Self-focused Piezoelectric Micromachined Ultrasonic Transducer And Its Application In Cell Delivery

Micromachined ultrasonic transducers (MUT) have many advantages such as miniaturization, low power consumption, and easy to fabricate transducer arrays. They are now being widely researched in areas such as imaging, photo acoustic imaging, and NDT. Integrating MUT with micro channels facilitats sononporation in micro environment that utilizes local high temperature, high pressure and shock wave to aid the cell uptake of DN A and drug molecules. It does not require high electric field or bio assays that will alter the cell culture environment. It also has higher delivery rate and lower death rate than other electroporation. Gene delivery in microfluidic environment is a promising research area. The most challenging work to achieve gene delivery in microfluidic environment is to build a micro ultrasonic transcuder with suitable output energy level that can be easily integrated with micro channel.Basing on this idea, we propose a self-focused PMUT array which has a dome shape that produces higher output acoustic pressure and has higher coupling coefficient. Taking advantage of this dome shaped PMUT, we can maximize the acoustic power radiated into the micro channel. By numerical simulation, we were able to verify the superiority of dome shaped structure. We also studied the influence of its shape on the performance.Fabrication of the three dimensional dome shaped PMUT is the first challenge in this project. This is solved by hot imbossing with the size of the hemisphere easily controllable.On top of the substrate with dome shaped array, we deposited ZnO as the piezoelectric material to obtain the self-focused flexible transducer. We worked systematically on the optimization of ZnO sputtering parameters. The influence of sputtering pressure, power, gas ration on the preferred orientation, deposition speed, grain size and internal stress. Basing on these experiments, we obtained the best deposition parameter. The deposited ZnO thin film was found to be highly textured with good crystalline quality.Finally, PMUT arrays were integrated with PMDS micro channel and gene transfection were carried out on this system. Preliminary results showed that NDA were sucessfully delivered into cells, which verifies the possibility of gene delivery in microfluidic environment by PMUT. The transfection efficiency can be enhanced when more transducers are turned on simultaneously. Therefore, high transfection efficiency was possible by using large PMUT arrays.