Toru Mori

Ferroelectric Properties of Sol-Gel Derived Pb(Zr, Ti)O3 Thin Films

Pb(Zr, Ti)O3 thin films of thickness ranging from 55 nm to 625 nm were synthesized on Pt/Ti/SiO2/Si substrates using a sol-gel process. The film thickness dependence of both microstructure and electrical properties was investigated. The synthesized films showed columnar structure. The diameter of each column was around 100 nm regardless of the film thickness. The 328 nm-thick film exhibited a dielectric constant (e) of 1000, remanent polarization (Pr) of 20 µC/cm2, and coercive field (Ec) of 47 kV/cm. Both e and Pr decreased and Ec increased with decreasing film thickness. This behavior is attributed to the existence of a low-dielectric-constant interface layer. The results of leakage current measurement were in good agreement with the model of space-charge-limited current.

Difference in microstructure between PZT thin films on Pt/Ti and those on Pt

Abstract PZT thin films were synthesized by sol-gel on a Pt/Ti double layer bottom electrode or on a Pt single layer bottom electrode to investigate the bottom electrode dependence of PZT film structure. On Pt/Ti, oriented perovskite grains with 50–100 nm lateral size were densely packed. On Pt, large perovskite grains (2−3 μm) were surrounded by fine pyrochlore grains (about 5 nm), and no certain orientation was observed. TEM and EDX analyses suggested that a fraction of Ti in the Pt/Ti layer diffused along Pt grain boundaries up to the Pt surface and was oxidized during the PZT annealing process. A model for the crystallization of sol-gel derived PZT was proposed, in which TiOx particles at the Pt surface act as nucleation sites for PZT crystallization. This model well explained the experimental results.

Dielectric Properties and Crystal Structures in Ternary System Pb(Mg1/2W1/2)O3-Pb(Ni1/3Nb2/3)O3-PbTiO3 Ceramics

Over the entire range of composition in ternary system Pb(Mg1/2W1/2)O3-Pb(Ni1/3Nb2/3)O3-PbTiO3 (PMW-PNN-PT), crystal structures and dielectric properties were investigated. On the compositional line of 30 mol% PNN content, dielectric relaxation, D-E hysteresis loop and long-range order parameter were measured in order to understand the effect of PMW content. From the results, a morphotropic phase boundary (MPB) was found on the compositional line with 45 to 50 mol% PT content. It was found that the PMW component was incorporated into ordered clusters in solid solutions in a PMW-rich compositional region. The degree of ordering was evaluated by the long-range order parameter S. The relationship between the long-range order parameter S and dielectric properties, especially compositional dependence of Curie temperature, in this system was discussed.

Variable Thermal Emittance Radiator Using Metal-Insulator Phase Transition in La1-xSrxMnO3

A variable-emittance radiator device, made of thin and light ceramic tiles, has been developed for thermal control applications on spacecraft. The ceramic material used is La1-xSrxMnO3 with a perovskite structure, and shows a phase transition from ferromagnetic metal to paramagnetic insulator at around 290 K (Tc). This device automatically controls a spacecrafts temperature without electrical or mechanical instruments. Below the Tc, the device is metallic with a low thermal emittance of 0.3, and above the Tc, it becomes insulative with a high thermal emittance of 0.7. For the ceramic tiles, two different fabrication processes were studied to reduce the cost and weight; one is a conventional ceramic wafer process and the other is a thick film process on zirconia substrates. Total thickness of the ceramic tiles obtained is less than 70 µm and the weight is 450 gr/m2.

Transmission electron microscopy study of B‐site cation configurations in perovskite‐structured Pb(Mg1/2W1/2)O3‐Pb(Ni1/3Nb2/3)O3‐PbTiO3 ceramics

Configurations of B‐site cations in the perovskite‐structured ternary system Pb(Mg1/2W1/2)O3‐Pb(Ni1/3Nb2/3)O3‐PbTiO3 (PMW‐PNN‐PT) of interest for multilayer ceramic capacitors were studied by transmission electron microscopy. The evaluated specimens were four PMW/PNN/PT compositions: 10/30/60, 30/30/40, 50/30/20, and 70/30/0 on a compositional line with 30 mol % PNN content. A ‘‘core‐shell‐type’’ microstructure was seen in the 10/30/60 specimen composition, which has a ‘‘normal’’ ferroelectric characteristic, along with typical ferroelectric domain structures. The B‐site cation ordering in the 10/30/60 composition was not detectable in the selected‐area electron diffraction pattern. On the other hand, an ‘‘island‐type’’ microstructure, consisting of clusters (∼1–2 nm) with B‐site cations 1:1 ordered, was observed in the 30/30/40, 50/30/20, and 70/30/0 compositions, which have relaxor‐type characteristics. In the 70/30/0 composition, larger stripe‐shaped ordered regions (∼20–200 nm) were also observed. The...

High-Capacitance Thin-Film Capacitors on a Polymer Film

Pb(Zr,Ti)O3 (PZT) thin film has been crystallized at below 450°C by means of a sol–gel process that employs a PT-seeding method, and it has been used to fabricate a PZT thin-film capacitor on polyimide film at a high decomposition temperature. The capacitor structure includes a 4-layer bottom electrode: Pt(200 nm)/Ti(50 nm)/Mo(600 nm)/Ti(50 nm). Capacitance density is 12 nF/mm2 in the effective capacitance area. Despite the use of PZT, a high-k material, this thin-film capacitor still offers high insulation resistance (6.2 GΩ at 3 Vdc) and reliability sufficient for use as a decoupling capacitor.

Improved Reliability in Thin-Film Capacitors Fabricated with Mn-Doped Pb(Zr,Ti)O3 Annealed at Low Temperatures

Mn-doped Pb(Zr,Ti)O3 (PMZT) thin film have been successfully crystallized in a sol–gel process at 440 °C, at which temperature polyimide film does not decompose. With a 6.8 V DC applied bias (272 kV/cm) in the effective capacitance area, capacitance density is 20 nF/mm2, and leakage current density is 0.2 µA/cm2. With a continuously applied 6.8 V DC bias, 0.2 mol % Mn-ion doping results in an increase from 4.0 to 12.5 years in the time to dielectric breakdown, as extrapolated to 85 °C, without degrading capacitance. Mn-doped Pb(Zr,Ti)O3 (PZT) thin-film capacitors on polymer film appear to offer capacitance and reliability that are both high enough for use as decoupling capacitors.

Research and development of relaxor ferroelectric ceramics at NEC

The authors describe the development of many systems containing relaxor ferroelectrics studied for multilayer ceramic capacitors at NEC Corporation since 1975. These ceramics were composed of complex perovskite compound containing lead ion and were categorized into three types. The complex perovskite systems containing Pb ions and W ions were suitable for a low firing temperature and showed a high dielectric constant with a smaller grain size than a BaTiO/sub 3/ system. Multilayer capacitors with large capacitance have been manufactured from these systems. Pyrochlore compound was effective for suppression of grain growth and resulted in bend strength increases, The use of alkoxide powder was very promising. The multilayer ceramic capacitors made from this powder showed a very high capacitance per volume.<<ETX>>

Variable Thermal-Emittance Radiator Using La1-xSrxMnO3 Thick Film on PSZ Substrate

We have developed a variable-emittance radiator device, made of thin, and light ceramic tiles, for thermal control applications on spacecraft. The ceramic material used is La1-xSrxMnO3 with a perovskite structure, which shows a phase transition from a ferromagnetic metal with a low thermal emittance of 0.35 to a paramagnetic insulator with a high thermal emittance of 0.75 at around 300K. This device automatically controls the temperature of a spacecraft without requiring electrical or mechanical instruments. The fabrication process for the ceramic tiles was designed to reduce production costs and weight. The tiles are less than 70-microns thick and weigh 450g/m 2 . Both a conventional type of ceramic wafer and a thick film type were developed and tested for their durability under various environmental and radiation conditions. The results showed no degradation. These variable emittance radiators made of ceramic tiles have been used for the MUSES-C spacecraft designed to probe asteroids, and are also scheduled to be used for the INDEX spacecraft designed to observe the earth.

Dielectric properties and crystal structures of entire compositions in the ternary system Pb(Mg/sub 1/2/W/sub 1/2/)O/sub 3/-Pb(Ni/sub 1/3/Nb/sub 2/3/)O/sub 3/-PbTiO/sub 3/

Crystal structures and dielectric properties were investigated over the entire range of composition in the system Pb(Mg/sub 1/2/W/sub 1/2/)O/sub 3/-Pb(Ni/sub 1/3/ Nb/sub 2/3/)O/sub 3/-PbTiO/sub 3/(PM A morphotropic phase boundary (MPB) was found on the compositional line with 45 to 50 mol.% PT content. The PT-rich composition with Tc>100 degrees C showed a steep temperature dependence of the dielectric constant. The PMW-rich composition with Tc around room temperature or below showed a diffuse phase transition. Superlattice reflections due to the ordering of Mg and W ions in the perovskite B-site were observed in the X-ray diffraction patterns of the PMW-rich composition. The results obtained indicate that PMW-rich compositions were relaxor ferroelectric. A downward Curie temperature shift as a function of PMW content was saturated in the PMW-rich compositional region, which suggests that the PMW-rich region is not a simple solid solution but a nanometer composite of an ordered region and a disordered region.<<ETX>>