| Film bulk acoustic resonator (FBAR) is a kind of small size,high frequency, low cost and integrated piezoelectric device, which has been commercially applied in fields related to a new generation wireless communications. In addition, FBARs bring new life to sensors such as mass-loaded sensor, pressure sensor and biochemical sensor because of the high sensitivity. The biochemical sensors usually work in liquid. The Q factor damps seriously in liquid when FBARs work in traditional longitudinal. mode,while the thickness shear mode can acquire high Q factor in liquid. This paper takes the lateral field-excited thickness shear mode as the object of study. The main results of this paper are listed as follows:1. The lateral field excited by parallel electrodes was theoretically derived based on the analysis of the traditional longitudinal mode FBAR.And the corresponding mathematical mode was established. The influence of electrode gap, length and width on the resonator performance was studied by the finite element method to optimize the structure of the FBAR. The results showed that the lateral electric field distribution and Q factor were closely dependent on the electrode gap.The electrode width had an effect on the particle displacement distributes in the active area. The electrode length had no obvious influence on the Q factor and the distribution of the electric field.2. Based on the result of finite element optimization, the thickness shear mode FBAR with solidly mounted resonator was fabricated by micro-nano processing technology. The impedance and conductance characteristics of the device were measured in three typical environments which were air, water and phosphate buffered saline. The Q factor of 183 in phosphate buffered saline is decrease seriously than in air (537) and in water (453). The equivalent circuit models of FBAR were established for three different testing environments thanks to the circuit parameters in Modified Butterworth-Van Dyke (MBVD) extracted successfully.Through the performance analysis of electrical devices, we found that the conductivity of solution increased the loss of the device.3. The resonance frequency of FBAR is sensitive to the viscosity of loaded solution. Based on the requirement of biochemical sensor,the thickness shear mode FBAR is suitable to the measurement of coagulation. And the possibility of lateral field-excited FBAR in biochemical sensing was verified. In the extrinsic pathway of blood clotting, there were no obvious viscosity changes occurred during the formation of thrombin, which represented to the plateau phase of frequency. When fibrinogen conversed to fibrin, the blood viscosity increased continuously, making the frequency decreased. Until fibrin eventually polymerized into fibers, the blood viscosity returned to a steady state without the further frequency change. The 95% decreasing points was chosen as the end point of the coagulation, after comparison with standard coagulometer. What's more, the influence of Ca2+ ions on clotting time was studied. With higher Ca2+ ion concentration, the clotting strength is stronger and the clotting time is shorter. |
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