Synchrotron radiation analysis of microstructures

The outstanding spectral and spatial characteristics of synchrotron radiation make it a powerful analytical tool in microstructure technology. We apply absorption spectroscopy to study foils of electroplated Permalloy (NiFe), and of nickel phosphorus, because they are of interest to microfabrication for their soft magnetic properties and their selective etching behaviour, respectively. In particular, we show that in the electroplated Permalloy foils Ni keeps the structure of pure Ni while Fe changes from b.c.c. to f.c.c. NiP foils become increasingly amorphous with growing P content. In this way, radial elemental distributions which determine magnetic or other properties can be monitored sensitively to improve electroplating process control, even in situ. We also measure the radial thickness profile of a gold layer sputtered on top of a chromium coated silicon wafer. This technique might be extended to measure a given layer in a multilayer structure selectively and non-destructively even when hidden or opaque.     

Electrochemical process for the lamination of magnetic cores in thin-film magnetic components

The lamination of the core in thin film magnetic components is necessary to reduce the eddy current losses of the structure at high frequencies. The usual way to achieve lamination of the core is by physical vapor deposition (PVD) techniques. These methods are however costly and the deposition of layers is non selective. In this article, an almost entirely aqueous-based electrochemical process for the lamination of magnetic cores is presented. The process uses an electrodepositable photoresist Eagle 2100 ED codeposited with a catalyst (palladium). The Eagle layer is left as an insulator and the catalyst allows the activation of the layer for subsequent metallization. The process can be reproduced as many times as required for producing the multilayers. It is also selective: it does not require multiple photolithography steps. As a demonstration of the multilayer process, a core constituted of two layers of Ni/sub 80/Fe/sub 20/ (6 /spl mu/m each layer), separated by an Eagle insulating layer, electroplated over three-dimensional structures, was produced.     

A novel reluctance actuator employing an embedded ferromagnetic foil

In this paper we present a reluctance actuator which contains laser cut ferromagnetic structures for flux guidance made of Mumetal foil. By means of analytic calculations and numeric simulations it is shown that much higher magnetic forces are achievable by using the Mumetal foil compared to electroplated ferromagnetic alloys like nickel–iron. Furthermore, the processing of such foils and the integration of foil structures into the actuator are described.     

Multistep sequential batch assembly of three-dimensional ferromagnetic microstructures with elastic hinges

In this paper, we have developed a process for multistep sequential batch assembly of complex three-dimensional (3-D) ferromagnetic microstructures. The process uses the magnetic torque generated by an external magnetic field perpendicular to the substrate to lift hinged structures. We found that a dimensionless factor that depends on the volume of the magnetic material and the stiffness of the hinges determines the sensitivity of the hinged microstructures to a magnetic field. This factor was used as a criterion in designing a process for sequential batch assembly, i.e., for setting appropriate differences in sensitivity. Using a dimensionless factor in the design of the sequential assembly simplified the assembly process, which requires only placing the structures on a permanent magnet, and which can be used to carry out multistep sequential batch assembly. We fabricated hinged microstructures, which consist of 4.5-/spl mu/m-thick electroplated Permalloy plates and 200-nm-thick nickel elastic hinges of various sizes. In an experiment, four plates (600 /spl mu/m/spl times/800 /spl mu/m) were lifted sequentially and out-of-plane microstructures were assembled in a four-step process. Assembly of more complex out-of-plane microstructures (e.g., regular tetrahedrons, 800 /spl mu/m long on one side) was also shown to be feasible using this method of sequential batch assembly. [1351].     

A variable reluctance stepping microdynamometer

 A magnetic variable reluctance stepping micromotor fabricated using LIGA processing is described which is integrated with an external planar coupled gear train and electromagnetic brake. Variable mechanical loading of the micromotor through the electrically controlled brake allows dynamometry measurements to be performed. All components are fabricated from electroplated 78 Permalloy. A planar gear coupling is achieved by using involute gear teeth as the salient elements in the rotor. The rotor used for testing has a pitch radius near 500 μm with 180 μm thickness and is complemented with a stator which provides for a step rotation of 2.4°. Coil windings are implemented with assembled spring clip coil forms with 400 turns of 50 AWG magnet wire. Improved coil efficiency is responsible for decreasing the minimum power required for rotor rotation to 52 microWatts. Maximum speeds near 8000 rpm are achieved although stepping action is affected by stepping instabilities which are a function of excitation magnitude and frequency. Calibration of the electromagnetic brake is accomplished with static beam bending measurements and indicates a maximum peripheral rotor output force of 0.6 milliNewton corresponding to an output torque near 0.3 microNewton-meter. Dynamometry measurements indicate a maximum mechanical power output of 20 microWatts. Received: 30 October 1995 / Accepted: 25 January 1996     

Electromagnetic Two-Dimensional Scanner Using Radial Magnetic Field

In this paper, we present the design, fabrication, and measurement results of a two-dimensional electromagnetic scanning micromirror actuated by radial magnetic field. The scanner is realized by combining a gimbaled single-crystal-silicon micromirror with a single turn electroplated metal coil, with a concentric permanent magnet assembly composed of two concentric permanent magnets and an iron yoke. The proposed scanner utilizes the radial magnetic field rather than using a lateral magnetic field oriented 45deg to the horizontal and vertical scan axes to achieve a biaxial magnetic actuation. The single turn coil fabricated with electroplated copper achieves a nominal resistance of 1.2 Omega. A two-dimensional scanner with mirror size of 1.5 mm in diameter was fabricated. Maximum optical scan angle of 8.8deg in horizontal direction and 8.3deg in vertical direction were achieved. Forced actuation of the gimbal at 60 Hz and resonant actuation of the micromirror at 19.1-19.7 kHz provide slow vertical scan and fast horizontal scan, respectively. The proposed scanner can be used in raster scanning laser display systems and other scanner applications.     

Magnetic actuation of hinged microstructures

We have investigated magnetic actuation of hinged, surface micromachined structures. Electroplated magnetic material (Permalloy) is integrated with two types of hinged microstructures and the magnetic actuation process has been experimentally characterized. Under a given external magnetic field, the angular displacement of a hinged structure is determined by the volume of the magnetic material or by the stiffness of an auxiliary flexural loading spring. We have demonstrated parallel actuation of large arrays of hinged microstructures under a global (wafer scale) external magnetic field. The design rules for achieving a prescribed asynchronous actuation sequence among a group of microstructures have been determined to enable efficient parallel assembly of three-dimensional (3-D) microstructures     

Micromechanical characterization of electroplated permalloy films for MEMS

In order to improve the reliability of MEMS designs, evaluating the mechanical properties of soft magnetic materials is needed. In this paper, we present a tensile testing method to characterize the mechanical properties of microscale electroplated permalloy (80 wt% Ni, 20 wt% Fe) films. The gauge section of the specimen is 50 μm wide, 100 μm long and 5 μm thick. The measured Young’s modulus of permalloy films is 96.4 GPa, and the tensile strength is 1.61 GPa. The fracture strain measured by the images of specimens is about 2%.     

Design, fabrication, and testing of a bistable electromagneticallyactuated microvalve

A bistable electromagnetically actuated microvalve was designed, processed, and tested. The valve was designed to control a water flow of 0.05-0.5 μs from a reservoir at a pressure of 1-2000 Pa. The two valve components were fabricated in silicon, the upper piece comprises an electroplated gold coil, and the lower piece is an Ni/Fe alloy beam. The bistable capability was achieved by balancing the elastic forces on the beam with the magnetic forces due to a 46-μm-thick rolled magnetic foil. The design includes the flow through the orifice, squeeze film damping due to beam motion, beam elasticity, and electromagnetics. The microvalve was tested for power consumption, flow rate, time response, Ni/Fe alloy composition, and magnetic foil properties. The valve operates at 1-2 V in both air and water     

Magnetic composite electroplating for depositing micromagnets

This paper reports a novel magnetic composite materials deposition technique called magnetic composite electroplating (MCE). Thin films and micromagnets arrays of a composite matrix consisting of magnetic particles and a ferromagnetic alloy have been fabricated based on this technique. In a typical MCE process, magnetic particles are electrochemically and mechanically embedded into electroplated ferromagnetic thin films to form a magnetic particle-alloy composite. The magnetic particle selected is a barium ferrite magnet (BaFe/sub 12/O/sub 19/) and the ferromagnetic matrix is a pulse-reverse electroplated CoNiP alloy. The particle embedded fraction (w.t. %) directly affects magnetic properties and is experimentally determined by its energy dispersive spectrum (EDS). Various factors including electrolyte particle concentration, applied current, electrolyte pH, and the presence of cationic surfactants affecting the particle embedded fraction are experimentally investigated. Arrays of BaFe/sub 12/O/sub 19/-CoNiP magnets with a variety of dimensions and features as small as 8/spl mu/m have been realized by MCE. Experimental analysis shows that the composite exhibits magnetic properties, such as a high coercivity (H/sub c/) of up to 1.75/spl times/10/sup 5/ A/m, particularly well suited for MEMS actuators.     

A universal electromagnetic microactuator using magneticinterconnection concepts

This paper describes a new universal electromagnetic microactuator that makes use of novel magnetic interconnection concepts. In order to realize the universal actuator, planar microinductors are fabricated on a substrate which already contains anisotropically etched Ni/Fe permalloy-electroplated magnetic vias or through-holes. The inductor, which acts as a flux generator, is physically located on one side of the wafer, but is magnetically connected to the opposite side of the wafer where actuation occurs. This approach to actuator design provides for maximum flexibility in the range of applications. In addition, it allows the actuator to be readily connected to driving circuitry without interfering with the actuating device. Multi-layer 3D inductive components are fabricated using a LIGA-like thick photoresist lithography process. The fabricated coils consist of a horseshoe-shaped permalloy-electroplated magnetic core and electroplated copper conductor lines that form the windings around the core. Initial testing using a prototype cantilever beam structure has proven functionality and indicates that the new device has much potential as a low power magnetic microactuator. Many magnetic MEMS applications require an electromagnetic actuator with high efficiency, and some areas which this device is expected to impact include microfluidics, micromotors, optics, and resonating devices     

Fabrication of a freestanding micro mechanical structure using electroplated thick metal with a HAR SU-8 mold

In this thesis, fabrication technology of a freestanding micro mechanical structure using electroplated thick metal with a high-aspect-ratio SU-8 mold was studied. A cost-effective fabrication process using electroplating with the SU-8 mold was developed without expensive equipment and materials such as deep reactive-ion etching (DRIE) or a silicon-on-insulator (SOI) wafer. The process factors and methods for the removal of SU-8 were studied as a key technique of the thick metal micro mechanical structure. A novel method that removes cross-linked SU-8 completely without leaving remnants of the resist or altering the electroplated microstructure was utilized. The experimental data pertaining to the relationship between the geometric features and the parameters of the removal process are summarized. Based on the established SU-8 removal process, an electroplated nickel comb structure with high-aspect-ratio SU-8 mold was fabricated in a cost-effective manner. In addition, a freestanding micro mechanical structure without a sacrificial layer was successfully realized. The in-plane free movements of the released freestanding structure are demonstrated by electromagnetic actuation. This research implies that various types of MEMS devices can be developed at a low-cost with design flexibility.     

Mechanical property evaluation and failure analysis of cantileveredLIGA nickel microposts

An experimental apparatus has been built to measure the elastic modulus and bending strength (modulus of rupture) of LIGA nickel posts. The apparatus uses the static cantilever beam bending approach to measure mechanical properties in a direction parallel to the growth direction. Experimental results are presented for two sets of largely identical posts constructed using an overplating method. One set was electroplated using a Watts bath, and the other set was electroplated using a sulfamate bath. For the Watts bath, the measured modulus of elasticity was slightly lower than that of bulk nickel (182 GPa), while, for the sulfamate bath, it was approximately half (93 GPa). The strength properties of the two sets of posts also differ dramatically. Microhardness measurements, Focused Ion Beam (FIB) images of grain structure, and scanning electron microscopy (SEM) micrographs of failure regions are used to further characterize and explain the differences in the results. This integrated testing approach yields a consistent set of data regarding material properties, grain size/structure and failure mechanisms. Potential sources of experimental error are also identified and improvements in experiment design are suggested to reduce these errors     

Development and fabrication of magnetic thin films

For designing and fabricating electromagnetic microactuators as pursued within the collaborate research center “Design and Fabrication of Active Microsystems” (Sonderforschungsbereich 516), soft and hard magnetic materials are required to create and guide magnetic flux. The investigations on the development of suitable materials and their deposition technologies are presented in this paper. In the area of soft magnetic materials, the application of Cobalt–Iron (CoFe) as an alternative to Nickel–Iron (NiFe, Permalloy) was investigated. The benefit of CoFe over NiFe is its greater saturation flux density. The technology utilized for the deposition was electroplating. In the area of hard magnetic materials, gas flow sputtering was applied for depositing Samarium–Cobalt (SmCo). This technology enables the deposition of pure SmCo layers at high deposition rates and without high vacuum. Furthermore, the dependence of the magnetic properties of the SmCo on the film composition was examined.     

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.     

Ni electroplating on a resist micro-machined by proton beam writing

In this paper we report fabrication of high-aspect-ratio micro-structure of Ni by electroplating, using a micro-machining technique of resists using proton beam writing (PBW) at Japan Atomic Energy Agency (JAEA). A micro-structure of 5 μm thick PMMA was fabricated by exposure using PBW at 1.7 MeV and by development. A Ni structure was then formed by electroplating on the micro-structure of PMMA. Vertical and smooth side walls observed by a scanning electron microscope (SEM) indicate that PBW can be a versatile tool for fabrication of resists and metal microstructure in combination with electroplating. The electroplated Ni structure can be used as a resolution standard, which enabled us to focus the proton beam down to 130 nm.     

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.     

一种用于测试坡莫合金薄膜机械性能的拉伸模型

坡莫合金(Ni80Fe20)薄膜是微机电系统常用的磁性材料之一.介绍了一种用于测试其机械性能的单轴拉伸试验模型.此模型的特点是微小试件两端固定、且与加载机构集成在基片上,从而可减少操作工作量、提高对准精度.整个机构以微细加工方法制成:坡莫合金拉伸试件以光刻和电镀技术成型,其余的加载机构以湿法蚀刻制成.实验表明:使用此机构可以简单且高精度地对薄膜试件进行拉伸试验,获得多项力学性能参数,从而为MEMS器件设计和分析提供可靠的理论基础.     

Two-axis micro fluxgate sensor on single chip

We present a two-axis micro fluxgate sensor on single chip for electronic compassing function. To measure X- and Y-axis magnetic fields, functional two fluxgate sensors were perpendicularly aligned and connected each other. The fluxgate sensor was composed of square-ring shaped magnetic core and solenoid excitation and pick-up coils. The solenoid coils and magnetic core were separated by benzocyclobutane which had high insulation and good planarization characters. Copper coil patterns of 10 μm width and 6 μm thickness were electroplated on Ti (300 Å)/Cu (1,500 Å) seed layers. 3 μm thick Ni_0.8Fe_0.2 (permalloy) film for the magnetic core was also electroplated under 2,000 gauss. Excellent linear response over the range of ?100 μT to +100 μT was obtained with the sensitivity of ～280 V/T. Actual chip size was 3.1×3.1 mm². The sine and cosine signals of two-axis fluxgate sensor had a good function of azimuth compass.     

An ab initio study of the magnetic and electronic properties of Fe, Co, and Ni nanowires on Cu(001) surface

Magnetism at the nanoscale has been a very active research area in the past decades, because of its novel fundamental physics and exciting potential applications. We have recently performed an ab initio study of the structural, electronic and magnetic properties of all 3d transition metal (TM) free-standing atomic chains and found that Fe and Ni nanowires have a giant magnetic anisotropy energy (MAE), indicating that these nanowires would have applications in high density magnetic data storages. In this paper, we perform density functional calculations for the Fe, Co and Ni linear atomic chains on Cu(001) surface within the generalized gradient approximation, in order to investigate how the substrates would affect the magnetic properties of the nanowires. We find that Fe, Co and Ni linear chains on Cu(001) surface still have a stable or metastable ferromagnetic state. When spin–orbit coupling (SOC) is included, the spin magnetic moments remain almost unchanged, due to the weakness of SOC in 3d TM chains, whilst significant orbital magnetic moments appear and also are direction-dependent. Finally, we find that the MAE for Fe, and Co remains large, i.e., being not much affected by the presence of Cu substrate.