Florent Cros

Integrated vertical screen microfilter system using inclined SU-8 structures

A multidimensional, vertical screen filter system is developed in which structures analogous to the mesh of a window screen are extended vertically through the cross-sectional area of a simultaneously-formed flow channel. Vertical screens with heights of up to 400 microns and aperture sizes of 10 microns have been achieved in a simple, multiexposure fabrication approach without the need for stacking or lamination. A triple filtering system with multiple inlet and outlet streams and three different mesh sizes of 57.3 /spl mu/m, 27.3 /spl mu/m, and 10.0 /spl mu/m in its horizontal diagonal has been simultaneously fabricated with flow channels and tested. Each mesh filters out microparticles larger than 35 /spl mu/m, 18 /spl mu/m, and 6 /spl mu/m, accordingly. In addition to microfiltering, the utility of the vertical screen filter structure as a passive micromixer has been demonstrated.

Very high-Q inductors using RF-MEMS technology for System-On-Package wireless communication integrated module

We present the fabrication and the characterization of very high-Q suspended RF-MEMS inductors for RF applications in C-band, X-band and Ku-band. The fabrication technique relies on conventional MEMS micro-machining on a low cost ceramic RF substrate. This low temperature, low cost manufacturing technique is therefore compatible with the fabrication of a complete S-O-P wireless integrated module. A physical based model of the inductors is presented. It takes into account the influence of substrate losses and radiation losses. The fabricated devices exhibit very high performances such as Q above 100 and self-resonance frequency as high as 50 GHz.

A sacrificial layer approach to highly laminated magnetic cores

The incorporation of laminations into micromachined magnetic components has the potential to reduce eddy current losses induced in the cores of these components. This paper reports a manufacturing technique for the fabrication of highly laminated cores. The approach is based on an alternating, conformal sequential electroplating of layers of NiFe and Cu, followed by selective sacrificial etching of the Cu. Since the copper sacrificial interlayer is itself conducting, it can act as a plating base for the subsequent deposition of NiFe without the necessity of multiple vacuum steps, multiple coating of insulating layers, or multiple photolithography steps. Highly laminated structures can therefore be achieved merely by alternating plating baths during fabrication, followed by selective removal of the Cu layers to provide electrical insulation between the magnetic layers. The fabrication approach can be readily adapted to a wide range of core geometries. To illustrate the improvements in magnetic properties achievable using this technique, the magnetic core fabrication technology has been successfully combined with integrated solenoid-like coils in order to fabricate a complete integrated inductor, which has been designed to operate in the low MHz range for power conversion applications. Inductors with highly laminated cores fabricated using the sacrificial layer approach exhibit quality factors exceeding those of unlaminated core devices by a factor of 2-3 at a frequency of 1 MHz.

Magnetic induction machines integrated into bulk-micromachined silicon

This paper presents the design, fabrication, and characterization of laminated, magnetic induction machines intended for high-speed, high-temperature, high-power-density, silicon-based microengine power generation systems. Innovative fabrication techniques were used to embed electroplated materials (Cu, Ni/sub 80/Fe/sub 20/, Co/sub 65/Fe/sub 18/Ni/sub 17/) within bulk-micromachined and fusion-bonded silicon to form the machine structures. The induction machines were characterized in motoring mode using tethered rotors, and exhibited a maximum measured torque of 2.5 /spl mu/N/spl middot/m.

Electroplated metal microstructures embedded in fusion-bonded silicon: conductors and magnetic materials

Fabrication methods for integrating thick (tens or hundreds of micrometers) electroplated metallic microstructures inside fusion-bonded silicon wafers are proposed and validated. Cu and Ni/sub 80/Fe/sub 20/ (permalloy) test structures were embedded inside of cavities in silicon wafers, which were fusion-bonded at 500/spl deg/C for 4h with nearly 100% yield. Resistance tests validated the electrical integrity of the metals after annealing, and magnetic measurements indicated the Ni-Fe maintained its magnetic performance after annealing. Additional mechanical tests verified a strong, uniform bond, and that the presence of the metals does not degrade the bond strength. These results demonstrate the ability to integrate conductive and magnetic materials in wafer-bonded silicon, a method useful for a variety of multiwafer, MEMS devices.

Vertically laminated magnetic cores by electroplating Ni-Fe into micromachined Si

The fabrication and characterization of vertically laminated, electrodeposited Ni-Fe magnetic cores in micromachined silicon for the low megahertz frequency range is presented. Laminated cores were fabricated by etching vertical trenches (60-180 /spl mu/m wide and 525 /spl mu/m deep) through silicon wafers and directly plating Ni-Fe onto the etched sidewalls. The Ni-Fe was plated over a range of thicknesses (3-53 /spl mu/m) in order to study the influence of eddy currents. The measured impedances in the range 10 kHz-40 MHz confirm the reduction of eddy current losses. This work demonstrates a simple fabrication method for achieving high-aspect-ratio, vertically laminated magnetic cores where the geometry of the structures can be easily tailored for various applications.

Magnetic induction micromachine-part II: fabrication and testing

This paper presents the realization of a magnetic induction machine. The development of this machine is part of an ongoing project to create high-power density electric microgenerators for use in portable-power applications. The results reported here focus on testing a first-generation nonlaminated electromagnetic actuator, a metrology device designed for exploring and characterizing the fabrication process and the operating behavior of the magnetic induction micromachine. Achieving high power density requires large electrical currents and magnetic fluxes, which necessitate thick, multilayered microstructures that are difficult to fabricate. The batch-fabrication schemes developed as part of this work are based on low-temperature micromolding that makes extensive use of various ultra-thick photoresists and electroplating of electrical conductors (Cu) and ferromagnetic materials (Ni-Fe 80%-20%), resulting in the successful fabrication of a multilayer two-phase planar stator and a planar rotor. To evaluate the performance of the complete machine (stator plus rotor), a 4-mm-diameter, 500-/spl mu/m-thick electroplated Ni-Fe rotor is tethered to a series of flexible structures that prevent it from making a complete revolution, but allow accurate torque performance extraction. The tethered induction micromotor studied here exhibits torque production as high as 4.8 /spl mu/N/spl middot/m.

Planar spiral inductors with multilayer micrometer-scale laminated cores for compact-packaging power converter applications

Ultralow (0.4 mm) profile spiral inductors with multilayer micrometer-scale NiFe laminated cores were developed for compact-packaging power applications. A simple sacrificial Cu etching process was used to realize seven layers of 1.8-/spl mu/m-thick laminations, forming the magnetic cores. The laminated cores were combined with a spiral coil to fabricate the spiral inductor in a hybrid fashion. The dimension of a complete device is 40 /spl times/ 15 mm. In situ electrical characterization verified compatibility with compact-packaging applications. The inductor was implemented in a boost converter (5-10 V) operating at 2.2 MHz, which demonstrated 2-W output with overall efficiency exceeding 70%.

A High Torque Density MEMS Magnetic Induction Machine

Most micro-scale electric and magnetic machines developed over the last decade lack the torque and power density to support many practical applications. The micro-scale magnetic induction machine reported here attempts to transcend this practicality barrier by offering a torque density exceeding 15% of that exhibited by macro-scale magnetic machines. The experimental magnetic induction motor described here is a two-phase planar motor fabricated from electroplated NiFe and Cu. It is approximately 8 mm in diameter, including end-turns, and 2 mm thick. Its rotor is suspended above its stator on tethers, or springs, so as to permit accurate torque measurements. The rotor-stator air gap is approximately 5 µm. With a balanced phase excitation of 2.5 A peak, the motor produces a torque of 1.2 µNm. Therefore, if the phase excitation is raised to 13 A peak, which has been achieved experimentally, a torque of 32.4 µNm is expected, corresponding to a torque density over 322 Nm/m3.