Preparation And Characterization Of Zn And Mn Ions Co-dopant BTO Thin Films By Sol-Gel Method

Barium titanate that first investigated in1945is a kind of perovskite ferroelectric materials. Ferroelectric materials which are researched and developed rapidly own excellent ferroelectric, piezoelectric, dielectric and pyroelectric qualities. This kind of materials has higher dielectric constant, better piezoelectric and ferroelectric properties with the simplicity of its crystal structure. Due to the dielectric constant and ferroelectricity, it can be applied in film capacitors, high-capacity dynamic random access memories (DRAM) and ferroelectric random access memory (FRAM). In addition, it can be used in underwater acoustic detection and piezoelectric gyroscope because of its piezoelectric properties. Due to the development of thin film deposition technology, the films with preferred orientation can be deposited when temperature of substrates is lower. It makes the combination of ferroelectric thin films technology and semiconductor process technology, and also makes integrated ferroelectric devices possible.The ferroelectric properties of undoped BTO films are usually poor, with higher leakage current and unsaturated P-E hysteresis loops. BTO thin films with B site accommodated different dopants such as Zn, Mn, Fe show more excellent properties. And that have been focused on by extensive research activities except co-dopant investigation. This thesis studies on this problem. After the experiments we find that doping metal ions, especially co-doping, can improve the ferroelectricity of thin films.In this article, undoped and doped BTO films are prepared by the Sol-gel method. That is a simple and easy way to manipulate, which can be used to prepare ferroelectric thin films with low cost. By comparison, the better conditions of process are deduced and the high-purity BTO thin films are produced. Crystal structures, surface morphologies, optical and electronic properties of undoped and doped BTO films are investigated.The achievements of this thesis are as follows:1. The principle of the chemical solution for preparing BTO thin films is firstly analyzed, and then the high quality BTO thin films are fabricated on Si (100) and LNO/Si (100) substrates by multi-times repeats of spin-coating/rapid thermal process cycle. In order to deep digest the effects of different doping levels on the microstructure and ferroelectricity of BTO thin films, Zn doped, Mn doped and Zn-Mn co-doped BTO films are also deposited by the same way. The theory shows that the better way to produce BTO thin films is using titanium tetrabutoxide and barium acetate as raw materials, and acetic acid as the solution mixed with the appropriate amount of chelating agent acetyl acetone and water.2. The crystal structures and the surface morphologies of doped BTO thin films are characterized by X-ray diffraction and atomic force microscope. XRD patterns indicate that LNO deposited between Si substrate and BTO thin films makes the preferred orientation of BTO lattice growth better. Little amount of Zn and Mn dopants can improve the crystal quality without changing perovskite structure. AFM micrographs show that the surfaces of all these films are uniform and dense, consistent with the calculation results obtained by XRD.3. For investigating the Zn and Mn doping effects on the optical properties of BTO thin films, spectroscopic ellipsometry and Raman spectra are measured. By comparisons of the optical constant refractive index and extinction coefficient of BTO thin films with different doping levels in the wavelength from400nm to1000nm, it obtained that the addition of Zn and Mn dopants can lead to the increases in the properties of deterioration and optical band gap of BTO thin films. The mechanism of the influence of Zn doping to the microstrucrure of BTO crystal is further discussed by analyzing Raman shifts.4. Undoped and doped BTO films are deposited on LNO/Si conductor substrates, and then capacitance structure is fabricated by Sputtering Pt electrode on BTO films. Ferroelectric properties of undoped and doped BTO films are measured respectively. A better defined P-E loop with11.26μC/cm2shows that Zn and Mn co-doped play a potential role in ferroelectric improvement.