| In recent years, ferroelectric thin films has become one of the hottest high-tech research. Ferroelectric thin films have been widely used in various fields. Depending on the properties of ferroelectric thin films, such as ferroelectricity, piezoelectricity, pyroelectric property, etc, it can be used to make many kinds of devices. Currently, the ferroelectric thin film research still focused on conventional perovskite materials, such as PZT, BST, etc. However, the conventional ferroelectric perovskite thin film which was applied to Si-based ferroelectric memory, has been shown to have a lot of difficulties, such as ferroelectric size effect, the degradation which comes from crystallization heat treatment, a small band gap, and mismatch with Si interface.Recently several groups found that Hf0.5Zr0.5O2 appeared ferroelectricity under some certain conditions. As high-K candidate dielectric materials, HfO2 and ZrO2 with dielectric properties will undoubtedly meet the requirements of ferroelectric thin films. The mature technology of combination with silicon can guarante the stability and reliability of the device, and the smaller thickness limit let the miniaturization and three-dimensional of the device possible.Therefore, making the new ferroelectric thin film Hf0.5Zr0.5O2 becomes the object of study. Pulsed laser deposition was used to prepare Hf0.5Zr0.5O2 film on Pt(111) / Si(001) substrates.And Systematic analysis and experiments were taken on the growth process and heat treatment of the films. The main work and conclusions are shown as follows:1. Pulsed laser deposition was used to deposit the Hf0.5Zr0.5O2 ferroelectric film. XRD analysis shows that there is orthorhombic phase peak(102) at 38.5 °.this non-centrosymmetric structure leads to the existence of ferroelectricity.2. We explored the growth process of the Hf0.5Zr0.5O2 ferroelectric thin films. The results show that the improve of oxygen partial pressure during film growth helps improve film quality, which 20 Pa is the best partial pressure of oxygen. When the film thickness increases from 60 nm to 140 nm the leakage current density decreases from 2.3×10-3A/cm2 to 4.1×10-5A/cm2 at 5V.The Hf0.5Zr0.5O2 film has the best ferroelectric properties and crystalline properties when the substrate temperature is 400℃.With laser energy as 140 mJ the film has better crystal quality, and the surface become smooth and compact. Annealed in nitrogen, the leakage current density of the film is large, which reached 2.6×10-4A/cm2 at 5V. Annealed in oxygen helps reduce leakage current density, which reached 7.3×10-6A/cm2 at 5V. Therefore, the optimal deposition growth process of the Hf0.5Zr0.5O2 thin film deposition on Pt/Si by PLD are:oxygen partial pressure of 20 Pa, 140 nm in the thickness, the substrate temperature 400 ℃, laser energy 140 mJ, and in situ annealing in oxygen at 500 ℃.3. Leakage current mechanism of the films are analyzed. The results shows that nitrogen annealed films is under the joint action of the Pool-Frenkel(PF) mechanism and Schottky emission mechanism. Oxygen annealed thin film mainly composed of a Schottky emission mechanism effect. P-E were tested and the results shows that when Hf, Zr composition ratio is 1:1, the films shows best ferroelectricity. Remanent polarization of the film first increases, then decreases with increasing annealing temperature. With the increasing of the test voltage, the film’s Remanent polarization strength and coercive field increases. The leakage current also increases and saturated at about 10 V. The remnant polarization reaches 8.58μC/cm2. C-V test shows that the relative dielectric constant of the film is about 27-29. With the annealing temperature increasing, the dielectric constant and the loss rate of the film increases. Fatigue tests shows that after 2×109 inversion, the reversible polarization of Hf0.5Zr0.5O2 films declined 24.6%. |
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