Harrie A. C. Tilmans

Pull-in voltage analysis of electrostatically actuated beam structures with fixed–fixed and fixed–free end conditions

In this paper, a closed-form expression for the pull-in voltage of fixed–fixed beams and fixed–free beams is derived starting from the known expression of a simple lumped spring-mass system. The effects of partial electrode configuration, of axial stress, non-linear stiffening, charge re-distribution and fringing fields are all included in the final expression. Further, the results obtained are summarized and validated with other existing empirical and analytical models as well as with finite element simulation results. The model agrees well with finite element simulation results obtained with COVENTORWARE software.

Equivalent circuit representation of electromechanical transducers: I. Lumped-parameter systems

Lumped-parameter electromechanical transducers are examined theoretically with special regard to their dynamic electromechanical behaviour and equivalent circuits used to represent them. The circuits are developed starting from basic electromechanical transduction principles and the electrical and mechanical equations of equilibrium. Within the limits of the assumptions on boundary conditions, the theory presented is exact with no restrictions other than linearity. Elementary electrostatic, electromagnetic, and electrodynamic transducers are used to illustrate the basic theory. Exemplary devices include electro-acoustic receivers (e.g., a microphone) and actuators (e.g., a loudspeaker), electromechanical filters, vibration sensors, devices employing feedback, and force and displacement sensors. This paper forms part I of a set of two papers. Part II extends the theory and deals with distributed-parameter systems.

MEMS for wireless communications: ‘from RF-MEMS components to RF-MEMS-SiP’

Wireless communication has led to an explosive growth of emerging consumer and military applications of radio frequency (RF), microwave and millimeter wave circuits and systems. Future personal (hand-held) and ground communications systems as well as communications satellites necessitate the use of highly integrated RF front-ends, featuring small size, low weight, high performance and low cost. Continuing chip scaling has contributed to the extent that off-chip, bulky passive RF components, such as high-Q inductors, ceramic and SAW filters, varactor diodes and discrete PIN diode switches, have become limiting. Micro-machining or MEMS technology is now rapidly emerging as an enabling technology to yield a new generation of high-performance RF-MEMS passives to replace these off-chip passives in wireless communication (sub)systems. This paper reviews the progress in RF-MEMS from a device and integration perspective. The worldwide state-of-the-art of RF-MEMS devices including switches, variable capacitors, resonators and filters are described. Next, it is stipulated how integration of RF-MEMS passives with other passives (as inductors, LC filters, SAW devices, couplers and power dividers) and, active circuitry (ASICs, RFICs) can lead to the so-called RF-MEMS system-in-a-package (RF-MEMS-SiP) modules. The evolution of the RF-MEMS-SiP technology is illustrated using IMECs microwave multi-layer thin-film MCM-D technology which today already serves as a technology platform for RF-SiP.

The indent reflow sealing (IRS) technique-a method for the fabrication of sealed cavities for MEMS devices

A variety of microelectromechanical system devices requires encapsulation of their crucial fragile parts in a hermetically sealed cavity for reasons of protection. Hermeticity of the cavity and controllability of the ambient (gas pressure and gas composition) can be critical to the device performance. In order to minimize damage during handling, the cavity is preferably realized at the same time the device is fabricated, i.e., at wafer level. This paper reports the development of a hermetic packaging technique satisfying all the above. The method is referred to as the indent-reflow-sealing (IRS) technique, which relies on a multiple-chip fluxless solder-based joining technique and seal. Key process steps are the creation of an indent in the solder, the plasma pretreatment of the bonding surfaces, the pre-bonding (or sticking) of the chips and, the closing of the indent during a low-temperature (220/spl deg/C-350/spl deg/C) solder reflow in a clean controlled ambient using a designated oven. As opposed to other methods, the IRS method allows a greater flexibility with respect to the choice of the sealing gas and pressure, thereby offering a very hermetic seal and compatibility with low-cost high-throughput batch fabrication techniques. Flip-chip assemblies based on SnPb (67/37) solder and Au as the top surface metallization, have been reflowed in a forming gas ambient and have next been characterized on shear strength, hermeticity, and susceptibility to thermal stresses. The method has been successfully implemented in the process flow of an electromagnetic microrelay for the realization of the cavity housing the electrical contacts.

Design considerations and technology assessment of phased-array antenna systems with RF MEMS for automotive radar applications

Planar array antennas are attractive for use in future automotive radar systems due to their flexibility in design and control of radar beams. The complexity and cost of a radar front-end phased array can be decreased by applying a beam-steering/switching concept, which reduces the number of parallel RF and baseband signal paths. RF-microelectromechanical systems (MEMS) subsystems are employed because of their excellent RF properties and potential low-cost manufacturability. We present design considerations for prototypical automotive applications of RF-MEMS-based automotive radar front-ends using phased-array antennas based on phase shifters or a Rotman lens. The single RF-MEMS switch is optimized with respect to its RF and thermomechanical behavior taking into account automotive requirements. The respective RF-MEMS subsystems, i.e., phase shifters and single-pole-multiple-throw switching networks are presented in conjunction with packaging and mounting approaches. We evaluate two different wafer-level packaging technologies using glass-frit sealing or polymer sealing. Finally, functional packaged devices are demonstrated: a glass-frit-sealed and flip-chip-mounted RF-MEMS switch and a benzocyclobutene-packaged single-pole-quadruple-throw switch network.

A fully-packaged electromagnetic microrelay

Fully integrated electromagnetically actuated micromachined relays have been successfully fabricated and have been enclosed in ceramic and plastic packages. A multilayer Cu coil is used to actuate a movable NiFe armature, thereby closing the Au contacts. With the current design, magnetic forces of around 1 mN can be achieved. The fabrication process starts with two chips, which, after processing, are flip-chip bonded together using a low-temperature (<350/spl deg/C) solder joining process. The electrical contacts are housed in a hermetically sealed cavity with a predetermined atmosphere. The relay size is about 5/spl times/4/spl times/1 mm/sup 3/ (excluding the package). Typical performance characteristics of the packaged relay include: ON-resistance of 0.4 /spl Omega/, OFF-resistance greater than 10/sup 13/ /spl Omega/, life under low level load of 10/sup 7/ cycles, operate time of 1 ms, and, actuation voltage, current and power of 2 V, 8 mA and 16 mW, respectively.

The influence of mechanical shock on the operation of electrostatically driven RF-MEMS switches

A closed-form relationship between the insertion loss, the externally applied mechanical shock and the RF signal voltage of a capacitive RF-MEMS shunt switch is derived. It is shown that, based on this relationship, the minimum required mechanical stiffness of the suspended structure can be calculated. This allows determination of the minimum electrostatic switching voltage in a given process flow. The results are illustrated for specifications regarding shock resistance of electronic equipment as set out in MIL-STD-883. Even under the least severe test conditions, the shocks can affect the insertion loss of RF-MEMS switches, and can provoke self-biasing. This paper gives guidelines to avoid such false operation modes. The method can also be extended to yield the sensitivity of RF-MEMS devices to harmonic vibrations.

An oscillator circuit for electrostatically driven silicon-based one-port resonators

Abstract This paper describes design considerations and characteristics of oscillator circuitry for electrostatically driven silicon-based one-port resonators, used as resonant strain gauges. The oscillation conditions for a general, single transconductance oscillator are theoretically derived. In order to start oscillation, guidelines to select proper bias conditions for the resonator are presented, taking the non-linear effects into account. An oscillator circuit has been designed in CMOS technology in order to verify the theory experimentally. Experimental results of the oscillator in combination with a silicon beam resonator are given.

CMOS foundry-based micromachining

This paper reports on the first results of a study of the possibilities of the fabrication of micromechanical structures for microsystems applications in a regular MPC run of a standard CMOS process, followed by post-processing. Two post-processing modules, i.e., the frontside bulk etching module and the surface micromachining module are investigated. Examples of the former are suspended spiral coils for high-frequency applications and of the latter, metal bridge resonators.

Hermeticity Testing and Failure Analysis of MEMS Packages

Several microsystem applications require hermetic or semi- hermetic packages. It is for this reason mandatory to be able to check the hermeticity of these packages. The standard tests, using gross leak and fine leak, work very well for large cavities, but might give erroneous results for small cavities as typically used for MEMS. We discussed different alternative test methods.