S. Los

Timing Performances of Large Area Silicon Photomultipliers Fabricated at STMicroelectronics

In this paper the results of charge and timing resolution characterization realized at Fermi National Accelerator Laboratory (Fermilab) on 3.5 × 3.5 mm2 Silicon PhotoMultipliers fabricated at STMicroelectronics Catania R&D clean room facilities are presented. The device consists of 4900 microcells and has a geometrical fill factor of 36%. Timing measurements were realized at different wavelengths by varying the overvoltage and the temperature applied to the photodetector. The results shown in this manuscript demonstrate that the device, in spite of its large area, exhibits relevant features in terms of low dark current density, fast timing and very good single photoelectron resolution. All these characteristics can be considered very appealing in view of the utilization of this technology in applications requiring detectors with high timing and energy resolution performances.

Development of Picoseconds Time of Flight Systems in Meson Test Beam Facility at Fermilab

We describe here the development of a time of flight (TOF) system with 10–20 ps resolution for particle identification in a beam line. The detector resolution also was measured with the start and stop counters close together in the 120 GeV proton beam of the Fermilab Test Beam Facility. We tested both microchannel plate photomultipliers (MCP PMT) and silicon photomultipliers (SiPMs), in both cases using Cherenkov light produced in fused silica (quartz) radiators. Published by Elsevier B.V.

Electro-Optical Performances of p-on-n and n-on-p Silicon Photomultipliers

Silicon photomultipliers (SiPMs) are fabricated in two different configurations: p-on-n and n-on-p junctions. p-on-n SiPMs turn out to be more suitable for application in positron emission tomography (PET), due to their higher sensitivity in blue wavelength range where common PET scintillators have their emission spectrum. In this paper, we report on the electro-optical performances of the first p-on-n SiPMs manufactured at STMicroelectronics, Catania. The results obtained on these devices are compared with those measured on the standard n-on-p technology.

Large-area SiPMs for the CMS hadron outer calorimeter

We report on the measurement of pulse shape, gain, leakage current, and photon detection efficiency in 4-9 mm2 state-of-the-art silicon photomultipliers (SiPMs) obtained recently from the Center of Perspective Technology and Apparatus (CPTA) in Russia, Center for Scientific and Technological Research (ITC-irst) in Italy, and Hamamatsu Corporation in Japan. The CPTA and IRST SiPMs were used to read out a hodoscope of scintillators designed for the outer layer of the hadron calorimeter of the compact muon solenoid (CMS) with muon and pion beams at CERN. A direct comparison with CMS production hybrid photodiodes (HPDs) show that the SiPMs give an order of magnitude improvement in the signal to noise for single minimum ionizing particles (MIPs) and that the dynamic range is sufficient to detect up to 450 MIPs for use as a tail-catcher for late-developing hadronic showers in CMS.

Enhanced blue-light sensitivity P on N Silicon Photomultipliers

Silicon Photomultipliers (SiPMs) have known a fast development in recent years, due to their excellent single photon detection capability and very fast timing response. In this paper we present the results of the electro-optical characterization performed on the first STMicroelectronics P on N SiPMs prototypes properly designed for their possible application in Positron Emission Tomography (PET). We will show that the performances of the new devices are extremely promising in terms of high photon detection efficiency and fast timing response in blue wavelength range.

A silicon photomultiplier signal readout using transmission-line and waveform sampling for Positron Emission Tomography

We are investigating a new way of SiPM signal readout for Time-of-flight Positron Emission Tomography detector. Our new method adopts a transmission-line connected to multiple SiPMs in a row and high speed waveform sampling technology. The event information are retrieved from the digitized waveform measured at the two ends of the transmission-line; the interaction position along the strip direction is inferred from the arrival time difference at the two ends. With this approach, the number of readout channels can be efficiently reduced for larger detection area coverage by exploiting the fast time characteristic of SiPM while preserving the advantages of its compact size. We have built prototype transmission-line boards which holds up to eight SiPMs (3.5x3.5 mm2 and 5.0 mm pitch) on the strip. The waveforms of signals from the strip were recorded using DRS4 evaluation board at 5 GHz sampling rate. From the tests using pulsed laser and light emitting diode, the position along the strip could be determined in ~1 mm FWHM from the measured time difference on the strip. The responses to 511 keV photon were measured also in a coincidence setup; two LYSO scintillators (3×3×10 mm3) were coupled to the SiPMs on each transmission-line board, and a 22Na source was placed in the middle of the two LYSO scintillators with the distance of 12 cm. Preliminary results show that the position resolution of ~3 mm along the strip-line is achieved with LYSO+SiPM signal in addition to ~15% energy resolution at 511 keV and ~560 ps FWHM of coincidence time resolution. The results indicate that the investigated approach is a promising way for SiPM signal readout for TOF PET.

High fill factor P-on-N Silicon Photomultipliers for blue light detection

Silicon Photomultipliers (SiPMs) are fabricated in two different configurations: P-on-N and N-on-P junctions. More particularly P-on-N SiPMs are more suitable for application in Positron Emission Tomography (PET), due to their higher sensitivity in blue wavelength range where common PET scintillators have their emission spectrum. In this paper we will report on the electro-optical performances of the first P-on-N SiPMs manufactured at STMicroelectronics-Catania. The results obtained on these devices are compared with those measured on the standard N-on-P technology. We will show that the performances of the new devices are extremely promising in terms of higher photon detection efficiency in blue wavelength range and lower cross talk effects.

Radiation damage studies on SiPMs for calorimetry at the Super LHC

A typical scintillating tile sampling calorimeter consists of multiple layers of scintillators coupled to wavelength shifting fibers viewed by a suitable photo-detector. Long clear fibers are used to connect the tiles to the readout modules. We have investigated the use of silicon photomultipliers (SiPMs) at the Super Lagre Hadron Collider (SLHC). Because radiation hardness is the main concern, two sets of radiation data were taken using a 212 MeV proton beam at Massachusetts General Hospital. In the first data set we radiated up to a dose of 3×1010 protons per cm2 using diodes from three different manufactures (i.e., FBK, CPTA and Hamamatsu). At a dose of 3x1010 protons per cm2 only small effects of PDE loss were detected due to very high dark count always occupying one or more cells in a multi-cell SiPM. A second set of data up to 1013 protons per cm2 using very high pixel density MAPDs with up to 40,000 cells per mm2. After each small radiation dose multiple scope traces were taken to look at the PDE and dark count of the devices. The increase in dark count due to the radiation was compared to the DC leakage current. Also a comparison was made between multi-cell and single-cell samples of the FBK-IRST diodes.

Study of timing properties of silicon photomultipiers

A new setup has been made at Fermilab for detector timing measurements at picosecond level. The core timing resolution of the amplifiers, discriminators and TAC/ADC combination is approximately 2 picosecond. We have made a study of a single photoelectron time resolution (SPTR) measured for signals coming from silicon photomultipliers (SiPm) made by different manufacturers. The obtained SPTR is of the order of 180 picosecond with SiPms illuminated by red (635 nm) PiLas laser light. IRST SiPms show better SPTR when illuminated by the blue laser light (405 nm). Most of the data were taken with 1 Volt of the overvoltage. The SiPms time resolution is inversely proportional to the square root of the number of photoelectrons. A time-of-flight (TOF) system with few tens of picosecond time resolution, based SiPms with quartz Cherenkov radiators looks practically achievable. A simple model is proposed to explain the difference in SPTR of the IRST SiPms when illuminating by the blue and red light. The explanation of the origin of the tail in the MPPC SiPm’s single photoelectron time spectra is presented. Finally, requirements for the SiPms temperature and bias voltage stability to maintain few picosecond time resolution are discussed.

Notch filtering of RF interference in PET data for simultaneous PET-MR acquisition

We have developed a filtering method to reduce RF interference in PET data for simultaneously acquired PET-MR. Data was acquired from a SiPM-based PET detector coupled to LYSO scintillators using a transmission-line readout scheme and high-speed waveform sampling. The detector was placed within a 9.4 T small animal MR system with either copper or no shielding, and PET data from a low-activity 22Na source and LYSO background were acquired while MR images were also acquired. MR images showed no image quality degradation. 4% and 7% of PET waveforms demonstrated RF interference with and without shielding. After applying a notch filter, the energy spectrum of RF-affected events was comparable to RF-unaffected events due to improved measurement of the waveform maximum amplitude. Differential time measurements of events on the transmission-line were also improved. This study demonstrates the utility of waveform sampling readout which allows straightforward post-processing in PET data acquisition for simultaneous PET-MR.