Micromachining and micro-electromechanical system (MEMS) technologies can be used to produce complex structures, devices and systems on the scale of micrometers. Initially micromachining techniques were borrowed directly from the integrated circuit (IC) industry, but now many unique MEMS-specific micromachining processes are being developed. In MEMS, a wide variety of transduction mechanisms can be used to convert real-world signals from one form of energy to another, thereby enabling many different microsensors, microactuators and microsystems. Despite only partial standardization and a maturing MEMS CAD technology foundation, complex and sophisticated MEMS are being produced. The integration of ICs with MEMS can improve performance, but at the price of higher development costs, greater complexity and a longer development time. A growing appreciation for the potential impact of MEMS has prompted many efforts to commercialize a wide variety of novel MEMS products. In addition, MEMS are well suited for the needs of space exploration and thus will play an increasingly large role in future missions to the space station, Mars and beyond. (Some figures in this article are in colour only in the electronic version)

https://iopscience.iop.org/article/10.1088/0964-1726/10/6/301/pdf

Microelectromechanical systems (MEMS):fabrication, design and applications

This paper discusses the history, current state of the art, and ongoing challenges for compact (less than a few cubic centimeters) magnetic power generation systems in the microwatts to tens of watts power range. These systems are of great interest for powering sensor networks, robotics, wireless communication systems, and other portable electronics. The paper considers the following topics. 1) The theoretical and practical implications of miniaturizing magnetic power generators. 2) The design and performance of previously demonstrated devices, which are summarized and compared. 3) Ongoing challenges for implementation, including integrated high-performance hard magnetic materials, microscale core laminations, low-friction bearings, high-speed rotor dynamics, and compact, high-efficiency power converters.

Review of Microscale Magnetic Power Generation

Preface. Microelectromechanical Systems (MEMS) and Radio Frequency MEMS. MEMS Materials and Fabrication Techniques. RF MEMS Switches and Micro Relays. MEMS Inductors and Capacitors. Micromachined RF Filters. Micromachined Phase Shifters. Micromachined Transmission Lines and Components. Micromachined Antennae. Integration and Packaging for RF MEMS Devices. Index.

RF MEMS and their applications

Surface-micromachined, batch-fabricated structures that combine plated-nickel films with polysilicon mechanical flexures to produce individually addressable, magnetically activated devices have been fabricated and tested. Individual microactuator control has been achieved in two ways: (1) by actuating devices using the magnetic field generated by coils integrated around each device and (2) by using electrostatic forces to clamp selected devices to an insulated ground plane while unclamped devices are freely moved through large out-of-plane excursions by an off-chip magnetic field. The present application for these structures is as micromirrors for microphotonic systems where they can be used either for selection from an array of mirrors or else individually for switching among fiber paths.

Magnetically actuated, addressable microstructures

A microfabrication technology capable of electrodepositing truly three-dimensional metal structures is introduced. Micrometer-scale nickel structures including a multicoiled helical spring have been fabricated. Electrodeposition is localized by placing a sharp-tipped electrode in a plating solution, near a substrate, and applying a voltage. Structures are built by moving the electrode appropriately with respect to the substrate. Vertical deposition rates of 6 /spl mu/m/s are observed, two orders of magnitude greater than those of conventional electrodeposition. The theory of mass transport to a region of localized field is discussed, and a model of deposition profile is presented. The process can potentially produce submicrometer feature sizes using a range of materials including pure metals, alloys, and polymers.

Three-dimensional microfabrication by localized electrochemical deposition

Complete integration and successful testing of a planar rotational magnetic micromotor have been demonstrated. The configuration is that of a three-phase variable reluctance stepping motor with 6 stator poles and 4 rotor poles. Stator and rotor heights of up to 300 mu m are available and rotor diameters of 285 mu m and 423 mu m were tested. Maximum rotational speeds which have been achieved with open loop excitation exceed 30000 rpm and show no change with operation in vacuum. After testing to more than 5*10/sup 7/ rotation cycles, deviations from initial operation are not observed. Vertical reluctance forces are used to levitate the rotor up to 50 mu m over the substrate. Position signals are available via integrated photodiodes which allow the rotor speed to be monitored and provide the groundwork for an active closed-loop system. >

A first functional current excited planar rotational magnetic micromotor

Initial experiments with externally excited LIGA fabricated magnetic micromotors have shown that excitations required to overcome nickel to nickel sliding friction are reasonably low. These encouraging results have prompted an effort to integrate current excitation into the micromotor as well as to provide a test to quantitatively measure performance and frictional behavior of a magnetic micromotor. Such measurements may he made by use of a dynamometer which consists of a motor, a coupling gear train, a generator to act as an active load, and associated control electronics. Integration of such a micromechanical system requires extensions of the basic LIGA process. Problems with obtaining an electrodeposited material with reasonable magnetic properties must be resolved in order to complete the implementation. >

T.S. Jung

Papers

A first functional current excited planar rotational magnetic micromotor

Preliminary results for a planar microdynamometer