Research On New Structure Surface Acoustic Wave Device Based On ZnO Thin Film

Surface acoustic wave(SAW)device,an electronic device for complex signal processing by surface acoustic wave,has been widely used in aerospace,environmental monitoring,information communication and so on,because of the advantages of high working frequency,small volume and reliable performance.Phononic crystals(PnCs),a new type of artificial composite structure,has attracted much more attentions in recent years.It has been widely used for the regulations of elastic wave propagation and thermal phonon,acquisition of energy,and manipulation of micro-fluid.In this thesis,the property improvements of Love wave devices by 2 dimension PnCs are studied,and the main contents are described briefly as follows:(1)The size influence on acoustic properties of 2 dimensional PnCs is studied by 3 di mension finite element method(3D-FEM)based on COMSOL 5.3a.The results show that t he nano-PnCs and(110)ZnO/41°YX-LiNbO₃structure vibrate in unison at the certain height of PnCs,named coupled resonance,which induces the frequency shift and mode transform ation of Love wave.Meanwhile,the occurrence of coupled resonance and the frequency shi fts of Love waves are also influenced by the structure parameters of nano-PnCs(the height and radius of PnCs).Then,when r _PnCs?0.8?m,the coupled resonance disappeared to be re placed by the significant decrease of cutoff point of higher-order mode of Love wave.As r _PnCs=0.8?m,the cutoff point of 1st mode Love wave is h _ZnO/?=0.1,which is much smaller t han that of structure without PnCs(h _ZnO/?=0.4).Finally,the phenomenon that the cut-off po int of high-order mode Love wave in advance is verified by the band structure of two-dime nsional PnCs.(2)The acoustic properties of SAW in(110)ZnO/IDTs/41°YX-LiNbO₃structure are theor etically investigated by 3D-FEM.The influences of different PnCs,including nano-PnCs and micro-PnCs,on SAW properties are simulated.Firstly,the coupled resonance between the PnCs and(110)ZnO/41°YX-LiNbO₃structure occurred at the certain height of ZnO nano-PnCs,leads to the dramatic shift of frequency and improvement of mass sensitivity of Love wave devices.The maximum S_mof 1455m²/kg is obtained as the occurrence of second cou pled resonance(h _PnCs=1880nm,r _PnCs=80nm),which is 45 times higher than the PnCs-free Lo ve wave devices(S_m=32.09m²/kg).These results provide the theoretical basis for the fabricat ion of Love wave device with high mass sensitivity.Secondly,it is found that the propertie s of 1st mode Love wave are greatly influenced by the Ni micro-PnCs,that is,the moving ahead of cutoff point(h _ZnO/?=0.05)and the increase of electro-mechanical coupling coeffici ent(k²_max=16.54%),which are superior to that of PnCs-free Love waves devices(h _ZnO/?=0.4,k²_max=8.53%).Meanwhile,compared to that of PnCs-free Love wave devices,the S_mincrea sed 2 and 3 times for the first two order modes,respectively.Finally,the parameter influen ce of Ni PnCs(r _Niand h _Ni)on the performances of Love wave devices are calculated.The results indicate that the different properties of Love devices can be improved by adjusting the structure parameters of PnCs,which provides more choices for designing SAW devices applied in different fields.All the results mentioned above show that the PnCs can not onl y be used for the development of SAW devices with high frequency and high sensitivity,b ut also reduce effectively the fabrication difficulty of high frequency SAW devices.