Atsushi Tomozawa

Preferred Orientations of NiO Films Prepared by Plasma-Enhanced Metalorganic Chemical Vapor Deposition

Thin films of nickel oxide (NiO) with NaCl-type structure were prepared on glass substrates at 400°C by plasma-enhanced metalorganic chemical vapor deposition using nickel acetylacetonate as a source material. The relationship between O2 flow rate, and preferred orientation and microstructure of the NiO films was investigated. Highly crystalline NiO film with (111) orientation was obtained at O2 flow rates as low as 3 cm3/min. As the O2 flow rate increased from 3 to 70 cm3/min, the orientation of NiO films changed from (111) to (100) and deposition rate decreased from 17 to 11 nm/min. Films with both (111) and (100) orientation had columnar structure. The origin of the preferred orientation of the NiO films was discussed.

Preparation of (001)-oriented Pb(Zr,Ti)O/sub 3/ thin films and their piezoelectric applications

Preparation of (001) oriented Pb(Zr,Ti)O3 (PZT) thin films and their applications to a sensor and actuators were investigated. The (001) oriented PZT thin films were epitaxicially grown on (100)Pt/(100)MgO single crystal substrates by rf-magnetron sputtering. The PZT thin films on (100)Pt/(100)MgO buffer layer/glass substrates and (11 l)Pt/Ti/Si substrates also had high (001) orientation. All of these thin films showed the excellent piezoelectric properties without a poling treatment. These PZT thin films were applied to the angular rate sensor with a toning fork for a car navigation system, the dual-stage actuator for positioning a magnetic head of high-density hard disk drive (HDD) and the actuator for a inkjet printer head.

NaCl-Type Oxide Films Prepared by Plasma-Enhanced Metalorganic Chemical Vapor Deposition

Thin films of MgO, NiO and CoO with NaCl-type structure were prepared by plasma-enhanced metalorganic chemical vapor deposition using metal acetylacetonato complexes as source materials. Soda-lime glass, Si(111), stainless steel and fused silica were used as the substrates. X-ray diffraction patterns indicated that (100) preferred-orientation NaCl-type oxide films were obtained at substrate temperatures of 150°C or above, independent of the kind of substrate. Scanning electron microscopy images showed that each film had a smooth surface and a columnar structure with growth perpendicular to the film surface.

Preparation of cobalt oxide films by plasma-enhanced metalorganic chemical vapour deposition

Co oxide films were prepared on glass substrates at 150–400°C by plasma-enhanced metalorganic chemical vapour deposition using cobalt (II) acetylacetonate as a source material. NaCl-type CoO films were formed at low O2 flow rate of 7cm3 min−1 and at a substrate temperature of 150–400°C. The CoO films possessed (100) orientation, independent of substrate temperature. Deposition rates of the CoO films were 40–47 nm min−1. The CoO film deposited at 400 °C was composed of closely packed columnar grains and average diameter size at film surface was 60 nm. At high O2 flow rate of 20–50 cm3 min−1, high crystalline spinel-type Co3O4 films were formed at a substrate temperature of 150–400°C. The Co3O4 film deposited at 400°C possessed (100) preferred orientation and the film deposited at 150°C possessed (111) preferred orientation. Deposition rates of the Co3O4 films were 20–41 nm min−1. Both Co3O4 films with (100) and (111) orientation had columnar structure. The shape and average size of the columnar grains at the film surface were different; a square shape and 35 nm for (100)-oriented Co3O4 film and a hexagonal shape and 60 nm for (111)-oriented film, respectively.

Preparation of (001) oriented Pb(Zr,Ti)O 3 thin films and their piezoelectric applications

Preparation of (001)-oriented Pb(Zr,Ti)O3 (PZT) thin films and their applications to a sensor and actuators were investigated. These thin films, which have a composition close to the morphotropic phase boundary, were epitaxially grown on (100)MgO single-crystal substrates by RF magnetron sputtering. These (001)-oriented PZT thin films could be obtained on various kinds of substrates, such as glass and Si, by introducing (100)-oriented MgO buffer layers. In addition, the (001)-oriented PZT thin films could be obtained on Si substrates without buffer layers by optimizing the sputtering conditions. All of these thin films showed excellent piezoelectric properties without the need for poling treatment. The PZT thin films on the MgO substrates had a high piezoelectric coefficient, d31, of -100 pm/V, and an extremely low relative dielectric constant, epsivr, of 240. The PZT thin films on Si substrate had a very high d31 of -150 pm/V and an epsivr = 700. These PZT thin films were applied to an angular rate sensor with a tuning fork in a car navigation system, to a dual-stage actuator for positioning the magnetic head of a high-density hard disk drive, and to an actuator for an inkjet printer head for industrial on-demand printers.

Preparation of La‐modified PbTiO3 thin films on the oxide buffer layers with NaCl‐type structure

La‐modified PbTiO3(PLT: Pb0.9La0.1Ti0.975O3) thin films by rf magnetron sputtering were prepared on the preferred (100)‐oriented oxide buffer layers with NaCl‐type structure, which were prepared by plasma‐enhanced metalorganic chemical vapor deposition. Fused silica, (111)Si, soda‐lime glass, and stainless steel were used as the substrates to prepare the oxide buffer layers. The c‐axis and a‐axis preferred oriented PLT thin films were obtained on the buffer layer, independent of the kind of substrate. Further, highly c‐axis oriented PLT thin films were obtained when the substrate had a large thermal expansion coefficient. Significant pyroelectric currents were detected without a poling treatment. The NiCr/PLT/(100)Pt/(100)MgO/stainless steel structure had a dielectric constant of 250, a dielectric loss factor tan δ of 0.8%, and a pyroelectric coefficient of 3.8×10−4 C/m2 K.

Preferred orientations and microstructure of MgO films prepared by plasma-enhanced metalorganic chemical vapor deposition

Abstract NaCl-type magnesium oxide (MgO) films with (110) or (100) preferred orientation were prepared on glass substrate at 400°C by plasma-enhanced metalorganic chemical vapor deposition using Mg(C5H7O2)2 as a source material. The effect of deposition conditions, such as O2 flow rate, carrier gas N2 flow rate and total pressure during the deposition, on the preferred orientation of the MgO films were investigated. The total pressure during the deposition as well as the flow rate ratio of O2 to Mg source material were found to play a significant role in the preferred orientation of the films. (110)-oriented MgO films were obtained at low pressure under 0.15 Torr, while (100)-oriented MgO films were obtained at high pressure of 1.0 Torr, under the condition of a constant ratio of O2 to Mg source material. Rutherford backscattering and Auger electron spectra indicated that the O/Mg ratios of the films with (110) and (100) orientation were 0.97 and 1.61, respectively, and no impurities were contained in both the oriented films. Scanning electron micrographs showed that both films with (110) and (100) orientation were composed of closely packed columnar grains of diameter about 60 nm.

Iron oxide films with spinel, corundum and bixbite structure prepared by plasma-enhanced metalorganic chemical vapor deposition

Iron oxide films of spinel, corundum and bixbite structure were prepared on glass substrates at 150–450°C by plasma-enhanced metalorganic chemical vapor deposition and the formation diagram was determined by X-ray diffraction and conversion electron Mossbauer spectroscopy measurements. Spinel-type Fe3O4+δ films were formed in the low O2 flow rate range of 10–25 cm3 min−1 and the films deposited at 300°C or above possessed the (100) preferred orientation. For high O2 flow rate in the range of 30–45 cm3 min−1, corundum-type α-Fe2O3 films were formed at high substrate temperatures of 350–450°C and bixbite-type β-Fe2O3 films were formed at low substrate temperatures of 200–400°C. (100) oriented NaCl-type FeO coexisting with the Fe3O4+δ films were infrequently formed under deposition conditions for (100) oriented Fe3O4+δ films. The following two step growth model of preferentially (100) oriented Fe3O4+δ films is proposed: (1) formation of a (100) oriented FeO film, (2) transformation of the FeO film into (100) oriented Fe3O4+δ films by means of plasma oxidation during deposition. The deposition rate of the films increased with increasing RF power.

Preparation and pyroelectric properties of (Pb, La)(Zr, Ti)O3 (PLZT) thin films

PLZT films around 3 μm thick with compositions of ((Pb 0.925 La 0.075 )(Zr y Ti 1-y ) 0.981 +0.5 mass%MnO 2 } where y = 0-0.10, which have an appropriately small relative dielectric constant (∼200) were deposited on Pt(100)/MgO (100) by rf-magnetron sputtering. The pyroelectric properties of PLZT films as element materials for pyroelectric IR sensors were investigated in detail. Assuming that the volume specific heat C v of the present films is 3.2 J/cm 3 .K, the PLZT films exhibited the highest F.M. of 1.4 X 10 -10 C.cm/J and F.M.D* of 1.6 X 10 -8 C cm/J, which were around 1.8 times and 1.5 times larger than those of PLT films, respectively. Consequently, the figures of merit for the pyroelectric IR sensors could be improved by adding a small amount of Zr to PLT.

Crystallographic Orientations of MgO Films Prepared by Plasma-Enhanced Metalorganic Chemical Vapor Deposition

Thin films of magnesium oxide (MgO) were prepared on glass substrates by plasma-enhanced metalorganic chemical vapor deposition (PE-MOCVD) and the relationship between deposition conditions and crystallographic orientations were studied. Highly crystalline and highly (100)-oriented MgO film was obtained at the vaporizing temperature of 210° C, O2 flow rate of 200 cm3 min-1, rf power of 400 W and substrate temperature of 400° C. The orientation of MgO films is changed from (100) to (110) upon increasing the vaporizing temperature from 210 to 240° C or upon decreasing the O2 flow rate from 200 to 50 cm3 min-1. These results indicated that the films deposited at the high arrival ratios of oxygen to magnesium precursor (O/Mg) onto the substrate had a (100) orientation, while those deposited at the low arrival ratios of O/Mg had a (110) orientation. The intrinsic stress of the (100) oriented film was tensile and the magnitude was 0.25 GPa.