AT-cut Quartz Crystal Resonator Research Articles

Electro-magnetically enforced rotary barrel finishing for fabricating spherically contoured quartz crystal blanks

Spherically contoured AT-cut rectangular quartz crystal resonators have been fabricated by electro-magnetically enforced rotary barrel finishing system. Shape and frequency responses of the fabricated blanks have also been measured and compared with those of the blanks fabricated without using the electro-magnets. In previous work by the authors, the fixed abrasive method, in which abrasive papers are used instead of powder abrasives, was introduced as a new rotary barrel finishing method for fabricating the spherically contoured rectangular quartz crystal blanks. By adopting the fixed abrasive method, accurate shape transferring, dustless clean working environment, and short turnaround time has been realized. In this paper, in order to further shorten the process time, electro-magnets are used for generating additional machining pressure. As a result, the process time required for complete shape transferring has been decreased to 67% of the turnaround time obtained by previous work.

Tapping mode quartz crystal resonator based scanning force microscopy

We have built a high-speed, tapping mode scanning force microscope using a high frequency quartz crystal resonator. In our design, a cantilever tip was attached to the end of an optical fiber which was glued to a thickness shear mode, AT-cut quartz crystal resonator so as to vibrate in the longitudinal direction. This design allows the microscope to be operated in tapping mode with the flexibility of shear mode operation, which leads to an expected improvement of image quality. Furthermore, combining this geometry with an optical microscope leads to the possibility of commercial applications.

Frequency responses of spherically contoured rectangular AT-cut quartz crystal resonators fabricated by fixed abrasive method

Frequency responses of spherically contoured rectangular AT-cut quartz crystal resonators fabricated by fixed abrasive method have been analyzed experimentally. Not only the required mode, but also many spurious modes can exist on rectangular AT-cut plates. Empirically, in order to eliminate the spurious modes and to achieve high stable and reliable quartz crystal resonators, quartz crystal blanks have been polished into lens-like shape (spherically contoured shape). The spherically contoured blanks have a drastic effect on the decoupling of modes by restricting the vibrating area of the plate within its central region (energy trapping effect). However, a long process time is necessary to fabricate the quartz blanks into spherically contoured shape. In our previous works, a fixed abrasive method has been introduced as a new rotary barrel finishing method for finishing the spherically contoured blanks. In this paper, the frequency responses and the shape of the spherically contoured resonators fabricated with different process times have been presented and discussed. As a result, resonators with very little spurious at 15 MHz within 2 MHz bandwidth have been successfully fabricated.

A thickness-shear quartz resonator force sensor with dual-mode temperature compensation

An AT-cut thickness-shear quartz crystal resonator (QXR) has been used as a force sensing and self-temperature-sensing (STS) element to develop a digital output force sensor. The QXR is fixed in a two-line mounting configuration in a cylindrical metal shell by double diaphragms, through which a diametric force proportional to the unknown force is applied to the QXR. The double diaphragms improve the reliability and the mechanical stability of the sensor significantly. In order to increase the measurement range and the sensitivity, the energy trapping-based QXR is cut to a symmetrical, incomplete circular shape to decrease stress concentration. Because operating the QXR in dual-mode excitation allows the separation of force change effects from temperature change effects, force measurement and STS are accomplished simultaneously with the same QXR. The structure and the configuration are optimized with theoretical analysis and FEM. The dual-mode STS and temperature compensation are described in detail, as well as a trimming method to reduce activity dips of AT-cut QXRs.

SELF-ASSEMBLED MONOLAYER BASED QUARTZ CRYSTAL BIOSENSORS FOR THE DETECTION OF ENDOTOXINS

ABSTRACT A quartz crystal microbalance (QCM) biosensor was developed for the detection of endotoxin (lipopolysaccharide, LPS). Polymyxin B (PMB), which binds to endotoxins of gram-negative bacteria, was immobilized on the self-assembled monolayer (SAM) modified 10 MHz AT-cut quartz crystal resonator. The SAM's were activated with 1-[3-(dimethylamino)propyl]-3-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) prior to PMB immobilization. The resulting frequency change due to the adsorption of endotoxin was measured. The linear correlation could be obtained from 2.5 to 20 pg/mL.

Off-centre load-insensitive digital quartz resonator force sensor

A digital output force sensor has been developed utilising a unique elastic structure and an AT-cut quartz crystal resonator (QXR) based on an energy trapping effect as sensing element. The force-sensitive QXR is preloaded into the elastic structure, through which a force proportional to the applied force is exerted on the QXR, and the force measurement is accomplished by measuring frequency changes. The elastic structure consists of several flexible hinges and has the advantages of no mechanical friction and no clearance, and therefore nonelastic effects of the digital force sensor are minimised. The elastic structure is specially configured to avoid measurement error induced by off-centre loads. To compensate the temperature coefficient of sensitivity, a dual-harmonic-mode self-temperature-sensing method is employed to measure the applied force and the in situ temperature simultaneously with the same QXR. A practical design is developed and the dependence of the measurement range on the elastic structure dimensions as well as the changes of the quality factor of QXR before and after preloading are discussed. FEM simulation and experimental results show that the force sensor has good performance and is insensitive to off-centre load. Detailed specifications of the force sensor are given.

Force-frequency coefficient of symmetrical incomplete circular quartz crystal resonator.

The changes in the resonance frequencies of the thickness-shear vibration of symmetrical incomplete circular AT-cut quartz crystal resonators (QXRs), which are used as sensing elements in digital force sensors or pressure transducers, by the application of diametrical forces are discussed by considering the piezoelectric effect and the anistropic characteristics of crystal plates. Two-dimensional motion equations for predicting the frequency changes are derived from three-dimensional piezoelectricity equations, and equations deduced by Janiaud for solving the stress distribution in crystal plates are used to calculate the force-frequency coefficients of incomplete circular resonators. The results show that the piezoelectric effect of crystal plates decreases the force-frequency coefficient of the azimuth angle 0 degrees by 7% as compared with no piezoelectricity assumption. The incomplete circular shape can be applied to a larger load than the circular disc because the flat regions of the incomplete shape provide a distributed load application without the problems of stress concentration of a point force inherent to a circular disc. The incomplete shape gives an increased force sensitivity when compared with the complete disc near azimuth angle 0 degrees. The theoretical curves agree well with Ratajski's experimental results.

High sensitivity microgravimetric biosensor for qualitative and quantitative diagnostic detection of polychlorinated dibenzo-p-dioxins.

A piezoelectric immunosensor system was developed for the rapid detection of polychlorinated dibenzo-p-dioxins (PCDDs). The system uses a competitive inhibition enzyme immunoassay (EIA) based on a mouse monoclonal antibody that is specific for 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) and a conjugate of a dioxin-like competitor coupled to the enzyme horseradish peroxidase (HRP). The anti-dioxin antibody was deposited on a 10 MHz AT-cut quartz crystal resonator modified with a self-assembly monolayer of dithiobis-N-succinimidyl propionate. PCDDs at different concentrations in the range 0.001-10 ng mL-1 were mixed with a constant amount of HRP-conjugated competitor. The frequency responses due to the adsorption of the mixed samples on the biosensor surface were measured. The results show that 2,3,7,8-TCDD can be quantitatively detected with the developed immunosensor in the concentration range 0.01-1.3 ng mL-1. Cross-reactivities of the biosensor to various PCDD congeners were also investigated. The sensitivity and selectivity of the quartz crystal microbalance (QCM) biosensor is comparable to EIA and ELISA methods in the detection of polychlorinated dibenzo-p-dioxins. The developed QCM immunosensing system offers significant improvements in speed, sample throughout and cost for the qualitative and quantitative detection of PCDDs compared with GC-MS.

Suppression of lower harmonic responses on overtone AT-cut quartz crystal resonators

This paper proposes a method to suppress harmonic responses lower than a specified overtone mode in an overtone quartz crystal resonator, by providing a subelectrode in addition to the main electrode. An analysis is performed assuming isotropic elasticity. It is pointed out that energy trapping in the finite plate is well represented by considering the phase shift of the vibration displacement in the main electrode region. The vibration displacement at the plate edge is calculated, and the equivalent series resistance is estimated. It is found that the vibration displacement of the fundamental mode can be increased more than that of the third overtone mode, by appropriately setting the energy trapping factor. It is also shown that the above tendency is enhanced when the subelectrode is made thicker than the main electrode. An experiment was performed for the 93-MHz third overtone quartz crystal resonator, and it is shown that the oscillator operates without a coil. © 1999 Scripta Technica, Electron Comm Jpn Pt 3, 83(4): 92–102, 2000

Energy trapping behavior of AT-cut quartz crystal resonators with a groove ring on main electrodes

This paper considers an energy trapping AT-cut quartz crystal resonator, and proposes a quartz crystal resonator with a groove ring having a cutoff frequency higher than that of the periphery, located near the outer periphery of the electrode. A numerical analysis is performed from the viewpoint of the purely elastic and isotropic cases. The results are verified by numerical calculation by the three-dimensional finite-element method. It is shown that the following properties are realized for any geometrical parameters of the main electrodes by providing the groove ring structure. (1) The frequency difference between the main resonant frequency and the anharmonic spurious component can be increased on the order of 10%. (2) If the frequency difference between the anharmonic spurious components is kept the same, the displacement of the quartz crystal substrate edge can be reduced by several tens of percent. These properties help to reduce vibration energy leakage from the edge support, and to reduce the size of the quartz crystal resonator. © 1999 Scripta Technica, Electron Comm Jpn Pt 3, 82(4): 48–55, 1999

A 3-Terminal AT-Cut Quartz Resonator with Shield Electrodes

In this paper a 3-terminal AT-cut quartz crystal resonator with shield electrodes is proposed. The resonator has three terminals connected to three electrodes on the quartz substrate. The 1st and 2nd terminals are connected to two main electrodes to drive piezoelectrically, and the 3rd terminal is connected to a shield electrode which is located just outside the main electrodes. The resonator with shield electrodes enables the separation of the intrinsic capacitance from the stray capacitance which affects the increase of effective resistance. Experimental data show fairly good agreement with the intrinsic capacitance predicted by material constants of AT-cut quartz crystal. In the application of oscillators, a common-emitter Colpitz oscillator circuit is proposed in this paper instead of the widely used “common-corrector” one, because the stray capacitance can be included in 2-phase inverting capacitors. Experimental data on the resonator having a 2-divided electrode connected in a lattice with shield electrodes is also presented.

Organic vapor detection using quartz crystal sensors coated by sputtering of porous sintered-polymer targets

A lipophilic hydrocarbon–polymeric film applicable to hydrocarbon gas sensing at the ppm level was prepared by radiofrequency sputtering of a porous sintered-polyethylene (PE) disk on to an AT-cut quartz crystal resonator as a mass transducer. The hydrocarbon polymeric structure was confirmed by hydrogen forward scattering–Rutherford backscattering spectroscopy and X-ray photoelectron spectroscopy. This thickness-shear mode acoustic wave sensor was also sensitive to polar organic vapors owing to the incorporation of 8% of oxygen. Fluoropolymer films without oxygen can also be produced by rf sputtering of a porous sintered-poly(vinylidene fluoride) (PVDF) disk. The sorption behaviors of the PE and PVDF films for 20 ppm primary alcohols showed proportional and inversely proportional relationships, respectively, with the polarizabilities of solute molecules. Although 100 ppm toluene vapor did not induce mechanical damping of the PE film owing to its swelling or softening, its sorption capacity strongly decreased during iterative sorption tests. However, 100 ppm ethanol vapor did not cause such an abrupt decrease in sorption capacity over 10-cycle iterative tests.

Response of a thickness-shear mode quartz crystal resonator upon hydrogel formation

The response of an AT-cut quartz crystal piezoelectric resonator operating in the thickness shear mode (TSM) during polymer gel formation has been examined by acoustic network analysis. The series and parallel resonant frequencies as well as the amplitude and phase of the impedance of the TSM resonator were monitored in real-time when a layer of polyacrylamide gel was formed on one side of the sensor. Various concentrations of radical initiator and crosslinking agents were used to control the rates of polymerization and crosslinking during the hydrogel formation. The increase in the magnitude of the minimum impedance and the decrease in the maximum phase angle were observed as a result of the damping of both the magnitude-frequency and phase-frequency curves, caused by the transformation of the contacting medium from a viscous liquid to a viscoelastic hydrogel. Significant difference was observed between the responses of series and parallel resonant frequencies. The series resonant frequency increases while the parallel resonant frequency decreases during gel formation, and the magnitude of change in the parallel frequency is several times that in the series frequency. Small variations in the gelforming solutions such as the depletion of buffer and addition of double-stranded DNA cause distinct changes in the response profiles of the quartz resonator.

Reviews Of Acoustical Patents

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Ultrasonic micromachining on Al thin film using atomic force microscopy combined quartz crystal resonator

We have developed a novel micro-mechanical modification by combining a quartz crystal resonator and an atomic force microscope which has a very sharp diamond tip mounted on the end of a cantilever. The sample is deposited on the surface of AT-cut quartz crystal resonator which is able to oscillate the surface laterally at its resonance frequency of 5 MHz. The surfaces of the evaporated Al thin films were scratched with x—y scanning of 3 × 3 μm 2 with the loading force of 0.3–18.9 μN, and the topographies of the scratched areas were observed. The hollow areas which were scratched with the surface oscillation were several times deeper than the areas which were scratched without the surface oscillation. The depths of scratched hollows were dependent on the loading force, the repetition numbers of scanning scratches and scanning speed.

Nanometer-Scale Layer Removal of Aluminum and Polystyrene Surfaces by Ultrasonic Scratching

An atomic force microscope combined with a quartz crystal resonator have been employed for nanometer-scale layer removal by ultrasonic scratching. The atomic force microscope has a very sharp diamond tip mounted on the end of a cantilever for surface scratching. Sample thin films are deposited on the surface of an AT-cut quartz crystal resonator which is able to oscillate the surface laterally at its resonance frequency of 5 MHz. Surfaces of aluminum and polystyrene were scratched with x-y scanning of 3×3 µ m2 with a micronewton loading force, and the topographies of the scratched areas were observed. Scratching with surface oscillation can result in deep carving of the surface in spite of a low loading force which is not sufficient for removal of the surface without oscillation. The hollow bottom of the polystyrene surface which was scratched with surface oscillation was obviously flat in comparison with the surface scratched without oscillation.

Stress Sensitivity Distribution Measurement Using a Low-Frequency Sound Wave and Its Application to Quartz Crystal Microbalances

A new method for measuring the stress sensitivity distribution on a resonator surface, including a region without electrodes, using a low-frequency sound wave is described. The experimental results for an AT-cut quartz crystal resonator obtained using the proposed method and the current pulsed-laser method are shown. Additionally, we applied this method to the design of quartz crystal microbalances using multiple resonance modes.

Development of a chemical vapor sensor using piezoelectric quartz crystals with coated unusual lipids

Piezoelectric quartz crystal sensors were developed using lipids with various properties for highly sensitive detection of chemical vapors. Lipids with varying lengths of alkyl chains were coated onto 10 MHz AT-cut quartz crystal resonators and the response of these modified crystals to chemical vapors were measured. It was shown that hydrophilic compounds, such as ethanol and methanol, could be recognized efficiently by lipids having shorter alkyl chains, whereas lipids with longer alkyl chains showed affinity to more hydrophobic vapors, such as toluene, hexane and cyclohexane. Frequency changes caused by adsorption of alcohols could be enhanced when cholesterol was co-immobilized in the lipid layer. To confirm the assumption that the sensor-response might be affected by the properties of lipids derived from acyl chains, we have examined the effects of two types of newly synthesized unusual lipids on sensor response. When lipids having one triple bond each at different positions on their alkyl chains were coated onto quartz crystals separately, lower responses were observed compared to responses obtained for a sensor with immobilized, saturated phosphatidylcholine. Lipids containing α-branched acyl chains, however, showed good affinity for organic vapors, and sensor responses improved 4–5-fold. Moreover, these sensors were shown to have sensitivity of the same order as the humans' sense of smell (10 −5–10 −6 w/w in liquid paraffin) when measured using standard odorants (isovaleric acid, skatole, etc.) for an olfactometry established in Japan.

Silica and polyimide coated quartz crystal resonators for analysis of liquids

Silica and polyimide coatings were successfully applied to both sides of 10 MHz AT-cut quartz crystal resonators with silver and gold electrodes. A similar oscillation was observed for the uncoated and coated resonators in air, deionised water, 0.1 M NaCl and propylene glycol, in terms of the complex impedance analysis. The impedance module decreased with increasing conductance of the surrounding media while the resonant frequency appeared to depend on the liquid viscosity and density. However, differences in the oscillation were evident when these devices were immersed in waste water from a clean room for microelectronic fabrication. Relevant chemical analyses were also made on the waste water samples. Hourly testing results indicated that changes in the impedance were due to metal ions (Na +, K +, Ca 2+, etc.) and the frequency shift comes from the complicated interaction between the solute molecules (propylene glycol) and the coatings or electrodes. This study highlights that the multi-sensors with various coatings and electrodes provide possibilities to monitor waste water in real-time.

Impedence analysis and circuit simulation of quartz resonator in water at different temperatures

A 5 MHz AT-cut quartz-crystal resonator has been totally immersed in distilled water at different temperatures between 5 and 95°C. The oscillation has been characterized by an impedance analyzer around the fundamental frequency. The complex impedance has been found to increase with rising water temperature. An equivalent circuit including inductance, resistance and capacitance has been designed to simulate the experimental data within an error of 3.5%. The simulated parameters (resistance, capacitance, inductance, etc.) have been related to the physical properties of water by comparison with literature data. This fundamental approach results in the realization of a simple and cheap monitor for practical use in continuously detecting the general pollution of waste water in terms of the impedance modulus and resonance frequency of the immersed quartz resonator.