Toshiaki Yachi

Experimental investigation of dependence of electrical characteristics on device parameters in trench MOS barrier Schottky diodes

Measurements of forward and reverse electrical characteristics of trench MOS barrier Schottky diodes with various device parameters reveal that the resistivity and width of the mesa region are the main parameters which affect device characteristics. An on/off current ratio of two orders is obtained.

Conduction power loss in MOSFET synchronous rectifier with parallel-connected Schottky barrier diode

The conduction power loss in an MOSFET synchronous rectifier with a parallel-connected Schottky barrier diode (SBD) was investigated. It was found that the parasitic inductance between the MOSFET and SBD has a large effect on the conduction power loss. This parasitic inductance creates a current that is shared by the two devices for a certain period and increases the conduction power loss. If conventional devices are used for under 1 MHz switching, the advantage of the low on-resistance MOSFET will almost be lost. To reduce the conduction loss for 10 MHz switching, the parasitic inductance must be a subnanohenley.

A compact buck-converter using a thin-film inductor

We have developed a compact buck-converter using a thin-film inductor that is suitable for portable electronic equipment. The inductor consists of planar Cu coils and CoZrTa magnetic layers on a Si substrate; it is fabricated by a dry process. The converter is 3 mm thick and 10/spl times/6 mm in area; it operates at 1.6 MHz and has an efficiency of up to 85%.

Analytical approach to breakdown voltages in thin-film SOI power MOSFETs

Abstract The breakdown voltage behavior of thin-film SOI power MOSFETs is described using an analytical approach. Simple expressions for the vertical and horizontal characteristics of the device are developed one-dimensionally to analytically predict the critical impurity concentration of the drift region and the breakdown voltages. Using this modeling, the effect of device parameters is also examined. The validity of the analytical expressions is demonstrated by comparison with the extensive results of numerical simulations.

Device characteristics of a 30-V-class thin-film SOI power MOSFET

A 30-V thin-film SOI power MOSFET having a tungsten polycide gate with a linear gate topology has been fabricated at a practical device level. Its electrical characteristics were successfully demonstrated for the first time. The experimental device has 1010 unit cells and a total gate width of 4.04 cm, It has a specific on-resistance of 92 m/spl Omega//spl middot/mm/sup 2/ and breakdown voltage of 33 V. The devices various parasitic capacitance characteristics were measured and compared with those of a lateral power MOSFET fabricated on a bulk-silicon substrate.

A novel high-frequency quasi-SOI power MOSFET for multi-gigahertz applications

We have fabricated a high-efficiency quasi-SOI power MOSFET for multi-gigahertz applications. The device was formed by reversed silicon wafer direct bonding which enables easy use of a high-resistivity substrate. The breakdown voltage of the quasi-SOI power MOSFET is more than twice that of a conventional SOI power MOSFET. Fmax of the quasi-SOI power MOSFET is 11.0 GHz, about 15% higher than that of the SOI power MOSFET. The fabricated device has the excellent power added efficiency of 68% at a 2 GHz under 3.6 V operation.

New power device figure of merit for high-frequency applications

A new power device figure of merit is proposed for high-frequency applications. Based on a theoretical analysis, the impacts of circuit topologies and material properties are examined. This figure of merit is very useful in optimizing or choosing a power device operating in high-frequency circuits. A thin-film SOI power MOSFET is taken as an example, and the effect of its device parameters on the power loss is analyzed to provide a basic guideline for optimization.

An LED Module Array System Designed for Streetlight Use

IEEE abstract currently, most outdoor illumination sources use high intensity discharge (HID) lamps as light sources. Global concerns have been raised regarding the amount of power consumed by HID lamps, and by extension, the amount of atmospheric CO2 released due to such power consumption. Because of this, light emitting diod (LED) array illumination has received attention recently as an energy-reducing light source. Because the illumination produced by an LED is relatively weak, LED light fixtures differ in several ways from traditional light sources, and it is necessary to incorporate numerous LEDs into a module array in order to use them for road illumination. Concerns exist that the failure rate of LED module arrays will increase with the use of large number of LEDs. In this paper, we calculate changes to array reliability over set periods of time, and propose a module array design composition that was found to offer high-reliability.

A new stand-alone hybrid power system with wind generator and photovoltaic modules for a radio base station

This work proposes a new stand-alone hybrid power system with a wind turbine generator and photovoltaic modules for a radio base station. We studied the system characteristics by simulation on Yonaguni Island, where the wind speed is over 4.0 m/s throughout the year, and the average annual wind speed is about 7.0 m/s. It was found that the base station equipment needs a wind generator output power of 8 kW, a photovoltaic output power of 7.4 kW and 177 kWh storage batteries for a system operation rate of 100%.

Switching Characteristics of a Thin Film SOI Power MOSFET.

This paper describes switching characteristics of a thin-film silicon-on-insulator (SOI) power metal-oxide-semiconductor field-effect transistors (MOSFETs) based on the results of numerically simulating thin-film SOI power MOSFETs in the 50-V class. The dependence of the rise time and fall time on the doping concentration of the substrate, on the doping type of the substrate, and on the thickness of the buried oxide layer are studied. In addition, the optimum device structure of the thin-film SOI power MOSFET for high-frequency switching application is also described.