Physics of Piezoelectric Shear Mode Inkjet Actuators Ju¨rgen Bru¨nahl Stockholm 2003 Doctoral Dissertation Royal Institute of Technology Condensed Matter Physics Akademiskavhandlingsommedtillst˚andavKunglTekniskaH¨ogskolanframl¨agges till offentlig granskning f¨or avl¨aggande av teknisk doktorsexamen m˚andagen den 2 juni 2003 kl 10.00 i C1, Electrum, Isafjordsgatan 22, Kungl Tekniska H¨ogskolan, Stockholm/Kista. ISBN 91-628-5675-8 TRITA-FYS-5289 ISSN 0280-316X ISRN KTH/FYS/FTS/R--03/5289--SE ' Ju¨rgen Bru¨nahl, 2003 Universitetsservice US AB, Stockholm 2003 Abstract This thesis describes work on piezoelectric shear mode actuators used in drop- on-demand ink printing applications. These actuators comprise an array of ink channels micromachined into bulk Pb(Zr Ti )O (PZT) ceramics. x 1−x 3 During this study, a new pulsed spectroscopic technique was developed to in- vestigate functional properties of a single channel wall of the actuator. The pulse techniqueis basedon recordingthe transientcurrentin response toa shortvoltage pulse applied to the channel wall. An electric field applied perpendicular to the polarization will cause a shear motion of the wall. If a voltage pulse with a fast rise time is high enough in amplitude to actuate the wall, it will act like a tuning fork and oscillate at it’s resonant frequencies. Because of the piezoelectric effect, the mechanical oscillations of the wall can be seen as oscillations in the transient current. Besidethepulsedtechnique,dielectricspectroscopy,ferroelectrichysteresisloop tracing and stroboscopy were used as characterization techniques. The results ob- tained are discussed in respect to temperature dependence, frequency dispersion, ferroelectric fatigue and acoustic resonance modes. Another field of interest was the temperature inside the actuator. An electric circuit,basedonthevoltagedividerprinciple,wasbuilttomonitortheinktemper- atureasafunctionoftheprintingpattern. ‘Dummywalls’,locatedatthebeginning and the end of the channel wall array, were used as temperature sensing elements. SincethedielectricpermittivityofthePZTchannelwallsdependsontemperature, the capacitance of the ‘dummy walls’ changes with temperature. The information obtained by this measurement technique was used to investigate alternative mate- rials for the passive components of the actuator. A further part was the development of a new actuator design called a ‘Chevron actuator’. Chevron actuators include an additional PZT layer with polarization in the opposite direction to the base plate polarization. Thus, the whole channel wall is used as the active part instead of using just the upper half as in the standard actuator. The main advantage of this technique is a reduced power consumption of the actuator and therefore less heat dissipation. Different approaches were used to construct Chevron actuators. Experiments determined the efficiency of the actuators and these results were used to make improvements. The Chevron actuators were characterized by the above mentioned techniques and compared with standard Xaar actuators. ISBN91-628-5675-8•TRITA-FYS-5289•ISSN0280-316X•ISRNKTH/FYS/FTS/R--03/5289--SE iii iv Preface ThepresentworkinthisthesiswascarriedoutatthedivisionofCondensedMatter Physics (KMF), Laboratory of Solid State Devices, in the Department of Micro- electronics and Information Technology, Royal Institute of Technology (KTH), in StockholmtowardsaSwedishDoctoraldegreefromOctober1999toJune2003and was funded by XaarJet AB and by the Swedish agency NUTEK. This thesis is divided into two parts. The first part, Introduction, gives a brief introduction into the field of inkjet printing. Different inkjet technologies are re- viewedwithmainemphasizeonXaar-typeshearmodeactuators. Chapter2reviews the properties of lead zirconate titanate (PZT), the piezoelectric material Xaar ac- tuators are made of. Chapter 3 describes the characterization techniques we have used. The second part, Our research, describes and discusses experiments and new actuatordesignsinChapters4to6. Chapter7containsasummaryoftheincluded papers and manuscripts with comments on my participation. This thesis is based on the following publications, manuscripts and patents I. “Dielectric and Pulsed Spectroscopy of Shear Mode PZT Microactuator” Ju¨rgen Bru¨nahl, Alex Grishin, and Sergey Khartsev Mat. Res. Soc. Proc. 657, EE4.6 (2000). II. “Non destructive Pulsed Technique to Characterize Functional Properties of Micromachined Bulk PZT” J. Bru¨nahl, A.M. Grishin, and S.I. Khartsev 3rd Asian Meeting on Ferroelectrics, Hong Kong, December 2000 Ferroelectrics 263, 187-192 (2001). III. “Thermometry Inside Inkjet Actuators” Werner Zapka, Ju¨rgen Bru¨nahl, Onne Wouters, and Mike de Roos Proc. DPP 2001, International Conference on Digital Production Printing and Industrial Applications, 392-396, (2001). v vi Abstract IV. “Piezoelectric shear mode inkjet actuator” Ju¨rgen Bru¨nahl, Alex M. Grishin, Sergey I. Khartsev, Carl O¨sterberg Mat. Res. Soc. Proc. 687, B1.4 (2002). V. “Piezoelectric shear mode drop-on-demand inkjet actuator” Ju¨rgen Bru¨nahl, Alex M. Grishin Sensors and Actuators A: Physical, Volume 101, Issue 3, 371-382 (2002). VI. ““Chevron”-type piezoelectric inkjet actuator” Ju¨rgen Bru¨nahl, Alex M. Grishin Proceedings of the 13th IEEE International Symposium on the Applications of Ferroelectrics, ISAF, 491-494 (2002). VII. “Droplet Deposition Apparatus” Werner Zapka, Ju¨rgen Bru¨nahl, Bosse Nilsson, and Mike de Roos Xaar Technology Limited, WO Patent no. 02/26500, (2001). VIII. “Fatigue of shear mode PZT actuator” Vincent Ferrer, Ju¨rgen Bru¨nahl, Alex Grishin Manuscript 2003. Thefollowingpapershavebeenpublishedorsubmitted,butarenotincludedin this thesis: I. “Piezoelectric Chevron Inkjet Actuator by In-Process Polarisation Reversal” Ju¨rgen Bru¨nahl, Gerald Richter, Thomas J¨ager, Werner Zapka Submitted to European Meeting on Ferroelectrics EMF 2003, Cambridge, UK. II. “DepolarisationDamagesofLeadZirconateTitanate(PZT)Ceramicsduring Micromachining” Ju¨rgen Bru¨nahl, Gerald Richter, Thomas J¨ager, Werner Zapka Submitted to European Meeting on Ferroelectrics EMF 2003, Cambridge, UK. III. “Increased Inkjet Printing Frequency From ’Offset Channel’ Printheads” Werner Zapka, Mark Crankshaw, Ju¨rgen Bru¨nahl, Lars Levin, Uwe Her- rmann, and G¨otz Mu¨nchow Submitted to NIP19: The l9th international Congress on Digital Printing Technologies 2003,New Orleans, USA. Acknowledgements First, I would like to thank my supervisors, Prof. Alex Grishin at KTH and Dr.WernerZapkaatXaarJet AB,fortheirprofessionalguidance,constructivecrit- icism, and not least for giving me the opportunity to study at the Department of Condensed Matter Physics. I would also like to thank Dr. Sergey Khartsev for sharing his knowledge on ferroelectrics with me as well as for his generous technical assistance and many useful discussions. Furthermore,IwouldliketothankXaarJetAB andallcolleaguesformakingall the equipment available for my work and more important, I am grateful for having the possibility to work freely and independently with the appliances. My special thanks to Jan Eriksson and Mike de Roos. I would like to thank all the people who joint me during the last years, Wolf- gangVoit,myfirstroommate,mycolleaguesatKMF,PeterJohnsson,S¨orenKahl, Mats Blomqvist, Vasyl Denysenkov, Jang-Yong Kim and Joo-Hyong Kim, and all the German students at Xaar, (even though unable to name all, I wish to thank JorritRouw´e,GerritGrunwaldandG¨otzMu¨nchow)forbeingsuchanicecompany. Last but not least, I would like to thank Jung-Hyuk Koh and family for their gen- erous hospitality during my Seoul visit. Ett stort tack till mina kompisar, Eva, ˚Asa, Cissi, Staffan och Christer. Finally, I want to thank Eva and Clara and my family for their constant en- couragement and support. vii viii Contents Abstract iii Preface iv List of Papers v I Introduction 3 1 Inkjet Technologies 5 1.1 History of inkjet technologies . . . . . . . . . . . . . . . . . . . . . 5 1.2 Continuous inkjet . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 1.3 Drop-on-demand inkjet . . . . . . . . . . . . . . . . . . . . . . . . 7 1.3.1 Thermal inkjet . . . . . . . . . . . . . . . . . . . . . . . . . 7 1.3.2 Piezoelectric inkjet . . . . . . . . . . . . . . . . . . . . . . . 8 1.4 Xaar-type shear mode inkjet actuator . . . . . . . . . . . . . . . . 11 1.4.1 Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 1.4.2 Drop generation . . . . . . . . . . . . . . . . . . . . . . . . 12 1.4.3 Manufacturing . . . . . . . . . . . . . . . . . . . . . . . . . 13 1.4.4 Print resolution . . . . . . . . . . . . . . . . . . . . . . . . . 15 1.4.5 Geometrical aspects . . . . . . . . . . . . . . . . . . . . . . 16 2 Lead Zirconate Titanate (PZT) ceramics 23 2.1 History of PZT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 2.2 Ferroelectricity and dipole structure . . . . . . . . . . . . . . . . . 23 2.2.1 Ferroelectric domains . . . . . . . . . . . . . . . . . . . . . 24 2.2.2 Polarization and poling . . . . . . . . . . . . . . . . . . . . 26 2.2.3 Ferroelectric hysteresis . . . . . . . . . . . . . . . . . . . . . 26 2.2.4 Dielectric permittivity and dielectric loss . . . . . . . . . . 27 2.2.5 Electromechanical coupling coefficient . . . . . . . . . . . . 28 2.2.6 Curie temperature . . . . . . . . . . . . . . . . . . . . . . . 28 2.3 Piezoelectricity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 ix x Contents 2.3.1 Definition of piezoelectric coefficients and directions . . . . 29 2.3.2 Piezoelectric effect . . . . . . . . . . . . . . . . . . . . . . . 29 2.3.3 Lead zirconate titanate (PZT) . . . . . . . . . . . . . . . . 30 2.3.4 Shear mode displacement . . . . . . . . . . . . . . . . . . . 30 3 Characterization techniques 33 3.1 Dielectric spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . 33 3.2 Manual resonance test . . . . . . . . . . . . . . . . . . . . . . . . . 35 3.2.1 Description . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 3.2.2 Behavior of PZT near mechanical resonance . . . . . . . . . 36 3.3 Pulsed spectroscopy technique. . . . . . . . . . . . . . . . . . . . . 38 3.4 Ferroelectric hysteresis P-E loop . . . . . . . . . . . . . . . . . . . 40 3.5 Stroboscope technique . . . . . . . . . . . . . . . . . . . . . . . . . 42 3.5.1 Drop velocity measurement . . . . . . . . . . . . . . . . . . 43 3.5.2 Drop volume measurement . . . . . . . . . . . . . . . . . . 43 II Our research 45 4 Physical properties of Xaar inkjet actuators 47 4.1 Temperature dependence of the dielectric properties . . . . . . . . 47 4.2 Frequency dispersion . . . . . . . . . . . . . . . . . . . . . . . . . . 48 4.3 Ferroelectric fatigue . . . . . . . . . . . . . . . . . . . . . . . . . . 50 4.4 Acoustic resonance modes . . . . . . . . . . . . . . . . . . . . . . . 53 4.5 Correlation with inkjet performance . . . . . . . . . . . . . . . . . 55 5 Thermometry inside inkjet actuators 57 5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 5.2 Theoretical background . . . . . . . . . . . . . . . . . . . . . . . . 58 5.2.1 Temperature compensation . . . . . . . . . . . . . . . . . . 58 5.2.2 Existing temperature compensation . . . . . . . . . . . . . 58 5.2.3 Temperature dependence of channel wall capacitance . . . . 59 5.3 Experimental setup . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 5.3.1 Modification of the printhead . . . . . . . . . . . . . . . . . 61 5.3.2 Electronics . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 5.4 Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 5.4.1 Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 5.4.2 Temperature differences induced by ink flow . . . . . . . . . 63 5.4.3 Temperature differences induced by print pattern . . . . . . 63 5.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67