Dependence of SAW resonator 1/f noise on device size

Experiments were conducted with eight 450-MHz surface acoustic wave (SAW) resonators which demonstrate that a resonator's 1/f noise depends approximately inversely on the active acoustic area of the device. This observation is consistent with a proposed theory that 1/f noise in acoustic resonators is caused by localized velocity or dimensional fluctuations.     

Surface-related phase noise in SAW resonators

With the advent of nanotechnologies, electronic devices are shrinking in thickness and width to reduce mass and, thereby, increase frequency and speed. Lithographic approaches are capable of creating metal connections with thickness and lateral dimensions down to about 20 nm, approaching the molecular scale. As a result, the dimensions of outer particles are comparable with, or even larger than, those of active or passive regions in electronics devices. Therefore, directing our attention toward the effect of surface fluctuations is of practical significance. In fact, electronic device surface-related phenomena have already received more and more attention as device size decreases. In connection with surface phase noise, selection of a suitable device with high surface sensitivity is important. In this paper, high Q-value surface acoustic wave resonators were employed because of their strong sensitivity to surface perturbation. Phase noise in SAW resonators related to surface particle motion has been examined both theoretically and experimentally. This kind of noise has been studied from the point of view of a stochastic process resulting from particle molecular adsorption and desorption. Experimental results suggest that some volatile vapors can change flicker noise 1/f and random walk noise 1/f ². An analysis has been made indicating that these effects are not associated with Q value variation, but are generated by the change in the dynamic rate of adsorption and desorption of surface particles. Research on particle motion above the device substrate might explain the differences observed from the model based only on the substrate itself. Results might lead to a better understanding of the phase noise mechanism in micro-electronic devices and help us to build oscillators with improved performance     

Conversion of 1/f fluctuations in crystal resonator within an inter resonance gap

This paper presents general relationships for transformation coefficients of BAW or SAW crystal resonator amplitude and phase fluctuations through the 1/f flicker noises of its motional and static equivalent parameters within the resonator inter resonance gap. Approximate functions of phase and amplitude power spectral densities are found based on Leeson's oscillator open loop model and are given with detailed consideration of Butler and Colpitts modes of operation with the assumption of full and zero inter noise correlation. It is also substantiated that a low-noise frequency region of crystal resonator operation exists in which the fluctuation influence of its motional inductance and capacity tend to zero in oscillators. Five examples are given as an illustration of a good agreement of the measured data with the prediction curves, giving a possibility of resonator power phase and amplitude spectral densities valuation at an arbitrary offset frequency from the carrier through the 1/f flicker noises of resonator parameters. Emphasis is laid in conclusion on the possible way of parameter spectral densities definition.     

1/f noise in etched groove surface acoustic wave (SAW) resonators

Measurements of 1/f (or flicker) frequency fluctuations in SAW resonators fabricated with etched groove reflectors on single crystal quartz have shown that the observed noise levels vary inversely with device size. These measurements were made on sixteen 450 MHz resonators of four different sizes. The 1/f noise levels were also evaluated on twenty-eight other SAW resonators ranging in frequency from 401 to 915 MHz. This additional data provides valuable information on the dependence of the flicker noise levels on resonator frequency. A model based an localized, independent velocity fluctuations in the quartz is proposed which correctly fits the observed size and frequency dependence of the measured 1/f noise levels. This model suggests that the velocity fluctuations originate in small regions (much less than ~5 mum in diameter) randomly distributed throughout the quartz with an average separation of about 5 mum between independent (incoherent) sources. The magnitude of the localized fractional velocity fluctuations, Deltav/v, averaged over a 5 micron cube is on the order of 1x10 (-9).     

The use of linear programming for the design of SAW filters andfilterbanks

A linear programming algorithm is proposed for designing surface acoustic wave (SAW) filters or filterbanks with arbitrary amplitude and phase responses. A modified sampling theorem representation is employed for the transducer frequency responses which allows the number of independent variables to be minimized without degrading the filter characteristics. The method can also be used as part of an iterative procedure to generate optimal corrections for second order effects such as diffraction and circuit loading. A simplified algorithm for this procedure is given, and the method is illustrated with theoretical and experimental data from a three channel contiguous SAW filterbank design. Although the method given in this paper is formulated primarily for SAW filters, it is equally applicable to FIR digital filter design     

Optimization of broadband withdrawal weighted interdigital transducers for high selective SAW filters

The problem under discussion is the design of highly selective broadband surface acoustic wave (SAW) interdigital transducers (IDT) with uniform electrodes. In most SAW filters, such transducers are used with apodized IDTs or instead of them. The proposed optimization algorithms are intended for improvement of IDT selectivity by means of a withdrawal weighting (WW) technique. Unlike the familiar methods of WW transducer optimization, these algorithms choose the best IDT structure on the basis of how well it meets the specifications, not in the time but in frequency domain directly. This approach is more effective for broadband WW transducers. A number of SAW filters have been designed using the described algorithms. Their experimental characteristics follow: bandwidths of 0.5 to 15%, stopband rejection of 40 to 50 dB, 3 dB/40 dB shape factors of 1.07 to 1.3.     

Platinum and palladium high-temperature transducers on langasite

There is a pressing need for the fabrication of surface acoustic wave (SAW) devices capable of operating in harsh environments, at elevated temperature and pressure, or under high-power conditions. These SAW devices operate as frequency-control elements, signal-processing filters, and pressure, temperature, and gas sensors. Applications include gas and oil wells, high-power duplexers in communication systems, and automobile and aerospace combustion engines. Under these high-temperature and power-operating conditions, which can reach several hundred degrees Centigrade, the typically fabricated aluminum (A1) thin film interdigital transducer (IDT) fails due to electro and stress migration. This work reports on high temperature SAW transducers that have been designed, fabricated, and tested on langasite (LGS) piezoelectric substrates. Platinum (Pt) and palladium (Pd) (melting points at 1769 degrees C and 1554.9 degrees C, respectively) have been used as thin metallic films for the SAW IDTs fabricated. Zirconium (Zr) was originally used as an adhesion layer on the fabricated SAW transducers to avoid migration into the Pt or Pd metallic films. The piezoelectric LGS crystal, used as the substrate upon which the SAW devices were fabricated, does not exhibit any phase transition up to its melting point at 1470 degrees C. A radio frequency (RF) test and characterization system capable of withstanding 1000 degrees C has been designed and constructed. The LGS SAW devices with Pt and Pd electrodes and the test system have been exposed to temperatures in the range of 250 degrees C to 750 degrees C over periods up to 6 weeks, with the SAW devices showing a reduced degradation better than 7 dB in the magnitude of transmission coefficient, /S21/, with respect to room temperature. These results qualify the Pt and Pd LGS SAW IDTs fabricated for the above listed modern applications in harsh environments.     

A multi-IDT input tunable surface acoustic wave filter

Tunable surface acoustic wave (SAW) filters (TSF) have been widely used in the wireless telecommunication systems. A prototype of multi-IDT (interdigital transducer) input TSF has been developed. The device consists of 11 IDTs paralleled in the SAW propagation path. Different SAW filter configurations are realized by selecting or combining various IDTs, resulting in the tunability of both center frequency and 3 dB bandwidth. The center frequencies of the SAW filter range from 126.8 to 199.1 MHz; the 3 dB bandwidths range from 15.2 to 58.9 MHz. Impedance weighting methods have been applied. The passband ripple has been reduced from 6.44 to 1.37 dB after resistance weighting     

Influence of leaky surface acoustic wave velocity of glass substrates on frequency variation of ZnO/glass SAW filters

During the manufacture of ZnO/glass surface acoustic wave (SAW) filters, two kinds of problems sometimes arise. One is that the average frequency of the SAW filters changes greatly depending on the production lot of glass sheets. The other is that SAW filters made from the same production lot of glass sheets have largely separated double peaks in the frequency distribution. Previously, it had been considered that the frequency variation of ZnO/glass SAW filters depended on such factors as the ZnO film thickness and its elastic quality. The authors focused on the glass substrates as the cause of this variation and measured the leaky SAW (LSAW) velocity on the glass substrates using an ultrasonic microscope to clarify the mechanism. As a result, it was clarified that the LSAW velocities on the glass substrates showed a large variation within and between production lots of glass sheets, and the frequency of ZnO/glass SAW filters largely depended on the LSAW velocity on glass substrates. Moreover, the authors clarified the cause of the difference in the LSAW velocity between glass substrates and were able to reduce the variation of the LSAW velocity.     

Influence of step-like portions on the surface of ZnO/glass SAWfilters on their frequency characteristics

The frequency amplitudes of surface acoustic wave (SAW) filters mass produced of zinc oxide (ZnO) films on glass were found to be different among the filters even when their center frequencies are the same. We attempted various experiments In order to reduce the deviation of amplitudes. We accidentally found that the frequency characteristics and the amplitude deviation could be improved by mirror-polishing the ZnO film surface. In a SAW filter with a ZnO/interdigital transducer (IDT)/glass substrate structure, periodic step-like portions due to the thickness of the finger electrode of IDT and fine roughness were present on the ZnO film surface. As a result of investigating the effect of surface structure on amplitude deviation, the step-like portions did not affect the electromechanical coupling factors but reduced the SAW phase velocities, experimentally and theoretically. In addition, it was clarified that the step-like portions due to the finger electrodes and fine roughness on the ZnO surface caused deviations in the SAW velocities and their reflections, causing the deviation in the amplitude characteristics     

Differential phase shift keying direct sequence spread spectrum single SAW based correlator receiver

This paper presents the design and measurement of a SAW device to be used in a correlator receiver for a differential phase shift keying direct sequence spread spectrum (DPSK/DSSS) system. The DPSK modulation format allows noncoherent data demodulation while the SAW device correlator acts as the despreading operator. In a conventional DPSK receiver, the received signal is normally split into a lower and upper path. One of the paths contains a correlator, and the other path contains a one data bit delay element and another correlator. The outputs of both paths are then fed to a noncoherent data demodulator. The device presented in this paper combines both the delay element and the two correlators in a single SAW device; therefore, a better temperature tracking mechanism, simplicity, as well as the elimination of the broadband SAW delay line are achieved. The SAW structure contains a broadband SAW transducer, and two serially coded pseudo noise (PN) DPSK filters. The SAW based correlator was built on lithium tantalate. The center frequency was set to 150 MHz, with a 63 chip PN spreading code and a data rate of 300 Kbps. Experimental measurements of the SAW device autocorrelation results are presented.     

On the 1/f frequency noise in ultra-stable quartz oscillators

The frequency flicker of an oscillator, which appears as a 1/f3 line in the phase noise spectral density, and as a floor on the Allan deviation plot, originates from two basic phenomena, namely, (1) the 1/f phase noise turned into 1/f frequency noise via the Leeson effect, and (2) the 1/f fluctuation of the resonator natural frequency. The discussion on which is the dominant effect, thus on how to improve the stability of the oscillator, has been going on for years without giving a clear answer. This article tackles the question by analyzing the phase noise spectrum of several commercial oscillators and laboratory prototypes, and demonstrates that the fluctuation of the resonator natural frequency is the dominant effect. The investigation method starts from reverse engineering the oscillator phase noise in order to show that if the Leeson effect was dominant, the resonator merit factor Q would be too low as compared to the available technology.     

SAW focusing by circular-arc interdigital transducers on YZ-LiNbO(3)

Using the angular spectrum theory and experimental velocity data of surface acoustic waves (SAW) on YZ-LiNbO(3), the focusing characteristics of a circular-arc interdigital transducer have been demonstrated. The calculated results show that the depth of focus is long and the compressed acoustic beam width is very narrow. The concept of a caustic is shown to be an excellent way of characterizing SAW focusing by a circular-arc interdigital transducer on YZ-LiNbO(3). Comparison between theoretical and experimental results shows good agreement.     

SAW quadrature binary modulation system applications

A surface acoustic wave (SAW) modulation system has been built, using a combination of a digital message sequence, an impulse driver, and different SAW modulator filters, for experimental testing of a wide variety of quadrature binary modulation schemes. The RF testbed is described and characterized for system distortion, dynamic range, and spurious responses, and system optimization is discussed. Nine different SAW modulator filters having different time- and frequency-domain responses were designed and fabricated for use in the system. Several of the designs are representative of new modulation schemes which offer better spectral confinement; and time-domain envelope uniformity than MSK. The results obtained with the designed SAW quadrature binary modulation system are presented. Excellent agreement between time- and frequency-domain measurements and theoretical predictions using the SAW modulation system are shown.     

The highly sensitive optical measurement of absolute SAW amplitudes for power flow analysis

The established optical method for the measurement of surface acoustic wave (SAW) amplitudes (simple probing) has been modified to result in the effective separation of scattered light from the SAW-diffracted light by means of two single mode optical fibers. In this way, the photodetector noise is drastically reduced, and absolute SAW amplitudes of 10/sup -12/ in can be detected easily. Using an additional precise measurement of the nondiffracted light by means of fiber shifting, the SAW amplitudes can be calibrated with an error of less than 3%. This method can be applied to deliver an accurate power flow analysis in SAW devices. As an example, for a YZ-LiNbO/sub 3/ transducer, the measured and calculated SAW power densities were found to agree within better than 6%.     

Recognition of organic solvents molecules by simultaneous detection using SAW oscillator sensors and optical fiber devices coated by Langmuir-Blodgett cadmium arachidate films

Surface acoustic waves (SAW) 433 and 315 MHz, two-port resonator-based oscillators coated with a Langmuir-Blodgett (LB) thin layer of chemosensitive cadmium arachidate (CdA) provide highly sensitive chemical acoustic sensors for detection and monitoring of organic vapors, at room temperature. LB CdA film-coated silica optical fibers (SOF) have been successfully fabricated and studied for organic solvents molecules sensing applications. The sensing performance of both types of acoustic and optical transducers has been compared for detecting six molecular species. Simultaneous measurements of frequency changes (delta f) and optoelectronic signal changes (deltaV) of the LB CdA film assembled onto SAW sensors and SOF devices have been realized for organic vapors recognition purposes. Six molecular species such as ethanol, methanol, isopropanol, ethylacetate, acetone, and toluene have been identified and recognized by a specific index (deltaf/deltaV), which can be considered a characteristic property of the chemosensitive material. The discrimination of the six molecular species examined also has been obtained by chemical patterns using a couple of specific index (deltaf433/deltaV; deltaf315/deltaV) measured by combining SAW 433 or 315 MHz oscillators and SOF sensing devices. Transient responses, calibration curves, intertransducer relationships, and chemical patterns are presented and discussed.     

Microwave interferometry: application to precision measurements and noise reduction techniques

A concept of interferometric measurements has been applied to the development of ultra-sensitive microwave noise measurement systems. These systems are capable of reaching a noise performance limited only by the thermal fluctuations in their lossy components. The noise floor of a real time microwave measurement system has been measured to be equal to -193 dBc/Hz at Fourier frequencies above 1 kHz. This performance is 40 dB better than that of conventional systems and has allowed the first experimental evidence of the intrinsic phase fluctuations in microwave isolators and circulators. Microwave frequency discriminators with interferometric signal processing have proved to be extremely effective for measuring and cancelling the phase noise in oscillators. This technique has allowed the design of X-band microwave oscillators with a phase noise spectral density of order -150 dBc/Hz at 1 kHz Fourier frequency, without the use of cryogenics. Another possible application of the interferometric noise measurements systems include “flicker noise-free” microwave amplifiers and advanced two oscillator noise measurement systems     

Surface acoustic wave characterization of PECVD films on galliumarsenide

Surface-acoustic-wave (SAW) measurement techniques can be effectively used to determine the acoustic properties of dielectric and piezoelectric films. Such films can be used for the development of semiconductor-integrated microwave-frequency surface and bulk acoustic wave devices. The acoustic properties of silicon nitride, silicon oxynitride, silicon carbide, and TEOS glass, deposited by plasma-enhanced chemical-vapor-deposition (PECVD) on GaAs, have been characterized using linear arrays of SAW interdigital electrodes operating in the harmonic mode over the frequency region from 30 MHz to above 1.0 GHz. The elastic constants of these amorphous films have been determined by fitting theoretical dispersion curves to the measured SAW velocity characteristics. Frequency-dependent SAW propagation-loss values have been determined from the observed linear change in loss as a function of transducer separation. Preliminary measurements of the temperature coefficient of frequency (TCF) for SAW propagation of the films on GaAs are also given     

Analysis of frequency response of IDT/ZnO/Si SAW filter using the coupling of modes model

A monolithic integration of filters on Si or GaAs substrates is highly desirable to miniaturize the outer dimensions of the cellular phones. But, direct monolithic integration of surface acoustic wave (SAW) filters is impossible with Si, which is nonpiezoelectric, and difficult with GaAs, which is weakly piezoelectric. One alternative is the deposition of a piezoelectric film on the semiconductor substrate. In this paper, we propose a modified coupling-of-modes (COM) approach, which can be used in the practical design of a layered ZnO/Si SAW filter. This is a dispersive SAW-layered filter, and some of the COM parameters become frequency dependent due to the phase velocity dispersion. The frequency response of the 3-step ladder type ZnO/Si SAW filter is analyzed and compared with the experimental results.     

Noise of piezoelectric accelerometer with integral FET amplifier

Since significant progress has been achieved in the development of low-noise piezoelectric (PE) accelerometers with integral FET amplifiers, detailed noise analysis of the system PE transducer-FET amplifier, and obtaining the engineering formula for its noise floor has become vital. As a result of this analysis, the formula for the noise floor of PE accelerometers in terms of acceleration spectral density is obtained at wide frequency band. Noise floor of the low-noise PE accelerometer comprising low-noise JFET charge amplifiers with some particular parameters of the PE transducer and the JFET amplifier was measured. The theoretical and experimental curves of the PE accelerometer's noise floor have a good correlation with each other at frequencies from 1 Hz to 10 kHz. The contribution of the different noise sources to the overall noise floor is shown. Those noise sources include the mechanical-thermal noise and electrical-thermal noise of the PE transducer and all main noise sources of FET amplifiers: the thermal noise voltage of the FET biasing resistor, the thermal noise of the series resistor between the PE transducer and the gate of the FET, the channel thermal noise voltage, the 1/f noise voltage, and the shot noise current in the gate circuit. At low frequencies, the f/spl les/50 Hz noise floor is determined mainly by the FET biasing resistor's thermal noise and the PE transducer's electrical-thermal noise. At frequencies from about 50 Hz to about 1 kHz, the contribution of the PE transducer's electrical-thermal noise dominates over the amplifier's noise sources by a factor of less than 2. At frequencies above 1 kHz, noise floor is determined mainly by the JFET channel thermal noise and the PE transducer's electrical-thermal noise.