Masatoshi Ono

A High‐Speed Passive‐Matrix Electrochromic Display Using a Mesoporous TiO2 Electrode with Vertical Porosity

Recently, the application of electronic paper (E-paper) has attracted considerable attention. Many types of reflective displays, such as reflective liquid crystal displays and electrophoretic displays, have been introduced and applied to E-paper. Among them, electrochromic materials, which change in color intensity when an appropriate potential is applied, are the subject of an increasing number of reports. Recently, polymers such as poly(3,4-ethylenedioxythiophene) (PEDOT) or catenanes were reported to show electrochromic behavior. The slow response time for coloring has been a serious problem with these kinds of polymers. As probable electrochromic materials, viologens have commonly been utilized for electrochromic displays (ECDs). Many studies have focused on viologen-modified microspheres or nanostructures to increase the switching speed. Viologens are basically blue in color, and it is thus difficult to realize a full-color display. Furthermore, these kinds of displays have a common drawback: poor background whiteness. To date, electronic displays have not been able to meet the requirements necessary for extensive practical applications. Currently, full-color reflective displays that demonstrate a fast response time are in much demand. Usually, display devices are driven by either active-matrix drive mode or passivematrix drive mode. Active-matrix drive mode is very fast, but it needs expensive thin-film transistors (TFT) for all the pixels of the display, which leads to a high price. Passive-matrix drive mode does not need such expensive electric elements, and it has a simple, low-cost structure. However, when ECD devices are driven by passive-matrix mode at high scanning speed, the drift of electrochromic materials around the electrode leads to poor resolution. That is, the display images are blurry. Herein, we aim to realize high scanning speed and high display quality. We focused on leuco dyes, which are well known as recording materials in thermal imaging systems, because the leuco dyes show a wide variety of colors and are commercially available. We demonstrated a high-speed and high-resolution electrochromic passive-matrix display using a leuco dye with a mesoporous TiO2 electrode with vertical pores (Figure 1). The vertical pores of the electrode can support effective diffusion of leuco dyes perpendicular to the electrode and can prevent the diffusion of the dye around the electrode. Since the colorless state of this kind of display is transparent, it exhibits better background whiteness, which improves readability and reduces eyestrain. Furthermore, the application of leuco dyes to ECD devices has high potential to realize a full-color reflective display with low production costs. These features are very desirable for future E-paper applications. Our device, which consists of two electrodes (working electrode and counter electrode) and electrolyte (Figure 1), was driven by the passive-matrix driving method (an addressing scheme used in earlier liquid crystal displays). Each electrode has striped indium–tin-oxide (ITO) layers 420 mm wide on a glass substrate (Figure 1b and Figure S1 in the Supporting Information). The mesoporous TiO2 film was grown only on the observation side of the working electrode. By improving the previous method, continuous TiO2 films with highly ordered mesostructure and vertical pores were uniformly prepared on the working electrodes by spin coating with a precursor solution. The film thicknesses were changed by using different spinning speeds. Thicknesses of approximately 300, 200, and 100 nm were realized by speeds of 2000, 4000, and 6000 rpm, respectively. Cross-sectional and topsurface SEM images showed that mesopores were oriented vertically with respect to the substrate (Figure S1c in the Supporting Information). The mesochannel walls are composed of periodically arranged cages with connecting necks between the neighboring cages (see the Supporting Information, in particular Figure S2, for details). The two electrodes sandwiched the electrolyte so that the striped ITO layers were orthogonally crossed (Figure 1b and Figure S3 in the Supporting Information). The electrolytic solution consisted of black leuco dye (2-(3’-trifluoromethylphenylamino)-6’[*] W. Weng, T. Higuchi, M. Suzuki, T. Fukuoka, Dr. T. Shimomura, Dr. M. Ono Funai Electric Advanced Applied Technology Research Institute Inc. 2-1-6 Sengen, Tsukuba, Ibaraki 305-0047 (Japan) E-mail: weng.w@funai-atri.co.jp

Amperometric determination of choline with enzyme immobilized in a hybrid mesoporous membrane.

Choline sensor is successfully prepared by using immobilized enzyme, i.e., choline oxidase (ChOx) within a hybrid mesoporous membrane with 12 nm pore diameter (F127M). The measurement was based on the detection of hydrogen peroxide, which is the co-product of the enzymatic choline oxidation. The determination range and the response time are 5.0-800 microM and approximately 2 min, respectively. The sensor is very stable compared to the native enzyme sensor and 85% of the initial response was maintained even after storage for 80 days. These results indicate that ChOx is successfully immobilized and well stabilized, and at the same time, enzyme reaction proceeds efficiently. Such ability of hybrid mesoporous membrane F127M suggests great promise for effective immobilization of enzyme useful for electrochemical biosensors.

Amperometric l-lactate biosensor based on screen-printed carbon electrode containing cobalt phthalocyanine, coated with lactate oxidase-mesoporous silica conjugate layer

A novel amperometric biosensor for the measurement of L-lactate has been developed. The device comprises a screen-printed carbon electrode containing cobalt phthalocyanine (CoPC-SPCE), coated with lactate oxidase (LOD) that is immobilized in mesoporous silica (FSM8.0) using a polymer matrix of denatured polyvinyl alcohol; a Nafion layer on the electrode surface acts as a barrier to interferents. The sampling unit attached to the SPCE requires only a small sample volume of 100 μL for each measurement. The measurement of l-lactate is based on the signal produced by hydrogen peroxide, the product of the enzymatic reaction. The behavior of the biosensor, LOD-FSM8.0/Naf/CoPC-SPCE, was examined in terms of pH, applied potential, sensitivity and operational range, selectivity, and storage stability. The sensor showed an optimum response at a pH of 7.4 and an applied potential of +450 mV. The determination range and the response time for L-lactate were 18.3 μM to 1.5 mM and approximately 90s, respectively. In addition, the sensor exhibited high selectivity for L-lactate and was quite stable in storage, showing no noticeable change in its initial response after being stored for over 9 months. These results indicate that our method provides a simple, cost-effective, high-performance biosensor for l-lactate.

Assembly of an artificial biomembrane by encapsulation of an enzyme, formaldehyde dehydrogenase, into the nanoporous-walled silica nanotube–inorganic composite membrane

We prepared silica nanotube with nanochannel-wall in the columnar pores of a commercial anodic alumina membrane (F127-MST), and then made up an artificial biomembrane consisting of a hierarchical structure by introducing an enzyme, formaldehyde dehydrogenase, into the silica nanochannels. The formaldehyde dehydrogenase confined in membrane showed a very high activity for the reduction of NAD+ similar to that of the native, besides much higher electron transfer to the electrode than the native. At the same time, we clarified that the encapsulation of enzymes into the nanochannels enables enzymes to accumulate in high density without aggregation and be arranged regularly. These results indicate that F127-MST can provide a favorable method for enzyme immobilization on the electrode.

Non-volatile high-speed resistance switching nanogap junction memory

Different voltage pulses were applied to Au nanogap junction to study the resistance switching characteristics. Consistent switching from a low to high resistance state was accomplished even at 20 ns pulse. Instead of setting current compliance for the reverse switching, we introduced a series resistance to the nanogap junction to limit the tunneling current and effectively performed the switching. The parasitic capacitance is shown to affect the programming speed. Upon reducing the capacitance, ns regime switching speed is achieved which indicates the potentiality of nanogap junction for high-speed random access memory.

Control of Laser Speckle Noise Using Liquid Crystals

Laser speckle noise occurs owing to the strong interference that originates in the high coherency of laser light and the surface topography of the screen. The suppression of the speckle noise is necessary for laser displays such as in an image projection system. In order to reduce speckle noise, we try to control the speckle pattern by using liquid crystals that have electrically controllable optical characteristics. The modulation of polarized light using the birefringence of liquid crystals is very effective. However, the ratio of noise reduction does not exceed 30%. This is because the polarized light transmitted through the liquid crystal medium is formed by only two optical eigenmodes. The wedge-type liquid crystal cell can control the position of the laser spot on the screen. The incident-angle modulation of laser light is also effective for noise reduction.

Control of Laser Speckle Noise by Using Polymer-Dispersed LC

Laser speckle noise occurs owing to the strong interference that originates in the high coherency of laser light and the surface topography of screen. The suppression of the speckle noise is necessary for laser displays such as an image projection system. To reduce the speckle noise, we have tried to control the speckle pattern by using liquid crystals (LCs). In this paper, we offer an idea for suppressing the speckle noise using a polymer-dispersed LC (PDLC) cell in which the speckle pattern can be varied in addition to the optical diffusive effect.

4kb nonvolatile nanogap memory (NGpM) with 1 ns programming capability

A 4k bits nonvolatile high-speed nanogap memory device was fabricated with a newly developed vertical nanogap structure and its memory characteristics were evaluated. The newly developed vertical nanogap structures realized controllable electrode gap and higher yield compared to the initial phase lateral type nanogap structure. The structures were integrated on a CMOS chip. The specially embedded measurement circuit revealed programming speed from a low resistance state to a high resistance state (from on to off state) to be 1 ns.

Reduction of laser speckle noise by using particle-dispersed liquid crystals

ABSTRACT Laser speckle noise occurs owing to the strong interference that originates in the high coherency of laser light and the surface topography of screen. The suppression of the speckle noise is necessary for laser displays such as an image projection system. To reduce the speckle noise, we have tried to control the speckle pattern by using liquid crystals (LCs). In this paper, we offer an idea for suppressing the speckle noise using particle-dispersed LC cells in which the speckle pattern can be varied in addition to the optical diffusive effect.

Effect of Wettability on Fabrication of PSCOF Liquid Crystal Cell

In this research, in order to realize the phase-separated composite organic film (PSCOF) structure of liquid crystal (LC) cell, we have researched in detail its fabrication conditions. Nematic and ferroelectric LCs have been used for the investigation. Furthermore, we try to realize the PSCOF cell by using photocurable LC monomers as polymer materials. The contact angle has been measured in LC and polymer materials to lots of alignment films. As a result, it is found that the important factors for the fabrication of PSCOF structure are the wettability of LC materials to alignment film and the molecular weight of monomer.