R. Wheadon

Radiation damage by neutrons and protons to silicon detectors

Abstract Observations have been made of the behaviour of silicon diodes and microstrip detectors after exposures of up to 2 × 10 14 neutrons cm −2 and 4 Mrad 60 Co photons. Results are presented on leakage currents and doping concentration of the substrate material of neutron damaged devices. Important changes in the effective doping of the substrate have been observed to take place during the room temperature annealing of the material, particularly after high neutron fluences. Over times of more than one year further doping changes occur which increase the depletion voltage of type inverted material and may set an ultimate lifetime limit for silicon detectors in future hadron colliders. Measurements have been made of the performance of double sided microstrip detectors constructed using a field plate isolation technique on the n-type surface. After high doses of both neutrons and photons good interstrip isolation is maintained. demonstrating one potential technique for radiation tolerant microstrip fabrication.

Radiation tolerance of single-sided silicon microstrips

Abstract The RD20 collaboration is investigating the design and operation of an LHC inner tracking detector based on silicon microstrips. Measurements have been made on prototype detectors after irradiation with electrons, neutrons, photons, and protons for doses up to 5 Mrad and fluences up to 10 15 particles/cm 2 . The annealing of effective doping changes caused by high neutron fluences, one of the major limits to detector lifetime at the LHC, is shown to be strongly inhibited by cooling below room temperature. Detailed results are presented on the critical issue of microstrip capacitance. We have also investigated bulk damage caused by high-energy protons, interstrip isolation after neutron irradiation, and MOS capacitors irradiated with electrons and photons.

Punch-through currents and floating strip potentials in silicon detectors

Punch-through currents flowing between adjacent p/sup +/ strips on the surface of silicon microstrip drift detectors have been observed. Measurements of the floating strip potential have shown that a p/sup +/ strip acquires a voltage such that the punch-through current and the leakage current are equal and opposite. The factors influencing the threshold for the punch-through effect have been compared with a simple computer model, and the predicted variation with the interstrip gap is found to be in reasonable agreement with measured values for a variety of detectors. >

Radiation damage studies of field plate and p-stop n-side silicon microstrip detectors

Abstract We present results from studies of the properties of dedicated n-side microstrip structures before and after irradiation, with photons to 7 Mrad and fast neutrons to 8 × 10 13 ncm −2 . Both p-stop and field plate devices were investigated, each having a range of strip geometries in order to determine optimal configurations for long-term viability and performance.

Calculation of the geometrical capacitance of silicon microstrip structures using a variational approach

Abstract A lower limit to the capacitance of strip-like detectors, for example microstrips, is set by the geometrical capacitance of the electrodes. It is important to estimate this accurately so that proper account can be taken of additional effects such as surface charge layers in the device. We present a method for the calculation of multi-strip structure capacitances based on a variational technique which avoids the need to solve Poissons equation numerically in two dimensions for the structure in question. Instead, the solution is achieved starting from an approximate charge distribution function. This method is both simple to implement and efficient to run. Experimental results from two types of test device are presented and compared with the calculations. Firstly, microstrip structures were produced, varying both width and pitch. Secondly, 5 mm square diodes with their surfaces divided into connected strips have been produced with a range of different strip pitches.

Silicon drift photodiodes

Abstract Low capacitance photodiodes based on the principle of the solid state drift chamber have been constructred and tested. The devices are based on a cellular design with an anode at the centre of each of five cells allowing electrons liberated by ionisation to drift up to 1 mm to the readout strip. Results on the performance of the detectors, including leakage current, capacitance and drift properties, are presented and compared with simulations. A second series drift photodiodes have been processed which incorporate improvements based on results acquired from the first design. They have leakage currents of a few nA and shorter drift times at the periphery of the drift cells. We present measurements showing the performance of the new devices.

Radiation tolerance studies of silicon microstrip detectors for the LHC

Selected results are presented from the investigations by the RD20 collaboration into the suitability of silicon microstrip detectors for operation as elements of an inner tracking detector for the LHC. Single-sided prototypes covering a wide range of geometries have been irradiated with electrons, neutrons, photons, and protons up to doses of 5 Mrad and fluences of 1015 particles/cm2.

Radiation damage studies on single-sided and double-sided silicon microstrip detectors

The RD20 collaboration is investigating the operation of silicon microstrips as part of an inner tracking system at the LHC, an environment which requires both high speed readout and good radiation tolerance. We present measurements from both single-sided and double-sided microstrip test devices after neutron, proton, and photon irradiation up to fluences of 1014 particles/cm2 and doses of 10 Mrad. The double-sided microstrips include both field plate and p-stop isolation techniques. Important results include temperature dependence of long term irradiation-induced doping changes, strip isolation performance, and strip capacitance measurements.

Capacitance measurements on silicon microstrip detectors

The results of capacitance measurements on both the junction and ohmic sides of detectors with various geometries are presented. Double-sided detectors with a second metal layer and different readout patterns are also studied. Measurements are presented of microstrip capacitance after irradiation with both neutrons and photons. These measurements are made as part of the research by the RD20 collaboration into all aspects of the use of silicon microstrips at the Large Hadron Collider at CERN. >

Development Of Silicon Drift Chambers For X-Ray Astronomy

Detectors for x-ray (1-10 keV) astronomy based on silicon drift chamber (SDC) devices offer significant advantages over some types of existing detector and the potential performance of such devices is summarised. Our development program is outlined together with a discussion of device designs which are being pursued. Results are presented from some recently acquired two-dimensional drift devices working at room temperature, and from some large area drift diodes working at low temperature.