ICTPP09 R. Kass Radiation-Hardness of VCSELs & PINs Richard Kass The Ohio State University OUTLINE Introduction/ATLAS pixel detector Radiation Hardness of VCSELs Radiation Hardness of PINs Summary A. Adair, W. Fernando, K.K. Gan, H.P. Kagan, R.D. Kass, H. Merritt, J. Moore, A. Nagarkar, S. Smith, M. Strang The Ohio State University M.R.M. Lebbai, P.L. Skubic University of Oklahoma B. Abi, F. Rizatdinova Oklahoma State University

ICTPP09 R. Kass The Current ATLAS Pixel Detector A pixel module contains: 1 sensor (2x6cm) ~40000 pixels 16 front end (FE) chips 2x8 array Flex-hybrid 1 module control chip (MCC) There are ~1744 modules ~1.85m Present Pixel Detector: ATLAS’s Inner most charged particle tracker Measures (x,y,z) to ~30  m Pixel detector is based on silicon Pixel size 50  m by 400  m ~80 million pixels Radiation hardness is an issue must last ~ 10 years ATLAS: an LHC detector designed to study 14 TeV pp collisions Pixel detector is inner-most system -> Radiation damage is the issue Detector upgrades planned: New Inner layer (“IBL”) & later a new pixel detector for Super-LHC

ICTPP09 R. Kass Present Pixel Opto-link Architecture Current optical link of pixel detector transmits signals at 80 Mb/s Opto-link separated from FE modules by ~1m transmit control & data signals (LVDS) to/from modules on micro twisted pairs Use PIN/VCSEL arrays Use 8 m of rad-hard/low-bandwidth SIMM fiber fusion spliced to 70 m rad-tolerant/medium-bandwidth GRIN fiber  Simplify opto-board and FE module production  Sensitive optical components see lower radiation level than modules  PIN/VCSEL arrays allow use of robust ribbon fiber VCSEL: Vertical Cavity Surface Emitting Laser diode VDC: VCSEL Driver Circuit PIN: PiN diode DORIC: Digital Optical Receiver Integrated Circuit optoboard holds VCSELs, VDCs, PINS ~80m optoboard ~1m

ICTPP09 R. Kass Radiation Dosage at SLHC VCSEL/PIN of current pixel detector are mounted on patch panel (PP0) instead of directly on the pixel module  much reduced radiation level compared with module VCSEL/PIN for pixel detector at SLHC will be mounted further away from pixel module  expected dosage at r = 37 cm for 3,000 fb -1 with 50% safety factor: u silicon: 7.2 x MeV n eq /cm 2 u GaAs: 2.8 x MeV n eq /cm 2 Assuming radiation damage scales with Non-Ionizing Energy Loss (NIEL)

ICTPP09 R. Kass Real Time Monitoring in T7 Beam Test 2009 Beam Tests used a simple system Real time monitoring of PIN current & optical power. PIN diode arrays VCSEL arrays laser spot = beam spot Control Room 24 GeV proton beam

ICTPP09 R. Kass 850 nm VCSEL Irradiation : 12-channel VCSEL arrays were irradiated to SLHC dosage AOC 2.5 Gb/s (obsolete), 5 Gb/s, 10 Gb/s ULM 5 Gb/s, 10 Gb/s Optowell 2.5 Gb/s insufficient time for annealing during irradiation 2008: AOC 5 Gb/s, 10 Gb/s Optowell 2.5 Gb/s 2009: AOC 10 Gb/s goal: 20 arrays actual: 6 arrays due to manufacturer problem MPO connector MPO adaptor Opto-pack

ICTPP09 R. Kass AOC 10 Gb/s VCSEL (2008) Optical power recovery by annealing is slow Almost recover the initial power after extended annealing VCSEL produces more power at lower temperature 7.6 x MeV n eq /cm 2 irradiation annealing

ICTPP09 R. Kass AOC 10 Gb/s VCSEL (2009) irradiation annealing 145  W w/o long twisted/coil ed fiber Good optical power for 6 arrays irradiated Await return of arrays to OSU for annealing/characterization need to irradiate a sample of 20 arrays in x MeV n eq /cm 2

ICTPP09 R. Kass Gb/sResponsivity (A/W) GaAs (4.4 x MeV n eq /cm 2 )PrePost ULM AOC Optowell Hamamatsu G Si (7.5 x MeV n eq /cm 2 ) Taiwan Hamamatsu S Hamamatsu S / PIN Irradiation Irradiated 2 arrays or several single channel devices of each type Hamamatsu devices: low bandwidth but more radiation hard Irradiated 20 Optowell arrays in 2009

ICTPP09 R. Kass Responsivity doesn’t depend on bias voltage before irradiation Can increase responsivity with higher bias after radiation Optowell ULM PIN Responsivity vs Bias Voltage AOC 4.4 x MeV n eq /cm 2 Optowell Pre-irrad (2008)

ICTPP09 R. Kass PIN Responsivity vs Bias Voltage Can fully recover pre-irradiation responsivity with large bias voltage Need to look at pulse shape at high bias voltage Optowell

ICTPP09 R. Kass Eye Diagram at High Bias Voltage Test limited to 1 40 V due to carrier board limitation Eye diagram looks reasonable  need more detailed characterization Optowell

ICTPP09 R. Kass Results on Optowell PIN Arrays 8.1 x MeV n eq /cm 2 20 Optowell PIN arrays irradiated August 2009 Good responsivity after irradiation average responsivity after irradiation ~0.3 A/W Pre-Irrad Post-Irrad Channels Responsivity (A/W) 10 arrays Analysis of additional ten arrays complicated by beam misalignment Need more detailed study, including eye diagram after cool down.

ICTPP09 R. Kass Summary AOC 10 Gb/s arrays have good optical power after irradiation VCSEL produces more power as room temperature decreases Need to repeat irradiation with large sample in 2010 Hamamatsu PINs are slow but more radiation hard Optowell PIN arrays have good responsivity after irradiation Can increase responsivity with higher bias voltage after radiation Will irradiate a large sample of AOC PIN arrays in 2010 AOC plans to release high-speed PIN arrays in 2010

ICTPP09 R. Kass extra slides

ICTPP09 R. Kass Real Time Monitoring in T7 Beam Test test of opto-board system used loop-back setup data DORIC clock PIN VDC VCSEL Opto-board VDCVCSEL bi-phase marked optical signal decoded data decoded clock Signal routed back to opto-baord via test board attached to 80-pin connector & test board Bit error test setup at CERN’sT-7 beamline 24 GeV protons Compare transmitted and decoded data Measure minimum PIN current for no bit errors Measure optical power In control room 25m optical fiber cable In beam Two VCSEL arrays from same vendor per opto-board Opto-Chip setup