John Berge

Tunable Solidly Mounted Thin Film Bulk Acoustic Resonators Based on Ba

Electrically tunable solidly mounted thin film bulk acoustic resonators based on BaxSr1-xTiO3 films are reported for the first time. The films are acoustically isolated from the silicon substrate by a Bragg reflector stack. Applying DC bias induces piezoelectric effect and an acoustic resonance at approximately 4 GHz. Under 10 V applied DC bias the resonance frequency of the resonators based on Ba0.25Sr0.75TiO3 films is tuned 1.2% to lower frequencies. The Q-factor of these resonators is approximately 120, and the electromechanical coupling coefficient is 0.5%. The resonant frequency of the BaTiO3 based resonators shifts upwards 1.3% under 10 V DC bias, and the -factor is approximately 30, with an electromechanical coupling coefficient of 6.2%.

_{x}{{\hbox{Sr}}_{1-x}}{\hbox{TiO}}_{3}

Modeling tunable bulk acoustic resonators based on induced piezoelectric effect in BaTiO[sub 3] and Ba[sub 0.25]Sr[sub 0.75]TiO[sub 3] films

Films

Electrically tunable solidly mounted thin film bulk acoustic resonators based on Ba0.25Sr0.75TiO3 and BaTiO3 films are fabricated and measured in wide dc bias voltage and temperature ranges. At room temperature, the tunability of the series and parallel resonances for the Ba0.25Sr0.75TiO3 resonator are 1.7% and 0.3%, respectively, for 15V bias voltage applied over the 350nm thick ferroelectric film (43V∕μm). The electromechanical coupling coefficient increases with dc bias up to 3.7% at 15V. The measured tunability and coupling coefficient are limited partly by the quality of the used films. Potentially, they may be substantially increased for high quality films allowing application of higher dc fields. The resonator quality factor is approximately 100. The measured resonator response is in good agreement with available models based on the electromechanical equations describing the ferroelectric film under applied dc and ac electric fields. Measurements of the resonance frequencies of the Ba0.25Sr0.75TiO3...

Modeling tunable bulk acoustic resonators based on induced piezoelectric effect in BaTiO[sub 3] and Ba[sub 0.25]Sr[sub 0.75]TiO[sub 3] films

Tunable 5.2 GHz bulk acoustic wave resonators utilizing Ba(x)Sr(1-x)TiO(3) ferroelectric films with similar intrinsic properties but different interface roughness are fabricated and characterized. Increase in roughness from 3.2 nm up to 6.9 nm results in reduction in Q-factor from 350 down to 150 due to extrinsic acoustic losses caused by wave scattering at reflections from rough interfaces and other mechanisms associated with roughness. The increased roughness is a result of distortion of Pt bottom electrode caused by formation of heterogeneous enclosures of TiO(2-x) in the Pt layer

Field and temperature dependent parameters of the dc field induced resonances in BaxSr1-xTiO3-based tunable thin film bulk acoustic resonators

A switchable and tunable bulk acoustic wave resonator based on a paraelectric phase Ba_0.25Sr_0.75TiO₃ thin film and an all-dielectric HfO₂/SiO₂ Bragg reflector is presented. The achieved tuning range (3.8%) and effective electromechanical coupling coefficient (7.1%) are the highest reported for solidly mounted tunable bulk acoustic wave resonators. The non-conductive Bragg reflector stack provides excellent integration possibilities.

Effect of interface roughness on acoustic loss in tunable thin film bulk acoustic wave resonators

A model and a robust extraction procedure for tunable thin-film bulk acoustic resonators (TFBARs) are proposed. The TFBARs are based on induced piezoelectricity in Ba<inf>x</inf>Sr<inf>1−x</inf>TiO<inf>3</inf> films. Their tunable characteristics as represented by the extracted model parameters are interpreted and discussed.

Tunable bulk acoustic wave resonators based on Ba 0.25 Sr 0.75 TiO 3 thin films and a HfO 2 /SiO 2 bragg reflector

A simple method for suppression of the resonant absorption of the microwave power in parallel-plate ferroelectric varactors is proposed and implement

Parameter extraction for tunable TFBARs based on Ba x Sr 1−x TiO 3

Parallel-plate capacitors based on ferroelectric thin films are considered as high density capacitors and varactors. Due to the small thickness of the ferroelectric films, typically less than 1.0 mu m, high electric fields are generated even at relatively low voltages inducing piezoelectric effect associated with electrostriction. This induced piezoelectric effect has negative impact on ferroelectric capacitors since it causes extra loss (electroacoustic transformation of microwave energy). In this work the use of Bragg reflectors between the substrate and ferroelectric film is proposed as a possible way of suppression of the enhanced losses associated with the piezoelectric activity of the ferroelectric film.

Electromechanical Modelling and Reduction of the Electroacoustic Losses in Parallel-Plate Ferroelectric Varactors

A reliable model of a tuneable bulk acoustic resonator based on BSTO film with induced piezoelectric effect is proposed. The estimation of resonance and antiresonance frequency shift of bulk acoustic resonator as a function of the applied voltage has been carried out. The results of the input impedance modelling of the BSTO bulk acoustic resonator are in agreement with the experimental data.

The effect of Bragg reflectors on the electromechanical performance of parallel-plate ferroelectric capacitors

Thin film Au/Pt/Ba0.25Sr0.75TiO3/Au/Ti varactors were fabricated on fused silica substrates using pulsed laser deposition of the ferroelectric films. Deposition temperature was optimized to improve varactor tuneability and loss tangent. The varactors were characterized in the frequency range 1-25 GHz at different dc bias voltage. The resonant absorption of the microwave power observed below 12 GHz, under dc field, is due to electrostriction and field induced piezoelectric effects. Above 12 GHz varactors on Au/Ti bottom electrode reveal loss tangent less than 0.02 and tuneability up to 35%. These parameters indicate the potential of Ba0.25Sr0.75TiO3 varactors for applications in tunable microwave devices. The estimated figure of merit of the phase shifters utilizing these varactors is more than 200 degree/dB at frequencies up to 20 GHz. A resonator may be tuned at more than 10 unloaded bandwidths at frequencies up to 25 GHz