Shigehiko Fujimaki

Properties Of Diamond-like Carbon Films And Its Application For Protective Layers Of Thin Film Magnetic Recording Disks

Wear rate of diamond-like carbon (DLC) protective layer deposited by a radio frequency plasma enhanced chemical vapor deposition method has been evaluated by continuous sliding tests using spherical sapphire pins. The influence of each property such as microstructure and microhardness on wear durability of the film is discussed. It has been found that the wear durability of the DLC film is several times superior to that of conventional sputtered carbon film. >

STRUCTURAL ANALYSIS OF HYDROGENATED CARBON FILMS OBTAINED BY REACTIVE DIRECT CURRENT MAGNETRON SPUTTERING

Amorphous hydrogenated carbon films were prepared by reactive direct current magnetron sputtering in argon plasma containing methane as the reactant gas. The films were characterized using various spectroscopic measurements such as Raman scattering, optical absorption spectroscopy in the ultraviolet–visible region, and infrared (IR) absorption spectroscopy. The spectral analyses indicated that changes in Raman spectroscopy intensity occurring with increasing methane gas content were determined to be caused by changes in optically resonant components in the films. Furthermore, a significant correlation was seen between the relative intensity of IR peaks and wear durability.

Effect of microstructure and hydrogen content on the characteristics of amorphous hydrogenated carbon protective coatings

Amorphous hydrogenated carbon films have splendid wear characteristics as protective coatings. In the present work we have studied the relation between wear durability and microstructure of the amorphous hydrogenated carbon films prepared with radio‐frequency plasma‐enhanced chemical vapor deposition. Wear rates of pin‐on‐disk sliding tests for the films deposited at various conditions have been compared with the results of spectroscopic analysis. Wear durability of the films has been found to be described with a combination of two factors, one is the shoulder‐to‐main peak ratio of Raman spectra and the other is content of chemically bonded hydrogen atom. The former factor stands for the amount of ‘‘graphitelike’’ regions and the latter stands for the amount of ‘‘organic’’ regions in the carbon films.

Properties of Diamond-Like Carbon Films Fabricated by the Filtered Cathodic Vacuum Arc Method

With the aim of evaluating the properties of diamond-like carbon (DLC) films, a comparison is made between tetrahedral amorphous carbon (ta-C) films fabricated by the double-bend-filtered cathodic vacuum arc (FCVA) method using no material gas and hydrogenerated amorphous carbon (a-C:H) films fabricated by the chemical vapor deposition (CVD) method using a hydrocarbon gas. It was found that the ta-C films are superior to the a-C:H films in terms of both wear resistance and combustion resistance. It was also determined that this superiority applies for ultra thin films as well.

H/sub c/ measurement of microscopic regions on thin film magnetic disc using longitudinal Kerr effect

A longitudinal Kerr magnetooptical microscope system with a read/write testing unit and a positioning unit was developed for nondestructive measurement of the coercive force (Hc) in thin-film magnetic disks. This system measures the magnetooptical hysteresis loop from an area 2-30 mu m in diameter on a disk with a C/CoNi/Cr layer. The magnetic field strength at the disk surface was estimated from the coil current in a Weiss-type magnet. The absolute value of the field strength was calibrated by a Hall sensor. The actual H/sub c/ values were measured and compared with the result obtained by a vibrating sample magnetometer in order to determine the accuracy, which was found to be within 2%. It took 36 min. to complete the H/sub c/ measurement at 144 points over a 5.25 in. disk for a mean spot size of 30 mu m. >

Control of Plasma Parameters for High-Quality Hydrogenated Amorphous Carbon Growth

The correlation between plasma parameters and film properties is demonstrated in the growth of device-grade hydrogenated amorphous carbon (a-C:H) from pure methane (CH4) by capacitively coupled plasma-enhanced chemical vapor deposition (CCP-CVD). The deposition rate, refractive index, film stress and film hardness are strongly correlated with the self-bias voltage, Vdc. Hard, rigid, and transparent a-C:H films can be fabricated when the self-bias voltage, Vdc, is around 160–200 V. The ion energy, which is determined by the Vdc, is used to rearrange the film structure. The Vdc of around 160–200 V corresponds to 70–80 eV of the C ion flux in the case of C2H5+ ions. According to the calculation using a modified Thomas-Fermi potential as the Coulomb screening potential, the incident C ion energy is estimated to penetrate the carbon film of 1.8 g/cm3 density to the depth of about 0.55 nm, which enables the densification of the a-C:H film.

DEPOSITION OF DLC FILMS USING MAGNETRON PLASMA IN AN UNBALANCED MAGENTIC FIELD

A new type of unbalanced magnetic field for planer magnetron cathode was applied to conduct PE-CVD by the assistance of dc magnetron discharge. A carbon thin carbon was formed on a negatively biased substrated by supplying Ar and CH4. This coating was found to have the physical properties equivalent to the DLC sample by ECR-CVD. This paper describes the sample and efficient DLC coating method based on the PE-CVD mechanism.

PREPARATION OF ULTRA THIN CARBON OVERCOAT FOR MAGNETIC RECORDING MEDIUM BY HOT FILAMENT PLASMA CVD

The deposition process of carbon coating by plasma CVD was studied for the development of a high-density magnetic disk with an ultra thin overcoat of about 4nm thickness. A hot filament discharge system was installed to disk production equipment for the simultaneous deposition of a carbon thin coating on both sides of the disk. The hot filament high-density plasma, in a low-pressure atmosphere of 0.5Pa, was found to be more advantageous, compared with other CVD sources, such as radio frequency plasma, in deposition of the hard carbon thin coating on a negatively biased substrate with ion incidence to the sample. Ion impinging on the substrate was evaluated by calculating its contribution ratio, roughly, from growth rate and bias current density, then examined in relation to the hardness of the carbon thin coatings. In conclusion, hot filament plasma, as a stable CVD source, enables the deposition of the hard carbon overcoat at over 10GPa at the rate of about 1 nm/s, by generating high-density plasma in a low-pressure atmosphere.