Kazunari Maki

Evaluation of Pb(Zr, Ti)O3 Films Derived from Propylene-Glycol-Based Sol-Gel Solutions

Crack-free PbZr0.52Ti0.48O3 (PZT) films up to almost 1 µm thick have been prepared on Pt/Ti/SiO2/Si substrates from stable propylene-glycol (diol)-based sol-gel solutions by a single coating. We have studied the film thickness dependence of various properties such as microstructure, crystal orientation, ferroelectric properties, and leakage current density for the PZT single-coated films. It was found that the 0.22-µm-thick PZT single-coated film was a dense film with (111)-orientation and exhibited good ferroelectric properties. In order to thicken the PZT dense film, we have studied a sol-gel technique involving multiple coatings of 0.22-µm-thick layers. Finally, the 0.66- and 1.10-µm-thick PZT multicoated films have been prepared on platinized silicon substrates by three and five coatings of 0.22-µm-thick layers. Various properties of the multicoated films have also been evaluated.

Preparation and Evaluation of Pb(Zr, Ti)O3 Thin Films for Low Voltage Operation

Pb(Zr, Ti)O3 (PZT) thin films with thickness of 120 nm were prepared on Pt/SiO2/Si substrate by using two types of sol–gel solutions. The film from modified solution consisted of uniform and small grain of perovskite phase, whereas the film from conventional solution consisted of large grain of perovskite phase and secondary phase. The film from modified solution had higher nucleation density for crystallization. That was why the different morphology between those two films occurred. The P-E hysteresis of the film from modified solution was well saturated at low applied voltage. Pr and Ec of the PZT(40/60) were 29.1 µC/cm2 and 58.3 kV/cm, respectively. This modified PZT sol–gel solutions enable to get thinner films, down to 120 nm, without degradation of the morphology and the properties.

Low-Temperature Crystallization of Sol-Gel Derived Pb(Zr0.4,Ti0.6)O3 Thin Films.

We have studied the crystallization of sol-gel derived Pb(Zr0.4Ti0.6)O3 [PZT(40/60)] thin films at 435 down to 420°C. The PZT(40/60) films were prepared at these temperatures on Pt/SiO2/Si substrates by a combination of diol-based solutions and modified film preparation processes. Various properties of the PZT(40/60) films such as microstructures, crystal orientation, ferroelectric properties, relative permittivity, and leakage current density were evaluated. It was found that PZT(40/60) films could be crystallized at 435 to 420°C by the diol-based solutions and the modified film preparation processes. The PZT(40/60) films had microstructures with perovskite-single-phase fine columnar grains and good electric characteristics such as remanent polarization (Pr) of 12 to 15 µC/cm2, relative permittivity (er) of 780, and breakdown voltage of more than 10 V.

Lowering of crystallization temperature of sol-gel derived Pb(Zr, Ti)O3 thin films

Abstract We have studied the low temperature preparation of sol-gel derived Pb(Zr0.4Ti0.6)O3 thin films on Pt/SiO2/Si substrates, we found that new stable sol-gel solutions and the modified film preparation processes were effective in lowering the crystallization temperature. The film processed at 450°C from the new solution had better ferroelectric properties than the films from other conventional solutions. Thinning of the annealed film (thin film annealing) and piling of the annealed thin films (multi-annealing) were especially effective in lowering the crystallization temperature, as compared with the conventional preparation process of annealing of piled amorphous films (single-annealing). The combination of the new solution and the modified film preparation processes enabled PZT film to crystallize at 435°C and PZT film crystallized at 450°C to have good ferroelectric properties. And we discussed the mechanism of nucleation and grain growth of PZT films, which were connected with the stress.

Low-temperature sintering of ferroelectric Pb(Zr, Ti)O3 thick films derived from stable sol-gel solutions

Abstract We have studied sintering and densification of PbZr0.52Ti0.48O3 (PZT) films derived from diol-based sol-gel solutions. We found that densification by sintering began at below 750°C and completed at 850°C in 5 min. Initially, 0.83- μm-thick PZT single-coated films were prepared on Pt/Ti/SiO2/Si substrates from stable propylene-glycol (l,2-propanediol)-based solutions by crystallization at 700°C. The crystallized films consisted of fine perovskite grains and voids. We studied the firing temperature dependence of various properties such as microstructure, crystallinity, and ferroelectric properties for the single-coated films. Finally, 0.54- μm-thick PZT single-coated dense films were prepared by firing at 850°C for 5 min. In order to prepare thicker PZT dense films, we studied low-temperature sintering of PZT multicoated thick films. Using this approach, 1.7- μm-thick PZT dense films were prepared by firing at 850°C for 5 min.

Preparation of PZT thin films for low voltage application by sol-gel method

PZT ultrathin films with film thickness of 90 nm were prepared by the sol-gel method. By using modified sol-gel solutions, 90 nm-thick PZT films with good surface morphology were obtained even on Pt/SiO/sub 2//Si substrates, in which nothing worked as a seeding layer. The obtained PZT films with various compositions were evaluated. Use of the modified solutions made it possible to make the film thinner without degradation of the properties. P-E hysteresis curves for PZT(30/70) films with film thickness of 90 nm were saturated at about 1 V and the Pr was 28 /spl mu/C/cm/sup 2/. As a result, PZT thin films from the modified solution exhibited potential for low voltage drive FeRAM applications.

Improvement of process stability for PZT thin films formation by using modified SOL-GEL solutions

Abstract Pb(Zr, Ti)O3 (PZT) thin films were prepared from conventional and modified sol-gel solutions with various Pb contents on Pt/SiO2/Si substrate and evaluated. Comparing relationships between surface morphology of the PZT films derived from the solutions and Pb content in the solutions, same tendency that nano-crystalline secondary phase began to generate on surface of PZT films when the Pb content decreased was observed. However, the modified solutions had much wider window to produce PZT perovskite films without the secondary phase, namely good electrical properties. This was because nucleation density in PZT gel films was different between two solutions. The origin of the difference was discussed. For mass production of high density FeRAM, the control of the microstructure is key to stabilize the properties. By using modified sol-gel solutions, process stability for PZT films preparation was improved.

Preparation and evaluation of sub-100 nm Pb(Zr,Ti)O3 films derived from modified sol-gel solutions for low-voltage operation of feram

Abstract Sub-100 nm PbZr0.3Ti0.7O3 (PZT) films were prepared on Pt/SiO2/Si substrates from modified sol-gel solutions without using any seeding layers. Firstly, we studied Pb content [Pb/(Zr+Ti)] dependence of 90-nm-thick films. In the wide Pb content region of 108 – 125%, the films had perovskite-single-phase fine columnar grains with (111)-orientation and no voids. Electric properties were dependent on Pb content. The film with good microstructure, rectangular hysteresis, high remanent polarization (Pr), and low leakage current was gained for Pb content of 116%. Secondly, we studied film thickness dependence of PZT(116/30/70) films. Films from 90 down to 61 nm in thickness were prepared. We found that the sub-100 nm films with good microstructures could be prepared from the modified solutions. The sub-100 nm films had saturation voltage of 1.25 V and high Pr even at 1 V or less. In particular, a 61-nm-thick film had high.Pr of 17 μC/cm2 at 0.75 V.