Surface Acoustic Wave Technique Research Articles

Determination of slow surface states in semiconductors by a surface acoustic wave technique

The surface impedance transformation concept is used to describe the attenuation of a surface acoustic wave (SAW) in the presence of a charged semiconductor surface. The slow surface state charges of the untreated semiconductor surface are deduced from a comparison of the theoretical and experimental results.

New specimen design for studying the growth of small fatigue cracks with surface acoustic waves

The study of small surface fatigue cracks in AISI 4140 quenched and tempered steel by a nondestructive surface acoustic wave technique is summarized. A novel cantilevered bending, plate-type fatigue specimen is described that is compatible with the acoustic method. Small cracks are initiated from a 25-μm deep surface pit produced by an electrospark machine. The importance of studying these cracks which closely approximate naturally occurring fatigue cracks is briefly discussed.

Characterization of mercury cadmium telluride surface and interface using surface acoustic wave technique

Hg 1− x Cd x Te is extensively used today as a versatile infrared detector material with increasing importance in the fabrication of focal plane arrays. In this work electronic properties of passivated and unpassivated Hg 1− x Cd x Te surfaces and SiO 2 interfaces are investigated using nondestructive SAW technique. The transverse acoustoelectric voltage (TAV) is monitored across the Hg 1− x Cd x Te sample which is placed in proximity of a LiNbO 3 delay line. The TAV is developed due to the nonlinear interaction between the electric field accompanying SAW, and the free carriers near the Hg 1− x Cd x Te surface. One- and two-beam contactless TAV and surface photovoltage spectroscopy have been carried out to determine the bandgap and thus the alloy composition, x, of Hg 1− x Cd x Te. The subbandgap spectral responses due to interface states energy levels within the bandgap have also been analyzed. The TAV versus voltage measurements are also performed for further investigation of Hg 1− x Cd x Te surface properties such as flatband potential, interface charge and surface state density as a function of location in the energy bandgap. This technique has also been applied to other semiconductors such as Si and GaAs. The above-mentioned parameters and others such as conductivity, generation lifetime and surface generation velocity have been measured for these semiconducting materials. Nondestructive depth profiling of the free carrier concentration and some of the above electrical properties have also been measured. Details of these results with emphasis on the HgCdTe samples are presented.

Characterization of mercury cadmium telluride surface and interface using surface acoustic wave technique

Hg 1− x Cd x Te is extensively used today as a versatile infrared detector material with increasing importance in the fabrication of focal plane arrays. In this work electronic properties of passivated and unpassivated Hg 1− x Cd x Te surfaces and SiO 2 interfaces are investigated using nondestructive SAW technique. The transverse acoustoelectric voltage (TAV) is monitored across the Hg 1− x Cd x Te sample which is placed in proximity of a LiNbO 3 delay line. The TAV is developed due to the nonlinear interaction between the electric field accompanying SAW, and the free carriers near the Hg 1− x Cd x Te surface. One- and two-beam contactless TAV and surface photovoltage spectroscopy have been carried out to determine the bandgap and thus the alloy composition, x , of Hg 1− x Cd x Te. The subbandgap spectral responses due to interface states energy levels within the bandgap have also been analyzed. The TAV versus voltage measurements are also performed for further investigation of Hg 1− x Cd x Te surface properties such as flatband potential, interface charge and surface state density as a function of location in the energy bandgap. This technique has also been applied to other semiconductors such as Si and GaAs. The above-mentioned parameters and others such as conductivity, generation lifetime and surface generation velocity have been measured for these semiconducting materials. Nondestructive depth profiling of the free carrier concentration and some of the above electrical properties have also been measured. Details of these results with emphasis on the HgCdTe samples are presented.

A surface acoustic wave technique for monitoring the growth behavior of small surface fatigue cracks

The theory of Kino and Auld which relates the reflection coefficient of acoustic waves from a crack to its size is summarized. A scattering model is evaluated from this theory concerning the reflection of surface acoustic waves (SAW) from a small surface fatigue crack at a frequency such that the crack depth is much smaller than the acoustic wavelength. Acoustic predictions of crack depth are compared to postfracture measurements of depth for small surface cracks in Pyrex glass, 7075-T651 aluminum, and 4340 steel. Additionally, the minimum detectable crack depth as limited by the acoustic noise level is determined for several typical aluminum and steel alloys. The utility of SAW reflection coefficient measurements for inferring crack depth, crack growth, and crack opening behaviorin situ during fatigue cycling is discussed.

Mechanism of operation and design considerations for surface acoustic wave device vapour sensors

Surface acoustic wave (SAW) devices offer many attractive features for application as vapour phase chemical microsensors. This paper describes the characteristics of SAW devices and techniques by which they can be employed as vapour sensors. The perturbation of SAW velocity by polymeric coating films is investigated both theoretically and experimentally. Highest sensitivity can be achieved when the device is used as the resonating element in a delay line oscillator circuit. A simple equation has been developed from theoretical considerations which offers reasonably accurate quantitative predictions of SAW device frequency shifts when subjected to a given mass loading. In this mode the SAW device behaves very like conventional bulk-wave quartz crystal microbalances except that the sensitivity can be several orders of magnitude higher and the device size can be several orders of magnitude smaller. Detection of mass changes of a few femtograms by a SAW device having a surface area of 10 −4 cm 2 is theoretically possible.

Nondestructive Characterization of RIE Induced Radiation Damage Using Surface Acoustic Wave

AbstractReactive ion etching (RIE) is extensively used as a high resolution pattern transfer process for fabrication of silicon devices. In this work dry etching radiation damage in p-type boron doped, silicon wafers was investigated using a nondestructive surface acoustic wave (SAW) technique. The transverse acoustoelectric voltage (TAV) is monitored across the silicon wafer which is placed in proximity of a SAW delay line. TAV is developed due to the nonlinear interaction between the electric field accompanying SAW and the free carriers near the silicon surface. TAV versus bias voltage (applied across the semiconductor) was obtained to measure the flatband voltage (VFB) shift. The flatband voltage shift of the etched wafer was determined as a measure of the amount of surface charge introduced into the surface by ion bombardment. SiO2films were etched in C4F8and C2H2with 2 W/cm2input power. The ion energy was determined by the self bias dc voltage developed on the cathode. It is shown that a magnetron RF discharge introduces an order of magnitude less damage than non-magnetron discharge.

Very Fast Signal Processors As a Result of the Coupling of Surface Acoustic Wave and Digital Technologies

The recent progress of the digital and the surface acoustic wave (SAW) technologies have made them compatible; and it is now possible to design signal-processing modules which benefit from the flexibility of the digital techniques and the very high computation speed of the SAW techniques. Very fast signal processors can now be built which are able to process several tens of megasamples per second and whose volume and power consumption are limited. This paper shows the compatibility of these technologies and the advantages yielded by their joint use. Several examples are described which relate to one- and two-dimensional Fourier and correlation processors.

Very Fast Signal Processors as a Result of the Coupling of Surface Acoustic Wave and Digital Technologies

The recent progress of the digital and the surface acoustic wave (SAW) technologies have made them compatible; and it is now possible to design signal-processing modules which benefit from the flexibility of the digital techniques and the very high computation speed of the SAW techniques. Very fast signal processors can now be built which are able to process several tens of megasamples per second and whose volume and power consumption are limited. This paper shows the compatibility of these technologies and the advantages yielded by their joint use. Several examples are described which relate to one- and two-dimensional Fourier and correlation processors.

Growth of Epitaxial ZnO Thin Films by Organometallic Chemical Vapor Deposition

Organometallic chemical vapor deposition of on sapphire, using the reaction of diethylzinc with , , and oxidizing gas systems, has been studied. Epitaxial films have been achieved at temperatures of 400° and 730°C, respectively, in the first two systems. The films have been characterized using scanning electron microscopy (SEM), reflection electron diffraction (RED), and surface acoustic wave techniques.

Contactless monitoring of impurity activation in ion-implanted silicon by surface acoustic wave techniques

The interaction between an implanted layer in silicon and a surface acoustic wave (SAW) traveling on a neighboring piezoelectric was studied, and the resulting transverse acoustoelectric voltage has been found to be an effective indicator of the activation of the implanted species in the silicon lattice obtained during annealing treatments following ion implantation. The method can be used to monitor an entire wafer and is nondestructive.

Determination of capture cross section and surface-states concentration profile using the surface-acoustic-wave convolver

Energy distribution of surface states and majority-carriers capture cross section is determined using the surface-acoustic-wave (SAW) convolver. The semiconductor is placed a small distance above the SAW delay line, with a uniform air gap between the two media. A fast rise time dc pulse is applied across the semiconductor-delay line structure, and the resulting change in the SAW propagation loss is observed. The transient response of the SAW propagation loss represents the emission or trapping of majority carriers from surface states. From this transient response, the capture cross section and the concentration profile of the surface states are determined. The results obtained agree with the already known distribution of fast surface states; it is constant at the middle of the gap and increases towards the conduction band, whereas the capture cross section is constant in the middle of the gap and decreases toward the conduction band. This new SAW technique is simple, sensitive, and requires no contact to the semiconductor surface.

S.A.W. technique of testing piezo-electric semiconductors

A surface Acoustic wave technique of testing piezo-electric semiconductors is described. The various advantages of the techniques are also pointed out.

A processor for pulse-doppler radar

Methods are presented for combining charge-coupled device (CCD) and surface acoustic wave (SAW) techniques to advantage for processing coherent radar signals in order to extract target range and velocity information. Experiments have validated a scheme of combined discrete CCD's to form an analog store with orthogonal input and output sequencing, feeding time-compressed data to a SAW spectrum analyzer. A design for an integrated CCD store is presented.

A processor for pulse-Doppler radar

Methods are presented for combining charge-coupled device (CCD) and surface acoustic wave (SAW) techniques to advantage for processing coherent radar signals in order to extract target range and velocity information. Experiments have validated a scheme of combined discrete CCD's to form an analog store with orthogonal input and output sequencing, feeding time-compressed data to a SAW spectrum analyzer. A design for an integrated CCD store is presented.

The acoustic properties of oxide films and their application to acoustic surface wave devices

Surface acoustic wave techniques represent a powerful tool for the study of the elastic properties of thin film layers. Simple arrays of interdigital transducers can be used to measure the velocity, attenuation, and piezoelectric properties of oxide films. Results of such measurements on zinc oxide and silicon dioxide films are given and the values compared to their bulk counterparts. High acoustic quality oxide films can be used effectively to enhance the performance of surface acoustic wave devices. Potential application areas are briefly summarized.

Acoustic properties of tungsten-vinyl composites : Lees, S., Gilmore, R. S., Kranz, P. R. 20 (January 1973) 1

Surface acoustic wave (SAW) devices offer many attractive features for application as vapour phase chemical microsensors. This paper describes the characteristics of SAW devices and techniques by which they can be employed as vapour sensors. The perturbation of SAW velocity by polymeric coating films is investigated both theoretically and experimentally. Highest sensitivity can be achieved when the device is used as the resonating element in a delay line oscillator circuit. A simple equation has been developed from theoretical considerations which offers reasonably accurate quantitative predictions of SAW device frequency shifts when subjected to a given mass loading. In this mode the SAW device behaves very like conventional bulk-wave quartz crystal microbalances except that the sensitivity can be several orders of magnitude higher and the device size can be several orders of magnitude smaller. Detection of mass changes of a few femtograms by a SAW device having a surface area of 10−4 cm2 is theoretically possible.