Morito Matsuoka

Ba–ferrite thin‐film disk for perpendicular magnetic recording

The authors have prepared Ba–ferrite film disks and evaluated their magnetic read/write characteristics. The c‐axis‐oriented Ba–ferrite thin films were formed epitaxially on c‐axis‐oriented ZnO films by means of a targets‐facing‐type sputtering system. The direction of easy magnetization in the film with perpendicular crystalline anisotropy is almost perpendicular to the film plane. Thus, the perpendicular remanence is more than 60 times as large as the in‐plane one. The simple Ba–ferrite films, however, have a coercive force, Hc⊥ above 2 kOe which is too large to write on by means of a conventional head. The substitution of In3+ in the Ba–ferrite films makes the Hc⊥ values decrease to about 1 kOe without increasing the critical temperature, Tcritical, of c‐axis orientation. The read/write characteristics of the films were measured with a MnZn–ferrite ring head. The reproduced signal exhibits clear dipulsive waveforms as the dipulse ratio exceeds 0.7. Furthermore, the overwrite ratio decreases below −28 d...

Magnetic field gradient effects on ion energy for electron cyclotron resonance microwave plasma stream

The effects of mirror field application on ion energy and its dispersion for electron cyclotron resonance (ECR) microwave plasma stream are discussed. Low‐energy ions with minimal dispersion are extracted from ECR microwave plasma in the mirror field. Mirror field effects on the ion energy profile are caused by a decrease in plasma microparameter distribution, including plasma potential, electron temperature, and plasma density. A highly dense ion stream is extracted from ECR plasma with the mirror field.

Formation of Ba-ferrite films with perpendicular magnetization by targets-facing type of sputtering

Ba-ferrite films have been prepared by means of Targets-Facing type of sputtering method which is very useful to prepare magnetic films at high rate without any bombardment of high energy particles such as γ-electrons and negative ions emitted from the targets and is favorable to obtain stoichiometric films of good quality. C-axis orientation of the films depends strongly on substrate temperature and crystal structure of substrate. C-axis well oriented BaM films are deposited on amorphous materials such as a-SiO 2 . The deposited films of 3000 A in thickness have ΔΘ 50 less than 1 degree, magnetic anisotropy constant of 3.2\times10^{6} erg/cc, saturation magnetization of 380 emu/cc and coercive force of 1.3 kOe. These films reveal much better c-axis orientation and surface smoothness than the films deposited by DC diode type of sputtering method and have almost the same composition as that of the targets.

Dense plasma production and film deposition by new high‐rate sputtering using an electric mirror

Production of a dense plasma for new high‐rate sputtering using an electric mirror has been achieved. The plasma, whose density is over 1012 cm−3, is generated by reciprocating an electron beam between two targets. Microwave excitation is detected in the dense plasma. Nonlinear interaction between the electron beam and the plasma plays an important role in dense plasma production. High deposition rates of over 3000 A/min have been realized for Al, Mo, Fe, etc. Low‐frequency instability, corresponding to E×B drift wave, also occurs in the plasma.

Preparation of Ba-ferrite films for perpendicular magnetic recording by RF targets facing type of sputtering

A rf Targets Facing Type of Sputtering(rf-TFTS) apparatus was used to deposit hexagonal magnetoplumbite type of Ba ferrite (BaO.6Fe 2 O 3 : BaM) films with c-axis orientation at high rate. Although high rate sputtering of BaM was possible under stable conditions in rf-TFTS, the film composition changed drastically with total gas pressure P total and input power P av during sputtering. These changes in film composition corresponded well to the change in the potential difference Vd between plasma and wall, that is, the deficiency in Ba content in the films increased as V d increased. These results indicate that the change in composition is caused by ion bombardment of the substrate during sputtering (i.e., Ba atom is resputtered preferencially), since the ions in plasma can bombard the substrate with energy about e.V d . The value of V d decreases as P total or P av increases and the BaM films with stoichiometric composition were obtained at high P total or at high P av . Therefore, sputtering must be performed under the condition of high sputtering power or of high sputtering gas pressure, where V d becomes small, to deposit stoichiometric BaM films.

Effect of additional element (Fe, Zr, Ta) for Co‐Cr films deposited by targets facing type of sputtering

In order to improve both magnetic properties and wear resistance of Co‐Cr films for perpendicular magnetic recording media, the effect of the addition of a small amount of Fe, Zr, and Ta to the Co‐Cr binary alloy films has been investigated. They were deposited with a targets facing type sputtering (TFTS) apparatus. (i) The addition of a small amount of Fe (<5 at. %) causes a significant decrease of the effective perpendicular magnetic anisotropy K⊥ (K⊥=Ku−2πM2s). The K⊥ has a negative value at Fe content above 1 at. %. Consequently, the recording characteristics become worse as Fe content increases. (ii) The addition of Zr leads to a remarkable decrease of grain size and improvement of surface smoothness along with an increase of wear resistance. It also causes evident decrease in Ku and saturation magnetization Ms. However, both K⊥ and remanence ratio Mr⊥/Mr∥ are increased by the addition of a small amount of Zr up to 0.5 at. %, though they decrease steeply with further increase of Zr content above 1 at...

Sputter deposition and read/Write characteristics of Ba-ferrite thin film disk

The nucleation mechanisms and the composition change in Ba ferrite films deposition by means of the Targets Facing Type of Sputtering system have been discussed in detail. In addition, an attempt to control their magnetic properties has been made and read/write characteristics of the films prepared on the disk substrates have been evaluated. The single phase Ba ferrite films composed of fine graines are deposited epitaxially on the c-axis well oriented ZnO layer even in the nucleation stage under a wide range of preparation conditions. Moreover, the film composition, the crystal structure and the magnetic properties depend strongly on oxygen partial pressure. The films sputtered from the targets of n=5 and 6 in the BaO.nFe203 system exhibit good crystallographic and magnetic properties under the wider range of sputtering conditions. The coercive force Hc can be decreased without increasing the critical temperature of c-axis orientation by substitution of In3+for Fe3+. Furthermore, the D50 increases and overwrite decreases with increase of In3+content. Consequently, high density perpendicular recording with D 50 of 88 kFRPI has been achieved by using a narrow gap (0.4 μm) ring head.

Low‐temperature epitaxial growth of BaTiO3 films by radio‐frequency‐mode electron cyclotron resonance sputtering

BaTiO3 (BTO) films have been deposited on SrTiO3 (STO) wafers by a rf‐mode electron cyclotron resonance sputtering system. The substrate surface is pretreated in several ways before film deposition. The oxygen plasma irradiation is the best way of pretreating the substrate surface. Single‐crystal BTO films with smooth surfaces are deposited on STO at temperatures ranging from 350 to 650 °C at total gas pressures ranging from 0.02 to 0.1 Pa. BTO films with (100) orientation are obtained at temperatures as low as 200 °C. The dielectric constant of films grown at 350 °C reaches 470 and that of films grown at 550 °C reaches 880.

ELECTROLUMINESCENCE OF ERBIUM-DOPED SILICON FILMS AS GROWN BY ION BEAM EPITAXY

Sharp and well-split electroluminescence has been achieved from light-emitting diodes (LEDs) fabricated from as-grown erbium–oxygen codoped silicon films, where all elements were in situ incorporated during film growth. The LEDs were fabricated using ion beam epitaxy with an electric mirror sputtering-type metal ion source in an ultrahigh vacuum. Electroluminescence was observed from the LEDs under both forward and reverse biases. Each luminescence line corresponded well to the intra-4f transitions of Er+3 ions with almost single local coordination. The electroluminescence quenching factor with temperature under a forward bias was similar to that for photoluminescence. Sharp luminescence was, however, still observed even at room temperature under a forward bias. Under a reverse bias, strong electroluminescence was observed at room temperature without quenching.

Crystal structures and optical properties of ZnO films prepared by sputtering-type electron cyclotron resonance microwave plasma

This paper describes the crystal structure and photochromism of Zn oxide films fabricated by sputtering‐type electron cyclotron resonance microwave plasma. C‐plane preferential orientation and (101) plane preferential orientation are achieved in Zn oxide films deposited on glass substrates below 200 °C. These films have strong crystallite orientation. Films with (101) plane orientation exhibit typical photochromic characteristics induced by x‐ray irradiation. Photochromism is probably caused by a color center, that is, the oxygen vacancy in Zn oxide films. The absorption center exists in an energy range of 1.5 to 4 eV. The activation energy in the fading process is ∼0.03 eV.