• Journal of the Korean Vacuum Society
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• v.15 no.6
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• pp.619-623
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• 2006

The most important factor which determines resonance characteristics of FBAR(Film Bulk Acoustic Resonator) is the piezoelectricity of piezoelectric film. The piezoelectric properties of ZnO thin films which is strong as FBAR piezoelectric film is determined by the degree of c-axis preferred orientation with (002) plan. Therefore, many researchers have been interested in the study on the preferred orientation of the piezoelectric thin film. This paper has studied the preferred orientation of ZnO piezoelectric thin films using the helped seed layer of ZnO. The result shows that the c-axis ZnO thin films with columnar grains that the value of standard $deviation(\sigma)$ of XRD rocking curve is of $\sigma=1.15^{\circ}$ have the excellent piezoelectric property.

• Structural Engineering and Mechanics
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• v.42 no.5
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• pp.677-699
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• 2012

This article studies the secondary resonances of a clamped-clamped microresonator under combined electrostatic and piezoelectric actuations. The electrostatic actuation is induced by applying the AC-DC voltage between the microbeam and the electrode plate that lies at the opposite side of the microbeam. The piezoelectric actuation is induced by applying the DC voltage between upper and lower sides of piezoelectric layer. It is assumed that the neutral axis of bending is stretched when the microbeam is deflected. The drift effect of piezoelectric layer (the phenomenon where there is a slow increase of the free strain after the application of a DC field) is neglected. The equations of motion are solved by using the multiple scale perturbation method. The system possesses a subharmonic resonance of order one-half and a superharmonic resonance of order two. It is shown that using the DC piezoelectric actuation, the sensitivity of AC-DC electrostatically actuated microresonator under subharmonic and superharmonic resonances may be tuned. In addition, it is shown that the tuning domain of the microbeam under combined electrostatic and piezoelectric actuations at subharmonic and superharmonic conditions is larger than the tuning domain of microbeam under only the electrostatic actuation.

• Journal of Satellite, Information and Communications
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• v.6 no.1
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• pp.28-31
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• 2011

In this paper, a new set of structural and sacrificial material that is diamond like carbon (DLC)/photoresist for high performance piezoelectric RF-MEMS switches which are actuated in d33 mode is suggested. To avoid curing problem of photoresist sacrificial layer, DLC structure layer is deposited at room temperature by radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) method. And lead zirconate titanate (PZT) piezoelectric layer is deposited on structure layer directly at room temperature by rf magnetron sputtering system and crystallized by rapid thermal annealing (RTA) equipment. Particular attention is paid to the annealing of PZT film in order to crystallize into perovskite and the variation of mechanical properties of DLC layer as a function of annealing temperature. The DLC layer shows good performance for structure layer in aspect to Young's modulus and hardness. The fabrication becomes much simpler and cheaper with use of a photoresist.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.21 no.6
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• pp.503-508
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• 2008

In order to reduce the piezoelectric field originated from the well layer which resides in InGaN/GaN light emitting diode, InGaN/GaN superlattice buffer layers were grown at the bottom and the top of the active layer. Measuring the photoluminescence spectra with different reverse bias voltages clearly revealed the condition of the flat band under which the transition energy is maximized and the linewidth is minimized. Accordingly, the piezoelectric field of $In_{0.15}Ga_{0.85}N$ in our sample was estimated as -1.08 MV/cm. It is less than half the value reported in the previous studies, and it is evidenced that the strain has reduced due to the superlattice buffer layers.

• Journal of the Korean Society for Precision Engineering
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• v.19 no.11
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• pp.120-128
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• 2002

Interfacial cracks in a piezoelectric layer bonded to dissimilar elastic layers under the combined anti-plane mechanical shear and in-plane electrical leadings are considered. By using Fourier cosine transform, the mixed boundary value problem is reduced to a singular integral equation which is solved numerically to determine the stress intensity factors. Numerical results for the effects of the material properties and layer geometries on the stress intensity factors are obtained.

• Smart Structures and Systems
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• v.4 no.1
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• pp.35-46
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• 2008

In this paper the authors address the problem of comparing two different smart damping techniques using the numerical modelling of the electro-mechanical impedance for plate structures partially treated with active constrained layer damping treatments. The paper summarizes the modelling procedures including a finite element formulation capable of accounting for the observed behaviour. The example used is a smart cantilever plate structure containing a viscoelastic material (VEM) layer sandwiched between a piezoelectric constrained layer and the host vibrating plate. Comparisons are made between active constrained layer and active damping only and based on the resonance frequency amplitudes of the electrical admittance numerically evaluated at the surface of the piezoelectric model of the vibrating structure.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2000.04a
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• pp.204-209
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• 2000

It is the first step to establish the exact vibration model of the structure when constructing the smart structure with desired vibration scheme. In this paper, vibration model of beam with piezoelectric element boned on the surface is presented by considering the thickness effect of the bond layer. In contrast to the previous papers which neglect the effect of bond layer, the presented vibration model considers the effect of bond layer assuming the prefect bond condition. The perfect bond condition is tested by comparing the controllability of beams with three types of bond layer. An optimal vibration control of the beam can be performed when there exists perfect-bond condition between the piezoelectric element and the main structure.

• Advances in nano research
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• v.13 no.3
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• pp.233-245
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• 2022

Resently, the use of smart structures has been heightened up rapidly. For this issue, vibration analysis related to a graphene nanoplatelet composite (GPLRC) nanodisk which is attached to a piezoelectric layer and is subjected to thermal loads is explored in the current paper. The formulation of this study is obtained through the energy method and nonlocal strain gradient theory, and then it is solved employing generalized differential quadrature method (GDQM). Halpin-Tsai model in addition to the mixture's rule are utilized to capture the material properties related to the reinforced composite layer. The compatibility conditions are presented for exhibiting the perfect bounding between two layers. The results of this study are validated by employing the other published articles. The impact of such parameters as external voltage, the radius ratio, temperature difference, and nonlocality on the vibrational frequency of the system is investigated in detail.

• Structural Engineering and Mechanics
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• v.89 no.6
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• pp.571-578
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• 2024

The bistable thin cylindrical shell is developable structure with the ability to transition between its two stable configurations. This structure offers significant potential applications due to its excellent deformability. In this paper, the composite thin cylindrical shell consisting of the composite layer and the piezoelectric layer was investigated. The material and geometric parameters of the shell were found to influence its stable characteristics. The analysis model of the composite thin cylindrical shell incorporating the piezoelectric layer was developed, and the expressions for its strain energy were derived. By applying the minimum energy principle, the impact of the electric field intensity on the bi-stable behaviors of the cylindrical shell was analyzed. The results showed that the shell exhibited the bistability only under the appropriate electric field strength. And the accuracy of the theoretical prediction was verified by simulation experiments. This study provides an important reference for the application of deployable structures.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.10
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• pp.856-865
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• 2008

Damage mechanisms in bending piezoelectric actuators under electric fatigue loading are addressed in this work with the aid of an acoustic emission (AE) technique. Electric cyclic fatigue tests have been performed up to $10^7$ cycles on the fabricated bending piezoelectric actuators. An applied electric loading range is from -6 kV/cm to +6 kV/cm, which is below the coercive field strength of the PZT ceramic. To confirm the fatigue damage onset and its pathway, the source location and distributions of the AE behavior in terms of count rate and amplitude are analyzed over the fatigue range. It is concluded that electric cyclic loading leads to fatigue damages such as transgranular damages and intergranular cracking in the surface of the PZT ceramic layer, and intergranular cracking even develops into the PZ inner layer, thereby degrading the displacement performance. However, this fatigue damage and cracking do not cause the final failure of the bending piezoelectric actuator loaded up to $10^7$ cycles. Investigations of the AE behavior and the linear AE source location reveal that the onset time of the fatigue damage varies considerably depending on the existence of a glass-epoxy protecting layer.