Piezoelectric actuators for ultrasonic wire bonding applications

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Piezoelectric actuators for ultrasonic wire bonding applications


Author: Tang, Kwan-wai
Title: Piezoelectric actuators for ultrasonic wire bonding applications
Degree: M.Phil.
Year: 2001
Subject: Wire bonding (Electronic packaging)
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Applied Physics
Pages: xvii, 164 leaves : ill. ; 30 cm
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b1599543
URI: http://theses.lib.polyu.edu.hk/handle/200/4524
Abstract: Soft lead zirconate titanate (PZT-552 from PKI Inc.) and lead magnesium niobate - lead titanate (0.9PMN-0.1PT) are used in this project for fabricating multilayer actuators because of their large strain responses. PZT-552 has the largest piezoelectric coefficient compared to other PZTs and 0.9PMN-0.1PT has high field induced strain of about 0.1 % under an electric field of 1 kV/mm. Moreover, 0.9PMN-0.1PT is a relaxor ferroelectric material which has no displacement hysteresis. According to the results of materials characterizations including measurements of the polarization - electric field (P-E) loop, elastic properties, perovskite phase purity, dielectric permittivity and most importantly the strain response, 0.9PMN-0.1PT of 1 wt% excess of lead oxide (PbO) and I wt% excess of magnesium oxide (MgO) with a sintering temperature of 1250oC shows the best results. Hence, this composition and sintering temperature are used in the 0.9PMN-0.1PT multilayer actuator fabrications. Guided by the result of thermogravimetric analysis (TGA) and by sandwiching the green multilayer samples in-between two brass plates during binder burnout to release heat, the PZT multilayer actuator with 70 active layers and the 0.9PMJ-0.lPT multilayer actuator with 60 active layers are fabricated without cracks or delaminations in a faster process. The electrical properties of the two multilayer actuators including impedance measurement of the PZT actuator, dielectric property and P-E loop of the 0.9PMN-0.1PT actuator are presented in this thesis. When voltage is applied to the actuators, they deform and generate displacements due to piezoelectricity or electrostriction. Moreover, for 0.9PMN-0.1PT actuator, piezoelectricity will be induced under a dc bias voltage. According to the piezoelectric effect of PZT and dc bias voltage induced piezoelectric effect of 0.9PMN-0.1PT, the PZT and 0.9PMN-0.1PT multilayer actuators can generate displacements of 3.8 um and 5.2 um respectively, under a dc voltage of 100 V. Because of the advantages of having compact size, lightweight and fast response, the PZT and 0.9PMN-0.1 PT multilayer actuators are installed into wireclamps as driving elements. The opening motions of the two modified wireclamps are monitored under dc and ac driving signals in order to show the feasibility of using piezoelectric / electrostrictive actuators in wireclamp applications. Under a dc voltage of 100 V, the PZT and 0.9PMN-0.1PT wireclamps can generate displacements of 35 um and 53 um respectively, which are about 10 times that of the driving elements. The displacement can be further amplified by improving the design of the wireclamp or by increasing the number of layers in the actuator.

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