Linear frequency tuning of SAW resonators

Frequency tuning in SAW (surface acoustic wave) resonator-stabilized oscillators is normally accomplished via utilization of a voltage-controlled phase shifter. The design of abrupt junction varactor diode-inductor networks which employ impedance transformation techniques to obtain linear frequency tuning of two-port SAW resonators is reported. The approach is similar to that previously developed for linear tuning of bulk wave, quartz crystal resonators. This technique uses varactor diode parallel inductance to provide a linear reactance versus voltage network, which is effectively connected in series with the resonator motional impedance in order to tune the effective resonator center frequency. Typical tuning ranges are significantly larger than those achievable using the phase shifter approach, and are on the order of 400 ppm for the 320-MHz resonator used.     

Theoretical and experimental mass-sensitivity analysis of polymer-coated SAW and STW resonators for gas sensing applications

Polymer-coated surface transverse waves (STW) resonators have recently been successfully studied for organic gas sensing applications. The first results indicate increased absolute and even relative sensitivity as compared to similar resonators with surface acoustic waves (SAW). However, the gain in sensitivity is accompanied by the adverse effect of an increased attenuation and the advantage frame is difficult to establish quantitatively. In this paper, a new set of experimental samples with Parylene C-coated quartz substrates are studied. The samples are matched in frequency and wavelength. The results are compared and the obtained features explained using available theoretical algorithms for analyzing layered SAW and Love configurations, and a recently developed STW algorithm. The approximate limits of advantageous applicability of the STW resonator gas sensors are discussed.     

Gas sensitivity comparison of polymer coated SAW and STW resonators operating at the same acoustic wave length

Results from systematic gas sensing experiments on polymer coated surface-transverse-wave (STW) and surface-acoustic-wave (SAW) based two-port resonators on rotated Y-cut quartz, operating at the same acoustic wavelength of 7.22 /spl mu/m, are presented. The acoustic devices are coated with chemosensitive films of different viscoelastic properties and thicknesses, such as solid hexamethyldisiloxane (HMDSO), semisolid styrene (ST), and soft allyl alcohol (AA). The sensor sensitivities to vapors of different chemical analytes are automatically measured in a sensor head, evaluated, and compared. It is shown that thin HMDSO- and ST-coated STW sensors are up to 3.8 times more sensitive than their SAW counterparts, while SAW devices coated with thick soft AA-films are up to 3.6 times more sensitive than the STW ones. This implies that SAWs are more suitable for operation with soft coatings while STWs perform better with solid and semisolid films. A close-to-carrier phase noise evaluation shows that the vapor flow homogeneity, the analyte concentration, its sorption dynamics, and the sensor oscillator design are the major limiting factors for the sensor noise and its resolution. A well designed ST-coated 700 MHz STW sensor provides a 178 kHz sensor signal at a 630 ppm concentration of tetra-chloroethylene and demonstrates short-term stability of 3/spl times/10/sup -9//s which results in a sensor resolution of about 7 parts per billion (ppb).     

Design and properties of STW asynchronous resonators on quartz

In a surface transverse wave (STW) asynchronous resonator, grating phase shifters are placed between interdigital transducers and reflectors to obtain the incident and reflected waves in phase, and the resonance frequency is located near the center frequency of the reflectors. In this paper, the scattering matrix method is used for design of such resonators with one dominant longitudinal mode. At a frequency of about 509.5 MHz, insertion loss, and loaded and unloaded quality factors of about 6 dB, 5,300 and 11,000, respectively, were obtained. The measured and calculated parameters of this resonator are in good agreement. Design guidelines and comparison of synchronous and asynchronous resonators are presented. Compared to synchronous resonators, low spurious signals' level, location of the resonance frequency near the center frequency of the reflectors, and simple design method make the asynchronous resonators more attractive for manufacture and practical applications.     

The state of the art of flicker frequency noise in BAW and SAW quartz resonators

Experimental results of the last 15 years are reviewed. Noise properties of crystal filters and oscillators are reported, along with practical measurements. It is shown that the additional phase fluctuations are compensated by frequency fluctuations and vice versa. With the assistance of these theoretical results the flicker and white frequency noise coefficients, h(-1) and h(0), respectively, are plotted versus unloaded Q and carrier frequency f(0) for the measured and published crystal oscillator noise characteristics. The dependence of h(-1) approximately 10(-12.75) Q(2) (u) is verified.     

Imaging of deformed metal surfaces using ion bombardment

The growing interest in studies of ion sputtering is mostly related to the wide application areas of the phenomenon. It offers new ways of forming materials with well-predicted properties such as wear-resistant coatings and amorphous films as well as to develop high sensitivity methods for surface analysis (SIMS) etc. In this paper the features of the ion sputtering of deformed metal surfaces are considered. The change in sputtering yields of a number of metals under mechanical strain is shown, X-ray microprobe analysis enables us to detect enrichment with carbon and silicon atoms and depletion of argon in surface layers of copper and steel samples exposed to argon bombardment. In the binary alloy of Sn_0.13 Cu_0.87 a segregation of the tin and copper atoms in the deformed surface regions was observed. The preferential sputtering and modification of the atom contents in deformed parts of the metal surface causes a pattern contrast on the surface which can be detected visually. An explanation of the observed regularities is given and the opportunities for their application towards the visualization of the locally deformed surface regions are discussed.     

Metallurgical applications of ion implantation and ion bombardment

The physical background to the metallurgy of ion implantation is discussed. For instance, the fate of implanted atoms is considered in the content of the precipitation processes which occur as a consequence of exceeding the solubility limit during implantation.The Metallurgical applications of ion implantation and ion bombardment are discussed under the following headings: surface and interfacial energies, surface applications, superconductivity and void formation.     

Analysis and suppression of side radiation in leaky SAW resonators

This paper discusses side acoustic radiation in leaky surface acoustic wave (LSAW) resonators on rotated Y-cut lithium tantalite substrates. The mechanism behind side radiation, which causes a large insertion loss, is analyzed by using the scalar potential theory. This analysis reveals that side radiation occurs when the guiding condition is not satisfied, and the LSAW most strongly radiates at the frequency in which the LSAW velocities in the grating and busbar regions approximately correspond to each other. Based on these results, we propose a "narrow finger structure," which satisfies the guiding condition and drastically suppresses the side radiation. Experiments show that the resonance Q of the proposed structure drastically improves to over 1000 by suppressing the side radiation, which is three times higher than for a conventional structure. Applying the proposed resonators to the ladder-type SAW filters, ultra-low-loss and steep cut-off characteristics are achieved in the range of 800 MHz and 1.9 GHz.     

Characterization of thin films using heavy ion beams

Thin films are used in many technological applications. The characterization of thin films requires compositional information as a function of sample depth. Ion beam analysis techniques, such as Rutherford backscattering spectrometry and elastic recoil detection (ERD), can provide this information in a uniform way for all elements and as absolute concentrations without relying on standards. These techniques can fully be exploited when projectile beams of heavy ions such as Si or Au are used. This improves the elemental resolution and the depth resolution when compared with standard He ion beam analysis. The use of gas ionization detectors increases detection efficiency and minimizes the beam exposure of the samples, so that the analysis is essentially nondestructive. The sampling depth of a few micrometers makes these techniques ideal for the stoichiometric analysis of the surface region of homogeneous materials and, in particular, thin surface films.     

Enhanced bioactivity of polyvinylidene chloride films using argon ion bombardment for guided bone regeneration

Polyvinylidene chloride (PVDC) is a long chain carbon synthetic polymer. The objective of this study was to improve the bioactivity of PVDC films through surface modification using argon (Ar) ion bombardment to create Ar-modified PVDC films (Ar-PVDC) to address the clinical problems of guided bone regeneration (GBR), which is technique-sensitive, and low bone regenerative ability. First, the effects of Ar ion bombardment, a low temperature plasma etching technique widely used in industry, on PVDC film wettability, surface chemistry, and morphology were confirmed. Next, fibroblast-like and osteoblast-like cell attachment and proliferation on Ar-PVDC were assessed. As a preclinical in vivo study, Ar-PVDC was used to cover a critical-sized bone defect on rat calvaria and osteoconductivity was evaluated by micro-computed tomography analysis and histological examinations. We found that the contact angle of PVDC film decreased by 50° because of the production of –OH groups on the PVDC film surface, though surface morphological was unchanged at 30 min after Ar ion bombardment. We demonstrated that cell attachment increased by about 40 % and proliferation by more than 140 % because of increased wettability, and 2.4 times greater bone regeneration was observed at week 3 with Ar-PVDC compared with untreated PVDC films. These results suggest that Ar ion bombardment modification of PVDC surfaces improves osteoconductivity, indicating its potential to increase bone deposition during GBR.     

Calculation and experimental verification of the acoustic stress at GHZ frequencies in SAW resonators

High power applications of Surface Acoustic Wave (SAW) devices may lead to acoustomigration in their thin metal electrodes, which deteriorates the performance or may even destroy the SAW device. It is confirmed in this paper that the mechanism of acoustomigration is caused by the SAW-induced stress in the metal. The quantitative calculation of this stress will be shown in detail, starting from the widely used P-Matrix model as a standard analysis tool. The combination with the partial wave method (PWM) yields the stress distribution inside the metal. This approach provides the flexibility to determine the stresses for any given point in a SAW device, for any input power, frequency, wavetype, device geometry, or metal layer. In order to confirm the absolute values of the stress components, we calculated and measured displacements as a function of input power and frequency.     

Nonequilibrium structures and decay processes of clusters sputtered by ion bombardment

A phenomenon of fragmentation of clusters sputtered by ion bombardment and containing both stable and metastable states is considered. The suggested kinetic model is based on the competition of three processes: detachment of atoms from metastable and stable states and drift-diffusion transfer from the former to the latter. Major regimes of fragmentation are identified and conclusion is made on the effect of the time of the diffusion transfer on the preexponential factor and fragmentation kinetics equation.     

Absolute energy measurement of heavy ion beams using a resonant time-of-flight system

A resonant time-of-flight measurement system has been put into operation at the ATLAS facility for the determination of the energy of heavy ion beams. The system provides continuous, nondestructive monitoring of the beam energy. The system provides relative energy determination with a precision of . Absolute energy is determined to an accuracy of 10⁻³. A variety of beam tests have been performed to study the properties of the system.     

Effect of particle bombardment on the orientation and the residual stress of sputtered AlN films for SAW devices

We present a study of the effect of particle bombardment on the preferred orientation and the residual stress of polycrystalline aluminum nitride (AlN) thin films for surface acoustic wave (SAW) applications. Films were deposited on silicon (100) substrates by radio frequency (RF) sputtering of an aluminum target in an argon and nitrogen gas mixture. The main deposition parameters were changed as follows: the total pressure from 4 mTorr to 11 mTorr, the N2 content in the gas mixture from 20% to 80%, and the substrate self-bias voltage from -10 V to -30 V. If a sufficiently high negative substrate self-bias voltage is induced, (00.2)-oriented films are obtained over the full ranges of pressure and N2 content. Such films have values of residual stress ranging from -3 GPa to +1 GPa, depending on the deposition conditions. Our results suggest that the energy of the Ar ions colliding with the substrate controls the preferred orientation of the films, whereas the directionality of the ions (for the same energy) is the main factor determining the residual stress. To demonstrate the suitability of our material for the intended application, SAW filters with good electroacoustic response have been fabricated using AlN thin films with optimized (00.2) orientation and controlled residual stress.