Yoshifumi Watabe

A high performance amorphous Si/sub 1-x/C/sub x/:H thermistor bolometer based on micro-machined structure

A high performance micro-bridge structured thermistor bolometer of D*=8.0/spl times/10/sup 8/ cm Hz/sup 1/2//W has been realized without using vacuum packaging. The temperature change in the bolometer was simulated by a newly developed method based on laminar film theory. The calculated values were found to be in excellent agreement with the experimental data. By optimizing deposition parameters of hydrogenated amorphous silicon carbide (a-Si/sub 1-x/C/sub x/:PI) thin film, we have successfully fabricated superior thermistors with a high temperature coefficient of resistance a and low electronic excess noise. The noise dramatically decreases as the amount of Si-CH/sub 3/ and C-H/sub n/ bonds in a-Si/sub 1-x/C/sub x/:H thin films decreases and as the doping level increases.

Fabrication of a 7.6-in.-diagonal prototype ballistic electron surface-emitting display on a glass substrate

A prototype ballistic electron surface-emitting display (BSD) was fabricated on a TFT or PDP glass substrate by using a low-temperature process. A 84 x 63-pixel, 7.6-in.-diagonal full-color BSD shows excellent performance, comparable to the previously reported 2.6-in. model. This result demonstrates the strong possibility of large-panel BSDs.

Characteristics of Thermally Induced Ultrasonic Emission from Nanocrystalline Porous Silicon Device under Impulse Operation

To clarify the mechanism of thermoacoustic effects in a nanocrystalline porous silicon (nc-PS) device, ultrasonic emission characteristics have been investigated in relation to dynamic behavior. The nc-PS ultrasonic emitter is composed of a surface heater electrode, an nc-PS layer, and a single-crystalline silicon (c-Si) substrate. Due to a completely flat frequency response, this device emits an ideal impulse acoustic output with no reverberations for pulse driving. The relationship between acoustic output and transient surface temperature change can be well interpreted quantitatively by taking the heat capacity of the heater electrode into account. The experimental fact that the transient surface electrode temperature change is induced uniformly over the whole range of the emission area ensures the directivity of the acoustic pulse output.

39.3: Development of a Low Temperature Process of Ballistic Electron Surface-Emitting Display (BSD) on a Glass Substrate

Ballistic electron Surface-emitting Display (BSD) is successfully fabricated on a glass substrate with low temperature process. 168 (RGB) × 126 pixels, 2.6 inches diagonal full-colour BSD exhibits excellent performance as a flat panel display. Main fabrication process is an anodisation and subsequent electrochemical oxidation process at a low temperature, which will contribute to larger panel size and process-cost reduction.

14.1: Invited Paper: Fabrication of Ballistic Electron Surface-Emitting Display on Glass Substrate

It is demonstrated that the Ballistic electron Surface-emitting Display (BSD) can be fabricated onto both quartz and TFT Glass substrates and performed excellent characteristics. We also demonstrate the 2.6 inches diagonal 84(RGB)×63 pixels multicolour flat panel display on a quartz glass substrate. BSD promise the possible application to the flat panel display in near future.

28.4: Matrix Flat-Panel Application of Ballistic Electron Surface-Emitting Display

Ballistic electron Surface-emitting cold cathode based on porous polysilicon exhibits excellent performance as a novel flat panel display. It is demonstrated that emission current is stable up to an ambient pressure of 10 Pa. 53(RGB) × 40 pixels multicolour matrix panel is fabricated and evaluated its performance. Fabricating process is mainly based on conventional silicon process and anodisation process, for which we can expect lower production cost at larger panel fabrication.

Tunable Output Directivity of Thermally Induced Ultrasound Generator Based on Nanocrystalline Porous Silicon

To confirm the usefulness of thermally induced ultrasonic emission from nanocrystalline porous silicon (nc-PS) as a probing source for object sensing in air, its characteristics have been investigated in terms of the input pulse width dependence of both the sound pressure amplitude and the ultrasound emission directivity. The device is composed of a silicon wafer substrate, an nc-PS layer, and a thin metal film surface heater electrode. When the device is driven under a pulse input with various widths, the output sound pressure amplitude remains almost constant, whereas the emission directivity changes from the isotropic mode to the directional mode: the measured directivity angles at pulse widths of 50 and 10 µs are 180 and 71.6°, respectively. These results can be explained consistently with theoretical analyses. The observed controllability of the emission angle is attractive for the development of a three-dimensional ultrasonic image sensor with an area-selective function by a simple pulse-width modulation.

Effects of Thermal Effusivity in Nanocrystalline Porous Silicon on Long-Term Operation of Thermally Induced Ultrasonic Emission

Due to a strong quantum confinement effect, both the thermal conductivity α and heat capacity per unit volume C of nanocrystalline porous silicon (nc-PS) are extremely lower than those of single-crystalline silicon (c-Si). This high contrast between the thermal properties of nc-PS and c-Si makes it possible to produce an efficient ultrasound emitter device for various sensors, speakers, and actuators. The most important parameter in this device is assumed to be the thermal effusivity (αC)1/2 of nc-PS, since the theoretical acoustic output is inversely proportional to the (αC)1/2 of the nc-PS layer. To confirm this assumption, the output stability during a long-term operation has been studied in relation to a change in (αC)1/2. The obtained experimental results indicate that the acoustic output deteriorates with a gradual increase in (αC)1/2 due to the oxidation of nc-PS and that an appropriate nanostructure control with a passivated surface against oxidation is the key issue for obtaining a practical operation time.

Development and evaluation of a palm-sized optical PM2.5 sensor

ABSTRACT A new palm-sized optical PM2.5 sensor has been developed and its performance evaluated. The PM2.5 mass concentration was calculated from the distribution of light scattering intensity by considering the relationship between scattering intensity and particle size. The results of laboratory tests suggested that the sensor can detect particles with diameters as small as ∼0.3 µm and can measure PM2.5mass concentrations as high as ∼600 µg/m3. Year-round ambient observations were conducted at four urban and suburban sites in Fukuoka, Kadoma, Kasugai, and Tokyo, Japan. Daily averaged PM2.5 mass concentration data from our sensors were in good agreement with corresponding data from the collocated standard instrument at the Kadoma site, with slopes of 1.07–1.16 and correlation coefficients (R) of 0.90–0.91, and with those of the nearest observatories of the Ministry of the Environment of Japan, at 1.7–4.1 km away from our observation sites, with slopes of 0.97–1.23 and R of 0.89–0.95. Slightly greater slopes were observed in winter than in summer, except at Tokyo, which was possibly due to the photochemical formation of relatively small secondary particles. Under high relative humidity conditions (>70%), the sensor has a tendency to overestimate the PM2.5 mass concentrations compared to those measured by the standard instruments, except at Fukuoka, which is probably due to the hygroscopic growth of particles. This study demonstrates that the sensor can provide reasonable PM2.5 mass concentration data in urban and suburban environments and is applicable to studies on the environmental and health effects of PM2.5. Copyright

Effect of Bilayer Structure on the Long-Term Stability of Nanocrystalline Porous Silicon Ultrasonic Emitter

Due to a strong quantum confinement effect, both the thermal conductivity α and heat capacity per unit volume C of nanocrystalline porous silicon (nc-PS) are extremely lowered in comparison to those of single-crystalline silicon (c-Si). This high contrast between the thermal properties of nc-PS and c-Si makes it possible to produce an efficient ultrasound emitter device based on interfacial thermoacoustic transfer with no mechanical surface vibrations. The most important parameter of this device is the thermal effusivity (αC)1/2 of the nc-PS layer, since the theoretical acoustic output is in inversely proportional to (αC)1/2. To stabilize the acoustic output by suppressing possible change in (αC)1/2 during a long-term operation, a bilayer structure is introduced into the nc-PS layer in this work. Due to the increased stability against oxidation, the device operates for a long time without any significant degradation. The observed long-term stability ensures the applicability of this emitter in functional acoustic devices such as sensors, speakers, and actuators.