Preface. Microelectromechanical Systems (MEMS) and Radio Frequency MEMS. MEMS Materials and Fabrication Techniques. RF MEMS Switches and Micro Relays. MEMS Inductors and Capacitors. Micromachined RF Filters. Micromachined Phase Shifters. Micromachined Transmission Lines and Components. Micromachined Antennae. Integration and Packaging for RF MEMS Devices. Index.

RF MEMS and their applications

This book gives the fundamental principles and device design techniques for surface acoustic wave filters. It covers the devices in widespread use today: bandpass and pulse compression filters, correlators and non-linear convolvers and resonators. The newest technologies for low bandpass filters are fully covered such as unidirectional transducers, resonators in impedance element filters, resonators in double-mode surface acoustic wave filters and transverse-coupled resonators using waveguides.The book covers the theory of acoustic wave physics, the piezoelectric effect, electrostatics at a surface, effective permittivity, piezoelectric SAW excitation and reception, and the SAW element factor. These are the main requirements for developing quasi-static theory, which gives a basis for the non-reflective transducers in transversal bandpass filters and interdigital pulse compression filters. It is also needed for the reflective transducers used in the newer devices. It is a thorough revision of a classic on surface acoustic wave filters first published in 1985 and still in print. It uniquely combines easy-to-understand principles with practical design techniques for all the devices in widespread use today. It includes complete coverage of all the latest devices which are key to mobile phones, TVs and radar systems; and, a new foreword by Sir Eric Albert Ash.

Surface Acoustic Wave Filters: With Applications to Electronic Communications and Signal Processing

In this paper, novel in-plane acoustic reflectors are proposed to enhance the quality factor (Q) in lateral-mode micromachined resonators. Finite element coupled-domain simulation is used to model anchor loss and to estimate the relative change in the resonator's performance without and with the inclusion of acoustic reflectors. Several 27 and 110 MHz AlN-on-silicon resonators are fabricated and measured to validate the theoretical and simulated data. An average Q enhancement of up to 560% is reported for specific designs with reflectors over the same resonators without reflectors. The measured results trend well with the simulated data and support that the acoustic reflectors can reduce the overall anchor loss with minimum modification in the resonator design.

https://iopscience.iop.org/article/10.1088/0960-1317/21/8/085021/pdf

In-plane acoustic reflectors for reducing effective anchor loss in lateral?extensional MEMS resonators

A survey is given of SAW sensor systems. Three categories of sensors are defined as transit-time, resonator and chirp-type devices and each category is subdivided into active and passive signal-processing systems. In these, the mechanical change of the SAW device is evaluated by difference measurements of the transit time, phase or resonance frequency, which are described quantitatively. To show the high resolution of active sensor systems, an electronic spirit level (based on SAW resonators) is described. New SAW chirp sensors allow the dispersive interdigital transducer or reflector geometry to be adjusted to the sensor system resolution and measurement range. In passive systems the sensor device is connected to an antenna. The SAW is excited by an interrogating radio impulse. After a SAW transit time, the sensor radiates back to the interrogator an impulse containing the sensor's information. The time and frequency response of all sensor categories and the possibilities of temperature compensation are discussed.

Mechanical sensors based on surface acoustic waves

Due to more and more stringent requirements on SAW filter performance, it is mandatory to precisely characterize the SAW propagation characteristics as a function of manufacturing variations (metal thickness, mark-to-space ratio, etc.). Several authors have already proposed experimental characterizations using sets of test devices. One of the main difficulties of this experimental approach is the accuracy of both the geometrical and electrical measurements. On the other hand, precise numerical methods have been developed to advantageously replace experiments. Generally speaking, these methods are CPU time consuming. However, due to the continuing improvement of computer power, they are becoming more and more time efficient when applied to the analysis of SAW filters. The overall efficiency depends on the numerical integration methods used. In this paper we present a review of the numerical programs that have been developed during the past few years. For both infinite and finite grating modeling, we developed numerical mixed FEM/BEM (Finite Element Method-Boundary Element Method) models using an efficient interpolation function basis that takes into account the singularity at both edges of each electrode. First we propose a model for the simulation of finite transducers with arbitrary geometries. This numerical code has been successfully used to analyze a SPUDT (Single Phase UniDirectional Transducer) on the Y+36/spl deg/ cut of LiTaO/sub 3/. For an infinite periodic grating, it is convenient to solve the propagation problem in the Fourier domain (wave number space and harmonic excitation) and important efforts have been spent to properly integrate the so-called periodic harmonic Green's function. Using this numerical model together with the general P-matrix formalism, it is possible to compute all the basic parameters with a very good accuracy: these consist of the single strip reflectivity, acoustic wave-phase velocity, and phase offset between reflection and transduction centers. Simulations and comparisons with experiments are shown for each model.

Numerical methods for SAW propagation characterization

An overview of surface acoustic wave (SAW) filter techniques available for different applications is given. Techniques for TV IF applications are outlined, and typical structures are presented. This is followed by a discussion of applications for SAW resonators. Low-loss devices for mobile communication systems and pager applications are examined. Tapped delay lines (matched filters) and convolvers for code-division multiaccess (CDMA) systems are also covered. Although simulation procedures are not considered, for many devices the theoretical frequency response is presented along with the measurement curve. >

SAW devices for consumer communication applications

The most frequently used models for surface acoustic wave (SAW) devices are the impulse model, the equivalent circuit models, the Coupling-of-Modes model, and the matrix models. While the impulse-model is only a first order model the other models include second order effects, e.g. reflections, dispersion, and charge distribution effects. The influence of diffraction and refraction on the transfer function of a SAW filter can be described by the angular spectrum of straight-crested waves model. A survey of these different models will be given. The simulation of low-loss filters requires flexible analysis tools, which can cope with different geometries and substrates. Operating with a parameter set, which depends only on the substrate crystal and not on the specific geometry of the SAW filter, is advantageous. Due to the high insertion attenuation of conventional transversal filters the requirements on the accuracy of the analysis are focused on S21, whereas for low-loss filters all elements of the S-matrix are important. The comparison of simulations with a P-matrix model, which fulfills the above mentioned prerequisites, and measurements of different types of low-loss filters, e.g. SPUDT, DMS, and transverse-mode coupled resonator filters are presented

Review of models for low-loss filter design and applications

For years linear optimization algorithms have been used successfully in bandpass filter design. This method has been adopted for the design of pulse compression filters with low time-bandwidth products. In the bandpass filter design, the sidelobe level in the frequency domain is optimized for a fixed impulse response length. In case of the design of a low time-bandwidth product filters, we optimize the sidelobe suppression in the time domain for a fixed overall bandwidth. We get the optimum time response for a given frequency bandwidth and width of the compressed pulse. The spurious time response is minimized. The corresponding optimum frequency response is split up onto expander and compressor, each consisting of two chirped and apodized IDTs. As an example, an expander-compressor pair at 350 MHz with a 3 dB bandwidth of approximately 11 MHz, an overall bandwidth of approximately 33 MHz, and a chirp time of 1.0 ms was designed. The sidelobe suppression in the design is better than 40 dB. The measured filters exhibit a sidelobe level close to -40 dB. Design and measurement are in excellent agreement

Optimum design of low time-bandwidth product SAW filters

Reflective structures consisting of arrays of single or interconnected metallic strips exhibit surface to bulk wave conversion at frequencies above a certain threshold frequency The resulting attenuation of the reflected SAW-signal due to bulk wave losses is of concern, if either very low loss (VLL) filters have to be built, or if a well defined, potentially small amount of reflectivity is desired In contrast to traditional simulation methods for reflectors, we employ a self-consistent approach based on the Green's function formalism Its main advantage is the fact that the finite extent of the grating as well as surface wave-bulk wave interaction are both taken into account accurately We discuss the bulk wave conversion properties of open, shorted and mixed (so called open-shorted) finite reflectors made of strips in strictly periodic or chirped arrangement, and the design of bulk wave conversion gratings

Surface wave to bulk wave conversion in SAW reflectors on strong coupling substrates

This paper shows how the spurious transverse mode response of a two-port SAW resonator can be accurately determined by the method of vector-valued Signal Flow Graph analysis. We demonstrate that the occurrence of transverse modes is primarily determined by the transversal width of the resonator's cavity and the angle-dependent reflection factor of the grating for which we give an approximation obtained from a one-dimensional grating model. Beside the transverse mode response, this method also allows us to predict the diffraction-induced resonator loss and shift in center frequency. The measured responses of several resonators with different apertures and cavity lengths are compared with simulations. Excellent agreement between theory and experiment is obtained

K.C. Wagner

Papers

SAW devices for consumer communication applications

Review of models for low-loss filter design and applications

Optimum design of low time-bandwidth product SAW filters

Surface wave to bulk wave conversion in SAW reflectors on strong coupling substrates

Signal flow graph analysis of transverse modes in a two-port SAW resonator