Romain Stefanini

Miniature MEMS Switches for RF Applications

This paper presents a new way to design MEMS (microelectromechanical system) metal contact switches for RF applications using miniature MEMS cantilevers. A single 25 × 25 μm switch is first demonstrated with a Au-to-Ru contact, C_u = 5 fF and R_on = 7 Ω at an actuation voltage of 55 V. The measured switching time is 2.2 μs and the release time is <;1 μs. The switch is robust to stress effects (residual and stress gradients) which increases its yield on large wafers. To reduce the effective switch resistance, 10-20 miniature RF MEMS switches have been placed in parallel and result in equal current division between the switches, an up-state capacitance of 30-65 fF and a down-state resistance of 1.4-1.5 Ω. Furthermore, 10-20 element back-to-back switch arrays are developed and result in a marked improvement in the reliability of the overall switching device. A series-shunt design is also demonstrated with greatly improved isolation. The device has a figure-of-merit of f_c = 1/(2πR_onC_u) = 3.8 THz (R_onC_u = 42 fs).

Ku Band High-Q Tunable Surface-Mounted Cavity Resonator Using RF MEMS Varactors

This paper presents a 14 GHz high-Q (quality factor) tunable resonator using microelectromechanical system (MEMS) varactors. A brass surface mountable cavity has been bonded on a fused silica wafer on which are processed three 1.1 mm long MEMS varactors. Their location has been optimized in order to obtain a wide frequency shift, when the cantilevers are actuated on the substrate. 15% tuning range from 11.9 GHz to 14.2 GHz has been obtained with a continuous shift from 11.9 GHz to 13.6 GHz. Measurements result in an average unloaded quality factor (Qu) of 480 over the operating frequency band.

Compact 2-pole and 4-pole 2.4–2.8 GHz dual-mode tunable filters

Compact 2-pole and 4-pole dual-mode tunable filters have been developed to cover the 2.4–2.8 GHz bandwidth. The filters are based on magnetic coupling (2-pole) and on a mixed-mode coupling (4-pole) so as to result in a near-constant fractional bandwidth over the tuning range. An unloaded tunable filter Q of 50–130 was achieved for both designs, which is quite high when using Silicon Schottky varactor diode for the tunable elements. The filters are integrated on an ɛr=10.2 substrate, are quite small, and result in relatively low insertion loss (2–6 dB) and excellent rejection. The application areas are in reconfigurable communication systems.

Miniature RF MEMS metal-contact switches for DC-20 GHz applications

This paper presents the design and measurements of a miniature RF MEMS (Micro-Electro-Mechanical System) metal-contact switch. The dimensions (25×24×1.6 µm) and shape of the beam and actuation pad have been optimized to result in a 12–25 µN contact force at 52–60 V actuation, with a corresponding restoring force of 15 µN. Measured S-parameters on a single switch show an up-state capacitance of 5 fF and a 13–14 Ω contact resistance for a Au-Ru contact under an actuation voltage of 55 V. In order to reduce the effective switch resistance, 10 miniature RF MEMS switches have been placed in parallel and result in an up-state capacitance of 30 fF and a switch resistance of 1.4 Ω. The measured switching time is 2.2 µs and the release time is &#60; 1 µs. The switch is robust to stress effects (residual and stress gradients) which increases its yield on large wafers. To our knowledge, this is the first demonstration of a miniature RF-MEMS metal-contact switch and with an excellent figure-of-merit (f<inf>c</inf>=1/(2.π.R<inf>on.</inf>C<inf>u</inf>)=3.8 THz).

Compact SMD packaged tunable filter based on substrate integrated coaxial resonators

A surface mountable tunable SIW filter based on coupled coaxial resonators is presented in this paper. A CPW vertical transition is designed in order to provide input/output access to the device. Biasing components are also integrated in the same substrate and accessed through castellated via holes. The proposed filter presents a very compact size and constant fractional bandwidth. Measured results including the effect of the vertical transition show low insertion losses while keeping a constant fractional bandwidth along the tuning range.

Compact 2-pole and 4-Pole 1.5–0.9 GHz constant absolute bandwidth tunable filters

Compact 2-pole and 4-pole tunable filters have been developed to cover the 0.9–1.5 GHz bandwidth. The proposed filters are based on a mixed coupling to ensure a near constant absolute bandwidth during tuning operation. They are fabricated on a duroid substrate (εr=3.2) and tuned using varactor diodes. The 2-pole and 4-pole filters respectively result in a 60 +/−9 MHz and a 74 +/− 15 MHz 3-dB absolute bandwidth on a wide tuning range (> 40 %).

Compact thin-film packaged RF-MEMS switched capacitors

This paper presents the design, the realization and the measurement of a thin-film packaged RF-MEMS switched capacitors. Packaging is included in microelectronics fabrication process, with Silicon Nitride thin film. The capacitors are actuated by deflecting thin gold metal membranes towards the package dielectric, increasing the capacitance by a factor 2.3. The device size, including its packaging, is 50 × 40μm2. Pull-in and release voltages have less than 5V variation between 20°C and 85°C. The device has been tested with 20 dBm applied power and shows no sensitivity to incident power.