Design and fabrication of novel micro electromagnetic actuator

This study designs, fabricates, and characterizes a novel micro electromagnetic actuator comprising a PDMS diaphragm, a polyimide-coated copper micro coil, and a permanent magnet. When an electrical current is passed through the micro coil, a magnetic force is induced between the coil and the magnet which causes the diaphragm to deflect, thereby creating an actuation effect. The experimental results demonstrate that the diaphragm deflection can be accurately controlled by regulating the current passed through the micro coil. It is shown that the maximum diaphragm deflection within elastic limits is 150 μm; obtained by passing a current of 0.6 A through a micro coil with a line width of 100 μm. The micro actuator proposed in this study is easily fabricated and is readily integrated with existing bio-medical chips due to its planar structure.     

The design and fabrication of a low-field NMR probe based on a multilayer planar microcoil

The nuclear magnetic resonance (NMR) probe has great influence on signal transmission and reception in NMR technology applications. In this paper, we present a design, fabrication, and test of an NMR probe comprised of a multilayer planar microcoil with a polydimethylsiloxane (PDMS) microchannel. First, geometric parameters of the probe are determined through theoretical analysis. Second, based on a glass substrate, the multilayer planar microcoil is manufactured using repeated photolithography and electroplating processes. During the fabrication process, the polyimide layer is used to package the coil, and the PDMS interlayer is used to adjust the distance from centerlines between the coil and the sample chamber. Third, the resistance and the quality factor of the coil are found to be 1.2158 Ω and 7.217, respectively, at a Larmor frequency of 28.1 MHz. Finally, the NMR probe is tested in an NMR experiment. The transverse relaxation time T₂ for the solid PDMS is 20.6 ± 0.4 ms, which is in agreement with 21.1 ± 0.2 ms obtained by a Bruker Minispec MQ60. Results show that the design and fabrication of this NMR probe are feasible for time-domain NMR applications.     

Geometrical analysis of planar coil design for fluxgate magnetometer

This paper presents geometrical analysis on the design of planar coupled coils for use as magnetic sensors. Inductance and magnetic coupling of the coil are analyzed using field solver analyzer ASITIC. Effects of different coil parameters, such as winding number, spacing, and width are discussed in detail. As results, the coil design considers not only the inductance value and the height of magnetic coupling, but also the geometrical area consumed. The analysis is verified by experimental data from coupled coil fabricated using surface micromachining techniques. An outer coil area having a typical dimension of 1.8 × 1.8 mm² and a fix inner coil diameter of 500 μm was fabricated. Coupling factor of about 0.7 and self inductance of 12.7 nH were achieved, which show a reasonably good agreement with the simulated results. The coil platform developed offers an integrated solution for the design of fluxgate magnetometer.     

Micropatterning of sandwiched FeCuNbSiB/Cu/FeCuNbSiB for the realization of magneto-impedance microsensors

This work presents the fabrication of magnetic field microsensors based on the magneto-impedance phenomenon and dedicated to NDC applications. The multilayer structure, ferromagnetic/conductive/ferromagnetic, is composed of a copper layer sandwiched with two Finemet^? alloy films. The later, initially an amorphous material, is nanocrystallized by heat treatment. The fabrication process has been optimized in order to minimize coercivity and induce transversal anisotropy. The technological defects induced by the lift-off and sputtering processes change the magneto-impedance properties of the sensors. Eliminating these defects permits the sensor to reach to a sensitivity of 1,200 V/T/A at 30 MHz with a bias field larger than the anisotropy field and without hysteresis. The angular dependence of the sensitivity shows that the sensor is only sensitive to the axial component of the magnetic field.     

MEMS based humidity sensor using Si cantilever beam for harsh environmental conditions

The RF applications like voltage controlled oscillators, tunable filters, resonators etc., requires tunable capacitors in their designs. This paper presents the design of wide range MEMS tunable capacitors for RF applications. This design consists of an air suspended bottom plate and a fixed top plate. The top fixed plate and the suspended bottom plate form the tunable capacitor. The capacitance range of this tunable capacitor is from 69.172 to 138.344 nF. This range is wider compared with the conventional MEMS tunable capacitors of tuning ranges in pico Farads. The fabrication process is similar to that of the existing standard integrated circuit fabrication processes, which makes this design suitable for integrated RF applications.     

Electromagetically driven microvalve

We discuss photolithographic fabrication techniques and experimental results for a prototype electromagnetically driven microvalve. The valve is constructed on a silicon substrate, using a magnetic suspension spring with a valve cap, a valve plate with a 30 μm diameter bore, and an external coil for driving the valve cap. The external electromagnetic drive approach was chosen for its ease of use and practicality in controlling the valve actuator. The valve cap, made of soft magnetic material (NiFe) and supported by the spring, moves vertically as a result of the magnetic field applied by the external coil. To precisely adjust both the valve cap and the valve plate bore and to minimize fluid leakage, a new self-alignment process was developed. The valve is controlled by a 0.1–100 Hz rectangular magnetic field applied by the external coil. The resulting minimum gas flow rate can be controlled to within the neighborhood of 3 × 10⁻⁵ torr·l/s.     

Characterization of flexible RF microcoils dedicated to local MRI

In magnetic resonance imaging (MRI), the electrical performance of the RF coil is critical to achieve sufficient signal to noise ratio (SNR), especially when microscopic structures [about (100 μm)³] have to be observed. In this field of application, we have developed a device (microcoil) based on the original concept of monolithic resonator, dedicated to superficial region imaging (human skin) or small animal imaging. This paper presents the developed process based on micromoulding. Flexible thin films of polymer have been used as dielectric substrate so that the microcoil could be form-fitted to non-plane surfaces. First, electrical characterizations of the RF coils have been performed. The results were compared to the expected values. A flexible RF coil of 15 mm diameter was then used to perform proton MRI of a saline phantom. When the coil was form-fitted to the phantom surface, a maximum SNR gain of 2 was achieved with respect to identical but plane RF coil. Finally, the flexible coil was used to perform MRI in vivo with high spatial resolution on a mouse using a small animal dedicated scanner operating at 2.35 T.     

High standoff dual-mode-actuation MEMS switches

MEMS switches based on a dual-mode actuation scheme that simultaneously allows for large standoff heights and low clamping voltages have been designed and fabricated. These devices are based on the use of a transient external magnetic field to bring the actuating portion of the switch close to a dielectric-coated clamping electrode, followed by application of an electrostatic clamping voltage to keep the switch closed. Since the clamping voltage is applied when the switch is closed, this voltage can be relatively small. This approach is particularly attractive for RF applications such as arrays of switches in reconfigurable aperture antennas. The arrays of switches are simultaneously closed by the magnetic field generated by an external magnetic source, then selected switches are clamped by electrostatic force using low voltages to maintain the ON state. Their utility in such an array has been demonstrated and several different design variations have been explored to improve switch performance. Contact resistance as low as 0.37 Ω has been achieved, with actuating field strength of 40 Gauss. These switches possess a large open state air gap (25 μm), and are able to pass high currents in excess of 1 A under low frequency or DC operation. The large OFF state impedance allows for their usage in switching applications in RF devices. Their high frequency functionality has been tested to find that their open-state impedance was identical to that of a perfect open up to 9 GHz and their RF reconfigurability has been demonstrated in a monopole/dipole test bed.     

Design, fabrication and testing of a high performance silicon piezoresistive Z-axis accelerometer with proof mass-edge-aligned-flexures

This paper presents design, fabrication and testing of a quad beam silicon piezoresistive Z-axis accelerometer with very low cross-axis sensitivity. The accelerometer device proposed in the present work consists of a thick proof mass supported by four thin beams (also called as flexures) that are connected to an outer supporting rim. Cross-axis sensitivity in piezoresistive accelerometers is an important issue particularly for high performance applications. In the present study, low cross-axis sensitivity is achieved by improving the device stability by placing the four flexures in line with the proof mass edges. Various modules of a finite element method based software called CoventorWare^™ was used for design optimization. Based on the simulation results, a flexure thickness of 30 μm and a diffused resistor doping concentration of 5 × 10¹⁸ atoms/cm³ were fixed to achieve a high prime-axis sensitivity of 122 μV/Vg, low cross-axis sensitivity of 27 ppm and a relatively higher bandwidth of 2.89 kHz. The designed accelerometer was realized by a complementary metal oxide semiconductor compatible bulk micromachining process using a dual doped tetra methyl ammonium hydroxide etching solution. The fabricated accelerometer devices were tested up to 13 g static acceleration using a rate table. Test results of fabricated devices with 30 μm flexure thickness show an average prime axis sensitivity of 111 μV/Vg with very low cross-axis sensitivities of 0.652 and 0.688 μV/Vg along X-axis and Y-axis, respectively.     

Design of MEMS switch for RF applications

Components like passive electronically scanned (sub) arrays, T/R modules, reconfigurable antennas etc., in RF applications are in need of MEMS switches for its re-configurability and polarization. This paper presents the analysis, design and simulation of a MEMS switch. The switch proposed in this paper is intended to work in the frequency range of 4–8 GHz. The proposed switch fulfills the switching characteristics concerning the five requirements loss, linearity, high switching speed, small size/power consumption, low pull down voltage following a relatively simple design, which ensures reliability, robustness and high fabrication yield. The switch implemented in this paper is based on the integration mode of operation and widely used in RF applications.     

Modeling, microfabrication and experiments of a free–free cantilever bistable micro mechanism supported with a diamond configuration

Bistable micro mechanisms are gaining great attention in MEMS applications. This paper presents the mechanical modeling and experimental characterization of a bistable torsion/cantilever micro latching mechanism for performing low power bistable relay applications. The bistable micro mechanism consists of two cantilevers which form symmetrical rocker levers. The free–free cantilever is suspended by a diamond skeleton which in turn is attached to a torsion cantilever. A permanent magnet is placed beside for holding the closed state with a permalloy soft magnetic circuit. The special diamond support is designed to enhance the stiffness of the overhang beams. In order to deduce the spring stiffness of system, a mechanical modeling of the leveraged torsion/cantilever system was performed by Castigliano’s theorem. Meanwhile, the magnetostatic latching force was also deduced by the Maxwell electromagnetism theory. Then the device has been prepared by a laminated copper sacrificial layer process. This process can facilitate the fabrication complexities of traditional magnetic device with coil structures. Finally, mechanical performance was characterized by an atomic force microscopy, combined with finite element simulation using ANSYS^™ package and analysis model as well. Two stable states of the micro mechanism were hold successfully with no power consumption by interferoscope profilometry of WYKO optical profiling system.     

A magnetic bead-based DNA extraction and purification microfluidic device

This article introduces a novel magnetic bead-based DNA extraction and purification device using active magnetic mixing approach. Mixing and separation steps are performed using functionalised superparamagnetic beads suspended in cell lysis buffer in a circular chamber that is sandwiched between two external magnetic coils. Non-uniform nature of magnetic field causes temporal and spatial distribution of beads within the chamber. This process efficiently mixes the lysis buffer and whole blood in order to extract DNA from target cells. Functionalized surface of the magnetic beads then attract the exposed DNA molecules. Finally, DNA-attached magnetic beads are attracted to the bottom of the chamber by activating the bottom magnetic coil. DNA molecules are extracted from magnetic beads by washing and re-suspension processes. In this study, a circular PMMA microchamber, 25 μL in volume, 500 μm in depth and 8 mm in diameter was fabricated to purify DNA from spiked bacterial cell cultures into the whole blood sample using Promega Magazorb DNA extraction kit. The lysis efficiency was evaluated using a panel of Gram-positive (Bacillus subtilis) and Gram-negative (Escherichia coli) bacterial cells cultures into the blood sample to achieve approximately 100,000 copy levels inside the chip. Manufacturer’s standard extraction protocol was modified to a more simplified process suitable for chip-based extraction. The lysis step was performed using 5 min incubation at 56 °C followed by 5 min incubation at room temperature for binding process. Temperature rise was generated and maintained by the same external magnetic coils used for active mixing. The yield/purity and recovery levels of the extracted DNA were evaluated using quantitative UV spectrophotometer and real-time PCR assay, respectively. Real-time PCR results indicated efficient chip-based bacterial DNA extraction using modified extraction protocol comparable to the standard bench-top extraction process.     

A micro electromagnetic low level vibration energy harvester based on MEMS technology

This paper presents a micro electromagnetic energy harvester which can convert low level vibration energy to electrical power. It mainly consists of an electroplated copper planar spring, a permanent magnet and a copper planar coil with high aspect ratio. Mechanical simulation shows that the natural frequency of the magnet-spring system is 94.5 Hz. The resonant vibration amplitude of the magnet is 259.1 μm when the input vibration amplitude is 14 μm and the magnet-spring system is at resonance. Electromagnetic simulation shows that the linewidth and the turns of the coil influence the induced voltage greatly. The optimized electromagnetic vibration energy harvester can generate 0.7 μW of maximal output power with peak–peak voltage of 42.6 mV in an input vibration frequency of 94.5 Hz and input acceleration of 4.94 m/s² (this vibration is a kind of low level ambient vibration). A prototype (not optimized) has been fabricated using MEMS micromachining technology. The testing results show that the prototype can generate induced voltage (peak–peak) of 18 mV and output power of 0.61 μW for 14.9 m/s² external acceleration at its resonant frequency of 55 Hz (this vibration is not in a low ambient vibration level).     

Fabrication of a spiral microcoil using a 3D-LIGA process

LIGA processes have been developed generally in the 2.5D world. We introduced techniques of 3D X-ray lithography and worm injection molding with a unscrewing release mechanism, and succeeded in the development to three dimensions of LIGA process. We called this technology 3D-LIGA process, and came to be able to fabricate the plastic molded product with a spiral microstructure. Furthermore, we succeeded in the trial production of a spiral microcoil using 3D-LIGA process and metallization technique combining flat and smooth electroplating with a leveling agent and an isotropic chemical etching. The diameter of this microcoil was 0.5 mm and the length was 1 mm. The width of the Cu coil line was 10 μm, and the pitch was 20 μm. Moreover, we measured characteristics of this microcoil as an inductor. The inductance and the quality factor at the frequency of 1 GHz were 91 nH and 5.8, respectively. This is the first time successful fabrication of an electric device with a 3D form like a spiral microcoil using the 3D-LIGA process has been achieved.     

A low voltage vertical comb RF MEMS switch

Design and simulations of a novel RF MEMS switch is reported as a solution to many RF wireless applications. A new comb structure for RF MEMS switch is proposed for low voltage and high frequency operations. Isolation degree and actuation voltage, both improved by the new structure. The mechanical and electromagnetic simulation results show better performance for this new switch compared to parallel plate switch. The simulation is done by the intellisuit and HFSS softwares. The Simulation results show that the actuation voltage is decreased by 13% and the linearity of the switch displacement with respect to the actuation voltage is improved by 22% compared to the parallel plate structure. The HFSS simulation results indicate an insertion loss better than 0.33 dB at 50 GHz and isolation greater than 13.4 dB at 50 GHz.     

Novel U-shape gold nanoparticles-modified optical fiber for localized plasmon resonance chemical sensing

A novel fiber-optic localized plasma resonance (FO-LPR) sensor composed of a U-shape optical fiber was proposed and demonstrated in this study. The U-shape optical fiber was fabricated by a femtosecond laser micromachining system. The dimensions of the U-shape zone were 100 μm in depth measured from the surface of the polymer jacket layer, 80 μm in width in the jacket layer, 60 μm in width in the cladding layer. The total length is 5 mm. After laser annealing treatment, the average surface roughness was 205.8 nm as determined by Atom Force Microscope (AFM). The exposed surface of the U-shape fiber was modified with self-assembled gold nanoparticles to produce the FO-LPR sensor. The response of the sensor shows that the signal increases linearly with increasing refractive index. The sensor resolution of the sensor was determined to be 1.06 × 10⁻³ RIU.     

Hard and soft magnetic materials for electromagnetic microactuators

An important aspect of the development of electromagnetic microactuators is the search for suitable materials as well as the development of the respective deposition and patterning processes. Within the Collaborative Research Center 516 “Design and Fabrication of Active Microsystems”, it is the task of the subproject B1 “fabrication of magnetic thin films for electromagnetic microactuators” to perform these investigations. The materials of interest can be divided into two groups: hard magnetic materials and soft magnetic materials. Materials with optimized properties and fabrication processes have been developed within both groups. An example is Samarium–Cobalt (SmCo), which can either be deposited using magnetron sputtering as Sm₂Co₁₇ with a very high energy product or in the SmCo₅ phase using gas flow sputtering with very high deposition rates. In the area of soft magnetic materials, investigations on Nickel-Iron (NiFe) especially NiFe81/19 were followed by the evaluation of NiFe45/55, which features a higher saturation flux density B _s and relative permeability μ _r. Furthermore, current investigations focus on Cobalt-Iron (CoFe) and its further increased saturation flux density B _s and relative permeability μ _r. Current tasks include the stabilization of the fabrication processes to achieve good material properties (i.e. electroplating of CoFe) or a shortening (e.g. by using heated substrates during deposition) by using process alternative not used so far. Another topic is the integration into fabrication processes, i.e. the investigation of process stability and compatibility.     

Customized trapping of magnetic particles

This paper presents an efficient technique for trapping of magnetic particles in confined spatial locations using customized designs of micro-coils (MCs). Large magnetic field gradients of up to 20 T/mm and large magnetic forces in the range of 10⁻⁸ Newton on magnetic particles with diameter of 1 μm have been achieved using MCs with several planar geometrical configurations. A large magnetic field gradient is generated and enhanced by two structural parameters: the small width and high aspect ratio of each single conductor and the ferromagnetic pillars positioned at high-flux density locations. This arrangement creates very steep magnetic potential wells, in particular at the vicinity of the pillars. The system allowed capturing of suspended magnetic particles as far as 1,000 μm from the center of the device. Magnetic particles/cells have been trapped and confined in single and in arrays of deep magnetic potential wells corresponding to the MCs configuration.     

Design of coplanar waveguide multilayer square spiral inductors for monolithic microwave integrated circuits

A square indicator using multilayer coplanar waveguide transmission lines on a GaAs fabricated by using monolithic microwave integrated circuits (MMIC) technology is presented. The polyimide layer formation, curing and dry etching processes are used in an attempt to obtain high quality dielectric layers suitable for MMIC applications. The experimental fabrication progress provides two metal layers with two polyimide spacer dielectric layers. A brief overview of the electromagnetic design process is included. The performance of the proposed spiral inductor is investigated experimentally and with electromagnetic simulations (Sonnet em) up to 20 GHz using RF‐on‐water measurements. A very good agreement is achieved, despite the highly three‐dimensional nature of the structure. ©1999 John Wiley & Sons, Inc. Int J RF and Microwave CAE 9: 86–92, 1999     

Surface micromachined on-chip transformer fabricated on glass substrate

On-chip micro-transformer on high resistive glass substrate has been developed. The transformer consists of stacked spiral coil with square interwinding coil structure which is fabricated using surface micromachining technique. The performance of the micro-transformer is illustrated through low and high frequency measurements. The characteristics of glass based transformer are compared with conventional Si-based micro-transformer. The results show that the RF performance of the glass-based transformer is improved compared to that of silicon-based transformer. The process fabrication of the device is simple, highlighting a good prospect for the future three-dimensional RF-MEMS device application.