Applications of surface acoustic and shallow bulk acoustic wavedevices

Surface acoustic wave (SAW) device coverage includes delay lines and filters operating at selected frequencies in the range from about 10 MHz to 11 GHz; modeling with single-crystal piezoelectrics and layered structures; resonators and low-loss filters; comb filters and multiplexers; antenna duplexers; harmonic devices; chirp filters for pulse compression; coding with fixed and programmable transversal filters; Barker and quadraphase coding; adaptive filters; acoustic and acoustoelectric convolvers and correlators for radar, spread spectrum, and packet radio; acoustooptic processors for Bragg modulation and spectrum analysis; real-time Fourier-transform and cepstrum processors for radar and sonar; compressive receivers; Nyquist filters for microwave digital radio; clock-recovery filters for fiber communications; fixed-, tunable-, and multimode oscillators and frequency synthesizers; acoustic charge transport (ACT); and other SAW devices for signal processing on gallium arsenide. Shallow bulk acoustic wave (SBAW) device applications include gigahertz delay lines, surface-transverse-wave resonators employing energy-trapping gratings and oscillators with enhanced performance and capability     

Convolution and correlation using light diffraction from bulk acoustic waves

Bulk acousto-optic signal processors using simultaneous light diffraction in high-figure-of-merit materials are described in the letter and some experimental results are reported.     

High-stability acousto-optical devices using bulk acoustic waves in TeO2

Acousto-optical devices are currently being developed for various applications, including laser Doppler anemometers (l.d.a.s.)     

Behaviour of device structures based on IDT-launched bulk acoustic waves in a parallel-sided plate of lithium niobate

We present device responses due to fast shear and longitudinal waves, which propagate between a pair of IDTs on an upper surface via a reflection from the lower surface of a parallel-sided plate of 41°-rotated Y-cut lithium niobate. Single-mode response can be obtained by removing unwanted modes using saw cuts in the crystal substrate. Centre-frequency and bandwidth enhancement of a factor of two or more are achievable compared with the SAW response of the same IDTs.     

Temperature stability of surface-generated bulk waves

Theoretical and experimental analyses have been performed on the temperature stability of a new type of bulk-wave device in which the signal is launched and received by a pair of interdigital transducers located on one surface of a Y-cut quartz crystal. Excellent temperature stability is obtained.     

Visualisation of surface acoustic waves

A simple method for acoustic-surface-wave visualisation is described which is applicable to both piezoelectric and non-piezoelectric surfaces. Briefly, a uniform layer of small particles, comparable to the wavelength, is distributed over the acoustic surface. The acoustic-beam pattern of an incident surface wave is then traced out by scattering the particles out of the propagation path. Experiments at 100 MHz on lithium-niobate surfaces are described.     

Electromagnetic modeling of thin-film bulk acoustic resonators

This paper introduces a novel technique for the electromagnetic analysis of thin-film bulk acoustic-wave resonators. The piezoelectric/acoustic linear equations are coupled to and solved together with Maxwell's equations. For the acoustic propagation, locally monodimensional behavior is assumed, while full-wave three-dimensional Maxwell's equations are rigorously solved for the complete circuit. The proposed approach is validated for single resonators by comparison with experimental data, providing very good agreement with reduced computational resources. Hence, a complete Agilent Technologies' nine-resonator passband filter is simulated in order to demonstrate a typical application to a real-world complex problem.     

An insulated shallow extension structure for bulk MOSFET

This brief proposes possible a replacement of shallow p-n junction with insulated shallow extension (ISE) structure for bulk MOSFET. The shallow extension is defined by the sidewall thermal oxide rather than the implanted p-n junction. With this insulator for extension and main junction, a heavier halo doping concentration can be used. Thus, the threshold-voltage roll-off and the junction leakage current can be minimized simultaneously. This structure can be a good alternative for junction structures in sub-100-nm regimes.     

Optical probing of surface acoustic waves

Light diffraction by surface acoustic waves is used in studying the propagation characteristics of Rayleigh waves on y-cut z-oriented LiNbO3. In reflection, only the surface deformation contributes to the diffracted light. In transmission, the photoelastic effect, which is incident beam polarization dependent, must also be considered. Such optical probing has been used to study the Fresnel diffraction radiation pattern of an interdigital transducer, to measure beam steering effects related to transducer misalignment on an anisotropic substrate, and to measure reflection and transmission coefficients of an electrically loaded transducer. Attenuation measurements have been made over frequencies as high as 3.5 GHz. The power dependence of attenuation and harmonic generation is also examined.     

Wavefront visualisation of acoustic surface waves

Acoustic surface waves (a.s.w.) propagating on yz-cut lithium niobate have been visualised by two imaging techniques. The wavefronts of straight-crested and convergent a.s.w. have been rendered visible on the screen of a storage oscilloscope.     

Surface acoustic waves and SAW materials

Material parameters necessary for optimum design of surface-acoustic-wave (SAW) devices are reviewed. Velocity, coupling coefficient, power flow angle, temperature coefficients, propagation loss (including air loading, diffraction, and beam steering), and equivalent circuit parameters are considered. A brief introduction to the nature of surface waves is followed by sufficient theoretical information to allow full understanding and derivation of the properties and parameters cited above. A convenient tabular summary of important SAW material properties is included.     

Directional coupler using acoustic surface waves

The properties of interdigital transducers have been used to construct a directional coupler. The coupler consists basically of an array of eight transducers etched from an aluminium film deposited on a lithium-niobate substrate. Experimentally, a directivity of 17 dB was obtained at 75 MHz.     

Wavelength-switchable fiber laser using acoustic waves

We report a wavelength-switchable fiber ring laser that includes a Bragg grating-based acoustooptic superlattice modulator. Wavelength switching of the laser emission is achieved by controlling the peak reflectivity of the different reflection bands that appear on both sides of the Bragg wavelength when a longitudinal acoustic wave propagates along the grating.     

Ridge guides for acoustic surface waves

A low-velocity flexural mode has been excited on acoustic-surface-wave topographic guides. With structures offering some hope of realisation at high frequencies, very strong confinement of the guided wave is obtained. Q factors in excess of 1000 have been observed on a ring resonator only ten wave lengths in diameter.     

Image processing using acoustic surface waves

An application of acoustic surface waves for image processing is reported. The information compression of videophone signals takes advantage of the so-called Hadamard transformation. Acoustic-surface-wave tapped delay lines are efficient for the achievement of such a transform in a low-cost real-time device. The results of initial experiments are reported.     

AIN薄膜体声波谐振器性能分析

采用体硅微细加工工艺制备了背空腔型AIN薄膜体声波谐振器。研究了压电层、上电极及支撑层厚度对谐振器性能的影响。测试结果表明，谐振器所用AIN压电薄膜具有（002）择优取向，器件频率特性良好。当上电极、压电层、底电极和支持层的厚度分别为110，2600，110，200nm时，谐振频率为1．759GHz，机电耦合系数3．75％，品质因数79．5。结合Mason等效电路模型模拟分析与实验结果，分析了各层厚度对频率特性的影响机理。     

AlN薄膜体声波谐振器性能分析

采用体硅微细加工工艺制备了背空腔型AlN薄膜体声波谐振器。研究了压电层、上电极及支撑层厚度对谐振器性能的影响。测试结果表明,谐振器所用AlN压电薄膜具有(002)择优取向,器件频率特性良好。当上电极、压电层、底电极和支持层的厚度分别为110,2600,110,200nm时,谐振频率为1.759GHz,机电耦合系数3.75%,品质因数79.5。结合Mason等效电路模型模拟分析与实验结果,分析了各层厚度对频率特性的影响机理。     

Temperature-compensated film bulk acoustic resonator above 2 GHz

Two different types of temperature-compensated film bulk acoustic resonators (FBARs) are designed, fabricated, and tested. One is formed by integrating FBAR with a surface-micromachined air-gap capacitor, which passively reduces the FBAR's temperature coefficient of frequency (TCF) by about 40 ppm//spl deg/C at 2.8 GHz. With this approach, zero TCF would easily have been achieved if the FBARs were built on AlN rather than ZnO. The other type of temperature compensated FBAR is built on a surface-micromachined SiO/sub 2/ cantilever that is released by XeF/sub 2/ vapor etching of silicon. The Al-ZnO-Al-SiO/sub 2/ FBAR is measured to have a TCF of -0.45 ppm//spl deg/C (between 85/spl deg/C and 110/spl deg/C) at 4.4 GHz.