This paper describes the design, fabrication, and measurement of an electrically tunable film bulk acoustic resonator (FBAR) that is formed by integrating FBAR with an electrostatic microelectromechanical systems actuator. Around 1.47% tuning of the series resonant frequency ( Deltaf cong 22.5 MHz) at 1.5 GHz is experimentally obtained with an electrostatic actuation voltage of 7 V. This is the highest frequency tuning reported for FBAR operating at above 1 GHz without any extra power consumption. Two integration approaches of FBAR and air-gap capacitor are presented and compared, in terms of fabrication process and Q factor. The approach that minimizes any possible energy loss in the acoustic wave propagation path shows a quality factor (160-304) significantly higher than the one having a capacitor right on top surface of the FBAR's piezoelectric film. Furthermore, we have characterized the electrical tuning of FBAR through piezoelectric stiffening due to an applied DC electric field and report a linear frequency shift of about -8 ppm/V at 3.4 GHz.

Electrical Frequency Tuning of Film Bulk Acoustic Resonator

In accordance with an embodiment, an RF system includes a transmit path having a transmit RF filter and an adjustable transmit phase shifter/matching network coupled between the transmit RF filter and a transmit antenna port, where the adjustable transmit phase shifter/matching network is configured to transform an impedance of the transmit RF filter at a receive frequency from a first lower impedance to a first higher impedance at the transmit antenna port; and a receive path having a receive RF filter and an adjustable receive phase shifter/matching network coupled between the receive RF filter and a receive antenna port, where the adjustable receive phase shifter/matching network is configured to transform an impedance of the receive RF filter at a transmit frequency from a second lower impedance to a second higher impedance at the receive antenna port.

System and method for a radio frequency filter

Lithium niobate has been extensively used in the Surface Acoustic Wave (SAW) industry for its excellent piezoelectric properties. In the last twelve years, the interest has been raised towards making this material available in the thin film form for SAW or Bulk Acoustic Wave (BAW) applications, and even for Lamb wave devices. This paper reviews both deposition or thin film transfer techniques to obtain lithium niobate thin films. It also gives a brief overview of the applications of these thin films. Finally, we open new perspectives for this technology with the emerging field of tunable acoustic filters, which need extremely large piezoelectric properties to demonstrate satisfying performance.

Acoustic filters based on thin single crystal LiNbO 3 films: Status and prospects

Coupled resonator filters (CRFs) are the new generation of BAW filters recently designed for the front-end modules of mobile transmission systems. Looking for designers' requirements, CRF devices have been characterized and modeled. The model based on equivalent circuits relies on material constants such as stiffness and electro-coupling coefficients, and works only for linear-mode propagation. Because of their positions between antennas and power amplifiers, they often work under high RF power, inducing nonlinear response in the AlN piezoelectric layer. In this work, we analyze for the first time the nonlinear behavior of AlN material particularly for coupled BAW resonators. To characterize the nonlinear effects in CRFs, we measure the 1-dB gain compression point (P1dB) and the intercept point (IP3). Then, we develop a nonlinear model of CRFs using harmonic balance (HB) simulation in commercially available software. The HB environment allows fitting simulations to measurements in terms of P1dB and IP3. We find that a high RF power induces nonlinear changes in the material constants' real parts: elastic stiffness c33 (4.9%), piezoelectric e33 (17.4%), and permittivity e33 (5.2%). These nonlinear variations of material constants describe the nonlinear behavior of CRF devices using the same deposit process for AlN material.

Acoustic, piezoelectric, and dielectric nonlinearities of AlN in coupled resonator filters for high RF power levels

This article presented the design of two band reject filters in the BAW technology. The two designs show different benefits. The ladder T topology has a better rejection bandwidth than the ladder topology because the bandwidth is controlled by resonance and antiresonance frequencies, which are selected by the loading layer. Moreover, the bandwidth is adjustable by the design. This setup presents a steeper rejection slope. The insertion loss can be reduced by increasing the bottom electrode's thickness. However, the fabrication process and the control of resonance frequency are more difficult since antiresonance frequencies of series resonators depend on the thickness of the loading layers.

Stopband filters built in the BAW technology [Application Notes]

We present a tunable bandpass BAW-filter based in a first step on a hybrid integration concept to demonstrate the validity of our architecture and to evaluate the potential of such filters. The filter consists of two cascaded lattices incorporating four BAW resonators, coupled with high-Q inductors and wide tuning range active varactors. The simulated results show that it is possible to compensate ±1% deviation on the filter center frequency. The prototype is currently in manufacturing and the experimental results will be available for the conference.

A Tunable Bandpass BAW-Filter Architecture and Its Application to WCDMA Filter

Design of Bulk Acoustic Wave RF resonators and filters based on advanced Bragg reflector

A bulk acoustic wave filter, which can be used in EDGE transmitter, is presented in this paper. It attenuates power amplifier harmonic frequencies and out-of-band noise generated by sigma-delta modulator needed in linear architecture. This filter achieves 2.4 dB insertion loss including matching network to 50 Omega and more than 15 dB of return loss. Power handling capability and linearity performance of bulk acoustic wave devices are detailed and satisfy to power application requirements. Antenna mismatch effect has been evaluated using an active load-pull bench. This filter is connected in series to power amplifier to form a prototype of power amplifier module for GSM/EDGE standard in the DCS frequency band. The power amplifier is realized using STMicroelectronics 0.25 mum BiCMOS technology

Linear Transmitter Architecture Using BAW Filter

This paper presents a bandpass filter for DCS/EDGE transmitter using bulk acoustic wave technology. It is designed to filter PA's harmonic frequencies and out-of-band noise generated by sigma-delta modulator in DCS/EDGE architecture. The filter is based on solidly mounted resonators electrically coupled in a ladder type topology; it achieves 2.4 dB insertion loss including matching network to 50 Omega, more than 15 dB of return loss over the 75MHz DCS band. Linearity and power handling capability characterizations are detailed. This filter is combined with a power amplifier using STMicroelectronics' 0.25 mum BiCMOS technology, it is a first step to develop a power amplifier module for GSM/EDGE standard in the DCS frequency band

F. Dumont

Papers

A Tunable Bandpass BAW-Filter Architecture and Its Application to WCDMA Filter

Design of Bulk Acoustic Wave RF resonators and filters based on advanced Bragg reflector

Linear Transmitter Architecture Using BAW Filter

Efficient BAW Filtering Solution for EDGE Transmitter