One-port Resonator Research Articles

Improved equivalent circuits for acoustic plate wave devices

This paper presents improved equivalent circuits for the analysis and design of acoustic plate wave devices. The method uses a mixed equivalent circuit for the interdigital transducer consisting of both active and passive sections placed on the surface of a piezoelectric plate. The values of the various circuit elements are obtained by carrying out a best fit between theoretical and experimental frequency dependence of the real and imaginary parts of transducer input impedance. Knowledge of the equivalent circuit parameters allows one to optimize design of the devices. The method has been successfully employed for the design of one-port shear-horizontal wave resonators on Y– X lithium niobate plates. The proposed method can also be utilized for determining acoustic wave velocity with high accuracy.

Impact of SAW device passivation on RF performance.

Passivation layers consisting of sputtered A12O3 have been deposited onto SAW devices for the purpose of reducing the incidence of shorts. A coupling-of-modes model was used with one-port resonators, coupled resonator filters (CRF), and test structures. The passivation layer stiffens the surface with a velocity increase proportional to tau/lambda, where tau is the passivation layer thickness. Attenuation is increased slightly, producing a 0.25-dB increase in the loss of a one-port resonator at 314 MHz. The effect on reflectivity is minimal and of much lesser importance to the designer.

Effects of bulk wave radiation on IDT admittance on 42 degrees YX-LiTaO3.

This paper investigates the effects of bulk acoustic wave (BAW) radiation on the admittance of interdigital transducers (IDTs) with significant internal reflections of shear horizontal (SH) type leaky surface acoustic waves (SAWs) on 42 degrees YX-LiTaO3 (42-LT). Theoretical analysis is made by using the discrete Green function theory, and synchronous one-port resonators are analyzed. It is shown that the BAW radiation significantly affects the IDT characteristics even for resonators; under certain circumstances, BAWs launched from an IDT are converted into SH-type SAWs by the strong internal reflections, and they interact with the BAWs radiated by the IDT. Then, the net amount of the radiated BAW power is highly dependent upon the number of IDT finger pairs. For the precise simulation of devices based on the SH-type SAWs with strong internal reflections, the BAW radiation should carefully be taken into consideration. If the BAW radiation is ignored, the radiated power of the SH-type SAWs may seem to be negative above the BAW cut-off frequency.

Application of a one-port dielectric resonator for measurement of the intermodulation in high temperature superconducting films

A technique for characterization of intermodulation performance of unpatterned high TC superconducting (HTS) films, based on the application of the resonator with a single coupling probe is proposed. It allows us to sufficiently increase the sensitivity in comparison with the conventional method based on the resonator with two coupling probes. The measurements of the power at mixed frequency as a function of input power are performed for epitaxial HTS films of various surface resistance and thickness. From the experimental data an intermodulation coefficient α is determined, which provides the film intermodulation properties independently on the measuring system.

Waveguide coupling of SAW resonators with different properties

In contrast to conventional transversely coupled resonator filters, waveguide coupling of two one-port resonators with different resonance frequencies is described. The different resonance frequencies are implemented by different central finger gaps or gratings differing by a scaling factor. Consequently, the equivalent fingers and reflecting strips of different resonators are shifted with respect to each other, and the waveguide modes are, therefore, no longer independent of each other. This effect is called mutual coupling of waveguide modes and requires a new type of modeling. The main characteristics of the new modeling method are described. The advantage of the design principle consists of a wider bandwidth without changing the waveguide parameters and different input and output impedance.

Scattering matrix approach to one-port SAW resonators

The scattering matrix method was used to derive an expression for the reflection coefficient of a one-port SAW resonator. This expression was applied to calculations of an input admittance of a synchronous resonator on ST-cut quartz. Very good agreement was obtained between calculated and measured parameters of the resonator.

LADDER TYPE SAW FILTER AND ITS APPLICATION TO HIGH POWER SAW DEVICES

SAW filters with one-port SAW resonators being connected in a ladder structure, which is called ladder type SAW filter, have many features such as low insertion-loss, wide pass-band and simple filter design and so on. The design methodology, features of characteristics, and developments of higher frequency filter are described for an application in cellular phones. Furthermore, in order to apply to high power SAW devices such as the antenna duplexer of cellular phones, the material of inter-digital transducers (IDT) was improved to have high power durability. The optimum design in a ladder type SAW filter, the improvement in materials for IDT, and the optimum design of the package, all contributed the success of realizing a small SAW antenna duplexer.

Ladder Type Saw Filter and its Application to High Power Saw Devices

SAW filters with one-port SAW resonators being connected in a ladder structure, which is called ladder type SAW filter, have many features such as low insertion-loss, wide pass-band and simple filter design and so on. The design methodology, features of characteristics, and developments of higher frequency filter are described for an application in cellular phones. Furthermore, in order to apply to high power SAW devices such as the antenna duplexer of cellular phones, the material of inter-digital transducers (IDT) was improved to have high power durability. The optimum design in a ladder type SAW filter, the improvement in materials for IDT, and the optimum design of the package, all contributed the success of realizing a small SAW antenna duplexer.

Intermodulation measurements in YBaCuO films

A technique for measuring the intermodulation signal arising in a nonlinear high-temperature superconductor film is suggested. Using a one-port resonator, the technique significantly increases sensitivity of the measuring system as compared to that of a two-port-resonator design. Specifically, it lowers the minimum measurable power at a given magnetic field strength on the film surface. Measurements of the intermodulation signal power as a function of the input power for YBaCuO films differing in surface resistance and thickness are reported. Based on the measured data, the intermodulation characteristic magnetic field is computed. The quantity characterizes nonlinear film properties of the regardless of the measuring system employed.

Conductance measurements on a leaky SAW harmonic one-port resonator

Conductance measurements are reported on a leaky SAW (LSAW) harmonic one-port resonator on a 64 degrees Y-X LiNbO(3) substrate. This employed a short three-finger IDT for fundamental and second harmonic operation together with long reflection gratings. Conductances were measured with and without the end gratings. From an analysis of the measurements, it was deduced that, for optimum second harmonic performance, the grating stop-band frequency should be higher than the IDT unperturbed center frequency. This result is in contrast to fundamental frequency resonator designs in which the end grating stop-band frequency is placed below the IDT center frequency for optimum performance.

Design of SAW synchronous resonators on ST cut quartz

Surface acoustic wave (SAW) resonators on ST cut quartz, with synchronous placement of the interdigital transducers (IDT), were designed, fabricated, and measured. The basic structure of the resonators was a two-port one. The one-port resonators were obtained by parallel connection of the two IDT or by short circuiting one of them. The IDT were apodized to eliminate coupling to spurious modes. The transfer function of the two-port resonators was calculated by using the scattering matrix method. Several models of these resonators were investigated in the frequency range from about 300 to 715 MHz. By matching the theoretical and experimental transfer functions, the loss coefficient as a function of frequency and the SAW velocity in the reflector area as a function of aluminium layer thickness were determined. The responses of the resonators were free of any spurious modes.

Propagation characteristics of longitudinal leaky SAW in Al-grating structure

New orientations for longitudinal leaky SAW with small propagation losses and high velocities in lithium niobate (LN) and lithium tantalate (LT) have been found. Their velocities are 6100 to 6500 m/s in LN and 5200 to 5800 m/s in LT. Their propagation losses are almost negligible only in the case of an Al-grating structure. For example, the Al thickness relative to the SAW wavelength must be 8.4% for 171 degrees YZ'-LN; for 133 degrees YZ'-LT, the value must be 9.2%. These propagation properties were obtained by using a simulator that combined both finite-element and analytical methods. These results were also well confirmed by measuring the impedance responses of one-port SAW resonators.

Electromechanical Modelling Of Electrostatically Driven Micro Resonators, Part I: Basic Theory

Mechanical resonators operating in a flexural mode of vibration are examined theoretically with special regard to their electromechanical behaviour and equivalent electric circuits used to represent them. Electrostatic transducer elements are used for excitation and detection of the vibration. The differential equation of motion is solved in conjunction with the constitutive equations of the transducer elements. Arbitrary electrode shapes are accounted for in the model. The theory presented is exact with no restrictions other than linearity. General expressions of the network functions, e.g., the driving-point admittance of a one-port resonator, are derived, and subsequently used as a basis to develop equivalent electric circuits that accurately describe the resonator electromechanical behaviour. Resonators configured as an electric one-port as well as a two-port are considered in detail. Extensions of the equivalent circuit representation to accomodate N-ports are indicated.

Chemical sensor based on surface acoustic wave resonator using Langmuir-Blodgett film

A one-port surface acoustic wave (SAW) resonators incorporating Langmuir-Blodgett (LB) films has been investigated. SAW sensors are one potential applications of SAW devices. Most of the work reported on SAW sensor concerns delay lines. In this paper we characterize the mass loading effects of one-port resonators by depositing successive monolayers of LB films onto the surface. A 90 MHz SAW gas-phase sensor has been fabricated on an ST cut quartz substrate, and one-port resonator configurations have been used as the sensing element. Ultra thin monolayers of arachidic acid and arachidic acid ethyl ester have been deposited using the LB method. The resonant frequencies and the Q values have been measured as sensor response. Experimental results show that the Q values and the resonant frequencies of the one-port SAW resonator vary with film mass loading on the SAW device surface.

Behaviour of Leaky Surface Acoustic Wave Propagation at Discontinuous Region of Periodic Grating

This paper describes the leaky surface acoustic wave (LSAW) propagation characteristics at a discontinuous region in a grating structure. First, the dispersion relation of LSAWs propagating under a multielectrode-type grating is analysed. Then, the LSAW propagation on the discontinuous region is characterised by simply assuming that the LSAW behaviour under periodic part of the structure is identical with that under a totally periodic grating structure. It is concluded that the phase lag considerably decreases at the discontinuous region. This suggests that the energy storing effect may be weakened at the region where the periodic structure is broken. The simulation of one-port LSAW resonators shows that device performances are sufficiently evaluated only by taking account of the constant phase lag for a simulation tool based on the coupling-of-modes theory.

An oscillator circuit for electrostatically driven silicon-based one-port resonators

This paper describes design considerations and characteristics of oscillator circuitry for electrostatically driven silicon-based one-port resonators, used as resonant strain gauges. The oscillation conditions for a general, single transconductance oscillator are theoretically derived. In order to start oscillation, guidelines to select proper bias conditions for the resonator are presented, taking the non-linear effects into account. An oscillator circuit has been designed in CMOS technology in order to verify the theory experimentally. Experimental results of the oscillator in combination with a silicon beam resonator are given.

Q-factor dependence of one-port encapsulated polysilicon resonator on reactive sealing pressure

Micromachined encapsulated polysilicon resonators have been fabricated in different reactive sealing pressure, 200, 50 and 20 mTorr, in order to investigate the dependence of the Q-factors on the sealing pressure. Q-factors as high as 2700 have been measured. The experimental results show that the q-factors of one-port encapsulated resonators are proportional to 1/p and the resonant frequency is independent of the sealing pressure. However, the measured Q-factors are more than two orders of magnitude lower than theoretical prediction.

Electrostatically driven vacuum-encapsulated polysilicon resonators Part I. Design and fabrication

Basic design issues and a fabrication process based on surface-micromachining techniques for electrostatically driven vacuum-encapsulated polysilicon resonators are presented. A novel freeze-drying method that does not require vacuum equipment is presented. Reactive sealing with LPCVD silicon nitride is used to create the evacuated cavity, resulting in cavity pressures close to the deposition pressure. Design issues regarding choice of materials, technology and layout are discussed. First experimental results, including an admittance plot of the one-port resonator and a plot indicating the dependence of the Q-factor on the resonator geometry and ambient pressure, are presented.

Surface Acoustic Wave Filter Composed of Interdigitated Interdigital Transducers and One-Port Resonators

This paper describes a design method for low-loss surface acoustic wave (SAW) filters with a large stop-band attenuation. The method employs a conventional interdigitated interdigital transducer (IIDT) SAW filter and conventional one-port SAW resonators, which are constructed on one chip and connected electrically. The resonators provide a large attenuation in a specified stop band. On the other hand, the resonators act as an element in a matching circuit for the IIDT SAW filter in the passband. An 880 MHz filter was designed and fabricated according to the proposed method. The side-lobe attenuation of 45 dB in the specified stop band and the insertion loss of 2.5 dB in the passband were realized.

Equivalent networks for SAW interdigital transducers

An equivalent network approach is described for the analysis of surface-acoustic-wave interdigital transducers. Circuit parameters can he theoretically determined by applying the finite-element method to an infinite array. In this approach, all the effects of piezoelectric perturbation, mechanical perturbation, and energy storage are taken into account, To show the validity and usefulness of this approach, examples are computed for both single- and double-electrode interdigital transducers and one-port resonators. For single- and double-electrode interdigital transducers on 128/spl deg/Y-X LiNbO/sub 3/, X-112/spl deg/Y LiTaO/sub 3/,/sub 45//spl deg/X-Z Li/sub 2/B/sub 4/O/sub 7/, and ST-X quartz substrates, the dependence of excitation characteristics on electrode thickness and metallization ratio is investigated in detail. For a 128/spl deg/Y-XLiNbO/sub 3/ substrate, frequency responses of various one-port resonators are also investigated.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>