K.T. McCarron

Solidly mounted resonators and filters

Acoustic resonators require material interfaces that confine waves to a finite volume in an efficient manner. Conventionally this is achieved by using air or vacuum interfaces at the electrodes. Another technique is to fabricate the resonator onto a set of quarter wavelength thick layers attached to a substrate to form a solidly mounted resonator (SMR). The SMR concept has been used to fabricate low insertion loss filters for GPS and other applications. Filters for GPS having less than 3 dB insertion loss and 40 dB out-of-band rejection have been demonstrated. These filters are composed of ladder networks with series and shunt resonators.

Temperature compensated bulk acoustic thin film resonators

Thin film resonators have been made that exhibit a high degree of temperature compensation. These resonators are composed of piezoelectric aluminum nitride films, aluminum top and bottom electrodes, and are compensated with layers of silicon dioxide within the resonator. The resonators are fabricated with the solidly mounted resonator (SMR) configuration using a sequence of aluminum nitride and silicon dioxide reflector layers. Silicon dioxide has a positive temperature coefficient and can be used to offset the -25 ppm per degree C coefficient of aluminum nitride. Results are reported on hermetic packaging, temperature cycle testing, temperature coefficient measurements, and preliminary ageing.

High performance stacked crystal filters for GPS and wide bandwidth applications

Stacked Crystal Filters, (SCF), are composed of multi-layers of piezoelectric and metal layers. Normally these filters have a complex frequency spectrum containing near-in spurious responses. However, by having the SCF formed in a Solidly Mounted Resonator (SMR) format, the performance of the device is greatly improved by the finite bandwidth of the SMR reflector. The conventional SCF also has a bandwidth that is too small for some wireless applications. This paper will describe the design and performance issues associated with stacked crystal filters using bulk wave thin films with aluminum nitride as the piezoelectric. Filters without spurious responses, filters having wide bandwidths, and filters operating at frequencies up to 8.5 GHz will be described in addition to GPS filters.

Improved bulk wave resonator coupling coefficient for wide bandwidth filters

Resonator coupling coefficient plays a key role in determining the bandwidth of acoustically or electrically coupled resonator filters. This paper presents a method using high mechanical impedance electrodes to increase the effective coupling coefficient for bulk acoustic wave (BAW) resonators in the solidly mounted resonator (SMR) or membrane (FBAR) configurations.

Development of miniature filters for wireless applications

Miniature filters have been under development for wireless applications from 500 MHz to over 6 GHz using thin piezoelectric films on common substrates. Ladder filters have achieved insertion losses in the 3 dB range using aluminum nitride films for the piezoelectric and appropriate substrates such as silicon, sapphire, and glass. The ladder filters consist of interconnected series and shunt resonators forming a monolithic structure on a single die. This paper discusses recent results in the development of miniature filters with application to cellular phone, GPS, PCN, and other wireless systems.<<ETX>>

Wide bandwidth thin film BAW filters

Wide bandwidth filters are of interest in current and emerging wireless and system applications for use in IF circuits or as front end filters. Filters for the new GPS M code and for wireless LAN are required to have bandwidths approaching 4% of center frequency. The paper describes design and fabrication methods for obtaining wide bandwidth filters for GPS and wireless LAN applications using coupled resonator filters. Experimental results are presented.

Bulk acoustic wave resonators and filters for applications above 2 GHz

Bulk acoustic wave (BAW) devices are of interest for applications at higher microwave frequencies above 2 GHz. As frequencies increase, BAW devices require thinner films which decreases processing times and makes the technology more cost effective. However, the area of resonators and associated filters also decreases and begins to impact device performance and packaging requirements. This paper summarizes the technical requirements of BAW devices in the 2 to 20 GHz frequency range and shows specific results for resonators, ladder filters, and stacked crystal filters operating up to 20 GHz.

High Q microwave acoustic resonators and filters

The authors present recent experimental and modeling results for high-Q microwave acoustic resonators and filters for use in oscillators and other frequency control applications. Overmoded resonators have exhibited an FQ product greater than 1*10/sup 14/ Hz (e.g. Q=68000 at 1.6 GHz) with a strong inductive response suitable for one-port and two-port oscillator feedback circuits. Ladder filters fabricated with overmoded resonators have loaded Qs greater than 40000 with 76-kHz bandwidth at 1.6 GHz. Aluminum nitride films were used for transduction on Z-cut sapphire substrates.<<ETX>>

Filter banks implemented with integrated thin film resonators

Filter banks composed of five or more bandpass filters fabricated on a single die have been demonstrated and are under continuing development. Such filters will find applications in multi-channel radios, spectrum analyzers, and in other frequency control applications. Fabrication of ladder bandpass filters requires that resonators be built at two or more frequencies for each filter. In the simplest form of the ladder filter, at least one frequency is needed for the series resonator and a lower frequency for the shunt resonator. This paper reports on a technique to fabricate multiple frequency resonators and experimental results for a simple five channel filter bank.

Thin film bulk acoustic wave resonator and filter technology

This paper presents a short summary of progress made in the development of thin film resonators and filters. Over 300 different filter and resonator products have been developed spanning a frequency range of 500 MHz to over 12 GHz. While most of these products are custom designed for Government and commercial customers a number of filters and resonators are sufficiently generic to be discussed at this conference. All products share common issues of bandwidth, packaging, manufacturing, reliability, and temperature coefficients. Specific examples are given of resonators or filters designed and produced for commercial GPS and other markets.