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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 i SIMULATION AND FABRICATION OF PIEZOELECTRIC MEMS INKJET PRINT HEAD by PHAM VAN SO A BSTRACT 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 (1 st version-InkjetVer1) done in our STD Lab, the computer simulation and validation of inkjet have been investigated, and then the 2 nd version (InkjetVer2) with the modified nozzle shape was fabricated and characterized. In details, firstly the simulation of piezoelectric MEMS inkjet with the electro- mechanical-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 (3 rd 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. ii 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. iii DEDICATION To my parents Mr. Pham Van Vinh and Mrs. Le Thi Anh iv Table of contents ABSTRACT i A CKNOWLEDGMENTS ii Table of contents iv List of figures vi List of tables viii C HAPTER 1. INTRODUCTION 1 1.1 Piezoelectricity 2 1.1.1 Piezoelectric effect 2 1.1.2 Lead zirconate titanate (PZT) 3 1.2 Piezoelectric MEMS inkjet print head 5 1.3 Numerical simulation 7 1.3.1 Role of numerical simulation 7 1.3.2 General principle of numerical simulation 8 1.3.3 Numerical simulations of piezoelectric MEMS inkjet with CFD-ACE+ 9 1.4 References 10 C HAPTER 2. 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 C HAPTER 3. SIMULATION OF MICRODROP GENERATION IN PIEZOELETRIC MEMS INKJET PRINT HEAD 26 3.1 Introduction 27 3.2 Modeling and simulation settings 27 v 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 C HAPTER 4. 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 C HAPTER 5. 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 vi List of figures Fig.1-1. Direct piezoelectric effect in open circuit (a) and in shorted circuit (b) 2 Fig. 1-2. Converse piezoelectric effect: (a) free displacement and blocking force and (b) static and dynamic operation 3 Fig. 1-3. Structure of PZT unit cell: (a) Cubic (T≥T c ) an (b) tetragonal (T< T c ) 4 Fig. 1-4. Phase diagram for the PbZrO 3 -PbTiO 3 system. C: Cubic, T: Tetragonal, R I : Rhombohedral (high temp form), R II : Rhombohedral (low temp form), A: rthorhombic, M: MPB, and T c: Curie temperature 4 Fig. 1-5. Deformation mode of piezoelectric inkjet actuator: (a) squeeze, (b) bend, (c) push and (d) shear mode 6 Fig. 1-6. A typical approach to MEMS application from concept to devices 7 Fig. 1-7. Steps of overall solution procedure 8 Fig. 1-8. Modeling settings for design of piezoelectric MEMS inkjet. Computations are performed using CFD-ACE+ package software. 9 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 500- 600 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 (F max ) and maximum displacement (δ max ) 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 vii 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 5 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 9V- 21V and frequency above 15 kHz 37 Fig. 4-1. Schematic of piezoelectric inkjet print head structure (side view): (a) Inkjet version 1 and (b) Inkjet version 2 with the modified nozzle shape at locations marked 1 &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 1 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 [...]... ink chamber, channel and ink reservoir In the case of inkjet heads, print resolution is one of the primary measures of product performance When printing with inkjet heads, smaller, more tightly spaced droplets of ink result in sharper print quality However, this produces a smaller print area, resulting in an increased printing time To optimize both print quality and speed, a printer head must deliver... ink-jet printing system, is a combination of microfluidics and microfabrication (MEMS) and is used to eject small amounts of fluid on target surfaces 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 In addition, Piezoelectric inkjet print heads... CHAPTER 2 NUMERICAL AND EXPERIMENTAL STUDY ON ACTUATOR PERFORMANCE OF PIEZOELECTRIC MEMS INKJET PRINT HEAD Abstract In this study, we focused on considering the actuator performance of a piezoelectrically actuated inkjet print head with the numerical and experimental analysis The actuator part consisting of multi-layer membranes, such as piezoelectric, elastic and other buffer layers, and ink chamber was... background of piezoelectricity, types of piezoelectric MEMS inkjet head and general principle of numerical simulation 1 1.1 Piezoelectricity 1.1.1 Piezoelectric effect All polar crystals show piezoelectricity, since any mechanical stress T will result in strain because of the elastic properties of the materials And the strain will affect the polarization since the polarization is caused by a displacement of. .. technique) 6 1.3 Numerical simulation 1.3.1 Role of numerical simulation A typical approach to MEMS application from concept to devices can be shown in Fig 1-6 The approach consists of several steps such as specifications of MEMS device, design, modeling to evaluate performance, fabrication and testing Reviews of the modeling and test results enable optimization of the performance of the MEMS device Fig 1-6... method (FDM), finite volume method (FVM) and finite element method (FEM) So far, there have been a lot of commercial softwares developed based on these methods such as ANSYS, FEMLAB Intellisuite, CFD-ACE+, etc… Fig 1-7 Steps of overall solution procedure 8 1.3.3 Numerical simulations of piezoelectric MEMS inkjet with CFD-ACE+ Piezoelectric MEMS inkjet print head is a complex device integrated electromechanical-fluidic... characteristics of actuator membrane of piezoelectric MEMS inkjet head highly depend on this fluid-structure coupling Therefore, fluid-structure interaction is one of the primary concerns when studying piezoelectric inkjet head The later considers the generation of microdroplets which is influenced by a strong competition between cohesive and disruptive forces (i.e., driving force, viscous force and surface... The simulations have been performed by CFD-ACE+ package software known as a multiphysics modeling tool The details of simulation settings will be described in chapter 2 and chapter 3 The goals of these simulations are indicated in Fig 1-8 Fig 1-8 Modeling settings for design of piezoelectric MEMS inkjet Computations are performed using CFD-ACE+ package software 9 1.4 References [1] Paul Calvert, Inkjet. .. the destabilization of the ink liquid and generates the droplets if the competition between cohesive and descriptive forces occurs favorably Fig 1-5 Deformation mode of piezoelectric inkjet actuator: (a) squeeze, (b) bend, (c) push and (d) shear mode Piezoelectric MEMS inkjet structures used the piezoelectric thin film as main component of actuator part which has forcing function, and were integrated... transparencies as well as industrially printing information on cans or bottles Recently it has been used as free-form fabrication method for building three dimensional parts (maskless fabrication) and is also being used to produce arrays of proteins and nucleic acids The objective of this thesis is to investigate the piezoelectric MEMS inkjet print head from design to fabrication Therefore, this chapter . Piezoelectric MEMS inkjet print head 5 1.3 Numerical simulation 7 1.3.1 Role of numerical simulation 7 1.3.2 General principle of numerical simulation 8 1.3.3 Numerical simulations of piezoelectric MEMS. background of piezoelectricity, types of piezoelectric MEMS inkjet head and general principle of numerical simulation. 2 1.1 Piezoelectricity 1.1.1 Piezoelectric effect All polar crystals show piezoelectricity,. Science and Engineering Graduate School of SungKynKwan University MASTER OF SCIENCE SUPERVISOR LEE. JAICHAN SIMULATION AND FABRICATION OF PIEZOELECTRIC MEMS INKJET PRINT HEAD