Mykhailovych V. Design and production of oxide dielectric materials at the nanometric scale for electronic devices

Mykhailovych V. V. Design and production of oxide dielectric materials at the nanometric scale for electronic devices. Thesis on search for the Doctor of Philosophy degree in specialty 104 «Physics and Astronomy». - Yuriy Fedkovych Chernivtsi National University, Ministry of Education and Science of Ukraine, Chernivtsi, 2023. Nowadays, dielectric materials play a key role in main electronic devices, like for example capacitors, supercapacitors, sensors, field effect transistors, etc. Towards the minimalization trend, the preparation and functionalization of nanoscale dielectric materials are of primary interest. Among a wide range of dielectrics, one of the most interesting are the materials with high dielectric constant (high-k). One of the brightest representatives of high-k materials are oxide-based dielectrics, from which barium titanate perovskites and metal chromite spinels can be figured out. These two types of compounds show a growing interest as they possess high dielectric, ferroelectric, piezoelectric, pyroelectric and other properties, which makes them a perfect candidate for application in micro- and nano-electronics. In this context, the present thesis focusses on preparation, functionalization and integration of nanoscale perovskite-type BaTiO3 and spinel-type ZnCr2O4 in planar high-k capacitors. The thesis is organized as following; The Іntroduction justifies the relevance of the topic of the dissertation research, indicates its connection with scientific programs, plans and topics, formulates the purpose and tasks of the dissertation, emphasizes its scientific and practical significance, presents information about the publications and personal contribution of the recipient, approves the project results, their structure and amount. Chapter 1 is structured in four main sections which consist of (i) state of the art, (ii) properties of nanosized dielectric oxide particles; (iii) nanostructuration and organization methods of dielectric nanoparticles as thin films and (iv) integration of dielectric nanoparticles in electronic devices as active elements. The chapter ends with partial conclusions. Chapter 2 describes the main techniques used for dielectric oxide nanomaterials characterization. Chapter 3 is devoted to synthesis and characterization of perovskite-type dielectric nanoparticle systems. Thus, a series of barium titanate nanoparticles systems have been obtained, with controlled morphology and size: cubic nanoparticles (with the mean size of about 15 nm), edge-truncated cuboidal nanoparticles (with a size about 100 nm) and truncated rhombic dodecahedron (with a size about 110 nm). It has to be mentioned here that the truncated rhombic dodecahedron and cuboidal edge-truncated morphologies for BaTiO3 has been obtained and described for the first time. Chapter 4 describes the methodology of morphology tailoring in spinel type systems and its impact on the dielectric properties. The experimental results strongly suggest that several factors, including the burning time of gel, the combustion temperature, and the enthalpy of combustion of the solid chelating/fuel agents, influence the size, band gap and dielectric properties of the obtained spinel nanoparticles. Chapter 5 is dedicated to the integration of the spinel and perovskites nanoparticles in electronic devices. First step on this road was the surface functionalization of the nanoparticles in order to obtain a stable ink suspensions which will be used for the thin films deposition. Various methods were used for the thin film fabrication, namely drop casting, dielectrophoresis and spin coating. Despite the dielectrophoresis and spin coating methods allowed as to obtain thin films with a high order degree of the nanoparticles, these techniques are limited by the continuity of the thin layers on large surfaces. This issue has been overcome by using drop casting method. For both, perovskite and spinel nanomaterials the thickness of the prepared thin films vary from 400 nm to 4300 nm. The surface quality and elemental composition of the films has been investigated by Field-emission Scanning Electron Microscopy, and EDX analyses. As a next step, after elaboration of characterization of thin films the planar capacitors have been fabricated by deposition of silver electrodes onto the both sides of the dielectric films. The performance of the fabricated planar capacitors was studied by Broadband Dielectric Spectroscopy. Thus, we obtained the following values for the electrical capacitance: 1 nF for ZnCr2O4 based capacitor, 200 nF for cuboidal BaTiO3 based capacitors and 2 nF for the truncated rhombic dodecahedron BaTiO3 based capacitors.