Ryo Imura

Silicon pn junction imaging and characterizations using sensitivity enhanced Kelvin probe force microscopy

We observed the surface potential of silicon pn junctions using a Kelvin probe force microscope whose sensitivity was about five times better than that of a conventional one. It was achieved by three major improvements: electrostatic force detection using the second cantilever resonance, cantilever Q‐value enhancement by operating in a vacuum, and direct cantilever resonance frequency detection using the frequency modulation technique. It was demonstrated that the surface potential of the pn junctions made by thermal diffusion varies gradually compared to those made by ion implantation, possibly reflecting their gradual dopant concentration profile.

An ultra small individual recognition security chip

The manufacturing and distribution of goods requires good quality and inventory control. The RFID (radiofrequency identification) enabled microchips small size and low cost make it suitable for attachment to paper media and small products, aiding counterfeit prevention and product tracking in market environments.

Vacuum compatible high‐sensitive Kelvin probe force microscopy

A vacuum compatible Kelvin probe force microscopy (KPFM) is presented. Difficulties in operating KPFM in a vacuum were overcome by utilizing the direct cantilever resonance frequency detection in the tip height control whereas the indirect resonance frequency detection scheme was used in primordial KPFM. The potential measurement sensitivity was improved by 14 dB compared to that in air. It is due to the increased cantilever Q value and the reduction in the interference from the tip height detection signal because potential measurement is conducted using the cantilever’s second resonance while tip height control was conducted using the first resonance. A silicon wafer whose surface is partially doped with arsenic by ion implantation was observed, and surface potential difference at the junctions were clearly imaged.

Powder LSI: an ultra small RF identification chip for individual recognition applications

A powder-like 0.09 mm/sup 2/ 2.45 GHz RF identification chip for wireless recognition applications is described. This chip is fabricated in a 0.18 /spl mu/m CMOS process, and its thickness is 60 /spl mu/m. A two-surface connection technique is adopted to facilitate antenna attachment. The distance between the chip and a reader is 300 mm for a reader power of 300 mW.

Magnetic and electrical properties of single‐phase, single‐crystal Fe16N2 films epitaxially grown by molecular beam epitaxy (invited)

The average magnetic moment per Fe atom for a single‐phase, single‐crystal Fe16N2(001) film epitaxially grown on a GaAs(001) substrate by molecular beam epitaxy has been confirmed to be 3.5μB at room temperature by using a vibrating sample magnetometer (VSM) and Rutherford backscattering. The value was in good agreement with that obtained by using a VSM and by measuring the film thickness (3.3μB per Fe atom). The saturation magnetization 4πMs has been found to increase with decreasing temperature, obeying T3/2 law at lower temperatures. The slope was steeper than that of a pure Fe film, suggesting a lower exchange constant for Fe16N2. The g factor for Fe16N2 has been accurately measured to be 2.17 by using ferromagnetic resonance with changing frequencies of 35.5–115 GHz, which is not unusual compared with the g factor of 2.16 for pure Fe. The resistivity for Fe16N2 has been measured to be around 30 μΩ cm at room temperature compared with 10 μΩ cm for pure Fe and decreases linearly with decreasing tempera...

FIELD EVAPORATION OF GOLD ATOMS ONTO A SILICON DIOXIDE FILM BY USING AN ATOMIC FORCE MICROSCOPE

To investigate whether field evaporation of gold atoms is responsible for dot formation in an atomic force microscope (AFM) gold‐coated tip/vacuum/SiO2 film/p‐type Si substrate configuration, we have performed elemental analysis of the dots and measured the dependence of the threshold voltage on SiO2 thickness with both polarities for the dot formation. The experiments demonstrate that it is feasible to form gold dots on SiO2 films 17–107 A thick by adjusting the pulsed voltages applied to the gold‐coated AFM tip. Energy dispersive x‐ray spectroscopy (EDX) shows that the dots include gold. The threshold voltages increase almost linearly with the SiO2 thickness. Furthermore, the voltage with negative polarity is lower than that with positive polarity. These results provide evidence that the dot formation on the SiO2 film using AFM occurs by field evaporation.

Stoichiometry measurement and electric characteristics of thin‐film Ta2O5 insulator for ultra‐large‐scale integration

Elastic recoil detection and Rutherford backscattering were adapted to a stoichiometric study of thin Ta2O5 films deposited on Si substrates by means of the reactive sputtering (SP) and chemical‐vapor‐deposition (CVD) method. Before annealing the samples it was observed that (i) the atomic ratio of oxygen to tantalum in the SP films agreed with 5/2 within the experimental accuracy and (ii) the CVD films have less oxygen content than the other samples. The specimens were annealed for 30 min under the following three conditions: (a) in dry oxygen ambient at 800 °C; (b) in ozone atmosphere under ultraviolet irradiation (UV ozone) at 300 °C; and (c) two‐step treatment of (a) after the (b) process. Each oxidizing process has shown a certain positive effect on the thin CVD samples. Among them, the two‐step treatment has proven to be very effective to restore the stoichiometry of 5/2 in the CVD films. Additionally the thickness of contaminant carbon films on the surface of the samples has been reduced by anneali...

Ion-implanted and permalloy hybrid magnetic bubble memory devices

Hybrid bubble memory devices have been proposed and operated with the memory density of 4 Mbit/cm2. In the hybrid bubble memory devices, minor loops are composed of ion-implanted tracks with 4-µm period, and major lines and functional parts including block-replicate and swap gates are composed of Permalloy tracks with a longer period of 12 µm. Passive junctions between ion-implanted and Permalloy tracks have been developed, introducing the tapered ion-implantation technique. Improving the characteristics of the functional parts composed of Permalloy tracks, the hybrid bubble memory devices with block-replicate and swap gates have been operated, and the feasibility of the devices has been confirmed. In addition, the possibility of higher memory density has been shown.

Method of making magnetic bubble memory device by implanting hydrogen ions and annealing

A method of implanting a magnetic garnet film with ions is disclosed in which a covering film is provided on a monocrystalline magnetic garnet film for magnetic bubbles, and hydrogen ions are implanted in a desired portion of a surface region in the magnetic garnet film through the covering film. According to this method, it is possible to form an ion-implanted layer in which the ion concentration distribution in the direction of depth is uniform, and moreover the inplane anisotropy field in the ion-implanted layer decreases only a little with time in an annealing process.

Nanoscale modification of phase change materials with near-field light

Scanning near-field optical microscope (SNOM) was applied to the formation of ultrasmall phase change domains to investigate the feasibility of ultrahigh density data storage. Phase change domains ranging 60 – 100 nm in diameter, which is far beyond the diffraction limit, could be successfully written in amorphous GeSbTe recording film by point heating with pulsed laser light (λ=785 nm, 7 mW, 0.5 ms) through the optical fiber probe whose aperture size was nearly 50 – 100 nm. The detected power in observation of these recorded domains is 102 – 103 times as high as that in magneto-optical observation. It indicates that phase change recording with SNOM has a potential to achieve ultrahigh density data storage (more than 100 Gb/in2) with high signal detection efficiency.