Bill J. Hunsinger

Unusual Parametric Effects on Line Acoustic Waves

Absrruct-Line acoustic wave (LAW) devices, in which waves are guided in a narrow region along an edge, permit one to achieve high local strains with relatively Little total power. One would expect to observe strong harmonic generation and parametric conversion, resulting from the fust-order elastic nonlinearity. However, first-order nonlinear effects are nulled out to a high degree by the symmetry properties of the LAW. Conventional pumping produces only small effects and second harmonic generation is weak. Pumping at one-half the usual frequency, however, interacts with the seconderder nonlinear elastic coefficient which is not subject to nulling and produces useful outputs which increase rapidly at higher frequencies. Experimental results obtained with a LiNb03 LAW device at 100 and 200 MHz are presented.

SURFACE WAVES CIRCULATING ON PIEZOELECTRIC SUBSTRATES

Surface waves circulating on closed paths have been observed on lithium niobate and quartz crystals. More than 12 circulations on a 25‐μsec quartz delay line have been achieved providing processing times in excess of 300 μsec. Surface‐wave attenuation and reflection which vary with the surface curvature are reported.

Numerical model for electrical charge injection in the acoustic charge-transport device

A two dimensional model is developed to study the electrical charge injection process at the input of a GaAs buried-channel acoustic charge-transport device. The model allows for nonuniform impurity doping profiles, variable epitaxial layer configurations, and arbitrary structural designs of the input electrode architecture. The acoustic wave potential is incorporated as a time- and space-varying doping density that adds directly to the impurity doping density. The wave-induced doping density is obtained from the piezoelectric displacement charge that accompanies the acoustic wave. The partial differential equations which form the mathematical basis of the charge injection process are derived from the semiconductor transport equations and solved numerically. The algorithm for simulating charge injection and the results of a simulation are presented. This model provides a means for characterizing the electrical performance of the acoustic charge-transport device input circuit in terms of device physics. >

Canceling Surface Acoustic Wave Reflections from Metallic Strips on GaAs Using a Bimetal Geometry

Ahstmcr-The magnitude of surface wave reflections from metallic electrodes may be reduced by employing a bimetal geometry. Material properties’of the substrate and metals are used to determine the required electrode composition. Various reflector may devices were fabricated on semi-insulating GaAs substrates and the measured reflection coefficients are presented. This bimetal technique is expected to be useful for eliminating spurious signals due to reflections in SAW signal processing devices.

SPATIAL MODULATION OF LIGHT USING SURFACE WAVES IN AN INTERFEROMETER

An optical phase grating has been generated by introducing surface waves on one face of a Fabry‐Perot interferometer. This device called SWIM (Surface Wave Interference Modulator) produces a diffraction pattern at the Fourier plane in which the light intensity of the first‐order modulated beam is 1% of the zeroth order with an acoustic power of 0.85 mW/mm beam width. First‐order intensities greater than 10% have been realized; however, the process is not linear at this modulation depth.

A note on the determination of the diffraction pattern of interdigital surface-wave devices [Correspondence]

The diffraction pattern of piezoelectric surface waves generated by interdigital grids corresponds closely to a Fresnel diffraction pattern. A simple method for calculating this diffraction pattern and determining the direction of energy flow is shown and compared with experimental measurements.

SURFACE WAVE COUPLING THROUGH A FLUID INTERFACE

A method to determine the coupling length for optimum transfer of surface wave energy from one substrate through an interface to a second substrate is presented. Less than 10 dB of energy loss is measured for coupling surface waves (20 MHz) on Y cut Z propagation (YZ) lithium niobate substrates through a water interface.

Input I-V and sampling time characteristics of the ACT device

The input I-V and sampling-time characteristics of the acoustic charge transport (ACT) device are presented for ohmic-contact charge injection and Schottky-gate-modulated charge injection. A computationally efficient analysis technique is developed to calculate the I-V and sampling-time data from two-dimensional potential and carrier-density distributions. Device physics and architecture are incorporated into the analysis through a numerical charge-injection model which is used to compute the potential and carrier-density distributions. Theoretical results are presented to demonstrate the charge injection characteristic of some typical device structures. The effects that the injection method, the epitaxial layer structure and the acoustic wave amplitude have on device performances are discussed. The physical basis of the analysis enables it to be used to study several other design parameters. Experimental measurements of a device I-V and input transconductance show good agreement with calculated data. This analysis technique provides a means of assessing the performance potential of new device designs. >

Optical Probing of HF Guided Wave Surface Displacements with Arbitrary Profile

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Analysis of an Interferometer with Acoustic Surface Waves on One Mirror

It has been demonstrated that surface waves propagating on one mirror of an interferometer form an optical diffraction grating. Experimentally confirmed analyses of an interferomet er with 95.5% reflectivity mirrors now indicate that a surface wave power density of 0.028 mW/mm.MHz is required to diffract 1% of transmitted light into the first order beam. This power can be diminished by a factor of more than 20 by increasing the mirror reflectivity to 99%.