P.M. Zavracky

Study of contacts in an electrostatically actuated microswitch

Surface micromachined, electrostatically actuated microswitches have been developed at Northeastern University. Microswitches have an initial contact resistance of 0.5-1 /spl Omega/, and current handling capability of about 20 mA. Typically, contact resistance degrades progressively when the switches are cycled beyond approximately 10/sup 6/ cycles. In this work, the microswitch contact resistance is studied on the basis of a simple, clean metal contact resistance model. Comparison of measured contact resistance (measured as a function of contact force) with the characteristics predicted by the model shows the measured resistance to be higher than the prediction, approximately by an order of magnitude, suggesting that insulating films at the contact interface need to be taken into account. Microswitches with a large number of parallel contacts have also been developed, and measurement data is presented showing that these devices have a current handling capability greater than 150 mA.

Integrated self-biased hexaferrite microstrip circulators for millimeter-wavelength applications

Planar microstrip Y-junction circulators have been fabricated from metallized 130-/spl mu/m-thick self-biased strontium hexaferrite ceramic die, and then bonded onto silicon die to yield integrated circulator circuits. The impedance matching networks needed to transform the low-impedance circulator outputs were deployed on low-loss alumina or glass dielectrics to minimize circuit losses. These magnetically self-biased circulators show a normalized isolation and insertion loss of 33 and 2.8 dB, respectively, and a 1% bandwidth for an isolation of 20 dB. Application of small (H<1.5 kOe) magnetic bias fields improved the isolation and insertion loss values to 50 and 1.6 dB, respectively. This design may form the basis for future monolithic millimeter-wave integrated circulator circuits that do not require magnets.

Electrostatically actuated micromechanical switches

Micromechanical switches and relays realized by a simple surface micromachining process are presented. The devices use a nickel cantilever beam and gold-to-gold electrical contact, and are electrostatically actuated. They have lifetimes exceeding 109 cycles, and a current handling capability of 150 mA.

Theory and experiment of thin-film junction circulator

We have calculated the S-parameters and losses in ferrite-film-junction circulators using a new effective-field theory assuming TEM-like propagation. Conductivity loss dominates the dielectric and magnetic losses in Y-junction circulators fabricated on ferrite films with thicknesses less than 200 /spl mu/m. It is plausible to fabricate Y-junction thin-film circulator at X-band with insertion loss less than 0.5 dB if the film thickness is larger than 100 /spl mu/m. The quality of the conductor plane is important in reducing the overall insertion loss of the thin-film-junction circulator.

Measurement and modelling of surface micromachined, electrostatically actuated microswitches

Electrostatically actuated micromechanical switches have been reported in earlier work by the authors. In the present work, a simple contact resistance model of the microswitch is discussed. Preliminary contact resistance measurements are presented, and compared with the modeled contact resistance characteristics.

A monolithic single-crystal yttrium iron garnet/silicon X-band circulator

Production of truly monolithic microwave integrated circuits that incorporate ferrite passive control elements has been hindered by the material property mismatches between ferrites and semiconductors. In this work, monolithic Y-junction circulators were fabricated by bonding 100-μm-thick single-crystal yttrium iron garnet films to silicon at 195/spl deg/C, and then removing the gadolinium gallium garnet substrate. S-parameter measurements on the circulator and matching microstrip circuit yield an isolation of 20 dB over a 1 GHz bandwidth at 9 GHz, with a minimum insertion loss near 1 dB. Improvements in circuit design and fabrication techniques may yield monolithic circulators that are fully compatible with large-scale semiconductor manufacturing methods.

Influence of nonuniform magnetic field on a ferrite junction circulator

We have analytically formulated the problem that a ferrite circulator junction is biased by a nonuniform magnetic field. Interport impedances of the junction can, therefore, be solved numerically. Nonuniform-bias field will reduce the transmission bandwidth, and the circulation condition is apt to be altered if the bias field shows nonuniformity near the center of the junction. Our calculation compares very well with measurements.

Theoretical Modeling of Microstrip Thin-Film Circulators

We have calculated the S-parameters and losses in ferrite film junction circulators using a new effective-field theory assuming TEM-like propagation. At X-band conductivity loss dominates the dielectric and magnetic losses in Y-junction circulators fabricated on low-loss ferrite films with thicknesses less than 200 /spl mu/m. Our calculations compare closely with experiments.