This review article presents recent advancements in the design and fabrication of thin-film (<3 μm) lead zirconate titanate (PZT) microelectromechanical system (MEMS) devices. The article covers techniques for optimizing highly (001)/(100) oriented chemical solution deposited PZT films to achieve improved piezoelectric coefficients. These PZT films combined with surface and bulk micromachining techniques are fabricated into actuators and transducers for radio frequency (RF) switches, nanomechanical logic, resonators, and power transformers for use in communication systems and phased-array radar. In addition, the large relative displacements generated by PZT thin films have been used to demonstrate mechanical mobility in MEMS devices, including insect-inspired flight actuators and ultrasonic traveling wave motors. In conjunction with actuation, PZT films are being developed for feedback sensors for the integrated control of insect-inspired robots.

PZT-Based Piezoelectric MEMS Technology

We have measured electromagnetic energy harvesting properties of all-thin-film magnetoelectric (ME) heterostructures on Si cantilevers. The devices are built on a silicon oxide/nitride/oxide stack, and the ME layers consist of a magnetostrictive Fe0.7Ga0.3 thin film and a Pb(Zr0.52Ti0.48)O3 piezoelectric thin film. The harvested peak power at 1 Oe is 0.7 mW/cm3 (RMS) at the resonant frequency (3.8 kHz) with a load of 12.5 kΩ. The resonant frequency was found to display DC bias magnetic field dependence indicative of a magnetization canting with respect to the cantilever easy axis as a result of interplay between the anisotropy and Zeeman energies.

Energy harvesting properties of all-thin-film multiferroic cantilevers

This paper presents results on a surface micromachined RF microelectromechanical switch that uses piezoelectric actuators. The switch uses solution chemistry-derived lead zirconate titanate thin films spun deposited onto a high-resistivity silicon substrate with coplanar waveguide transmission lines. Actuation voltages, applied via circuits independent of the RF circuitry, average less than 10 V, with switch operation demonstrated as low as 2 V. The series switch exhibits better than 20-dB isolation from dc up to 65 GHz and as large as 70 dB below 1 GHz. In the closed state, the switch has an insertion loss less than 1 dB up to 40 GHz, limited in this demonstration by substrate losses from the elastic layer used to stress control the piezoelectric actuators. Switching speeds for the different designs are in the range of 40-60 ms. Thermal sensitivity measurements show no change in isolation observed for temperatures up to 125degC. However, an increase in actuation voltage is required at elevated temperatures.

Surface Micromachined Microelectromechancial Ohmic Series Switch Using Thin-Film Piezoelectric Actuators

Development of Integrated Optical Circuits depends greatly on progress in coupling light to and between chip devices. Exemplary disclosed embodiments provide a system and method of fabricating couplers for optical chips that may allow for access to devices on the entire chip surface. Cantilever couplers comprising optical waveguides are deflected out-of-plane creating access to remote portions of devices. An exemplary system and method may provide waveguides with tunable angles of deflection creating greater flexibility in optical coupling options.

Cantilever couplers for intra-chip coupling to photonic integrated circuits

Piezoelectrically actuated and sensed microscale resonators have been widely studied for filtering, communication and sensing applications. In this effort, to characterize these resonators, the nonlinear frequency-response behavior of these resonators is examined and parametric identification is carried out. A nonlinear beam model is used with a single-mode approximation to produce a forced Duffing oscillator. Nonlinear analysis is used to obtain the frequency-response equation, and this equation is used along with a least-squares minimization scheme to identify the linear and nonlinear parameter values in oscillator models describing the microscale structures. A linearized analytical model of the stepwise axially varying resonator is also used to obtain additional system parameters. The experimentally identified parameter values are found to be in agreement with predicted values obtained from a nonlinear beam model. Parameter values obtained from multiple sets of data for PZT and AlGaAs microresonators are used to observe trends with respect to a variety of operating conditions.

https://iopscience.iop.org/article/10.1088/0960-1317/16/8/021/pdf

Parametric identification of piezoelectric microscale resonators

An approach to compensate for the residual thin film stress deformation of multilayer microelectromechanical systems (MEMS) devices is presented based upon analytical and numerical modeling and in-process thin film characterization. Thermal and intrinsic deposition stresses can lead to the warping of released MEMS structures. This detrimental phenomenon in many cases can prevent proper device operation. Ellispsometric and laser wafer bow measurements yield thickness and film stress values that are used to update the deflection model during device fabrication, allowing for the compensation of the fabrication process variability. The derivations of linear and nonlinear residual film stress induced deflection models are presented. These models are based upon Bernoulli–Euler beam theory and are thus restricted to the associated geometric constraints. The models are initially validated by comparison with surface micro-machined sol–gel lead–zirconate–titanate cantilever structures; with initial experimental res...

Gabe Smith

Papers

Mitigation of residual film stress deformation in multilayer microelectromechanical systems cantilever devices