Electron‐beam‐pumped light sources using graphite nanoneedle field emitters and Si electron‐transparent films

Sputter‐induced carbon nanoneedle field emitters and Si electron‐transparent films have been developed for electron‐beam‐pumped light sources. The sputter‐induced carbon nanoneedle field emitters exhibited a stable electron emission of 0.1 mA at an average field of 13 V/µm. The 1.5‐µm thick Si electron‐transparent films achieved an electron transmittance of about 60% at an acceleration voltage of 27 kV. An electron‐beam‐pumped light source was demonstrated from the excitation of N₂ gas, and a N₂ gas spectrum was clearly observed. The increase of the beam current is important for increasing the light intensity. Copyright © 2007 Institute of Electrical Engineers of Japan© 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Materials,effects and components for tunable micro‐optics

An overview of recent activities in the area of tunable micro‐optical components is given. These include polymer‐based deformable mirrors for adaptive optics, tunable microlenses and arrays using fluids and membranes, pneumatically actuated scanning micromirrors and tunable Bragg filters and mirrors using swelling polymers. For each device, the structure, essential fabrication technology and optical characteristics, as well as a discussion of application areas are presented. Copyright © 2007 Institute of Electrical Engineers of Japan© 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Cell adhesion characteristics of chemically modified silicon nitride surfaces

We investigated the fundamental characteristics of cell adhesion during cell culture on the Si₃N₄ surface for using it as the gate insulator in field‐effect devices. The culture medium and the surface condition of Si₃N₄ were controlled for cell culture on the Si₃N₄ substrate. When we measure electrical characteristics of cell adhesion and cell function using field‐effect devices, we require a stable measurement of the electrical signals. The serum in the culture medium includes a number of proteins, which cause instability of the potential behavior. In this paper, we show that the cell‐adhesive molecules on the Si₃N₄ surface used as a gate insulator should be designed and controlled when cell culture is performed in the culture medium without the serum. Copyright © 2007 Institute of Electrical Engineers of Japan© 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Localized thermal processing with a laser‐trapped and heated metal nanoparticle

We report localized thermal processing using a laser‐trapped and heated metal nanoparticle. A metal nanoparticle trapped by a focused, continuous wave (CW), near‐infrared laser was heated by photothermal conversion and acted as a remotely controllable nanosized thermal tool for processing a workpiece. We demonstrated the processing of a glass substrate with an optically trapped gold nanoparticle (diameter 200 nm) irradiated by a Nd:YAG laser (λ = 1.064 µm, CW). Laser irradiation caused local melting of the substrate and a crater‐like nanosized imprint on the substrate, demonstrating thermal nanoprocessing of an optically transparent material. Copyright © 2007 Institute of Electrical Engineers of Japan© 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Fabrication of metallic nanopatterns using the vacuum type UV‐NIL equipment

Nanoscale dot patterns of cobalt alloy were formed on a silicon substrate using the ultra‐violet nanoimprint lithography (UV‐NIL) technology in combination with an electrodeposition process. We developed an improved UV‐NIL equipment that can evacuate the chamber during imprinting. Using this equipment, we successfully imprinted 240‐nm dot patterns with 500 nm pitch on a photocurable resin with high dimensional accuracy. Thickness control of the resin and imprinting under vacuum are important issues to obtain fine nanopatterns. Using these resin patterns as a mask layer, 300‐nm cobalt alloy patterns are successfully formed by the electrodeposition process. Copyright © 2007 Institute of Electrical Engineers of Japan© 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Devices,structures, and processes for optical MEMS

New processes and devices in the area of optical microelectromechanical systems (MEMS) as researched in the Berkeley Sensor & Actuator Center (BASC) are described. A technique and fabrication procedure is presented to produce high‐quality microlenses at selected locations in a micro‐optical system. Polarization beam splitters are produced by another process, and their performance is measured and described. A new, much simplified process to fabricate vertically offset comb actuating structures is applied in the design of high‐performance scanners, which are in turn used to control a laser ablation system. Very favorable performance comparisons are demonstrated between the researched system and a conventional commercial laser ablation system. A second system demonstration is a prototype Shack–Hartmann (SH) sensor, in which microlenses are mounted in carriages that can be individually addressed using the selectivity of their mechanically resonant mountings. This design is shown to increase markedly the dynamic range in wave aberration to which the SH sensor can be applied. A final application of optical MEMS design is to a reduced‐size, enhanced‐performance, phase shifting interferometer. Copyright © 2007 Institute of Electrical Engineers of Japan© 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

In situ visualization of degradation of silicon field emitter tips

This paper deals with the simultaneous observation of both the electron field emission from nanoscopic tips by electrical means and their structural shape change by an ultra‐high resolution transmission electron microscope (TEM). Nanoneedles with sharp tips of radius in the nanometer range were fabricated with semiconductor micromachining technology. A correlation between the electron field emission characteristics and the structural change of the emitter tip was clearly observed. Copyright © 2007 Institute of Electrical Engineers of Japan© 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Pressure sensing by electrical admittance measurement of a comb‐drive actuator

This paper describes a micromachined pressure sensor that senses pressure not by a diaphragm structure but by a resonantly vibrating comb‐drive actuator. The electrical admittance of the comb‐drive actuator was directly measured using a lock‐in amplifier, and its pressure dependence was examined. From the experiment, it was found that the resonant frequency of the comb‐drive actuator gradually drops as the pressure increases. The sensitivity of the comb‐drive actuator as a pressure sensor was 0.34 Hz/MPa at atmospheric pressure and 0.1 Hz/MPa at 0.4 MPa absolute pressure. Copyright © 2007 Institute of Electrical Engineers of Japan© 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Towards mechanical characterization of biomolecules by MNEMS tools

Single‐molecule micromanipulations have provided information that has been awaited for a long time. However, these experiments relying on optical tweezers (OT) or magnetic tweezers (MT) have a low throughput since the molecular preparation is done one at a time. In order to move towards systematic biological or medical analysis, micro‐nano‐electromechanical systems (MNEMS) are the appropriate devices, as they integrate accurate molecular level engineering tools and can be cheaply produced with highly parallel fabrication processes. This paper investigates the ability of MNEMS tweezers to perform molecular manipulations. The mechanical forces relevant in biological interactions are first reviewed and compared to the performances of biophysical instruments. MNEMS tweezers are then presented. The tweezers integrate opposing sharp tips to capture the molecules, an actuator to stretch them and a displacement sensor to measure in real time the produced molecular extension. DNA molecular bundles are readily assembled and manipulated. The sensor provides a 0.3‐nm stretching resolution, equivalent to the interbase pair distance in double‐stranded DNA. Copyright © 2007 Institute of Electrical Engineers of Japan© 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Exploration of communication models in the design of distributed embedded systems

Distributed embedded systems involve communication in various layers, and therefore their design is more difficult than of single embedded systems. This paper presents how communication exploration can be done in a design process of distributed embedded systems using an example of event‐triggered and time‐triggered communication. A design process begins from abstract specification without assuming any communication category, then explores the categories in a stepwise manner, followed by physical implementation synthesis. This encourages stepwise decision making, component and framework reuse, and early stage verification. Copyright © 2007 Institute of Electrical Engineers of Japan© 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Fast calculation method for fine‐tuned design of need‐based collateralized debt obligation (CDO)

In this paper we propose a speed‐up method for need‐based collateralized debt obligation (CDO) that meets the investor needs of the attributes of the CDO. We note the fact that the computing time to derive the best portfolio is proportional to the number of generated contract conditions that constitute the portfolio. Our method reduces the number of portfolios that can never be the best portfolios by skipping the generation of redundant contract conditions of Super Senior (SS) debt and Equity debt, which is the main cause for the increase of the generated contract conditions. A comparative experiment indicates that the proposed method makes it possible to double the types of tranches or to raise the calculation accuracy nearly 6‐fold, keeping the urgency of the calculation. Copyright © 2007 Institute of Electrical Engineers of Japan© 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Advanced silicon microstructures,sensors, and systems

This paper presents the progress in silicon‐based biomedical microstructures, material characterization techniques, and mechanical microsystems by the authors' research team. Microneedle and microelectrode arrays with fluidic through‐wafer vias and electrical contacts were developed. The structures are designed for dermatological and biological applications such as allergy testing, surface electromyography, and spatially resolved impedance spectroscopy. The characterization of thin films has relied on the bulge test. By the formulation of more powerful models, the application range of the bulge test was extended to elastically supported thin‐film multilayers. This enables the mechanical properties of thin films to be determined reliably. Finally, progress in the operation and application of novel stress sensors based on CMOS diffusions and field effect transistors and exploiting the pseudo‐Hall effect is reported. Their integration into powerful single‐chip microsystems is described. Applications include stress mapping, force and torque measurements, and tactile surface probing of microcomponents. Copyright © 2007 Institute of Electrical Engineers of Japan© 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Fabrication of densely arrayed Si needles with large height for transdermal drug delivery system application

The effects of varying etching conditions for microneedle fabrication were investigated in order to form densely arrayed, sharply angled Si needles with large height for application in transdermal drug delivery systems (DDSs). A sharply angled needle shape could be fabricated by using 34.0 wt% KOH (representing a typical etching‐rate diagram at a highly alkaline etching solution concentration). The needle height could be increased by 20% by adding a compensation mask pattern or by increasing the KOH concentration to 51.0 wt%. The trade‐off relationship between the maximum needle height and the needle density was calculated. These experiments provided useful parameters for designing densely arrayed, sharply angled Si needles for transdermal DDS application. Copyright © 2007 Institute of Electrical Engineers of Japan© 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Separation of stimulus‐selective and nonselective components in intrinsic optical signals

Optical imaging based on intrinsic optical signals has been widely used in studies on the functional organization of visual cortical areas. The presentation of a visual stimulus usually generates non‐stimulus‐selective global darkening and stimulus‐selective localized spots superposed on it. It is critical to extract the stimulus‐selective component for the investigation of the cortical functional organization. In this study, we propose a novel method based on a principal component analysis (PCA) of the spatial optical response patterns, and apply it to the separation of the global darkening in the cat visual cortex. The images submitted to PCA were those responding to the gratings with eight orientations from 0° to 180° in steps of 22.5°. The first principal component represents most of the common signals such as the global darkening and large blood vessels, and occupies more than 80% of the signal energy. By removing the first principal component, the stimulus‐selective dark patches in the reconstructed images have higher contrasts and high orientation selectivity consistent with electrophysiological single‐cell recording. The results suggest that the proposed method can be used to exclude the stimulus‐nonselective component, which provides an alternative method for signal extraction. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Design and modeling of compliant micromechanism for mechanical digital‐to‐analog conversion of displacement

A microelectromechanical digital‐to‐analog converter (MEMDAC) converts digital motion of shuttle actuators operated by the corresponding bits of a binary code into an output displacement proportional to the analog value represented by the input code. In this paper a MEMDAC with improved kinematic design is devised that allows large travel range and high positioning resolution while making the microfabrication process less critical. A lumped‐parameter model of the compliant mechanism of an N‐bit MEMDAC is derived and used to determine the stiffness ratio of flexible members needed for proper mechanical digital‐to‐analog conversion. Furthermore, we analytically investigated the effect of nonuniformity in the device geometry due to the limitations of the microfabrication processes on the linearity of the output displacement. Successful fabrication and release of a 12‐bit MEMDAC demonstrated the manufacturability of the new mechanism, revealing opportunities for MEMS applications in which micropositioners with open‐loop operation, relatively large output range, fine positioning resolution and high repeatability are required. Copyright © 2007 Institute of Electrical Engineers of Japan© 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Low cross talk design and simple fabrication process of electrostatic vertical comb‐drive actuators for positioning application

In this paper, different types of vertical electrostatic comb‐drive actuators are proposed. The aim of design is to minimize the cross talk between vertical and lateral motions with a relatively simple fabrication process, namely, with only two ICP‐RIE steps from the front side with layered masks. Three designs are analyzed by MEMCAD, a finite‐element modeling package, combined with a micromachining process simulator. After optimization based on the calculation, all types were fabricated and tested. The experimental results are qualitatively in good agreement with the calculations. Because of the excess undercutting in our ICP‐RIE machine, the supports were softer than designed. The displacement was larger than expected. According to obtained results, we can expect to generate a vertical force of 0.5 µN per tooth at around 50 V. The measured cross talk between vertical motion and the horizontal motion was 20%. The resonant frequency of a typical device is 9 kHz and the displacement is 1.5 µm at 50 V. Copyright © 2007 Institute of Electrical Engineers of Japan© 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Low‐temperature direct bonding of poly(methyl methacrylate) for polymer microchips

A low‐temperature, direct bonding method for poly(methyl methacrylate) (PMMA) plates has been developed by employing surface treatment by atmospheric pressure oxygen plasma, vacuum oxygen plasma, ultraviolet (UV)/ozone or vacuum ultraviolet (VUV)/ozone. Reasonable bonding strength, as evaluated by a tensile test, was achieved below the glass transition temperature (T_g). The highest bonding strength among the achieved results is 1.43 MPa (about three times the value for conventional direct bonding) at an annealing temperature of 50 °C and an applied pressure of 2.5 MPa for 10 min. Low‐temperature bonding prevents deformation of the PMMA microstructure. A prototype PMMA microchip that has fine channels of 5 µm depth was fabricated by hot‐embossing using a Si mold. After atmospheric pressure oxygen plasma activation, direct bonding was carried out at an annealing temperature of 75 °C and an applied pressure of 3 MPa for 3 min. The method gives good bonding characteristics without deformation and leakage. This low‐temperature bonding technology can be applied to polymer micro/nano structures. Copyright © 2007 Institute of Electrical Engineers of Japan© 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Fabrication of high‐quality two‐dimensional photonic crystals based on porous alumina

We fabricated porous alumina templates with a well‐ordered pore array by a pre‐triggered anodization method. The arrangement of pores in the fabricated templates was set by a Ni‐dot stamper. The structure of the templates was analyzed by field emission scanning electron microscopy (FESEM), two‐dimensional Fourier transformation of FESEM images and optical means. It was found that the porous alumina templates have a high‐quality, extended, two‐dimensional hexagonal lattice, which can be used in the fabrication of two‐dimensional magnetophotonic crystals (2D‐MPCs). © 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Novel fabrication method for long silicon microneedles with three‐dimensional sharp tips and complicated shank shapes by isotropic dry etching

This paper proposes a novel fabrication method for long solid microneedles made of silicon, which have a three‐dimensional sharp tip, by using isotropic dry etching. Since the fabrication is done in a direction parallel to the surface of the silicon substrate, there is no limit for the needle length. Also, the shank shape of this needle is freely designed three‐dimensionally by defining the mask on the silicon surface. For example, a jagged or harpoon shape is possible by using the proposed method, which may be effective for some medical applications. First, several three‐dimensional, complicated‐shaped needles with sharp tip angles were fabricated by changing the mask pattern. Second, a penetration experiment with them on an artificial skin was carried out, and easy penetration comparable with a conventional metal solid needle was confirmed. For an example of lancet application for diabetics, one of the needles was inserted into a human skin, and bleeding was confirmed. Copyright © 2007 Institute of Electrical Engineers of Japan© 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Cellular automaton simulation of micropowder blasting with mask erosion

Development of a two‐dimensional (2D) micropowder blasting simulator for microfabrication of a glass substrate with a patterned polymer mask is reported. In order to investigate the effect of mask erosion on a processed glass profile, a cellular automaton simulation in which erosion of the glass and the polymer mask were taken into account was applied to the micropowder blasting process for the first time. From a comparison of the simulation result with the processed glass profile in the experiment, it was demonstrated that the processed glass profile with the mask erosion could be simulated using our simulator. Furthermore, it was confirmed that the processed profile in the glass depended on the mask profile and the ratio of the deformation wear and the cutting wear of a mask. Copyright © 2007 Institute of Electrical Engineers of Japan© 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.