A novel NO 2 gas sensor using dual track SAW device

Carbon dioxide (CO2) gas sensor using surface acoustic wave (SAW) device based on Zinc oxide (ZnO) was developed and fabricated in this paper. The center frequency of SAW device is 203.528 MHz. The input and two output interdigital transducers (IDT) apodized by Morlet wavelet function can improve the side lobe rejection compared with uniform IDT. The ZnO film sensitive to CO2 gas was fabricated in measurement acoustic track of SAW device. Experiments results confirm that the CO2 gas sensor using SAW device based on ZnO film has good response characteristics to different concentrations CO2 gas. Furthermore, the CO2 gas sensor using SAW device based on ZnO film has good stability and linearity.

Nanotechnology for SAW devices on AlN epilayers

Dual channel surface acoustic wave (SAW) oscillators of two-port SAW resonators were designed for sensor application. A feedback loop were determined by measuring the corresponding open loop and adjusting the point of 0° total phase to exist near to the point of peak gain by variation of coupling inductance value. Two such feedback loops, a mixer and a TTL invertor comprise a dual channel SAW sensor oscillator. To achieve a stable oscillation, incorporation of a power conditioning components and the use of microstrip techniques (50 Ω characteristic impedance and the least inductance path for RF return currents) are necessary. The standard deviation of difference frequency stability of the oscillator of 433.92 MHz is about 3.92. Finally, the dual channel SAW sensor oscillator is used to detect dimehylmethylphosphonate (DMMP) vapor.

The development of mobile communication sets higher demands on high frequency surface acoustic wave (SAW) devices. The layout of interdigital transducers (IDT) in SAW devices is in plane and the traditional methods of improving frequency for SAW devices are the increase of acoustic velocity and the reduction of wavelength. However, these methods have a limit due to the limited acoustic velocity and the photolithography limit. This work proposes a new way for the development of high frequency SAW devices by redesigning the layout of IDT in three dimensions (3D). The set of IDTs is split into two layers, i.e. the ground electrodes on one layer and the signal electrodes on the other layer. This 3D layout of IDTs dramatically narrows the horizontal gap between two adjacent electrodes, which can significantly increase the frequency. The frequency and the electromechanical coupling factor (K 2 ) of the four structures of SAW devices with the 3D layout of IDTs were studied by the finite element method (FEM). The results show that the frequency can be doubled under the same critical resolution of lithography due to the shortening of wavelength, and the 3D layout of IDTs is available for SAW devices based on piezoelectric thin film or piezoelectric single crystal. This work develops a new alternative to increase the working frequency of SAW devices.

The regions of anomalous (decelerating) influence of piezoelectricity on the phase velocities of surface and bulk acoustic waves are numerically found near the orientations where the phase velocities of two acoustic modes coincide. Calculations of surface acoustic waves (SAWs) are performed for a potassium niobate crystal. An unusual, inverse in sign, velocity shift of Rayleigh-type SAWs caused by electrical shorting at the surface of the crystal is accompanied by a rise of the tranverse (shear-horizontal) displacement component. Nevertheless, the velocity shift is inverse in sign even in the case when this transverse component tends to zero. Bulk acoustic waves are studied in a semiconductor selenium crystal. The cone of angles confining the region of anomalous “piezoelectric softening” with increasing the conductivity of the crystal is determined.

A surface acoustic wave (SAW) sensor for measurement of humidity in ambient atmosphere is presented. The majority of the SAW sensors have utilized the effect of mass loading. In this paper, we propose a new SAW humidity sensor based on the changes in the film conductivity rather than the mass. The phase velocity and propagation loss were computed for the SAW propagating on a piezoelectric substrate which is coated with a hygroscopic conductive polymer. In experiments, a 30 MHz dual SAW delay line fabricated on 128/spl deg/ YX LiNbO/sub 3/ was coated with the sodium salt of polystyrene sulfonate. This hygroscopic polymer coating caused the SAW velocity change of 20 m/s per 10% in the relative humidity. The response was quite linear in the range from 40 to 80%RH.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A surface acoustic wave (SAW) sensor for measurement of humidity in ambient atmosphere is presented. SAW technology is increasingly being used in sensors. The majority of the work reported on SAW sensors to date has studied the effect of mass loading. In this paper, we propose a new SAW humidity sensor that uses the changes in the film permittivity rather than the mass. A 30 MHz dual SAW delay line fabricated on 128° YX LiNbO3 was coated with cellulose acetate. This hygroscopic polymer coating caused a SAW velocity change of 0.36 m/s per 10% relative humidity. The response was linear in the range from 10% to 80% in relative humidity.

Rapid, sensitive and selective detection of bioparticles is of prime importance in point of care diagnostic devices and various micro- and nano-systems [1] relying on microfluidics are being developed. This paper reports a design of a new optoacoustic microfluidic device which can quantitatively detect the concentration of micron sized bioparticles in a solution. In our previous work [2], we have introduced a new sensing scheme utilizing surface acoustic wave (SAW) detection of the photoacoustic (PA) signal generated from optical absorption of bioanalytes present in the microfluidic channel. In the current work, we combine a SAW based particle concentration on a microfluidic reservoir with the SAW-PA sensor to enable rapid, quantitative and sensitive microparticle detection (polystyrene) on a single piezoelectric substrate. The detection of analytes from the bulk of the solution, along with the mechanical scanning, particle concentration and continuous fluid flow, highlights the device capability to handle clinically relevant sample volume (millilitres) in comparison to the low throughput (microlitre sample) of the existing devices. &nbsp; A schematic view of the device is illustrated in Fig. 1. Orthogonal interdigital transducers (IDT) on the 1280 YX lithium niobate (LiNbO3) piezoelectric substrate is used for actuating and sensing. An IDT excited at 15.8 MHz (labelled &lsquo;A&rsquo;) oriented in the Y direction is used for particle concentration inside the microfluidic reservoir. The IDT at centre frequency of 10 MHz oriented in the X direction is used for sensing. The numerical simulation results confirms that the SAW-PA frequency for a 10 &mu;m (diameter) polystyrene particle is sensitive for frequencies less than 50 MHz. Table I shows the SAW device specifications. A pulsed laser at repetition rate of 10 Hz at a wavelength of 532 nm is used, with an optical spot size of 200 &mu;m. A mechanical scanner focusses the laser spot across the particles located inside the microfluidic reservoir. Fig. 2 shows the schematic of the experimental setup used for sensing. Black polystyrene microparticles with an optical absorbance of ~ 0.7 at 532 nm is used as the sensing sample for the experiment. &nbsp; Fig. 3 shows 10 &mu;m particles aggregating after SAW exposure for 40-50 sec. The particles are concentrated at a vertical height close to the liquid-air free surface. The preconcentration before detection bounds the mechanical scanning to only half of the cavity, thereby reducing the detection time. Fig. 4 shows the experimental results for the detection of the 10 &mu;m particles for a concentration varying from ~10-200 particles per 10 &mu;L. The power spectral density of the SAW-PA signals for varying particle concentration demonstrates a quadratic response, with a detection of 7 particles in 10 &mu;L of solution. The sensitivity can be improved further to a single particle by optimizing the SAW design to match the acoustic frequency generated due to microfluidic channel resonance. Furthermore, utilizing dual SAW IDTs aggregates the particles at a preferred location, thereby eliminating the mechanical scanner. Thus, a rapid (few sec) and sensitive (single) particle detection device could be envisaged, comparable to the 3D droplet detection device[3].

High-performance wideband surface acoustic wave (SAW) devices are essential components for wireless communication systems in the new age, and spurious modes and temperature stability are two important properties for wideband devices. Nevertheless, preparing wideband spurious-free SAW devices with low temperature drift is still a big challenge. To achieve four strengths including large bandwidth, low temperature drift, suppressed Rayleigh mode and suppressed transverse modes in the meantime, this work proposes and theoretically investigates SAW devices based on three structures including SiO2/Cu/Y-X LiNbO3/69°Y-90°X quartz, Cu/Y-X LiNbO3/69°Y-90°X quartz, and Al/41°Y-X LiNbO3/69°Y-90°X quartz. The characteristics of these devices are revealed and some optimized designs based on these structures are provided. Wideband SAW devices with nearly-zero temperature coefficients of frequency and suppressed Rayleigh mode can be achieved when SiO2/Cu/Y-X LiNbO3/69°Y-90°X quartz structure is applied. Transverse modes are weakened by quartz and can be more effectively suppressed if transverse mode suppression designs of interdigital transducers are applied, so the four strengths can be achieved meanwhile. The devices based on the other two structures can have at least two strengths as well as some unique properties such as ultra-large electromechanical coupling factor of 34.20% and suppressed transverse mode generation, which are suitable for different applications. This work provides more possible structures and designs for the engineers in filter design, and promotes the development of high-performance wideband SAW devices.

ABSTRACTIn this paper, we utilized a Stroh based formulation for solving problems of surface waves in layered piezoelectric media, and then, applied it to analyze surface acoustic wave (SAW) devices. The determination of the optimal cut of a piezoelectric crystal and the choice of the best propagation of SAW devices were given. The dispersion induced by a thin metal layer on SAW propagation in a SAW device was analyzed and discussed. Finally, we applied the formulation to calculate the effective permittivity and phase velocity dispersion of a LiNbO3/Diamond layered SAW device. Both of the null frequency bandwidth and the insertion loss of the dispersive SAW device were obtained.

Synchronization phenomena for coupled delay-line oscillators

IntroductionSince 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, 2001Ruppel, , 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.comAcoustic 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. Multilayered structures as materials for SAW devicesAs described above, the increasing requirements to the substrate materials, on one side, and rapid development of thin film deposition technologies, on the other side, gave rise to the novel class of materials for SAW devices -layered or multilayered structures.One or more films of different materials deposited on a regular substrate can improve its characteristics significantly.A proper combination of a substrate and a thin film helps to overcome the limitations of the conventional SAW substrates.In this section, a brief overview of the layered structures will be given.The examples presented here are currently investigated by different research groups as promising compound SAW substrate materials or found already some applications in SAW devices.The focus is made on the recent achievements in material research mostly motivated by challenges of the rapidly developing market of communication devices.Based on this overview, a generalized multilayered structure, www.intechopen.com

This paper reviews the basic properties of shear-horizontal (SH)-type surface acoustic waves (SAWs) and bulk acoustic waves (BAWs). As one of the simplest cases, the structure supporting Bleustein-Gulyaev-Shimizu waves is considered, and their excitation and propagation are discussed from various view points. First, the formalism based on the complex integral theory is presented, where the surface is assumed to be covered with an infinitesimally thin metallic film, and it is shown how the excitation and propagation of SH-type waves are affected by the surface perturbation. Then, the analysis is extended to a periodic grating structure, and the behavior of SH-type SAWs under the grating structure is discussed. Finally, the origin of the leaky nature is explained.

Introduction. One of the dominant second order effects in devices based on surface acoustic waves (SAW) is the excitation of parasitic bulk acoustic waves (BAW). Attention is drawn to the lack of effectiveness of traditional BAW suppression ways. Traditional ways of suppressing the bulk acoustic waves. Provides an overview of how suppression of parasitic BAW to SAW filters. One way allows to reach a record level of BAW suppression (−65 dB) due to the significant mechanical weakening of the acoustic line of the filter. Narrowband surface acoustic wave filter. It is found that in the SAW filter with an extremely high level of out-of-band suppression (−72 dB) traditional ways do not provide the required level of suppression of BAW. Wave heterogeneity of special shape. Tested the effectiveness of the authors proposed way of BAW suppression in a narrow-band SAW filter with an extremely high level of out-of-band suppression. A deep closed groove which is cut in the lower surface of the acoustic line of filter reduces the level of BAW to −70 dB, and the strength of the acoustic line of filter is almost not reduced. The dependence of suppression the bulk acoustic waves from the parameters of the wave heterogeneity. The dependence of the relative level (B) of suppression the slow quasi-shear bulk acoustic waves from the depth of the closed groove was investigated. It was found a monotonic increase in the level of B with increasing groove depth. Level B = −70 dB was obtained when the thickness of the gap between the bottom of the groove and the working surface of the acoustic line was (for different filter samples). Conclusion. The effectiveness of the authors proposed way of suppression the slow quasi-shear BAW in SAW filters is proved. A deep closed groove which is cut into the bottom surface of the acoustic line of filter can suppress slow quasi-shear BAW to a level of −70 dB.

Surface acoustic wave (SAW) devices are widely used for physical, chemical, and biological sensing applications, and their sensing mechanisms are generally based on frequency changes due to mass-loading effects at the acoustic wave propagation area between two interdigitated transducers (IDTs). In this paper, a new sensing mechanism has been proposed based on a significantly enhanced mass-loading effect generated directly on Au IDT electrodes, which enables significantly enhanced sensitivity, compared with that of conventional SAW devices. The fabricated ultrahigh-frequency SAW devices show a significant mass-loading effect on the electrodes. When the Au-electrode thickness increased from 12 to 25 nm, the Rayleigh mode resonant frequency decreased from 7.77 to 5.93 GHz, while that of the higher longitudinal leaky SAW decreased from 11.87 to 9.83 GHz. The corresponding mass sensitivity of 7309 MHz·mm2·μg-1 (Rayleigh mode) is ∼8.9 × 1011 times larger than that of a conventional quartz crystal balance (with a frequency of 5 MHz) and ∼1000 times higher than that of conventional SAW devices (with a frequency of 978 MHz). Trinitrotoluene concentration as low as 4.4 × 10-9 M (mol·L-1) can be detected using the fabricated SAW sensor, proving its giant mass-loading effect and ultrahigh sensitivity.