Tetsuo Tabei

An Infrared Silicon Optical Modulator of Metal–Oxide–Semiconductor Capacitor Based on Accumulation-Carrier Absorption

A silicon optical modulator of a metal–oxide–semiconductor (MOS) capacitor based on free-carrier absorption has been proposed and successfully developed. In this report, its modulation performance with accumulation-mode absorption instead of inversion-mode absorption is described expecting better absorption performance due to the relatively smaller carrier mobility of holes. The device consists of an 8-mm-long and 1.5-µm-thick (110) silicon-on-insulator core and a surrounding clad of 1.5-µm-thick buried oxide underneath and doped polycrystalline silicon on top. Infrared light absorption by accumulation carriers is not sufficiently strong in the 1.55-µm-infrared-wavelength regime. However, an optical response of 13% at a gate voltage of -30 V is obtained. Preliminary analysis has also been conducted for the potential of the optical modulator based on accumulation-carrier absorption. It is predicted that this modulator will be more effective in deeper-infrared regions unlike other modulators such as the Mach–Zehnder interferometer.

Fabrication of Si Nanowire Field-Effect Transistor for Highly Sensitive, Label-Free Biosensing

We fabricated a biosensor based on a silicon nanowire field-effect transistor (SiNW FET) with a Si3N4 gate insulator for highly sensitive detection of target biomolecules. The fabricated SiNW FET acted as an ion-sensitive FET that could detect the charge density in solutions flowing along the gate surface by responding to the pH of the solutions. The SiNW FET also detected charged protein molecules in solution, suggesting that our device can be used in highly sensitive, label-free biosensing.

Proposal of a Metal–Oxide–Semiconductor Silicon Optical Modulator Based on Inversion-Carrier Absorption

A novel silicon optical modulator, originally based on inversion-carrier absorption, with a metal–oxide–semiconductor capacitor structure has been proposed and successfully developed. In this report, we will describe experimental results for a modulator that is fabricated on a silicon-on-insulator (SOI) substrate. The device consists of a 2- to 5-mm-long and 1.5-µm-thick (110) SOI core and a surrounding clad of 1.0-µm-thick buried oxide underneath and doped polysilicon on top. Infrared light absorption by inversion carriers is not large enough in the 1.55 µm wavelength regime. However, an optical response of 0.24% at a gate voltage of 11.5 V is obtained. Preliminary analysis has been also conducted for the potentiality of the optical modulator based on inversion-carrier absorption. It is predicted that this modulator will be more effective in deeper infrared regions unlike other modulators such as the Mach–Zehnder interferometer.

Potentiality of Silicon Optical Modulator Based on Free-Carrier Absorption

Light propagation in metal-oxide-semiconductor (MOS) optical modulator based on free-carrier absorption is analyzed theoretically and compared with experimental results. The coincidence is sufficient enough to confirm validity of the simulation. However, practical use of the modulator is limited since extinction ratio is still small due to weak interaction between light and inversion carrier at around 1.55 mum light.

Fabrication of High-Density Diamond Nanotips by Electron Beam Lithography

For application to fabricating of diamond field emitters, nanosize hard masks for forming high-density diamond nanotips were produced on polycrystalline diamond wafers by electron beam lithography. Fabricated hard masks are of two kinds: one is a TiN–Al stack mask, which forms a uniquely shaped diamond tip after etching because of the difference in etching characteristics between TiN and Al, and the other is an amorphous Si mask, which replaces the conventional Al mask in order to form much smaller diamond tips. These hard masks were arrayed on a diamond wafer at a pitch of 200 or 300 nm. The diameters of a TiN–Al stack mask and of an amorphous Si mask are 100–110 nm and 70–80 nm, respectively. The density of diamond nanotips fabricated using hard masks is 25 pieces per µm2 (200 nm pitch), and the dispersion in diamond tip height is 5% or less.

Potentiality of Metal–Oxide–Semiconductor Silicon Optical Modulator Based on Free Carrier Absorption

Light propagation in a metal–oxide–semiconductor optical modulator based on free carrier absorption is analyzed theoretically. The analysis is based on Marcatilis approximation taking account of absorption by free carriers in the inversion layer. The gate voltage and wavelength dependences of propagation loss and extinction ratio are also evaluated. The free carrier absorption in the proposed modulator is appropriately confirmed by comparing theoretical results with the experimental results of fabricated optical modulators on silicon-on-insulator wafers; however, practical use of the device is limited since the extinction ratio remains small owing to a weak interaction between light and inversion carriers at 1.55-µm-wavelength light. By theoretical analyses, a large extinction ratio is obtained for possible applications in the deeper infrared regime because free carrier absorption increases with wavelength. A much larger extinction ratio is expected when the interaction between guided waves and surface plasmons occurs.

Evaluation of Front-Opening Unified Pod with Attached UV/Photocatalyst Cleaning Unit

We have developed a wafer box for 300 mm Si wafers with an attached cleaning system for organic contamination gas. The front-opening unified pod (FOUP) is modified to be attached to the UV/photocatalyst cleaning unit. It is found that the reliability degradation of metal oxide semiconductor (MOS) capacitors fabricated using wafers stored in the FOUP with the cleaning unit is suppressed compared with that of MOS capacitors fabricated using wafers stored in the FOUP without the cleaning unit.

Influence of surface smoothing on spin Seebeck effect of Ce1Y2Fe5O12 deposited by metal organic decomposition

Thus far, Bi1Y2Fe5O12 (Bi:YIG) films deposited by metal organic decomposition (MOD) are mainly used for magnetic insulation film of spin Seebeck devices. In order to increase the power conversion efficiency of these devices, we focused on Ce1Y2Fe5O12 (Ce:YIG), which has a larger Faraday rotation than Bi:YIG. Since there has been no report, except for the patent document, concerning the deposition of Ce:YIG films by MOD, we investigated the appropriate annealing temperatures, and we found that Ce:YIG films are crystallized when the annealing temperature is over 800 °C. However, since no electromotive force has been observed, we checked the surface roughness of Ce:YIG films by atomic force microscopy (AFM). Since their surfaces of Ce:YIG films were very rough, it was mechanically polished (MP). Then, an electromotive force of, at most, 11.3 µV was generated. This is the first report concerning the spin Seebeck effect of Ce:YIG deposited by MOD.

Proposal of a Silicon Optical Modulator Based on Inversion-Carrier Absorption

To overcome increased propagation delay of metal wiring in advanced sub-micron LSIs, on-chip optical interconnect has long been proposed these more than ten years. To meet the requirement, optical switches have to be integrated on silicon chip. Some candidate of Mach-Zehnder-type MOS transistor optical switch based on refractive index variation was proposed [1]. Prior to that work, the authors had proposed a silicon optical switch [2] based on free-carrier absorption. This report will describe successful results for the proposed device of which fundamental structure is shown in Fig. 1. Obtained performance of optical response of less than 1 % at this moment may not be large enough for practical use, free-carrier absorption mechanism should be made good use of.

Fullerene-Containing Electrically Conducting Electron Beam Resist for Ultrahigh Integration of Nanometer Lateral-Scale Organic Electronic Devices

An outstanding issue with organic devices is the difficulty of simultaneously controlling the lateral size and position of structures at submicron or nanometer scales. In this study, nanocomposite electron beam (EB) organic resists are proved to be excellent candidates for electrically conductive and/or memory component materials for submicron or nanometer lateral-scale organic electronic devices. The memory and the resist patterning characteristics are investigated for a positive electron beam resist of ZEP520a containing [6,6]-phenyl-C61 butyric acid methyl ester (PCBM). Regarding the memory characteristics, good programming and excellent retention characteristics are obtained for electrons. The carrier transfer and retention mechanisms are also investigated. Regarding the resist patterning characteristics, it is found that line patterns (square patterns) of ZEP520a containing PCBM can be made with widths (side lengths) of less than 200 nm by using an extremely simple process with only EB exposures and developments. The distribution of PCBM molecules or their aggregations is also clarified in ZEP520a containing PCBM. The results of this study open the door to the simple fabrication of highly integrated flexible memories and electrical wires as well as of single-electron or quantum devices, including quantum information devices and sensitive biosensors for multiplexed and simultaneous diagnoses.