Research On Surface Acoustic Wave Device With New Structure

Surface acoustic wave?SAW?device,a signal processing electronic component combined acoustic technology and electronics,has been widely used in mobile communication,aerospace,bio-medicine and other fields because of the advantages of easy signal processing,miniaturization,low power consumption and high compatibility.Phononic crystals?Pn Cs?,one kind of acoustic meta-materials composed of periodic medium or periodic geometry,can control and manipulate the propagation of elastic waves,such as an-isotropic propagation,acoustic band gap,abnormal dispersion?negative refraction?,etc.,which have attracted great attention in the past two decades and have wide applications in many fields.In this thesis,the properties of SAW devices based on functional materials?including Pn Cs and nano-materials?are studied,and the main contents are described briefly as follows:?1?The 3 dimension finite element method?3D-FEM?based on COMSOL 5.3a is employed to study theoretically the properties of Love wave in layered structures of Pn Cs/?110?Zn O/R-sapphire substrate,in which the Nickel hole Pn Cs and Nickel pillar Pn Cs are modeled.The characteristics of the Love wave devices,including the insertion loss?IL?and vibration displacement in time domain,as well as admittance,phase velocity?v_p?and electromechanical coupling coefficient?k²?in frequency domain,are theoretically calculated.The results show that the introductions of Ni Pn Cs increase the IL of Love wave devices.Meanwhile,due to the binding of acoustic energy by the Pn Cs and the reflection of acoustic energy to the in-put in the form of reflected waves,a larger increasing of IL??6d B?is observed for the Love wave device based on Ni Pillars/?110?Zn O/R-sapphire structure.Secondly,the similar characteristics of Love waves in Ni Holes/?110?Zn O/R-sapphire structure and Pn Cs-free structure are found,including the admittance,phase velocity,electromechanical coupling coefficient,etc.However,the properties of Love waves in Ni Pillars/?110?Zn O/R-sapphire structure have obviously changed,for example,the early appearance of cutoff point for 1st mode(h _{Zn O}/?=0.0625),as well as the improvement of electromechanical coupling coefficient?1.85%?.Finally,the performances of Love wave device are optimized by the optimization of the geometrical parameters of Ni pillar,and the maximum electromechanical coupling coefficient(k²_max)of 3.27%is obtained as r=1.4?m and h=5.4?m.All of the results indicate that the performances of the Love wave device based on Ni Pillars/?110?Zn O/R-sapphire structure are superior to that of Pn Cs-free structure.Furthermore,due to the higher k² and smaller cutoff point,the 1 st Love waves are more suitable for the fabrication of high frequency and wide-band SAW devices.?2?The Love wave resonator based on Pn Cs/?110?Zn O/R-sapphire structure is modeled by COMSOL 5.3a software.And the band properties of Pn Cs,as well as the influence of Pn Cs structures?the radius r and depth h?on the Love wave band-gaps,are studied by 3D-FEM.The results show that,for the Love wave resonators with the square lattice hole Pn Cs,the phononic band-gaps in?-X direction is 169.7 MHz-193.8 MHz as the parameters of Pn Cs are r=1.5?m,h=2?m and a=8?m.And the width of the phononic band-gaps first increases and then decreases slowly with r increasing,the maximum band-gap of 51.93 MHz is obtained as r=3?m.Secondly,according to the band-gaps mentioned above,the design of SAW resonator based on Pn Cs are carried out,and the Love wave resonator with operation frequency of 185 MHz and Q value of582.9 is obtained.Finally,the performances of the Love wave resonator are optimized by re-arranging the structures of Pn Cs,such as the vibration of Love wave resonator significantly increased,and the maximum displacement of the standing wave is as high as 0.42 nm,which is 0.25 nm before optimization.These theoretical results can be used for the design of new SAW resonator based on Pn Cs.?3?The properties of Love waves in Si O₂/ST-90°X Quartz structures,including v_p,k²,and the mass sensitivity?S_m?are investigated by 3D-FEM.The maximum S_m of 126 m²/kg is obtained as h_s/?=0.20 associated with v_pof 4480 m/s and k² of 0.05%.In addition,the variations of Love wave device induced by the introducing of Zn O nanorods are studied,that is the device with the structure of Zn O nanorods/Si O₂/ST-90°X Quartz.The results indicate that,at the certain heights,the Zn O nanorods and Si O₂/ST-90°X Quartz structure vibrate in unison,which is named the coupled resonance,leading to the transformation from inertial loading to elastic loading,and induced the specific performances:the increasing of resonant frequency and mass sensitivity of the Love wave devices.Meanwhile,the effect of the density of surface Zn O nanorods?SNRD?on the properties of Love wave devices is investigated.With SNRD increasing,the height of Zn O nanorods corresponding to the coupled resonance is gradually decreased,while the resonance frequency and mass sensitivity are increased.For SNRD=3.5,the first coupled resonance occurs with a frequency shift of 70 MHz and the maximum S_m is 1930 m²/kg as h_z=385 nm,which is more than 10 times higher than the S_m of Love wave device without coupled resonance.These results provide a theoretical basis for the development of Love wave devices with high sensitivity.