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Simulation and Fabrication of Piezoelectric mems Inkjet Print head
MASTER OF SCIENCE SUPERVISOR LEE JAICHAN SIMULATION AND FABRICATION OF PIEZOELECTRIC MEMS INKJET PRINT HEAD A Thesis Presented by PHAM VAN SO Department of Materials Science and Engineering Graduate School of SungKynKwan University MASTER OF SCIENCE SUPERVISOR LEE JAICHAN SIMULATION AND FABRICATION OF PIEZOELECTRIC MEMS INKJET PRINT HEAD A Thesis Presented by PHAM VAN SO Submitted to the Graduate School of SungKynKwan University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE in Materials Science and Engineering June 2007 Department of Materials Science and Engineering Graduate School of SungKynKwan University SIMULATION AND FABRICATION OF PIEZOELECTRIC MEMS INKJET PRINT HEAD by PHAM VAN SO ABSTRACT Microelectromechanical systems (MEMS) have played an increasingly important role in sensor and actuator applications And its key contribution is that it has enabled the integration of multi-components (i.e., electronics, mechanics, fluidics and etc) on a single chip and their integration has positive effects upon performance, reliability and cost Compared to conventional electrostatic, thermal or magnetic actuating schemes, piezoelectric MEMS inkjet has the advantages of lower power consumption, lower voltage operation and relatively larger driving force Based on the primary design and fabrication of piezoelectric MEMS inkjet (1st version-InkjetVer1) done in our STD Lab, the computer simulation and validation of inkjet have been investigated, and then the 2nd version (InkjetVer2) with the modified nozzle shape was fabricated and characterized In details, firstly the simulation of piezoelectric MEMS inkjet with the electromechanical-fluid interaction has been performed In order to verify the simulation results, a fabrication and characterization of actuator part consisting of PZT-based actuating membrane and ink chamber was carried out These treatments are to determine how much “dynamic force”, in terms of membrane’s maximum displacement, maximum force and driving frequency, can be produced by the actuator membrane Secondly, a simulation of microdroplet generation in inkjet has also been done This work gives an understanding about the droplet generation process, and the effects of driving characteristics, fluid properties and geometrical parameters on droplet generation Especially, this simulation helps to predict how much “dynamic force” is required to generate mirodroplets The combination of both results (i.e., how much “dynamic force” produced and required) gives an effective guideline in designing inkjet structure Thirdly, in the experimental work, the fabrication of InkjetVer2 was carried out based on MEMS techniques And then its electrical, mechanical characteristics as well as possibility of ink ejection were also tested Finally, the feedback information from these simulation and experimental work helps to suggest a new design (3rd version - InkjetVer3) which is expected to produce enough “dynamic force” and possibly generate microdroplets Then, mask design and fabrication of InkjetVer3 have also been proceeding i ACKNOWLEDGMENTS First, I would like to thank my supervisors, Prof Dr Jaichan Lee and Assoc.Prof.Dr Dang Mau Chien for their professional guidance, constructive criticism and, last but not least, for giving me a good opportunity to study at the Semiconductor and thin film devices Lab, Department of Materials Science and Engineering, SungKyunKwan University I would also like to thank PhD candidate Sanghun Shin and MSc Jangkwen Lee for sharing their knowledge on MEMS processing with me as well as for their useful discussions Furthermore, I would like to thank Prof Minchan Kim and Dr Dongwon Lee in Jeju National University for their generous assistance on my simulation work And I’m so grateful to KIST, KITECH and other labs for sharing all the equipments available for my experimental work I would like to thank all STD lab’s members: Dr Leejun Kim, Dr Teakjib Choi, Dr Juho Kim, MSc Cho Ju Hyun, MSc Chul Ho Jung; PhD candidates Phan Bach Thang, Do Duc Cuong, Ong Phuong Vu and Eui Young Choi; Master candidates Hyun Kyu Ahn, Jihyun Park, Sukjin Jong and Byun Jun Kang; and lab’s secretaries for their invaluable help during my MSc course And my thanks send to my friends in SKKU, N.T.N Thuy, N.T Tien, N.T Xuyen and N.D.T Anh, for their helpful discussion and argument about my results Finally, I want to thank my parents and relatives for their constant encouragement and support ii DEDICATION To my parents Mr Pham Van Vinh and Mrs Le Thi Anh iii Table of contents ABSTRACT i ACKNOWLEDGMENTS ii Table of contents iv List of figures vi List of tables viii CHAPTER INTRODUCTION 1.1 Piezoelectricity 1.1.1 Piezoelectric effect 1.1.2 Lead zirconate titanate (PZT) 1.2 Piezoelectric MEMS inkjet print head 1.3 Numerical simulation 1.3.1 Role of numerical simulation 1.3.2 General principle of numerical simulation 1.3.3 Numerical simulations of piezoelectric MEMS inkjet with CFD-ACE+ 1.4 References 10 CHAPTER NUMERICAL AND EXPERIMENTAL STUDY ON ACTUATOR PERFORMANCE OF PIEZOELECTRIC MEMS INKJET PRINT HEAD 11 2.1 Introduction 12 2.2 Modeling and simulation settings 13 2.3 Experimental procedure 16 2.4 Results and discussion 17 2.4.1 Performance characteristics of PIPH actuator in air 17 2.4.2 Performance characteristics of PIPH actuator in liquid 18 2.5 Conclusion 20 2.6 References 21 CHAPTER SIMULATION OF MICRODROP GENERATION IN PIEZOELETRIC MEMS INKJET PRINT HEAD 26 3.1 Introduction 27 3.2 Modeling and simulation settings 27 iv 3.3 Results and discussion 29 3.3.1 Microdrop generation process 29 3.3.2 Effect of actuating characteristics 29 3.3.3 Effect of fluid properties 30 3.3.4 Effect of geometrical parameters 32 3.4 Conclusion 32 3.5 References 34 CHAPTER FABRICATION AND CHARACTERIZATION OF PIEZOELECTRIC MEMS INKJET PRINT HEAD 38 4.1 Introduction 39 4.2 Experiments 39 4.3 Results and discussion 41 4.4 Conclusion 42 4.5 Rerefences 44 CHAPTER CONCLUSION AND SUGGESTION 50 5.1 Conclusion 50 5.2 Suggestion (new design) 50 Appendix A Python Source Script for simulation of microdroplet generation (effects of driving characteristics and fluid properties) 52 Appendix B Pattern conditions for fabrication of Inkjetver2 54 Appendix C Dry etching conditions 55 v List of figures Fig.1-1 Direct piezoelectric effect in open circuit (a) and in shorted circuit (b) Fig 1-2 Converse piezoelectric effect: (a) free displacement and blocking force and (b) static and dynamic operation Fig 1-3 Structure of PZT unit cell: (a) Cubic (T≥Tc) an (b) tetragonal (T< Tc) Fig 1-4 Phase diagram for the PbZrO3-PbTiO3 system C: Cubic, T: Tetragonal, RI: Rhombohedral (high temp form), RII: Rhombohedral (low temp form), A: rthorhombic, M: MPB, and Tc: Curie temperature Fig 1-5 Deformation mode of piezoelectric inkjet actuator: (a) squeeze, (b) bend, (c) push and (d) shear mode Fig 1-6 A typical approach to MEMS application from concept to devices Fig 1-7 Steps of overall solution procedure Fig 1-8 Modeling settings for design of piezoelectric MEMS inkjet Computations are performed using CFD-ACE+ package software Fig 2-1 Model of a piezoelectric inkjet print head (PIPH) structure: (a) design and (b) CFD-ACE+ symmetric model with meshing grids 23 Fig 2-2 Flowchart of fabrication process (a) and SEM images (b) of PIPH actuator 23 Fig 2-3 Maximum displacement of PIPH actuator membrane (300 um): (a) simulation and (b) experiment Simulation was extended with membrane width of 500600 um 24 Fig 2-4 Dependence of actuator performance on geometrical parameters: (a) maximum displacement vs thickness ratio (PZT/support layer) and (b) maximum force (Fmax) and maximum displacement (δmax) vs membrane width 24 Fig 2-5 Resonance frequency (in air) of PIPH actuator membrane: (a) FEMLAB simulation and (b) experiment with HP4194A impedance analyzer 24 Fig 2-6 Deflection shape of actuator membrane interacting with liquid: (a) & (b) dome shape with one peak at low frequencies and (c) & (d) unexpected shape with more than one peak at higher frequencies (above 125 kHz < 379 kHz resonance frequency in air ) 25 Fig 2-7 Resonance frequency (in liquid) of PIPH actuator membrane: (a) simulation and (b) experiment 25 vi Fig 3-1 Inkjet head geometry, (a) Three dimensional (3D) and (b) 2D symmetric section in CFD-ACE+ 35 Fig 3-2 Microdrop generation process at driving displacement with amplitude of μm and frequency of 30 kHz 35 Fig 3-3 Droplet properties: no-droplet, single droplet and satellite droplets at various driving displacements (2~5um, 50 kHz) 36 Fig 3-4 Time duration for droplet generation at various actuating characteristics: (a) amplitude and (b) frequency Droplets are generated in one cycle or several cycles 36 Fig 3-5 Time duration for droplet generation with fluid properties: (a) surface tension and (b) viscosity High surface tension or viscosity makes cohesive forces predominant 36 Fig 3-6 Geometrical parameters: (a) relative chamber X1/X2, (b) aspect ratio d/h and (c) diffuser 37 Fig 3-7 Time duration for droplet generation vs.: (a) relative chamber size (A-type) and (b) aspect ratio (B-type & C-type) 37 Fig 3-8 Time duration for droplet generation vs driving characteristics of the selected structure (B-type) Microdroplet can be generated at an applied voltage of 9V21V and frequency above 15 kHz 37 Fig 4-1 Schematic of piezoelectric inkjet print head structure (side view): (a) Inkjet version and (b) Inkjet version with the modified nozzle shape at locations marked &2 45 Fig 4-2 Masks used for fabrication of PIPH : M1-M6 (wafer 1) and M7- M10 (wafer2) 45 Fig.4-3 Fabrication process flow of PIPH: (a) wafer 1-actuator and chamber and (b) wafer 2-channel and nozzle Both wafers are bonded by Eutectic bonding method 46 Fig 4-4 SEM and optical micrographs of the fabricated PIPH structure 47 Fig 4-5 Preparing for ejection test: (a) 4-inkjet heads on cell and (b) PCB-wire bonding and tube attachment 48 Fig 4-6 Ejection testing by high speed digital camera system 49 Fig 4-7 Meniscus vibration under an applied voltage of 10V-40 kHz 49 Fig 5-1 Model of InkjetVer3 (3-silicon wafers) 51 Fig 5-2 Masks used for fabrication of InkjetVer3 51 vii ... and fabrication of piezoelectric MEMS inkjet (1st version-InkjetVer1) done in our STD Lab, the computer simulation and validation of inkjet have been investigated, and then the 2nd version (InkjetVer2)... background of piezoelectricity, types of piezoelectric MEMS inkjet head and general principle of numerical simulation 1.1 Piezoelectricity 1.1.1 Piezoelectric effect All polar crystals show piezoelectricity,... Numerical simulations of piezoelectric MEMS inkjet with CFD-ACE+ 1.4 References 10 CHAPTER NUMERICAL AND EXPERIMENTAL STUDY ON ACTUATOR PERFORMANCE OF PIEZOELECTRIC MEMS INKJET PRINT HEAD