Table of contents

In this paper, fabrication and testing of a miniaturized microcantilever-based particulate matter detector with integrated electrostatic on-chip ultrafine particle (UFP) separation and collection are presented. Mass added to the sensor causes a resonance frequency shift. To attract naturally charged particles, the cantilever is equipped with a collection electrode. In addition, a µ-channel is integrated, to improve the particle collection efficiency and to enable a size/mass-related particle separation. For electrical read-out, piezo-resistive struts are attached to the cantilever sidewalls near its clamping. This design offers high miniaturization potential, since no integration of transducing electronics on the cantilever beam is needed. The sensors are fabricated using Si bulk material and standard micromachining technology; the cantilevers have a thickness of 3  ±  0.5 µm, a width of 3.1  ±  0.3 µm, 5.9  ±  0.4 µm or 10.5  ±  0.4 µm and a length of 118.7  ±  0.8 µm, 168.8  ±  0.8 µm or 171.2  ±  1 µm, respectively. To this end, a front-side release process using cryogenic inductive-coupled plasma reactive ion etching was developed, which does not require additional sidewall passivation steps. Testing of the resonator function by operating the sensor inside a scanning electron microscope and reference measurements inside a temperature-controlled test chamber using synthetic carbon UFPs (~160 nm average mass concentration distribution) and a fast mobility particle sizer as a reference instrument were carried out. Here, the ability to detect low UFP mass concentrations in the range  <10 µg m⁻³ could be shown with a limit of detection of ~1 µg m⁻³ and a collection time of ~10 min. In addition, a voltage dependence of the collection efficiency was found at constant UFP-concentration conditions, which is an indication of size-selective UFP collection.

A passively temperature-compensated micromechanical resonator based on an electrical stiffness frequency pulling technique was demonstrated. In particular, a 2.92 MHz free–free beam resonator achieved by a 0.35 µm 2-poly-4-metal complementary metal-oxide semiconductor microelectromechanical systems (CMOS-MEMS) process platform yields a nearly zero first-order temperature coefficient of frequency (TCF₁), from  −69.78 ppm °C⁻¹ of an uncompensated version to  +0.43 ppm °C⁻¹, and a 12×  lower overall frequency drift from the uncompensated 5885 ppm to 496 ppm between 0 °C and 85 °C. The electrical stiffness compensation technique previously demonstrated on a CMOS-incompatible poly-Si surface micromachining process consumes no dc power consumption in contrast to other active methods. In this work, an improved design of the in-plane U-shaped compensating electrode allows not only the employment by a standard CMOS process but also layout-defined temperature dependency of the electrical stiffness via varying the length of the compensating electrode. A theoretical model predicts the thermally induced extension of the compensating electrode and further leads to an optimum electrode length which allows the use of only one voltage source for both compensation and polarization bias voltages. The measured results are compared with the analytical model prediction and discussion on the effects of process induced device parameter variations is presented.

Single-crystalline magnesium oxide (MgO) is a material with outstanding high-temperature resistance and huge potential for use in high-temperature devices, light emitting devices and optical display fields. The investigation of fabricating a microstructure on the MgO substrate using wet etching process is conducted. The temperature and concentration dependence of the etching rate on the materials, and the surface roughness of the microstructure, are explored and analyzed. A microcavity with good profile and low roughness, 80.7 µm in depth and 4 mm in diameter, has been generated on a MgO substrate with a 50% H₃PO₄ etchant solution at ~100 °C. Optical microscopy, atomic force microscopy, scanning electron microscopy, x-ray photoelectron spectroscope and x-ray diffraction analysis are employed to demonstrate the successful application of wet etching for improving the etching rate and surface morphology without the deterioration of the surface roughness. Our work is of fundamental importance in the fabrication of MgO-based devices (such as pressure sensors, vibration sensors and photonic resonators) and the improvement of growth condition of oxide films on MgO substrates.

Magnetic fluids have been around since the 1940s. They come in different forms: magnetorheological fluids (MR fluids) and ferrofluids. MR fluids characterise themselves by having a large change in viscosity under the influence of a magnetic field. Ferrofluids have a significantly smaller change in viscosity, however ferrofluids are colloidal suspensions. After their discovery many applications followed, such as the MR clutch, magnetic damper and bearing applications, in which the fluids are subjected to ultra high shear rates. Little information is available on what happens to the rheological properties under these conditions. In general, the characteristics determined at lower shear rates are extrapolated and used to design new devices. Magnetic fluids have potential in the high tech and high precision applications and their properties need to be known in particular at shear rates around 10⁶ s⁻¹. Commercially available magnetorheometers are not able to measure these fluids at ultra high shear rates and are limited to 10⁵ s⁻¹. Therefore a new magnetorheometer is required to measure ultra high shear rates. In this paper the physical limitations of current measuring principles are analysed and a concept is designed for ultra high shear rate rheometry in combination with a magnetic field. A prototype is fabricated and the techniques used are described. The prototype is tested and compared to a state of the art commercial rheometer. The test results of the prototype rheometer for magnetic fluids show its capability to measure fluids to a range of 10⁴ s⁻¹– s⁻¹ and the capability to measure the magnetorheological effect of magnetic fluids.

The vertical integration of multiple silicon nanowires (multi-SiNWs) has an outstanding ability to enhance drive current, sensitivity and noise immunity by maximizing nanowire density. However, the crystal plane of the SiNW prepared by the present technology for the vertical stacked integration is indeterminate and has plasma damage. In this paper, a novel fabrication method for vertically stacked SiNWs with inverted triangular and diamond-shaped cross-sections on (1 0 0) single crystal silicon wafer is developed and presented, using conventional micromachining processes. The fabrication is based on the crystal plane distribution and anisotropic etching characteristics of (1 0 0) single crystal silicon. An iteration process of self-aligned dry etching and wet etching is first designed to form vertically stacked triangular and diamond-shaped silicon columns. After thermal oxidation thinning and removal of the oxide layer, the vertically stacked triangular and diamond-shaped SiNWs without plasma damage are obtained in the double silicon columns. The vertically integrated approach not only precisely controls the position and shape of the SiNWs but also determines the crystal plane and orientation of the SiNWs. In addition, the triangular and diamond-shaped SiNWs have a larger surface-to-volume ratio than circular and rectangular-shaped SiNWs with the same cross-sectional area and the same length. Therefore, this method can provide a novel, controllable, and economical way to vertically stack more SiNWs with larger surface-to-volume ratio into one chip for high-performance device applications.

We present theory for operation and experimental results for a nanoscale pump implemented in silica thin films that uses electrostatic actuation. The devices were implemented on silicon substrates using standard microfabrication recipes. Using pressures induced by capillary forces, the pressures exerted on pump membranes through electrostatic forces, and the approximate displacement per stroke we predict the pump speed operating the device over a range of frequencies and voltages. For membranes 100 nm thick, 170 V was required for pump actuation, providing exquisite control of pumping rates of less than 1 fl s⁻¹ per nanochannel.

A new method for continuous separation of microparticles in viscoelastic fluid is reported. A series of sharp corners were fabricated at one side of a microchannel, which induced the curved streamline and the asymmetric distribution of the elastic force. The Newtonian sheath flow was utilized to squeeze microparticles to the side wall with sharp corners at the inlet. Particles were subjected to inertial forces, elastic force and viscous drag force, all of which pointed to the straight wall side. Stronger forces were exerted on larger particles, leading to size-dependent migration of particles across the interface between the Newtonian and the viscoelastic fluids. The influence of the flow rate ratio on the particle separation was also studied. The results show that the sharp corners and the co-flowing fluid system significantly enhanced particle lateral migration, achieving complete particle separation at a low flow rate and in a short channel length. The particle separation efficiency was further increased at a higher flow rate ratio (sheath flow/sample flow). With a simple structure and small footprint, this device has great potential to be used in a variety of particle separation processes for lab-on-a-chip applications.

Planar splitting and recombining micromixers have already been investigated due to their high mixing performance and simple fabrication process. However, there is still a lack of research on the mixing process under various geometrical parameters, especially the turning angles. Our research aims to investigate the characteristics of flow fields and the mixing performance of planar splitting and recombining micromixers with different asymmetric structures, using combined mixing experiments and numerical simulation. Four kinds of asymmetric structures, including the circular structure and the rhombic structure featured with three turning angles (30°, 45° and 60°), were designed and fabricated during the current research. The mixing performance was enhanced by the chaotic advection derived from secondary flows. The form and the intensity of the secondary flows differed between the four kinds of asymmetric structures due to the sharpness and the position of the changes in flow direction varying. A nondimensional parameter F, which considers both the mixing performance and the pressure drop, was presented to evaluate the overall performance of the micromixers. Compared with micromixers with symmetric structures, micromixers with asymmetric structures had a better overall performance. The micromixer with circular asymmetric structures exhibited the best overall performance, owing to the fully filled Dean vortices and a greater existing area of Dean vortices. In the case of rhombic asymmetric structures, a larger turning angle led to the better mixing performance, but the overall performance was affected by the higher pressure drop. The results obtained indicate that the planar splitting and recombining micromixer with circular asymmetric structures provides a satisfactory choice in the fluids mixing process of microfluidic systems.

The fabrication of micro products is gradually expanding due to their need in micro feature-based frameworks, which require a multitude of functions to be integrated. Electro discharge deposition (EDD) is an emerging additive manufacturing process to create micro products. In the present paper, simulation of an EDD process has been investigated in the presence and absence of maximum magnetic flux density. In the first stage of simulation, a thermo–physical model has been developed to find the melt volume in single pulse discharge. In the second stage, initially the optimum orientation and location of the magnet to be placed around the EDD plasma are identified, and subsequently, in the presence of maximum magnetic flux density, heavy species transport is used to study the impact of the process on the height and weight of deposition. Experiments are carried out to validate the simulation results. From the results obtained it is observed that the height of deposition is increased by 23.5% in the presence of the magnetic field.

In this paper, we demonstrate the fabrication and characterization of lithium niobate (LN) based Lamb wave mode (S0 and SH0) resonators that address the stringent requirements of RF filtering for modern communication systems. The devices consist of a 400 nm-thick X-cut LN membrane anchored from two ends with interdigitated transducer (IDT) on the top. We present a frequency-scalable process flow using e-beam lithography for the fabrication of ultra-high frequency ( to Hz) devices. Our fabricated devices yield the highest reported electromechanical coupling () of 31% and 40% for S0 and SH0 modes, respectively, in X-cut LN. We also investigate the influence of IDT material and coverage on and quality factor () by fabricating identical devices with aluminum and platinum electrodes with electrode coverages ranging from 20% to 70%.

Flexible pressure sensing plays a critical role in the human–machine interaction; therefore highly sensitive pressure sensors have promising potential in such applications. Capacitive pressure sensors have inherent attributes of simple configuration and fast response time. However, the existing applications of sensors are limited by the limited sensitivity as well as complex manufacturing. Herein, a highly sensitive ionic pressure sensor with the microstructured dielectric layer has been proposed. The polycarbonate membrane is used as the template to manufacture the microstructure of the concave meniscus. By packing the top electrode, dielectric layer and bottom electrode, the ionic pressure sensor is fabricated. The sensor presents a sensitivity of 35.96 k Pa⁻¹ with an excellent robustness of tolerating repeated pressure for at least 200 000 cycles without fatigue. In addition, the response time of the sensor is 21 ms and the limit of detection is 0.61 Pa. The ionic pressure sensor offers a highly sensitive sensing device for robotics and human–machine interaction. Furthermore, the concave meniscus realized by the template-based method provides a novel guideline for other microstructure-enabled devices.

In this work, the development of an active high-density transverse intrafascicular micro-electrode (hd-TIME) probe to interface with the peripheral nervous system is presented. The TIME approach is combined with an active probe chip, resulting in improved selectivity and excellent signal-to-noise ratio. The integrated multiplexing capabilities reduce the number of external electrical connections and facilitate the positioning of the probe during implantation, as the most interesting electrodes of the electrode array can be selected after implantation. The probe chip is packaged using thin-film manufacturing techniques to allow for a minimally invasive electronic package. Special attention is paid to the miniaturization, the mechanical flexibility and the hermetic encapsulation of the device. A customized probe chip was designed and packaged using a flexible, implantable thin electronic package (FITEP) process platform. The platform is specifically developed for making slim, ultra-compliant, implantable complementary metal-oxide-semiconductor based electronic devices. Multilayer stacks of polyimide films and HfO₂/Al₂O₃/HfO₂ layers deposited via atomic layer deposition act as bidirectional diffusion barriers and are key to the hermetic encapsulation. Their efficacy was demonstrated both by water vapor transmission rate tests and accelerated immersion tests in phosphate buffered saline at 60 °C. Using the hd-TIME probe, an innovative implantation method is developed to prevent the fascicles from moving away when the epineurium is pierced. In addition, by transversally implanting the hd-TIME probe in the proximal sciatic nerve of a rat, selective activation within the nerve was demonstrated. The FITEP process platform can be applied to a broader range of integrated circuits and can be considered as an enabler for other biomedical applications.