Study And Application Of AlN And ZnO Based Film Bulk Acoustic Resonators In Biological Environment

In the 1960s,the piezoelectric biosensor has developed to a new type of biosensors,via the main electro-acoustic conversion devices,which can monitor the acoustic output signal of the transducer to reflect the physical and chemical changes of the measured substance.At present,three main types of electroacoustic transducer are quartz crystal microbalance?QCM?,surface acoustic wave sensor?SAW?and thin film bulk acoustic resonator?FBAR?.Among which,FBAR has the obvious merits such as high resonant frequency,small in size,high sensitivity,and compatibility with IC technology.Nowadays many work based on FBAR biosensor have been carried out and become the research hotspots in the fields of biology,medicine,environment monitoring,and food safety,etc.In this research,solidly mounted resonator?SMR?has been prepared based on two kinds of piezoelectric film,by means of controlling the growth direction of piezoelectric film,which can work in longitudinal wave mode and thickness shear mode to be suitable for the applications in gas phase and liquid phase.Using the specific binding system of the antigen-antibody,avidin-biotin and Hg²⁺ nucleic acid ligands,various biological sensitive layers have been self-assembled on the FBARs,and the fabricated biosensors were used to test the CEA,MUC1 and Hg²⁺.As the characteristics of FBAR sensor are greatly influenced by temperature,Mg doped the piezoelectric film was introduced into FBAR and aimed at the decrease of the temperature coefficient of frequency?TCF?.The main work and results are shown as follows:1.Radio frequency magnetron sputtering was adopted to prepare high c-axis and inclined AIN thin film,c-axis high quality ZnO thin film.The technology of the Bragger acoustic reflection layer and the patterned top electrode was presented.The fabricated SMR can be suitable for the application of air phase and liquid phase.2.An AlN-based film bulk acoustic resonator has been fabricated using a magnetron sputtering method,which was employed as a biosensor for detection of CEA.The resonant frequency of the bare FBAR was recorded at 1997.05 MHz with an insertion loss of about-21.22 dB.The CEA binding aptamers were self-assembled on the top gold electrode as the sensitive layer to capture the CEA molecules.When the sensitive layer absorbs the target molecules,the resonance frequency of the sensor decreases proportionally in response to the increase of the mass loading.The resonant frequency shifts of various CEA concentrations in the range of 0.2-1.0 mg/ml were measured.The sensor modified with the CEA aptamer exhibits a high mass sensitivity of 2284 Hz cm2/ng,Q value around 520 and good selectivity,exhibiting a high performance.3.FBAR operated in shear mode was fabricated and integrated with a microchannel for detection of CEA.C-axis inclined AlN film was deposited on the Bragg reflector by rotating the substrate holder plate using a reactive magnetron sputtering.The polydimethylsiloxane?PDMS?microchannel was integrated with the fabricated resonator.The XRD results exhibited coexisting?002?and?101?orientations corresponding to the c-axis inclined AIN film.The resonant frequency of the FBAR was located near at 1.2 GHz.The average electromechanical coupling factor Kt2 and quality factor Q were 3.19%and 170,respectively.The frequency shift of the biosensor was proportionately increased as the concentration of the immobilized anti-CEA aptamer increased.The CEA binding ratio was initially increased with antibody concentration reaching a highest value at 47.04%.The mass sensitivity of the fabricated biosensor was calculated to be approximately 2045.89 Hz cm2/ng.4.The resonant frequency of the prepared AIN based FBAR with a porous gold electrode was 1214.58 MHz,which was modified by the Hg²⁺ nucleic acid ligands to form a sensitive layer.Based on the T-Hg²⁺-T double base pair specific reaction,the resonant frequency shifts of various Hg²⁺ concentrations in the range of 50-1000 nM were measured.The resonance frequency of the sensor decreases proportionally in response to the increase of the mass loading in the range of 100-1000 nM.The modified sensor exhibits a high sensitivity of 677.07 Hz/nM and good selectivity.5.A ZnO-based film bulk acoustic resonator has been fabricated using a magnetron sputtering method,which was employed as a biosensor for detection of MUC1.The resonant frequency of the FBAR was located near at 1503.3 MHz.The average electromechanical coupling factor Kt2 and quality factor Q were 2.39%and 224,respectively.Using the specific binding system of avidin-biotin,the streptavidin was self-assembled on the top gold electrode as the sensitive layer to capture the MUC1 molecules.When the sensitive layer absorbs the target molecules,the resonance frequency of the sensor decreases proportionally in response to the increase of the mass loading in the range of 50-400 nM.The sensor modified with the streptavidin exhibits a high sensitivity of 4642.6 Hz/nM and good selectivity.6.Mg doped ZnO piezoelectric film has been prepared and depicted by the methods of SEM,EDS,XRD,XPS,etc.FBAR based on Zn1-xMgxO piezoelectric thin film has been fabricated.When the doping concentration is quite lower,the average electromechanical coupling factor Kt2 is weak increase,however,a bit doping will decrease the Kt2 value.When the mass fraction of Mg in Zn1-xMgxO film is 2.23%,the TCF of the device is-16.8 ppm/?in the ranging of 20-100 ?,which is greatly lower than the value-69.5 ppm/? of the pure ZnO based FBAR.