Nonreciprocity of Gigahertz Surface Acoustic Wave Based on Mode Conversion in an Inclined Phononic Crystal Heterojunction (original) (raw)

Non-reciprocal SAW devices for RF applications

2000 IEEE Ultrasonics Symposium. Proceedings. An International Symposium (Cat. No.00CH37121)

The combination of the electronic properties of a semiconductor heterostructure and the acoustic properties of strongly piezoelectric crystals yields promising hybrids for potential acousto electric applications. The nonlinear interaction between an intense SAW on a LiNbO 3 substrate and the free carriers in a semiconductor quantum well can be exploited to result in strongly non-reciprocal devices for RF applications.

A Novel Saw Device in CMOS: Design, Modeling, and Fabrication

IEEE Sensors Journal, 2000

The design, finite element modeling, fabrication, and characterization of a novel surface acoustic wave (SAW) delay line for bio/chemical and telecommunication applications in CMOS technology are introduced. A full modeling was carried out. The devices are designed in a standard semiconductor foundry 1.5-µm two-metal two-poly process. A unique maskless postprocessing sequence is designed and completed. The three postprocessing steps are fully compatible with any standard integrated circuit technology such as CMOS. This allows any signal control/processing circuitry to be easily integrated on the same chip. ZnO is used as the piezoelectric material for SAW generation. A thorough characterization and patterning optimization of the sputtered ZnO was carried out. The major novelties that are introduced in the SAW delay line features are the embedded heater elements for temperature control, compensation, and acoustic absorbers that are designed to eliminate edge reflections and minimize triple transit interference that is amplified by edge reflections. Both of these attributes are designed by using CMOS materials without disturbing SAW performance.

Complete bandgap SAW phononic resonant topologies

2014 IEEE International Ultrasonics Symposium, 2014

Resonant surface acoustic wave (SAW) structures employing 2D phononic gratings with hexagonal symmetry are micro-fabricated and tested in a proof of principle study. The proposed structures have the advantage of being compatible with the planar SAW technology, while ensuring operation within the complete frequency bandgap of the phononic grating. More specifically, 2D phononic gratings exhibiting a complete frequency bandgap are employed in the design of three distinct types of resonant test structures. The proposed test structures are fabricated on to a 128° YX LiNbO 3 substrate by means of low resolution photolithography. Frequency response measurements of the SAW phononic resonators confirmed operation within the complete frequency bandgap of each grating structure. The experimental results obtained demonstrate that surface phononic gratings can be successfully used in the design of SAW resonators. The proposed research paves the way for subsequent implementation of the phononic bandgap technology in high performance micro-acoustic RF components.

From phononic crystals to SAW devices

We investigate the possibility of obtaining phononic crystals using materials commonly employed in device microfabrication. This study gathers the latest research on micro-phonon crystals, design techniques, material considerations, microfabrication processes, characterization methods and reported devices. Particularly are highlighted the advantages of these crystals in SAW device structures and theirs micro fabrication processes. We focus our attention to theoretical method of waves propagations in two-dimensional phononic crystals made of cylindrical holes drilled in an active piezoelectric matrix. First numerical results for the simulation of propagation of acoustic waves in a SAW device with phononic crystals are obtained by our work group. The present work provides evidences that these phononic crystals can be using in microdevices and increases the performances of SAW devices.

Complete bandgap SAW phononic resonators

2014 European Frequency and Time Forum (EFTF), 2014

2D composite grating building blocks with hexagonal symmetry are proposed as efficient reflectors and transducers in the design of surface acoustic wave (SAW) resonators. Design parameters ensuring complete bandgap characteristics are deduced by means of finite element analysis (FEA). SAW resonators employing phononic building blocks with complete bandgaps are designed, fabricated and tested. Further, the influence of the phononic grating over the spurious responses and the busbar quality are experimentally tested. All test structures are fabricated on 128 Y-X LiNbO 3 using low resolution optical lithography and standard metal deposition and etching routines.

SAW Devices –A Comprehensive Review

Surface Acoustic Waves (SAWs) are elastic waves travelling along the surface of solid piezoelectric materials with amplitude that decays exponentially with depth. Using an Interdigital Transducer (IDT), these waves can be demonstrated and reproduced in the laboratory in devices called SAW devices. Such devices find many applications as delay lines, filters, resonators and sensors. The present paper provides a snapshot review and description of the functioning, operation and latest technical advancements seen in these devices over the period from 2003-2012. For improvement in design, development, fabrication and characterization of these devices, computational modeling plays a prominent and pivotal role. Employing unique custom made software algorithms based on well established principles of physics, these devices are accurately modeled and simulated and a short review and description of the strategy adopted for the same is also provided.

Multilayered Structure as a Novel Material for Surface Acoustic Wave Devices: Physical Insight

InTech eBooks, 2011

Since 70-ies, when the first delay lines and filters employing surface acoustic waves (SAW) were designed and fabricated, the use of SAW devices in special and commercial applications has expanded rapidly and the range of their working parameters was extended significantly (Hashimoto, 2000; Ruppel, 2001, 2002). In the last decade, their wide application in communication systems, cellular phones and base stations, wireless temperature and gas sensors has placed new requirements to SAW devices, such as very high operating frequencies (up to 10 GHz), low insertion loss, about 1 dB, high power durability, stable parameters at high temperatures etc. The main element of a SAW device is a piezoelectric substrate with an interdigital transducer (IDT) used for generation and detection of SAW in the substrate. The number of single crystals utilized as substrates in SAW devices did not increase substantially since 70ies because a new material must satisfy the list of strict requirements to be applied in commercial SAW devices: sufficiently strong piezoelectric effect, low or moderate variation of SAW velocity with temperature, low cost of as-grown large size crystals for fabrication of 4-inch wafers, long-term power durability, well developed and non-expensive fabrication process for SAW devices etc. Today only few single crystals are utilized as substrates in SAW devices: lithium niobate, LiNbO 3 (LN), lithium tantalate, LiTaO 3 (LT), quartz, SiO 2 , lithium tetraborate, Li 2 B 4 O 7 (LBO), langasite, La 3 Ga 5 SiO 14 (LGS) and some crystals of LGS group (LGT, LGN etc.) with similar properties. The SAW velocities in these single crystals do not exceed 4000 m/s, which limit the highest operating frequencies of SAW devices by 2.5-3 GHz because of limitations imposed by the line-resolution technology of IDT fabrication. The minimum achievable insertion loss and maximum bandwidth of SAW devices depend on the electromechanical coupling coefficient, which can be evaluated for SAW as k 2 ≈2ΔV/V, where ΔV is the difference between SAW velocities on free and electrically shorted surfaces. The largest values of k 2 can be obtained in some orientations of LN and LT. Ferroelectric properties of these materials are responsible for a strong piezoelectric effect. As a result, k 2 reaches 5.7% in LN and 1.2% in LT, for SAW. For leaky SAW (LSAW) propagating in rotated Y-cuts of both crystals, the coupling is higher and can exceed 20% for LN and 5% for LT. However, LSAW attenuates because of its leakage into the bulk waves when it propagates along the crystal surface. As a www.intechopen.com Acoustic Waves-From Microdevices to Helioseismology 422 result, insertion loss of a SAW device increases. Attenuation coefficient depends on a crystal cut and IDT geometry. For example, in 36º to 48º rotated YX cuts of LT and in 41º to 76º YX rotated YX cuts of LN, high electromechanical coupling of LSAW can be combined with low attenuation coefficient via simultaneous optimization of orientation and electrode structure (Naumenko & Abbott, US patents, 2003, 2004). When these substrates are utilized in radiofrequency (RF) SAW filters with resonator-type structures, low insertion loss of 1dB or even less can be obtained. Today such low loss filters are widely used in mobile communication and navigation systems. The main drawback of these devices is high sensitivity of the characteristics to variations of temperature because the typical values of temperature coefficient of frequency (TCF) vary between-30 ppm/ºC and-40 ppm/ºC for LT and between-60 ppm/ºC and-75 ppm/ºC for LN. Contrary to LN and LT, quartz is characterized by excellent temperature stability of SAW characteristics but low electromechanical coupling coefficient, k 2 <0.15%. Hence, even in resonator-type SAW filters with very narrow bandwidths, about 0.05%, where the loss of radiated energy is minimized due to the energy storage in a resonator, the best insertion loss achieved in a SAW device with matching circuits is only 2.5-4 dB. In some orientations of LBO, LGS and other crystals of LGS group, zero TCF is combined with a moderate electromechanical coupling coefficient. However, these crystals have limited applications in commercial SAW devices because low SAW velocities restrict highfrequency applications on LGS and LBO dissolves in water and acid solutions, which prohibits application of conventional wafer fabrication processes to this material and finally results in an increased cost of SAW devices. Hence, none of available single crystalline materials provides a combination of large piezoelectric coupling, zero TCF and high propagation velocity. A strong need in such material exists today, especially for application in SAW duplexers and multi-standard cellular phones, where the temperature compensation is the key issue because of necessity to divide a limited frequency bandwidth into few channels with no overlapping allowed in a wide range of operating temperatures. As an alternative to conventional SAW substrates, layered or multilayered (stratified) materials were studied extensively since 80-ies but only in the last decade some of these structures found commercial applications in SAW devices, due to the recent successes of thin film deposition technologies and development of robust simulation tools for design of SAW devices on layered structures.

Super-High-Frequency SAW Resonators on AlN/Diamond

IEEE Electron Device Letters, 2000

This letter describes the procedure to manufacture high-performance surface acoustic wave (SAW) resonators on AlN/diamond heterostructures working at frequencies beyond 10 GHz. In the design of SAW devices on AlN/diamond systems, the thickness of the piezoelectric layer is a key parameter. The influence of the film thickness on the SAW device response has been studied. Optimized thin films combined with advanced e-beam lithographic techniques have allowed the fabrication of one-port SAW resonators with finger width and pitch of 200 nm operating in the 10-14 GHz range with up to 36 dB out-of-band rejection.

INTEGRATION OF SAW FILTERS ON Si

Up to now, RF front-end and interstage surface acoustic wave (SAW) filter for mobile communication are mainly fabricated on LiNbO 3 and LiTaO 3 substrates. A monolithic integration of these filters on GaAs or Si substrates is highly desirable to miniaturize the outer dimensions of the cellular phones. But, direct monolithic integration of SAW filters is impossible with Si which is non piezoelectric , and difficult with GaAs which is weakly piezoelectric. One alternative is the disposition of a piezoelectric film on the semiconductor substrate. In this paper, we propose a modified coupling of modes (COM) approach, which can be used in the practical design of a layered ZnO/Si surface acoustic wave filter. The frequency response of the 3-step ladder type ZnO/Si SAW filter is analysed and compared with the experimental results.