Yuji Tsukamoto

Mechanical properties of thin films: Measurements of ultramicroindentation hardness, Young's modulus and internal stress☆

Abstract The ultramicrohardness, Youngs modulus and internal stress are measured for various thin films and surfaces by using a newly developed tester. The tester consists mainly of an indenter actuator, a load detecter with a resolution of 0.1 microN, a displacement sensor with a resolution of 4 nm and a personal computer system. The ultramicrohardness is calculated from a load-indentation depth curve for a surface layer with a depth range of up to 0.1 microm. Youngs modulus and stress tests are based on the fact that both ends of a composite beam are supported. The measurable film thickness is in the 0.01 microm range for Youngs modulus and stress. This tester can be used not only as an instrument for measuring mechanical properties but also as a characterization tool for thin films and surfaces. Applications for some thin films, such as diamond-like carbon films and ohms-tricosenoic acid Langmuir-Blodgett films, are also described.

Microindentation adhesion tester and its application to thin films

Abstract Adhesion measurements are made for various thin films with submicron thickness using a newly developed tester. The tester consists mainly of an indenter actuator, a load detector with a 0.1 μN resolution, an optical displacement sensor with a 4 nm resolution, an acoustic emission (AE) analyzer, and a personal computer system. Prominent features of the tester are a piezo-electric ceramic indenter to detect feeble AE signals owing to thin film delamination from a substrate, and an inclined sample holder to apply shear force to an interface. Measurable maximum adhesion strength is about 500 MPa for a sputtered SiO 2 film/quartz glass substrate specimen. Applications for some thin films, such as a sputtered carbon and various Au alloy films, are also described. The experimental results provide quantitative information about mechanical or atmospheric durability of various thin film devices.

Mechanical properties of diamondlike carbon films

Diamondlike carbon (DLC) films have been deposited onto room‐temperature silicon substrates, which are placed on a cathode, in a dc plasma of methane (CH4) and hydrogen (H2) gas mixture. Ultramicroindentation hardness and Young’s modulus for the films were measured. The mechanical properties of DLC films change greatly in two different anode positions relative to the cathode. In the case of an upward anode position (so‐called parallel electrode), the maximum ultramicroindentation hardness value is 200 GPa(3700 Hv) and the maximum Young’s modulus value is 480 GPa. At a sideward anode position, the maximum ultramicroindentation hardness value and Young’s modulus value are 480 GPa(7500 Hv) and 850 GPa, respectively, which are much higher values than those at the upward anode position. The contact‐start‐stop test results indicate that DLC films have a possibility for use as a wear‐resistant protective layer.

Head-Disk Interface Design For In-Contact Recording Using Wet Systems

The authors have investigated head-disk interface design for in-contact recording using wet systems. The design concept of the wet systems is to realize a low bouncing height of sliders by using the meniscus attractive force of the lubricant between slider and disk. The lubricant offered high wear performance at the same time. It was found that lubricants with high surface energies suppressed the bouncing height of contact sliders. A bouncing height of 3 nm was achieved for a combination of 30% contact sliders and lubricants of maleic anhydride modified polybutene. A contact slider design, with a meniscus-controlled contact pad, is proposed for contact sliders using wet systems. The bouncing of the slider was suppressed by regulating the etching depth of the meniscus-controlled contact pad. High wear performance of the in-contact recording system was confirmed by both the drag test for disks and the seek test for heads. The large readback signal and the pulse width measured at 50% amplitude (PW50) for the in-contact recording, compared with flying heads, has been demonstrated.

Nanometer‐scale recording, erasing, and reproducing using scanning tunneling microscopy

We demonstrate using a scanning tunneling microscope reproducible and reversible recording and erasing of marks about 10 nm in size. Studies on both data storage devices and nanometer fabrication using a scanning tunneling microscope have been carried out, involving a variety of techniques and materials. However, most studies neglect erasing, despite the fact that erasing is a major requisite, as well as recording and reading. Using a thin layer of a vanadate glass deposited on vanadium bronze, β‐NaxV2O5, has made it possible to record, erase, and read 10 nm level marks at ambient temperature and pressure. The main mechanism for reversible recording is sodium ion migration between the vanadium bronze crystal phase and the vanadate amorphous phase along the electric field. The organic medium of a hemiquinone molecule was proposed for higher recording speed.

Mechanical properties and wear characteristics of various thin films for rigid magnetic disks

The relationships between mechanical properties and wear characteristics are described for carbon, SiO/sub 2/ and CoNi-on-Cr thin films. The films are prepared on various rigid substrates in the submicron thickness range by RF magnetron sputtering. Mechanical properties examined include microhardness, Youngs modulus and internal stress. Wear resistances are evaluated for thin films sliding against a thin film head Al/sub 2/O/sub 3/-TiC slider. There is no correlation between the microhardness and the wear resistance. However, the load-indentation depth curves provide useful information, since the curve profile varies reflecting the presence of microdefects closely related to wear characteristics. A clear and common relationship holds between Youngs modulus and wear resistance which is a maximum at 0.8-0.9 times the modulus. The wear resistance of CoNi films decreases as the tensile stress increases in the Cr substrates. The properties of carbon films depend on their own internal stress; an increase in compression stress leads to deterioration in their wear resistance. >

Measurement of Sidewall Roughness by Scanning Tunneling Microscope

A scanning tunneling microscope (STM) is a highly effective tool for observing a microfabricated pattern. However, it is difficult to measure sidewall roughness using a conventional STM because of the restriction of the tip shape and one-dimensional servo system. The main objective of this study is to develop a sidewall roughness characterization tool. The electron-beam deposition method is applied to preparing a novel STM tip shape. A two-dimensional servo system, with a subnano-vibration mode to provide vibrations below 1 nm for x- and z-directions to a tip during scanning, has been developed for sidewall roughness measurement.

Thermal and magnetic stability of unidirectional anisotropy in spin-valve magnetoresistive heads

The temperature and time dependencies of magnetic anisotropies for NiFe layers pinned by two typical antiferromagnetic films, NiO and FeMn, were studied to understand the stability of unidirectional anisotropy. Torque curves were measured isothermally after application of a magnetic field from a direction perpendicular to the unidirectional anisotropy for certain time periods. Applying the field caused the torque curve to shift toward the field direction and its amplitude to decrease. The amount of shift and the normalized decrease in the torque amplitude were proportional to the logarithmic time of the applied perpendicular field. The changes observed in the NiO/NiFe film are twice as large as those in the NiFe/FeMn film at the same holding time and temperature. The external magnetic field caused rotation in the direction of the unidirectional anisotropy and a reduction in the exchange coupling strength. These changes may be explained by the thermal fluctuation aftereffect model. The unidirectional anisotropy in the NiO/NiFe film was less stable compared with that in the NiFe/FeMn film.

Structural and Magnetic Properties of Ni-O/Ni-Fe Bilayer Films

Investigations on the relationship between the magnetic properties and structure of Ni–O/Ni–Fe bilayer sputtered films were conducted. The Ni–O/Ni–Fe films were prepared under various Ar gas pressures during Ni–O layer deposition and various distances between targets and substrates. The exchange coupling field decreased as the Ar gas pressure was increased, although the coercive force remained constant. The distance between the target and the substrate does not affect the magnetic properties. Structural analysis revealed that the Ni–O layer exhibits a rhombohedral structure distorted in the direction of from the cubic NaCl structure. The interaxial angle α, which is the angle between two crystallographic axes in the rhombohedral unit cell, gradually decreases as the Ar gas pressure increases until finally the cubic NaCl structure is formed. We found that there is a linear relationship between the values of the exchange coupling field and α which corresponds to the degree of distortion from the NaCl structure. It is considered that the structural distortion of the Ni–O layer affects its antiferromagnetic state, then the exchange coupling between Ni–O and Ni–Fe layers is affected as a result.

Extremely durable CD-ROM with a novel structure

This paper describes an extremely durable CD-ROM and its reliability. A pit pattern was fabricated through a sol-gel process utilizing a 2P/epoxy work stamper. Excellent stability was guaranteed by a layered structure, such as the SiO2-ZrO2 over coat on a chemical strengthening glass substrate and the Si/SiO2-ZrO2/Cr tri- layered reflector on a sol-gel layer. Accelerated tests were implemented to estimate its lifetime. The CD-ROM lifetime at 30 degree(s)C (DOT) 90% RH was estimated to be more than 300 years. This exceedingly long lifetime was determined on the basis of the following two experimental results. Little degradation was observed in Cl error rate during about 50 days at 120 degree(s)C (DOT) 90% RH. A main degradation mode, which was observed on longer aging, was Cr film peeling-off. It was found that activation energy for Cr peeling-off process was 0.91 eV by an in-situ peeling detection tester, based on the acoustic emission method.