Matthieu Chatras

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).

A Two-Pole Lumped-Element Programmable Filter With MEMS Pseudodigital Capacitor Banks

This paper presents a novel two-pole reconfigurable bandpass filter on alumina substrate for applications in X- and S-bands. An analytical approach was followed for synthesis of multiple filtering characteristics. A microstrip network on alumina was then optimized to implement a set of switched filtering functions. Finally a reconfigurable filter was fabricated and tested in order to validate the proposed approach. This filter exploits five 3-bit capacitor banks controlled with microelectromechanical systems ohmic switches to achieve 12 states with 37.5% tuning range between 1.51-2.26 GHz. Several tuning mechanisms are demonstrated including frequency, bandwidth tuning, and frequency + bandwidth tuning. Good agreement with theoretical results has been obtained.

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.

A surface-mountable membrane supported filter

A silicon micro-machined filter with a simple planar integration on an other substrate is proposed in this article. The excitation is made from the top of the shielding substrate of a membrane supported micro-machined filter. Packaging and inter-connection are included in the design. Experimental results are presented on a two pole 30 GHz, 4% fractional bandwidth filter with a quality factor of 602 and insertion loss of 1.8 dB. Such a filter can be easily integrated in any circuit using flip-chip technology.

Bulk acoustic wave filters synthesis and optimization for multi-standard communication terminals

This article presents a design methodology for bulk acoustic wave (BAW) filters. First, an overview of BAW physical principles, BAW filter synthesis, and the modified Butterworth-van Dyke model are addressed. Next, design and optimization methodology is presented and applied to a mixed ladder-lattice BAW bandpass filter for the Universal Mobile Telecommunications System (UMTS) TX-band at 1.95 GHz and to ladder and lattice BAW bandpass filters for the DCS1800 TX-band at 1.75 GHz. In each case, BAW filters are based on AlN resonators. UMTS filter is designed with conventional molybdenum electrodes whereas DCS filters electrodes are made with innovative iridium.

Compact quasi planar silicon bandpass filters based on metallic periodic structure for Q and V band applications

Small size filters are presented here, they are based on a periodic lattice of metallic holes that form coupled silicon resonators. The first structure is a filter at 45 GHz with 8% bandwidth at -3 db, realized on 430 /spl mu/m thick high resistivity silicon wafer using a wet etching process. I/O CPW feeds are printed on the top of the substrate. The second structure is a filter at 58.5 GHz with 2% bandwidth at -3 db. The via holes lattice is realized with deep RIE process and the filter is bonded to a PCB with a flip chip technique. Based on the same principle, a CPW to waveguide transition is finally presented.

A micromachined tunable cavity resonator

This paper focuses on a tunable resonator fabricated using bulk and surface micro-machining techniques. The resonator consists of a silicon micro-machined metalized cavity coupled with a MEMS bridge capacitor for tunability purposes. The resonator is excited using coplanar waveguide lines to avoid losses from transitions and facilitate measurements. The unloaded quality factor of the device is about 150 depending on the MEMS varactor position and the simulated tuning range is 0.4 GHz (1.45%) at 27.8 GHz.

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.

A pressure sensor based on a HBAR micromachined structure

In this work, we propose a pressure sensor fabricated on compound LiNbO3/Silicon/Silicon substrates obtained by Au/Au bonding at room temperature and double face lapping/polishing of LiNbO3/silicon stack and a final gold bonding with a structured silicon wafer. Sensitivity of the final sensor to bending moments then is tested and results show pressure sensitivity of such devices.

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).