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Acoustical attenuation and velocity parameters for Carbon Doped Oxide (CDO) thin films at GHz frequencies are needed to design Coupled Resonator Filters (CRF). CDO exhibits longitudinal acoustical impedance in the range of 2 to 11 MRayls, velocity of 2400 to 4000 m/s, and acoustical attenuation of 300 to 5000 dB/cm @ 1 GHz. A novel short loop acoustical technique is presented to make these measurements. An FBAR resonator, operating at the quarter wavelength (λ/4) frequency f cdo , excites a CDO thin film. The CDO is made λ/4 thick in order to de-couple the CDO film from the FBAR. From the measured thickness t CDO and λ/4 frequency of the CDO, the velocity v may be calculated: v=4t CDO f CDO . From the measured quality factor Q and wave number k=∞/v, the attenuation constant α ∼ k/(2Q) is calculated. By building matched λ/4 thick resonator/CDO film stacks at different frequencies, the CDO attenuation versus frequency is obtained. A linear (f1) attenuation, not the usual quadratic (f2), dependence on frequency is found. The measurement technique will be described in detail, as well as limitations on the range of validity. A series of CDO film compositions on FBARS were made. Synthesis of the CDO films was discussed previously [1]. A typical CDO film exhibited acoustical v=3250 m/s, impedance=4.7 MRayls, and α=2000 dB/cm @ 1 GHz, (f2) dependence. For well matched λ/4 FBAR resonators and CDO films, the short loop results were quite accurate. When the quarter wavelength condition of either the FBAR or CDO film was violated, there is a slight error in the velocity and attenuation measured. In either case the results are compared to those of values obtained by detailed analysis of the measured scattering parameters in a Mason equivalent circuit.

Recently, a new standard has been proposed to augment the performance of future Global Positioning System (GPS) receivers, and is generally referred to as the Global Navigation Satellite System (GNSS) band. By also requiring differential signals from the output of the filter to the cell phone receiver, further performance improvements can be obtained. To accommodate the new GNSS specifications and to provide single-ended to differential (SE-DE) mode conversion, new filter designs are required. In this work, we describe a two-stage, SE-DE filter design for GNSS that is based on coupled resonator filter (CRF) technology. The design provides insertion loss better than −2.5 dB over a frequency range greater than 56 MHz. Out-of-band rejection is greater than 40 dB from DC to 6 GHz, and better than 60 dB below 2 GHz. As a stand-alone filter, excellent phase and amplitude balance are achieved without the need for external inductors. In a frontend module consisting of the filter and an Avago LNA, we have measured >13 dB gain over the GNSS band. The module also shows excellent rejection and true differential output equivalent to surface acoustic wave filter solutions.