Daiji Noda

Fabrication of Diffraction Grating with High Aspect Ratio Using X-ray Lithography Technique for X-ray Phase Imaging

The use of conventional X-ray radiography is limited due to weak absorption. This problem is resolved by using phase-sensitive imaging methods to improve the contrast, such as X-ray Talbot interferometry. With a spatially coherent light source and two diffraction gratings for Talbot interferometry, we measured the phase change differential. Using this technique, diffraction gratings were designed to have a fine high-accuracy high-aspect-ratio structure. Then, we fabricated a high-aspect-ratio diffraction grating using a deep X-ray lithography technique. A diffraction grating with a period of 8 ?m and a height of about 30 ?m was fabricated. This diffraction grating can be used for X-ray phase imaging for X-ray Talbot interferometry.

Preparation of Heavily N-Type ZnSe Doped by Iodine in Remote Plasma Enhanced Metal Organic Chemical Vapor Deposition.

Iodine-doped zinc selenide (ZnSe:I) layers were grown by remote plasma enhanced metal organic chemical vapor deposition (RPE-MOCVD) using n-butyliodide (n-BtI). The carrier concentration was controlled from 2×1016 to 8.2×1019 cm-3 by the dopant flow rate, where the mobilities renged from 200 to 50 cm2 V-1 s-1, respectively. The low-resistivity of 7.3×10-4 Ω cm was attained at the highest doping level.

Fabrication of X-Ray Gratings Using X-Ray Lithography Technique for X-Ray Talbot Interferometer

The X-ray radiographic imaging technique is very important in medical, biological, inspection, material science, and other fields. However, it is not enough to obtain a clear X-ray image of samples with low absorbance materials, such as biological soft tissues. Then, we have used an X-ray phase-imaging method of an X-ray Talbot interferometer. In this method, X-ray gratings were required to have a narrow pitch and high aspect ratio structure. Therefore, we have developed and fabricated high-aspect-ratio X-ray gratings with a pitch of 5.3 μm, a height of 30 μm, and a large effective area of 100 X 100 mm using X-ray lithography and narrow electroforming techniques. In this paper, we discuss the fabrication process of X-ray gratings with a narrow pitch and high-aspect-ratio structure, and results of X-ray phase tomography using an X-ray Talbot interferometer with these X-ray gratings.

Fabrication of Si field emitter array in local vacuum package

We have fabricated the local vacuum package with Si field emitter array on Si substrate. To keep the pressure for electron emission, the titanium getter of evaporation type was made a bridge structure with Si field emitter array in local vacuum package. The local vacuum package technique adapted to the IC process for on-chip device. Therefore, this technique is very useful for many applications with high performance.

Epitaxial Growth and Nitrogen Radical Doping of CdZnTe

Epitaxial cadmium zinc telluride (CdZnTe) films have been grown on GaAs(100) substrates by the remote plasma-enhanced metallorganic chemical vapor deposition method. The growth was carried out at a low substrate temperature of 200°C. In this system, we obtained Cd 1-x Zn x Te epitaxial films with composition x in the range 0-1. When nitrogen radicals were introduced in addition to hydrogen radicals, p-type CdZnTe films with nitrogen acceptors were obtained. Although as-grown samples showed high resistivity of more than 10 Ω cm, after annealing treatment at 600°C for 10 min, the resistivity and carrier concentration at an x value of 0.96 were measured as 3.7 × 10 -2 Ω cm and 1.2 × 10 19 cm -3 , respectively.

Electron Emission Properties of ZnS-Based Thin-Film Cold Cathode for Field Emission Display

A thin-film cold cathode emitter has been produced for application in flat-panel displays. This structure is fabricated by modifying a thin-film electroluminescence device. The thin-film cold cathode employs hot electrons generated in a ZnS accelerating layer by a high electric field, with these electrons being emitted through a thin Au electrode. The thin-film cold cathode emitter exhibited emission properties over large areas with excellent uniformity. For application to field emission displays, a matrix of electrodes was fabricated using thin-film cold cathodes. Although the pixel pitch was fine, electron emission exhibited spatial uniformity. This feature makes this device attractive for flat-panel displays and other applications.

Effect of insufficient temporal coherence on visibility contrast in X-ray grating interferometry

X-ray grating interferometry, which has been spotlighted in the last decade as a multi-modal X-ray imaging technique, can provide three independent images, i.e., absorption, differential-phase, and visibility-contrast images. We report on a cause of the visibility contrast, an effect of insufficient temporal coherence, that can be observed when continuous-spectrum X-rays are used. This effect occurs even for a sample without unresolvable random structures, which are known as the main causes of visibility contrast. We performed an experiment using an acrylic cylinder and quantitatively explained the visibility contrast due to this effect.

High-efficiency MOSFET bridge rectifier for AlN MEMS cantilever vibration energy harvester

We developed a high-efficiency MOSFET bridge rectifier for use in an aluminum nitride (AlN) piezoelectric MEMS cantilever vibration energy harvester (VEH). The bridge rectifier consists of four MOSFETs with a circuit configuration similar to that of a typical diode bridge rectifier. The output voltage of the full-wave rectification via the MOSFET bridge was simulated with an equivalent circuit model of the AlN VEH, which is extracted from an experimental result. The channel width of the MOSFET was designed to be adopted for use with a high-voltage and low-current AlN VEH. The designed rectifier was fabricated using the 0.18 µm high voltage technology of a commercially available CMOS foundry. The AlN VEH with our bridge rectifier generated a DC power of 0.514 µW at 2.49 V under an applied vibration with an acceleration amplitude of 0.5 m/s2 at a frequency of 46.6 Hz. The DC power is 1.4 times higher than that generated by the same AlN VEH with a MOSFET bridge consisting of commercially available discrete MOSFETs.

Millisecond-order X-ray phase tomography with compressed sensing

We report on millisecond-order X-ray tomography with grating-based X-ray imaging using a white synchrotron X-ray beam. We performed a compressed sensing technique for tomographic reconstruction and successfully obtained a phase tomogram for a polypropylene sphere with a temporal resolution of 2.0 ms. Our approach will make it possible to realize millisecond-order four-dimensional X-ray tomography but also to markedly reduce the radiation damage of samples including polymer and biological materials, and will be widely used in various fields of material and life sciences in the near future.

Fabrication of Local Micro Vacuum Package Incorporating Si Field Emitter Array and Ti Getter

Field emitter has high speed response characteristics at over 100 GHz because they utilize the electron emission in a vacuum. Therefore, field emission device are very suitable for use as high speed switching elements, and practical field emitters can be fabricated by using Si process. Consequently we have fabricated a local vacuum package on a Si substrate that is adapted to IC process for on-chip integrated devices. This has the great advantage that devices can be aligned on a micro mater size, and is very useful for many applications involving high performance on-chip integrated devices.