scholarly journals Fabrication of AlGaN High Frequency Bulk Acoustic Resonator by Reactive RF Magnetron Co-sputtering System

Materials ◽  
2021 ◽  
Vol 14 (23) ◽  
pp. 7377
Author(s):  
Yu-Chen Chang ◽  
Ying-Chung Chen ◽  
Chien-Chuan Cheng
Keyword(s):  
Aluminum Gallium Nitride ◽  
High Frequency ◽  
Electromechanical Coupling ◽  
Acoustic Resonator ◽  
Bragg Reflector ◽  
Center Frequency ◽  
Electromechanical Coupling Coefficient ◽  
Axis Orientation ◽  
Sputtering Power ◽  
Sputtering System

In this study, aluminum gallium nitride (AlGaN) thin films are used as the piezoelectric layers to fabricate solidly mounted resonators (SMR) for high frequency acoustic wave devices. AlGaN film is deposited on a Bragg reflector, composed of three pairs of Mo and SiO2 films, through a reactive radio frequency (RF) magnetron co-sputtering system at room temperature. The optimized deposition parameters of AlGaN film have a sputtering power of 175 W for Al target, sputtering power of 25 W for GaN target, N2 flow ratio (N2/Ar + N2) of 60%, and sputtering pressure of 10 mTorr. The obtained AlGaN film has a smooth surface, uniform crystal grains, and strong c-axis orientation. The contents of Al and Ga in the AlGaN film, analyzed by energy dispersive X-ray spectroscopy (EDS) are 81% and 19%, respectively. Finally, the frequency response S11 of the obtained SMR device shows that the center frequency is 3.60 GHz, the return loss is about −8.62 dB, the electromechanical coupling coefficient (kt2) is 2.33%, the quality factor (Q) value is 96.93 and the figure of merit (FoM) value is 2.26.

scholarly journals Fabrication and Characterization of High-Frequency Ultrasound Transducers Based on Lead-Free BNT-BT Tape-Casting Thick Film

Sensors ◽  
2018 ◽  
Vol 18 (9) ◽  
pp. 3166 ◽  
Author(s):  
Junshan Zhang ◽  
Wei Ren ◽  
Yantao Liu ◽  
Xiaoqing Wu ◽  
Chunlong Fei ◽  
...  
Keyword(s):  
Thick Film ◽  
High Frequency ◽  
Electromechanical Coupling ◽  
Ultrasonic Transducer ◽  
Tape Casting ◽  
Lead Free ◽  
Center Frequency ◽  
Electromechanical Coupling Coefficient ◽  
High Frequency Ultrasound ◽  
Casting Method

A lead-free 0.94(Na0.5Bi0.5) TiO3-0.06 BaTiO3 (BNT-BT) thick film, with a thickness of 60 μm, has been fabricated using a tape-casting method. The longitudinal piezoelectric constant, clamped dielectric permittivity constant, remnant polarization and coercive field of the BNT-BT thick film were measured to be 150 pC/N, 1928, 13.6 μC/cm2, and 33.6 kV/cm, respectively. The electromechanical coupling coefficient kt was calculated to be 0.55 according to the measured electrical impedance spectrum. A high-frequency plane ultrasound transducer was successfully fabricated using a BNT-BT thick film. The performance of the transducer was characterized and evaluated by the pulse-echo testing and wire phantom imaging operations. The BNT-BT thick film transducer exhibits a center frequency of 34 MHz, a −6 dB bandwidth of 26%, an axial resolution of 77 μm and a lateral resolution of 484 μm. The results suggest that lead-free BNT-BT thick film fabricated by tape-casting method is a promising lead-free candidate for high-frequency ultrasonic transducer applications.

scholarly journals Fabrication of a 3.5-GHz Solidly Mounted Resonator by Using an AlScN Piezoelectric Thin Film

Coatings ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 1151
Author(s):  
Chan-Yu Chung ◽  
Ying-Chung Chen ◽  
Yu-Cheng Chen ◽  
Kuo-Sheng Kao ◽  
Yu-Chen Chang
Keyword(s):  
Thin Film ◽  
Resonance Frequency ◽  
Coupling Coefficient ◽  
Electromechanical Coupling ◽  
Bragg Reflector ◽  
Electromechanical Coupling Coefficient ◽  
Axis Orientation ◽  
X Ray ◽  
Aln Film ◽  
Piezoelectric Thin Film

In this study, a 3.5-GHz solidly mounted resonator (SMR) was developed by doping scandium in aluminum nitride to form AlScN as the piezoelectric thin film. Molybdenum (Mo) of 449 nm thickness and silicon dioxide (SiO2) of 371 nm thickness were used as the high and low acoustic impedance films, respectively, which were alternately stacked on a silicon substrate to form a Bragg reflector. Then, an alloy target with atomic ratio of 15% Sc was adopted to deposit the piezoelectric AlScN thin film on the Bragg reflector, using a radio frequency magnetron sputtering system. The characteristics of the c-axis orientation of the AlScN thin films were optimized by adjusting sputtering parameters as sputtering power of 250 W, sputtering pressure of 20 mTorr, nitrogen gas ratio of 20%, and substrate temperature of 300 °C. Finally, a metal top electrode was coated to form a resonator. The X-ray diffraction (XRD) analysis showed that the diffraction peak angles of the AlScN film shifted towards lower angles in each crystal phase, compared to those of AlN film. The energy dispersive X-ray spectrometer (EDX) analysis showed that the percentage of scandium atom in the film is about 4.5%, regardless of the sputtering conditions. The fabricated resonator exhibited a resonance frequency of 3.46 GHz, which was a small deviation from the preset resonance frequency of 3.5 GHz. The insertion loss of −10.92 dB and the electromechanical coupling coefficient of 2.24% were obtained. As compared to the AlN-based device, the AlScN-based resonator exhibited an improved electromechanical coupling coefficient by about two times.

scholarly journals Effects of Thermal Annealing on the Characteristics of High Frequency FBAR Devices

Coatings ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 397
Author(s):  
Yu-Chen Chang ◽  
Ying-Chung Chen ◽  
Bing-Rui Li ◽  
Wei-Che Shih ◽  
Jyun-Min Lin ◽  
...  
Keyword(s):  
Thin Film ◽  
Thin Films ◽  
Thermal Annealing ◽  
Electromechanical Coupling ◽  
Zno Thin Films ◽  
Electromechanical Coupling Coefficient ◽  
Back Side ◽  
Zno Thin Film ◽  
Frequency Responses ◽  
Sputtering System

In this study, piezoelectric zinc oxide (ZnO) thin film was deposited on the Pt/Ti/SiNx/Si substrate to construct the FBAR device. The Pt/Ti multilayers were deposited on SiNx/Si as the bottom electrode and the Al thin film was deposited on the ZnO piezoelectric layer as the top electrode by a DC sputtering system. The ZnO thin film was deposited onto the Pt thin film by a radio frequency (RF) magnetron sputtering system. The cavity on back side for acoustic reflection of the FBAR device was achieved by KOH solution and reactive ion etching (RIE) processes. The crystalline structures and surface morphologies of the films were analyzed by X-ray diffraction (XRD) and field emission scanning electron microscope (FE-SEM). The optimized as-deposited ZnO thin films with preferred (002)-orientation were obtained under the sputtering power of 80 W and sputtering pressure of 20 mTorr. The crystalline characteristics of ZnO thin films and the frequency responses of the FBAR devices can be improved by using the rapid thermal annealing (RTA) process. The optimized annealing temperature and annealing time are 400 °C and 10 min, respectively. Finally, the FBAR devices with structure of Al/ZnO/Pt/Ti/SiNx/Si were fabricated. The frequency responses showed that the return loss of the FBAR device with RTA annealing was improved from −24.07 to −34.66 dB, and the electromechanical coupling coefficient (kt2) was improved from 1.73% to 3.02% with the resonance frequency of around 3.4 GHz.

Surface acoustic wave resonator from thick MOVPE-grown layers of GaN(0001) on sapphire

2002 ◽  
Vol 743 ◽  
Author(s):  
Sverre V. Pettersen ◽  
Thomas Tybell ◽  
Arne Rønnekleiv ◽  
Stig Rooth ◽  
Veit Schwegler ◽  
...  
Keyword(s):  
Acoustic Wave ◽  
Surface Acoustic Wave ◽  
Electromechanical Coupling ◽  
Film Surface ◽  
Center Frequency ◽  
Electromechanical Coupling Coefficient ◽  
Nitride Film ◽  
Wave Resonator ◽  
Lift Off ◽  
Definition Of

ABSTRACTWe report on fabrication and measurement of a surface acoustic wave resonator prepared on ∼10m thick GaN(0001) films. The films were grown by metal-organic vapor phase epitaxy on a c-plane sapphire substrate. The surface morphology of the films were examined with scanning electron and atomic force microscopy. A metallic bilayer of Al/Ti was subsequently evaporated on the nitride film surface. Definition of the resonator interdigital transducers, designed for a wavelength of λ=7.76m, was accomplished with standard UV lithography and lift-off. S-parameter measurements showed a resonator center frequency f0=495MHz at room temperature, corresponding to a surface acoustic wave velocity of 3844m/s. The insertion loss at center frequency was measured at 8.2dB, and the loaded Q-factor was estimated at 2200. Finally, measurements of the resonator center frequency for temperatures in the range 25–155°C showed a temperature coefficient of -18ppm/°C. The intrinsic GaN SAW velocity and electromechanical coupling coefficient were estimated at νSAW=383 1m/s and K2=1.8±0.4·10−3.

Improved Frequency Responses of Saw Filters with Interdigitated Interdigital Transducers on ZnO/Diamond/Si Layered Structure

2007 ◽  
Vol 23 (3) ◽  
pp. 253-260 ◽  
Author(s):  
C.-M. Lin ◽  
T.-T. Wu ◽  
Y.-Y. Chen ◽  
T.-T. Chou
Keyword(s):  
Layered Structure ◽  
Electromechanical Coupling ◽  
Effective Permittivity ◽  
Local Maximum ◽  
Side Lobe ◽  
Center Frequency ◽  
Electromechanical Coupling Coefficient ◽  
Side Lobe Level ◽  
Pass Band ◽  
Frequency Responses

AbstractThere are many investigations on surface acoustic wave (SAW) filters with interdigitated interdigital transducers (IIDT) in the last two decades; however, the same is not true for the case of IIDT SAW filters fabricated on layered piezoelectric substrates. Therefore, the aim of this study is to explore the characteristics of the IIDT structures on layered piezoelectric media and further, to improve the frequency response of layered IIDT SAW filters with the unique dispersive properties of a layered piezoelectric structure. A method based on the effective permittivity approach, the coupling of modes (COM) model, and the H-matrix is utilized to analyze the characteristics of IIDT on the ZnO/Diamond/Si layered structure. In this study, it is shown that by optimizing the ratio of input to output IDT pairs, the side-lobe level of frequency responses on the ZnO/Diamond/Si layered structure could be suppressed, similar to that on the half-space substrate. In addition, it is also proved that the notched pass-band could be flattened out by designing the center frequency on the local maximum of the electromechanical coupling coefficient dispersion curve.

Fabrication of a 40 MHz Single Element Ultrasonic Transducer Using a PMN-PT Single Crystal

2006 ◽  
Vol 321-323 ◽  
pp. 978-983 ◽  
Author(s):  
Dong Guk Paeng ◽  
Hyung Ham Kim ◽  
Sang Goo Lee ◽  
Sung Min Rhim ◽  
Min Joo Choi
Keyword(s):  
Single Crystal ◽  
High Frequency ◽  
Electromechanical Coupling ◽  
Ultrasonic Transducer ◽  
Electromechanical Coupling Coefficient ◽  
Single Element ◽  
Transducer Arrays ◽  
High Dielectric ◽  
Pulse Echo ◽  
Piezoelectric Constants

PMN-PT, a piezoelectric single crystal, has been known to be a better material for transducer arrays due to its high electromechanical coupling coefficient (k33) and high dielectric and piezoelectric constants. It may also be good even for high frequency single element transducers using relatively high kt and low attenuation and velocity dispersion. However, it’s challenging to fabricate high frequency transducers using PMN-PT since it is easily breakable and requires small area and thickness of the transducer. A KLM model was used to simulate a 40 MHz single element transducer including 2 matching layers and a conductive backing. The simulation showed that the PMN-PT transducer turned out to be better in sensitivity and bandwidth than a 40 MHz LiNbO3 transducer. A 40 MHz PMN-29%PT transducer was fabricated and the pulse echo signals were obtained and analyzed. Its sensitivity was found to be –48 dB and –6dB bandwidth was about 48 %.

scholarly journals Influence of Etching Trench on Keff2 of Film Bulk Acoustic Resonator

Micromachines ◽  
2022 ◽  
Vol 13 (1) ◽  
pp. 102
Author(s):  
Chao Gao ◽  
Yang Zou ◽  
Jie Zhou ◽  
Yan Liu ◽  
Wenjuan Liu ◽  
...  
Keyword(s):  
Electromechanical Coupling ◽  
Great Influence ◽  
Acoustic Resonator ◽  
Superior Performance ◽  
Electromechanical Coupling Coefficient ◽  
Rf Filters ◽  
Acoustic Resonators ◽  
Rf Communication ◽  
Film Bulk Acoustic Resonators ◽  
Film Bulk

As radio-frequency (RF) communication becomes more ubiquitous globally, film bulk acoustic resonators (FBAR) have attracted great attention for their superior performance. One of the key parameters of an FBAR, the effective electromechanical coupling coefficient (Keff2), has a great influence on the bandwidth of RF filters. In this work, we propose a feasible method to tune the Keff2 of the FBAR by etching the piezoelectric material to form a trench around the active area of the FBAR. The influence of the position of the etching trench on the Keff2 of the FBAR was investigated by 3D finite element modeling and experimental fabricating. Meanwhile, a theoretical electrical model was presented to test and verify the simulated and measured results. The Keff2 of the FBAR tended to be reduced when the distance between the edge of the top electrode and the edge of the trench was increased, but the Q value of the FBAR was not degraded. This work provides a new possibility for tuning the Keff2 of resonators to meet the requirements of different filter bandwidths.

Synthetic Properties of the c-Axis Tilted AlN Thin Films

2010 ◽  
Vol 654-656 ◽  
pp. 1780-1783
Author(s):  
Chung Jen Chung ◽  
Ching Liang Wei ◽  
Po Tsung Hsieh ◽  
Chao Yu Huang ◽  
Jen Fin Lin ◽  
...  
Keyword(s):  
Thin Film ◽  
Thin Films ◽  
High Frequency ◽  
Electromechanical Coupling ◽  
Piezoelectric Materials ◽  
Rf Sputtering ◽  
Electromechanical Coupling Coefficient ◽  
Crystalline Orientation ◽  
Nano Indentation ◽  
Bonding Condition

Aluminum nitride (AlN) is one of the most popular piezoelectric materials for high frequency resonators, filters and sensors. The piezoelectric property, i.e. electromechanical coupling coefficient, of AlN thin film is highly related to its crystalline orientation. AlN thin films with various c-axis-tilted angles can be fabricated by the RF sputtering technique. The crystallization and grain growth orientations of AlN thin film are examined by XRD, SEM, and TEM, while the bonding condition and nano-mechanical properties are investigated by a raman system and a nano-indentation technique.

Selective Band Gap to Suppress the Spurious Acoustic Mode in Film Bulk Acoustic Resonator Structures

2018 ◽  
Vol 140 (3) ◽  
Author(s):  
Rafik Serhane ◽  
Fayçal Hadj-Larbi ◽  
Abdelkader Hassein-Bey ◽  
Abdelkrim Khelif
Keyword(s):  
Band Gap ◽  
Electromechanical Coupling ◽  
Lamb Waves ◽  
Phononic Crystal ◽  
Longitudinal Mode ◽  
Acoustic Resonator ◽  
Electromechanical Coupling Coefficient ◽  
Spurious Mode ◽  
Film Bulk Acoustic Resonator ◽  
Film Bulk

In this work, we investigate numerically the propagation of Lamb waves in a film bulk acoustic resonator (FBAR) structure formed by piezoelectric ZnO layer sandwiched between two Mo electrodes coupled with Bragg reflectors; the system is thus considered as a phononic-crystal (PnC) plate. The aim is to suppress the first-order symmetric Lamb wave mode considered as a spurious mode caused by the establishment of a lateral standing wave due to the reflection at the embedded lateral extremities of the structure; this spurious mode is superposing to the main longitudinal mode resonance of the FBAR. The finite element study, using harmonic and eigen-frequency analyses, is performed on the section of FBAR structure coupled with the PnC. In the presence of PnC, the simulation results show the evidence of a selective band gap where the parasitic mode is prohibited. The quality factor of the FBAR is enhanced by the introduction of the PnC. Indeed, the resonance and antiresonance frequencies passed from 1000 and 980 (without PnC) to 2350 and 1230 (with PnC), respectively. This is accompanied by a decrease in the electromechanical coupling coefficient from 10.60% to 6.61%.

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