T. Kohriki

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.

Construction and performance of the ATLAS silicon microstrip barrel modules

Abstract The ATLAS Semiconductor Tracker (SCT) consists of four barrel cylinders and 18 end-cap disks. This paper describes the SCT modules of the barrel region, of which more than 2000 are about to be constructed. The module design is fixed. Its design concept is given together with the electrical, thermal and mechanical specifications. The pre-series production of the barrel modules is underway using mass-production procedures and jigs. The pre-series modules have given satisfactory performances on noise, noise occupancy, electrical as well as mechanical and thermal properties. In addition, irradiated modules were demonstrated to work successfully. Also first results from a 10-module system test are given.

Proton irradiation on p-bulk silicon strip detectors using 12 GeV PS at KEK

Abstract P-bulk n-strip silicon strip detectors were irradiated with a 12 GeV proton beam at the KEK Proton Synchrotron in order to investigate a radiation damage due to high fluence of high energy protons. Primary 12 GeV protons extracted at the EP1-A beam line was used for the irradiation. The detectors were irradiated with the fluences of 1.1 × 10 14 and 4.3 × 10 13 protons/cm 2 for the high and low fluence exposures, respectively. Bias voltage for achieving the full depletion of the irradiated p-bulk detectors was observed to be significantly higher than that for the n-bulk detectors. The full depletion voltage did not increase monotonically as the fluence increased; it showed little variation up to about 5 × 10 13 p/cm 2 and then started to increase. The behaviour could be explained by assuming a contribution from three processes: effective acceptor creation, persistent acceptor component, and acceptor removal.

Double-sided microstrip sensor for the barrel of the SDC silicon tracker

Abstract A full-size prototype microstrip sensor for the silicon tracker of the SDC detector to be used at the Superconducting Super Collider has been fabricated at Hamamatsu Photonics. The sensor is double-sided, using an AC-coupled readout with 50 μm pitch strips. The sensor size is 3.4 × 6.0 cm 2 . Polycrystalline silicon is used as a bias feeding resistor on both surfaces. Each ohmic strip is isolated by a p + blocking line. The detailed requirements for the silicon tracker and the corresponding specifications as well as how to achieve them are discussed. The static performances of this prototype sensor are presented.

Deep sub-micron FD-SOI for front-end application

In order to confirm benefits of a deep sub-micron FD-SOI and to identify possible issues concerning front-end circuits with the FD-SOI, we have submitted a small design to Oki Electric Industry Co., Ltd. via the multi-chip project service of VDEC, the University of Tokyo. The initial test results and future plans for development are presented.

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.

Radiation Resistance of SOI Pixel Devices Fabricated With OKI 0.15

Silicon-on-insulator (SOI) technology is being investigated for monolithic pixel device fabrication. The SOI wafers by UNIBOND allow the silicon resistivity to be optimized separately for the electronics and detector parts. We have fabricated pixel detectors using fully depleted SOI (FD-SOI) technology provided by OKI Semiconductor Co. Ltd. The first pixel devices consisting of 32×32 pixels each with 20 μm square were irradiated with ⁶⁰Co γ’s up to 0.60 MGy and with 70-MeV protons up to 1.3×10¹⁶ 1-MeV n<inf>eq</inf>/cm². The performance characterization was made on the electronics part and as a general detector from the response to RESET signals and to laser. The electronics operation was affected by radiation-induced charge accumulation in the oxide layers. Detailed evaluation using transistor test structures was separately carried out with covering a wider range of radiation level (0.12 kGy to 5.1 MGy) with ⁶⁰Co γ’s.Silicon-on-insulator (SOI) technology is being investigated for monolithic pixel device fabrication. The SOI wafers by UNIBOND allow the silicon resistivity to be optimized separately for the electronics and detector parts. We have fabricated pixel detectors using fully depleted SOI (FD-SOI) technology provided by OKI Semiconductor Co. Ltd. The first pixel devices consisting of 32times32 matrix with 20 mum times 20 mum pixels were irradiated with 60Co gammas up to 0.60 MGy and with 70-MeV protons up to 9.3times10 60Co p/cm2. The performance characterization was made on the electronics part and as a photon detector from the response to reset signals and to laser. The electronics operation was affected by radiation-induced charge accumulation in the oxide layers. Detailed evaluation of the characteristics changes in the transistors was separately carried out using transistor test structures to which a wider range of irradiation, from 0.12 kGy to 5.1 MGy, was made with 60Co gammas.

\mu {\rm m}

Nonirradiated and irradiated ATLAS silicon microstrip barrel and endcap modules have been beamtested with 4-GeV/c pions. Pulse shapes confirmed the peaking time of the amplifier to be 22 ns with slight deterioration in the irradiated modules. Median charges saturated around 3.8 fC, both in the nonirradiated and the irradiated modules. Signal/noise ratios, using the noise estimates from the in-situ calibration, were >16 in the nonirradiated (>150 V) and >10 in the irradiated (>300 V) barrel modules. No excess common-mode noise was observed.

FD-SOI Technology

Abstract We have examined experimentally some existing ideas for improving the radiation hardness of silicon microstrip sensors. We confirm that the extended electrode and the deep implant-strip proposed on the basis of simulation studies works effectively to suppress micro-discharge as well as junction breakdown of the bias or guard ring. For an integrated coupling capacitor a double layer structure of SiO 2 and Si 3 N 4 provides better radiation hardness than that of single SiO 2 coupling in our design conditions. The onset voltage of the micro-discharge on the bias/guard ring has been studied for an extended electrode and a floating guard ring.

Beamtest of non-irradiated and irradiated ATLAS SCT microstrip modules at KEK

We describe a new pixel detector development project using a 0.15 μm fully-depleted CMOS SOI (silicon-on-insulator) technology. Additional processing steps for creating substrate implants and contacts to form sensor and electrode connections were developed for this SOI process. A diode test element group and several test chips have been fabricated and evaluated. The pixel detectors are successfully operated and first images are taken and sensibility to β-rays is confirmed. Back gate effects on the top circuits are observed and discussed.