Microsystem Applications Research Articles

Nano-mechanical and tribological characteristics of ultra-thin amorphous carbon film investigated by afm

The mechanical as well as tribological characteristics of coating films as thin as a few nm become more crucial as applications in micro-systems grow. Especially, the amorphous carbon film has a potential to be used as a protective layer for micro-systems. In this work, quantitative evaluation of nano-indentation, scratching, and wear tests were performed on the 7nm thick amorphous carbon film using an Atomic Force Microscope (AFM). It was shown that AFM-based nano-indentation using a diamond coated tip can be feasibly utilized for mechanical characterization of ultra-thin films. Also, it was found that the critical load where the failure of the carbon film occurred was about 18μN by the ramp load scratch test. Finally, the wear experimental results showed that the quantitative wear rate of the carbon film ranged 10-9~10-8 mm3/N cycle. These experimental methods can be effectively utilized for a better understanding the mechanical and tribological characteristics at the nano-scale.

Electrodeposited nickel?manganese: an alloy for microsystem applications

A process has been developed, using LIGA fabrication techniques, for the electrodeposition of a high strength, heat resistant Ni–Mn alloy to meet the requirements of a mechanical microsystem component. The electrolyte bath chemistry consists of Ni sulfamate to which a small amount of manganese chloride is added. The Mn content for the electrodeposited alloys of interest is generally equal to or less than about 1 wt%. It is shown that its co-deposition with Ni is insensitive to feature aspect ratio and therefore not limited by mass transport effects, permitting uniform alloy deposition. While plating of this alloy at a constant current density yields a high strength deposit, it also results in a highly stressed film that makes the fabrication of thick section deposits problematic.To counter this, a pulsed deposition scheme is employed to fabricate a nanostructured film consisting of alternating nm-thick regions of low stress, relatively soft Ni, and high strength, and highly stressed, NiMn alloy. This moderates the high plating stress of the NiMn alloy and enables the deposition of thick deposits. Yield strengths of over 800 MPa are achievable in the pulse-plated material, with good as-plated ductility (∼6%). The material loses only about 15% of its original strength after a one hour, 600 °C anneal, and no embrittlement is observed since no sulfur-bearing additives are employed. To the contrary, ductility measured as strain to failure is improved.

Oxide dispersion strengthening of nickel electrodeposits for microsystem applications

Oxide dispersion strengthened nickel (ODS-Ni) electrodeposits were fabricated to net shape in a nickel sulfamate bath using the LIGA process. A 20 g/l charge of 10 nm Al{sub 2}O{sub 3} powder was suspended in the bath during electrodeposition to produce specimens containing an approximately 0.001-0.02 volume fraction dispersion of the alumina particulate. Mechanical properties are compared to baseline specimens fabricated using an identical sulfamate bath chemistry without the Al{sub 2}O{sub 3} powder charge. Results reveal that the as-deposited ODS-Ni exhibited significantly higher yield strength and ultimate tensile strength than the baseline material. This increase in as-deposited strength is attributed to Orowan strengthening. The ODS-Ni also showed improved retention of room temperature strength after annealing over a range of temperatures up to 600 C. Microscopy revealed that this resistance to anneal softening was due to an inhibition of grain growth in the presence of the oxide dispersion. Nanoindentation measurements revealed that the properties of the dispersion strengthened deposit were uniform through its thickness, even in narrow, high aspect ratio structures. At elevated temperatures, the strength of the ODS-Ni was approximately three times greater than that of the baseline material although with a significant reduction in hot ductility.

Low frequency wireless powering of microsystems using piezoelectric–magnetostrictive laminate composites

This paper presents a new wireless powering technique for microsystems based on low frequency (<100 Hz) excitation of a piezoelectric–magnetostrictive laminate (i.e., magnetoelectric effect). The laminate composites subjected to a magnetic field have been used to generate an electric voltage (up to 285 V). Adequate power levels (10–80 μW) for many microsystem applications have been generated by inserting a piezoelectric PZT sheet between two highly magnetostrictive Terbium Dysprosium Iron alloy (Terfenol-D) layers (strains of the order of 10 −3 at 2–3 kG). Comparing with other remote powering techniques, this method possesses much higher voltage generation efficiency per generator volume.

Packaging and integration of high-speed optical components

Packaging of high-speed optical components is a complex process involving many interdisciplinary engineering efforts. The design of a packaged component is an interesting combination of optical, mechanical, electrical, and process engineering. This article shows how solving assembly and packaging problems can accelerate the progress in microsystem applications. In this article, automated assembly integrates over 50 specific functions into an array for a low-cost component. The techniques are applicable for other measurement microsystems in different fields of applications for measurement, control, and communications.

Flexing of scratch drive actuator plates: modelling and experimentation

The scratch drive actuator (SDA) is a key element in microelectromechanical-system (MEMS) technology. This type of actuator can be designed to travel over very long distances with precise step sizes. The MEMS designer requires models of the SDA to incorporate these devices into their microsystem applications. Models are developed for the SDA in its working state, building on previous work reported in the literature. A suspended SDA plate actuated by electrostatic forces has been analysed. A mathematical model has been established based on electrostatic coupled mechanical theory. Two SDA modes have been analysed namely the noncontact mode and the contact mode. The noncontact mode allows the designer to establish the threshold voltage after which the actuator plate snaps down. For the contact mode, the relationship between applied voltage and contact length is first obtained. Subsequently, the geometrical model of a bent plate is used to determine the relationship between contact distance and step size. These two results are then combined to obtain the value of actuator step size against applied voltage. A coupled-field electromechanical simulation of the microactuators has been performed using the commercially available software tool, IntelliSuite. On the experimental front, a Veeco NT1000 surface profiling tool has been used to measure the bending of the SDA plate. The results obtained from modelling, simulation and experimentation are compared.

Integrated microsystems for controlled drug delivery

Efficient drug delivery and administration are needed to realize the full potential of molecular therapeutics. Integrated microsystems that incorporate extremely fast sensory and actuation capabilities can fulfill this need for efficient drug delivery tools. Photolithographic technologies borrowed from the semiconductor industry enable mass production of such microsystems. Rapid prototyping allows for the quick development of customized devices that would accommodate for diverse therapeutic requirements. This paper reviews the capabilities of existing microfabrication and their applications in controlled drug delivery microsystems. The next generation of drug delivery systems—fully integrated and self-regulating—would not only improve drug administration, but also revolutionize the health-care industry.

Applications of LIGA technology to precision manufacturing of high-aspect-ratio micro-components and -systems: a review

The by far leading technology for manufacturing MEMS devices is Si-micromachining with its various derivatives. However, many applications of microsystems have requirements on materials basis, geometry, aspect ratio, dimensions, shape, accuracy of microstructures, and number of parts that cannot be fulfilled easily by mainstream silicon-based micromachining technologies. LIGA, an alternative microfabrication process combining deep X-ray lithography, plating-through-mask and molding, enables the highly precise manufacture of high-aspect-ratio microstructures with large structural height ranging from hundreds to thousands of micrometers thick. These tall microstructures can be produced in a variety of materials with well-defined geometry and dimensions, very straight and smooth sidewalls, and tight tolerances. LIGA technology is also well suited for mass fabrication of parts, particularly in polymer.Many microsystems benefit from unique characteristics and advantages of the LIGA process in terms of product performance. The LIGA technology is briefly reviewed. The strengths of the manufacturing method and its main fields of application are emphasized with examples taken from various groups worldwide, especially in micromechanics and microoptics.

Sandia’s $462.5m future MESA complex

Ground breaking has launched Microsystems and Engineering Sciences Applications, the largest project that Sandia has ever undertaken. This is a short news story only. Visit www.three-fives.com for the latest advanced semiconductor industry news.

Microsystems in health care: Part 6. Designing patient safety into the microsystem.

This article explores patient safety from a microsystems perspective and from an injury epidemiological perspective and shows how to embed safety into a microsystem's operations. MICROSYSTEMS PATIENT SAFETY SCENARIO: Allison, a 5-year-old preschooler with a history of "wheezy colds," and her mother interacted with several microsystems as they navigated the health care system. At various points, the system failed to address Allison's needs. The Haddon matrix provides a useful framework for analyzing medical failures in patient safety, setting the stage for developing countermeasures. The case study shows the types of failures that can occur in complex medical care settings such as those associated with pediatric procedural sedation. Six patient safety principles, such as "design systems to identify, prevent, absorb, and mitigate errors," can be applied in a clinical setting. In response to this particular case, its subsequent analysis, and the application of microsystems thinking, the anesthesiology department of the Children's Hospital at Dartmouth developed the PainFree Program to provide optimal safety for sedated patients. Safety is a property of a microsystem and it can be achieved only through thoughtful and systematic application of a broad array of process, equipment, organization, supervision, training, simulation, and team-work changes.

Ablation and cutting of planar silicon devices using femtosecond laser pulses

Although lasers are generally able to machine silicon, the major material in many microsystems applications, doing so without influencing the physical properties of the bulk material remains an important challenge. Ultrafast lasers, in particular, with their potential to precisely ablate all kinds of solid materials, are able to perform such processes with high efficiency and accuracy. This article starts with an overview of the general interaction of ultrafast laser radiation with semiconductors, explaining the absorption processes and different fluence regimes for the ablation of silicon. Major parameter influences, especially for cutting processes in thin silicon, are described. By varying pulse energies, beam shaping methods, the beam polarization, and temperatures, the cutting quality and speed can be significantly influenced. One important quality aspect, besides kerf widths and surface roughness, is the amount of back-side chipping when cutting brittle materials. Achievements in speed enhancement using linear focus shapes are presented, with cutting speeds up to five times higher than by conventional spot-focusing. On the other hand, laser processes that cut with a spot focus offer the possibility of free-shape cutting, which is explained using the example of wafers carrying silicon chips with highly increased package densities.

Electrochemical micromachining, polishing and surface structuring of metals: fundamental aspects and new developments

Electrochemical micromachining (EMM) has emerged as a versatile process for machining and surface structuring of metallic materials for biomedical and microsystems applications. From a fundamental point of view EMM presents many similarities with electrochemical machining (ECM) and electropolishing (EP) provided one takes into account the scale dependence of phenomena. In the present paper the role of mass transport, current distribution and passive films for shape control and surface smoothing is discussed and illustrated with examples. The usefulness of numerical simulation using simplified models is stressed. New developments in EMM of titanium are presented, including oxide film laser lithography permitting EMM on non-planar surfaces without photoresist and the fabrication of two-level and multi-level structures. Scale resolved electrochemical surface structuring of titanium leads to well-defined topographies on the micrometer and nanometer scales, which are of interest for biomedical applications.

Microfrictional properties of diamond-like carbon films sliding against silicon, sapphire and steel

The low contact pressure characteristic of the microtribological regime relative to macro and nanosystems is suited for testing the microfrictional properties of different types of thin films. Motivated by macro as well as microsystem applications, this study investigates the microfrictional properties of different types of diamond-like carbon (DLC) films, prepared using low- and high-frequency plasma-assisted chemical vapor deposition (HF-PACVD) and the vacuum arc method. Testing was performed with a reciprocating precision microtribometer. Silicon, sapphire and steel balls were used as counterbodies. Friction–load curves suggest that, for applied forces in the μN to mN regime, two properties have a strong influence on the microfriction: first, the chemical composition plays a dominant role and second, the film roughness. With silicon and steel balls, the microfriction of hydrogen-free DLC films was greater than the hydrogen-containing films. With sapphire counterbodies, the results indicate that microfriction is inversely proportional to the film roughness. Also, for the films tested, microfriction was determined to be independent of the sliding velocity. For the force (pressure) regimes tested, mild wear was observed on silicon and some steel counterbodies, while no wear could be detected on any of the DLC films. These results illustrate the utility of implementing microtribological testing in comparative coating studies.

Advanced X-ray analysis techniques to investigate aging of micromachined silicon actuators for space application

Applications of Microsystems in the aerospace create a strong demand in quality control and failure analysis. In this paper, it is shown that high-resolution X-ray diffraction techniques can be used to investigate aging of microelectromechanical systems. This is shown for micromachined silicon actuators for space applications.

Experimental Study of the Microstructure and Stress of Electroplated Gold for Microsystem Applications

Gold, used as an X-ray absorber for lithography and as a structural or conducting material in microsystems, was deposited from a commercially available sulfite electrolyte. The effects of current type and an arsenic additive on the gold microstructure and residual stress were studied. Using a simple bent strip method, good agreement with literature stress values determined via other methods was obtained. Without arsenic, residual stresses are tensile regardless of current type. With 25 ppm arsenic, the stress is compressive for direct current (ca. with pulsed current reducing the stress to compressive; this has been noted previously with thallium as an additive. The addition of arsenic does not appreciably change the film grain size but does lower the twin density and modify texture. Pores were observed in all the gold films, but were larger and less concentrated for films produced with arsenic; for the case of direct current with arsenic, the pores were concentrated at the grain boundaries. Consistencies in the microstructural observations and thin film stress theories are discussed. © 2003 The Electrochemical Society. All rights reserved.

Wettability enhancement by rough surfaces generated by thin film technology

Wettability is a very important property of surfaces, especially in microsystem applications. It can be manipulated directly by surface properties—especially by the roughness of the surface. The wettability of smooth hydrophilic surfaces is improved by roughening them. The contrary effect is observed with smooth hydrophobic surfaces—by roughening, the contact angle will increase. In this article, a thin film process with excellent edge coverage is demonstrated. A sputtered tin (Sn) layer forms a reproducible, well-defined rough surface with an average roughness of approximately 188 nm. Wettability can be manipulated in a wide range with a Wenzel-relation of approximately r=2.6.

NdFeB thick films prepared by tape casting

NdFeB films of thickness between 100 and 800 μm were prepared by tape casting of a slurry containing 84–95 wt% of commercial NdFeB powder (MQP-B, -Q and -S). After curing the flexible green tapes at 120°C non-porous magnetic films are obtained. The remanence of the films is in the range of 350–450 mT and the coercivity is between 300 and 800 kA/m depending on the type of MQP powder used. The magnetic properties of the films are discussed in relation to film composition and type of magnetic material. For MEMS applications the thick films are magnetized with a multi-pole stripe pattern with 1 mm pole pitch. The induction at the surface of the films was measured with a Hall probe and compared to theoretical calculations. The results indicate that the films are completely magnetized regardless of the film thickness. Tape-casted NdFeB thick films are promising candidates for applications in micro-systems or actuators. Miniaturization of the magnet components is one of the key issues in the development of electromagnetic micro-systems, thus creating a need for replacement of small sintered magnets by magnetic thick film components. Other applications include encoders.

Thermophysical Properties of Ni Films for LIGA Microsystems

ABSTRACTThis work reports temperature dependent thermophysical properties characterization of electrodeposited Ni and NiMn alloys intended for LIGA Microsystems applications. A steady-state method is used to determine the in-plane thermal conductivity. Anisotropic thermal diffusivity characterization is performed using a photothermoelectric technique. The measured thermal properties are dependent on the deposition method and also on subsequent temperature annealing steps. The thermal transport measurement results are correlated with scanning electron microscopy studies of the grain structure and measurements of the electrical transport properties.

Communication Buses and Protocols for Sensor Networks

This paper overviews existing digital communication buses which are commonly used in sensor networks, discusses sensor network architectures, and introduces a new sensor bus for low power microsystem applications. The new intra-module multi-element microsystem (IM2) bus is nine-line interface with 8b serial data which implements several advanced features such as power management and plug-n-play while maintaining minimum hardware overhead at the sensor node. Finally, some issues in wireless sensor networking are discussed. The coverage of these issues provides a guideline for choosing the appropriate bus for different sensor network applications.

Development and Characterization of Co-Ni Alloys for Microsystems Applications

A chloride plating bath, containing boric acid and saccharin has been optimized to obtain homogeneous Co-Ni deposits over substrate. The goal is to explore the synergy of these layers in microsystems applications. Anomalous codeposition occurs and both electrochemical and structural results indicate that obtained Co-Ni layers correspond to solid solutions of face-centered cubic (fcc) structure, whose composition may be varied as a function of the electrodeposition parameters. Results of the electrochemical and magnetic characterization carried out are presented, showing the trends of a soft magnetic material, i.e., high saturation magnetization (1.2 T) and low coercivity. Smooth surfaces and a steady deposition rate were observed in the Co-Ni deposits on silicon-based unpatterned substrates. In order to check the versatility and the compatibility of this Co-Ni electrodeposition with the standard microsystems fabrication technology, two processes, surface- and bulk-technology based, have been carried out. Due to the high selectivity and homogeneity of the Co-Ni layer, it has been possible to pattern the deposits with a definition down to 10 μm, as well as to fabricate 3D structures. Methods to liberate the Co-Ni films from the silicon-based substrate have been developed; as a result, low-stressed freestanding structures are presented. © 2002 The Electrochemical Society. All rights reserved.