Study On Highly Dense P(VDF-TrFE) Film Preparation Process And Flexible Acoustic Resonator

With the rapid development of flexible electronics,the demand for flexibility of MEMS devices such as surface acoustic wave resonators(SAW)and thin film bulk acoustic wave resonators(FBAR),which have been widely used in the field of sensors,is becoming stronger and stronger.PVDF and its copolymers,as a high-performance piezoelectric polymer,have become a hot spot for research and are the material for making flexible SAW and FBAR,which is essential for achieving SAW and FBAR devices have greater potential for low-cost,ultra-performance flexible sensors.This project is an innovative research on flexible acoustic wave resonators and their sensing applications,from both material and device aspects,to address the problems and difficulties encountered in flexible SAW and FBAR devices at this stage.The main contents of the research include: the preparation of new P(VDF-TrFE)films,the design and preparation of sound surface wave devices and bulk acoustic wave devices based on these films,and the study of the sensing characteristics of the devices and the exploration of their applications.The details of the study are shown below:1.To address the current situation that P(VDF-TrFE)films are limited in the fabrication of SAW and FBAR devices due to internal holes and defects,this paper improves the conventional film process and develops an ICP etching-based "polishing" process for the film surface to obtain the optimal parameter conditions for the fabrication of films.The obtained films exhibit excellent properties: dense and nonporous interior,flat surface,β-phase content up to 89%,and piezoelectric coefficient up to 42 pm/V.2.We investigated the device design approach of P(VDF-TrFE)films as SAW and FBAR piezoelectric layers.The effects of each structural parameter of FBAR devices were evaluated by ADS and COMSOL,respectively.Simulation design of SAW devices was performed using COMSOL finite element simulation in conjunction with the transport matrix model.3.Based on the high performance dense film fabricated by the new process,a new micro and nano processing scheme was designed based on the chemical properties of P(VDF-TrFE)itself,and the flexible P(VDF-TrFE)FBAR was successfully fabricated,and the resonant frequency of the obtained device was 45.6MHz,and the electromechanical coupling coefficient was as high as 14.5%,and its resonant characteristics were greatly improved compared with the conventional porous P(VDFTrFE)The resonant characteristics are greatly improved compared with those of conventional porous P(VDF-TrFE)films and commercially available PVDF piezoelectric films,demonstrating the superiority of the film fabrication process in this paper.The flexible FBAR also exhibits ultra-high temperature and humidity sensitivity.The frequency-temperature coefficient reaches 3329 ppm/K and has good stability without hysteresis,which can be used as a high-performance flexible temperature sensor with good application prospects.The frequency humidity coefficient is134.77ppm/%RH,which also has a large potential for application in the field of flexible humidity sensing.4.We explored the application of flexible FBAR in wearable devices and designed a respiration sensor for real-time respiration monitoring based on its high temperature and humidity sensitivity,which has excellent sensitivity and excellent repeatability and stability for respiration detection.Based on the FBAR device,a pressure sensor with adjustable range is designed to achieve pressure sensing with a resolution of 0.1N,and the pressure sensor is successfully used to detect heartbeat,detect different modes of breathing,and read heartbeat and breathing rate simultaneously,which greatly explores the application scenarios of flexible FBAR.5.A new SAW device structure and processing process have been designed to fabricate SAW devices that operate in three modes,of which the Lamb wave device has achieved full flexibility.The Rayleigh-wave device and the Lefebvre-wave device exhibit lower temperature sensitivity of 166.77 ppm/K and 77.78 ppm/K,respectively,under temperature sensing,and have the potential to fabricate strain sensors that need to maintain stable operation under temperature changes.The foundation for the development of new flexible SAW devices is laid.