly susceptible to moisture damage, through chemical vapor deposition of hexamethyldisiloxane, we increase the hydrophobicity of our electrostatic devices to a water contact angle 90 ± 3°. With this technique, we determine the effective shear stiffness of both dry and hydrated samples for a range of soft substrates. Using computational and analytical models, we compare our empirically determined effective shear stiffness with existing characterization methods, rheology, and nanoindentation, for samples with shear moduli ranging from 5–320 kPa. This work introduces a new approach for microscale assessment of synthetic materials that can be used on biological materials for basic and applied biomaterials research.

We report on the fabrication of 3D buried micro-structures in fused silica glass using the selective chemical etching along femtosecond laser irradiated zones. Specifically, we have exploited a novel approach combining two different etching agents in successive steps. The widely used hydrofluoric acid solution, which provides fast volume removal, and potassium hydroxide solution, which exhibits high selectivity, are used to fabricate microfluidic structures. We demonstrate that this hybrid approach takes advantage of both of the individual etchants' special characteristics and facilitates prototyping and fabrication of complex geometries for microfluidic devices.

In this paper, a two-dimensional (2D) model of the terminating-type power sensor is established under different input powers. The 2D heat transfer equation is applied to describe the temperature distribution, and Fourier series is used to obtain the solution based on the boundary conditions. In order to demonstrate the validity of the 2D model, finite-element method (FEM) simulation using ANSYS software was performed. The sensitivity from the 2D model and FEM is 0.25 mV mW⁻¹ and 0.28 mV mW⁻¹ respectively, while the sensitivity from the 1D model is 0.34 mV mW⁻¹, which indicates that the presented 2D model is closer to the simulation than the 1D model. The terminating-type power sensor was designed and fabricated by MEMS technology and the GaAs MMIC process. The measured return loss is less than −26 dB for a frequency up to 10 GHz. The power measurement was performed and a good linearity of the output thermovoltage with respect to the input power is obtained. The measured sensitivity is close to 0.26 mV mW⁻¹, 0.23 mV mW⁻¹ and 0.16 mV mW⁻¹ at 0.1, 1 and 10 GHz, respectively. Moreover, the frequency dependence measurement demonstrates that the measured thermovoltage decreases with increasing the frequency. The measurements demonstrate that the measured results agree with the presented 2D model for low frequency while the measured thermovoltage deviates from the expectation at high frequency. The reason is that the electromagnetic coupling loss of the coplanar waveguide and the parasitic loss of the load resistor become higher at high frequency.

This paper describes the development, fabrication and examination of an atom chip through silicon vias (TSV), which is anodically bonded with a Pyrex glass cell to form an ultra-high-vacuum system for the application of Bose–Einstein condensation (BEC) experiments. The silicon via is etched by the inductively coupled plasma reactive ion etch and filled by copper plating technology. The metal wires on both sides of the atom chips are patterned by the lithography process. Three different sizes of TSV are made and tested by continuously applying a maximum current of 17 A under the vacuum (70 Torr) and in air. In addition, after the thermal cycling of an anodic bonding process (requested at 350 °C) and a high electric field of 1000 V m⁻¹, the TSV on atom chips can still hold the ultra-high vacuum (UHV). The conductive and vacuum yields of the TSV improved from 50% to 100% and from 75% to 81.25%, respectively after the modification of the fabrication process. Finally, the UHV test of TSV on atom chips at room temperature can be reached at 8 × 10⁻¹⁰ Torr, thus satisfying the requirements of atomic physics experiments under the UHV environment.

We introduce a new technique for compensating stress anisotropy across the thickness of sputter-deposited metal films. Our technique balances the film vertical stress gradient by altering the substrate bias during sputtering and by controlling the ion flux and energy that bombards the growing film. Sputter-deposited metal films are appealing materials for microfabrication of freestanding and out-of-plane structures, especially because of their low thermal budget. These microstructures extend the design space of micro-electro-mechanical systems (MEMS)-based devices, and they overcome some of the limitations of in-plane processing. Unfortunately, most elemental metals and alloys when sputter deposited have a substantial stress gradient across their thickness that can deteriorate their mechanical properties and severely distort the shape of the fabricated freestanding microstructures. The stress gradient across the thickness of a sputtered film can be compensated (balanced) by embedding a layer in the film with the opposite stress polarity compared to that of the bulk of the film. The force exerted by the stress mismatch between this layer and the bulk of the film easily overcomes the film's vertical stress gradient. This compensating force guarantees that a released freestanding structure remains flat and does not curl upward. This virtual layer is introduced to the growing film by altering the substrate bias voltage during the sputtering process. The substrate bias voltage controls the ion flux and energy that bombards the film, and it enables tailoring the film stress parameters. This technique has enabled us to fabricate freestanding microstructures up to 500 µm long with negligible stress-related deformation.

We propose a batch fabrication method for a double-layer microscale metamaterial resonator operating in the terahertz (THz) region. The proposed method takes advantage of scalloping structures formed by a general deep etching process. The scalloping structures function as a shadow mask. The shadow mask structure allows for the simultaneous fabrication of multiple metal layers with only a one-time evaporation step. The evaporated metal layers are electrically isolated from each other. In this paper, we fabricated a double-layer split-ring resonator (SRR) on a silicon substrate. The typical length of an arm of the SRRs was 40 µm, and the interlayer distance was 4 µm. Using energy-dispersive x-ray analysis, we confirmed that there was a nonevaporation area between the two SRR layers. We also confirmed that the fabricated sample functioned as a metamaterial in the THz region by transmittance measurements and simulation. These results prove that our method could lead to the realization of multilayer metamaterials.

This paper presents a comprehensive study on the performance of a polydimethylsiloxane-based microfluidic device for the detection of continuous distributed static and dynamic loads. The core of this device is a single-compliant polymer microstructure integrated with a set of electrolyte-enabled distributed transducers, which are equally spaced along the microstructure length. The microstructure converts continuous distributed loads to continuous deflection, which is translated to discrete resistance changes by the distributed transducers. One potential application of this device is to measure spatially varying elasticity/viscoelasticity of a heterogeneous soft material, through quasi-static, stress relaxation and dynamic mechanical analysis tests. Thus, by controlling the displacement of a rigid probe, three types of loads (i.e., static, step and sinusoidal) are exerted on the device, and the performance of the device is experimentally characterized and analytically examined. As a result, this work establishes not only an experimental method for characterizing the performance of the device under various loading conditions, which can be directly adopted to measure the spatially varying elasticity/viscoelasticity of a heterogeneous soft material, but also the correlation of the device performance to its design parameters.

The nematode Caenorhabditis elegans (C. elegans) receives attention as a bioindicator, and the C. elegans condition has been recently analyzed using microfluidic devices equipped with an imaging system. To establish a method without an imaging system, we have proposed a novel microfluidic device with which to analyze the condition of C. elegans from the capacitance change using a pair of micro-electrodes. The device was designed to culture C. elegans, to expose C. elegans to an external stimulus, such as a chemical or toxicant, and to measure the capacitance change which indicates the condition of C. elegans. In this study, to demonstrate the capability of our device in a toxic aqueous environment, the device was applied to examine the effect of cadmium on C. elegans. Thirty L4 larval stage C. elegans were divided into three groups. One group was a control group and the other groups were exposed to cadmium solutions with concentrations of 5% and 10% LC₅₀ for 24 h. The capacitance change and the body volume of C. elegans as a reference were measured four times and we confirmed the correlation between them. It shows that our device can analyze the condition of C. elegans without an imaging system.

This paper presents a robust Q-control approach based on an all-electrical feedback loop enhancing the quality factor of a resonant microstructure by using the self-sensing capability of a piezoelectric thin film actuator made of aluminium nitride. A lock-in amplifier is used to extract the feedback signal which is proportional to the piezoelectric current. The measured real part is used to replace the originally low-quality and noisy feedback signal to modulate the driving voltage of the piezoelectric thin-film actuator. Since the lock-in amplifier reduces the noise in the feedback signal substantially, the proposed enhancement loop avoids the disadvantage of a constant signal-to-noise ratio, which an analogue feedback circuit usually suffers from. The quality factor was increased from the intrinsic value of 1766 to a maximum of 34 840 in air. These promising results facilitate precise measurements for self-actuated and self-sensing MEMS cantilevers even when operated in static viscous media.

We present the fabrication and characterization of opto-mechanical micro-resonators developed to detect radiation-pressure coupling between light and a macroscopic body. The major achievements of this work are the development of complex high aspect ratio shapes by using the deep-RIE Bosch process and the integration of a high-reflectivity dielectric mirror. The micro-resonators were used as an end-mirror of a Fabry–Perot cavity, attaining an optical finesse of about 6 × 10⁴, and at cryogenic temperature (about 10 K) we measured a mechanical quality factor up to 2 × 10⁶ at about 90 kHz. These features make our devices particularly suitable for experiments on quantum-opto-mechanics.

Transdermal drug delivery using microneedles is a technique to potentially replace hypodermic needles for injection of many vaccines and drugs. Fabrication of hollow metallic microneedles so far has been associated with time-consuming steps that restrict batch production of these devices. Here, we are presenting a novel method for making metallic microneedles with any desired height, spacing, and lumen size. In our process, we use solvent casting to coat a mold, which contains an array of pillars, with a conductive polymer composite layer. The conductive layer is then used as a seed layer in a metal electrodeposition process. To characterize the process, the conductivity of the polymer composite with respect to different filler concentrations was investigated. In addition, plasma etching of the polymer was characterized. The electroplating process was also studied further to control the thickness of the microneedle array plate. The strength of the microneedle devices was evaluated through a series of compression tests, while their performance for transdermal drug delivery was tested by injection of 2.28 µm fluorescent microspheres into animal skin. The fabricated metallic microneedles seem appropriate for subcutaneous delivery of drugs and microspheres.

We present a novel method for the fabrication of void-free copper-filled through-glass-vias (TGVs), and their application to the wafer-level radio frequency microelectromechanical systems (RF MEMS) packaging scheme. By using the glass reflow process with a patterned silicon mold, a vertical TGV with smooth sidewall and fine pitch could be achieved. Bottom-up void-free filling of the TGV is successfully demonstrated through the seedless copper electroplating process. In addition, the proposed process allows wafer-level packaging with glass cap encapsulation using the anodic bonding process, since the reflowed glass interposer is only formed in the device area surrounded with silicon substrate. A simple coplanar waveguide (CPW) line was employed as the packaged device to evaluate the electrical characteristics and thermo-mechanical reliability of the proposed packaging structure. The fabricated packaging structure showed a low insertion loss of 0.116 dB and a high return loss of 35.537 dB at 20 GHz, which were measured through the whole electrical path, including the CPW line, TGVs and contact pads. An insertion loss lower than 0.1 dB and a return loss higher than 30 dB could be achieved at frequencies of up to 15 GHz, and the resistance of the single copper via was measured to be 36 mΩ. Furthermore, the thermo-mechanical reliability of the proposed packaging structure was also verified through thermal shock and pressure cooker test.

NiFe alloy arrays with various geometry sizes and shapes were designed, fabricated and investigated. Electrodeposition was introduced as a highly effective integrated method to fabricate the alloy film. The influence of dimensional size and geometry shape of the array unit was discussed. With decreasing size, the soft magnetic properties of the samples are improved with a 78.6% decrease of coercivity and an 65.0% decrease of squareness ratio. Compared with square and rectangular arrays, circular arrays exhibit smaller coercivity, higher permeability and smaller squareness ratio. Additionally, different compositional arrays were also tested for their crystal structures. It is found that the alloy with a content of Ni₈₀Fe₂₀ can achieve a face-centered cubic structure and realize the best soft magnetic properties. A coercivity of 0.383 Oe, a squareness ratio of 4.21 × 10⁻⁴ and a saturation magnetization of 4.2 T have been successfully achieved in circular arrays within an area of 2000 × 2000 µm².

The study of cells in a well-defined and chemically programmable microenvironment is essential for a complete and fundamental understanding of the cell behaviors with respect to specific chemical compounds. Flow-free microfluidic devices that generate quasi-steady chemical gradients (spatially varying but temporally constant) have been demonstrated as effective chemotaxis assay platforms due to dissociating the effect of chemical cues from mechanical shear forces caused by fluid flow. In this work, we demonstrate the fabrication and characterization of a flow-free microfluidic platform made of polyethylene glycol diacrylate (PEG-DA) hydrogel. We have demonstrated that the mass transport properties of these devices can be customized by fabricating them from PEG-DA gels of four distinct molecular weights. In contrast to microfluidic devices developed using soft lithography; this class of devices can be realized using a more cost-effective approach of direct photopolymerization with fewer microfabrication steps. This microfluidic platform was tested by conducting a quantitative study of the chemotactic behavior of Escherichia coli (E. coli) RP437, a model microorganism, in presence of the chemo-effector, casamino-acids. Using the microfabrication and characterization methodology presented in this work, microfluidic platforms with well-defined and customizable diffusive properties can be developed to accommodate the study of a wide range of cell types.

A dynamic microelectromechanical system and a nanoelectromechanical system are designed to operate over a desired frequency range. There exist different types of frequency tuning mechanisms such as tuning due to the electrostatic softening effect and the hardening effect because of the axial tension. These two effects are discussed quite often in many studies. In this paper, we discuss about the case where both the effects can be accounted simultaneously to obtain frequency tuning. To model the effects, we take a fixed–fixed beam separated by a bottom and a side electrode. Subsequently, we solve the coupled elasticity and electrostatic equation using a Galerkin method to obtain the frequencies of two orthogonal modes, namely, the in-plane and out-of-plane modes. After validating the model with experimental results available in the literature, we study the coupled effects of these two modes on the pull-in effect and frequency tuning. It is found that the pull-in voltage can be increased by the intermodal coupling. The coupling region of the two modes can be controlled by selecting appropriate gaps between the beam and the side and bottom electrodes, respectively.

This paper describes the transfer of thin gold films deposited on rigid silicon substrates to polydimethylsiloxane (PDMS) with reliable and strong bonding. Modification of the Au surfaces with (3-mercaptopropyl)trimethoxysilane (MPTMS) as a molecular adhesive was carried out to promote adhesion between Au and PDMS. The degree of bonding with respect to the concentration of MPTMS, treatment time and methods of deposition was investigated by a simple adhesion test using two different adhesive tapes. The effect of hydrolysis of MPTMS is discussed based on the bonding mechanism of MPTMS to the PDMS prepolymer. Also, the adsorption of MPTMS on Au deposited by different methods is discussed. The results indicate that liquid deposition of MPTMS provides the strongest adhesion between Au and PDMS among the different deposition methods and the different linker molecules. Based on these studies, the Au patterns with linewidth of less 2 µm were successfully transferred to PDMS with reliable and strong bonding in a full 3 inch wafer scale, using a dry peel-off process.

We introduce a novel, low-cost and high-performance hot-wire air flow sensor which utilizes a bond-wire as the sensing element. Standard wire-bonding methods are used to form the hot-wire sensor, similar to those used in post-process integrated circuit (IC) packaging, so sensor fabrication is IC-compatible. The bond-wire extends above the surface of the substrate, saving the valuable chip area and allowing the formation of dense arrays of sensors for this and other applications such as inertial sensors. This hair-like hot-wire anemometer offers high accuracy, high sensitivity and wide dynamic range. Fabricated aluminum and platinum wire flow sensors have a measurement range from 1 cm s⁻¹ to 17.5 m s⁻¹, with an accuracy of 0.06% (platinum wire, 3.3 V) in the low flow regime (<50 cm s⁻¹) and 2.5% (aluminum wire, 3.3 V) in the high flow regime (>2 m s⁻¹).

This paper describes the development of a novel ruggedized high-temperature pressure sensor operating in lateral field exited (LFE) Lamb wave mode. The comb-like structure electrodes on top of aluminum nitride (AlN) were used to generate the wave. A membrane was fabricated on SOI wafer with a 10 µm thick device layer. The sensor chip was mounted on a pressure test package and pressure was applied to the backside of the membrane, with a range of 20–100 psi. The temperature coefficient of frequency (TCF) was experimentally measured in the temperature range of −50 °C to 300 °C. By using the modified Butterworth–van Dyke model, coupling coefficients and quality factor were extracted. Temperature-dependent Young's modulus of composite structure was determined using resonance frequency and sensor interdigital transducer (IDT) wavelength which is mainly dominated by an AlN layer. Absolute sensor phase noise was measured at resonance to estimate the sensor pressure and temperature sensitivity. This paper demonstrates an AlN-based pressure sensor which can operate in harsh environment such as oil and gas exploration, automobile and aeronautic applications.

Adhesion energies are determined for three different polymers currently used in adhesive wafer bonding of silicon wafers. The adhesion energies of the polymer off-stoichiometry thiol-ene-epoxy OSTE+ and the nano-imprint resist mr-I 9150XP are determined. The results are compared to the adhesion energies of wafers bonded with benzocyclobutene, both with and without adhesion promoter. The adhesion energies of the bonds are studied by blister tests, consisting of delaminating silicon lids bonded to silicon dies with etched circular cavities, using compressed nitrogen gas. The critical pressure needed for delamination is converted into an estimate of the bond adhesion energy. The fabrication of test dies and the evaluation method are described in detail. The mean bond energies of OSTE+ were determined to be 2.1 and 20 J m⁻² depending on the choice of the epoxy used. A mean bond energy of 1.5 J m⁻² was measured for mr-I 9150XP.

The work herein analyzes the bending stress required to separate and rupture die from notched silicon wafers. Trenches are formed on the wafers using either a dicing or Bosch deep reactive ion etching (DRIE) process. Weibull distribution parameters are reported for all variations of the fracture experiments. Additionally, the relative defect rate associated with DRIE-based die separation are compared with traditional saw methods for a variety of notch depths. Results indicate that the DRIE-based separation technique offers improved rupture strength over the traditional methods, but can also greatly reduce die strength if performed improperly. Dies completely separated by the DRIE process showed a mean failure stress of 1.16 GPa with a Weibull standard deviation of 682 MPa compared to 452 and 65 MPa mean and standard deviation stress for die completely separated by a traditional dicing saw.

A measuring system for mechanical characterization of thin films based on a compact in situ micro-tensile tester and scanning electron microscope (SEM) moiré method is proposed. The load is exerted by the tensile tester and the full field strain is measured by SEM moiré method. The configuration of the tensile tester and the principle of SEM moiré method are introduced. In the tensile tester, a lever structure is designed to amplify the displacement imposed by lead–zirconate–titanate (PZT) actuator. The SEM moiré method is applied to measure the strain of the thin film, including both the average strain in the gage section and the local strain distribution at a specific region. As an application, the measuring system is applied to characterize the mechanical property of the free-standing aluminum thin film. The experimental results demonstrate the feasibility of the system and its good application potential for mechanical behavior analysis of film-like materials.

We report on the utilization of densely packed (∼10 SWCNTs µm⁻¹), well-aligned arrays of single-chirality single-walled carbon nanotubes (SWCNTs) as an effective thin-film for integration into a gas sensor with a microtripolar electrode, based on field ionization by dielectrophoretic assembly from a monodisperse SWCNTs solution obtained by polymer-mediated sorting. The sensor is characterized as a field ionization electrode with sorted SWCNTs acting as both the sensing material and transducer gas concentrated directly into an electrical signal, an extractor serving to improve electric field uniformity and a collector electrode completing the current path. The gas sensing properties toward flammable and noxious gases, such as CO and H₂, were investigated at room temperature. Besides the high sensitivity, the as-fabricated sensor exhibited attractive behaviors in terms of both the detection limit and a fast response, suggesting that our sensor could be used to partly circumvent the low sensing selectivity, long recovery time or irreversibility and allow for a preferential identification of the selected flammable and noxious analytes. Interestingly, the excellent sensing behaviors of the sensors based on the field ionization effect derive directly from the combined effects of the high-quality, low defect SWCNTs arrays, which leads to a small device-to-device variation in the properties and the optimization of electrode fabrication, highlighting the sensor as an appealing candidate in view of nanotube electronics.

The focusing of particles has a variety of applications in industry and biomedicine, including wastewater purification, fermentation filtration, and pathogen detection in flow cytometry, etc. In this paper a novel inertial microfluidic device using two secondary flows to focus particles is presented. The geometry of the proposed microfluidic channel is a simple straight channel with asymmetrically patterned triangular expansion–contraction cavity arrays. Three different focusing patterns were observed under different flow conditions: (1) a single focusing streak on the cavity side; (2) double focusing streaks on both sides; (3) half of the particles were focused on the opposite side of the cavity, while the other particles were trapped by a horizontal vortex in the cavity. The focusing performance was studied comprehensively up to flow rates of 700 µl min⁻¹. The focusing mechanism was investigated by analysing the balance of forces between the inertial lift forces and secondary flow drag in the cross section. The influence of particle size and cavity geometry on the focusing performance was also studied. The experimental results showed that more precise focusing could be obtained with large particles, some of which even showed a single-particle focusing streak in the horizontal plane. Meanwhile, the focusing patterns and their working conditions could be adjusted by the geometry of the cavity. This novel inertial microfluidic device could offer a continuous, sheathless, and high-throughput performance, which can be potentially applied to high-speed flow cytometry or the extraction of blood cells.

We demonstrate a peristaltic micropump that utilizes traveling waves on polymer membranes to transport liquids. This micropump requires no valves and, more importantly, the traveling waves can be generated by a single actuator. These features enable the design of simple, compact devices. This micropump has a hydraulic displacement amplification mechanism (HDAM) that encapsulates an incompressible fluid with flexible polymer membranes made of polydimethyl siloxane. A microchannel is attached to the top side of the HDAM. We used a cantilever-type piezoelectric actuator to oscillate the flexible membrane at the bottom of the HDAM, while the top-side membrane drives the liquid in the channel. This format enables rectangular parallelepiped micropumps as compact as 36 mm long, 10 mm wide and several millimeters high, depending on the channel height. Experiments using the fabricated micropumps equipped with microchannels of various heights revealed that the flow rate was dependent on the ratio of the amplitude of the traveling waves to the height of the fluidic channel. The manufactured micropump could successfully generate a maximum flow rate of 1.5 ml min⁻¹ at 180 mW.

In this paper we introduce two new ways of measuring the pull-in voltage and the transient behavior of parallel-plate capacitive microelectromechanical systems (MEMS) transducers. The advantages in the measurement speed and resolution of the so-called fast MEMS test will be discussed. Also an enhanced method, the time-resolved dynamic measurement, will be shown. With the second method, we can visualize the integral displacement of a membrane while measuring the voltage drop of a high-frequency signal over a shunt resistor/capacitor. With a more advanced charge amplifier circuit, also a force-free resonance measurement of the membrane and electrode is possible in one step. All this offers a robust and cheap option for tracing moving structures without the need of an optical line of sight.

In this work, we have developed novel methods to fabricate conductive silver tracks and dots directly from silver nitrate solution by transfer-printing and nanoimprinting lithography techniques, which are inexpensive and can be scaled down to the nanometer scale. The silver nitrate precursor can be reduced in ethylene glycol vapor to form silver at low temperatures. Energy dispersive spectrometric analysis results indicate that the silver nitrate has been converted to silver completely. In order to obtain smooth and continuous conductive patterned silver features with high resolution, the silver lines with widths of a few tens of micrometers to nanometers were patterned by using a spin-coating approach. Using a 14 M silver nitrate solution, continuous silver conductive lines with a resistivity of 8.45 × 10⁻⁵ Ω cm has been produced.