PZT Microcantilever Research Articles

Piezoelectric unimorph microcantilevers for measuring direct and converse piezoelectric coefficients

In this study, we propose a new piezoelectric measurement method using unimorph microcantilevers to evaluate precise values of direct and converse piezoelectric coefficients for piezoelectric microelectromechanical system applications. We fabricated unimorph microcantilevers comprising 3-μm-thick polycrystalline Pb(Zr,Ti)O3 (PZT) thin films on a 20-μm-thick silicon (Si) layer. The converse piezoelectric coefficient was measured as |e31,f| = 3.9–5.8 C/m2, which was in good agreement with the measurement results of PZT thin films without microfabrication. The direct piezoelectric properties of the PZT microcantilevers were measured at the resonance frequency of each microcantilever, and |e31,f| was ∼2 C/m2, which was consistent with previous reports on the piezoelectric properties of a PZT thin film on Si. Since the measurement results included the effects of the stress condition and microfabrication damage, the measurement method of this study can evaluate the actual piezoelectric coefficient of piezoelectric properties in microdevice structures.

New corn-based sacrificial layer for MEMS based on screen-printed PZT ceramics

This paper demonstrates the use of a new screen-printed corn starch-based sacrificial layer that decomposes entirely thermally at ∼550 °C. A comparison with a polyester-based sacrificial layer used in previous work is made. Both are used to make PZT microcantilevers and discs in a fully screen-printed fabrication process. Both designs are released during the sintering of the ceramics at 900 °C using the new sacrificial layer, with porosities of 6.7% and 2.2% for microcantilevers and discs, respectively.

E-beam Evaporated Polysilicon for Lead Zirconate Titanate-Based Micro-Actuators

This letter reports the application of ultra-high vacuum E-beam evaporated polysilicon (UHVEEPoly) film for lead zirconate titanate (PZT)-based piezoelectric micro-electro-mechanical systems (MEMSs) for the first time. The UHVEEPoly film is employed as a passive structural layer in unimorph piezoelectric cantilever micro-actuators to demonstrate its applicability in PZT-based MEMS. Two sets of PZT micro-cantilever actuators have been fabricated and characterized in this letter. The first set has 4- $\mu \text{m}$ -thick UHVEEPoly as a structural layer while the second set is made of $4~\mu \text{m}$ thick single crystalline silicon structural layer obtained from an active layer of a silicon-on-insulator wafer. The static and dynamic behaviors of the two sets of actuators including their initial deflection profiles have been measured and compared. Results confirmed that the two sets of actuators exhibit similar characteristics, indicating the unique suitability of the UHVEEPoly films for realizing PZT-based MEMS that enables a cost effective process and formation of versatile MEMS structures.

Rapid discrimination of DNA strands using an opto-calorimetric microcantilever sensor.

A rapid technique for quantitative detection and discrimination of DNA strands without using immobilized probe molecules is demonstrated using an opto-calorimetric, self-powered sensor based on a Pb(Zr(0.52)Ti(0.48))O3 (PZT) microcantilever. Microcalorimetric infrared (IR) spectroscopy provides excellent chemical selectivity based on the unique molecular vibrational characteristics of each nucleotide in the mid IR region. The piezoelectric and pyroelectric properties of the PZT microcantilever were exploited in the quantitative detection and discrimination of adsorbed DNA strands with their spectral characteristics. We report the unique spectral characteristics of different DNA nucleotides that are monitored by wavelength-dependent temperature variations for different relative molar ratio of each nucleotide. This approach offers a fast, label-free technique which is highly sensitive and selective for the detection of single nucleotide differences in DNA strands and has the potential to be used as a rapid prescreening biosensor for various biomolecules.

Flow sensing and energy harvesting characteristics of a wind‐driven piezoelectric Pb(Zr0.52, Ti0.48)O3microcantilever

Wind flow regarded as a renewable energy source is present everywhere in indoor or open environments. A self-sustained flow-sensing microsystem is especially desirable in future applications of smart home, remote sensing and environmental monitoring. Piezoelectric thin films are commonly adopted in microenergy harvesters for converting the mechanical strain into an electrical charge based on the piezoelectric effect. It is also a promising candidate for flow sensors because of its passive nature, that is, the detectable output charge is a function of flow rate. The aim of this reported work has been to investigate the flow sensing and energy harvesting capabilities of a flexible piezoelectric Pb(Zr0.52, Ti0.48)O3 (PZT) microcantilever under wind flow. A self-sustained flow-sensing microsystem is possible by integrating the arrays of PZT microcantilevers, which measure the flow rate of ambient wind by one microcantilever and scavenge wind-flow energy as a power source by the rest.

Fabrication of a piezoelectric microcantilever array with a large initial deflection and an application to electrical energy harvesting

This paper presents a new method to fabricate a multi-layered PZT microcantilever with a large upward initial deflection and the application for energy harvesting. The upward initial deflection is obtained by asymmetrically distributed residual stresses in the thin multilayer. The numerical analysis is carried out to simulate the upward deflection only based on the temperature history of process. In particular, the proposed method using the metal etching of the adhesion layer of tantalum and the plasma ashing of parylene-C is compared with that using the dry etching of polycrystalline silicon as a sacrificial layer to release the microcantilever from the substrate in fabrication simplicity and process time. An experimental evaluation confirmed that the proposed fabrication method is very simple and effective. The feasibility of the electricity generation is also measured on the PZT vibration test bed. A nano-watt electrical output is obtained, much higher than noise level. Also, a large output is obtained at a large length of the microcantilever with a large initial deflection.

Monolithic integration of Pb(Zr,Ti)O3 thin film based resonators using a complete dry microfabrication process

Monolithic fabrication of lead zirconate titanate [Pb(Zr,Ti)O3 or PZT] based thin film resonant devices such as microcantilevers, Lamb wave and bulk acoustic wave resonators are demonstrated. High-performance PZT thin films with a thickness of 2.6 μm are prepared on a silicon on insulator wafer by a sputtering deposition process. A highly selective reactive ion etching process is employed for micro-patterning of PZT, platinum electrodes, and SiO2 insulation layer. Self-actuation of the PZT microcantilevers is demonstrated and the frequency response is characterized using a laser Doppler vibrometer. The frequency response of the Lamb wave resonator is evaluated by measuring its transmission characteristic using a network analyzer. For a Lamb wave resonator with a length of 240 μm and an interdigital period of 80 μm, the 1st order and 2nd resonance frequencies are 15.3 and 41.8 MHz, respectively.

Design and fabrication of PZT microcantilevers with freestanding structure

For developing freestanding piezoelectric microcantilevers with low resonant frequency, some critical mechanical considerations, especially cantilever bending, were given in this study. Two strategies, using piezoelectric thick films and adding a stress compensation layer, were calculationally analyzed for mitigating the cantilever bending, and then was applied for the fabrication of PZT freestanding microcantilevers. (100) oriented PZT thick films with the thickness of 6.93 μm were grown on the Pt/SiO2/Si substrate by chemical solution deposition (CSD), and the SiO2 layer with the thickness of 1.0 μm was kept under the PZT layer as a stress compensation layer of the freestanding microcantilevers. The freestanding microcantilevers fabricated with the micromachining process possessed the resonant frequency of 466.1 Hz, and demonstrated no obvious cantilever bending.

Electromechanical Properties of Microcantilever Actuated by Enhanced Piezoelectric PZT Thick Film

Pb(Zr0.53, Ti0.47)O3 (PZT) films with thicknesses of 0.8μm, 2μm and 4μm are prepared by a sol-gel method and their longitudinal piezoelectric coefficients are analysed. The results show that the PZT thick films, whose density is closer to bulk PZT, has the better crystallization, with d33 and density much larger than those of PZT thin films. A piezoelectric microcantilever actuated by a 4-μm-thick PZT film is fabricated and its displacement is measured in different frequencies and voltages. The displacement increases linearly with the increasing bias, and the maximum displacement of 0.544 μm is observed at 30kHz for 5V bias. The resonant frequency obtained in the experiment matches quite well with the theoretical result, and it is shown that the resonant frequency of PZT microcantilever could be controlled and predicated.

EFFECT OF SILICON CARBIDE PASSIVATION FILM ON THE RESONANCE CHARACTERISTICS OF CANTILEVER

ABSTRACT We have used silicon carbide (SiC) thin films as an insulating material of the PZT micro cantilevers for electrical and biological passivation. The use of SiC thin films as a passivation layer of the PZT microcantilevers is also seemingly viable to insure the high mass sensitivity as well as the stable passivation. In this study, we report the effect of SiC passivation layer on the performance of the PZT microcantilevers. The micromachined PZT microcantilevers having a structure of SiNx/Ta/Pt/PZT/Pt were fabricated through MEMS processes. In order to improve the mass sensitivity and the passivation, SiC thin films of the high elasticity material were deposited on the cantilever using plasma enhanced chemical vapor deposition (PECVD) at the temperature of 400°C. Plane-strain modulus of SiC thin film was measured by nanoindentation. We observed that SiC thin films showed higher Young's modulus than Si and SiO2. Before and after the deposition of SiC thin films, the end-tip deflection and the resonant frequency change of microcantilevers were measured by a confocal microscope and an impedance analyzer. It was confirmed that end-tip deflection of microcantilever was reduced by 13∼18% through the deposition of SiC thin films, indicating the stress relaxation of the microcantilevers.

Measurement on the actuating and sensing capability of a PZT microcantilever

PZT thin film devices are very competitive when charge signal and force outputs are demanded. A Pb(Zr0.5Ti0.5)O3 thin film with 24 coating layers is deposited by a sol–gel method. An array of three piezoelectric microcantilevers is fabricated using the wet and dry combined bulk micromachining techniques. Each microcantilever has a two-segment top electrode in different dimensions. The actuating and sensing capability of the six segments on the three microcantilevers are measured. It is proved that the proposed piezoelectric microcantilevers have both actuating and sensing functions; different proportion partition results in the diversity of the actuating and sensing capability. At the same location, the longer the piezoelectric segment is, the stronger actuating and sensing capability it has. The maximum actuating sensitivity and sensing sensitivity before poling treatment are 16.7 µN V−1 and 13.44 pC µm−1, respectively, which become about twice as big after poling. We may choose the appropriate microcantilevers to satisfy our purpose on some specific condition where force feedback and object manipulation are needed simultaneously. A hysteresis phenomenon is encountered in the actuating process while not in the sensing process.

Fabrication and electromechanical properties of a self-actuating Pb(Zr0.52Ti0.48)O3 microcantilever using a direct patternable sol-gel method

The use of direct-patternable lead zirconate titanate (PZT) films produced using photosensitive stock solutions with ortho-nitrobenzaldehyde and UV (365 nm) irradiation has reached an advanced stage of application in microdetection systems. Electromechanical properties of direct patterned PZT microcantilevers on SiNx∕Ta∕Pt∕PZT∕Pt∕SiO2 structure were measured by a laser vibrometer system as a function of cantilever length. The gravimetric sensitivity of cantilevers in air was characterized by Au deposition, and the mass detecting resolution was 38Hz∕ng. These results suggested a possibility that microelectromechanical systems may be fabricated relatively easily and without high cost processes, for example, by PZT dry etching.

A self-excited micro cantilever biosensor actuated by PZT using the mass micro balancing technique

A micro biosensor, which can be applied to a Lab-On-a-Chip (LOC), is developed in order to detect biomaterials such as protein or DNA. The biomaterials are detected by mass micro-balancing technique, which measures the change of the resonant frequency of the sensor structure. The sensor structure consists of a micro cantilever actuated by piezoelectric PZT film. The PZT film is designed to act as both a sensor and an actuator. The geometry of the micro cantilever is determined so as to maximize the sensitivity of the sensor, and environmental effects such as added mass effect in liquid are also considered in the structural analysis. The micro cantilever is 100 μm in length, 30 μm in width and 5 μm in thickness, and the PZT film thickness and length are 2.5 and 50 μm, respectively. The first resonant frequency of the PZT micro cantilever is 1.2 ∼ 1.3 MHz. Lastly the fabricated micro-biosensor using the self-excited PZT-micro cantilever is tested by detecting the human insulin-anti human insulin binding protein, the poly T-sequence DNA, the K20-Thiol DNA and the K40-Thiol DNA in air.

Fabrication and characterization of piezoelectric cantilever for micro transducers

Piezoelectric microcantilever transducers based on lead zirconate titanate (PZT) thin film have received considerable interest because of their wide potential applications in nanotechnology, biosensors and microelectromechanical systems. However, thin film cracking, device short-circuiting and substrate surface degrading are commonly encountered in PZT microcantilever fabrication using chemical solution deposition (or CSD) and wet etching processes. In this work, through patterning the pyrolyzed PZT thin film by wet etching before post-annealing for crystallization, these problems are successfully eliminated and workable micro cantilever transducers are fabricated with greatly improved yield. This novel fabricating process could make the integration of piezoelectric components into micro-electromechanical systems much easier.

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 15 V in level, 0.2 μs in duration with a period of 10 μs is found to be a promising driving signal for the designed structure. The top temperature of the tip is about 200 °C, which is believed to be effective for softening polymethylmethacrylate film. Within the period of 10 μs, the tip can be cooled down to near the room temperature.

Fabrication and structural characterization of a resonant frequency PZTmicrocantilever

The fabrication and structural characterization of a surface micromachined,resonant frequency, Pb(Zr, Ti)O3 (PZT) microcantilever will be presented. ThePZT microcantilever was fabricated using surface micromachining techniques,and used a low-stress silicon nitride thin film as the base material for themicrocantilever onto which a PZT thin film was incorporated. The PZT thin filmis used as both the microsensor and the microactuator. A unique fabricationprocedure was developed in order to eliminate the step of encapsulating thePZT during the removal of the spacer layer. The encapsulation step was avoidedbecause of the difficulty in finding a suitable material, which would protectthe PZT during the removal of the spacer layer yet not affect its materialproperties. This predicament was resolved by removing the spacer layer priorto the deposition of the PZT. The microcantilevers were characterized extensivelyusing an atomic force microscope in an unusual manner. The atomic force microscope wasmodified in such a fashion that the deflection at the tip of themicrocantilever could be measured as the frequency of an electrical signalapplied to the PZT thin film was varied. In addition, an impedance analyzerwas used to characterize the microcantilevers. Simple thin-film, laminatedplate theory was used to obtain a closed-form solution for the modal responseof the microcantilever, while ANSYS was used to obtain modal and harmonicsimulation results. It will be shown that the experimental, numerical, andtheoretical modal results are within ±10% of one another. The experimentaland numerical harmonic results differ by an order of magnitude; however, thenumerical model is currently being modified to more accurately represent thePZT microcantilever. From the information gathered during the structuralcharacterization of the PZT microcantilever, it will be shown that certainhigher-order resonant frequency modes have very large mechanical responses.These higher-order resonant frequency modes give designers another parameterto adjust when trying to optimize the design of their resonant frequencydevice.

Physical characteristics of photo-sensitive sol-gel derived PZT films for microcantilever

A direct fine-patterning process using photosensitive gel film derived from PZT precursor solution has been used to fabricate the piezoelectric cantilever from lead acetate trihydrate, zirconium n-propoxide and titanium isopropoxide modified with onitrobenzyl alcohol (NBA). Two main heating schedules were used to investigate the effect of various NBA amounts on microstructure, surface morphologies, and electrical properties of PZT films. As NBA was added above 1 wt%, it shows detrimental effect on crystal phase, microstructure evolution and electrical properties of PZT films. With increasing NBA content, both pyrochlore phase and pore formation was promoted. However, prior to next coating, a pre-pyrolysis is required to reduce the pore formation and obtain good piezoelectric characteristics. The mechanical coupling k31 measured for PZT micro-cantilever is about 0.26 which is comparable to those reported for bulk ceramics.

Self-excited piezoelectric PZT microcantilevers for dynamic SFM—with inherent sensing and actuating capabilities

Currently three crucial components are necessary for the dynamic SFM, they are the microcantilever, oscillator, and cantilever deflection sensor. We demonstrate a piezoelectric microcantilever made of PZT thin films for SFM. This PZT microcantilever can perform the same functions which have to be done by the three crucial components. It is able to excite itself when an ac voltage is applied to it, and actuate itself in z-directional displacement by a superimposed dc voltage, while force sensing is executed concurrently. Since the motional admittance can be derived from the piezoelectric current output when the PZT microcantilever is vibrated at resonance frequency, the motional admittance will vary as the change of vibrational amplitude. Thus the topography of the sample can be recorded as the trace of the difference between output signals of motional admittance. The piezoelectric coefficient d 31 of the PZT layer is about −58 pC/N. The dimensions of piezoelectric microcantilevers used are 125×50×3.8 μm. The actuating ability is estimated as 75 nm/V. The vertical resolution of the self-excited PZT microcantilever can be derived as 1.2 Å at the bandwidth of 125 Hz. Very clear images of a 1.0 μm pitch Au coated SiO 2 grating and an evaporated gold film on a smooth glass plate are obtained by an SFM using this self-excited force sensing PZT microcantilever. The invention of this smart PZT microcantilever endows the possibility of constructing a stand-alone micro SFM system and a multiprobe SFM system.

Development of a piezoelectric self-excitation and self-detection mechanism in PZT microcantilevers for dynamic scanning force microscopy in liquid

We report on the first successful operation of a cyclic contact scanning force microscope (SFM) using a self-excited cantilever in liquid. Based on a new structure including a PZT reference pattern and a free-standing PZT cantilever, the piezoelectric self-excitation and self-detection mechanism for a PZT microcantilever was developed successfully. The topography is recorded by measuring the piezoelectric current variation, which corresponds to the vibration. Since the acoustic excitation from the external oscillator no longer exits, a clear single resonance peak can be obtained by using this self-excited force sensing PZT cantilever. Clear grating imaging in liquid was demonstrated, and it is compatible with the image taken in air. The future potential of applying this piezoelectric SFM to the characterization of biological samples in liquid is very promising.

Novel high vacuum scanning force microscope using a piezoelectric cantilever and the phase detection method

A novel high vacuum scanning force microscope (HV-SFM) using a piezoelectric cantilever and the phase detection method was developed. A self-excited force sensing PZT microcantilever with dimensions of 125×50×3.58 μm is vibrated in vacuum at its resonance frequency by applying an ac voltage to its PZT layer. The piezoelectric microcantilever possesses a spring constant of 16.7 N/m and a vibrational quality factor of 300 in air and 807 in vacuum. As we know, force gradients acting on the vibrating cantilever cause changes in vibration amplitude and phase. The change of the phase of the output piezoelectric current, which corresponds to the phase variation of cantilever vibration, is measured as the controlling signal in this method. The piezoelectric HV-SFM that was constructed has been proved to be stable and easy to handle in vacuum. Its vertical resolution is higher than 1.1 Å. High resolution images of an evaporated Au film can be obtained in vacuum by this new dynamic HV-SFM. Grains of about 5 nm can be seen clearly. The theoretical sensitivity of phase detection with piezoelectric cantilevers is also analyzed and compared with that of amplitude slope detection in this article.