Th.G.S.M. Rijks

Dynamics and squeeze film gas damping of a capacitive RF MEMS switch

We report on measurements of the time-dependent capacitance of an RF MEMS shunt switch. A high time-resolution detection set-up is used to determine switching time and motion of the device. From the equation of motion the damping force is extracted. The measured damping force is found to be approximately proportional to the speed over the gap to the third power (FD v/z3), in good agreement with squeeze film damping theory. Significant influence of slip–flow effects on the motion is observed. Measurements at low pressure show underdamped harmonic oscillations in the opening motion and contact bounce effects in the closing motion. Effects of dielectric charging on the C–V curves are discussed. Experimental results are compared with electromechanical and damping simulations.

RF MEMS tunable capacitors with large tuning ratio

MEMS tunable capacitors have been fabricated in a thin-film technology for passive integration. Using a dual-gap relay-type design, continuous and reversible capacitance tuning with a tuning ratio up to 17 has been demonstrated, while requiring an actuation voltage of only 20 V. A quality factor of 150 to 500 has been measured in the frequency range of 1 to 6 GHz, making these devices very suitable as building blocks in many RF applications. These are the highest tuning ratio and quality factor reported to date for parallel-plate tunable capacitors.

Microelectromechanical tunable capacitors for reconfigurable RF architectures

This paper reports on metal-based MEMS tunable capacitors, fabricated in a thin-film process on high-ohmic silicon. Continuous and reversible tuning has been demonstrated with an average tuning ratio of 4.5. A quality factor between 100 and 300 has been obtained in a frequency range of 0.5 to 4 GHz. The combination of a high quality factor and large tuning range makes these tunable capacitors very suitable as building blocks in many radio-frequency (RF) applications. The tuning speed, temperature stability and RF power handling have been studied in terms of self-actuation. Finally, the need for a hermetic package as well as a packaging concept which can potentially provide this has been demonstrated. After packaging, the devices can be handled as standard silicon dies, making them fit very well with a system-in-package approach.

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.

Application of giant magnetoresistive elements in thin film tape heads

We studied the applicability of Ni/sub 80/Fe/sub 20//Cu/Ni/sub 80/Fe/sub 20//Fe/sub 50/Mn/sub 50/ GMR multilayers for thin film tape heads. A method involving crossed anisotropies is applied for avoiding noise in the GMR response. We compare and analyse the sensitivities of AMR and GMR heads. >

GIANT MAGNETORESISTANCE MATERIALS FOR READ HEADS

The sensitivity of magnetoresistive read heads can be increased by using layered magnetic materials showing the giant magnetoresistance effect, instead of a single magnetic film showing the anisotropic magnetoresistance effect. For this purpose, exchange-biased spin-valve layered structures are very suitable. For well-chosen compositions and nanometer-scale layer thicknesses these materials combine a fair giant magnetoresistance effect with a very small field interval in which the resistance change takes place. In this paper we give an overview of aspects which determine the functioning of materials of this class in read heads, including their preparation, magnetotransport properties and the magnetic interactions which determine the magnetization reversal process.

Giant magnetoresistance and its application in recording heads

A short overview is given of the giant magnetoresistance (GMR) effect and its device applications. As an example of present research topics, the optimization of the ferromagnetic-layer composition of spin valves for application in recording heads is discussed. The influence on output voltage and stability has been investigated in test structures and compared with material parameters that were experimentally obtained from unpatterned films. It is found that in practical applications a small addition of cobalt is advantageous, since, although the output voltage is decreased, it leads to an improvement in reproducibility, linearity, signal-to-noise ratio and dynamic range.

Grain size and strain in thin sputter-deposited Ni0.8Fe0.2 and Cu films

The average grain size and strain in the direction parallel to the surface of thin Ni0.8Fe0.2 and Cu films, sandwiched between Ta layers, have been determined as a function of layer thickness by grazing incidence X-ray diffraction. The in-plane grain size and grain size distribution were also assessed by plan-view transmission electron microscopy. Standard θ-2θ X-ray powder diffraction was used to determine the uniform strain in the direction perpendicular to the surface. Both for Ni0.8Fe0.2 and Cu, an elongation of the lattice parameter perpendicular to the surface and a compression of the lattice parameter in the plane of the film is observed, which decreases with increasing film thickness. Additionally, for Ni0.8Fe0.2 a non-uniform elongation of the perpendicular interactomic distance at the Ta interfaces is deduced by fitting a kinematical model to the θ-2θ diffraction spectrum. This study illustrates the strength and the complementary character of standard powder X-ray diffraction, grazing incidence X-ray diffraction and transmission electron microscopy for the structural analysis of thin metal films.

MEMS-based MCM VCO for space applications

This paper presents the implementation and test of prototype RF MEMS based voltage controlled oscillators (VCO) for space applications. RF MEMS tunable capacitors based on a dual gap architecture have been manufactured with a thin film technology on silicon and have demonstrated high tuning ratio (Cmax/Cmin ~ 4) and high Q factors (up to 100) with a good reproducibility. These tunable capacitors have been integrated as frequency tuning element in the LC tank of multi chip modules (MCM) VCO operating around 1.6 GHz with a tuning range greater than 16% and a phase noise as low as -125 dBc/Hz at 1 MHz offset from the carrier