K. Yamamura

Development of Multi-Pixel Photon Counter (MPPC)

MPPC is a novel solid-state photon counting device, which composed of Geiger-mode APD and quenching resistor. We released three kinds of pixel number of MPPC, which have 1600, 400 and 100 pixels. The basic characteristics are promising as a photon counting purpose, but existence of after-pulse and cross-talk are realized in these days [1]. We did rough measurement for these parameters. The recovery time of MPPC is determined by the value of quenching resistance and pixel capacitance. We irradiated the MPPC with high rate light pulse using by picosecond light pulser, and confirmed that the MPPC can output full height pulse after pulse length. We developed the enhanced active area type, array type and new package type MPPCs. The 3 × 3 mm type MPPC (3600pixels) achieved 13% of energy resolution (FWHM).

Microdischarges of AC-coupled silicon strip sensors

Abstract Microdischarge at the edges of strips in AC-coupled silicon strip sensors has been investigated. A steep increase in the leakage current (breakdown) and a sudden onset of burst noise were observed at a low reverse-bias voltage when the bias potential was across the AC-coupling capacitor. This can be explained by the occurrence of microdischarges along the edges of strips. These discharges have been confirmed by observing IR light emission. A calculation of the field strength at the strip edge suggests that a fringe field of the external electrode generates the microdischarge at the strip edge when the bias voltage is 50–80 V. This is consistent with our observations. We discuss a design for AC-coupled sensors that eliminates this discharge problem.

Optimal p-stop pattern for the N-side strip isolation of silicon microstrip detectors

We present a study that shows that charge collection efficiency in silicon microstrip detectors depends on the geometry of the p-stop used to isolate the strips on the Ohmic side. Detector signals for four kinds of p-stops were studied using a laser test stand. We propose an optimal p-stop geometry which realizes acceptable charge collection efficiency as well as low interstrip capacitance and low noise.

DESIGN OPTIMIZATION OF RADIATION-HARD, DOUBLE-SIDED, DOUBLE-METAL, AC-COUPLED SILICON SENSORS

Abstract A double-sided, double metal, AC coupled readout silicon microstrip sensor (DDSMS) has been developed for the SVX-II, the upgrade vertex detector for CDF. Key issue in the development is to achieve sufficient radiation hardness for survival in the radiation environment of several kGy/yr. The required high-voltage capability and the reduction of the readout capacitance of the double-metal side were critical design goals. Detailed design methods to radiation-hard silicon sensors are discussed.

Development of a gamma-ray imager using a large area monolithic 4 × 4 MPPC array for a future PET scanner

We report the development of a monolithic MPPC array, which consists of 3 × 3 mm2 elements arranged as a 4 × 4 array manufactured by Hamamatsu applicable to next generation PET scanners. We show that the MPPC is suitable for time of flight PET applications by simple measurement using coincident back-to-back 511 keV gamma rays. We demonstrated that the MPPC has much better timing resolution of ~ 600 ps than the APD. We coupled the monolithic MPPC array with the Ce:LYSO and Pr:LuAG scintillator matrices as gamma-ray detectors. The energy resolutions were evaluated as ~ 14% with 662 keV gamma-rays and the Ce:LYSO achieved the best. We also used a resistor network readout circuit with some optimization. The averaged positional resolution is estimated as ~ 0.27 mm in both x and y directions, while the energy resolution of each pixel was 9.9% for 662 keV gamma rays. Finally we applied the GHz class fast sampling waveform acquisition system to improve performance, and demonstrated efficient noise reduction by the clear detection of 22 keV gamma rays.

Application oriented development of multi-pixel photon counter (MPPC)

This paper describes the development of a large area monolithic array type MPPC and its package. The 16 channel 3×3mm elements are fabricated onto one die. A new buttable and non-magnetic type package was also developed for the monolithic array. Finally we describe the time resolution improvements by increasing the quenching resistor parallel capacitance.

Radiation effects of double-sided silicon strip sensors

Abstract A series of proton-beam irradiations was performed in order to investigate the radiation damage of silicon photodiodes and double-sided silicon strip sensors. Measurements were made for the leakage current, bias resistance, interstrip isolation, annealing and responses to an infrared light pulse and β-rays. Some problems in the production of radiation-hard double-sided strip sensors were observed. However, it has been shown that most of them can be resolved by adequately designing the strip structure, the implantation density and the materials used for various parts of the sensor. It is therefore possible to obtain a double-sided silicon strip sensor which works even after charged-particle irradiation of 20 kGy.

A study on the interstrip capacitance of double-sided silicon strip detectors

Abstract In high energy physics experiments, double-sided silicon strip detector are recognized as fast and highly precise tracking devices. There are still several key performances to be improved for more accurate and reliable measurements. One of them is the strip capacitance that dominate the signal-to-noise ratio. In order to study the capacitance of strips on each side of the double-sided silicon strip detector, several dedicated devices were designed and fabricated. We also tested the effects of radiation on the strip capacitance by exposing the detectors to 60 Co γ-rays.

High resolution phoswich gamma-ray imager utilizing monolithic MPPC arrays with submillimeter pixelized crystals

We report the development of a high spatial resolution tweezers-type coincidence gamma-ray camera for medical imaging. This application consists of large-area monolithic Multi-Pixel Photon Counters (MPPCs) and submillimeter pixelized scintillator matrices. The MPPC array has 4 × 4 channels with a three-side buttable, very compact package. For typical operational gain of 7.5 × 105 at + 20 °C, gain fluctuation over the entire MPPC device is only ± 5.6%, and dark count rates (as measured at the 1 p.e. level) amount to ≤ 400 kcps per channel. We selected Ce-doped (Lu,Y)2(SiO4)O (Ce:LYSO) and a brand-new scintillator, Ce-doped Gd3Al2Ga3O12 (Ce:GAGG) due to their high light yield and density. To improve the spatial resolution, these scintillators were fabricated into 15 × 15 matrices of 0.5 × 0.5 mm2 pixels. The Ce:LYSO and Ce:GAGG scintillator matrices were assembled into phosphor sandwich (phoswich) detectors, and then coupled to the MPPC array along with an acrylic light guide measuring 1 mm thick, and with summing operational amplifiers that compile the signals into four position-encoded analog outputs being used for signal readout. Spatial resolution of 1.1 mm was achieved with the coincidence imaging system using a 22Na point source. These results suggest that the gamma-ray imagers offer excellent potential for applications in high spatial medical imaging.

Characteristics of the irradiated Hamamatsu p-bulk silicon microstrip sensors

Microstrip silicon sensors with p-bulk and n-readout are investigated as a radiation hard device for the Super LHC experiment. We evaluated the radiation hardness of the sensors fabricated by Hamamatsu Photonics through irradiation with 70-MeV protons up to the fluence of 5 × 1015 1-MeV neq/cm2 and with 60Co γs at a rate foreseen at the Super LHC. The strip isolation and punch-through properties are characterized in detail. Various strip isolation structures, p-stop, p-spray and both combined, are examined. The results are compared among commercially available MCZ and two types of FZ wafers.