Glenn J. T. Leighton

In-plane excitation of thin silicon cantilevers using piezoelectric thin films

This paper deals with the actuation of in-plane and out-of-plane motions of silicon cantilevers, using a single thin film of lead zirconate titanate with a divided electrode configuration. In-plane actuation is demonstrated practically, and excellent agreement is obtained between theoretically predicted and experimentally measured resonant amplitudes, for the fundamental out-of-plane and in-plane modes of vibration of the fabricated test cantilevers.

Accurate measurement of the piezoelectric coefficient of thin films by eliminating the substrate bending effect using spatial scanning laser vibrometry

One of the major difficulties in measuring the piezoelectric coefficient d33, f for thin films is the elimination of the contribution from substrate bending. We show by theoretical analysis and experimental measurements that by bonding thin film piezoelectric samples to a substantial holder, the substrate bending can be minimized to a negligible level. Once the substrate bending can be effectively eliminated, single-beam laser scanning vibrometry can be used to measure the precise strain distribution of a piezoelectric thin film under converse actuation. A significant strain increase toward the inside edge of the top electrode (assuming a fully covered bottom electrode) and a corresponding strain peak in the opposite direction just outside the electrode edge were observed. These peaks were found to increase with the increasing Poissons ratio and transverse piezoelectric coefficient of the piezoelectric thin film. This is due to the non-continuity of the electric field at the edge of the top electrode, which leads to the concentration of shear stress and electric field in the vicinity of the electrode edge. The measured d33, f was found to depend not only on the material properties such as the electromechanical coefficients of the piezoelectric thin films and elastic coefficients of the thin film and the substrate, but also on the geometry factors such as the thickness of the piezoelectric films, the dimensions of the electrode, and also the thickness of the substrate.

Dimensional reduction study of piezoelectric ceramics constitutive equations from 3-D to 2-D and 1-D

Accurate performance evaluation is crucial to the design and development of macro/micro-sized piezoelectric devices, and key to this is the proper use of the stiffness/ compliance and piezoelectric coefficients of the piezoelectric ceramics involved. Although the literature points out effective piezoelectric coefficients e31,f and d33,f for thin film materials and reduced dimensionality of equations for bulk material, the elastic and piezoelectric coefficients remain unchanged from the 3-D equations in most reported 1-D and 2-D analyses of the macro/micro-sized devices involving the e form of the constitutive equations. The use of unchanged coefficients leads to variations between numerically predicted and experimental results in most devices. To understand effects of the dimensional reduction from 3-D to 2-D and 1-D on stiffness/compliance and piezoelectric coefficients, this paper derives the 2-D and 1-D constitutive equations from the 3-D equations, focusing on the discussion of often-required device configurations for sensor and actuator design and analysis. Two modified coefficients are proposed, termed reduced and enhanced, which enable better understanding of effects of the dimensional reduction and also effects on the design and analysis of sensors and actuators.

Dynamic Operational Stress Measurement of MEMS Using Time-Resolved Raman Spectroscopy

A dynamic-stress analysis method, based on time-resolved micro Raman spectroscopy, has been developed for reliability studies of microelectromechanical systems. This novel technique is illustrated by measuring temporally and spatially resolved stress maps of a piezoelectrically actuated silicon microcantilever when driven at its first- (6.094 kHz) and second-order (37.89 kHz) resonant frequencies. Stress amplitudes of up to 180 plusmn 10 MPa were measured at the maximum stress locations. The time-resolved Raman stress measurements are compared to the results of finite-element analysis and laser Doppler vibrometry.[2008-0003].

Impedance measurements for determination of elastic and piezoelectric coefficients of films

Abstract Abstract Most of those techniques used for the measurement of elastic coefficients for bulk piezoelectric ceramics are not applicable to films deposited on thick substrates because the measured properties, such as the resonant frequency, are usually dominated by the presence of the thick substrate. This work presents a preliminary study for the application of the automatic iterative method of Alemany et al. for the determination, from complex impedance measurements, of the film properties using a conventional self-supported cantilever design used in microelectromechanical system applications and fabricated from a PZT thick film on a Si based substrate.

Low-profile and wearable energy harvester based on plucked piezoelectric cantilevers

The Pizzicato Energy Harvester (EH) introduced the technique of frequency up-conversion to piezoelectric EHs wearable on the lateral side of the knee-joint. The operation principle is to pluck the piezoelectric bimorphs with plectra so that they produce electrical energy during the ensuing mechanical vibrations. The device presented in this work is, in some ways, an evolution of the earlier Pizzicato: it is a significantly more compact and lighter device; the central hub holds 16 piezoelectric bimorphs shaped as trapezoids, which permits a sleek design and potentially increased energy output for the same bimorph area. Plectra were formed by Photochemical Machining of a 100-μm-thick steel sheet. To avoid the risk of short-circuiting, the plectra were electrically passivated by sputtering a 100 nm layer of ZrO2. Bench tests with the steel plectra showed a very large energy generation. Polyimide plectra were also manufactured with a cutting plotter from a 125μm-thick film. Besides bench tests, a volunteer wore the device while walking on flat ground or climbing stairs, with a measured energy output of approximately 0.8 mJ per step. Whereas most of the tests were performed by the traditional method of discharging the rectified output from the EH onto a resistive load, tests were performed also with a circuit offering a stabilised 3.3 V supply. The circuit produced a stable 0.1 mA supply during running gait with kapton plectra.

A Straightforward Route to Sensor Selection for IoT Systems

Overview: The Internet of Things (IoT) allows for remote management and monitoring of many aspects of everyday life at the individual and industrial levels. However, designing these systems within constraints of cost and operational context can be a real challenge. The sensor network must be strategically designed, which means selecting the most appropriate sensors to collect a specific measurement in a specific environment and then optimizing their deployment and utilization. To facilitate sensor selection, we propose a straightforward, color-coded, three-sieve selection tool and demonstrate the efficacy of this method through real-life exemplars. The selection tool could be applied to other kinds of technologies as well.

Interferometry for Piezoelectric Materials and Thin Films

Piezoelectricity is the coupling between the mechanical and electric property of materials, which manifests itself by the generation of electric charge upon a pressure or conversely the produce of strain under an electric field.