Jiaru Chu

A Novel Wet Etching Process of Pb(Zr,Ti)O3 Thin Films for Applications in Microelectromechanical System

The wet etching of Pb(Zr,Ti)O3 (PZT) thin films has gained considerable attention in microelectromechanical systems (MEMS) since it is economical and effective compared with dry-etching methods. In this paper, a novel wet-etching process is proposed for PZT thin film patterning using 1BHF:2HCl:4NH4Cl:4H2O solution as the etchant, where NH4Cl is used as an additive to decrease the undercutting of the obtained PZT pattern. According to energy dispersion spectroscopy (EDS) analysis and X-ray diffraction (XRD) patterns, PbClF particles were left as residues on the substrate after etching using 1BHF:2HCl:4NH4Cl:4H2O solution. Therefore, an additional 2HNO3:1H2O etching process was applied to convert PbClF to PbCl2, which can be dissolved completely in deionized water. This process exhibits a high etching rate (0.016 µm/s) and good selectivity over the photoresist and Pt bottom electrode. Using this technique, PZT patterns with acceptable undercutting (1.5:1) can be obtained.

Design, fabrication and characterization of a bulk-PZT-actuated MEMS deformable mirror

This paper describes the design, fabrication and characterization of a bulk-PZT-actuated MEMS deformable mirror (DM). An analytical model was employed to optimize the DMs structure. The fabrication techniques for PZT thick film actuators were also experimentally explored, including the bonding of bulk PZT ceramics and a silicon wafer by epoxy resin, and the thinning of the bulk PZT ceramics using a wet-etching method. A 10 × 10 array of 1.75 mm × 1.75 mm PZT thick film actuators was successfully fabricated. The PZT actuators showed a stroke of about 4.5 µm at 100 V. When a 36 µm thick silicon membrane mirror was assembled, the measured mirror deflection at 100 V was approximately 3.8 µm. The assembled DM showed an operating frequency bandwidth of 21 kHz and an influence function of approximately 30%. The displacement hysteresis was greatly eliminated by using the method of staying on the same segment.

Preparation of a high-quality PZT thick film with performance comparable to those of bulk materials for applications in MEMS

High-quality lead zirconate titanate (PZT) thick films have been prepared on silicon substrates by combining PZT–Si bonding and wet-etching technology. The bulk PZT wafer was first bonded to the silicon substrate using a 2 µm thick intermediate layer of epoxy resin with a bonding strength higher than 10 MPa. Then the bulk PZT was thinned by a wet-etching method. The thickness of the final PZT films depends on the etching time. The PZT thick films after being polished showed a surface roughness of about 20 nm (RMS), which can satisfy most of the requirements in MEMS. The prepared PZT thick films show a dielectric constant as high as 2400 below 100 kHz, remnant polarization of 13 µC cm−2, piezoelectric constant d31 of about −280 pm V−1 and Youngs modulus of about 63 GPa. The measured electromechanical properties of the PZT thick films were comparable to those of the corresponding bulk ceramics. This approach makes it possible to obtain high-quality PZT films because it separates the PZT wafer fabrication from the target substrate and consequently allows integration of the PZT thick films onto many kinds of substrates. Finally, a self-sensing bulk PZT thick film actuator was fabricated as an example of a basic PZT–Si diaphragm structure that can be used in piezoelectric micropumps, and its sensing and actuating performances were also demonstrated.

Preparation of Thick Pb(Zr, Ti)O3 (PZT) Film by Electrostatic Spray Deposition (ESD) for Application in Micro-System Technology

A Pb(Zr, Ti)O3 (PZT) thick film was prepared by electrostatic spray deposition (ESD) using a sol-gel solution as the precursor. The steady spray, which is suitable for large area and uniform PZT film deposition, can be achieved at an applied electric potential of 4500 volts and solution flow rate of 0.6 ml/h for the 0.4 M sol-gel PZT solution. The use of 100-nm-thick sol-gel PZT as a buffer layer affected the ESD-deposited PZT films nucleation and growth behavior and enhanced the PZT (100) orientation. By using sol-gel PZT as the intermediate layer to increase the density of the ESD-deposited PZT film, the relative dielectric constant of as high as 960 can be achieved. Our primary results proved that ESD is a promising method for the preparation of thick PZT films with good piezoelectric properties.

Microstructure and electrical properties of Pb(Zr, Ti)O3 thick film prepared by electrostatic spray deposition

Abstract Strongly pervoskite (1xa00xa00)-oriented lead zirconate titanate (PZT) films were prepared by the electrostatic spray deposition (ESD). The microstructure and crystalline-granular texture of the films were investigated by scanning electron microscope (SEM) and atomic force microscope (AFM), respectively. The films deposited at substrate temperature of 25xa0°C and 100xa0°C were found to have the same crystallite-size distribution around 150–200xa0nm. With given properties of the spray cloud and the precursor solution, well-crystallized PZT thick films with dense microstructure can be obtained at low deposition temperature. The relative dielectric constant of the 2xa0μm thick ESD-deposited PZT films with sol–gel PZT films as intermediate layers was as high as 960. The films also exhibit excellent remanent polarization and coercive fields of 12.5xa0μc/cm2 and 32xa0kV/cm, respectively.

Influences of environmental humidity on micro object handling efficiency

Micro object handling efficiency is a noteworthy problem since automated assembly systems have been developed for batch assembly. Efficiency is significantly influenced by the environmental humidity because the adhesion forces between two contacted micro objects are affected by that. We constructed a humidity-controllable micro assembling system to handle objects of tens to hundreds of microns in size by adhesion forces. In experiments, micro polymer spheres and silicon-nitride-coated micro spheres were handled on the silicon substrate and gold-covered substrate under various humidity conditions. The results indicate that both the contact interface cracking process and the adhering process during micro object handling are remarkably affected by the environmental humidity. The micro object release success rate increases with the environmental humidity, and the pickup success rate also shows a tendency to increase but followed by a rapid decrease. Our experimental results can be utilized to instruct the selection of environmental parameters for various micromanipulators. It is possible to obtain a satisfactory handling efficiency by controlling the environmental humidity in a proper range. For our adhesive type manipulator, the best handling efficiency will be obtained when the environmental relative humidity is between 65% and 85%.

Fabrication of thick Pb(Zr,Ti)O 3 (PZT) films by modified sol–gel methods for application in MEMS

Pb(Zr,Ti)O 3 (PZT) films with thickness ranging from 2 μm to 10 μm have successfully been prepared using the sol-gel-based ceramic-ceramic 0-3 composite method, polyvinylpyrrolidone (PVP)-assisted sol-gel method and electrostatic spray deposition (ESD) with satisfied film properties on Pt/Ti/SiO 2 /Si substrate. Using PVP and PZT powders as additives, the critical thickness of sol-gel derived PZT film can be sufficiently increased to 0.9 μm and 0.5 μm, respectively. The crystal-orientation of the films was investigated by X-ray diffractometer. It was found that the use of buffer layer was effective to affect the films nucleation and growth behavior and enhance the pervoskite (100) orientation. According to the atomic force microscope images, these films exhibit uniform grain size distribution. The relative dielectric constants of the film prepared by these modified sol-gel techniques, 1050, 600 and 960, were measured, which are satisfied for application in MEMS.

Design and simulation of a microheater actuated by a PZT microcantilever for high density data storage

Abstract In this paper, a microheater actuated by a Pb(Zr,Ti)O 3 microcantilevers array was designed for parallel high density data storage with high data rate and long lifetime. The mechanisms of thermomechanical data writing and heat dissipation from the microheater were studied. The heat conduction through the cantilever to the base was found to be the dominant fact of heat dissipation, and the effects of the other two modes, convection and radiation, can be omitted. A 3D model of the microcantilever was built in ANSYS 5.7 and several simulations of the microheater thermal behavior were executed. As a result, an electrical pulse of 15xa0V in level, 0.2xa0μs in duration with a period of 10xa0μs is found to be a promising driving signal for the designed structure. The top temperature of the tip is about 200xa0°C, which is believed to be effective for softening polymethylmethacrylate film. Within the period of 10xa0μs, the tip can be cooled down to near the room temperature.

Anodic oxidation of polycrystalline 3C-silicon carbide thin films during MEMS operation

In this paper, we provide the first report of corrosion occurring at the anode of polycrystalline 3C-silicon carbide MEMS electrodes under high relative humidity and applied voltage. This unusual phenomenon is determined to be electrochemical in nature. Electrode pair and canary wire corrosion behavior are investigated to yield a detailed evaluation of the stability and oxidation rate during corrosion. The effects of film stress on anodic oxidation are discussed, and suggestions to prevent damage due to corrosion are presented.

Vortex-induced Vibration Control by Micro Actuator

The control of vortex-induced vibration of two side-by-side circular cylinders in a cross flow is carried out experimentally. One cylinder is elastically supported and the other is fix-supported at both ends. The two cylinders vibrate under the action of the unsteady flow-induced forces. A micro actuator is embedded on the surface of each cylinder to perturb the boundary layer. The spacing ratio is set at 1.2. The measurement shows that the structural vibration can be suppressed significantly when the reduced excitation frequency is around 2.655.