Irradiated Dogleg Tests
Craig Macwaters, John Matheson and Tony Weidberg
26/7/02
Introduction
A complete module 0 style dogleg with a Taiwan VCSEL/PIN opto-package, DORIC4A and VDC and all the passive components was irradiated at T7 in August 2001. The fluence of 24 GeV/c protons was 3 1014 cm-2. The opto-package contained Truelight silicon PIN diodes and VCSELs[1]. Samples of the passive components used on the dogleg were also irradiated.
Passive Components.
The following passive components were irradiated:
Type of component / Manufacturers number / Component Value / Number IrradiatedResistor / MCR01M2SF1000 / 100 / 4
Resistor / MCR01M2SF1001 / 1 k / 5
Capacitor / CC0402CX7R103KTR / 10 nF / 5
Capacitor / CC0604CX7R104KTR / 100 nF / 5
The resistors were all within 1% of nominal value before and after irradiation.
The capacitors were all within 10% of the nominal value before and after irradiation.
The samples irradiated were taken from the reels that will be used in production.
PIN Diodes and Data link
The Pin responsivity before irradiation was ~ 0.33 A/W. The PIN responsivity versus bias voltage was measured after irradiation and the results shown in Figure 1. The behaviour is very similar to that seen with irradiation studies of bare PIN diodes. Note that the Centronic silicon PIN diodes use thinner active volumes and even after irradiation are fully depleted at 5V. The AC performance was checked by measuring the BER versus the DAC value which controls the VCSEL output power in the TTC link and the results are shown in Figure 2. These scans show that the TTC links work well and the performance is very similar to that seen before irradiation.
Figure 1 PIN responsivity versus bias voltage.
Figure 2 BER scans for the TTC link.
VCSELs and Data Links
The VCSELs initially showed a large threshold shift which annealed very rapidly after annealing with 20 mA current. The LI curves were measured while sending pseudo-random data at 40 Mbits/s and the optical power was corrected for the 50% duty cycle. The LI curves for the two VCSELs after 48 hours of annealing at 20 mA current is shown in Figure 3. The VCSELs showed threshold shifts of about 1 mA compared to before irradiation, which is typical for these types of VCSELs[1].
Figure 3 LI curves for the two VCSELs on the irradiated dogleg after annealing for 48 hours at 20 mA.
The eye diagrams on a ‘scope were very clean for the data links. The results of BER measurements versus the DAC value which sets the receiver threshold in OptIF are shown in and the results look very similar to similar measurements before irradiation.
Figure 4 BER scans for the data links.
Conclusions
The irradiated passive components (resistors and capacitors) showed no significant degradation. The degradation in the performance of the VCSELs and PIN in the Taiwan opto-package was as expected from previous studies of the irradiation of bare VCSELs and PINs and the irradiation of complete opto-packages. The data and TTC links were fully operational after the irradiation.
1
[1] The VCSELs were of the type that will be used in SCT but we will use Centronic silicon PIN diodes instead of the Truelight silicon PIN diodes used in these tests.
[1] Radiation Hardness and Lifetime Studies pf the VCSELs for the ATLAS SemiConductor Tracker, submitted to NIM, preprint available on