This paper presents a high-performance substrate-integrated-waveguide RF microelectromechanical systems (MEMS) tunable filter for 1.2-1.6-GHz frequency range. The proposed filter is developed using packaged RF MEMS switches and utilizes a two-layer structure that effectively isolates the cavity filter from the RF MEMS switch circuitry. The two-pole filter implemented on RT/Duroid 6010LM exhibits an insertion loss of 2.2-4.1 dB and a return loss better than 15 dB for all tuning states. The relative bandwidth of the filter is 3.7 ± 0.5% over the tuning range. The measured Qu of the filter is 93-132 over the tuning range, which is the best reported Q in filters using off-the-shelf RF MEMS switches on conventional printed circuit board substrates. In addition, an upper stopband rejection better than 28 dB is obtained up to 4.0 GHz by employing low-pass filters at the bandpass filter terminals at the cost of 0.7-1.0-dB increase in the insertion loss.

A 1.2–1.6-GHz Substrate-Integrated-Waveguide RF MEMS Tunable Filter

The RF community has long been searching for the ideal switch since the birth of electronics, and it is defined as a device having virtually no insertion loss (Ron = 0 Ω) over a wide frequency range, very high isolation [off-state capacitance (Coff)] = 0 fF), extremely high linearity (IIP2 and IIP3 → infinite), medium- to high-power handling (100 mW to 1 kW), and no dc power consumption. Our entire RF infrastructure ecosystem, from communication system networks, to satellite systems, to wideband spectral analysis, to instrumentation and radar systems, uses a variety of switches for signal routing and control (attenuation, phase shifting, etc.). The ideal switch was achieved long time ago using electromechanical relays, and even after nearly 100 years, it is still the best RF switch ever made from an electrical perspective [1]. It has very low insertion loss (Ron <;1 Ω), very high isolation (Coff of few fF), very high linearity and high power handling (100 mW to 50 W). However, it is bulky, expensive, and has an average lifetime of few million cycles.

The Search for a Reliable MEMS Switch

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, Cu = 5 fF and Ron = 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 fc = 1/(2πRonCu) = 3.8 THz (RonCu = 42 fs).

Miniature MEMS Switches for RF Applications

This paper presents an electrostatic RF microelectromechanical systems (MEMS) metal contact switch based on a tethered cantilever topology. The use of tethers results in a design that has low sensitivity to stress gradients, biaxial stresses, and temperature. A switch with a footprint of 160 × 190 μm2 and based on a 8-μm-thick gold cantilever with an Au/Ru contact is implemented on a high-resistivity silicon substrate and results in a total contact force of 0.8-1.2 mN at 80-90 V, a restoring force of 0.5 mN, a pull-in voltage of 61 V, an up-state capacitance of 24 fF, and an actuation time of 6.4 μ s. The device achieves a switch resistance of 2.4±1.4 Ω to 1.8±0.6 Ω at 90-100 V in open laboratory environments (nonpackaged). This design has the potential to replace conventional electromagnetic relays in application areas such as automated testing equipment and high-performance switching networks.

RF MEMS Metal-Contact Switches With mN-Contact and Restoring Forces and Low Process Sensitivity

This paper presents the design and characterization of compact high-power RF microelectromechanical system single-pole single-throw (SPST) and single-pole four-throw (SP4T) metal-contact switches. The SPST design results in a contact force of 1.9-2.8 mN at 80-90 V distributed over eight contacts and using four independent quadrants for actuation. The SP4T is a derivative of the SPST and results in a contact force of 0.45-0.7 mN per switch at 80-90 V. S-parameter measurements show an up-state capacitance of 70 and 17 fF along with a down-state resistance of 1-2 and 2-4 Ω using Au-to-Ru contacts for the SPST and SP4T switches, respectively. The switch pull-in and release voltages are 50 and 45 V, respectively, and the switching time is t on ~ 10 μs and t off ~ 2 μs. The SPST and SP4T are capable of handling 10 and 2 W up to 100 million cycles, and the SPST has been tested with 30 W of power up to 30 million cycles before failure (all cold switched). The application areas are in compact high-power applications such as wireless communication systems and base-stations.

Compact High-Power SPST and SP4T RF MEMS Metal-Contact Switches

Here, we propose a practical single pole double throw (SPDT)-structured radio frequency microelectromechanical system (RF MEMS) switch for RF applications. This SPDT switch has a very low insertion loss of 1.0dB and a high isolation of 40dB, up to 10GHz. The fabricated switch is compact in size (5.2×3.0×1.8 mm3) with a Land Grid Array Package. The research and development of an RF MEMS switch has been ongoing in our laboratory for years, and we have achieved practical reliability by using a low vibration actuator against a natural frequency. We describe the correlation between contact reliability and the low vibration actuator, as well as the high frequency performance of our new SPDT switch.

Y. Adachi

Papers

Development of SPDT-structured RF MEMS switch