Showing papers on "Interdigital transducer published in 2004"

Interdigital sensors and transducers

Abstract: This review paper focuses on interdigital electrodes-a geometric structure encountered in a wide variety of sensor and transducer designs. Physical and chemical principles behind the operation of these devices vary so much across different fields of science and technology that the common features present in all devices are often overlooked. This paper attempts to bring under one umbrella capacitive, inductive, dielectric, piezoacoustic, chemical, biological, and microelectromechanical interdigital sensors and transducers. The paper also provides historical perspective, discusses fabrication techniques, modeling of sensor parameters, application examples, and directions of future research.

Analytical evaluation of the interdigital electrodes capacitance for a multi-layered structure

Abstract: The widespread use of interdigital electrodes in such applications as microwave filters, surface acoustic wave devices, electro-optic shutters as well as on chemical and biological sensing and even on the electrical and dielectric characterization of materials requires that we improve our description of their electrical performance. In this paper, we present new analytical expressions for the capacitance between the two comb electrodes of a periodic interdigital capacitive sensor, based on conformal mapping techniques. This proposed model is general and quite independent of the particular application and can be applied for any space and finger width as well as for any number of layers with different thickness and permittivity. The capacitance for a particular sensor configuration is a function of the dielectric permittivity of the materials, the fingers length and of two geometric non-dimensional parameters: (i) the ratio between the space and finger widths; (ii) the ratio between the thickness of the sensitive layer and the spatial sensor wavelength. Comparisons with previously published models as well as with experimental data and finite element analysis were made.

Passive wireless acoustic wave chemical sensor

Abstract: A passive wireless acoustic wave chemical sensor can be utilized for monitoring the concentration of an analyte in a substance such as blood. Such an acoustic wave chemical sensor can be configured to include one or more interdigital transducers and a selective coating formed upon a piezoelectric substrate. The coating and the interdigital transducer(s) can be used to convert electrical signal to surface waves thereof. An antenna can be connected to the acoustic wave device, wherein the antenna receives one or more input signals, which excite the acoustic device and to produce an output signal that is related to the concentration of the analyte of interest.

Acoustic touch sensor with low-profile diffractive grating transducer assembly

Abstract: A touch sensor having an acoustic substrate, an acoustic transducer, and an acoustically diffractive grating is provided. The grating is disposed between the transducer and the substrate, so that acoustic energy from the transducer is coupled to an acoustic wave propagating along the surface of the substrate. If used in a display device, the combination of the transducer and grating may provide a low profile that allows the assembly to be more easily placed between the acoustic substrate and a bezel placed in front of the substrate. No acoustic components need be mounted on the rear surface of the substrate, allowing the acoustic substrate to be formed on the front surface of the display device.

An experimental study on the ZnO/sapphire layered surface acoustic wave device

Abstract: In this study, ZnO thin films with different thicknesses were deposited on C-plane sapphire substrates by radio-frequency magnetron sputtering. Properties of interdigital transducer/ZnO/sapphire layered surface acoustic wave device including surface wave velocity, electromechanical coupling coefficient, and propagatiion loss were measured and discussed. Combining the effective permittivity approach and the coupling-of-modes (COM) model, the dispersion characteristics and frequency responses of the ZnO/sapphire layered structure were simulated. By substituting the measured parameters into the COM model, the simulated frequency response has shown good agreement with the experimental results.

Intelligent tires based on wireless passive surface acoustic wave sensors

Abstract: The structure and principle of an intelligent tire based on wireless passive surface acoustic wave (SAW) sensors are described. The SAW sensor is made by two identical delay lines on both sides of the substrate symmetrically. In each delay line, there were two reflectors with difference distance from interdigital transducer (IDT). The sensor was hermetically sealed in an all-quartz-package (APQ) technology and embedded in the tire. It can measure the tire pressure and temperature parameters automatically. According to the measurement result, the sensor systems can estimate the tire state intelligently and present the driver an alarm when the pressure or temperature was abnormal. The theory of measuring pressure and temperature is discussed and analysis for measures with pressures from 150 kPa to 300 kPa and temperatures from 25/spl deg/C to 95/spl deg/C is conducted. The results of measurement agree with the theory well.

Acoustic wave sensor with reduced condensation and recovery time

Abstract: An acoustic wave sensor apparatus is disclosed, which generally includes a piezoelectric substrate having a surface thereon. One or more interdigital transducers and a passivation layer can be formed upon the piezoelectric substrate. Additionally, an absorbent material can be formed upon the acoustic path (IDTs, electrodes, etc), such that the interdigital transducers respond to a plurality of acoustic waves propagating across the surface of the piezoelectric substrate, thereby providing data indicative of humidity in the vicinity of the piezoelectric substrate, along with the passivation layer and the interdigital transducers. Additionally, one or more heaters can be formed upon a side of the piezoelectric substrate opposite the side of the piezoelectric substrate upon which the interdigital transducers, the passivation and the absorbent material are located. The heater can be preferably configured from a material such as platinum.

Resonator filters using shear horizontal-type leaky surface acoustic wave consisting of heavy-metal electrode and quartz substrate

Abstract: The authors have succeeded in exciting a new type of leaky surface acoustic wave (LSAW) having only a shear horizontal (SH) component that has a large electromechanical coupling factor, a large reflection coefficient, and excellent temperature stability, by combining interdigital transducers (IDTs) and reflectors made of heavy-metal films such as gold (Au), tantalum (Ta), and tungsten (W) on the ST-cut 90/spl deg/ X propagation (direction perpendicular to the X-axis) quartz substrate. This LSAW does not have a propagation decay. The square of the electromechanical coupling factor is 2.1-2.7 times larger than, the reflection coefficient is 30 times larger than, and the temperature characteristic is the same as those of a Rayleigh wave on an ST-cut X propagation quartz substrate. The authors applied this SH LSAW to resonators and resonator filters. As a result, we succeeded in developing the low loss and very small-sized resonators and resonator filters (1/5-1/4 of conventional device sizes) with IDTs with a small number of finger pairs and very small reflectors, for the first time.

Embedded interdigital transducers for high-frequency surface acoustic waves on GaAs

Abstract: We investigate high-performance, high-frequency interdigital transducers (IDTs) for the generation of surface acoustic waves (SAWs) on GaAs substrates, where the metal fingers are embedded in the substrate. We demonstrate that the acoustic reflections and the scattering of the surface modes into the substrate become considerably reduced in these transducers, leading to an increased output power. The finger embedding process is particularly relevant for the generation of powerful beams of high-frequency SAWs on weak piezoelectric substrates (such as most of the semiconducting materials) using long IDTs. We also show that the reflection reduction is important for the design of focusing single-finger IDTs, since it minimizes the effects of the finger grating on the angular dependence of the phase velocity.

Directional scholte wave generation and detection using interdigital capacitive micromachined ultrasonic transducers

Abstract: Directional generation and detection of Scholte waves and other guided modes in liquids and microfluidic channels by capacitive micromachined ultrasonic transducers (cMUTs) is reported An interdigital transducer structure along with a phased-excitation scheme is used to enhance the directionality of Scholte interface waves in microfluidic environments Finite element models are developed to predict the performance of the devices in both fluid half-spaces and microchannels Experiments on the interdigital cMUTs show that a five-finger-pair device in a water half-space has 12 dB of directionality in generating Scholte waves at the design frequency of 10 MHz A 10-finger device operating at 10 MHz in a water-filled microchannel has 134 dB of directionality These directionality figures agree well with the modeling results Using the results of the finite element model of a cMUT in a fluid half-space, it was determined that 41% of the acoustic power radiated into the fluid is contained in the Scholte wave propagating in the desired lateral direction Transducers are demonstrated to perform bidirectional pumping in fluid channels with input power levels in the milliwatt range Interdigital cMUTs fabricated using low temperature processes can be used as compact ultrasonic transducers with integrated electronics for sensing and actuation in fluidic environments

Interdigital capacitor and method for adjusting the same

Abstract: An interdigital capacitor includes a semiconductor substrate, and a pair of comb-like electrodes formed on the semiconductor substrate. At least one of the pair of comb-like electrodes includes a cutting target portion.

Design considerations on surface acoustic wave resonators with significant internal reflection in interdigital transducers

Abstract: This paper discusses, both qualitatively and quantitatively, the operation and the design principle of current surface acoustic wave (SAW) resonators in which the internal reflection within interdigital transducers (IDTs) is not negligible and lower capacitance ratio is necessary. For the purpose, the p-matrix expression is used with the help of the coupling-of-modes theory. The internal reflection causes: deformation of the IDT passband shape, frequency dependence of the effective SAW velocity within IDTs, and suppression of higher-order resonances. It is shown that these features can be effectively used to enhance performances of both one-port SAW resonators and two-port double-mode SAW (DMS) filters. In addition, under proper designs accounting for the internal reflection, most of all structural discontinuities can be removed, and is most preferable for the reduced scattering loss at the discontinuity. Design criteria also are presented for DMS filters of wide bandwidth, and it is demonstrated how device performances are improved by proper design accounting for the criteria.

Surface acoustic wave transducer

Abstract: A unidirectional surface acoustic wave (SAW) transducer has a substrate which is piezoelectric or electrostrictive, a first IDT (interdigital transducer) electrode disposed on a surface of the substrate and having a plurality of first electrode fingers, and a second IDT electrode disposed on the surface of the substrate and having a plurality of second electrode fingers alternating with the first electrode fingers, and structural elements disposed on the surface of the substrate and arranged periodically in a propagating direction of surface acoustic waves. The structural elements comprise grooves or dielectric films each having a width of λ 0 /4 or λ 0 /2, for example, where λ 0 represents a wavelength corresponding to a fundamental operating frequency of the unidirectional surface acoustic wave transducer.

Active SAW devices on 2DEG heterostructures

Abstract: Active surface acoustic wave filters with voltage-controlled insertion losses have been achieved using AlGaN/GaN 2DEG heterostuctures as piezoelectric substrates. Transfer control is performed by moderate DC voltages between the fingers in either or both input and output interdigital transducers. These filters can be integrated into future MMIC circuits based on AlGaN/GaN high electron mobility transistors.

An SU-8 liquid cell for surface acoustic wave biosensors

Abstract: One significant challenge facing biosensor development is packaging. For surface acoustic wave based biosensors, packaging influences the general sensing performance. The acoustic wave is generated and received thanks to interdigital transducers and the separation between the transducers defines the sensing area. Liquids used in biosensing experiments lead to an attenuation of the acoustic signal while in contact with the transducers. We have developed a liquid cell based on photodefinable epoxy SU-8 that prevents the presence of liquid on the transducers, has a small disturbance effect on the propagation of the acoustic wave, does not interfere with the biochemical sensing event, and leads to an integrated sensor system with reproducible properties. The liquid cell is achieved in two steps. In a first step, the SU-8 is precisely patterned around the transducers to define 120 μm thick walls. In a second step and after the dicing of the sensors, a glass capping is placed manually and glued on top of the SU-8 walls. This design approach is an improvement compared to the more classical solution consisting of a pre-molded cell that must be pressed against the device in order to avoid leaks, with negative consequences on the reproducibility of the experimental results. We demonstrate the effectiveness of our approach by protein adsorption monitoring. The packaging materials do not interfere with the biomolecules and have a high chemical resistance. For future developments, wafer level bonding of the quartz capping onto the SU-8 walls is envisioned.

Passive wireless piezoelectric smart tire sensor with reduced size

Abstract: A surface wave device (300) can be configured to include an interdigital transducer and an acoustic coating (302) formed upon a piezoelectric substrate (304), wherein the interdigital transducer (306) is selected to introduce negligible electrical coupling to surface waves thereof. Additionally, an antenna (308) can be integrated with the surface wave device, wherein the antenna receives one or mores signals, which excite the acoustic wave device to produce multiple modes frequency outputs in which temperature and pressure effect changes are separated from one another for analysis thereof.

Electrostatics of interdigital transducers

Abstract: Interdigital transducers are systems of conducting strips on a piezoelectric halfspace; in some systems, the groups of strips repeat periodically over a transducer counting hundreds of strips that can be considered infinite. An infinite planar periodic system of groups of strips with adequate period, sufficiently large if necessary, is considered to model an electric field in the plane of strips. There are electric charge distributions on strips either resulting from an external voltage source applied to the strips or induced by a propagating surface acoustic wave in the piezoelectric substrate. The latter case is equivalent, in the electrostatic approximation applied in this paper, to strips embedded in an already existing, spatially variable electric field. A method is presented for evaluation of the spatial spectrum of charge distribution that is responsible for either the surface wave generation or the scattering by strips in weak piezoelectrics. It overcomes certain numerical difficulties arising when Fourier transform is computed from the already evaluated numerical representation of the square-root singular charge distribution at the strip edges.

Simulation of surface acoustic wave devices

Abstract: The Mason crossed-field circuit model is generalized to simulate apodized interdigital transducers without channel division. The apodized transducer model is based on the transmission line model, and the artificial transformer with different voltage and current coupling ratios is used to independently obtain the transfer function and radiation admittance. In addition, a heuristic expression for transformer current ratios is used to approximate the radiation admittance of apodized transducers. Through comparing with the multichannel model, this unichannel model is illustrated to successfully describe the frequency response of apodized interdigital transducers.

Deposition of preferred-orientation ZnO films on the ceramic substrates and its application for surface acoustic wave filters

Abstract: Polycrystal ZnO films with c-axis (002) orientation have been successfully grown on the lead-based ceramic substrates by rf magnetron sputtering technique. The deposited films were characterized as a function argon-oxygen gas flow ratio and rf power. Crystalline structures of the films were investigated by x-ray diffraction, scanning electron microscopy, and atomic force microscopy. Highly oriented films with c-axis normal to the substrates can be obtained by depositing under a total pressure of 10 mTorr containing 50% argon and 50% oxygen and rf power of 70 W. The phase velocity, electromechanical coupling coefficient, and temperature coefficient of frequency of surface acoustic wave (SAW) device with ZnO/IDT/PT (IDT: interdigital transducer; PT:PbTiO3 ceramics) structure were investigated. It shows that the preferred oriented ZnO film is beneficial for improving the electromechanical coupling coefficient of SAW device.

Surface acoustic wave filter and communication unit

Abstract: A surface acoustic wave filter having a balance/unbalance converting function for improving the degree of balance, and a communication unit comprising it. A longitudinal coupling resonator type surface acoustic wave filter section (501) comprises a first interdigital electrode part (503), a central interdigital electrode part (504), a second interdigital electrode part (505), and first and second reflectors (506, 507) sandwiching them. One comb-shaped electrode at the central interdigital electrode part (504) is divided substantially symmetrically into first and second comb-shaped electrodes (516, 517) along the propagating direction of surface acoustic wave. Between the first and second comb-shaped electrodes (516, 517), at least one of design parameters of the interdigital electrode parts (503, 504, 505) and the reflectors (506, 507) is differentiated between one and the other sides sandwiching an imaginary central axis A orthogonally intersecting the propagating direction of surface acoustic wave.

Compact high-impedance surfaces incorporated with interdigital structure

Abstract: A novel compact high-impedance surface structure is presented. The periodic branched elements cross over like interdigital capacitors. This structure is adopted to increase the fringe capacitor in order to compress the overall size of the high-impedance surface. Measured results show that 30-40% size reduction could be obtained.

Minimum-loss short reflectors on 128/spl deg/ LiNbO/sub 3/

Abstract: We consider the interaction of surface acoustic waves (SAWs) with short electrode gratings encompassing only few electrodes on 128/spl deg/ lithium niobate (LiNbO/sub 3/). The qualifications of the reflectors are evaluated by comparing the part of incident SAW energy scattered by the structure into the bulk to the energy reflected back as a SAW.

Surface acoustic wave sensing system and method for measuring pressure and temperature

Abstract: A surface acoustic wave (SAW) sensor and an interrogator that transmits a noise source to the sensor for receiving an interrogation signal that is processed and compared to the source signal provides pressure and temperature measurements. One SAW sensor a single interdigital transducer serving as both an input and an output transducer for generating and detecting a SAW, and coded reflectors in a mirrored arrangement opposing the single interdigital transducer. The piezoelectric substrate is supported in a hermetically sealed package such that pressure on the package causes distortion of the substrate transducer surface and thus SAW velocity changes that reflect changes in pressure. Characteristic temperature coefficients of delay for the substrate are directly translated into a temperature value.

Wafer-level surface acoustic wave filter package with temperature-compensating characteristics

Abstract: A SAW filter is fabricated at a wafer level for providing desirable temperature characteristics. The filter includes a piezoelectric substrate bonded to a carrier substrate, wherein the coefficient of thermal expansion of the carrier substrate is less than the coefficient of thermal expansion of the piezoelectric substrate. Interdigital transducers are formed on the piezoelectric substrate so as to form a SAW composite die structure. A cap substrate having a coefficient of thermal expansion similar to that of the carrier substrate is bonded to the SAW composite die structure for enclosing the interdigital transducers. Plated vias form signal pad interconnects to input and output pads of the interdigital transducer and a sealing pad formed on the surface of the piezoelectric substrate bonds the SAW composite die structure to the cap substrate.

Surface-acoustic-wave component adapted to electronic circuit and device, and manufacturing method therefor

Abstract: A surface-acoustic-wave component that comprises a first piezoelectric layer composed of zinc oxide (ZnO), a second piezoelectric layer composed of lithium niobate (LiNbO 3 ), and a protective layer, which are sequentially formed on a silicon substrate, on which electrodes (e.g., interdigital transducers) are further formed. Alternatively, it comprises a conductive layer composed of zinc oxide (ZnO), a piezoelectric layer composed of lithium niobate (LiNbO 3 ), and a protective layer, which are sequentially formed on a silicon substrate, on which electrodes are further formed. The piezoelectric layer can actualize preferable orientation so as to improve the electromechanical coupling coefficient (K 2 ). Thus, it is possible to produce surface-acoustic-wave components that contribute to manufacturing of highly-integrated electronic circuits such as frequency filters and oscillators as well as electronic devices such as portable telephones.

SAW sensors on Aln/diamond/Si structures

Abstract: In this work we present preliminary results on surface acoustic waves (SAW) chemical sensors based on a new AlN/diamond/Si multilayered structure. The high SAW velocity in diamond allows it to operate at higher frequencies at moderate interdigital transducer (IDT) line-width resolution in order to increase the sensor output signals, with the aim to increase the sensor sensitivity. Aluminium nitride has been chosen as piezoelectric layer because of its high SAW velocity together with excellent electrical, mechanical and chemical properties. The SAW phase velocity in the experimented structure is 10716 m/s for the Sezawa mode, more than three times that in ST-cut quartz. Both SAW delay line and 1-port resonator have been implemented and tested, under the following propagation conditions: acoustic wavelength /spl lambda/=8 /spl mu/m, normalized AlN film thickness h//spl lambda/=0.225, operation frequency f/spl cong/1.35 GHz. The thickness of the diamond layer (22 /spl mu/m) is such that it can be considered as a semi-infinite substrate. The two test structures have been coated by thermal evaporation with a sensible thin (10 nm) layer of Co-tetra-phenyl-porphyrin which allowed us to detect small concentrations of ethanol and CO.

Stacked capacitor and method for preparing the same

Abstract: The present invention discloses a stacked capacitor having interdigital electrodes and method for preparing the same The stacked capacitor comprises a first interdigital electrode, a second interdigital electrode and a dielectric material sandwiched between the first interdigital electrode and the second interdigital electrode The first and the second interdigital electrodes comprise a body and a plurality of fingers electrically connected to the body, and the dielectric material can be silicon nitride or silicon oxide Preferably, fingers of the first interdigital electrode are made of titanium nitride, while fingers of the second interdigital electrode are made of polysilicon The body of the first and the second interdigital electrodes are preferably made of titanium nitride

Phases of the SAW reflection and transmission coefficients for short reflectors on 128/spl deg/ LiNbO/sub 3/

Abstract: We study numerically the phase of surface acoustic waves reflected by or transmitted through short reflectors comprising only 1-3 aluminium electrodes on 128/spl deg/ YX-cut lithium niobate (LiNbO/sub 3/). The electrodes have a finite thickness, and they are either open-circuited or grounded. The center-to-center distance between adjacent electrodes d corresponds roughly either to half of the characteristic wavelength d/spl prop//spl lambda//sub 0//2 or to d/spl prop//spl lambda//sub 0/, for the reflectors operating at the fundamental and second harmonic modes, respectively. We use software based on the finite-element and boundary-element methods (FEM/BEM) for numerical experiments with a tailored test structure having 3 interdigital transducers (IDTs), simulating experimental conditions with an incident wave and reflected and transmitted surface acoustic wave (SAW). Using artificial enhancement of time resolution in conjunction with the fast Fourier transform (FFT) and time-gating, calculation of the Y-parameters in a relatively wide frequency range allows us to determine the phase of the reflection and transmission coefficients.

Surface acoustic wave filters and duplexers including the same

Abstract: A surface acoustic wave filter includes: an input interdigital transducer (11) and an output interdigital transducer (11) that are formed on a piezoelectric substrate; a capacitance (C) that is provided between the input terminal (4) of the input interdigital transducer and the output terminal (5) of the output interdigital transducer; a first common ground terminal (8) that connects the ground terminal of the input interdigital transducer and the ground terminal of the output interdigital transducer; and an inductance (4) that is provided between the first common ground terminal and a ground (9).

Saw Filter With Improved Selection or Insulation

Abstract: A surface acoustic wave (SAW) filter includes a piezoelectric substrate, and acoustic tracks on the piezoelectric substrate. The acoustic tracks are adjacent and electrically interconnected. The acoustic tracks include electro-acoustic transducers. The electro-acoustic transducers include an input transducer and an output transducer. The SAW filter also includes a shielding structure that is metallic and that is connected to ground. The shielding structure is between the acoustic tracks. The shielding structure shields a first electro-acoustic transducer in a first acoustic track from a second electro-acoustic transducer in a second acoustic track.