Deformation control of microbridges for flow sensors

To obtain good performance from a microbridge flow sensor, we have investigated the buckling mechanism of microbridges by fabricating various shapes of bridges. We have achieved deformation control for both the longitudinal axis and the transverse axis of Pt/SiNx double-layered microbridges by appropriate selection of the residual bridge stress of Pt/SiNx structures and of the stress gradient between the Pt film and the SiNx film. The deformation directions of the longitudinal axis of bridges for the beam bridge (Type I) are all the same as that of cantilevers and may be predicted via the stress gradient between the Pt and SiNx films of the bridges. The deflection of the transverse axis of the table bridge supported by four beams (Type II) changes linearly with the residual bridge stress of the Pt/SiNx structure and the deformation changes for the transverse axis are the same as that of completely free films, as predicted from the stress gradient between the Pt film and the SiNx film. The interesting result is that the deformation direction for the longitudinal axis of the Type II bridge is opposite to that of the Type I with the same film structure. We discuss the reason for this opposition via differences in the progress of the anisotropic etching. We consider that this result will expand the range of manufacturable shapes and film structures of microbridges.     

Finite element analysis of a IBM suspension integrated with a PZT microactuator

This paper presents a piezoelectric-based microactuator concept that could provide an economical and easily integrated option for dual stage actuation used in hard disk drives (HDDs). A simple cantilever beam integrated with the PZT actuator was simulated first in order to testify the driving mechanics of the new design. A modern suspension (IBM Deskstar DTLA-307015) integrated with the developed PZT actuator was then simulated by finite element method (FEM). Theoretical dynamic and electrostatic analyses were performed to investigated the resonant frequency and displacement sensitivity. Good dynamic characteristics were obtained. Further simulation was done based on the optimized structure of the actuator/suspension assembly and results show that >1 μm tip stroke can be obtained while the driving voltage is only 20 V. A 10 V is sufficient to get >1 μm tip stroke if double layer PZT actuator is used.     

Integration of displacement sensor into bulk PZT thick film actuator for MEMS deformable mirror

Bulk PZT thick film actuator integrated with displacement sensor, the so-called self-sensing actuator, is presented in this paper. The PZT film is used as not only an actuating layer but also a displacement sensor, which is achieved by dividing the electrode on the top surface of the PZT film into two parts: central top electrode for actuating and outer annular sensor electrode for piezoelectric displacement detection. When the actuator moves, the piezoelectric charge is induced in the outer annular PZT due to the piezoelectric effect. The total amount of accumulated charge is proportional to the stress acting on the PZT, which is in turn proportional to the actuator displacement. By collecting the piezoelectric charge, the actuator displacement can be detected. A theoretical model is proposed to determine the structure parameters of the sensor and predict the sensor sensitivity. Experiments were performed on the micro-fabricated sensor integrated PZT thick film actuator, and the measured piezoelectric charge is close to the theoretical predictions. The integrated piezoelectric sensor has a displacement sensitivity of approximately 4 pC/nm. In addition, the integration of displacement sensor into the actuator needs no additional fabrication process and has no influence on the actuator performances.     

A Novel Bistable Two-Way Actuated Out-of-Plane Electrothermal Microbridge

In this paper, we report the design, simulation, fabrication, and testing of a novel electrothermally actuated buckled microbridge for out-of-plane actuation. The new structure consists of a bridge supported by two springs and two "legs" at both supporting ends. The bridge and the spring are trilayer structures: low-stress plasma-enhanced chemical-vapor-deposition (PECVD) oxide (2.5 mum), high compressive stress PECVD oxide (1 mum), and phosphorus-doped silicon (2 mum). The "legs" consist only of 2-mum-thick phosphorus-doped silicon. The overall size of the actuator is 1200 mum by 100 mum excluding the contact pads. Analytical expressions used to determine torsional and axial stiffnesses at the supporting ends are derived. Together with bistability criteria developed by Michael and Kwok, the microbridge structure is designed to exhibit a bistable behavior. It is also designed to have a two-way actuation capability. Electrothermal analysis and thermomechanical finite element ANSYS simulations are performed to determine the switching waveforms for the two-way actuation and verify the bistability. Actuation of the fabricated structure from the buckled-up to the buckled-down states required a 7-V voltage pulse for 1 ms across the "legs," followed by a 5-V pulse for 4 ms across the bridge. A 9-V pulse for 0.5 ms only to "legs" enabled the switching of the bridge from the buckled-down to the buckled-up states. An out-of-plane movement of 31 mum is demonstrated for a 1200-mum-long microbridge. Larger movement can be obtained by increasing the microbridge length and the compressive stress of the stressed oxide layer of the bridge.     

Thin-Film Piezoelectric Unimorph Actuator-Based Deformable Mirror With a Transferred Silicon Membrane

This paper describes a proof-of-concept deformable mirror (DM) technology, with a continuous single-crystal silicon membrane reflecting surface, based on$ PbZr _0.52 Ti_0.48 O _3$(PZT) unimorph membrane microactuators. A potential application for a terrestrial planet finder adaptive er is also discussed. The DM comprises a continuous, large-aperture, silicon membrane “transferred” onto a 20$,times,$20 piezoelectric unimorph actuator array. The actuator array was prepared on an electroded silicon substrate using chemical-solution-deposited 2-$mu m$-thick PZT films working in a$d _31$mode. The substrate was subsequently bulk-micromachined to create membrane structures with residual silicon acting as the passive layer in the actuator structure. A mathematical model simulated the membrane microactuator performance and aided in the optimization of membrane thicknesses and electrode geometries. Excellent agreement was obtained between the model and the experimental results. The resulting piezoelectric unimorph actuators with patterned PZT films produced large strokes at low voltages. A PZT unimorph actuator, 2.5 mm in diameter with optimized PZT/silicon thickness and design showed a deflection of 5.7$~mu m$at 20 V. A DM structure with a 20-$mu m$-thick silicon membrane mirror (50 mm$times,$50 mm area) supported by 400 PZT unimorph actuators was successfully fabricated and optically characterized. The measured maximum mirror deflection at 30 V was approximately 1$~mu m$. An assembled DM showed an operating frequency bandwidth of 30 kHz and an influence function of approximately 30%. 1738     

激光微刻蚀柔性红外热敏悬浮微桥研究

本文研究使用激光微刻蚀方法制作红外热敏悬浮微桥的新工艺.用激光微刻蚀法制作了铂/聚酰亚胺热敏悬浮微桥,对微桥初样的热敏特性进行了测试,测试结果证实所制作的热敏微桥具有较好的热隔离性能.     

Pb-based ferroelectric thin film actuator for optical applications

Novel PZT thin film actuators for optical applications were proposed. Key issues for realizing the actuators such as PZT thin film processes, mechanical properties evaluation of thin films, and design for laminated structure were described. [1 1 1]-oriented PZT films were obtained by anneal/non-anneal sputtering process. Also for PZT dry etching, it was made clear low pressure and low temperature conditions were advantageous for high selectivity and etch rate. ECR etcher was used and etch rate of 1000 A/min and selectivity of 0.56 to photoresist mask were obtained. Young’s modulus and built-in stress of PZT film, measured by load-deflection method, were 72 GPa, −335 MPa respectively. Using these results, calculated deflection of each actuator was on the order of a few microns to 20 microns. It was confirmed that deflection of actuators would be enough for the application.     

Piezoelectric unimorph miroactuators with X-shaped structure composed of PZT thin films

In this study, we report piezoelectric microactuators composed of Pb(Zr,Ti)O₃ (PZT) films for low-voltage RF-MEMS switches. In order to realize a flat beam shape as well as a large displacement, we have adopted an X-shaped connector at the center of the beam. Finite element method (FEM) simulation indicates that the bending motion of the beam is almost same as two connected cantilevers, and the maximum displacement reaches 3.2 μm/5 V. To fabricate the microactuators, piezoelectric PZT films were deposited on Si substrates using rf-sputtering and microfabricated into the PZT/Cr unimorph actuators of 800 μm in length and 200 μm in width, respectively. Although the X-shaped connector effectively releases the stress of the multilayered beam so that the beam shape is almost flat, small residual stress caused slight concave curvature along the width. The displacement at the center of the beam was measured using a laser Doppler vibrometer. The measurement revealed that the displacement was 0.5 μm/5 V which was lower than the FEM result. The reduction of the displacement is attributed to the increase of the stiffness of the beam due to the concave curvature of the beam width.     

基于压电陶瓷的柔性机器人主动抑振控制策略研究

柔性机器人因其轻质、高效、低能耗等优点已被广泛应用于航空航天,工业制造等诸多领域。然而,柔性机构易产生弯曲变形,引起系统振动而大大降低机器人的工作精度。为提高柔性机器人的工作性能,多种抑振策略得以研究与应用。提出了基于压电陶瓷（PZT）的柔性机器人振动主动抑制策略。其中,PZT传感器和PZT制动器分别被用来检测和抑制柔性臂的振动。本文构建了基于PZT材料的单自由度柔性机械臂的理论模型,并获得了传感电压与制动电压的传递函数。设计了一个可变控制方案的抑振器以抑制系统在不同频率下的振动。在COMSOL中进行仿真,获得了系统的抑振率。根据仿真结果显示,柔性臂在前三阶振动下,臂的末端位移分别得到了57.04%,57.76%与58.96%的抑制;系统的动能得到了57.95%,71.19%与87.81%的抑制。     

Microbridge testing on symmetrical trilayer films

In this paper, we extended the microbridge testing method to characterize the mechanical properties of symmetrical trilayer thin films. Theoretically, we analyzed the deformation of a trilayer microbridge sample with a deformable boundary condition and derived load-deflection formulas in closed-form. The slope of a load-deflection curve under small deformation gives the relationship between the bending stiffness and the residual force of a trilayer microbridge. Taking this relationship, we were able to assess simultaneously the Young's modulus of two kinds of materials composing the symmetrical trilayer film and the thickness-averaged residual stress of the film. Experimentally, we fabricated symmetrical trilayer microbridge samples of SiO/sub 2//Si/sub 3/N/sub 4//SiO/sub 2/ on 4-inch p-type (100) silicon wafers and conducted the microbridge tests with a load and displacement sensing nanoindenter system equipped with a microwedge indenter. The experimental results verified the proposed microbridge testing method. The thickness-averaged residual stress of the 1.1-/spl mu/m trilayer thin films was determined to be 8.8 MPa, while the Young's modulus of the 0.3-/spl mu/m silicon oxide layers and the Young's modulus of the 0.5-/spl mu/m silicon nitride layer were evaluated to be 31 GPa and 294 GPa, respectively.     

Effects of corner frequency on bandwidth and resonance amplitude in designing PZT thin-film actuators

In the last decade, lead zirconate titanate oxide (PZT) thin-film actuators have received increasing attention because of their high frequency bandwidth, large actuation strength, fast response, and small size. The PZT film thickness is usually less than several microns as opposed to hundreds of microns for bulk PZT patches that are commercially available. As a result, PZT thin-film actuators pose unique vibration issues that do not appear in actuators with bulk PZT. Two major issues affecting actuator performance are the frequency bandwidth and the resonance amplitude. As an electromechanical device, a PZT thin-film actuator's bandwidth and resonance amplitude depend not only on the lowest natural frequency ω_n of the actuator's mechanical structure but also on the corner frequency ω_c of the actuator's RC-circuit. For PZT thin-film actuators, the small film thickness implies large film capacitance C and small ω_c. When the size of the actuator decreases, ω_n increases dramatically. As a result, improper design of PZT thin-film actuators could lead to ω_c ≪ ω_n substantially reducing the actuator bandwidth and the resonance amplitude. This paper is to demonstrate this phenomenon through theoretical analyses and calibrated experiments. In the theoretical analyses, frequency response functions of a PZT thin-film actuator are obtained to predict 3 dB actuator bandwidth and resonance amplitude for cases when ω_c ≪ ω_n, ω_c ≈ ω_n and ω_c ≫ ω_n. In the experiments, frequency response functions of a fixed–fixed silicon beam with a 1 μm thick PZT film are measured through use of a laser Doppler vibrometer and a spectrum analyzer. The silicon beam has multiple electrodes with a wide range of resistance R and corner frequency ω_c. The experimental results confirm that the actuator bandwidth and resonance amplitude are substantially reduced when ω_c ≪ ω_n.     

Swing-arm-type PZT dual actuator with fast seeking for optical disk drive

 In this paper, a swing-arm-type dual positioning mechanism using a voice coil motor (VCM) and bimorph PZT actuators is proposed for the possible application to the future optical disc drive actuator. A VCM is used as a coarse motion actuator, and a set of piezoelectric actuators is used for fine motion. The two pairs of PZT actuators are arranged in parallel and are carefully designed to deflect in `S' shape such that tension and compression forces are generated simultaneously and thus the hysteresis is minimized. The static and dynamic analyses are performed and the parameter studies on the key dimensions of the set of PZT actuators are investigated. For fast seeking motion, time optimal control scheme combined with PD algorithm is adopted for the fast seeking motion of VCM. Positive position feedback (PPF) control is used to suppress residual vibration for the PZT actuator beams by activating it at the end of VCM swing motion. The feasibility of the suggested actuator system and the control scheme is demonstrated through simulations and experiments. Received: 5 July 2001/Accepted: 21 December 2001     

Development of piezoelectric MEMS deformable mirror

This paper reports on piezoelectric micro-electro-mechanical systems deformable mirrors with high-density actuator array for low-voltage and high-resolution retinal imaging with adaptive optics. The deformable mirror was composed of unimorph structure of lead zirconate titanate (PZT) thin film deposited on Pt-coated silicon on insulator substrate and a diaphragm of 10?mm in diameter formed by backside-etching the Si handle wafer. 61 hexagonal electrodes were laid out on the PZT thin film for the high-density actuator array. In order to reduce the dead space for the lead lines between the electrodes and connecting pads, a polyimide layer with through holes on the electrodes was patterned as an electrical insulator. To confirm the application feasibility of the fabricated DMs, displacement profiles of the actuators were measured by a laser Doppler vibrometer. Independent applications of voltages on individual actuators were confirmed.     

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.     

A novel design and fabrication of a micro-gripper for manipulation of micro-scale parts actuated by a bending piezoelectric

In this study, a novel micro-gripper using a piezoelectric actuator was designed and improved by the design of experiments (DOE) approach. Using a bending PZT actuator connected to the micro-gripper by a rigid wedge can be considered as a novel approach in this field. Almost all of the similar grippers in this category were former actuated by a piezo-stack which has some limitations and difficulties like fabrication in MEMS proportions. The basic design was borrowed from compliant mechanisms that are suitable for MEMS application and easy to manufacture in micro-scale because of the intrinsic integration characteristic. Since stress concentration is common in flexure hinge compliant mechanisms, our focus was to consider strength as an important factor in our design. Finite element analysis tools were used to implement the DOE based on two criteria; minimizing stress concentration and maximizing the output displacement in the micro-gripper structure as much as possible with the consideration of the total size of the gripper. The experiment was performed to validate the simulation results and experiment results agreed well with the simulation one. The slight geometrical discrepancy in significant portions of structure like flexure hinges partially contributes to the accumulated error between the simulation and the experiments.

     

Modified BVD model of PZT actuator using high-voltage square pulse method for micropumps

The field of micro–electro–mechanical systems and microfabrication has produced micro-total-analysis systems, which are widely used in medicine, diagnostics, and biological and chemical research. For the development of high precision drug delivery systems, micropumps with a lead zirconate titanate (PZT) actuator, which has a fast response time and high resolution, are most likely to be applied in implementations. To improve the performance of PZT micropumps utilized in the microfluidics field, suitable models are required to enable the optimization of the PZT actuator driving circuits. This study proposes a modified Butterworth–Van Dyke (BVD) model which consists of a BVD model in series with an electrical resistance that describes a PZT actuator driven by a square pulse with a relatively high voltage and low frequency for micropump applications. Experiments were conducted to assess parameters of the model at various voltages; they indicate that the electrical resistance is essential for modeling the PZT actuator of the micropump. The electrical model was verified using a SPICE simulation, whose numerical results were compared with the experimental data for the current response of the PZT actuator. The results show a close correlation between the simulation of the electrical model and the measurements of the PZT actuator under real operating conditions.     

Design and control of a single-stage dual-actuator system for high-precision manufacturing

This paper proposes a design for the linear state feedback control of the dual-actuator system, which is a dual-input single-output system for the high-precision manufacturing stage. The proposed control prevents saturation or reduces the unnecessary movement of the piezoelectric (PZT) actuator at the transient response by tracking the error between the estimated and actual positions of the coarse-actuator system at each control sample. Also, a new mechanism of the single-stage dual actuator is introduced. The axes of the stepper motor and the PZT actuator are co-axial. The coupling effects between the stepper motor and the PZT actuator are considered. Both the simulation and experiment results show that the proposed algorithm successfully prevents unwanted motions of the PZT actuator at the transient response. The experiment results show that the settling time and overshoot were enhanced by 45.7 and 95.9 %, respectively, for the proposed algorithm when the reference distance was 10 μm, which exceeds the stroke of the PZT actuator.     

Electric and ferroelectric properties of PZT/SBT multilayer films prepared by photochemical metal-organic deposition

The electric and ferroelectric properties of lead zirconate titanate and strontium bismuth tantalate multilayer films prepared using photosensitive starting precursors were characterized. The electric and ferroelectric properties were investigated by characterization of the effect of stacking order of four ferroelectric layers of PZT or SBT in the multilayer films of 4-PZT, PZT/2-SBT/PZT, SBT/2-PZT/SBT, and 4-SBT. The P_r value of the 4-SBT multilayer film was relatively small (6 μC/cm²) and a two times higher value (12 μC/cm²) was obtained with the SBT/2-PZT/SBT multilayer film. The films with SBT layers at the top and bottom showed improved leakage current and fatigue resistance compared to the films with PZT layers at the top and bottom. It was revealed that the defect dipole was reduced at the SBT/Pt interface due to a self-regulation layer such as (Bi₂O₂)²⁺ in the SBT film. Also, the bottom layer on the Pt substrate showed a significant influence on the growth orientation of the entire ferroelectric films.     

Development of novel PZT thin films for active sliders based on head load/unload on demand systems

 Micromachined active sliders based on head load/unload on demand systems is an interesting concept technology for ultra-high magnetic recording density of more than 100 Gb/in². The active sliders that we proposed use PZT thin films as a microactuator and control the slider flying height of less than 10 nm. It is necessary to develop high performance microactuators in order to achieve active sliders operating at very low applied voltage. This paper describes the development of novel PZT thin films for active sliders. The sol–gel fabrication process for PZT thin films is developed and the fundamental characteristics for the PZT thin films are investigated. It is confirmed that the PZT thin films have good ferroelectric properties. Furthermore, novel thin film microactuators are proposed. The feature is that the sol–gel PZT thin films (thickness 540 nm) are deposited on the sputtered PZT thin films (thickness 300 nm) fabricated on bottom Pt/Ti electrodes. Therefore, the novel thin films consist of a thermal SiO₂ layer and the sputtered and sol–gel PZT thin films layers sandwiched with upper Pt and bottom Pt/Ti electrodes on a Si slider material. Fabricating the diaphragm microactuator, the piezoelectric properties for the novel composite PZT thin films are studied. As a result, the piezoelectric strain constant d ₃₁ for the novel PZT thin films is identified to be 130 × 10⁻¹² m/V. This value is higher than conventional monolithic PZT thin films and it is found that the novel composite PZT thin films have the good piezoelectric properties. This suggests the feasibility of realizing active sliders operating at lower voltage under about 10 V. Received: 22 June 2001/Accepted: 17 October 2001     

Effect of creep in RF MEMS static and dynamic behavior

This paper presents the experimental characterization of the creep effect in electrostatically actuated gold microstructures. The tested specimens follow the typical configuration of the microbridge based radio frequency microelectromechanical systems switches and varactors. Initially, the plastic creep strain accumulation with time is measured for the specimens with different geometric dimensions and at different actuation voltages and temperatures. To avoid the size and cumulative heating effects, three specimens with the same geometric dimensions, actuation voltages and constant temperatures are tested. The test results allowed decoupling the permanent plastic strains due to the creep effect and reversible anelastic strains due to the viscoelastic behavior. The pull-in voltage and natural frequency values measured before and after the creep tests are compared, revealing the mechanical stiffness decrease caused by creep.