Paul Bradley

Acoustically coupled thin-film resonators having an electrode with a tapered edge

Acoustically coupled resonators include a first and a second acoustic resonator. Both the first and second acoustic resonators include a first electrode, a layer of piezoelectric material, and a second electrode. The first electrode is adjacent a first surface of the layer of piezoelectric material. The second electrode is adjacent a second surface of the layer of piezoelectric material. At least the second electrode has an edge that is tapered.

A BAW antenna duplexer for the 1900 MHz PCS band

Miniature antenna duplexers are used in modem cellular telephone handsets. We present a new solution utilizing micro-machined, thin Film Bulk Acoustic Resonators (FBAR). A 1900 MHz duplexer with dimensions 5/spl times/8/spl times/2 mm is achieved. The duplexer, a three port device, achieves low loss from transmitter (Tx) to antenna (Ant) ports with a filter at 1880 MHz and from Ant to receiver (Rx) ports with a filter at 1960 MHz. High isolation from Tx to Rx port is achieved by coupling the two filters with a quarter wavelength line. Filter bandwidth is /spl sim/3%. The filters are realized as 21/2 or 31/2 section ladder connected FBARs with the shunt FBARs tuned 3% lower in frequency than the series FBARs to provide a flat pass band. Individual FEAR resonators are free membranes formed of Aluminum Nitride piezoelectric and metal electrode films micro-machined on a silicon substrate. Resonators with electro-acoustic coupling k/sub t//sup 2//spl sim/3 to 5% and Q/spl sim/300 are achieved. Filters fabricated in this manner achieve minimum insertion loss /spl sim/1 dB, out-of-band rejection of /spl sim/20 dB, 60 MHz bandwidth, and an input power capability of 2 Watts. Duplexers are assembled from one each Tx and Rx filter, and a lumped /spl lambda//4 line of two inductors and a capacitor. These duplexers have insertion loss <2 dB in the pass bands, and Tx to Rx isolation >45 dB.

FBAR resonator figure of merit improvements

Free-standing Bulk Acoustic Resonator (FBAR), as one type of bulk acoustic wave (BAW) devices, has extremely high Q to enable excellent filter performance, and has been successfully applied to the wireless communication market. The Bode equation to calculate the unloaded Q is used to map the Avago FBAR product line resonator Rp values. The manufacturing Rp values from old and new generations of FBAR products are collected and compared to demonstrate the importance of the figure of merit (FOM) improvements.

12E-0 2X Size and Cost Reduction of Film Bulk Acoustic Resonator (FBAR) Chips with Tungsten Electrodes for PCS/GPS/800 MHz Multiplexers

It is well known that using tungsten electrodes can boost the effective coupling coefficient, hence bandwidth, of film bulk acoustic resonator (FBAR) filters relative to lower acoustic impedance electrode materials. This effect is strongest for FBARs with much less A1N than would be used to achieve the maximum coupling. In the case of 800 MHz (cellband) duplexers, although the performance has been excellent, the cost of FBAR solutions has been too high due to large resonator and die size (1.8 mm2), even in the PCS/GPS/800 MHz multiplexer applications. A combination of the high effective coupling coefficient of tungsten electrode FBARs, a better duplexer design, tighter design rules, and a higher quality factor (Q) have contributed to a die size reduction to about 1 mm2. Performance is competitive with the best surface acoustic wave (SAW) devices we have seen These parts, when used in a PCS/GPS/800 MHz multiplexer provide a high-performance and cost-competitive RF front end filtering solution for CDMA handsets .

A generic 2.0 × 2.5 mm 2 UMTS FBAR duplexer based on 8-pole near-elliptic filters

UMTS antenna duplexers for handsets require high levels of wide-band rejection while still achieving high isolation, low insertion loss, and good return loss in-band. Several of the UMTS duplexers also require very steep filter skirts due to a very small guardband between transmit (Tx) and receive (Rx) frequency bands (Bands 2 and 8 have ∼1% guardband). Without sizeable inductors to stretch the bandwidth, this demands a higher effective coupling coefficient and a near-ideal placement of a large number of poles and zeroes to achieve steep filter skirts while maintaining acceptable insertion loss with so many resonators. Signifcantly higher quality factor (Q) than previously available is essential to maintain good insertion loss in these designs. Cross-coupling elements shift the frequency of existing ladder filter zeroes to place them near ideal alignment to meet in-band rejection requirements without the need for tight tolerance on components.

An Investigation of Lateral Modes in FBAR Resonators

Using first principles and the constitutive equations for a piezoelectric, we solve the 2-D acoustic wave inside a single, infinite, piezoelectric membrane to study the dispersion of thin film bulk acoustic resonator (FBAR) lateral modes, with and without infinitely thin electrodes. The acoustic eigenfunction is a dual wave, composed of longitudinal and shear components, able to satisfy the 2-D acoustic boundary conditions at the vacuum interfaces. For the single piezoelectric slab, we obtain analytical expressions of the dispersion for frequencies near the longitudinal resonant frequency (Fs) of the resonator. These expressions are more useful for the understanding of dispersion in FBARs and more elegant than numerical methods like finite-element modeling and various matrix methods. We additionally find that the interaction between the resonators electrodes and the acoustic wave modifies the lateral-mode dispersion when compared to the case with no electrodes. When correctly accounting for these interactions, the dispersion zero is placed clearly at Fs, unlike what is calculated from a 2-D model without electrodes where the dispersion zero is placed at Fp. This is important since all experimental evidence of measures FBAR resonators shows that the dispersion zero is at Fs. Furthermore, we introduce an electrical current-flow model for the propagating acoustic wave inside the electroded piezoelectric, and based on this model, we can discuss an electrode-loss mechanism for FBAR lateral modes which depends on dispersion. From our model, it results that lateral modes with real kx have higher electrode dissipation if they are closer to the resonant frequency. This is consistent with the typical behavior of measured FBAR filters where the maximum lateral mode damage on the insertion loss takes place for frequencies immediately below Fs.