AC-coupled Microstrip Detectors Research Articles

A possible role for silicon microstrip detectors in nuclear medicine: Compton imaging of positron emitters

Collimation of gamma-rays based on Compton scatter could provide in principle high resolution and high sensitivity, thus becoming an advantageous method for the imaging of radioisotopes of clinical interest. A small laboratory prototype of a Compton camera is being constructed in order to initiate studies aimed at assessing the feasibility of Compton imaging of positron emitters. The design of the camera is based on the use of a silicon collimator consisting of a stack of double-sided, AC-coupled microstrip detectors (area 6×6 cm 2, 500 μm thickness, 128 channels/side). Two APV6 chips are employed for signal readout on opposite planes of each detector. This work presents the first results on the noise performance of the silicon strip detectors. Measurements of the electrical characteristics of the detector are also reported. On the basis of the measured noise, an angular resolution of approximately 5° is predicted for the Compton collimator.

A computerised analysis tool for the electrical characterisation of microstrip detectors

We report on a computer tool, based on Perl programming language, providing automatic analysis of experimental data from microstrip detector parametric measurements. Besides handling graphical display of data and statistical calculations, the program is intended to check for possible process-related problems by correlating the various measurements. The proposed software has proved itself to be a useful tool for the development of double-sided AC-coupled microstrip detectors at IRST, successfully identifying several process-related defects, as confirmed by optical inspection of the wafers.

Radiation tests with foxfet biased microstrip detectors

The silicon detectors at the future Large Hadron Collider (LHC) at CERN have to survive large particle fluxes up to a few 10 14 particles per cm 2. These high fluxes cause dramatic changes in the behaviour of the silicon detectors, like inversion of n-type silicon to p-type silicon. Here, we report on the high-voltage behaviour of silicon mictrostrip detectors up to doses of about 10 14 particles/cm 2, and the changes in the depletion voltage and inter-strip capacitance. The CMS baseline choice for the biasing element of the AC-coupled microstrip detectors is a polysilicon resistor. The silicon detectors, tested here, are Foxfet biased. We measured the changes in the Foxfet characteristics. Such detectors have been reported to show, after irradiation, a noise which is higher than expected. Using a fast amplifier (PREMUX chip), we also measure a higher noise.

A comparative evaluation of integrated capacitors for AC-coupled microstrip detectors

The electrical reliability of integrated capacitors to be used for AC-coupled microstrip detectors has been investigated by characterizing a specially designed test chip. Capacitors employing different stacked dielectrics, including double-layer oxide, oxide-nitride, and oxide-nitride-oxide insulators, have been compared in terms of intrinsic breakdown field and extrinsic failure distributions. Results obtained from two fabrication runs are presented and discussed. The impact of the different technological options adopted on diode leakage current and bulk- and surface-generation parameters is also reported.

Gallium arsenide AC-coupled microstrip detectors with integrated resistors

GaAs microstrip detector prototypes for the ATLAS forward tracker have been fabricated and tested. They feature integrated capacitors for AC-coupling and a novel biasing technique based on the high-resistivity substrate material with ohmic contacts. The strips are wedge shaped and the detector has a 5.5 cm long off-axis edge cut. The detector has been tested with the LBIC binary read-out chip in a beam test performed at the CERN SPS with 120 GeV π −, showing a 97% detection efficiency.

High spatial resolution silicon read-out system for single photon X-ray detection

A prototype detection system has been built for single photon X-ray detection which provides precise position and good energy measurements. The detecting element is a silicon microstrip detector, originally developed for high-energy physics. The readout is provided by a 16 channel prototype VLSI circuit, each channel consisting of a low-noise preamplifier followed by an RC-CR shaper (shaping time of 1500 ns) and a discriminator. The self-triggering property of the chip allows efficient X-ray detection. Two readout chips have been connected to the p-side of a FOXFET biased double-sided AC-coupled microstrip detector. The system has been tested with a multi-energy X ray source and at an X-ray diffractometer. Energy calibration is shown together with a few images, proving the good performance of the system for X-ray imaging. A Debye-Scherrer diagram has been recorded.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Degradation of silicon AC-coupled microstrip detectors induced by radiation

Results are presented showing the radiation response of FOXFET (field-oxide field effect transistor) biased AC-coupled microstrip detectors and related test patterns to be used in the CDF microvertex detector. The radiation tolerance of detectors to gamma and proton irradiation has been tested, and the radiation induced variations of the DC electrical parameters have been analyzed. The long-term post-irradiation behavior of detector characteristics has been studied, and the relevant room-temperature annealing phenomena have been considered. The main radiation damage effects after gamma or proton irradiation of FOXFET biased microstrip detectors consist of an increase of the total leakage current, while both the detector dynamic resistance and FOXFET switching voltage decrease. No radiation-induced variation of the strip self bias Vso is measured up to 1 Mrad. The above variations are due to the generation of Si/SiO/sub 2/ interface traps and positive charge accumulation in the oxide film, as confirmed by C-V measurements on MOS capacitors. >

Radiation effects on ac-coupled microstrip silicon detectors

The radiation hardness of FOXFET biased ac-coupled microstrip detectors, foreseen for the upgraded version of the vertex detectors (SVX') of the CDF experiment, has been studied. The detectors have been irradiated with 60Co γ rays with doses up to 1 Mrad. Two basic effects have been investigated: a variation of the switching voltage up to 100% due to oxide charge accumulation and Si/SiO 2 interface trap formation, and a 12-fold increase of the total leakage current, likely to come from surface damage. Moreover, a 10-fold decrease of the FOXFET dynamic resistance is observed at low gate bias. Post-irradiation annealing effects at room temperature of the electrical detector parameters are currently under investigation, in particular on a single shot 1 Mrad irradiated device. Recovery phenomena toward the pre-irradiation values are observed only for the switching voltage due to the annealing of trapped oxide charge.

Quantitative device simulation of double-sided silicon microstrip detectors

We present device simulation results for various geometries of double-sided ac-coupled microstrip detectors to be used in the LEP experiments ALEPH and DELPHI. We pushed the study beyond the usual qualitative step, and calculate, with satisfactory precision, a crucial parameter for these position sensitive detectors: the intership resistance. For the DELPHI microvertex, electrical insulation of strips is achieved on the “ohmic” side by means of a novel technique based on MOS-like structures. We demonstrate the possibility of simulating the details of the features of these new detectors, including temperature effects as well as geometrical variations of about 1 μm.

Measurement of spatial resolution of a double-sided AC-coupled microstrip detector

Capacitively coupled Si strip detectors with readout on both the p-side and the n-side have been developed. A novel scheme to separate strips ohmically on the n-side by means of field depletion via a suitable potential applied to the readout strips has been successfully demonstrated. Results on the spatial resolution of these detectors for both sides measured in a high energy beam are presented. The spatial resolution of the n-side has been measured at different incident angles of the beam tracks with respect to a vertical plane through the n + strips at 0°, 20° and 40°.