Table of contents

This paper presents the design, fabrication and characterization of a linear-variable optical-filter (LVOF) that will be used in a micro-spectrometer operating in infrared (IR) for natural gas composition measurement. An LVOF is placed on top of an array of detectors and transforms the optical spectrum into a lateral intensity profile, which is recorded by the detectors. The IR LVOF was fabricated in an IC-compatible process using a photoresist reflow technique, followed by transfer etching of the photoresist into the optical resonator layer. The spectral range between 3 to 5 µm contains the absorption peaks for hydrocarbons, carbon-monoxide and carbon-dioxide. The resulting optical absorption is utilized to measure the gas concentrations in a sample volume. Two LVOF structures were designed and fabricated on silicon wafers using alternate layers of sputtered silicon and silicon-dioxide as the high- and low- refractive index materials. These filters consist of a Fabry–Pérot resonator combined with a band-pass filter designed to block out-of-band transmissions. Finally, the filters were fully characterized with an FTIR spectrometer and showed satisfactory agreement with the optical thin-film simulations. The characterization showed a spectral resolution of 100 nm, which can be further improved with signal processing algorithms. This method makes it possible to fabricate small and robust LVOFs with high resolving power in the IR spectral range directly on the detector array chip.

Metal thermocompression bonding is a hermetic wafer-level packaging technology that facilitates vertical integration and shrinks the area used for device sealing. In this paper, Au–Au bonding at 350, 400 and 450 °C has been investigated, bonding wafers with 1 µm Au on top of 200 nm TiW. Test Si laminates with device sealing frames of 100, 200, and 400 µm in width were realized. Bond strengths measured by pull tests ranged from 8 to 102 MPa and showed that the bond strength increased with higher bonding temperatures and decreased with increasing frame width. Effects of eutectic reactions, grain growth in the Au film and stress relaxation causing buckles in the TiW film were most pronounced at 450 °C and negligible at 350 °C. Bond temperature below the Au–Si eutectic temperature 363 °C is recommended.

Restrictor valves allow proportional control of fluid flow but are rarely integrated in microfluidic systems. In this study, an optically actuated silicon membrane restrictor microvalve is demonstrated. Its actuation is based on the phase transition of paraffin, using a paraffin wax mixed with a suitable concentration of optically absorbing nanographite particles. Backing up the membrane with oil (the melted paraffin) allows for a compliant yet strong contact to the valve seat, which enables handling of high pressures. At flow rates up to 30 µL min⁻¹ and at a pressure of 2 bars, the valve can successfully be closed and control the flow level by restriction. The use of this paraffin composite as an adhesive layer sandwiched between the silicon valve and glass eases fabrication. This type of restrictor valve is best suited for high pressure, low volume flow silicon-based nanofluidic systems.

We present the first micromachined double-sided contactless WR03 pin-flange adapter for 220–325 GHz based on gap waveguide technology. The pin-flange adapter is used to avoid leakage at the interface of two waveguides even when a gap between them is present and can be fitted onto any standard WR03 waveguide flange. Tolerance measurements were performed with gaps ranging from 30–100 µm. The performance of the micromachined pin flange has been compared to a milled pin flange, a choke flange and to standard waveguide connections. The micromachined pin flange is shown to have better performance than the standard connection and similar performance to the milled pin flange and choke flange. The benefits of micromachining over milling are the possibility to mass produce pin flanges and the better accuracy in the 2D design. Measurements were performed with and without screws fixing the flanges. The flanges have also been applied to measure two devices, a straight rectangular waveguide of 1.01 inch and a ridge gap resonator. In all cases, the micromachined pin flange performed flawlessly while the standard flange experienced significant losses at already small gaps.

In this paper, we have successfully synthesized and characterized poly(N-isopropylacrylamide) (PNIPAAm)–poly(ethylene glycol) diacrylate (PEGDA) microhydrogels. Various combinations of PNIPAAm-PEGDA microhydrogels were fabricated by the generation of monodisperse microdroplets whose sizes were comparable to a blood vessel of 260 and 320 µm with the help of a hydrodynamic focusing microfluidic device (HFMD), followed by synthesis of the microhydrogels through UV irradiation to the microdroplets. The thermo-responsive behaviors of the various microhydrogels were investigated by changing the PEGDA crosslinker concentration, which was found to be a dominant factor in tuning the shrinkage ratio in response to temperature change. As an in vitro embolization performance evaluation of the microhydrogels as chemo-embolic microspheres, the deliverability of the microhydrogels through a microcatheter was first confirmed and the compact occlusion of a channel was demonstrated based on a tapered microchannel in response to the temperature increase to physiological temperature of 36 °C. The controlled release behavior of the fluorescent dye from the microhydrogel was also investigated for chemotherapeutic purposes as a proof of concept study. The PNIPAAm-PEGDA microhydrogels could be used widely in embolization procedures based on the advantages of tunable thermo-responsive and controlled release behaviors.

In this paper, a low-cost and high-efficiency microprocessing modification technology for the surface of bisphenol A polycarbonate (BAPC) material was achieved (in particular, from hydrophilicity to hydrophobicity) at high laser scanning speeds (600–1000 mm s^− 1) and using an all-solid state, Q-switched, high-average power and nanosecond pulse Nd:YVO₄ laser (355 nm wavelength). During the modification, it was found that the laser fluence and pulse width were the two main parameters affecting the modification effect. Moreover, the modification had a significant effect on the water contact angle, wetting behavior, microstructure, average roughness and chemical composition of the surface. When the laser fluences applied were low (i.e., less than the so-called critical fluence of the UV laser modification of the BAPC material), the water contact angle was found to be a little less than the original, the hydrophilicity was slightly improved, the relative content of the oxygen-containing groups (e.g. O–C and COO⁻) increased, the microstructure and average roughness only had a very slight change, and the wetting behavior complied with the Wenzel regime. On the other hand, when the laser fluences applied were high, the water contact angle significantly increased, the hydrophilicity markedly decreased and the relative content of the oxygen-containing groups also increased. Here, a porous microstructure with periodical v-type grooves was generated and the average roughness had an obvious increase. In this case, the wetting behavior could be explained by the Cassie-Baxter regime, i.e., the microstructure and average roughness change played a deciding role. The reason for this might be that different laser parameters result in different material deformation and removal processes, thereby resulting in different surface chemical compositions, microstructures, roughnesses and wetting properties.

A micro-opto-mechanical system (MOMS) technology for the fabrication of fiber-optic optoacoustic emitters is presented. The described devices are based on the thermoelastic generation of ultrasonic waves from patterned carbon films obtained by the controlled pyrolysis of photoresist layers and fabricated on miniaturized single-crystal silicon frames used to mount the emitters on the tip of an optical fiber. Thanks to the micromachining process adopted, high miniaturization levels are reached in the fabrication of the emitters, and self-standing devices on optical fiber with diameter around 350 µm are demonstrated, potentially suited to minimally invasive medical applications. The functional testing of fiber-optic emitter prototypes in water performed by using a 1064 nm Q-switched Nd-YAG excitation laser source is also presented, yielding broadband emission spectra extended from low frequencies up to more than 40 MHz, and focused emission fields with a maximum peak-to-peak pressure level of about 1.2 MPa at a distance of 1 mm from the devices.

This paper presents the charging and characterization of an organic micro electret array for vibration energy harvesting. Micro sized electrets with stable and high surface potential are essential for the long-term effectiveness of micro electrostatic power generators which harvest low-level vibration energy. In this study, a localized corona charging method to obtain micro sized electret areas on non-patterned macro sized dielectric thin film has been proposed to solve the problem of low charging efficiency and fast charge decay of micro sized electrets. This method involves using a shadow mask to transfer charge patterns and a triode corona charging configuration to facilitate charge penetration. Charging efficiency of 93.6% is achieved on an electret area of 100 µm × 100 µm, and 87% of its initial surface potential remains on the shrunken area of 50 µm × 50 µm after 240 days of storage. A technique combining SEM surface topography and non-contact measurement of the average surface potential has been developed to map the charge distribution on locally charged dielectric thin film and measure the surface potential on the micro sized charged area by incorporating the layout characteristic of a micro electret array.

The fabrication and evaluation of silicon micromechanical resonators using neutral beam etching (NBE) technology is presented. An etching technique based on a low energy neutral beam of Cl₂/F₂/O₂ is introduced for making nano-trench patterns on 5 µm-thick silicon. The NBE technology has been investigated to form a highly-anisotropic etching shape. A 5 μm-deep trench pattern having smooth side walls with a gap width of 230 nm is achieved by using NBE. Additionally, a fabrication method for silicon resonators using NBE technology is proposed. The resonant frequency of the fabricated devices with a length of 500 μm, width of 440 μm and thickness of 5 μm is 9.66 MHz, and the average quality factor (Q) value is around 78 000. The devices fabricated by both deep reactive ion etching (DRIE) and NBE are evaluated and compared. The devices fabricated by NBE show that the motional resistances are reduced by almost 11 times from 645 kΩ to 59 kΩ and their output signals (insertion loss) are increased by approximately 15 dB in comparison with those fabricated by DRIE. Especially, devices fabricated by NBE provide the higher Q factors (average Q factor value of around 78 000) than those (average Q factor value of around 61 000) fabricated by DRIE in the same resonator parameters and measurement conditions.

This paper presents a new type of soft photo-mask which can be used in contact photolithography for achieving small line-width, large area, and high throughput ultraviolet (UV) patterning. It starts from a polydimethylsiloxane (PDMS) mold replicated from a silicon master mold. A carbon black photo-resist (PR) is spin-coated on top of the PDMS mold and then thermally cured. After a contact transfer process, the solidified carbon black PR exists only in the concave region of the PDMS mold, which converts the PDMS mold into a carbon-black/PDMS soft photo-mask. Due to its flexibility, this soft photo-mask can be used in contact photolithography on a slightly curved substrate. Experiments on preparing this new soft photo-mask and its application for fabricating patterned sapphire substrates (PSSs) used in the light-emitting-diode (LED) industry are carried out. Successful results are observed.

Capacitive micromachined ultrasonic transducers (CMUTs) have great potential to compete with traditional piezoelectric transducers in therapeutic ultrasound applications. In this paper we have designed, fabricated and developed an acoustic lens formed on the CMUT to mechanically focus ultrasound. The acoustic lens was designed based on the paraxial theory and made of silicone rubber for acoustic impedance matching and encapsulation. The CMUT was fabricated based on the local oxidation of silicon (LOCOS) and fusion-bonding. The fabricated CMUT was verified to behave like an electromechanical resonator in air and exhibited wideband response with a center frequency of 2.2 MHz in immersion. The fabrication for the acoustic lens contained two consecutive mold castings and directly formed on the surface of the CMUT. Applied with ac burst input voltages at the center frequency, the CMUT with the acoustic lens generated an output pressure of 1.89 MPa (peak-to-peak) at the focal point with an effective focal gain of 3.43 in immersion. Compared to the same CMUT without a lens, the CMUT with the acoustic lens demonstrated the ability to successfully focus ultrasound and provided a viable solution to the miniaturization of the multi-modality forward-looking endoscopes without electrical focusing.

A six-axis sensor array has been developed to quantify the 3D force and moment loads applied in scoliosis correction surgery. Initially this device was developed to be applied during scoliosis correction surgery and augmented onto existing surgical instrumentation, however, use as a general load sensor is also feasible. The development has included the design, microfabrication, deployment and calibration of a sensor array. The sensor array consists of four membrane devices, each containing piezoresistive sensing elements, generating a total of 16 differential voltage outputs. The calibration procedure has made use of a custom built load application frame, which allows quantified forces and moments to be applied and compared to the outputs from the sensor array. Linear or non-linear calibration equations are generated to convert the voltage outputs from the sensor array back into 3D force and moment information for display or analysis.

The demand for safe and clean energy sources has become more important than ever worldwide. Thermionic power generation is one of these energy sources, which directly converts heat into electrical energy using thermionic electrons. We developed a micro-gap thermionic power generator, which operates at relatively low temperature using SiC as an emitter. Electrons are emitted and travel from the heated SiC emitter to the collector electrode by thermionic emission. In this work, we have firstly demonstrated low temperature operation at 830 ^oC as a result of micro-gap between the emitter and collector electrodes. An output power density of 11.5 mW/cm² is obtained. In addition, the heat losses from the emitter electrode are evaluated. Thermal conduction to the collector is by far the predominant thermal loss. In order to validate this result, a thermal resistance measurement device is built and the thermal resistance of the micro-gap is measured. Its value of 2.4 K/W allows for estimating in a more realistic way the heat loss by thermal conduction from the emitter to the collector via the gap. The newly estimated value still corresponds to a predominant thermal loss, hence highlighting the need for downsizing the SiO₂ columns of the micro-gap in order to increase the power conversion efficiency.

A novel dual-unit piezoresistive pressure sensor, consisting of a sensing unit and a dummy unit, is proposed and developed for on-chip self-compensation for zero-point temperature drift. With an MIS (microholes inter-etch and sealing) process implemented only from the front side of single (1 1 1) silicon wafers, a pressure sensitive unit and another identically structured pressure insensitive dummy unit are compactly integrated on-chip to eliminate unbalance factors induced zero-point temperature-drift by mutual compensation between the two units. Besides, both units are physically suspended from silicon substrate to further suppress packaging-stress induced temperature drift. A simultaneously processes ventilation hole-channel structure is connected with the pressure reference cavity of the dummy unit to make it insensitive to detected pressure. In spite of the additional dummy unit, the sensor chip dimensions are still as small as 1.2 mm × 1.2 mm × 0.4 mm. The proposed dual-unit sensor is fabricated and tested, with the tested sensitivity being 0.104 mV kPa⁻¹ 3.3 V⁻¹, nonlinearity of less than 0.08% · FSO and overall accuracy error of ± 0.18% · FSO. Without using any extra compensation method, the sensor features an ultra-low temperature coefficient of offset (TCO) of 0.002% °C⁻¹ · FSO that is much better than the performance of conventional pressure sensors. The highly stable and small-sized sensors are promising for low cost production and applications.

Solar thermal power generation is an attractive electricity generation technology as it is environment-friendly, has the potential for increased efficiency, and has high reliability. The design, modelling, and evaluation of solar thermoelectric generators (STEGs) fabricated on a silicon-on-insulator substrate are presented in this paper. Solar concentration is achieved by using a focusing lens to concentrate solar input onto the membrane of the STEG. A thermal model is developed based on energy balance and heat transfer equations using lumped thermal conductances. This thermal model is shown to be in good agreement with actual measurement results. For a 1 W laser input with a spot size of 1 mm, a maximum open-circuit voltage of 3.06 V is obtained, which translates to a temperature difference of 226 °C across the thermoelements and delivers 25 µW of output power under matched load conditions. Based on solar simulator measurements, a maximum TEG voltage of 803 mV was achieved by using a 50.8 mm diameter plano-convex lens to focus solar input to a TEG with a length of 1000 µm, width of 15 µm, membrane diameter of 3 mm, and 114 thermocouples. This translates to a temperature difference of 18 °C across the thermoelements and an output power under matched load conditions of 431 nW.

This paper demonstrates that by utilizing a solar concentrator to focus solar radiation onto the hot junction of a TEG, the temperature difference across the device is increased; subsequently improving the TEG's efficiency. By using materials that are compatible with standard CMOS and MEMS processes, integration of solar-driven TEGs with on-chip electronics is seen to be a viable way of solar energy harvesting where the resulting microscale system is envisioned to have promising applications in on-board power sources, sensor networks, and autonomous microsystems.

This article presents the development of a one-finger gripper that uses a variable van der Waals force to grip, transport and actively release a single SiO₂ spherical-like nano/micro-sized object. The diameters of the objects used (spheres) were between 800 nm to 50 μm. The van der Waals force becomes the dominant force for such objects (from 60 nN to 8 μN) if the materials are not electrically charged or have magnetic characteristics, and if the medium between the object and the one-finger gripper is a vacuum. Furthermore, the van der Waals force is several times greater than the gravitational force for such objects, so a two-finger gripper becomes unreliable when actively releasing a nano/micro object. Usually, the nano/micro object remains attached to one of the fingers at an unknown position and orientation. Our newly developed one-finger gripper does not have such problems. The van der Waals force between the gripper and the nano/micro object is increased by the deposition of H₂O crystals on the gripper's tip (gripping procedure), and decreased by sublimation of H₂O crystals on the gripper's tip (releasing procedure). This article presents both the theoretical conditions for the gripping/releasing of rigid spherical-like objects and experimental proof of these conditions. The results of our practical experimentation show that the gripping/releasing method can be applied to any shape of object and also to different materials.

In this study, a multi-step current density method was investigated to fill TSVs with different aspect ratios (⌀20 µm × 120 µm, ⌀30 µm × 130 m, ⌀40 µm × 140 µm and ⌀50 µm × 150 µm) simultaneously without voids. First, the effects of current density and TSV size on the growth mode of electrodeposited Cu were investigated. The experimental results indicated that low current density (1 mA cm⁻²) was favorable to bottom-up filling for TSVs with small size (⌀20 µm × 120 µm). The medium current density of 6 mA cm⁻² was favorable to bottom-up filling for the TSVs with large sizes (⌀40 µm × 140 µm and ⌀50 µm ×150 µm). The high current density of 9 mA cm⁻² could only be used for bottom-up filling in the ⌀50 µm × 150 µm TSV. Second, three kinds of initial shape of Cu-TSV at the beginning of electroplating were proposed to discuss the growth mechanism of electrodeposited Cu in TSVs. Then, the effect of temperature on the filling mode of the TSVs was investigated. It was found that the deposition rate at different locations of the TSV sidewall was more uniform at low temperature, which was helpful to form the bottom-up filling mode. Finally, all the TSVs with different aspect ratios were simultaneously filled void free at 20 °C when the current densities of 3 and 6 mA cm⁻² were applied for 90 min.

This paper reports on the optimization of the design of piezoelectric transducer elements integrated on doubly-clamped microbeam resonators utilized as (bio)chemical sensors. We report and emphasize the often forgotten influence of membrane stresses on defining the dimensions and optimal position of the piezoelectric transducer elements. The study takes into account stress induced structural changes and provides models for the equivalent motional parameters of resonators with particular shapes of the transducers matching the flexural modes of vibration. The above is analyzed theoretically using numerical models and is confirmed by impedance measurements and optical measurements of fabricated doubly-clamped beam resonators. We propose various transducer designs and highlight the advantages of using higher order vibration modes by implementing specially designed mode matching transducer elements. It is concluded that the paper describes and highlights the importance of accounting for the membrane stresses to optimize the resonator performance and the low power in electronic feedback of resonating sensing systems.

This work investigates the flow instability of thermoplastic polymer melt that occurs on the flow front when it enters micro-cavities. On the flow front, it was observed that small balls are formed and coalesce with each other, creating many micro-weld lines. The experimental results in this work showed occurrence of this phenomenon for polypropylene and polyamide but not for high density poly(ethylene), poly(methylmethacrylate) or acrylonitrile butadiene styrene. It was found that onset of this instability is related to the spherulite size. The effects of temperature and geometry have been scrutinized. As a conclusion, the ratio of spherulite size and channel width has been proposed as a dimensionless number related to this instability.

This work demonstrates a continuous flow plasma/blood separator using a vertical submicron pillar gap structure. The working principle of the proposed separator is based on size exclusion of cells through cross-flow filtration, in which only plasma is allowed to pass through submicron vertical pillars located tangential to the main flow path of the blood sample. The maximum filtration efficiency of 99.9% was recorded with a plasma collection rate of 0.67 µl min⁻¹ for an input blood flow rate of 12.5 µl min⁻¹. The hemolysis phenomenon was observed for an input blood flow rate above 30 µl min⁻¹. Based on the experimental results, we can conclude that the proposed device shows potential for the application of on-chip plasma/blood separation as a part of integrated point-of-care (POC) diagnostics systems.