Ghosh, Head of the Center for providing the facilities to carry out the research work. I would like to thank Gowind for helping sort some of the experimental data. Finite Element Method (FEM) simulation shows that when the resonant frequency of the columns is close to the resonant frequency of the resonator, extraordinary changes in the mass load occur.
The pillars and the SAW resonator form a system of coupled resonators, and the deviations in the system frequency are large when the resonant frequencies of the two coupled systems are close. Total displacement profile at an antiresonant frequency of 98.5 MHz, (c) vertical particle displacement, (d) horizontal particle displacement.
List of Tables
List of Symbols
Types of surface acoustic waves
Surface acoustic waves, the wave propagates on the surface of the material, while bulk waves, the wave propagates throughout the mass of the solid. There are two basic types of wave motion: Longitudinal waves are of a type where the displacement of particles is parallel to the direction of wave propagation. The second type is transverse or shear waves, where the displacement is in any direction parallel to the wave front, normal to the direction of propagation [2].
Introduction to Surface Acoustic Wave Sensor
- Generation of surface acoustic waves
- SAW devices
- SAW devices in sensor applications
- Literature reports on SAW sensors
- Problem definition
- Scope of the thesis
- Thesis outline
- The equivalent circuit model
A SAW delay line consists of two IDTs on the surface of the substrate, separated by a few wavelengths. Let V1 and V2 be the speed of the SAW received in the receiver without and. a) A SAW delay line sensor and (b). Thus, a change in the properties of the detection medium will change the resonant frequency of the SAW resonator.
In the last part of the chapter, the FEM simulation and results of a single-port SAW resonator, the SAW delay line configuration, the mass sensitivity analysis of a SAW delay configuration and the SAW hydrogen sensor are reported. Validation of experimental results with FEM simulation of the SAW resonator with SU-8 resonant pillar structure is described in the chapter.
Modeling and Simulation of SAW Devices
- Coupling of mode model
- Solution of surface wave
- Finite element method (FEM)
- FEM Simulation of One-Port SAW resonator using COMSOL Multiphysics
- FEM simulation of a SAW delay line using COMSOL Multiphysics .1. The mathematical model for a SAW delay line
- FEM simulation of SAW sensor for studying mass loading effect
- FEM simulation of SAW hydrogen sensor
- Summary
According to Hooke's law, the stress components are a linear combination of the strain components. The required coefficients are given by the stiffness tensor CijklE or elasticity matrix, accordingly the stress due to mechanical deformation or Tij(mech) is given by. The material tensors—stiffness, permeability, and piezoelectric tensors—are defined with respect to the X, Y, and Z axes. Further, the problem domain must be discretized into smaller regions called elements that are connected at specific points called nodes, as shown in Figure 2.5 . The generated elements can be two- or three-dimensional and can have triangular, quadrilateral, tetrahedral or brick shapes, depending on the dimensionality.
The degrees of freedom of the right periodic boundary (ΓR) are set to be negative of those of the left periodic boundary (ΓL)[42]. Eigenfrequency response analysis is performed to find the resonance frequency of the SAW resonator. The displacement of the wave at the edge of IDT of NM finger pair can be written as.
Standing waves in the IDT transmitter propagate SAW in both directions of the IDT [45]. Critical damping is assumed at the receiver end (G3) and at the bottom of the entire device to avoid reflections in the delay line. To study the effect of mass loading on the SAW for the considered model, the Young's modulus and the density of the thin layer above the delay line are varied and the time domain analysis is performed for each trace.
The degrees of freedom of the right periodic boundary (ΓR) are set to be negative relative to those of the left periodic boundary (ΓL) (see Figure 2.12) [42]. Frequency response analysis was performed for the transmitter electrodes and the transmitter synchronous frequency was 100 MHz. The mass sensitivity of the SAW sensor model is studied by varying the Young's modulus and density of the film coated over the delay line.
The simulation of the SAW sensor is performed by varying the density, Young's modulus and volume of the assumed film above the delay line. Frequency response analysis is performed for transmitter IDT and transmitter synchronous frequency which is found to be 98 MHz.
Mass Loading Effects of High Aspect Ratio Structures and Thin Films
- Mass loading effect in SAW devices
- Development of SAW based humidity sensor based on mass loading effect
- FEM simulation study on mass loading effect of a high aspect ratio structures on SAW devices
- Mass loading effect of large number of high aspect ratio pillars attached to SAW resonator
- Finite element method simulation of a surface acoustic wave hydrogen sensor with palladium nano-pillars as sensing medium
- FEM simulation to study sensitivity and significance of size of high aspect ratio pillar sensing medium in SAW sensors
- Summary
- Fabrication of SAW devices
The measured resonant frequency of the SAW resonator humidity sensor for RH of 20% and 81% is shown in Figure 3.4. It is observed that the resonant frequency of the SAW resonator generally decreases for increase in the height of the pillars due to increased mass loading. However, at certain heights of the pillars, a sudden change in the resonant frequency of the SAW resonator is observed.
Resonance frequency shift of the SAW resonator versus the height of the pillars with a cross section of 200 nm × 200 nm. The plot of resonance frequency shift versus pile height for the first resonance mode is shown in Figure 3.13. Mesh pictures of the structures used in the simulation model (a) Part of the SAW resonator showing the quality of the mesh, (b) Part of the active area showing the dense mesh applied to its surface, and (c) A .
A small change in the resonant frequency of the attached structure will lead to a large shift in fo. Natural frequency analysis of the SAW resonator is observed for the presence of 0% to 3% hydrogen. In the first step, the natural frequency analysis of the SAW resonator without the pillar structure is performed and the resonant frequency (fo) of the SAW resonator is found.
The resonant frequency of the SAW resonator without pillars (fo|h=0) is found to be 850.43 MHz. However, at certain heights of the nano-pillars, a sudden change in the resonant frequency of the SAW resonator is observed. The frequency value for which the admittance is zero is the resonant frequency of the SAW resonator.
The resonant frequency of the SAW resonator is found to be 864.9 MHz for 0% hydrogen. The dimensions of the palladium nanopillars have been chosen such that the column resonance frequency is equal to the resonance frequency of the SAW resonator.
Micro Fabrication of SAW Devices and Resonant Structures
- Material selection for resonant structures
- Development of high aspect ratio (HAR) structures
- Fabrication of resonant structures SAW resonator
- Summary
- Important Substrate Materials Used in SAW Sensor Applications
- Matrix Technique for Crystal Axes Rotation to given Euler Angles
- Material Constants of Lithium Niobate
- Absorbing Boundary Conditions
- Mechanical Properties of SU-8
Because the minimum dimensions of the pattern to be written are 24.65 µm, lens 3 of the laser writer is used to create the mask patterns over the chrome plates. In a SAW sensor operating on the principle of mass loading, the volume or density or elastic properties of the sensing medium change in the presence of the measured variable, leading to a change in the mass loading on the acoustic path of the SAW device . In general, the photoresist manufacturing process is described in the manufacturer's data sheet.
The dimensions of the fabricated posts are measured by forcing them to collapse into the substrate. In the second test the surface of the substrate is made hydrophobic by coating it with hexamethyldisilazane (HDMS). The height of the poles is determined by measuring the length of the broken or fallen poles in the substrate.
It can be seen from the right part of the picture that the pillars are well attached to the base. The surface of the base is gently scratched with metal tweezers so that the vertical pillars fall to the base and thus the height can be calculated by measuring the length of the pillar. The square fields are drawn in the second layer layout so that they can form one SU-8 pillar per period along the SAW propagation path and one per wavelength along the aperture of the resonator device.
Optical microscope images showing the top view of fabricated SU-8 pillars on the surface of the SAW resonator. a) Image showing tightly packed pillars on the IDT and reflector electrodes, (b) Sample. In the case of removal of SU-8 layers from substrate or the SAW device for reusability of the wafers, the SU-8 must be removed with a separate process. Piranha solution does not help to clean the layers and it leads to black foam over the surface of the wafer and leads to permanent unusability of the wafer.
During such rotations, the stiffness matrix (CE), piezoelectric matrix (e) and dielectric matrix (ε) of the material are also transformed accordingly. To avoid reflection of waves from the boundaries or edges of the SAW devices, absorbing boundary conditions are applied in the FEM simulations.
Bibliography
Ache, “Development of a surface acoustic wave sensor array for the detection of methanol in fuel vapor,” Sensors and Actuators B, vol. Hunt, “Molecular recognition of electronic noses using surface acoustic wave immunoassay sensors,” IEEE Sensors Journal, vol. Mazumdar, “Spice Simulation of Surface Acoustic Waves of Interdigital Transducers,” IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, vol.
Tuli, “Macro-model of interdigital acoustic wave transducer transducer compatible with circuit simulation,” IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, vol. Lee, "Determination of inversion of mode coupling parameters of surface acoustic wave resonators," Japanese Journal Applied Physic., vol.41, p. Physical Review B, Vol.
Xu, “Numerical study of the effects of film properties on the mass sensitivity of surface acoustic wave sensors,” in Proc. Saitoh, “Chemical sensor based on surface acoustic wave resonator using langmuir-blodgett film,” IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control , vol. Eddy , “Surface acoustic wave humidity sensor based on a PolyXIO thin film,” Sensors and Actuators B, vol.
Ballandras, “Matching surface acoustic waves in a periodic array of mechanical resonators,” Applied Physics Letters, vol. Wu, “Passive wireless hydrogen surface acoustic wave sensor based on Pt-coated ZnO nanorods,” Nanotechnology , vol. Menendez, “An Analysis Technique for Asymmetrically Coupled Resonator Structures,” IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, vol.56, p.
List of Publications Related to Thesis
