Aluminum Nitride RF MEMS Resonators

Aluminum Nitride RF MEMS Resonators

Sandia has developed an aluminum nitride (AlN) process for fabricating RF MEMS micro resonators at frequencies ranging from 1 MHz to 3 GHz. This process uses the same equipment and materials that were developed to fabricate FBARS (film bulk acoustic resonators), which are widely used to implement cellular phone duplexers and filters at 1.9 GHz. Like FBARS, the piezoelectric transduction mechanism of these resonators allows the realization of low insertion loss filters. Unlike FBARS, Sandia's AlN process allows resonators at any frequency between 1 MHz and 3 GHz to be fabricated on the same wafer because the resonant frequency is determined lithographically. The AlN resonator process also includes Sandia's unique molded tungsten (W) capabilities. Incorporation of W into the AlN process eliminates the need for resonators that are suspended above the substrate by quarter-wave beams. It is this technology that allows the scaling of AlN resonators into the GHz range without introducing spurious modes, reductions in quality factor (Q), and with acceptable power handling for both the transmit and receive paths in full-duplex radios. This technology is most suited for realizing resonators from 1 MHz to 3 GHz, with Q's approaching 5000, and impedances less than 300 Ohms.

108 MHz Dual Mode AlN RF MEMS Filter

Measured and Simulated Response of the Dual Mode Filter with Different Termination Impedances

Narrow-gap Polysilicon RF MEMS Resonators

A polysilicon MEMS resonator process has been developed at Sandia for the fabrication of high-Q oscillator references and intermediate frequency (IF) filters. This process can achieve electrode-to-resonator gaps less than 100 nm, which is needed to reduce the impedance of capacitively transduced devices. While high frequency resonators can be implemented in this process, it is best suited for fabricating resonators below 200 MHz because the impedance levels are significantly lower at these frequencies. Advantages of these polysilicon resonators when compared to microfabricated piezoelectric resonators include much higher Q (> 60,000), low drift, tunability, and low vibration sensitivity. These properties make polysilicon µresonators ideal for implementing miniature oscillators and IF filter banks for RF MEMS applications.

52 MHz Lame' Mode PolySilicon RF MEMS Resonator

Measured Transmission of the Lame' Mode RF MEMS Resonator

RF MEMS Reliability

Through measurement, characterization and analysis, we provide customer feedback to improve operation, performance and reliability of MEMS components, specifically RF switches. We have testing capabilities at the DARPA standard for MEMS switches (RFMIP) of 10 GHz. We have conducted environmentally controlled studies of switch performance and lifetimes at temperatures ranging from -15C to 75C, including cycling. Through failure analysis, we have worked with our customers to enhance understanding of operation, mechanically and electrically. We have performed tests to understand contamination issues that have caused early failures. We are investigating functionality and performance of RF sensor applications to monitor corrosion and to predict critical component failures. By utilizing knowledge of MEMS and by providing unique measurement and characterization capabilities, we can be an integral part of any MEMS project.

Fuente: http://www.mems.sandia.gov/about/rf-mems.html

Cesar Augusto Suarez 

CI 17394384

CAF