H. J. Hyun

Performance Study of the Silicon Strip Detector

We designed and fabricated the DC-coupled double-sided silicon strip sensor and the AC/DC-coupled single-sided sensors. They showed the good electrical characteristics such as leakage current and capacitance. Good separation of signal from noise is important and we measured the signal-to-noise ratios of the developed sensors. This is defined as the ratio of the most probable energy deposit in the sensor to the noise RMS. We presented the measurement result of the signal-to-noise ratio with developed silicon strip sensor and readout electronics using 90Sr beta source and 45 MeV proton beam.

Development of a detector with two photo-strip sensors and a crystal scintillator between sensors

We fabricate single-sided strip sensors that are sensitive to light. The strip sensors are AC-coupled, which has coupling capacitors and bias resistors. The sensors are fabricated on a high resistivity and double-sided polished n-type silicon wafer. The sensor is designed as the single-side strip sensor but its backside (n-side) is modified to be sensitive to incoming light. This photo-strip sensor is designed to measure positions of incoming gamma ray and alpha particle. The photo-strip detector consists of two photo-strip sensors and one crystal scintillator. The sensors sandwiching opposite faces of a scintillator are oriented orthogonally to each other to provide two-dimensional position information. When particles enter a crystal, the scintillator light of a crystal is emitted and penetrates into the photo-strip sensors. The lights are then converted to electron-hole pairs in the sensors. The detector configuration provides not only two-dimensional position information, but also the depth of interaction (DOI). The DOI is given by comparing signal-to-noise ratio between the first and second photo-strip sensors. The fabricated sensors are electrically tested by varying bias voltages. The pulse heights of the detector are measured by using Am-241 alpha, Na-22 and Cs-137 gamma ray sources. The position information is obtained with one photo-strip sensor and the LYSO crystal scintillator by using Am-241 alpha source. An experiment to obtain two-dimensional position information with two photo-strip sensors and a scintillator crystal is on going.

Prototype development of an AC-coupled pad matrix detector

We designed and fabricated AC-coupled single-sided silicon pad matrix sensors in a 5-inch fabrication line, and developed the signal readout electronics system. The fabricated sensor is fully depleted below 60 V and the leakage current at operating voltage is measured to be ∼ 40 nA/cm2. Measurements of the coupling capacitance and bias resistance of the sensor show uniformity in their values. The analog signal from the silicon sensor is processed by VATA ASIC chip as frontend electronics. The linearity of the VATA is measured to be good and the signal-to-noise ratio is about 10, which needs the Minimum-Ionizing-Particle (MIP) correction. The phantom image with a Cu foil is also obtained with the fabricated matrix sensor.

Radiative and electroweak penguins at Belle

Radiative and electroweak penguin decays of B mesons are a sensitive probe of new physics beyond the Standard Model. We study the inclusive and exclusive radiative and electroweak penguin decays of B meson and also search an exotic particle seen by the HyperCP experiment. The measurements are based on a large data sample of 605 fb−1 containing 657 millions BB pairs collected at the Υ(4S) with the Belle detector at the KEKB energy asymmetric e+e− collider.

Development of the silicon photo-strip sensor

We have designed and fabricated silicon photostrip sensors with polysilicon resistors and coupling capacitors. This developed detector consists of two photo-strip sensors sandwiching opposite faces of a crystal scintillator and being oriented orthogonal to each other. This configuration is able to provides the 2 dimensional position information and to measure the energy. Therefore they can be used in nuclear and medical application. The developed sensor has p+ strip array for signal readout. On the other hand, the rear side is a light entrance window which has very thin n+ doping layer with anti-reflective coating to prevent light losing. These sensors are fabricated on a 5-in., 380 μm-thickness, n-type, high resistivity silicon wafer. The leakage currents of the fabricated sensors are measured as a function of the reverse bias voltages. The light responses of fabricated silicon photosensors coupled with a CsI(Tl) crystal are measured by using 241Am, 22Na and 137Cs radioactive sources. The energy resolutions of the photodiode coupled with the crystal are obtained to be 20.5 % and 13.8 % for the 22Na (511 keV) and the 137Cs (662 keV) γ-rays. The one-dimensional position information by the α particles (241Am) are clearly observed by the photo-strip sensor coupled with the crystal.

Signal-to-noise ratio measurement and radiation damage study of silicon PIN diode with a proton beam

We designed and fabricated silicon PIN diodes having p+ active area of 1.0 cm × 1.0 cm on a 5-in. high resistivity (≫5 kΩ⋅cm) n-type FZ (float zone), 380 μm-thick silicon wafer. For signal-to-noise ratio (SNR) measurement of the diode, we required that the fabricated diode should be fully depleted at the operation voltage and the level of the leakage current of the sensor should be less than 10 nA/cm2 at the operation voltage. The SNR of the diode was measured by using a 45 MeV proton beam from the MC-50 cyclotron at Korea Institute of Radiological and Medical Sciences (KIRAMS) in Seoul, Korea. Experiment was performed at room temperature and 46 volts was biased to fully deplete the diode. The SNR of the diode was measured to be 20.8 after corrected for the minimum ionizing particle. The different PIN diode which has relatively large leakage current was used for radiation damage test with the same proton beam. The leakage currents as a function of the reverse bias voltages were measured before and after the proton beam irradiation. The prototype was irradiated with 1.4 ×107 fluence. We annealed the diode after irradiation of the proton beam and measured the leakage current dependence on times at the operation voltage. We present the understanding of radiation-induced detector deterioration and the SNR of the silicon diode in this paper.

Performance test of the silicon PIN diode with radioactive sources

Silicon PIN diodes with an active area of 1 cm × 1 cm were fabricated on a high resistivity, (100)-oriented, n-type, 380-μm thick and 5-inch silicon wafer. These diodes were originally fabricated on purpose to monitor strip sensor fabrication processes. To evaluate the performance of the silicon PIN diode, we measured the signal-to-noise ratio (SNR) and energy resolution using radioactive sources. We measured the radiation detection responses of the silicon PIN diodes and observed photopeaks from radioactive sources, Am-241, Sr-90 and Cs-137. The spectrum by simulation was compared with those of the source tests to understand the measurement results. The tests with Am-241 and Cs-137 sources used random trigger because γ fully deposits its energy in a silicon PIN diode. Another PIN diode was used for trigger purpose with Sr-90, β source. Am-241 test showed a sharp peak of 59.5 keV γ as we expected. The γ peak was used for calibration that converts ADC value into energy. We used Cs-137 source to compare a resolution at the lower energy level (32 keV γ) with 59.5 keV γ. Two different conditions were set for Cs-137; without a lead-block and with 3mm-lead-block to reduce β background. In the test of Sr-90, the SNR of the silicon PIN diode was measured to be 36.0. We present the energy resolution and the SNR of the diode measured by using the radioactive sources.

Prototype development of silicon array sensor for x-ray detector

A prototype of silicon array sensor with 256 pixels and a frontend electronics system for its readout was developed for X-ray imaging. The characteristics of the sensor and some test results of the electronics system are presented.

Electron beam test results with a DC-coupled single-sided strip detector

Because silicon strip sensor has a high position resolution compared to the other detectors such as proportional chamber, drift chamber, etc., it has been used in medical imaging, high energy experiment, and space science. We designed and fabricated DC-coupled single-sided silicon strip sensors in a 5-inch fabrication line, and developed the signal readout electronics system. We reported the electrical characteristics of the sensors such as capacitances and leakage currents as a function of bias voltage in the 2005 Nuclear Science Symposium including results of the radiation damage test and charge collection efficiencies for various sensor designs, and the signal-to-noise ratio (SNR) measurement results by using a 90Sr beta-source and a 45 MeV proton beam were also reported in the 2006 Nuclear Science Symposium. In this meeting we present results of a beam test performed in September 2006 at CERN (European Organization for Nuclear Research) beam facility by using a 150 GeV electron beam with the DC-coupled single-sided silicon strip sensor including readout electronics.

Design and Development of AC-coupled Single-sided Silicon Strip Sensor

Semiconductor detectors, and in particular silicon detectors, have unique properties that make them very suitable for the detection of ionizing radiation. We reported the design and development processes of the DC-type double-sided silicon strip sensor in the 2005 Nuclear Science Symposium. In this meeting we present the design and development of the single-sided silicon strip sensor which has coupling capacitors and bias resistors. The silicon sensor concept, details of the sensor design and fabrication processes are presented and the measurement results of the electrical characteristics of the fabricated sensors are also reported.