Yuji Kasai

A post-silicon clock timing adjustment using genetic algorithms

A post-silicon clock timing adjustment architecture utilizing genetic algorithms (GA) is proposed, which has three advantages: (1) enhanced clock frequency leading to improved operating yields, (2) lower power supply voltages while maintaining operating yield, and (3) reductions in design times. Experiments with two different developed LSI chips and a design experiment demonstrated these advantages with a clock frequency enhancement of 25% (max), a power supply voltage reduction of 33%, and 21% shorter design times.

Self-limiting process for the bismuth content in molecular beam epitaxial growth of Bi2Sr2CuOy thin films

A new technology utilizing a self-limiting mechanism for the Bi content is demonstrated for Bi2Sr2CuOy (2201) thin film growth by an atomic layer controlled molecular beam epitaxy. This technology is based on peculiar behavior of the Bi sticking coefficient that depends on the kinds of oxide thin films to be grown. When Bi atoms are supplied in excess with ozone molecular beam, only Bi atoms, being necessary for forming the structural unit (2201 half unit cell), are just incorporated in the film. Surplus Bi is reevaporated from the surface. Using this technique, high quality 2201 thin films are obtained with good reproducibility.

An AI-calibrated IF filter: a yield enhancement method with area and power dissipation reductions

We have developed a large-scale integration (LSI) for Gm-C intermediate frequency (IF) filters, attaining a 63% reduction in filter area, a 26% reduction in power dissipation, compared with existing commercial products using the same process technology and filter topology, and a yield rate of 97%. The developed chip is calibrated within a few seconds by a genetic algorithm - an efficient AI technique for difficult optimization problems. Our calibration method, which can be applied to a wide variety of analog circuits, leads to cost reductions and the efficient implementation of analog LSIs.

Power dissipation reductions with genetic algorithms

Two cases of power dissipation reduction with post-fabrication adjustment using genetic algorithms is introduced in this paper. The first is a 1GHz ALU implementation, where power consumption has been reduced by 54% through clock-timing adjustment. The second case is the IF (intermediate frequency) filter analog LSI used in cellular phones, where the reduction in power dissipation is realized by circuit parameter adjustment. The IF filter has been widely used in commercial cellular phones since 2001.

Atomic absorption spectroscopy system for flux monitoring and atomic-layer control of molecular beam epitaxial growth of BiSrCaCuO

Atomic absorption spectroscopy (AAS) system for accurate and in situ atomic-flux-monitoring during molecular beam epitaxial growth is reported in detail. Hollow cathode lamps are used as light sources. They emit the light with inherent spectral lines of the elements to be measured. A turret system with multiple hollow cathode lamps and line pass filters is equipped, which is suited in particular for atomic layer-by-layer growth. The intensities of the transmitted light on both conditions in the presence and absence of atomic beam flux are measured. An analytic expression for in situ calculating the beam flux rate using these measured quantities is discussed. A method for determining an unknown constant included in this expression is described. This uses the inductively coupled plasma spectroscopy technique to estimate the amount of atoms impinging on the substrate. Within the range of BiSrCaCuO growth conditions, the AAS measurements are not influenced by changing either the substrate temperature or the c...

Molecular Beam Epitaxy Fabrication of SrTiO3 and Bi2Sr2CaCu2O8 Heterostructures Using a Novel Reflection High-Energy Electron Diffraction Monitoring Technique

SrTiO3 and Bi2Sr2CaCu2O8 layered structures were continuously grown by the molecular beam epitaxy technique with in situ reflection high-energy electron diffraction (RHEED). By using a new RHEED picture subtraction technique, we could display intensity changes due to only the topmost layer. This method allows us to sensitively detect roughness on the atomic scale and excess phase formation. The SrTiO3 layer could be grown by sequential shuttering as well as coevaporation. A heterostructure with a 60 A Bi2Sr2CaCu2O8 film had a superconducting transition temperature of 53 K.

Initial Evaluation of an Evolvable Microwave Circuit

Microwave circuits are indispensable for mobile and multi-media communication. However, these circuits are very difficult to design, because of the nature of distributed-constant circuits in the microwave range (i.e., over 1 GHz). These circuits are also difficult to adjust for optimum performance, even for experienced engineers. These related problems make development costs of microwave circuits very high. In order to overcome these problems, we propose an EHW-based microwave circuit where performance adjustment is carried out automatically by a GA. This new approach of integrating a performance adjustment function within the circuit eliminates many of the design problems with associated these circuits. In this paper, we present an EHW-based image-rejection mixer circuit, which we have developed with this approach, and experimental data that demonstrates that the automatically adjusting circuit is capable of outperforming a circuit adjusted by an experienced engineer.

In-situ growth of Bi-Sr-Ca-Cu oxide superconducting thin films by molecular beam epitaxy with a pure ozone source

Abstract Bi-Sr-Ca-Cu-O superconducting thin films have been grown in situ by molecular beam epitaxy using a new type pure ozone source. The films were deposited layer by layer under low pressure conditions of about 10 -4 Pa. We obtained films with the single phases of both Bi 2 Sr 2 CaCu 2 O x and Bi 2 Sr 2 Ca 2 Cu 3 O x by changing the shuttering sequences. In situ observation of the reflection high-energy electron diffraction showed clear streak patterns during the growth of Bi 2 Sr 2 CaCu 2 O x films on MgO(100) and LaAlO 3 (100) substrates, indicating epitaxial growth.

Molecular beam epitaxial growth of SrO and CaO with RHEED intensity oscillation

SrO and CaO, related compounds of BSCCO superconductor, are grown onto SrTiO3(100) substrates with molecular beam epitaxy(MBE) technique. During growth, the specular spots of RHEED patterns show intensity oscillations, indicating two dimensional growth. The periods of oscillations are utilized to calculate the atom fluxes. It is shown that sublimation processes of both Sr and Ca metals in the effusion cells are stable under the growth condition of oxide films. The periods of oscillations during the SrO growth are independent of substrate temperature, confirming that Sr atoms are oxidized immediately and stay on the substrate surface without re-evaporation. These informations are practically available for precise control of the atomic layer controlled MBE of BSCCO superconductor thin films.

A very low-cost low-frequency PLC system based on DS-CDMA for DC power lines

We propose a very low-cost low-frequency PLC (LF-PLC) system for DC power lines. The proposed LF-PLC system has three features: baseband transmission, unidirectional connection from a slave unit to a master unit, and multiplexing with Direct Spread Code Division Multiple Access (DS-CDMA). These features make it possible to implement multiplex communication with high tolerance for noise using very low-cost slave units. The effectiveness of the proposed method is demonstrated with a prototype system for monitoring separate thirty photovoltaic (PV) panels with the DC line within the PV system. The estimated mass-production cost of one transmitter is about 2 US Dollars. Thus, it is possible to dramatically reduce the maintenance costs because faulty panels can be detected quickly.