Kozo Sakamoto

X-ray computerized tomography using monochromated synchrotron radiation

An X-ray computerized tomographic (CT) imaging system using monochromated synchrotron radiation has been constructed and its performance has been evaluated. Spatial resolution is about 125 µm. Several CT images have been taken. Element mapping in a test sample has also been obtained using the difference between two CT images at different X-ray energies just above and below the absorption edge of the element.

Improvement of Spatial Resolution of Monochromatic X-ray CT Using Synchrotron Radiation

X-ray computed tomography using synchrotron radiation (SR) as X-ray source potentially provides CT images of improved quality, since SR produces tunable, monochromatized and collimated X-ray beams of high flux density. We can obtain CT images of small samples rapidly with better spatial resolution and contrast; we can also obtain the spatial distribution of a specific element using the absorption edge. In this paper, a method for improving the spatial resolution of such a system is presented, involving the magnification of projection images using asymmetric diffraction. First, the modulation transfer function (MTF) of projection images of an X-ray test chart is measured in order to evaluate the spatial resolution. Next, using this method, we show CT images of several industrial materials with spatial resolution of 15~30 µm and demonstrate the usefulness of SR-CT with a high spatial resolution.

Low on-resistance and low feedback-charge, lateral power MOSFETs with multi-drain regions for high-efficient DC/DC converters

Low on-resistance and low feedback-charge lateral power MOSFETs have been developed. This is achieved by using a new lateral power MOSFET structure with multi-drain regions. The high-efficiency factor R/sub on//spl middot/Q/sub gd/ of the proposed power MOSFETs is improved to less than half that of conventional trench gate power MOSFETs with tens of m/spl Omega/ of specific on-state resistance, R/sub on/. These new power MOSFETs are useful to improve the power convergent efficiency of DC/DC converters. With these lateral power MOSFETs it is also possible to integrate a CMOS pre-driver in the same chip in order to reduce parasitic gate impedance between the gate of the power MOSFET and the output of CMOS pre-drivers and to achieve high-frequency drive properly.

An intelligent power IC with reverse battery protection for fast-switching high-side solenoid drive

A highly reliable and fast-switching intelligent power IC (IPIC) for a high-side solenoid drive is described. There are two main features in this IPIC. The first feature is a built-in reverse battery protection method that can be used in both 12-V battery systems and 24-V battery systems in large vehicles. This protection is accomplished by using a high-voltage MOSFET to suppress a forward current of a parasitic diode in the reverse battery condition. The other notable feature is a device isolation structure and driving method using two sets of pull-down circuits to reduce the turn-off time for the inductive load current. The turn-off time for the inductive load is reduced to two-thirds that of a conventional IPIC. This is achieved by increasing the absolute value of the sustained negative output voltage from -18 to -34 V. This IPIC also has over-current protection, over-heating protection, over-voltage protection, and a self-diagnostic function as well as the conventional IPIC function. It is useful for high-side solenoid drivers frequently used in automotive electronics.

A 30-V, 75-m/spl Omega/*mm/sup 2/ power MOSFET for intelligent driver LSIs

An extremely low on-resistance Lateral DSA MOSFET(LDM0S) is developed for intelligent driver LSIs. This device has an improved meshed gate structure with double-layer A1 electrodes. Drain offset layer doping is introduced to decrease drain series resistance, and an A1 field plate is formed by the first A1 layer to reduce electric field at the substrate surface. A 30-V breakdown voltage and a 75-m!2=mm2 onresistance are obtained in the device fabricated by a 1.5pm BiCMOS process. The on-resistance is reduced 20% compared with conventional devices. An H-bridge driver is designed using those devices, and a very lowpower dissipation is achieved.

A three-terminal intelligent power MOSFET with built-in reverse battery protection for automotive applications

An intelligent power MOSFET with built-in reverse battery protection, which is important for automotive power switches, has been developed. The protection is accomplished by integrating an additional power MOSFET in series with a power MOSFET and the control circuit of the additional power MOSFET. The reverse battery protection is achieved without using external control signals. The positive drain breakdown voltage for the proposed MOSFET is 71 V and the negative drain current at a drain voltage of -16 V is only -750 /spl mu/A. The on-state resistance is 170 m/spl Omega/. This new intelligent power MOSFET can replace the conventional three-terminal power MOSFETs used in automotive applications.

A fast-switching intelligent power MOSFET with thermal protection and negative gate protection

Recently, thermal protection circuits have been added to power MOSFETs to improve their reliability. However, integrating a protection circuit into a power MOSFET causes parasitic bipolar transistors to form. These parasitic bipolar transistors cause a leakage that passes from the drain terminal to the gate terminal when a negative gate voltage is applied against a source voltage. Therefore, these MOSFETs cannot be used in a high-side switch circuit without some form of negative gate protection. To solve this problem, we proposed an intelligent power MOSFET with built-in thermal protection and negative gate protection, which we called the thermal FET. However, the switching speed of this MOSFET is fairly slow because it includes a gate resistor of about 5 to 10 k/spl Omega/ in its thermal shutdown circuit. Here, we describe a fast-switching intelligent power MOSFET whose switching speed is about two orders of magnitude faster than our previous thermal FET. This was achieved by replacing the gate resistor with a MOSFET. We also developed a new form of negative gate protection for the additional MOSFET. We call this highly reliable fast-switching intelligent power MOSFET an FS-Thermal FET. The FS-Thermal FET can be used in the upper arms of H-bridge circuits and high-side switch circuits, as well as in low-side switch circuits, with this new form of negative gate protection.

An intelligent power MOSFET with reverse battery protection for automotive applications

An intelligent power MOSFET with built-in reverse battery protection, which is essential for automotive power switches, has been developed. The reverse battery protection is achieved without using external control signals. This new power MOSFET can replace the conventional three-terminal power MOSFETs used in automotive applications. Its positive drain breakdown voltage is 71 V and the negative drain current at a drain voltage of -16 V is only -750 /spl mu/A. On resistance is 170 m/spl Omega/. Using the latest fabrication process now available for commercial products, the on-resistance can be reduced to less than 50 m /spl Omega/ in a TO-220 package.

An intelligent power IC with reverse battery protection for high-side solenoid drivers

A highly reliable and fast switching intelligent power IC (IPIC) for high-side switches that uses a junction isolation structure is described. This IPIC provides built-in reverse battery protection, which is essential for automotive power switches, not only in usual 12-V battery systems but also in the 24-V battery systems used in large vehicles. This protection is accomplished by integrating a high voltage MOSFET to avoid parasitic diode action. The other notable feature of this IPIC is that the turn-off time for the inductive load is reduced to two-thirds that of a conventional IPIC. This is achieved by increasing the absolute value of the sustained negative output voltage from -18 V to -34 V. This new IPIC is useful for high-side solenoid drivers frequently used in automotive electronics.

Power MOSFET with hold-type thermal shutdown function

A new intelligent discrete power MOSFET with hold-type thermal shutdown function is developed. This is achieved for the fist time by cost-effective monolithic technology. A critical temperature for turning off the MOSFET is about 155 OC with Vg=4 V. This device maintains the shutdown state until the gate terminal is reset. This hold function is obtained by using a new latch circuit with polysilicon resistance loads whose values are asymmetrical.