Piezoelectric Shear Mode Inkjet Actuator
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Piezoelectric Shear Mode Inkjet Actuator Jürgen Brünahla,b, Alex M. Grishina, Sergey I. Khartseva, and Carl Österberga,b. a Division of Condensed Matter Physics, Department of Microelectronics and Information Technology, Royal Institute of Technology, Stockholm - Kista, SE-16440, Sweden. b Department of Advanced Manufacturing Technologies, XaarJet AB, Järfälla, SE-17526, Sweden. ABSTRACT We report on comprehensive characterization of piezoelectric shear mode inkjet actuators micromachined into bulk Pb(Zr0.53Ti0.47)O3 (PZT) ceramics. The paper starts with an overview of different inkjet technologies such as continuous jet and drop-on-demand systems, whereat main attention is turned on piezoelectric systems particularly Xaar-type shear mode inkjet color printheads. They are an example of complex microelectromechanical systems (MEMS) and comprise a ferroelectric array of 128 active ink channels (75 µm wide and 360 µm deep). Detailed information about manufacturing and principles of operation are given. Several techniques to control manufacturing processes and to characterize properties of the piezoelectric material are described: dielectric spectroscopy to measure dielectric permittivity ε′ and loss tanδ; ferroelectric hysteresis P-E loop tracing to get remnant polarization Pr and coercive field Ec, and a novel pulsed technique to quantify functional properties of the PZT actuator such as acoustic resonant frequencies and electromechanical coupling factor. Stroboscope technique has been employed to find correlation between the degradation of ink-jet performance and heat/high voltage treatment resulting in ferroelectric fatigue. INTRODUCTION Inkjet technologies The first practical inkjet device was patented in 1948 by Siemens Elema in Sweden [1]. This invention used a pressurized continuous ink stream to record a signal onto a passing recording media. In the early 1960s, it had been demonstrated that by applying a pressure wave pattern, the ink stream could be broken into droplets of uniform size and spacing [2]. This printing process is known as continuous inkjet (see Figure 1). By the late 1970s first drop-on-demand inkjet methods appeared. A drop-on-demand device ejects ink droplets only when they are used in imaging on the media. Many of the drop-on-demand inkjet Ink Charging systems were invented, developed and produced Reservoir Electrode commercially in the 1970s and 1980s, e.g. Siemens PT-80 serial character printer [3]. In these printers, on the application of voltage pulses, ink drops are ejected by a pressure wave created by mechanical motions of Head Deflection Waste piezoelectric ceramic actuators. Structure Plates Reservoir In 1979, Canon invented a method where ink drops were ejected from the nozzle by growth and collapse Figure 1: The functional principle of a continuous inkjet system. of a water vapour bubble on the top surface of a small
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heater located near the nozzle [4] (see Figure 2). Canon called this technology bubble jet. Apparently, during the same time period Hewlett Packard independe
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