Lateral Field Excitation Device Research Articles

Resonance Analysis of Piezoelectric Bulk Acoustic Wave Devices Based on YCOB Crystals with Monoclinic Symmetry Excited by Lateral Electric Fields

The monoclinic YCOB crystal still maintains good piezoelectric properties at 800 °C; thus, it has a good application prospect in high-temperature piezoelectric acoustic wave sensors. However, due to the lower symmetry compared crystals in trigonal and tetragonal systems, the exciting characteristics of piezoelectric plates based on monoclinic YCOB crystals are more complicated. The vibration analysis model of lateral-field-excitation (LFE) devices based on monoclinic crystals is scarce; thus, the coupling relationships between different vibration modes and energy-trapping characteristics of the devices are unclear, which hinders the optimal design of devices. In this paper, by using Mindlin plate theory, the high-frequency vibrations of piezoelectric resonators based on monoclinic YCOB crystal plates excited by a lateral electric field are modeled and analyzed. The coupling relationships between the vibration modes of the device are clarified. The influences of the electrode width, electrode/plate mass ratio and electrode gap value on resonances and energy-trapping characteristics of the device are achieved. In addition, the effects of the structure parameters on the mass sensitivity of the monoclinic YCOB LFE devices are investigated, which are further verified by FEM simulations. The results are crucial to obtaining good resonance and sensing characteristics for LFE high-temperature piezoelectric sensors based on crystals with monoclinic symmetry.

Bulk Acoustic Wave Characteristics of Pseudo Lateral-Field-Excitation on LGT Single Crystal for Liquid Phase Sensing.

In the present study, pseudo lateral-field-excitation (LFE) bulk acoustic wave characteristics on LGT crystals are investigated to increase the sensitivity of LFE devices on the liquid characteristic variations. The cut orientation of LGT crystals for pseudo-LFE is investigated and verified experimentally. For an LFE device in the pseudo-LFE mode, the thickness shear mode wave is excited by the thickness field rather than the lateral field. The present work shows that when the (yxl) 13.8° LGT plate is excited by the electric field parallel to the crystallographic axis x, it operates in the pseudo-LFE mode. Moreover, characteristics of devices including the sensitivity and impedance are investigated. The present work shows that sensitivity of LFE devices to variation of the conductivity and permittivity of the aqueous solution are 9 and 3.2 times higher than those for AT-cut quartz crystal based devices, respectively. Furthermore, it has been found that the sensitivity of the LGT LFE sensor to liquid acoustic viscosity variations is 1.4 times higher than the one for the AT-cut quartz sensor. The results are a critical basis of designing high-performance liquid phase sensors by using pseudo-LFE devices.

Double-mode lateral-field-excitation bulk acoustic wave characteristics of Ca3TaGa3Si2O14 crystals.

The double-mode lateral-field-excitation (LFE) bulk acoustic wave characteristics of Ca3TaGa3Si2O14 (CTGS) crystals are investigated. It is found that LFE devices based on (yxl)-57° CTGS crystals can work on both pure-LFE and pseudo-LFE modes when the driving electric field direction is normal to the crystallographic x axis of the piezoelectric substrate. Several double-mode LFE bulk acoustic wave devices based on CTGS crystals are designed and tested. The experimental results conform to the theoretical prediction well. Being able to operate in pure-LFE and pseudo-LFE modes, the double-mode LFE sensors show high sensitivity to both mechanical and electrical property changes of analytes. The results provide the crystal cut for double-mode LFE sensors, which is a critical basis of designing high-performance chemical and biological sensors by using double-mode LFE devices.

Structure ordered Ca3TaGa3Si2O14 crystal-based liquid phase sensors with enhanced stability and sensitivity

In this study, lateral-field-excitation (LFE) bulk acoustic wave sensors based on the structure ordered Ca3TaGa3Si2O14 (CTGS) crystal are investigated. It is found that LFE devices using (yxl)-6° CTGS crystal can operate with the pseudo-LFE mode. The impedance characteristics and sensitivities of the devices are measured and compared with the LFE devices based on structure disordered langasite (LGS) crystal. The experimental results show that the CTGS LFE sensor can achieve higher Q-factors than the LGS LFE sensor, which indicates that the former has higher frequency-stability. In addition, the CTGS LFE sensor is nearly 2 times more sensitive to both liquid conductivity and permittivity changes compared to the LGS LFE sensor. For liquid acoustic viscosity changes, the CTGS LFE sensor is approximately 1.3 times more sensitive than the latter. In some chemical and biological analysis process, mechanical and electrical property changes of analytes need to be measured simultaneously, therefore the LFE sensors based on the structure ordered CTGS crystal have a good potential for use in liquid-phase sensing of chemical and biological systems.

Investigation of Pure-Lateral-Field-Excitation Bulk Acoustic Wave Sensor with Different Electrodes on (yxl)89° LiNbO<sub>3</sub> Single Crystal

Lateral field excitation (LFE) acoustic wave devices, which employ two electrodes on the same surface of a piezoelectric substrate, have been found attractive in sensing applications. However, up to now, the sensitivities of pure-LFE devices based on LiNbO3 single crystal is unknown. In this work, the effective LFE exciting electric field direction of (yxl)89° LiNbO3 is determined. The calculated results showed that when the driving electric field direction is perpendicular to the crystallographic X-axis of the piezoelectric substrate, (yxl)89° LiNbO3 LFE device works on pure-LFE mode. Based on this, several LiNbO3 pure-LFE bulk acoustic wave sensors with three different electrodes are designed and fabricated. The results show that the (yxl)89° LiNbO3 LFE sensor with interdigital electrodes is 11.1 times and 2.2 times more sensitive to changes in liquid conductivity compared to traditional LFE devices with single gap circular electrodes and Archimedes spiral electrodes, respectively. The results are important for investigating high-sensitivity LFE bulk acoustic wave sensors by using LiNbO3 single crystal.

Lateral-field-excited bulk acoustic wave sensors on langasite working on different operational modes

Lateral-field-excited (LFE) bulk acoustic wave sensors on langasite working on different operational modes are investigated and compared. Langasite LFE sensors on pure-LFE mode and pseudo-LFE mode are designed and fabricated. The sensitivities of the devices to changes in liquid electrical properties (e.g., conductivity or permittivity) and micro-mass changes on their surfaces were tested and compared. The experimental results show that compared with langasite pure-LFE devices, langasite pseudo-LFE devices have superior sensitivities to both liquid conductivity and liquid permittivity changes. For the micro-mass changes, the pure- LFE devices showed high sensitivity, whereas the pseudo-LFE devices do not, because they cannot resonate in air. On this basis, the physical interpretation of these results is discussed.

Impedance analysis for lateral field excited acoustic wave sensors

Lateral field excitation (LFE) acoustic wave devices have been recently investigated for liquid sensing applications. In the present study, the impedance characteristic of the LFE devices working in three operational modes was analyzed. The impedance of the pure-LFE coupling device at resonance can be equivalent to that of a Butterworth–Van Dyke circuit (BVD). It is found that the ( yxl)-16.51° LiTaO 3 LFE device has a much smaller resonance impedance in air due to the large LFE coupling factor and high dielectric constant. For the AT-cut quartz LFE device, there is no significant resonance peak observed in air due to the large resonance impedance. An equivalent circuit was present and used to analyze the impedance of the pseudo-LFE coupling device operating in liquids. It was well explained why the common used AT-cut LFE device is super sensitive to liquid electric property changes compared to a thickness-field-excited (LFE) device. The impedance changes in a single LFE-configuration device, working in a quasi-LFE mode, were also analyzed. And, the experiment results show that the impedance change at the resonance excited by the TFE is much larger than by the LFE in different concentrations of NaCl and 2-propanol water solutions.

Lateral field excited Y-cut langasite bulk acoustic wave sensor

Previous studies have shown that lateral field excited (LFE) devices on AT-cut quartz are sensitive to liquid electrical property changes. AT-cut quartz LFE devices have low piezoelectric coupling factors. To further improve electrical sensitivities of LFE sensors, it is necessary to study LFE sensors based on other piezoelectric materials with higher coupling factors. In this paper, LFE sensors on Y-cut langasite, which has twice the higher piezoelectric coupling factor of AT-cut quartz, are investigated. Several Y-cut langasite LFE sensors are designed, fabricated, and tested. The experimental results show that the devices are over 6 times more sensitive to liquid conductivity changes and about 2.5 times more sensitive to liquid permittivity changes compared to AT-cut quartz LFE devices. It was also found that the Y-cut langasite LFE devices are about 1.3 times more sensitive to changes in liquid acoustic viscosity compared to the AT-cut quartz LFE devices.

Lateral field excitation properties of langasite single crystal

In this work, bulk acoustic wave propagation properties of langasite single crystal excited by lateral electric field have been investigated. Three important crystal cuts have been identified for different operational modes of lateral field excitation (LFE) on langasite substrate, namely the (yxl)65° (pure-LFE mode), (yxl)45° (quasi-LFE mode), and (yxl)0° (pseudo-LFE mode). Devices on langasite substrate with the above cuts were fabricated and tested, and the experimental results agree well with the theoretical analysis. It is found that a pure thickness shear mode exists in the (yxl)65° langasite LFE device with the bare side facing liquid, and no spurious mode is found due to its moderately large piezoelectric coupling factor. In addition, (yxl)0° langasite LFE device is also found suitable for liquid phase sensing applications.

Energy-trapping mode in lateral-field-excited acoustic wave devices

We have analyzed the energy-trapping phenomenon of the thickness-shear vibration in lateral-field-excited (LFE) acoustic wave devices based on elastic wave propagation theory and the cutoff frequency. The standard LFE device does not support the energy-trapping effect, which is significantly different from thickness-field-excited devices. However, energy trapping in LFE devices can be achieved by placing an additional mass-loading layer in the gap region between the two working electrodes. A 5 MHz energy-trapping LFE device is fabricated and tested. The experimental results are in close agreement with the theoretical analysis.

Lateral-field-excitation properties of LiNbO3 single crystal

LiNbO3 has been found attractive for lateral field excitation (LFE) applications due to its high piezoelectric coupling. In this paper, bulk acoustic wave propagation properties for LiNbO3 single crystal excited by a lateral electric field have been investigated using the extended Christoffel–Bechmann method. It is found that the LFE piezoelectric coupling factor for c mode reaches its maximum value of 95.46% when Ψ = 0° for both (yxl)-58° and (yxwl)±60°/58° LiNbO3. The acoustic wave phase velocity of c mode TSM (thickness shear mode) changes from 3456 m/s to 3983 m/s as a function of Ψ. Here Ψ represents the angle between the lateral electric field and the crystallographic X-axis in the substrate major surface. A 5 MHz LFE device of (yxl)-58° LiNbO3 with Ψ = 0° was designed and tested in air. A major resonance peak was observed with the motional resistance as low as 17Ω and the Q-factor value up to 10353. The test result is well in agreement with the theoretical analysis, and suggests that the LFE LiNbO3 device can be a good platform for high performance resonator or sensor applications.