S.Hou, Academia Sinica Taiwan

2Outline Optical links for ATLAS Laser-driver  fiber  PIN-driver LHC modules in service Rad-hard requirement for LHC/SLHC Radiation tests for LHC application and beyond Beam LCU, IUCF, Tohoku VCSEL: very rad-hard and fast (>1 GHz) PIN: candidate fast, rad-hard Si, GaAs products NIEL scaling revisited

3 Optical links for ATLAS inner detector Opto-flex: Holds VDCs, DORICs, PINs, VCSELs VDC: VCSEL Driver Circuit DORIC: Digital Optical Receiver Integrated Circuit –Binary readout, two links per module (redundancy) to the ReadOut Drivers (RODs) Total ~17500 links (SCT+pixel), data 40Mbits/sec –TTC (clock, L1 Trigger, commands) to detector modules, one link per module & redundancy by link to neighbouring module.

4 On-detector opto-electronics Fibres in furcation tubing silicon silicon Redundancy links Opto-package with fibres

5 Radiation SLHC Detector modules use opto-electronics for readout and control Rad-hard is required for Laser, PIN, drivers and fibres Fluence expressed for 1 MeV neutron equivalent of the NIEL (Non-Ionizing Energy Loss) calculations NIEL factors for Neutrons [MeV] 1 20 GaAs [keV cm 2 /g] Si [keV cm 2 /g] 1.8 NIEL factors for Protons [MeV] GaAs [keV cm 2 /g] Si [keV cm 2 /g] [Summers, IEEE NS (1993)] Radiation

6 Rad-hard tests for opto-electronics VCSEL and PINs tested for LHC New components of Hamamatsu tested for SLHC Beam tests at Cyclotron facilities −Louvain-la-Neuve CRC: neutron 20 MeV (av) of deutron on Be target −Tohoku CYRIC: proton 30, 70 MeV −Indianna IUCF: proton 200 MeV  same test setup, perform NIEL comparison CYRIC control room CRC beam area IUCF beam area

7 Beam tests setup  Online/Passive irradiations to VCSELs L-I-V measurements in 10nA annealing to 50 hours  a switching circuit reading PIN current to VCSELs, by NI6024 PCMCIA to PC  Online/Passive PIN current w. LED on/off I-V scan 0 to -20V, LED/beam on/off PIN current to Keithley/Agilent to NI-USB to PC VCSEL DAQ IUCF irradiatedCYRIC irradiated

8 Opto-electronics, VCSEL characteristics VCSEL: Vertical Cavity surface emitting laser diode −GaAs, thin active layer ‹10 μm, very rad-hard −high speed (>2GHz), 850 nm matching to thin epitaxial Si PIN diodes −Little uniform temperature dependence Two types (by Truelight inc.) in use −Proton implant VCSEL (ATLAS on detector) −Oxide confined VCSEL (off-detector on ROD) high power (mW), ch-ch performance is very uniform, little temperature deviation L-I of an VCSEL array of 12 channels,

9 VCSEL degradation is linear to fluence online recorded by rad-hard fiber readout independent to Flux rate Fast annealing by charge injection operation current (10 nA) applied VCSEL irradiation online, and annealing L-I of VCSEL (oxide) vs. online Fluence L-I of VCSEL (oxide) vs. Annealing time

10 VCSEL annealing in time  Charge injection at the nominal 10 nA laser current  Fit to f(t)= f ∞ - a  exp( -t/ τ )  recovery time  ~ 5 hours  uniform, low systematics over channels

11 VCSEL degradation vs proton energy & fluence  CYRIC 30 and 70 MeV proton Annealed L/L(0) shows 1. linear to fluence, 2. twice damage with 30 MeV than 70 MeV  Systematic errors mechanical matching ~5% fluence due to beam profile ~10% 1. Aluminum plate + isotope measurement 2. Dosimetry by film HD Nucl.Asso

12 Summary on VCSEL rad-hard  VCSEL in proton radiation (ATLAS, Truelight)  linear L-I, fast (>2 GHz)  fast annealing (~5hrs) after irradiation linear shift toward higher threshold current  less damaged with higher proton energy deviates from the NIEL calculation GaAs solar cell Srour, IEEE TNS 50, 653 (2003) VCSEL (GaAs) at I=10 mA

13 Proton damage to PIN  Proton damage to PINs reduced P-N depletion, lower responsivity  Wave form to damage (4x MeV p/cm 2 ) rise/fall time < 1 ns (20%-80%) Truelight PIN for ATLAS

14 PIN responsivity online  Proton beam on/off with LED light on/off  do online PIN V R scan beam on, beam off Each strip is a 0-20V scan Beam off: + LED on + LED off Beam on: + LED on + LED off ATLAS LHC PIN, Truelight Epitaxial Si PIN LED on LEDoff Quick recovery expelling dark current Forward bias (30 MeV p)

15 Candidate high speed PINs for SLHC 0-20V scans Beam off: LED on LED off Beam on: LED on LED off

16 PIN I-V scan versus fluence I-V curves for PINs after cumulated fluences  ATLAS PIN is a thick device ø=100 μm, V R =10V  damage is at the very beginning  Significant increase on dark current ~ 100nA/ch Candidate Hamamatsu PINs ø=100 μm, V R =2V, fc=2 GHz ø=40 μm, V R =5V, fc=3 GHz I LED on I dark prior to irradiation

17 Summary on PIN proton damage Degradation of responsivity (I/L) proton 2E14 30 MeV 70 MeV V R fc diam. I/L I/L Dark I/L Dark Vol GHz μm A/W ratio nA ratio nA Truelight % 70 45% 50 S % % 20 S % % 10 S % % 50 G % 0 80% 0 G % 0 72% 0 G % 0 72% 0  PIN rad-hard depend on fabrication parameters thickness vs A/W vs speed & rad-hard  Proton energy dependence Si PIN : compatible damage by 30 and 70 MeV proton GaAs PIN : twice damage by 30 MeV than 70 MeV

18 Conclusion Conclusion − Optical link provides low mass, no cross talk key elements: laser and PIN are thin devices − VCSEL is very rad-hard and is fast for >GHz − PINs can be rad-hard and fast too − NIEL scaling does not apply for GaAs devices