Tiberiu Jamneala

7E-2 A De-Coupled Stacked Bulk Acoustic Resonator (DSBAR) Filter With 2 dB Bandwidth > 4%

Coupled resonator filters extend the use of classical FBAR/BAW filters by enabling them to convert single-ended signals into differential signals while using a much smaller wafer real estate. In lieu of the traditional multi-layer de-coupling structure we introduce a novel technique in which only a single thin polymer layer with appropriate acoustic impedance is used. In the de-coupled stacked bulk acoustic resonator design (DSBAR) we demonstrate a 0.4 x 0.5 mm single-ended filter operating at 2.45 GHz with a bandwidth at the 2 dB points of greater than 4%, in-band return loss of less than -10 dB and excellent out-of-band rejection. Cross-wafer variation and the temperature response of these filters are shown.

Improved coupled resonator filter performance using a carbon-doped oxide de-coupling layer

We describe a newly developed de-coupling material SiOCH for coupled resonator filter applications. The SiOCH films belong to a general class of low-k dielectrics often referred to as carbon-doped oxides (CDO). In this work, CDO replaces SiLK, significantly improving the performance of the resulting filters. In contrast to the spin-on and curing process used to deposit SiLK, the CDO films are deposited using plasma enhanced chemical vapor deposition. The resulting films possess a low acoustic impedance that can be varied over a range greater than 2∶1 through a choice of deposition conditions. The new filters possess several key advantages over the SiLK-based devices reported previously, including decreased filter insertion loss, a passband free of spurious notches, and a dramatically lower temperature coefficient of frequency.

GPS and WiFi single ended to differential CRF filters using SiOCH as a de-coupling layer

Two filter applications, GPS and Wi-Fi, using bulk wave coupled resonator filters (BWCRF) are discussed. The device consists of two FBAR resonators stacked one on top of the other and separated by a thin de-coupling layer. We refer to this device as a De-Coupled Stacked Bulk Acoustic Resonator or DSBAR. These devices can be used as stand-alone filters or together with similar devices to create very small filters capable of single-ended to single-ended or single-ended to differential conversion. Also, due to the unique arrangement of the two FBAR one on top of the other, an impedance transformer can be made. Lastly, these devices have a very short “ring-down” time compared to “classic” FBAR filters, important for OFDM applications.

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.