Yoshikata Nakajima

In-depth profiling of electron trap states in silicon-on-insulator layers and local mechanical stress near the silicon-on-insulator/buried oxide interface in separation-by-implanted-oxygen wafers

In-depth profiling of electron trap states in silicon-on-insulator (SOI) layers of separation-by-implanted-oxygen (SIMOX) wafers was carried out using the drain current-gate voltage characteristics of metal-oxide-semiconductor field-effect transistors (MOSFETs) with different SOI thicknesses, and the density of electron trap states in a gate oxide (GOX) layer thermally grown on them was measured using the gate tunneling current-gate voltage characteristics of MOSFETs. It was found that in-depth profiles of electron trap states in SOI layers have a broad peak at around 25 nm from the SOI/buried oxide (BOX) interface, and that the density of electron trap states in a GOX layer grown on the 25-nm-thick SOI layer reaches a maximum there. A morphology study using Auger electron spectroscopy and Raman spectroscopic study revealed a correlation among the density of trap states in an SOI layer, roughness, and local mechanical stress near the SOI/BOX interface. This correlation is understood to imply that local me...

Capture of nonmagnetic particles and living cells using a microelectromagnetic system

We develop a microelectromagnetic system to trap nonmagnetic materials such as micropolystyrene particles and yeast cells in particular areas. We fabricate gold films, the width of the central narrow part is 22 μm, and flow an electric current through the films. We then apply an external uniform dc magnetic field to weaken the local magnetic field at the narrow part so that a nonuniform magnetic field is produced. We demonstrate that the particles, which are dispersed in magnetic fluid, are successfully trapped at the narrow part of the film. We evaluate the driving force acting on a microparticle in the nonuniform magnetic field and carry out a Stokesian dynamics simulation of the motion of the particles. We show that yeast cells are also trapped at the narrow part of the film. Finally, we fabricate multichannel microelectromagnets so that yeast cells are trapped at multiple points in the microelectromagnetic system. The present system may be applied to cell transfection on a cell microarray and, therefo...

Correlation between high-density trap states and local stress near SOI/BOX interface in SIMOX wafers

Separation by implanted oxygen (SIMOX) wafers and bonded wafers are commercially available silicon-on-insulator (SOI) wafers. In particular, SIMOX process technologies have become important in system-on-a-chip (SoC) fabricated on SOI/Bulk hybrid substrates composed of SOI region for the logic circuits and Bulk region for the dynamic random access memories (DRAMs) in recent years [1].

Fabrication and characterization of sub-micron scale hall devices from 2-dimensional electron gas at the heterostrutcure of GaAs/AlGaAs

In this work, we report the fabrication and transport properties of sub-micron Hall devices to be used for nanomagnetic studies. Hall bars were fabricated using electron-beam lithography followed by wet etching of GaAs/AlGaAs heterostructures containing two-dimensional electron gas (2-DEG). Metallization using multiple metallic layers were used to achieve ohmic contacts with the 2-DEG which is about 240 nm below the surface. Detailed characterization of the metallic layers using X-ray Photoelectron Spectroscopy (XPS) demonstrate the role of alloy formation and diffusion to form ohmic contacts with the 2-DEG. Electronic transport measurements show the metallic character of the 2-DEG. Hall effect and magnetoresistance were measured to estimate the carrier mobility of 4.2×104 cm2/V-s at 5 K in dark.

Electrophoretic mobility and resultant zeta potential of an individual cell analyzed by electrophoretic coulter method

Electrophoretic mobility measurement by the electrophoresis method is one of the simplest methods for analyzing surface properties of particles and cells [1]. In order to estimate the electrophoretic mobility; moving image analysis or optical signal analysis has been intensively developed. However, electrical signals are much more favorable for system integration, using techniques well-established in semiconductor fields. We previously presented a new methodology by incorporating the Coulter method [2] into electrophoretic mobility measurement using micro-fluidic devices. This methodology named electrophoretic Coulter method enables us to characterize the size, number, and electrophoretic mobility of particles simultaneously using electrical signals [3]. In this study, we validated our system with sheeps red blood cells as a first step to application to bio-related particles

Ultraviolet Irradiation Effects on and Depth Profiles in X-ray Photoelectron Spectra of Poly(vinylpyridine) Thin Films

The N 1s core binding energies of spin-coated poly(vinylpyridine) (PVPy), quaternized PVPy, and UV-irradiated PVPy were determined using X-ray photoelectron spectroscopy, and the depth profiles were determined using Ar+ beam etching. In typical N 1s spectra, cationic nitrogen atoms appeared at a binding energy 2–3 eV higher than that of neutral pyridine (Py). Changes in alkylpyridiniums in N 1s and bromide in Br 3p were determined according to etching cycles. In our PVPy cases, two types of nitrogen appeared at a region of high energy compared with that of neutral Py, and the differences in the binding energies between those states and neutral Py were all less than 2 eV. These nitrogens can be assigned to hydrogen-bonded Py and a complex formed among Py rings. Neutral Py, the complex Py, and hydrogen-bonded Py are very close together, and they were located at 399.0, 399.7, and 400.6 eV, respectively. Traces of ionic species were observed only in IR spectra.