| Piezoelectric ultrasonic transducers is sound-electronic conversion device, which is generally used in the field of ultrasonic. The traditional PZT, however, has low transmission and receiving efficiency in the air because of the serious sound impedance mismatching between air and ordinary piezoelectric material(the sound impedance of air is 0.0004MRayl, but the sound impedance of piezoelectric material is 10~20MRayl). With the development of MEMS technology now, a new ultrasonic transducer capacitiv e microfabricated ultrasonic transducers appears. CMUT is fabricated by the surface microfabricated technology, many shortcoming of traditional PZT is overcame. What's more, it is a possible trend that CMUT will replace of the PZT because it has little vol- ume, low cost and it's anterior and back-end circuit can be integrated into a single chip, thus both the parasitic capacitances and noise level are reduced.First, the equivalent circuit model of CMUT is put forward in the paper, then the behavior of membrane vibration and mechanics with DC offset voltage of CMUT is analyzed which derive the expressions of all parameters in the equivalent circuit model. The two simulation methods are introduced and validated: one is mixing method using MATLAB and PSpice, it is that first all parameters by derived expressions in the equivalent circuit model is calculated by MATLAB, then circuit model built by PSpice is simulated; the other is FEA method, it is that first the finite element model of CMUT is built, then coupling field model is simulated. Next, practical structure and size of CMUT which will be fabricated is designed and simulated. On the basis of domestic practical machining ability, fabricated process and mask is designed, then whole mask which is used in the fabricated process is lay out. At last encapsulation of CMUT is design to prevent dust and connect expediently with peripheral circuit and the testing method of basic parameters of CMUT is introduce. |
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