Research On Capacitive Micro-ultrasonic Transducer Based On Polymer Fil

Since the 20th century,ultrasound technology has been widely used in non-destructive testing,medical imaging,diagnosis and treatment due to its advantages of non-invasive,non-contact,safety and easy control.With the development of MEMS(Micro-Electro-Mechanical System)processing technology,Capacitive Micromachined Ultrasonic Transducer(CMUT)as the core component of Ultrasonic technology has been widely studied.Compared with the traditional piezoelectric Ultrasonic Transducer,Capacitive ultrasonic transducers are widely used in medical imaging,industrial testing,resource exploration and chemical production due to their advantages of high acouto-electric conversion efficiency,high sensitivity,wide frequency band,high array density and no need for matching layer.At present,the research on ultrasonic transducer is in the ascendent at home and abroad,so the research on CMUT is of great significance to the development of ultrasonic equipment.At present,monocrystalline silicon,silicon dioxide,polysilicon or silicon nitride are commonly used as the diaphragm of CMUT.Flexible polymer diaphragm has the advantages of superior impedance matching performance,lower cost and simpler process steps,etc.,and has received a lot of attention and research in recent years.In this paper,a capacitive micro-ultrasonic transducer with polymer material as diaphragm is proposed.Firstly,modeling and simulation are carried out on the CMUT unit.Simulation and optimization are carried out on the DESIGNED CMUT unit in the finite element analysis software COMSOL,and parameters such as film radius,film thickness and cavity thickness of the optimized CMUT unit are obtained.The structures of CMUT cells and arrays based on polymer membrane are designed.On this basis,the sacrificial layer release technology suitable for polymer film with low cost is adopted in this paper.The cured SU-8 photoresist is used as the diaphragm,Omnicoat is used as the sacrificial layer,and metal chromium is used as the electrode.The designed CMUT unit and array are prepared by conventional semiconductor processing technology.In order to complete the preparation,morphology,scanning electron microscopy(SEM)and step meter tests were carried out on the CMUT chip.The results show that the graphic boundary is clear and accurate,and the cavity structure is intact and the thickness conforms to the design after release.Finally,a 17 × 28 CMUT array was selected for packaging and an electrical test system was built.The test showed that the electrical performance of CMUT was good and the transmission of ultrasonic signals could be realized.It is proved that CMUT made of polymer materials is feasible,with lower cost and simpler preparation steps,which provides more reference for the subsequent development of ultrasonic devices made of polymer materials.