Pascal Tristant

MEMS switchable interdigital coplanar filter

This paper presents a tunable interdigital coplanar filter with tapped-line feedings. Microelectromechanical systems capacitors are used as a high contrast capacitive switch between a quarter-wavelength resonator and an open-ended stub to perform the frequency shift. A two-pole tunable filter with a 13% relative bandwidth has been designed, fabricated, and measured. The center frequency can be switched from 18.5 to 21.05 GHz with low return losses (less than 15 dB) and low insertion losses (3.5 dB).

Dielectric less capacitive MEMS switches

This paper presents the fabrication and experimental results on a capacitive switch without dielectric. Using an appropriate design of the switch, acceptable performances have been obtained with Con/Coff ratio around 10. The key advantage of this switch is that dielectric charge trapping related failure modes are eliminated. An example is shown with measured intrinsic loss less than 0.3 dB at 15 GHz and isolation better than 15 dB at the same frequency.

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.

RF-MEMS Switched Varactor for High Power Applications

A new kind of MEMS switched varactor has been developed to handle high power RF signals, (P>1W), at S and X-band. The design principle is presented, as well as measurements results featuring an analysis of the reliability tests. The fabricated varactors have shown a capacitance ratio of 7-8 at 5 GHz and good performances reproducibility while undergoing 1 billion cycle tests under an input RF power of 1W @ 10GHz, and 250 million cycle tests under 5W @ 3GHz, both in hot switching conditions, without visible degradation

Microwave plasma enhanced CVD of aluminum oxide films: OES diagnostics and influence of the RF bias

Aluminum oxide films are obtained in a remote-microwave-plasma-enhanced chemical vapour deposition (RMPECVD) reactor. In this technique, only oxygen gas plasma is generated while trimethylaluminum (TMA) carried by argon is fed near the substrate holder which can be RF biased and deposition occurs at the surface of a silicon wafer. Optical emission spectroscopy (OES) is used in order to gain information on the plasma excitation of various species. The presence of an inert gas (argon) allows an evaluation of the relative densities of reactive species by the actinometry technique. A comparison has been done with and without RF biasing or TMA injection at different microwave powers in the same conditions of Ar and O2 flow rates. The RF biasing creates an additional plasma near the substrate holder but has a weak influence on the OES signal. The microwave plasma is the major mode in the present experimental set up. Less than 2% of TMA modifies the plasma chemistry by improving the atomic oxygen formation. In addition, the TMA decomposition involves a cooling effect of the electron energy. Although this dual mode configuration of the plasma production induces a slight decrease of the deposition rate, it limits the incorporation of impurities (O, H) in the layer by improving the ion bombardment and etching of the growing layer.

Effects of atmosphere on the reliability of RF-MEMS capacitive switches

The influence of atmosphere on capacitive RF-MEMS switches is studied. It is shown that ambient atmosphere not only induces an incremental effect on the degradation of MEMS switches but also completely changes the charging mechanism of the dielectrics, directly linked with RF-MEMS reliability behaviour of MEMS switches reliability. Operating RF-MEMS switches in a dry environment changes the mechanism of charging from surface charging to bulk charging.

Gamma radiation effects on RF MEMS capacitive switches

Dielectric-based RF MEMS capacitive switches were fabricated and characterized for their response to dielectric charging, thermal storage and cycling and to total dose gamma irradiations. The evolution of the switch electromechanical and RF characteristics (actuation and releasing voltages, insertion losses, isolation) were evaluated as a function of the applied stress (temperature or total ionizing dose). It is indicated that the thermal stress has a relatively minor impact on the switches (the switches remained functional with nearly the same electrical properties). Under our particular test conditions, C(V) and S-parameters measurements show that gamma radiation has low to moderate effects on the components behavior.

Low Loss Ohmic Switches For RF Frequency Applications

This paper focuses on the design of DC contact series switch built with MEMS technology. It uses a novel contact electrode that allows to have a high isolation and low insertion loss. This approach resulted in good performances with measured insertion loss of 0.1dB and 45 dB isolation at 2 GHz.

Remote microwave plasma-enhanced chemical vapour deposition of insulating coatings (SiO2) on metallic substrates: film properties

Abstract Silicon dioxide thin films were prepared on stainless steel substrates by remote microwave plasma-enhanced chemical vapour deposition (RMPECVD) using an oxygen plasma and a mixture of 5% silane in argon injected in the afterglow. The influence of the process parameters on the film properties was investigated by Fourier transform infrared (FTIR) spectroscopy and electron recoil detection analysis (ERDA). The content of hydrogen was deduced. The electrical insulation was analysed in terms of the dielectric constant, loss factor ( tan δ), resistivity and dielectric strength of the films. An increase in temperature or microwave power leads to a decrease in hydrogen incorporation and improves the insulation properties. Moreover, the use of a radiofrequency (r.f.) substrate bias voltage of 200 V aids the desorption of hydrogen.

High Power Applications of RF-MEMS

This paper presents recent results on the development of high power MEMS switched varactors. Design methodology as well as fabrication and measurement results are presented. The MEMS varactors are made of a thick metal gold cantilever, with a reduced contact area, that allows to control high power microwave signals. Operation up to 5 watts CW is demonstrated, with good reliability. First results on applications to phase shifters is presented