Microfluidic sensor based on aln vertical saw structure investigation, design and simulation

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VIETNAM NATIONAL UNIVERSITY, HANOI UNIVERSIRY OF ENGINEERING AND TECHNOLOGY ---------- BUI THU HANG MICROFLUIDIC SENSOR BASED ON ALN VERTICAL SAW STRUCTURE: INVESTIGATION, DESIGN AND SIMULATION MASTER THESIS in ELECTRONICS AND TELECOMMUNICATIONS TECHNOLOGY Hanoi – 2013 ---------- BÙ Ê B Ứ , Ằ Ế KẾ V M ẢM B Ế V LỎ S W Ứ L Ậ VĂ P Ỏ Ó Ấ Ê VẬ L SĨ l Ử-V Ễ à ội – 2013 Ú Microfluidic Sensor based on AlN Vertical SAW structure: Investigation, Design and Simulation TABLE OF CONTENT GLOSSARY .............................................................................................................. 3 ACKOWNLEDGEMENTS ..................................................................................... 4 LISTS OF TABLES ................................................................................................. 5 LISTS OF FIGURES ............................................................................................... 6 Chapter 1 Introduction ...................................................................................... 8 1.1 Motivation and Objectives............................................................................ 8 1.2 Organization of Thesis.................................................................................. 9 Chapter 2 Theoretical Analysis of the AlN-based Microfluidic Sensor ...... 12 2.1 Introduction ................................................................................................ 12 2.2 Surface Acoustic Waves ............................................................................. 13 2.2.1 Shear Horizontal Surface Acoustic Waves (SH-SAWs) ..................... 13 2.2.2 Rayleigh Surface Acoustic Waves (R-SAWs) .................................... 14 2.3 Propagation of Acoustic Waves in contact with a Liquid Medium ........... 16 2.3.1 Boundary Conditions ........................................................................... 19 2.3.2 Standing and Linear Motion Medium.................................................. 19 2.3.3 Moving Liquid Medium....................................................................... 20 2.4 Equivalent Circuit Model of SAW Devices ............................................... 21 2.4.1 Model Implementation ......................................................................... 21 2.4.2 Frequency Response ............................................................................ 22 2.4.3 Attenuation........................................................................................... 22 2.5 Conclusion .................................................................................................. 23 Chapter 3 3-D Design of AlN-based Microfluidic Sensor ............................. 24 3.1 General Description .................................................................................... 24 3.2 Design Principles ........................................................................................ 25 3.3 FEM Simulation for AlN-based Microfluidic Sensor ................................ 29 3.3.1 General Configuration ......................................................................... 29 3.3.2 Lithium Niobate ................................................................................... 30 3.3.3 Aluminium Nitride ............................................................................... 33 Bui Thu Hang Page 1 Microfluidic Sensor based on AlN Vertical SAW structure: Investigation, Design and Simulation 3.4 Masks designed........................................................................................... 35 Chapter 4 Results and Discussion ................................................................... 38 4.1 General Description .................................................................................... 38 4.2 Density and viscosity .................................................................................. 38 4.2.1 Lithium Niobate Crystal ...................................................................... 38 4.2.2 Aluminium Nitride Crystal .................................................................. 43 4.3 Sensing Liquid Status ................................................................................. 45 4.3.1 Constant Velocity ................................................................................ 45 4.3.2 Non-constant Velocity ......................................................................... 49 4.4 Conclusion .................................................................................................. 53 Chapter 5 Conclusions and Future Work ...................................................... 54 5.1 Conclusions ................................................................................................ 54 5.2 Future work................................................................................................. 54 Reference ................................................................................................................. 56 Appendix: Material Parameters for Piezoelectric Substrate ............................. 59 A. Lithium Niobate .......................................................................................... 59 B. Aluminium Nitride ..................................................................................... 59 Bui Thu Hang Page 2 Microfluidic Sensor based on AlN Vertical SAW structure: Investigation, Design and Simulation LOSS Y IDT InterDigital Transducer SAW Surface Acoustic Wave R-SAW Rayleigh Surface Acoustic Wave SH-SAW Shear-Horizontal Surface Acoustic Wave LiNbO3 Lithium Niobate Mo Molybdenum Al Aluminium AlN Aluminium Nitride Si Silicon SOI Silicon On Insulator Bui Thu Hang Page 3 Microfluidic Sensor based on AlN Vertical SAW structure: Investigation, Design and Simulation KOW LED EME S I would like to sincerely thank my advisor, Assoc. Prof. Chu Duc Trinh for their encouragement, guidance, and invaluable supports throughout the course of this study. He guided me in studying microfluidics and always gave me meaningful and profound explanations. I would like to gratefully acknowledge Dr. Tran Duc Tan and Assoc. Prof. Rusu Vasile Catelin for useful suggestions in my dissertation. Their guidance enabled me to complete my thesis work. I am also highly thankful to all teachers at Dept. of Electronics and Telecommunications for supports and encouragement. Many thanks to staff in department for their helps of thesis defence procedures. Finally, it is my profound gratitude to my family, especially my mom, my cousin Phan Quoc Vi for their moral supports and encouragement in my life. Bui Thu Hang Page 4 Microfluidic Sensor based on AlN Vertical SAW structure: Investigation, Design and Simulation L S S OF BLES Table 3.1: Physical properties of the chosen liquids. ................................................33 Table 3.2: Parameters of SAW device based on Aluminium Nitride Crystal. .........34 Table 3.3: Design parameters of AlN-based SAW device........................................34 Table 3.4: The design parameters for AlN-based microfluidic sensor with single channel. .....................................................................................................................36 Table 3.5: The design parameters for AlN-based microfluidic sensor with multichannel ......................................................................................................................36 Bui Thu Hang Page 5 Microfluidic Sensor based on AlN Vertical SAW structure: Investigation, Design and Simulation L S S OF F ES Figure 1.1: The flow chart for the development process of an AlN-based Microfluidic Sensor prototype. .................................................................................10 Figure 2.1: Acoustic wave propagation direction in a Cartesian coordinate system. ...................................................................................................................................13 Figure 2.2: (a) The typical SH-SAW structure. (b) Illustration of shear horizontal (SH) polarized displacement. ....................................................................................14 Figure 2.3: (a) Schematic of the particle motion for a Rayleigh wave. (b) Ultrasonic radiation into water by SAW when sensing channel placed on substrate.................15 Figure 2.4: (a) The simple SAW structure for sensing liquid. (b) Ultrasonic radiation into water when sensing channel is placed along the vertical axis of device. .......................................................................................................................16 Figure 2.5: Principle construction of multilayer SAW sensor. .................................17 Figure 2.6: Geometry of the problem for analysing propagation of Rayleigh waves. ...................................................................................................................................18 Figure 2.7: Mason equivalent circuit model. ............................................................21 Figure 3.1: Schematic drawing of the integrated inkjet system. ...............................26 Figure 3.2: Top and cross-view of one-channel microfluidic sensor........................27 Figure 3.3: Top and cross-view of two-channel microfluidic sensor. ......................28 Figure 3.4: Top and cross-view of one-input two-channel microfluidic sensor. ......28 Figure 3.5: Top and cross-view of multi-output microfluidic sensor. ......................29 Figure 3.6: Schematic illustration of two-channel R-SAW sensor and liquid well position. .....................................................................................................................30 Figure 3.7: Design parameters of Channel 1 and well size .......................................31 Figure 3.8: Meshed image of 3D SAW model with the well in the middle of the wave propagation path ..............................................................................................32 Figure 3.9: General view for all devices in one die. .................................................35 Figure 4.1: Total displacement of corresponding points in Channel 1 and Channel 2 with different well diameters ....................................................................................39 Bui Thu Hang Page 6 Microfluidic Sensor based on AlN Vertical SAW structure: Investigation, Design and Simulation Figure 4.2: Total displacement of the well behind points with three liquid types. ...40 Figure 4.3: Output voltage of Group 1 from the 3-D SAW model with and without deposited well from 0 to 130 nsec.............................................................................41 Figure 4.4: Output voltage of Group 2 from the 3-D SAW model with and without deposited well from 0 to 130 nsec.............................................................................43 Figure 4.5: (a) Total displacement envelops of points placed behind the well.........43 Figure 4.6: Electrical attenuation response (shown as insertion loss) for the SAW device. .......................................................................................................................44 Figure 4.7: The time delay of system with the well having liquid density =1, 3, 6, and 12 g/cm3. .............................................................................................................44 Figure 4.8: Potential amplitude at center frequency on the IDT receiver for linear group..........................................................................................................................45 Figure 4.9: Ratio coefficient of displacement amplitudes before and after the well for linear group. .........................................................................................................46 Figure 4.10: (a) Delay time and (b) Velocity decay coefficient when liquid moves linearly. ......................................................................................................................47 Figure 4.11: Attenuation corresponding to linear motion function. .........................48 Figure 4.12: Effect of SAWs on linear fluid flow.....................................................49 Figure 4.13: Potential amplitude at center frequency on the IDT receiver for exponential motion group. ........................................................................................50 Figure 4.14: Ratio coefficient of displacement amplitudes before and after the well for exponential motion group. ...................................................................................50 Figure 4.15: Velocity decay for exponential motion group. .....................................51 Figure 4.16: Delay time when liquid moves nonlinearly. .........................................51 Figure 4.17: Attenuation corresponding to exponential motion function. ................52 Figure 4.18: Effect of SAWs on exponential fluid flow. ..........................................52 Bui Thu Hang Page 7 Microfluidic Sensor based on AlN Vertical SAW structure: Investigation, Design and Simulation Chapter 1 ntroduction 1.1 Motivation and Objectives In recent years, microfluidic technology received a lot of attention because its widespread applications in printing, biomedicine. Device integration and miniaturization based on microfluidic technology has been growing up quickly. In addition, expected devices may have advantages such as: small size, facile usage and low cost, fast detection speed, high accuracy, less consumption power and high integration capability. One of the present microfluidic technologies utilizes surface acoustic wave (SAW) [1][2]. It is well-known owing to applications such as actuators, antennas and driven droplet manipulation using SAW atomization and jetting technique [3][4][5]. SAW devices are also widely utilized in sensors [6]. Such devices convert electrical energy into mechanical energy and vice versa. Specifically, when the transformation from electrical to mechanical energy occurs at the InterDigital Transducder (IDT) transmitter, acoustic waves travel through the surface. SAW waves include Rayleigh waves, and sliding shear waves. The amplitude of the Rayleigh-SAWs of around 10Å is very small and exponentially declines. Because wave penetration into the substrate is inversely proportional to frequency, in order to limit reflections and refractions at the bottom, the material size is large enough. This mechanical vibration on the surface continues until opposite transform process at the IDT receiver. Waves that do not retransform electrical energy at the receiver are absorbed by wax, polyimide placed before and after the input and output IDT. Sensing mechanism is electrical perturbation on the IDT receiver due to obstacles on the propagation path or even if R-SAWs travel through the different media [7]. Prominent advantages of SAW devices are micro derivation size for fluid, high sensitivity and fabrication ability on compatible material. The structure trend is vertical sensing channel. This suggests the requirement of the vertical SAW sensor. Bui Thu Hang Page 8 Microfluidic Sensor based on AlN Vertical SAW structure: Investigation, Design and Simulation Moreover, the acoustic wave propagation strongly depends on the properties of nanostructure sensing layers which in turn can be altered by the wave vibration itself. Here, it is able to be piezoelectric thin film on the substrate or piezoelectric crystal such as quartz, Lithium Tantalate (LiTaO3), Lithium Niobate (LiNbO3), especially Aluminium Nitride (AlN) because of high frequency and being compatible with the CMOS technology. Thus, it is necessary to understand both the wave propagation and the nanomaterial properties in order to uncover the sensing mechanism and improve the performance of acoustic sensors. This dissertation focuses: 1. Understanding the components and the propagation characteristics of liquid SAW devices. 2. Investigating the electrical and mechanical properties of SAW devices on common piezoelectric, LiNO3, and CMOS material, AlN, when there are impacts of fluid such as density, viscosity and motion in the sensing channel. 3. Developing novel SAW sensors for microfluidics. 4. Integration ability in ink sensing applications. 1.2 Organization of Thesis We adopt the development process in Figure 1.1. It is assumed that the SAW sensor works in an ideal environment. The theoretical derivation and analysis are performed to qualitatively verify the proposed design. In order to achieve the quantitative analysis, the finite element method (FEM) will be studied and implemented with the software Comsol Multiphysics. According to these verification results, it demonstrates the fabrication capacity of the AlN-based microfluidic sensor in the future. Bui Thu Hang Page 9 Microfluidic Sensor based on AlN Vertical SAW structure: Investigation, Design and Simulation Figure 1.1: The flow chart for the development process of an AlN-based Microfluidic Sensor prototype. The dissertation is organized as following: Chapter two describes the acoustic waves in the piezoelectric and liquid medium. It gives electrical properties of SAW devices through the equivalent Mason circuit. Also, the analysis of leaky phenomenon induced by Rayleigh wave interaction with the liquid medium is presented. Chapter three discusses the design and realization of SAW microfluidic sensor using LiNbO3, AlN. Modelling procedure is conducted by Finite Element Method (FEM). Optimization of sensor parameters in the simulation driving to enhanced amplitude fields and lower propagation loses; thereby increasing device sensitivity is discussed. Besides, several masks in the experiment are described. Bui Thu Hang Page 10 Microfluidic Sensor based on AlN Vertical SAW structure: Investigation, Design and Simulation Chapter four is the major simulation results for sensing density and status of liquid in the well, the explanations and analyses of obtained results. Chapter five summarizes the main contributions and provides suggestions for possible future studies. Bui Thu Hang Page 11 Microfluidic Sensor based on AlN Vertical SAW structure: Investigation, Design and Simulation Chapter 2 heoretical nalysis of the l -based Microfluidic Sensor 2.1 Introduction SAW devices have been studied in chemistry, biomedicine and telecommunication for many decades, especially sensors including automotive (torque and tire pressure sensors), medical applications (biosensors) and industrial, commercial applications (vapour, humidity, temperature and mass sensors) [8]. Measurands on acoustic wave sensor are wave velocity perturbation, changes of confinement dimensions, degree of the traveling wave damping and input-output variation [9]. An important distinction between types can be defined according to the natures of the acoustic wave and vibration modes. Traveling waves can be bulk acoustic waves (BAWs) propagating on the interior of the substrate and SAWs on the surface. To the SAW sensor, a mechanical wave, generated by piezoelectric crystal using metal electrodes or called interdigital transducers (IDTs), travels along the surface [6][10]. It includes a Rayleigh and a shear mode which propagate through the surface as shown in Figure 2.1. The Rayleigh mode, called Rayleigh wave, is a combination of longitudinal and shear vertical particle displacement while the shear mode, called Shear Horizontal – Surface Acoustic Wave (SH-SAW), is a shear horizontal wave on the surface [11][12]. Other surface waves are Love waves (LWs) where the acoustic waves are guided in the foreign layer and surface transverse waves (STW) where guiding waves are on a piezoelectric substrate under a shallow groove or on thin metal strip gratings [13]. Bui Thu Hang Page 12 Microfluidic Sensor based on AlN Vertical SAW structure: Investigation, Design and Simulation Figure 2.1: Acoustic wave propagation direction in a Cartesian coordinate system. (a) Compressional or longitudinal; (b) Shear vertical; (c) Shear horizontal. 2.2 Surface Acoustic Waves 2.2.1 Shear Horizontal Surface Acoustic Waves (SH-SAWs) A typical structure of SH-SAW device for liquid has a horizontal channel on the substrate (see Figure 2.2a). When the liquid is loaded on the propagating surface, the SH-SAWs can travel along the interface between the liquid and the substrate and are influenced by its properties as shown in Figure 2.2b. As the penetration depth of the shear horizontal (SH) particle into liquid is very low, SH-mode SAW sensors were utilized for sensing liquid without significant radiation losses [14]. For example, in 1977, Nakamura et al. proposed a pseudo SH-SAW on the 36-degree rorated Y-cut X-propagating LiTaO3 (36YXLT). In 1999, Shiokawa et al. presented a liquid-phase sensor using a SH-SAW on the 36YXLT [15]. Bui Thu Hang Page 13 Microfluidic Sensor based on AlN Vertical SAW structure: Investigation, Design and Simulation Figure 2.2: (a) The typical SH-SAW structure. (b) Illustration of shear horizontal (SH) polarized displacement. 2.2.2 Rayleigh Surface Acoustic Waves (R-SAWs) As mentioned above, Rayleigh wave is composed of compressional or longitudinal displacement and shear vertical displacements while the compressional component is confined at the surface down to a penetration depth of the order of the wavelength. The particle motion in the piezoelectric where Rayleigh waves pass is sought in the form of an ellipse as shown in Figure 2.3a [16]. Hence, Rayleigh with a particle displacement perpendicular to the device surface can be radiated into the liquid medium and cause an excessive attenuation if the contact between liquid and piezoelectric is too large. On the other hand, leaky SAWs that are converted from Bui Thu Hang Page 14 Microfluidic Sensor based on AlN Vertical SAW structure: Investigation, Design and Simulation SAWs are excited at a Rayleigh angle R in the boundary and consequently their energy radiates into the liquid in Figure 2.3b. It is difficult to realize a liquid-phase by the Rayleigh wave devices when the liquid is placed on the piezoelectric. Figure 2.3: (a) Schematic of the particle motion for a Rayleigh wave. (b) Ultrasonic radiation into water by SAW when sensing channel placed on substrate We proposed a novel vertical structure for the liquid sensing applications based on Rayleigh waves in Figure 2.4a [14]. The key is that the solid-liquid contact area, closing to surface, is smaller (as shown in Figure 2.4b). It is presented that there exists a liquid medium in the propagation path with the coordinate system, thereby the longitudinal component should have an inappreciable attenuation. Bui Thu Hang Page 15 Microfluidic Sensor based on AlN Vertical SAW structure: Investigation, Design and Simulation Figure 2.4: (a) The simple SAW structure for sensing liquid. (b) Ultrasonic radiation into water when sensing channel is placed along the vertical axis of device. 2.3 Propagation of Acoustic Waves in contact with a Liquid Medium As the SAW motion spreads below the surface to a depth of about one wavelength [7], the effect of the second layer below the piezoelectric might be ignored if the thin film is thick. So, it is assumed that the thin film is thick enough to prevent acoustic waves from reflecting on the bottom, reflection wave interference phenomenon may be cancelled. The geometry of acoustic waves propagating in a piezoelectric substrate in contact with a fluid and solid medium is shown in Figure 2.5. To satisfy the stress-free boundary, compression and shear waves propagate together on the substrate. It is assumed that the generalized surface acoustic wave Bui Thu Hang Page 16 Microfluidic Sensor based on AlN Vertical SAW structure: Investigation, Design and Simulation propagates in the (X1, X2) and has a displacement profile which varies with the depth X3 of the single-crystal (see Figure 2.6): ( ) [ where k is the wave number, ] ( ) (1), is the velocity of the wave, b is the decay constant of the wave in the X3 direction, X1, X2, X3 is the unit vectors and (l1, l2) is the set of propagation direction along the surface. The component X3 is perpendicular to the surface and W1, W2, W3 represent the displacement amplitudes of the X1, X2 and X3 directions, respectively. It is assumed that there exists a liquid medium positioned in the propagation path with the coordinate system. The Rayleigh wave is characterized by the absence of a transversal component. Thus Eq. 1 omits X2 and l1 equals to the unit. Hence, the travelling wave form is independent of the X2 coordinate. Since the displacement component u2 is removed, l2 is zero. Figure 2.5: Principle construction of multilayer SAW sensor. Bui Thu Hang Page 17 Microfluidic Sensor based on AlN Vertical SAW structure: Investigation, Design and Simulation Figure 2.6: Geometry of the problem for analysing propagation of Rayleigh waves. In the following, the fluid situation is considered. For a non-conducting, nonviscous fluid, the elastic constant matrix is presented in the Appendix. As the direction of fluid flow is across the X3 coordinate, generated the surface acoustic wave travels in the direction X1 and has a displacement profile that varies with depth X3 into the piezoelectric substrate as following: ( where k is the wave number, ( ) ( ) (2) ( ) ) (3) (4), is the acoustic wave velocity in the liquid medium, bf is the decay constant of the wave in the X3 direction and (l1, l2) is the set of propagation direction along the liquid medium and W2 is the weight of the potential . The component X3 is perpendicular to the surface and W1, W3 represent the displacement amplitudes of the X1 and X3 directions, respectively. ( ) is the fluid motion function which disturbs not only the acoustic wave velocity but also the decay constant bf. The fluid viscosity is ignored in Eq. 1. Bui Thu Hang Page 18
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