Studies of silicon strip sensors for the ATLAS ITK project Miguel Arratia Cavendish Laboratory, University of Cambridge 1
ITK project and radiation damage Unprecedented large fluences expected for the High Luminosity era of the LHC, with aim to collect 3000 /fb ITK-strip layers need to endure 10e15 neq 2
Outline Quality assurance of full-size ATLAS12 prototype sensors Radiation damage studies using irradiated mini-sensors 3
Electrical characterization of large-area ATLAS12 prototypt sensors. 4
Semi-automatic probe station 5
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IV curves 9
CV curves 10
Visual inspection with CMM 11
Sensor bow with CMM 11x11 grid with 9.440 mm spacing Flat plane fitted and subtracted to obtain net bow 12
Full strip tests Test of strip integrity, measurement of bias resistance and coupling capacitance (both with LCR measurement) 13
Faulty strips Searching for systematic pattern, but statistics of defects is very small. 14
Coupling capacitance, Bias resistance 15
Coupling capacitance, Bias resistance 16
Summary 17
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Outline Quality assurance of full-size ATLAS12 prototype sensors Radiation damage studies using irradiated mini-sensors 19
ATLAS miniature prototypes, aka baby 1x1 cm2 from same wafer of main sensor Main purpose is for R&D (variation of some features) and irradiation with beams or nuclear reactors. Need to study how charge collection degradates with radiation damage 20
Ingredients for charge collection efficiency measurement Plastic scintillator coupled with photomultiplier (trigger) Radioactive source (90Sr) Readout electronics 21
DAQ system Comercial FPGA based DAQ system developed by Liverpool, Barcelona and Valencia Uses the LHCb Beetle chip, readout at 40 MHz. Analogue readout, for R&D purposes 22
Readout daughterboad 23
Wirebonding I have learnt how to use this automatic wirebonder machine (time of technicians in our groups is too precious to be bothering them all the time for this) 24
Wirebond evaporation due to microdischarges Learnt the hardway to give ample clearance from HV to ground wirebonds! 25
Mounting setup 26
Setting up PMT 27
Dark box, lead shielding 28
Room Temperature setup 29
Working room temperature setup, ready for Run-1 30
Pedestals and noise levels 31
Time distribution 32
Clustering Very simple clustering algorithm. Start with hit with highest S/N, then add strips to cluster until S/N is below 1.8 sigma. 33
Landau distribution Charge of clusters follows a Landau distribution, convolved with Gaussian resolution. 34
Most probable value vs charge Textbook like example of MPV vs bias voltage. This sensor (ATLAS07) reaches full depletion at about 200 V 35
Upgrade to cold setup Why do we need to measure at cold temperature? Goal is to study radiation damage on silicon sensors. Defects created by irradiation can diffuse. Effect calling annealing. It is highly dependent on temperature. Freeze sensor tu suppress annealing, to study the initial damage. Example: Leakage current increases with irradiation fluence but sensor cures if annealed 36
Moving setup to the fridge 37
Daughter board does include temperature sensor. Problem: but is near frontend chip, and there is a temperature gradient to sensor. Fridge includes its own temperature sensor. Problem: not near enough sensor/frontend chip. Placed a temperature sensor very near Si-sensor, Arduino controlled. Temperature also checked IR camara (during data taking). 38
IR camera placed inside the fridge. It was stored in dry storage before to avoid condensation. No large variations in temperature registered during operation. But still did not last long before pixels started to fade away 39
Some simple CAD I even did design a plug, seal, for flow of nitrogen to My wife (mechanical engineer) helped me with software :D 40
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CCE vs fluence, proton irradiation 43
CCE vs fluence, protons and neutrons 44
Annealing studies Radiation-induced damage anneals with temperature. Important to quantify the good and bad annealing time scales. I use this enviromental chamber to cook the sensors at 60C for controlled periods of time, in dry atmosphere (N2 flushing) 45
LabVIEW scripts to automate CCE measurement I learnt LabVIEW to automate process, only way to get voltage scan from 100V to 1kV with 1.5 hours per point, different annealing times and different sensors 46
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Setup for IV measurements 48
Setup for CV measurement 49
Setup for interstrip resistance 50
Examples were I learnt the hard way 51
My setup over time 52