Fred S. Hickernell

Acoustoelectronics: history, present state, and new ideas for a new era

The application of high-frequency acoustic devices to the enhancement of electronics saw an extraordinary growth in both Eastern and Western countries in the sixties and seventies. A major impetus for these developments was the tension existing between the Soviet Bloc countries in the east and the former Allied countries in the west. Government military spending on both sides provided funding to explore new acoustoelectronic concepts in universities, institutes, and major defense companies. The direct exchange of visits between scientists and engineers of the East and West was limited until the 1980s, when travel restrictions were lifted on both sides and authors that has previously only been names in the open literature became face-to-face contacts and enjoyed exchanges at conferences of mutual interest. This resulted in a new era of cooperative work between the East and West and a large number of device applications that are seen in electronic systems around the world today. This paper explores the major acoustoelectronic developments of the sixties and seventies from an eastern and western perspective.

Shear horizontal BG surface acoustic waves on piezoelectrics: a historical note

In December of 1968 Jeffrey Bleustein of Yale University published an article predicting the existence of a new type of transverse surface acoustic wave (SAW) that could propagate on the surface of a piezoelectric crystal. This was followed within 20 days by the publication of an article by Yuri Gulyaev in January of 1969 predicting the same basic surface wave propagation. The wave took on the name Bleustein-Gulyaev or BG-wave, joining the names of Rayleigh, Love, Sezawa, and Stonely for distinct types of SAW. But is there more to the story than this? Were there works preceding those of Bleustein and Gulyaev which signaled an interest in exploring a new surface wave mode on piezoelectrics? What about the work of Shimizu, Nakamura, and Ohta, who in April of 1969 published both theoretical and experimental verification of the existence of such a wave independent of the knowledge of the Bleustein and Gulyaev papers? This paper explores the early roots and characteristics of the shear horizontal surface wave on a piezoelectric.

Evaluating Optical Contact Bonds Using Thin-Film ZnO Transducers

The bond integrity between optically bonded fused quartz blocks has been evaluated using ultrasonic waves in the frequency range from 200 MHz to 800 MHz. The ultrasonic waves were produced by thin-film zinc oxide (ZnO) transducers. By excitation of the thin film ZnO transducers on glass blocks of two different thicknesses and optically bonding their free surfaces opposite the transducers, the properties of the bonded area can be evaluated using transmission and reflection loss measurements. The measurements were made using pulse excitation and detection, and spectrum analyzer measurements

Evaluating ZnO thin film transducers by optical contact bonding of glass blocks

Evaluating sputtered ZnO thin film piezoelectric transducers for bulk wave applications has included a wide variety of techniques such as structural, electrical, and insertion loss measurements. The actual excitation, propagation, and detection of ultrasonic waves by the transducers is the most direct and useful criteria for determining transducer performance. By depositing thin film transducers on glass blocks of different thicknesses and optical contact bonding them, the transducers can be evaluated using transmission and reflection loss measurements. ZnO transducers were deposited on aluminum electroded photo-glass mask plates. A transducer matrix was developed with 20 sets of transducers in a 4 by 5 array on 2.36 mm and 1.57 mm thick plates. Each group had four circular electrodes of equal diameter on top of the ZnO with diameters of 0.89, 1.14, and 1.40 mm consistent with obtaining good impedance levels. The ZnO quality across the area was determined by pulse echo techniques. Those having strong piezoelectric activity, were contact bonded and the transmission insertion loss determined under tuned and untuned conditions. The lowest tuned transmission losses through the bonded glass at 500 MHz were 8 dB indicating an individual transducer loss of less than 4 dB. The loss in the glass plates at 500 MHz was approximately 1.0 dB. By characterizing the transducers under optical contact bonding conditions, it is also possible to compare the properties of non-permanent and permanent bonds between the blocks in subsequent tests and how well they approach the optimum bond condition.

P3L-2 The Evaluation of Nonpermanent Acoustic Bonding Agents

Nonpermanent acoustic bonding agents are important for the transfer of acoustic energy between materials. Their use extends over a wide range of applications which encompass industrial, medical, and research applications. One important use has been the characterization of the acoustic properties of solids by bonding transducers or a transducer block configuration to the solid under study. The work reported here characterizes the transfer efficiency of four selected nonpermanent bonding agents in the frequency region from 200 MHz to 800 MHz using two fused quartz blocks with zinc oxide transducers formed at each end and the bond material sandwiched between the blocks. The transfer efficiency is compared to an optical bond condition without the presence of the bond material. The nonpermanent bonding materials studied were glycerol, hysol resin, quartz wax, and black wax with which it was possible to obtain transfer efficiencies near 3 dB of the optically bonded blocks

The characterization of permanent acoustic bonding agents

Permanent acoustic bonding agents are important for affixing transducers to acoustic materials. They are used for electronic, industrial, medical, and research applications. An important research aspect has been the characterization of permanent and nonpermanent bonding materials. The work reported here characterizes the transfer efficiency of selected permanent bonding agents in the frequency region from 200 MHz to 800 MHz using two fused quartz blocks with zinc oxide transducers formed at each end and the bond material sandwiched between the two blocks. The transfer efficiency is compared to an optical bond condition without the presence of the bond material. The permanent bonding materials studied were epoxy type compounds with the best exhibiting transfer efficiencies within a few dB of the optically bonded blocks.

P3G-1 The Evaluation of Nonpermanent Acoustic Bonding Materials Incorporating Micron Size Particles

Nonpermanent acoustic bonding agents are important for the transfer of acoustic energy between materials without permanently bonding them. Their use extends over a wide range of applications which encompass industrial, medical, and research applications. In the case of bonding solids, nonpermanent bonding agents have elastic properties well below those of the solids to which they often are bonded. By increasing the density of the nonpermanent bonding agents their elastic properties come closer to those of the solid materials. The work reported here characterizes the transfer efficiency of selectively loaded nonpermanent bonding agents in the frequency region from 200 MHz to 600 MHz using two fused quartz blocks with zinc oxide transducers formed at each end and the loaded bond material applied between the blocks opposite the transducers. The nonpermanent bonding materials which could be most conveniently loaded with fine particles were waxes and resins. Micron size particles of aluminum oxide, diamond and silicon carbide, were the main particles used. The transfer efficiency is compared to both a bond condition without particle loading and an optical bond condition.

41 Degree lithium niobate: A study of harmonics

Various orientations of Lithium Niobate (LNB) have been used for Surface Acoustic Wave (SAW) devices. This study used 41 degree LNB in order to study the harmonics, loss characteristics, and the characteristics of damping intervening transducers on the free surface LNB. The original objective of this study was to determine how the loss characteristics of the harmonics varied with frequency over the extended frequency region from 40 MHz to 1500 MHz. The secondary objective was the damping of intervening transducers over the frequency region from 40 MHz to over 700 MHz. The frequency characteristics were determined using a double electrode transducer on the 41 degree LNB with a total of 8 transducers. The transducer had electrodes of 15 micron spaces and 10 micron gaps giving a total wavelength electrode spacing of 100 microns. There were 10.5 wavelengths at the fundamental. The study also included various conditions for intervening transducers which allowed the comparison of loss characteristics up to 700 MHz. The results of the study allowed the assignment of an average loss to each frequency. The loss increased with frequency in a systematic manner but the results at certain frequencies were higher loss than anticipated. This resulted in the re-evaluation of the modes of the transducer. Also above 1300 MHz the loss in the SAW mode became lower. As predicted, the PSAW mode loss is lower for the free surface of the 41° LNB.

Discerning the piezoelectric quality of CdS and ZnO crystals and films from etch properties

Several tests have been used over the years to determine the quality of piezoelectric crystals and films. Chemical etching, (destructive to a portion of the crystal or film), reveals information which can be related to its piezoelectric properties. Acid etching of CdS and ZnO crystals and films is highly anisotropic depending upon whether the acid attacks the cadmium-zinc face or the sulfide-oxide face, or laterally to the c-axis. The etch pit density per unit area is a useful parameter for both crystals and films and can be used for comparison with piezoelectric related properties. By controlling the percentage of the acid etchant in water, direct comparisons can be made of film properties under different deposition conditions. This paper presents the results of etching studies on CdS and ZnO crystals and sputtered thin-films with comparisons to their crystalline, piezoelectric, and device properties.

P6H-9 Discerning the Quality of ZnO Films from Their Etch Properties

Several tests have been used over the years to determine the quality of thin film zinc oxide. These tests have included coupling factor measurement, acoustic and optical loss, surface roughness, and grain size. One such test, which is especially useful when establishing the best ZnO deposition condition, is chemical etching. Chemical etching reveals considerable information about the density of the fiber grain structure, the film orientation, film strain, and can be related to coupling factor. Etching ZnO films or crystals is highly anisotropic depending upon whether the acid attacks its zinc face, its oxygen face, or laterally to its c-axis orientation. By controlling the percentage of the acid etchant in water, direct comparisons can be made of the film properties under different deposition conditions. Etch times extend as low as 100 Angstroms per second for ZnO films with dense uniform fiber grains and as high as 1000 Angstroms per second for nonuniform grain structures. This paper will present the results of etching studies on micrometer thick ZnO under a triode system of deposition which can produce very high quality films. Taking into account the etch rates and the etch pit density. Both can be used to predict the quality of the ZnO films for applications.