Advances in Development of Quartz Crystal Oscillators at Liquid Helium Temperatures

This work presents some recent results in the field of liquid helium {bulk acoustic wave} oscillators. The discussion covers the whole development procedure starting from component selection and characterization and concluding with actual phase noise measurements. The associated problems and limitations are discussed. The unique features of obtained phase noise power spectral densities are explained with a proposed extension of the Leeson effect.Comment: Cryogenics, 201

Performance optimization of lateral-mode thin-film piezoelectric-on-substrate resonant systems

The main focus of this dissertation is to characterize and improve the performance of thin-film piezoelectric-on-substrate (TPoS) lateral-mode resonators and filters. TPoS is a class of piezoelectric MEMS devices which benefits from the high coupling coefficient of the piezoelectric transduction mechanism while taking advantage of superior acoustic properties of a substrate. The use of lateral-mode TPoS designs allows for fabrication of dispersed-frequency filters on a single substrate, thus significantly reducing the size and manufacturing cost of devices. TPoS filters also offer a lower temperature coefficient of frequency, and better power handling capability compared to rival technologies all in a very small footprint. Design and fabrication process of the TPoS devices is discussed. Both silicon and diamond substrates are utilized for fabrication of TPoS devices and results are compared. Specifically, the superior acoustic properties of nanocrystalline diamond in scaling the frequency and energy density of the resonators is highlighted in comparison with silicon. The performance of TPoS devices in a variety of applications is reported. These applications include lateral-mode TPoS filters with record low IL values (as low as 2dB) and fractional bandwidth up to 1%, impedance transformers, very low phase noise oscillators, and passive wireless temperature sensors

Strategies for the Accurate Measurement of the Resonance Frequency in QCM-D Systems via Low-Cost Digital Techniques

In this paper, an FPGA (Field Programmable Gate Array)-based digital architecture for the measurement of quartz crystal microbalance (QCM) oscillating frequency of transient responses, i.e., in QCM-D (QCM and Dissipation) applications, is presented. The measurement system is conceived for operations in liquid, with short QCM transient responses due to the large mechanical load. The proposed solution allows for avoiding the complex processing systems typically required by the QCM-D techniques and grants frequency resolutions better than 1 ppm. The core of the architecture is a reciprocal digital frequency meter, combined with the preprocessing of the QCM signal through mixing operations, such as a step-down of the input frequency and reducing the measurement error. The measurement error is further reduced through averaging. Different strategies are proposed to implement the proposed measurement solution, comprising an all-digital circuit and mixed analog/digital ones. The performance of the proposed architectures is theoretically derived, compared, and analyzed by means of experimental data obtained considering 10 MHz QCMs and 200 μs long transient responses. A frequency resolution of about 240 ppb, which corresponds to a Sauerbrey mass resolution of 8 ng/cm2, is obtained for the all-digital solution, whereas for the mixed solution the resolution halves to 120 ppb, with a measurement time of about one second over 100 repetitions

DIRECT VOLTAGE MEASUREMENTS USING BULK ACOUSTIC WAVES IN LiNbO3

Accurate (\u3c 1%) direct measurement of high voltage pulse amplitudes above 10 kilovolts becomes challenging due to voltage breakdown limitations in materials, parasitic impedance effects that can distort the pulse shape, and pickup of extraneous signals resulting from electromagnetic interference effects. A piezoelectric crystal-based bulk acoustic wave sensor using lithium niobate (LiNbO3) that has applications to metrology, research, and power metering was developed to overcome these measurement issues with the factors of scalability, ease of use, and compactness in mind. A Y+36° cut LiNbO3crystal was coupled to two acoustic transducers, where direct current (DC) voltages ranging from 128—1100\u2009V were applied transversely to the crystal. An acoustic wave was used to interrogate the crystal before, during, and after voltage application. Both single and multiple pass measurements were performed and compared to linear piezoelectric theory. A comparison study between Y+36° and 0° X-cut LiNbO3 was performed to evaluate the influence of crystal cut on acoustic propagation. The study was extended to applying alternating current (AC), and pulsed voltages. The measured DC data was compared to a 1-D impedance matrix model that was based on a three port circuit with voltage-induced strain effects inputted as a model parameter. An uncertainty budget was carried out for both crystal cuts and compared. Environmental effects such as pressure and temperature were also measured to determine their influence on the sensor under ambient conditions. Published literature regarding material constants, such as elastic constants and piezoelectric constants, for LiNbO3 do not account for the influence of an electric field. In light of this, measurements of the acoustic velocities and material constants under the presence of a DC electric field were performed up to 896 V. This information was used to develop an uncertainty analysis for the determination of stress-charge form piezoelectric constants e15 and e22. All measured and calculated values were input into a Monte Carlo simulation to determine the error of the strain-charge form piezoelectric constants, dij, and how these new values can be used to predict the voltage sensor response

An Investigation into the Frequency Stability of Non-oven Controlled Crystal Oscillators

Temperature induced frequency deviation of quartz crystal oscillators can be reduced by tuning the oscillator to compensate for the thermal effects. A varactor tuned AT cut resonator is typically used to make a voltage controlled crystal oscillator. Compensation is then achieved by applying a "compensation voltage" to the varactor. The earliest compensation circuits comprised resistors and thermistors. Over the temperature range -40° C to +85°C resistive compensation circuits have achieved frequency stabilities of approximately + Ippm. Alternative analogue circuits have achieved frequency stability of < +0.5ppm. The research described in this thesis is an investigation of resistive networks in order to improve the levels of stability that can be achieved by this method of temperature compensation for crystal oscillators. The objective was to achieve a stability of < +0.5ppm over the temperature range -40°C to +85°C. Optimisation techniques have been employed to identify a new temperature compensation circuit. This new circuit uses an amplifier with temperature sensitive gain to modify thermistor characteristics and improve the compensation over the high part of the temperature range. Two forms of this circuit are presented. Computer simulation of this circuit has shown that it is capable of achieving frequency stability of < ±0.3ppm in an oscillator operating from a 4.5 V supply over the temperature range -40°C to +85°C

Acoustic Waves

The concept of acoustic wave is a pervasive one, which emerges in any type of medium, from solids to plasmas, at length and time scales ranging from sub-micrometric layers in microdevices to seismic waves in the Sun's interior. This book presents several aspects of the active research ongoing in this field. Theoretical efforts are leading to a deeper understanding of phenomena, also in complicated environments like the solar surface boundary. Acoustic waves are a flexible probe to investigate the properties of very different systems, from thin inorganic layers to ripening cheese to biological systems. Acoustic waves are also a tool to manipulate matter, from the delicate evaporation of biomolecules to be analysed, to the phase transitions induced by intense shock waves. And a whole class of widespread microdevices, including filters and sensors, is based on the behaviour of acoustic waves propagating in thin layers. The search for better performances is driving to new materials for these devices, and to more refined tools for their analysis

Modeling and Experimental Study of Bulk Acoustic Wave Resonator Sensor

Bulk acoustic wave (BAW) resonator as one of the simplest acoustic device, has been proven a most powerful tool for sensor applications with the advantage of precise frequency counting in electronic measurement. Meanwhile, with the improvement of device fabrication and material growth techniques, the resonator can be made with very small size, especially thin film bulk acoustic wave resonators (FBARs) based on ZnO and AlN have been attracted much interest for sensor application due to their high sensitivity induced by high resonance frequency. In this thesis, research focus is on the modeling and experimental study of bulk acoustic wave resonator sensor.Quartz thickness shear mode (TSM) resonator is adopted to characterize the viscoelastic properties of polymer nanocomposite thin films deposited on the resonators surface. The input electric admittance of multilayer loaded TSM acoustic wave resonator is firstly derived using transfer matrix method by taking into account the acoustic wave impedance of the polymeric layer. Nanocomposite thin films of multi-wall carbon nanotubes (MWCNTs) in copolymers of polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE) are deposited on TSM resonators through spin-on coating processing. The electric impedance spectra of the unloaded and loaded acoustic wave resonators are measured experimentally, and a data fitting approach is applied to extract the properties of the polymer nanocomposites films. It has been found that the thickness of the polymer layer plays a very important role in the extraction of the viscoelastic properties of the films through data fitting, and the reinforcement of the elastic shear modulus of polymer nanocomposite films is not significant. Quartz TSM resonator is also investigated for in-situ and real time detection of liquid flow rate. A 5MHz TSM quartz resonator is edge-bonded to the sensor mounting port of a special flow chamber with one side exposed to the flowing liquid and other side exposed to air. The fundamental, 3rd, 5th, 7th, and 9th resonant frequency shift due to flow pressure is found to be around 920 (Hz), 3572 (Hz), 5947 (Hz), 8228 (Hz) and 10300 (Hz) for flow rate variation from 0 to 3000 ml/min, which has a corresponding Reynolds number change from 0 to 822. Both theoretical and experimental investigation shows the resonant frequency shifts of different modes are quadratic with flow rate. The results indicate that quartz TSM resonators can be used for flow sensors with characteristics of simplicity, fast response, and good repeatability.FBARs based on c-axis tilted ZnO and AlN thin films have been theoretically analyzed. Material properties including elastic, dielectric and piezoelectric coefficients, bulk wave properties including acoustic velocity and electromechanical coupling coefficient, and impedance of FBARs are calculated and show strong dependence on the tilt angle of c-axis(¦È).Besides ¦È=90¡ã pure thickness shear mode occurs at 43¡ãfor ZnO and 46.1¡ãfor AlN, besides ¦È=0¡ã pure thickness longitudinal mode occurs at 65.4¡ã for ZnO and 67.1¡ãfor AlN. The electromechanical coupling coefficient of shear mode has a maximum value 13.1% at ¦È=33.3¡ãfor ZnO, and 6.5% at ¦È=34.5¡ãfor AlN; the maximum electromechanical coupling coefficient of longitudinal mode occurs at ¦È=0¡ãwith a value of 8.5% for ZnO, and 6% for AlN. The simulation results show that c-axis tilted ZnO and AlN thin films can provide more options for filter design and sensor application