Atlas Pixel Replacement/Upgrade and Measurements on 3D sensors Forskerskole 2007 by E. Bolle erlend.bolle@fys.uio.no
Outline Sensors for Atlas pixel b-layer replacement/upgrade UiO activities CERN 3D test results 3D radiation hardness
Atlas Pixel Pixel Detector: Pixel detector is based on silicon Pixel size 50µm by 400 µm Inner layer 5cm from interaction point Radiation hardness is an issue, must last ~ 10 years Current b-layer will last 3 years Pixel Module: 1 sensor (2x6cm) ~45000 pixels 16 front end (FE) chips 2x8 array Flex-hybrid 1 module control chip (MCC) There are: ~1700 modules ~80M pixels
B-layer Replacement/Upgrade Schedule: 2012 - The b-layer has to be ready, to be replaced in the winter machine shutdown and to be ready to operate in 2013 2016 - Willseea major upgrade of the LHC machine components to obtain an higher luminosity ( ~10 ) and also ATLAS foresees a major upgrade with a completely new internal tracker. Replacement - basically no R&D time, some prototyping before production, strong mechanical and service constraints Upgrade - R&D planned, extensive prototyping, some mechanical and service constraints Kick-off: http://indico.cern.ch/conferencedisplay.py?confid=18750
Upgrade/replacement sensor candidates Technologies: n-on-n (present technology) n-on-p (Silicon) Thin sensor (Silicon) 3D (Silicon) Diamond Gossip (Gas) Important Specs: Radiation hardness Up to 10 16 n/cm 2 High efficiency Reduce dead edge Reduce material budget Low noise Capacitance Speed Reduce bunch crossing and pileup Realistic power budget Yield, large area, cost, large scale production
UiO Activities Testing of 3D sensors at CERN with Atlas front-end electronics -> prove that 3D sensor can be used with standard Atlas readout Responsible for test beam in October Analyze test beam data Liaison with SINTEF Collaboration for Atlas Pixel replacement/upgrade Project with MPI/Interon Characterization of SiPM
CERN 3D Testing Test Results Ole Rohne (ole.rohne@cern.ch) and Erlend Bolle (erlend.bolle@fys.uio.no) University of Oslo
Test Setup Location: Pixel Lab. 304-R-010 Keithley 2410 1100V source meter. Used to measure sensor leakage current. HP E3631A Triple Supply Used to supply +5V and -5V to the TPCC card. Agilent E3646A Dual supply. Used to supply +2V digital and +2V analogue to the front end card. Crate with: Turbo PLL card from LBNL MXIbus card, VME-MXI-2 Computer Pentium 4 Software: TurboDAQ Module Analysis Detectors (Stanford): 4 x 2E 9 x 3E 4 x 4E 50µm 400µm 2E 3E 4E
3D versus planar particle 3D n + p + n + p + n + p + n + p + n + p + PLANAR ~ 500 µm + + - + - - - - + - + 300 μm - - - - - + + + + + i Active edge ~4μm 50 μm n + 3D Advantages: Active edge Radiation hard Low depletion voltage Fast signal collection
FECs 3D sensor flip-chipped on FE-I3 Atlas Pixel ASIC FEC from LBL and Bonn 1 standard 2D pixel module FE-I3 3D Sensor FEC
FE-I3 Tuning FE-I3 Specs 2880 channels 50µm x 400µm pixels Synchronous pipeline Self triggering TOT(Time Over Threshold) measurement. Measure charge 7 bit threshold DAC for each pixel 3 bit TOT DAC for each pixel Tune targets: 3200e - threshold, dispersion < 50e - 30 TOT correspond to 20000e -, dispersion < 1 TOT
Results from Threshold Tune
Results from TOT Tune
Noise Measurement Fixed threshold Charged increased Error function convolution between ideal step function for the discriminator and sensor/system noise Fit to data gives sigma (noise) Tobias Stockmanns, Universität Bonn
Noise vs Bias Compensated for drop in HV series resistor Noise level stable above 35V for 3D Large drop around 30V
Noise Study Noise from FE-I3 compared with capacitance and leakage current measurements Capacitance and leakage measured at University of Bergen Noise driven by sensor capacitance up to 30V
Time Walk Threshold triggered system Difference between t and t gives the time walk New bunch crossing every 25ns Need to cross threshold within 20ns to be accepted How much overdrive is needed to cross threshold within 20ns?
Time Walk Overdrive (non-irradiated) ASIC setting IP = 64 IP = 128 1 IP = 196 2 Sensor IL = 64 IL = 96 IL = 64 2E-A 1807e - 1119e - 813e - 3E-G 2798e - 1828e - 1434e - 4E-C 3338e - 2122e - 1597e - Planar 1244e - 1. 20% total power increase 2. 40% total power increase
Leakage Current Plot only of good sensors Logarithmic scale on y-axis! Breakdown above 45V 1uA correspond to approx. 350pA/pixel
3E-F
Source Response Data taken with Cd-109 and Am-241 Am-241 close to 1 MIP (spatial distribution very different) Used 3 layers of copper tape between Am-241 source and detector to filter out low energy x-ray
Charge Sharing Find events occurring at the same time Low trigger rate Time stamped raw data All charge shared events originate from 59.5 kev 13% charge shared events Summed events without charge sharing Charge shared events
Linearity TOT values for the different Am-241 energy peaks 0 TOT equals threshold target of 3200e - Shows good linearity up to 1 MIP
Rate vs Bias Spectrum normalized with acquisition time Increase in noise with lower bias Less hits in the peak with lower bias Close to full signal amplitude at 10V Plotted events with a window from 25 to 28 TOT
Summary Atlas Pixel replacement/upgrade started UiO involved with 3D and thin sensors Shown good results for the 3D sensor together with Atlas readout A few things still not completely understood.. 3D is radiation hard
Backup
TOT Calibration Find TOT for different VCAL Make a 2 nd order fit to TOT values Use fit to calibrate each pixel for TOT variations 450VCAL 0.898mV / VCAL 7.923 ff = = 19998e 1.602 10 C Charge[e ] 19 450VCAL is the injected VCAL that corresponds to 30 TOT in the graph above 7.923fF is the injection capacitor 0.95 mv per DAC step 1.602*10-19 is the electron charge
TOT Response Am-241 source with copper filter Same number of events in all spectra Noise counts below 15V Lower efficiency with lower bias? Noise Charge shared events 40V 5V