Planar Pixel Sensors Research Articles

Silicon Sensor Technologies for the ATLAS IBL Upgrade

An overview of radiation hard planar and 3D pixel sensor technologies currently under development for ATLAS upgrades is presented. T * he first upgrade will be the installation in 2013 of an additional pixel layer inside the current Detector, the Insertable B Layer (IBL). The two technologies are competing to equip the IBL. The IBL sensor qualification procedure is described. Beam test results of un-irradiated and irradiated planar and 3D sensors are presented.

Effects of Varying Substrate Thickness on the Collected Charge From Highly Irradiated Planar Silicon Detectors

The full exploitation of the physics potential of the LHC will require a significant upgrade program with detailed planning around proton-proton collisions running at 14 TeV with a target integrated luminosity of 3000 fb-1 implying innermost detector radiation levels approaching up to 2×1016 neqcm-2. Current experience with planar pixel sensors has been very positive in ATLAS, CMS and ALICE. Recent results by ourselves, and now by many others, have shown that the survival of planar processed silicon greatly exceeds expectations. It has been proposed that further advantages could be achieved by thinning detectors beyond the accepted standard of ~300 μm. In previous measurements, we have shown that thin detectors (140 μm) have higher collected charge and reverse current than standard thickness detectors (310 μm) after fluences of 2×1015 neqcm-2, where neq denotes the 1 MeV neutron equivalent fluence. In this paper, we extended our comparisons of collected charge and reverse current properties of micro-strip devices to three different bulk thicknesses: thin (140 μm), standard (310 μm) and thick (500 μm). These measurements confirm the trends seen in our earlier results.

Development of n-in-p silicon planar pixel sensors and flip-chip modules for very high radiation environments

Abstract In this paper we present RD small diodes were employed to investigate the width from the active diode to the dicing edge and the guard rings. Tests involving the diodes showed that the strong increase of leakage current was attributed to the edge current when the lateral depletion zone reaches the dicing edge and the lateral depletion along the silicon surface was correlated with the ‘field’ width. The onset was observed at a voltage of 1000 V when the width was equal to ∼400 μm. The pixel sensors that were diced at a width of 450 μm could successfully maintain a bias voltage of 1000 V. Hybrid flip-chip pixel modules with dummy and real chips were also fabricated. Lead (PbSn) solder bump bonding proved to be successful. However, lead-free (SnAg) solder bump bonding requires further optimization.

Radiation hardness studies of n+-in-n planar pixel sensors for the ATLAS upgrades

Abstract The ATLAS experiment at the LHC is planning upgrades of its pixel detector to cope with the luminosity increase foreseen in the coming years within the transition from LHC to Super-LHC (SLHC/HL-LHC). Associated with the increase in instantaneous luminosity is a rise of the target integrated luminosity from 730 to about 3000 fb−1 which directly translates into significantly higher radiation damage. These upgrades consist of the installation of a 4th pixel layer, the insertable b-layer IBL, with a mean sensor radius of only 32 mm from the beam axis, before 2016/17. In addition, the complete pixel detector will be exchanged before 2020/21. Being very close to the beam, the radiation damage of the IBL sensors might be as high as 5 × 10 15 n eq cm − 2 at their end-of-life. The total fluence of the innermost pixel layer after the SLHC upgrade might even reach 2 × 10 16 n eq cm − 2 . To investigate the radiation hardness and suitability of the current ATLAS pixel sensors for these fluences, n+-in-n silicon pixel sensors from the ATLAS Pixel production have been irradiated by reactor neutrons to the IBL design fluence and been tested with pions at the SPS and with electrons from a 90Sr source in the laboratory. The collected charge after IBL fluences was found to exceed 10 000 electrons per MIP at 1 kV of bias voltage which is in agreement with data collected with strip sensors. After SLHC fluences, still reliable operation of the devices could be observed with a collected charge of more than 5000 electrons per MIP.

Simulations of planar pixel sensors for the ATLAS high luminosity upgrade

A physics-based device simulation was used to study the charge carrier distribution and the electric field configuration inside simplified two-dimensional models for pixel layouts based on the ATLAS pixel sensor. In order to study the behavior of such detectors under different levels of irradiation, a three-level defect model was implemented into the simulation. Using these models, the number of guard rings, the dead edge width and the detector thickness were modified to investigate their influence on the detector depletion at the edge and on its internal electric field distribution in order to optimize the layout parameters. Simulations indicate that the number of guard rings can be reduced by a few hundred microns with respect to the layout used for the present ATLAS sensors, with a corresponding extension of the active area of the sensors. A study of the inter-pixel capacitance and of the capacitance between the implants and the high-voltage contact as a function of several parameters affecting the geometry and the doping level of the implants was also carried out. The results are needed in order to evaluate the noise and the cross-talk among neighboring pixels when connected to the front-end electronics.

The ATLAS Planar Pixel Sensor R&D project

Within the R&D project on Planar Pixel Sensor Technology for the ATLAS inner detector upgrade, the use of planar pixel sensors for highest fluences as well as large area silicon detectors is investigated. The main research goals are optimizing the signal size after irradiations, reducing the inactive sensor edges, adjusting the readout electronics to the radiation induced decrease of the signal sizes, and reducing the production costs. Planar n-in-p sensors have been irradiated with neutrons and protons up to fluences of 2 × 10 16 n eq / cm 2 and 1 × 10 16 n eq / cm 2 , respectively, to study the collected charge as a function of the irradiation dose received. Furthermore comparisons of irradiated standard 300 μ m and thin 140 μ m sensors will be presented showing an increase of signal sizes after irradiation in thin sensors. Tuning studies of the present ATLAS front end electronics show possibilities to decrease the discriminator threshold of the present FE-I3 read out chips to less than 1500 electrons. In the present pixel detector upgrade scenarios a flat stave design for the innermost layers requires reduced inactive areas at the sensor edges to ensure low geometric inefficiencies. Investigations towards achieving slim edges presented here show possibilities to reduce the width of the inactive area to less than 500 μ m . Furthermore, a brief overview of present simulation activities within the Planar Pixel R&D project is given.

Simulation of Radiation Damage Effects on Planar Pixel Guard Ring Structure for ATLAS Inner Detector Upgrade

We use ac and dc technology computer assisted design simulations to study the effects of radiation damage in the planar pixel sensors of the ATLAS inner detector upgrade, in particular on the active area and breakdown protection of different multiguard rings structure. Using a model of defect introduction into silicon band gap that agrees well with simulation up to fluences of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">15</sup> n <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eq</sub> /cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , we simulated how high radiation damage phenomena like space-charge sign inversion and double-junction formation affects the efficiency of different models of multiguard ring structures in n-type and p-type bulk. Depletion potential, potential distribution on guard rings, breakdown voltage, and leakage current were extracted from simulations to compare the behavior of the different models.