Tetsuya Ariyoshi

Development of Dielectric Microcalorimeter

A prototype dielectric microcalorimeter was fabricated from 0.99SrTiO3-0.01SrTa2O6, a dielectric material. To estimate the operation performance of the microcalorimeter, a simple evaluation model is introduced by employing the block diagram formalism. Pulse height and fall time constant of the detection signal are analyzed as a function of the thermal conductance of the heat link. The dielectric microcalorimeter maintained at 100mK was irradiated by 5.5 MeV α-particles emitting from an 241Am source. Responsivity was found to be 2.7x10−19C/eV.

Improvement of color separation characteristics of a side-illuminated color photo sensor

For easy color photography, we have proposed a method of irradiating a silicon photosensor from the side. This color imaging method applies a simple pixel structure without color filters, and prevents the generation of false colors and moire patterns. A test chip was fabricated using a 0.35 µm complementary metal–oxide–semiconductor 1-poly 4-metal process. The chip dimensions are 5000 × 5000 µm2. The pixel layout structure that we proposed previously was remodeled. We confirmed that the four colors blue, green, red, and near-infrared are isolated in the normal color wavelength range in a light irradiation experiment.

Side-Illuminated Color Photosensor

We have proposed a simple method for color imaging in which the photosensor is illuminated from the side. In this method, color imaging can be produced using single pixels and without generating false colors and moire patterns. A 5.0 ×5.0 mm2 test chip was fabricated using a 0.35 µm complementary metal oxide semiconductor (CMOS) 1-poly 4-metal process. Because the side illumination method is used, the side of the test chip was etched using a high-speed deep reactive ion etching (D-RIE) process. Light illumination experiments confirmed that four colors – blue, green, red, and near-infrared – could be separated using this method. We also estimated the color separation properties of a similar sensor based on a 0.18 µm CMOS process.

Improved Near-Infrared Sensitivity with a Side-Illuminated Photosensor

To improve the sensitivity of silicon photosensors to near-infrared light, we proposed a method in which the photosensor is illuminated from the side. That method allows the PN junction of the photodiode to be formed to a length that covers the entire depth of incident light penetration. The result is efficient collection of the photocharge produced by the injected light and improvement in quantum efficiency. We fabricated a 4.20 ×3.33 mm2 test chip using a 0.35-µm complementary metal oxide semiconductor (CMOS) 1-poly 3-metal process. Because side illumination is used, the side of the chip is etched by high-speed deep reactive ion etching (D-RIE). For a 150-µm-long photodiode, the quantum efficiency to 970-nm wavelength near-infrared light is 28 times as high as for a conventional device. It was confirmed that the effectiveness of the proposed method increases with the wavelength of the incident light.

Purity measurement of liquid methane by using the drift property of ionized electrons

The purity is important parameter for the collection of electrons ionized in an ionization chamber filled with the liquid methane. The methane gas purification system was developed for the liquid methane ionization chamber. After the condensation of the purified methane gas in the ionization chamber mounted with 241 Am alpha source, ionized electrons were collected by a charge sensitive preamplifier. The concentration of impurity of oxygen gas was obtained by analyzing a collected charge distribution. Pulse height distributions of a charge sensitive preamplifier were obtained for the detection of y rays and neutrons emitted from 60Co, 137Cs and Am-Be sources located outside the cryostat of the liquid methane chamber.

A Study of Microcalorimeter with Dielectric Thermomete

The microcalorimeter detects a single particle of radiation by means of the temperature rise in the absorber kept at low temperature below IK. A sensitive thermometer measuring the temperature rise is an important component in the microcalorimeter. Dielectric materials whose electric capacitances depend on temperature at low temperature can be utilized for the sensitive thermometer of the microcalorimeter. The temperature dependence of the electric capacitance d(ln Cd)/dT is an important parameter for the dielectric thermometer. We have studied the dielectric thermometer made of SrTiO3 based material and carried out measurement of the electric capacitance in the temperature range from 50mK to 120mK. By using experimental values of d(ln Cd)/dT an output signal of the dielectric microcalorimeter was estimated in the detection of a 5.5 MeV α-partice.

X-ray detection by an on-chip coil integrated superconducting tunnel junction

An on-chip coil integrated superconducting tunnel junction (OC2-STJ) was used for x-ray detection by applying the magnetic field produced by a superconducting microstrip coil integrated into the superconducting tunnel junction chip. The fabricated OC2-STJ chip was mounted in a cooling capsule attached to the mixing chamber of a compact 3He–4He dilution refrigerator. The OC2-STJ chip was held at a constant temperature in the capsule against the Joule heat generated in the current feed line of the strip coil during the detection operation. Stable operation of the OC2-STJ was demonstrated without using the usual external electromagnets.

Response of an On-Chip Coil-Integrated Superconducting Tunnel Junction to X-rays

An on-chip coil-integrated superconducting tunnel junction (OC2-STJ) was irradiated by X-rays emitted from an 55Fe source to the examine the performance of X-ray detection by applying a magnetic field produced by a superconducting microstrip coil integrated into the junction chip. Response characteristics were obtained for a diamond-shaped Nb-based tunnel junction with a sensitive area of 100×100 µm2 in the OC2-STJ chip. Two kinds of stable operation modes with different pulse heights were observed by changing the magnetic flux density in the barrier region of the junction. In the low-pulse-height mode, the pulse height distribution exhibits two full-energy peaks corresponding to signals created in the top and base electrodes. Stable operation of the OC2-STJ was demonstrated without using conventional external electromagnets.