Application Of Nano - Imprinting Technology In Ferroelectric Thin Film Materials

Ferroelectric films have excellent ferroelectric, piezoelectric and pyroelectric properties and have found a wide range of applications in non-volatile memory devices, sensors, and Microelectromechanical Systems (MEMS), etc. Recently, with the development of miniaturized thin-film transistors and data-storage memories, ferroelectric nanostructures have attracted increasingly scientific and technologic interests. The key challenge for submicron and nanoscale ferroelectric structures is the degradation of ferro-electricity firstly in ultra thin films due to the small thickness and secondly in nanoscale patterned structures due to damages and defects introduced by the conventional photo and e-beam lithography. Meanwhile, the fabrication of ferroelectric nanostructures of a controllable size and shape is of great interest not only for future applications but also from a fundamental point of view. Therefore, better method to control the quality of ultrathin ferroelectric films and alternative patterning techniques are urgently demanded.Nanoembossing technology is an emerging technique that promises rapid, lower-cost patterning of nanostructures. In this thesis, we apply nanoembossing to fabricate ferroelectric nanostructures, study the properties of the patterned films, and explore its applications in multi-bit storage, Ag particles self-assembly and cell cultures.In this work, the nanoembossing process of PZT thin film is investigated and PZT nanowire array with lateral size down to-60nm is fabricated. The structures of the embossed PZT films are studied by XRD and Raman measurements and the influences of hot embossing process and room temperature embossing process on properties of the embossed films are studied. Meanwhile, using the Radiant Ferroelectric Precision Tester, the electrical properties of the embossed PZT films and unembossed films are measured and compared. Furthermore, with the Piezoresponse Force Microscopy (PFM), the domain structures of the embossed films are studied at nanoscale. All above shed the light on the feasibility of the applications of this technology.We explore the following three applications of the ferroelectric nanoembossing tecnology.Firstly, it is widely understood that multi-bit operation could be one of the most efficient approaches to increase storage densities. In recent years, a great deal of efforts has been made on realizing multi-value storage through circuit design. One of the drawbacks is the additional budget of densities in circuit integration. There have been rarely reports on the research tackling the improvement of fabrication processes and device structures. In this work, we report our initial progress in developing a nanoembossing technique to achieve large arrays of ferroelectric PZT cells, which have potential application in multi-bit storage based on ferroelectric nanostructures. The ferroelectric films with different thickness need different coercive voltages. A staggered structure with two distinct thickness layers on a PZT thin film can be readily created by a one-step embossing process. In principle, the thinner layer should give rise to the lower switch voltage and the thicker layer to the higher switch voltage. The voltage magnitude corresponds to one of the two polarization charge levels stored in the ferroelectric memory cell. In this way, multiple bits of data can be obtained from a single ferroelectric memory cell by applying different voltages.Secondly, ferroelectrics with internal dipolar fields are able to internally drive apart photogenerated carriers via the bulk photovoltaic effect. The concept of using poled ferroelectric domains to direct the growth of nanoparticles is being explored and is known as ferroelectric lithography. Photochemical experiments on ferroelectrics have shown that the reduction reactions (for instance, the reduction of Ag+to Ag0) are favored on the surfaces of domains with positive polarization. In this work, we propose to use a nanoembossing technique to pattern domains in ferroelectric lithography with large-scale Ag particles dot array fabricated. Although the ferroelectric lithography with a probe bias tip is useful for fundamental studies, it is not feasible to apply it in practice. Herein, nanoembossing induced ferroelectric lithography presents us a route to large array of metal patterns by one-step exposure.Thirdly, ferroelectric film P(VDF-TrFE) has found wide applications in data storage, MEMS, etc. It has been widely used in bio-sensors due to its excellent bio-compatibility. However, most of bio-researchs reported were done on the bare P(VDF-TrFE) films, how is the biocell behavior such as attachment, proliferation on nanostructured P(VDF-TrFE) films has not been reported so far. In this work, we apply nanoembossing technology on P(VDF-TrFE) nanostructures fabrication and study the cell cultures on them. Meanwhile, by applying the external voltages on P(VDF-TrFE) films, we investigate the influences of the surface charges on the cell attachments. This work would push further applications of P(VDF-TrFE) in biology areas.