Magnetic Microelectromechanical Systems Research Articles

Pulse-Reverse Electrodeposited Nanograinsized CoNiP Thin Films and Microarrays for MEMS Actuators

This paper reports on a low residual stress hard magnetic CoNiP alloy electrodeposition technique for microelectromechanical systems (MEMS) applications based on techniques previously developed for CoNiP thin films for perpendicular magnetic recording. Besides electrolyte chemicals, various processing parameters including applied current density, film thickness, electrolyte agitation, electrolyte pH, and temperature are optimized to provide thick films with low residual stress. The resulting hard magnetic CoNiP alloy exhibits a relatively high perpendicular coercivity of around and a high saturation magnetization of . Thick films up to with a low residual stress have been realized using this CoNiP electrodeposition technique. In addition, CoNiP microarrays thick are surface micromachined for the integrations with magnetic MEMS devices. Experimental results confirm that these microarray configurations have a higher coercivity and maximum magnetic energy density, , than thin films in the perpendicular direction.

Nanoscale effects on the nanomechanical properties of multifunctional materials

Nanoscale measurements of mechanical and tribological properties play an important role in many emerging fields, such as surface engineering, magnetic storage disks, biomedical coatings and microelectromechanical systems. The understanding of scale effects is of great importance, since surface to volume ratio increases with miniaturization and surface phenomena dominate. Nanoindentation and nanoscratching tests are now commonly used for the evaluation of the functionality of the film–substrate compound and it can be satisfactorily used for the multifunctional materials characterization. In the present study nanoscale effects on the nanomechanical properties of flexible polymeric components and multilayered amorphous carbon (a-C) films using the nanoindentation and nanoscratching techniques, are considered. In specific, (i) Creep effects in nanoscale and the dependence of the dominant friction mechanisms and surface damage mechanisms on the applied load for flexible polymeric components. Load dependent transitions in the load range 1–15 mN, in both the scratch and the friction responses are considered and discussed as well as resultant deformation in nanoscale. The friction mechanism in the low-load range was adhesion. In the intermediate and high load ranges, adhesion, elastic and plastic deformations and ploughing mechanisms contributed to the friction behavior. (ii) The hardness behavior of multilayered a-C films and the role of the intrinsic material length, namely the total (100 nm) and bilayers thickness (10–45 nm), where it was found that the reduction of the bilayer thickness results in film’s strengthening.

Fabrication of hard magnetic microarrays by electroless codeposition for MEMS actuators

We report on a new electroless codeposition system for fabricating hard magnetic NdFeB particle–NiP alloy magnets for magnetic micro-electro-mechanical systems (MEMS) actuators. In the newly developed electroless codeposition process, an NdFeB hard magnetic particle, which cannot be independently deposited from aqueous electrolytes, is added to an acidic NiP alloy electroless plating electrolyte. An NdFeB (particle)-NiP (matrix) composite thin film has been successfully obtained using an optimized electroless codeposition technique. In addition, NdFeB–NiP microarrays magnets with a thickness of 20 μm have been realized by surface micro-machining techniques. These micromachined magnets exhibit good magnetic properties such as a large ( BH) max and a high perpendicular coercivity ( H c) that are particularly well suited for magnetic MEMS actuators. This deposition technique is compatible with many MEMS fabrication processes since it does not demand high processing temperatures.

Electrochemical Codeposition of Magnetic Particle-Ferromagnetic Matrix Composites for Magnetic MEMS Actuator Applications

This paper reports on a new electrochemical codeposition technique for microelectromechanical systems (MEMS) actuator application. Various magnetic composite materials can be obtained by incorporating hard magnetic particles with electrodeposited magnetic (either soft or hard ferromagnetic materials) metal matrices. The incorporated magnetic particle investigated is barium ferrite and the metal matrices are electroplated nickel, CoNiMnP, and an electroless plated nickel-phosphorus alloy. Scanning electron microscopy results show that particles can be successfully incorporated into all the investigated metal matrices. The resulting magnetic properties show that materials produced by the electrochemical codeposition technique have a high coercivity of up to 2120 Oe and a maximum magnetic energy density, of up to This indicates that the reported technique has the potential of becoming an important technique for the deposition of hard magnetic materials for magnetic MEMS actuators. © 2004 The Electrochemical Society. All rights reserved.

Modeling the effect of skewness and kurtosis on the static friction coefficient of rough surfaces

Engineering surfaces possess roughnesses that exhibit asymmetrical height distributions. However, the Gaussian distribution is most often used to characterize the topography of surfaces, and is also used in models to predict contact and friction parameters. In this paper, the effects of kurtosis and skewness on different levels of surface roughness are investigated independently. This is accomplished by adopting the Pearson system of frequency curves and used in conjunction with a static friction model for rough surfaces to calculate the friction force and friction coefficient. This study is the first attempt to independently model the effect of kurtosis and skewness on the static friction and friction coefficient. It is predicted that surfaces with high kurtosis and positive skewness exhibit lower static friction coefficient compared to the Gaussian case. More importantly, it is predicted that, for high kurtosis values, the static friction coefficient decreases with decreasing external force rather than increasing as seen with increasing skewness. This is a very promising result for applications involving smooth lightly loaded contacts such as magnetic storage devices and microelectromechanical systems. The practical significance of the present model is specifically demonstrated on static friction predictions in magnetic storage head–disk interfaces. Such predictions can be used to determine the optimal characteristics of such devices prior to fabrication to achieve lower friction in terms of surface roughness, mechanical properties, apparent contact area, and operational environment.

The application of chemical–mechanical polishing for planarizing a SU-8/permalloy combination used in MEMS devices

Abstract Chemical–mechanical polishing (CMP) allows the planarization of wafers with two or more materials at its surface. Subject of this investigation was to apply CMP for planarizing electroplated permalloy (NiFe 81/19) in micromolds formed by photosensitive epoxy (SU-8). This material remained in the structure as an insulation and planarization layer. This material combination was intended for fabricating magnetic Micro Electro-mechanical Systems (MEMS). For planarizing a SU-8/permalloy combination, metal CMP slurry was used in conjunction with standard CMP polishing pads. SU-8 effectively served as a polishing stop. For this reason it was necessary to optimize the SU-8 properties to exhibit an optimal hardness and wear resistance. The mechanical properties of the SU-8 depended on the thermal treatment during hard bake after development. The resulting SU-8 layer not only had a sufficient hardness to stop the removal of permalloy, but also could be planarized quite well.

Development of electroplated magnetic materials for MEMS

Permalloy (19%Ni–81%Fe alloy) and nickel have thus far found the most utility in magnetic-Micro Electro Mechanical Systems (MEMS), because the technologies necessary for depositing and micromachining them have been well-developed previously by the data storage industry. However, other high performance soft magnetic materials and hard magnetic materials have unique advantages that are driving their integration with MEMS/NEMS. These include enhanced magnetic properties, corrosion resistance, electrical resistivity, and reduced films stress. The primary issues associated with the integration of these magnetic materials in MEMS/NEMS are discussed.

Introduction to Tribology

Introduction to Tribology

Nanotribology

The study of friction and wear processes on the nanometer scale is related to the development of the atomic force microscope, where laser beams and piezoelectric elements are used to detect the motion of a micro tip across a surface in a controlled way. Friction on the nanometer scale has peculiar characteristics which are not revealed by macroscopic tools. Well-known concepts such as the coefficient of friction and the independence of friction from the scan velocity must be modified. The load dependence of friction is based on the non-linear relation f ? F?N; the velocity dependence is determined by thermally activated processes. The environment plays also an important role and different humidity conditions may lead to different friction, due to the formation of capillary necks in the contact area. A practical use of the atomic force microscope is to check the quality of surface preparation by comparing the responses of materials under different friction and wear conditions. Interesting applications are given by magnetic storage devices and micro-electromechanical systems.

Contact mechanics of multilayered rough surfaces

AbstractThe deposition of layers is an effective way to improve the tribological performance of rough surfaces. The contact mechanics of layered rough surfaces needs to be studied to optimize layer parameters. Since 1995 a lot of progress has been made in the development of numerical contact models, which analyze the contact behavior of layered rough surfaces with no assumption concerning the roughness distribution as well as the effect of interfacial liquid film on the contact statistics. These models predict the contact pressure profile on the interface and contact statistics, namely fractional contact area, the maximum value of contact pressure, von Mises and principal tensile stresses, and relative meniscus force. The results allow the specification of layer properties to reduce friction, stiction, and wear of layered rough surfaces. A comprehensive review of these numerical contact models is presented here. Based on the formulation of contact problems, these models are classified into three categories: direct formulation, weighted residual formulation, and minimum total potential energy formulation. The numerical methods applied in these models include Finite Difference Method (FDM), Finite Element Method (FEM), and Boundary Element Method (BEM). Typical examples of layered rough surfaces of contact simulated by those models are presented. The examples contain data for various surface topographies, elastic and elastic-plastic material properties, normal and tangential loading conditions, and dry and wet interfaces. A 3D BEM model based on a variational principle is described in detail for its capability to analyze the layered rough surfaces of contact involving a large number of contact points. Applications of the model to magnetic storage devices and MicroElectroMechanical Systems (MEMS) are presented. This review article contains 92 references.

A review of nanoindentation continuous stiffness measurement technique and its applications

Nanoindentation is now commonly used for the study of mechanical properties of materials on the nanoscale. One of the significant improvements in nanoindentation testing is the continuous stiffness measurement (CSM) technique. It offers a direct measure of dynamic contact stiffness during the loading portion of an indentation test and, being somewhat insensitive to thermal drift, allows an accurate observation of small volume deformation. Nanoscale damage caused by fatigue is of critical importance to the reliability of ultrathin protective overcoats and micro/nanostructures. The cyclic loading used in the CSM makes the technique useful for the evaluation of nanofatigue. Methodologies of the CSM technique used for the characterization of layered materials and nonhomogeneous composites are reviewed and discussed. Applications of the CSM technique to the measurement of contact stiffness, elastic modulus, hardness, creep resistance, and fatigue properties of the materials used in magnetic storage devices are presented. The nanoindentation CSM technique, in conjunction with nanoscratch and friction and wear tests, can be satisfactorily used for the materials characterization of magnetic storage and microelectromechanical systems (MEMS) devices and should find more application.

Smart magnetic structures for MEMS

By exploiting the special properties of magnetic materials, magnetic microelectromechanical system (MEMS) technology offers many challenging opportunities for useful device development in the future. This article discusses some of the magnetic materials used in MEMS devices and methods of fabricating them. Some key design issues are addressed, and applications of these technologies to electromagnetic devices developed at RMIT and to thermally controlled magnetic devices are examined.

Micromachined planar inductors on silicon wafers for MEMS applications

This paper describes three micromachined planar inductors (a spiral type, a solenoid type, and a toroidal meander type) with electroplated nickel-iron permalloy cores which have been realized on a silicon wafer using micromachining techniques. The electrical properties among the fabricated inductors are compared and the related fabrication issues are discussed, with emphasis on the low-temperature CMOS-compatible process, the high current-carrying capacity, the high magnetic flux density, the closed magnetic circuits, and the low product cost. The micromachined on-chip inductors can be applied for magnetic microelectromechanical systems devices, such as micromotors, microactuators, microsensors, and integrated power converters, which envisages new micropower magnetics on a chip with integrated circuits.

Micromachined thick permanent magnet arrays on silicon wafers

Using micromachining and electroplating techniques, micromachined thick CoNiMnP-based permanent magnet arrays have been designed, fabricated, and characterized for magnetic microelectromechanical systems (MEMS) device applications. The electroplated magnet arrays contain 1,500 magnets of 40 /spl mu/m/spl times/40 /spl mu/m/spl times/50 /spl mu/m in a cubic shape on the silicon substrate of 2.5 mm/spl times/2.5 mm, where the magnets have shown a fairly high magnetic vertical coercivity of 800-1300 Oe, a retentivity of 2.0-3.0 kG, a maximum flux saturation of 12.0-13.0 kG, and a maximum energy density of 14 kJ/m/sup 3/.

Atomic-Scale Friction Measurements Using Friction Force Microscopy: Part I—General Principles and New Measurement Techniques

Friction force measurements using modified atomic force microscopy, called here Friction Force Microscopy (FFM), are becoming increasingly important in the understanding of fundamental mechanisms of friction, wear, and lubrication, and to study interfacial phenomena in micro- and nanostructures used in magnetic storage systems and Microelectromechanical Systems (MEMS). FFMs can be used to study engineering surfaces in dry or wet conditions. A review of existing designs of FFMs and methods of friction force measurements is presented. In terms of friction force measurements, there are important issues related to the basic operation and calibration of these instruments which have not been fully studied. A new method of measuring friction fore using a commercial FFM and a calibration procedure for conversion of measured data to normal and friction forces are presented. Microscale friction data of selected materials are presented and discussed in light of macro-friction measurements.

Microtribology of Magnetic Media

Scanning tunnelling microscopy (STM), atomic force microscopy (AFM) and the modifications of AFM [such as friction force microscopy (FFM)] are becoming increasingly important in the understanding of fundamental mechanisms of friction, wear and lubrication and in studying the interfacial phenomena in micro- and nanostructures used in magnetic storage devices and microelectromechanical systems (MEMS). This paper describes modified AFM and FFM techniques and presents data on microtribological studies of magnetic media-magnetic tapes and disks. Local variation in microscale friction is found to correspond to the local slope, suggesting that a ratchet mechanism is responsible for this variation. Wear rates for magnetic tapes are approximately constant for various loads and test duration. However, for magnetic disks, the wear of the diamond-like carbon overcoat is catastrophic. Evolution of the wear has also been studied using AFM. AFM has been modified for nanoindentation hardness measurements. It has been shown that hardness of ultra-thin films can be measured using AFM. AFM has also been shown to be useful for nanofabrication.