Atsuhito Sawabe

Growth of diamond thin films by dc plasma chemical vapor deposition

Diamond thin films have been formed by dc plasma chemical vapor deposition with a high growth rate (∼20 μm/h). The diamond has been grown from methane (CH4) and hydrogen (H2) mixed gases on Si and α‐Al2O3 substrates at a pressure of 200 Torr without surface scratching by diamond or c‐BN powder. The obtained films have good crystallinity in the sense of electron and x‐ray diffraction. Vicker’s hardness of the film is the same as that of natural diamond (∼10 000 kg/mm2). The influence of the dc discharge in a low vacuum (∼200 Torr) on diamond synthesis will be discussed briefly.

Growth of diamond thin films by electron assisted chemical vapor deposition

Diamond thin films have been formed by the newly proposed electron assisted chemical vapor deposition on SiC with a high growth rate (3∼5 μm/h). The obtained films have good crystallinity in the sense of electron and x‐ray diffraction. Vicker’s hardness of the films is about 9000 kg/mm2. The influence of the electron bombardment on the initial island density on the substrate surface and on the decomposition of the reactant gases (CH4 and H2) is discussed relating to the growth process of the films.

Growth of diamond thin films by electron-assisted chemical vapour deposition and their characterization

Diamond thin films were produced by electron-assisted chemical vapour deposition which was originally proposed by the present authors. The films were produced mainly on SiC with a high growth rate (3–5 μm h−1) and at a relatively low temperature (823 K). The films obtained are characterized by electron and X-ray diffraction, electron energy loss spectrometry, Raman scattering, laser microprobe mass analysis, secondary ion mass spectrometry and IR absorption spectrometry. Their general properties such as hardness, thermal conductivity, specific gravity and electrical resistivity are also measured. From these results, diamond thin films formed by electron-assisted chemical vapour deposition are shown to have almost the same characteristics as natural diamond. The influence of the electron bombardment on the film growth is discussed in relation to the decomposition of reactant gases (CH4 and H2).

Growth and characterization of phosphorus doped n-type diamond thin films

Abstract n -Type semiconducting diamond thin films were successfully grown by microwave plasma CVD using phosphine (PH 3 ) as a dopant source. The addition of PH 3 in the gas ambient strongly influences the optimal growth condition for diamond. The {111} surface of diamond was found to be the best surface as a substrate for the growth of phosphorous (P) doped diamond. At a methane to hydrogen ratio of 0.15% and a substrate temperature of 950 °C, smooth {111} oriented homoepitaxial diamond thin films are obtained even with the addition of PH 3 up to 1000 ppm to CH 4 . The epitaxial films grown with PH 3 /CH 4 : 600–20 000 ppm have shown clear n -type conduction by Hall effect measurements over a wide temperature range. An activation energy of electron of 0.46 eV was deduced from the temperature dependence of the carrier concentration. For the best (600 ppm) sample, the Hall mobility of 28 cm 2 /V-s has been obtained at a temperature range around 400–600 K.

A magnetic thin film inductor and its application to a MHz switching dc-dc converter

The authors propose a novel structured magnetic thin film inductor using rotation magnetization only. The thin film inductor has a sandwich structure, which consists of a double-rectangular spiral coil between top and bottom CoZrNb amorphous thin films. The sputtered CoZrNb amorphous magnetic thin films have uniaxial magnetic anisotropy induced by direct current field annealing. The easy magnetization axis is directed to the main axis of the rectangular spiral coil. Hence, only the rotation magnetization process dominates in this device. The typical specifications are as follows; 3.5/spl times/5.5 mm in size, inductance of 1 /spl mu/H constant up to 10 MHz, and a quality factor of 10 at 10 MHz. A MHz switching chopper dc-dc converter has been developed by using this thin film inductor, bare-chip semiconductor devices (a power MOSFET and a Schottky barrier diode), and a multilayer ceramic capacitor. This converter with a 0.1 cc volume has an output power over 1 W at 5 MHz switching, and the power density exceeds 10 W/cc (160 W/in/sup 3/). >

Epitaxial Growth of Diamond on Iridium

Epitaxial growth of diamond on iridium thin films was performed by direct-current plasma chemical vapor deposition with ion irradiation pretreatment of the substrate. Pyramidal epitaxial diamond particles with a number density of ~108 cm-2 were grown on the iridium film. The epitaxial relation is written as (100) diamond//(100) iridium and [001] diamond//[001] iridium. Tilting of the epitaxial relation, as occasionally observed for diamond on silicon or beta silicon carbide, is scarcely observed. Erosion,as observed for diamond on nickel substrates, is not observed. The effect of the ion irradiation of the substrate is discussed briefly.

Growth of Diamond Thin Films by dc Plasma Chemical Vapor Deposition and Characteristics of the Plasma

Diamond thin films have been formed by dc plasma chemical vapor deposition from a gaseous mixture of methane and hydrogen (gas ratio (CH4/H2); 2/100, total gas pressure; 2.66×104 Pa) with a growth rate of ~20 µm/h. During the course of diamond growth, characteristics of the plasma were measured by the Langmuir single probe method and also by emission spectrometry. From the characterization of the plasma, it was found that the degree of ionization was rather low (~10-7), and the statistical temperature of hydrogen gas was ~5×103 K. By a thermodynamic investigation at the gas temperature around 5×103 K, it was revealed that the source gases (H2 and CH4) of over 99% are decomposed to neutral atomic hydrogen and atomic carbon.

Fabrication of Epitaxial Diamond Thin Film on Iridium

We have successfully grown smooth diamond thin films epitaxially on (001) iridium surfaces through a direct-current plasma chemical vapor deposition process with two steps: ion irradiation pretreatment and diamond growth. The epitaxial areas of diamond thin films with a mean thickness of about 1.5 µ m seem to act as optical mirrors. The average roughness (Ra) of the thin film, as measured by atomic force microscopy, is about 1 nm. Confocal Raman spectroscopy was used to investigate the depth profile of the thin film. Raman bands due to nondiamond carbon components were nominal at the diamond/iridium interface or at other depths.

Metal-insulator-vacuum type electron emission from N-containing chemical vapor deposited diamond

This letter presents a clear explanation of the electron emission mechanism of the high-resistivity N-doped diamond cathode. Due to the very low barrier to emission of electrons from the N-doped diamond conduction band into vacuum, electrons in the conduction band of diamond can establish an appreciable leakage current at very low anode voltage. When such a current starts to flow, there is a field which is developed across the diamond bulk. This field is observed as an increase in the electric field at the back contact, causing the injected tunneling current increases exponentially. This process leads to the low threshold emission from the high resistivity N-doped diamond cathode.

Characterizations of the dc discharge plasma during chemical vapor deposition for diamond growth

During the course of diamond growth by dc plasma chemical vapor deposition, characteristics of the plasma have been measured by means of the Langmuir single probe method and emission spectrometry. For the source gas system of hydrogen and methane (gas ratio: CH4/H2=2/100, total gas pressure: 2.66×104 Pa), it is revealed that the statistical temperatures of hydrogen atoms and electrons in the positive column of the plasma are obtained to be 4.8×103–5.3×103 K and 1×105–1.1×105 K, respectively. The amount of ionized species is fairly small. By calculating the equilibrium constant of gas molecules in these gas temperature ranges, it is found that molecules over 99% H2 and CH4 are decomposed to the neutral H and C atoms.