ALBERT

Description: In this study, n-dodecane used as the coupling layer for reusable acoustofluidic microchips was investigated. n-dodecane has the similar viscosity to that of water. However, it possesses much lower surface tension and higher boiling point compared to water. When dispensing a droplet of n-dodecane on lithium niobate (LiNO3) substrate with interdigital transducers and placing the polydimethylsiloxane microchannel on top of it, n-dodecane can easily wick through and completely occupy the interstitial space. Moreover, it can be readily removed from the substrate without leaving residue. The experimental results showed that the reusable acoustofluidic microchips can be operated at higher input voltages and longer duration when applying n-dodecane as the coupling layer. Attenuation of the acoustic radiant force was observed through decrease of the particle velocity, which is in agreement with the literature results. Decreasing the thickness of the coupling layer can alleviate the attenuation effect and a linear relationship between particle velocity and thickness on a semi-log plot was obtained.

Description: This research reports a micro-fabrication method for plastic microscale structures. Although a stepped shape, such as a cantilever, can be fabricated by micro electro mechanical systems (MEMS) deep etching technology, its disadvantages include the complicated fabrication process and its limited utilization with silicon only. Therefore, in this study, with an aim to address the aforementioned problems, we have realized the fabrication of a multi-stage structure using just a general photolithography process with high versatility. Specifically, it can be manufactured using only SU-8 resist and AZ resist, which are often used in the MEMS process. The AZ resist has the advantage of dissolving in the developer of the SU-8 resist, whether exposed or non-exposed. Thus, the sacrificial layer of AZ resist can be implemented with the SU-8 developer, thereby eliminating the need for dangerous chemicals such as hydrofluoric acid, which is used to etch silicon oxide. Herein, we have derived the optimum conditions by considering in advance the thickness of the AZ resist, the time taken to be etched in SU-8, and the desired features. Based on these optimum processing conditions, the structure could be suspended only in the region where the hole array was patterned. Although methods of using AZ resist as a sacrificial layer and floating SU-8 have been reported, in this study, both floating and fixed structures could be simultaneously fabricated by photolithography only. Accordingly, we successfully manufactured a gear structure and a MEMS sensor, both of which have floating and fixed structures. The above structures are made of highly transparent SU-8 on a glass substrate; hence, they are easily observable with a microscope. The reason for the widespread use of polydimethylsiloxane micro-channels is that they are transparent materials that can be observed under a microscope and fabricated by simple photolithography of the SU-8 resist, enabling non-microfabrication specialists to enter this field. These findings have the potential to form the foundation for developing new biochemical tests, such as actuators and sensors driven under a microscope.

Description: As compared with their bulk materials, III-nitride nanosheets, including gallium nitride, aluminium nitride, indium nitride, reveal wider bandgap, enhanced optical properties, anomalously temperature-dependent thermal conductivity, etc, which are more suitable for the fabrication of nano-photodetectors, nano-field electron transistors, etc, for the application in the fields of nano-optoelectronics and nano-electronics. Although the properties of III-nitrides have been predicted based on the first-principles calculation, the experimental realization of III-nitride nanosheets has been restricted primarily due to dangling bonds on the surface and strong built-in electrostatic field caused by wurtzite/zinc-blende structures. To tackle these issues, several effective approaches have been introduced, and the distinct progress has been achieved during the past decade. In this review, the simulation and prediction of properties of III-nitride nanosheets are outlined, and the corresponding solutions and novel developed techniques for realisation of III-nitride nanosheets and defect control are discussed in depth. Furthermore, the corresponding devices based on the as-grown III-nitride nanosheets are introduced accordingly. Moreover, perspectives toward the further development of III-nitrides nanosheets and devices are also discussed.

Description: We report a design method to enhance the output power of vibrational microelectromechanical system (MEMS) electrostatic energy harvesters by reducing the reactive power that does not contribute to the net output. The mechanism of enhancing the active current while reducing the reactive current is analytically studied using an equivalent circuit model of electret-based velocity-damped resonant-generator. Reduction of the internal parasitic capacitance associated to the contact pads and electrical interconnections significantly improves the power factor and increases the deliverable power. The design strategy is applied to an actual device that produces 1.3 mW from the vibrations of 0.65 G (1 G = 9.8 m s−2) at 158 Hz, suggesting a 2.9-fold enhancement of output power by increasing the buried oxide layer thickness from 1 µm to 3 µm.

Description: Objective. The role of the crypt microarchitecture and surrounding tissue curvature on intestinal stem/proliferative cell physiology is unknown. The utility of liquid lithography in creating polydimethylsiloxane (PDMS) micropillar stamps with controlled tip curvature was assessed. Using these stamps, the impact of microcurvature at the crypt base on intestinal cell and cytoskeletal behavior was studied. Approach. An SU-8 master mold as a support, polyols of varying surface energies as sacrificial liquids, and liquid PDMS as the solidifiable material were combined using liquid lithography to form PDMS micropillar arrays. Vapor phase deposition of organosilane onto the master mold was used to modify the surface energy of the master mold to shape the micropillar tips. Collagen was molded using the micropillar arrays forming a scaffold for culture of human primary colonic epithelial cells. Cell proliferation and cytoskeletal properties were assessed using fluorescent stains. Main results. Liquid lithography using low surface energy polyols (55 dynes cm−1) yielded concave-tipped PDMS micropillars. Gradients of octyltrichlorosilane deposition across a master mold with an array of microwells yielded a PDMS micropillar array with a range of tip curvatures. Human primary colonic epithelial cells cultured on micropillar-molded collagen scaffolds demonstrated a stem/proliferative cell compartment at the crypt base. Crypts with a convex base demonstrated significantly lower cell proliferation at the crypt base than that of cells in crypts with either flat or concave bases. Crypts with a convex base also displayed higher levels of G-actin activity compared to that of crypts with flat or concave bases. Significance. Liquid lithography enabled creation of arrays of in vitro colonic crypts with programmable curvature. Primary cells at the crypt base sensed and responded to surface curvature by altering their proliferation and cytoskeletal properties.

Description: There is a growing desire for cell rotation in the field of biophysics, bioengineering and biomedicine. We herein present novel microfluidic channels for simultaneous high-throughput cell self-rotation using local circular streaming generated by ultrasonic wave excited bubble arrays. The bubble traps achieve high homogeneity of liquid-gas interface by setting capillary valves at the entrances of dead-end bubble trappers orthogonal to the main microchannel. In such a highly uniform bubble array, rotation at different fields of bubble-relevant vortices is considered equal and interconvertible. The device is compatible with cells of various size and retains manageable rotation velocity when actuated by signals of varying frequency and voltage. Experimental observations were confirmed consistent with theoretical estimation and numerical simulation. Comparing with the conventional approaches of cell rotation, our device has multiple merits such as high throughput, low cost and simple fabrication procedure, and high compatibility for lab-on-chip integration. Therefore, the platform holds a promise in cell observation, medicine development and biological detection.

Description: This paper presents surface acoustic wave (SAW)-driven self-cleaning glass aimed at removing contaminants that occur on the surfaces of automotive sensors for autonomous driving. The proposed self-cleaning glass comprises an interdigitated transducer (IDT) patterned on top of the transparent piezoelectric substrate (LiNbO3) and a hydrophobic layer (Cytop) covering the IDT. First, the sliding angle and contact angle of a droplet on a hydrophobic layer are measured in different volumes without the application of any external forces. The experiment shows that the droplets smaller than 4 μl do not slide on the inclined surface. To investigate the effect of SAW on droplet removal, the traveled distances and speeds of droplets are measured in different volumes, viscosities, and applied voltages when the droplets are removed on the surface by the SAW operation of the fabricated self-cleaning glass. Then, it is also investigated that the motion of the droplets by SAW on the inclined substrate in the direction of gravity and the opposite direction. Quantitative tests on the droplet removal performance of the SAW-driven self-cleaning glass are carried out by analyzing captured images recorded during the droplet removal by the SAW operation. As proof of concept, the proposed self-cleaning technology is demonstrated on droplets formed on a lens surface of a camera on which the SAW device is mounted. The demonstration shows that the camera image distorted by droplets that occur on the initial glass cover of the camera module is quickly restored by the SAW operation. The proposed SAW-driven drop free glass can promptly remove various contaminants on the surface of the sensors. Hence, it can be applied not only for automotive sensors but also for outdoor security cameras for daily life safety and future industries such as smart factories and smart cities.

Description: In this paper, an analytical model of a micro-electromechanical (MEM) resonator used as a 4-bit digital-to-analog converter (DAC) is presented. First, we derive the dynamic equation of the 4-bit DAC device, and the nonlinear governing equation is solved by the Galerkin method combined with a shooting technique to simulate the static response, linear eigenvalue problem, and forced vibration response of the device for various electrostatic actuation cases. Also, we optimize the air gaps in the linear domain to ensure enhanced performance of the DAC. Further, to analyze the operation of the DAC in the nonlinear regime, two experimental samples powered by −2 dBm and −12 dBm AC inputs are examined. Forward and backward frequency sweeps are conducted experimentally and analytically. The proposed analytical results are validated by comparison with experimental data. The results indicate that the presented modeling, simulations, and optimization are effective tools for the design of MEM resonator-based circuits.

Description: In this paper, an integrated microprism matrix for light coupling and optical sensing systems is presented. The matrix was fabricated by use of controlled negative pressure glass thermal reflow process by the use of monocrystalline mold. The single glass microprism had height of 250 µm or 350 µm with base width respectively 350 µm or 500 µm. The matrix was formed by 10 × 10 microprisms with distance between the microprisms from 150 µm to 400 µm. It corresponded to total area of the matrixes from 28 mm2 to 74 mm2. The controlled coupling of the beam into a substrate was obtained through determination of optimal geometric dimensions of microprisms and configuration of a measurement setup. Optimal position of the fluorescence induction light source in relation to the matrixes (0.5 cm to 4.5 cm distance, 30° angle of incidence) and microfluidic channel (4 mm) were determined. The fluorimetric tests (with excitation by 470 nm laser diode in all the experiments) carried out using fluorescein solution, microbeads and porcine oocyte indicated the possibility of using a microprism matrix for fluorimetric image-based 500 nm long-pass detection in lab-on-a-chip platforms.

Description: Lead-free or low lead content perovskite materials are explored in photovoltaic devices to mitigate the challenges of toxic lead-based halides. However, the conversion efficiency from such materials is far below compared to its counterparts. Therefore, to make a humble contribution in the development of lead-free or low lead content perovskite solar cells (PSCs) for future thin-film photovoltaic (PV) technology, a simulation study of tin (Sn) and Pb mixed halide (MAPb0.5Sn0.5I3, 1.22 eV) PSC is carried out in this manuscript. The device is further optimized in terms of transport layer and thickness variation to get 15.1% conversion efficiency. Moreover, the optimized narrow bandgap halide (NBH) based device is further deployed in the monolithic tandem configuration with lead-free wide bandgap (1.82 eV) halide, i.e., Cs2AgBi0.75Sb0.25Br6, 1.82eV (WBH) PSC, to mitigate the thermalization as well as transparent Eg losses. Filtered spectrum, current matching, and construction of tandem J-V curve at the current matching point are utilized to design the tandem solar cell under consideration. Tandem device delivered short current density, JSC (15.21 mA.cm-2), open-circuit voltage, VOC (1.95 V), fill factor, FF (74.09 %) and power conversion efficiency, PCE (21.97%). The performance of the devices considered in this work is found to be in good approximation with experimental work.

Description: The pressure and temperature inside the tire is mainly monitored by the tire pressure monitoring system (TPMS). In order to improve the integration of the TPMS system, moreover enhance the sensitivity and temperature-insensitivity of pressure measurement, this paper proposes a microelectromechanical (MEMS) chip-level sensor based on stress-sensitive aluminum-silicon hybrid structures with amplified piezoresistive effect and temperature-dependent aluminum-silicon hybrid structures for hardware and software temperature compensations. Two types of aluminum-silicon hybrid structures are located inside and outside the strained menbrane to simultaneously realize the measurement of pressure and temperature. The model of this composite sensor chip is firstly designed and verified for its effectiveness by using finite element numerical simulation, and then it is fabricated based on the standard MEMS process. The experiments indicate that the pressure sensitivity of the sensor is between 0.126 mV/(V·kPa) and 0.151 mV/(V·kPa) during the ambient temperature ranges from -20 ℃ to 100 ℃, while the measurement error, sensitivity and temperature coefficient of temperature-dependent hybrid structures are individually ± 0.91℃, -1.225 mV/(V·℃) and -0.150%/℃. The thermal coefficient of offset (TCO) of pressure measurement can be reduced from -3.553%FS/℃ to -0.375%FS/℃ based on the differential output of the proposed sensor. In order to obtain the better performance of temperature compensation, Elman neural network based on ant colony algorithm is applied in the data fusion of differential output to further eliminate the temperature drift error. Based on which, the overall measured error is within 3.45 kPa, which is less than ±1.15%FS. The thermal coefficient of offset (TCO) is -0.017%FS/℃, and the thermal coefficient of span (TCS) is -0.020%/FS℃. The research results may provide a useful reference for the development of the high-performance MEMS composite sensor for the TPMS system.

Description: In this study, we propose an annular-shaped piezoelectric micromachined ultrasonic transducer (pMUT) based on a Pb(Zr,Ti)O3-based monocrystalline thin film. This pMUT is expected to increase the resonance frequency while maintaining displacement sensitivity, making it superior to an island-shaped pMUT, which is a conventional design. To demonstrate the validity of this assumption, annular- and island-shaped pMUTs with a 60-μm-diameter diaphragm were prototyped and characterized. As a result, the annular-shaped pMUT exhibited a resonance frequency of 11.9 MHz, a static displacement sensitivity of 2.35 nm/V and a transmitting figure-of-merit (FOM) of 28 nm∙MHz/V. On the other hand, the island-shaped pMUT exhibited a resonance frequency of 9.6 MHz and a static displacement of 2.5 nm/V and an FOM of 24 nm∙MHz/V. Therefore, the annular-shaped pMUT was experimentally demonstrated to provide a higher FOM compared to the island-shaped pMUT. In addition, the annular-shaped pMUT with the optimal dimensions is found to be able to keep a relatively large fabrication margin. This is an advantageous point for the practical device fabrication. We believe this design has a potential to become a standard design for high-performance pMUT devices.

Description: The organic thin film transistor (OTFT) has evolved in a big way, eventually replacing inorganic-based solid-state devices. An extensive survey of the literature reveals that the full potential of OTFTs has neither been explored nor exploited for circuit-level implementation for logic circuit design, despite the popularity of these devices. We have fabricated a PBTTT-C14 (poly (2,5-bis (3-tetradecylthiophen 2yl) thieno (3,2b) thiophene)) based OTFT by using a low-cost solution-processable technique via the floating transfer method (FTM). The fabricated OTFT using FTM shows better electrical behavior than its counterpart fabricated by using the conventional solution-processable technique. The superior electrical characteristics of the FTM-derived devices prompted us to develop a compact model of the p-channel OTFT. The compact modeling results of OTFT show a reasonably good agreement with our experimental results. We have also designed and implemented a PBTTT-C14 OTFT-based inverter circuit and ring oscillator circuit to explore the future of organic-based integrated circuits.

Description: The capability of trapping and collecting airborne particulate matter is of great applications in the fields of environmental engineering, healthcare systems, energy engineering, and so forth. In this work, we show a facile strategy of trapping and collecting airborne particulate matter by a simple and compact ultrasonic device system. In this device, a radiation plate is bonded with a Langevin transducer for generating circular standing flexural waves (CSFWs) in the plate. Under the excitation of the CSFWs in the radiation plate, an acoustic field and an acoustic streaming field can be induced in the air gap formed by the radiation plate and a sampling plate. Through numerical simulations, we find that the multiple acoustic streaming vortices symmetric about the central axis in the air gap are responsible for trapping and collecting airborne particulate matter onto the sampling plate, while acoustic radiation force contributes little. Also, it is numerically found and experimentally verified that the resonant acoustic field and the accompanying acoustic streaming field can be tuned by varying the thickness of air gap. Through experimentation, we investigate and clarify the dependency of collection performance on parameters such as the air gap thickness and radius, sonication time, driving voltage, and the angle between the radiation plate and the sampling plate. Due to its contactless and mild handling attributes, our ultrasonic airborne particulate matter sampler can circumvent the clogging and secondary pollution issues and ensure device reusability and little damage to samples compared with other airborne particulate matter processing methods.

Description: Paper electronics has emerged as an ecofriendly, light, low-cost, and recyclable material for the fabrication of flexible and printed transistors. In this study, we present fully printed organic electrochemical transistors using an active layer of PEDOT:PSS, carbon electrodes, cellulose-based electrolyte, and three different papers as substrates: bond, vegetal, and Lumi Silk, relating the electrical properties to the different morphologies of the paper surfaces. Each paper presents different regularity, diffusion capabilities, and roughness, with significant influence on the transistor performance. The more organized and smooth the surface, the better the electrical characteristics, the best of these being the Lumi Silk, with higher I on/I off ratio of 46, on-current of 8.3 × 10−5 A, V on of 1.3 V, and power gain of 43.5 dB associated with ultra-low hysteresis of 0.1 V, high transconductance of −57.3 μS, and suitablity for flexible electronics and sensors applications.

Description: We present a forward-looking, fiber-scanning endomicroscope designed for optical coherence tomography (OCT) and OCT-Angiography (OCT-A) imaging through the working channel of commercial gastrointestinal endoscopes and cystoscopes. 3.4 mm in outer diameter and 11.9 mm in length, the probe is capable of high-resolution volumetric imaging with a field-of-view of up to 2.6 mm and an imaging depth of up to 1.5 mm at a lateral resolution of 19 µm. A high-precision lens mount fabricated in fused silica using selective laser-induced etching (SLE) allows the tailoring of the optical performance for different imaging requirements. A glass structure fabricated by the same method encapsulates the optical and mechanical components, providing ease of assembly and alignment accuracy. The concept can be adapted to high resolution OCT/-A imaging of various organs, particularly in the gastrointestinal tract and bladder.