Agenda of SCT links meeting
 9:00 - 13:00 Thursday 18th Feb 1999   
 CERN Bat 40-R-D10

    


(1) PIN radiation/lifetime tests. G. Mahout
(2) Radiation tests of MITEL VCSELs I-M Gregor.
(3) Rad-hard fibre purchase. T. Weidberg
(4) Results with the new GEC VCSEL package. I-M Gregor/T. Weidberg
(5) BPM and DRX schedule. R. Wastie
(6) Further studies of DORIC4. I-M Gregor
(7) Cross-talk measurements for forward opto-packages T. Smith/Z. Dolezal/T. Weidberg
(8) Probe tests results for DORIC4 and radiation plans. D. White/T. Weidberg
(9) First tests of VDC I-M Gregor
(10) Results with the MITEL 4 channel PIN array. A. Rudge
(11) Results with the MITEL 4 channel VCSEL array. I-M Gregor
(12) Back of crate card status. M. Goodrick
(13) Fibre cavern cable. R. Wastie
(14) Dog-leg to low mass cable conenction. T. Weidberg
(15) New sources for rad-hard opto-packages. J. Dowell/T. Weidberg

Minutes

(1) PIN radiation and lifetime tests.
Gilles Mahout reported on the final results of the radiation tests of the PIN diodes.
The responsivity of the unirradiated sample was 0.48 +/- 0.01 A/W. The responsivity
of the smple irradiated to 10**15 n/cm**2 was 0.32 A/W. There was no significant
difference in responsivity for the samples irradiated to 3 10**14 and 10**15
n/cm**2. The depletion voltage was 5V (10V) for the samples exposed to neutron
fluences of 3 10**14 cm-2. The ageing tests have started using 96 PINs at a
temperature of 60C. No change in performance was observed over 4 days. Using an
activation energy of 0.6 eV, 1 week of operation at 60C is equivalent to 3 years of
LHC operation.
The transparencies are available here
ACTION on Gilles Mahout: Find out the temperature of the opto-package for the
forward SCT modules.

(2)Ingrid-Maria Gregor prsented results on radiation tests of MITEL VCSELs
The VCSELs were ST coupled MITEL 1A444
VCSELs. The VCSELs were exposed to 3 10**15 n/cm**2 at ISIS. All 4 devices
showed almost no optical output immediately after powering them on after the
exposure but showed rapid annealing and all four showed small threshold shifts after
annealing.
20 more VCSELs have been irradiated at ISIS and will be measured in Wuppertal.
Accelerated ageing tests will then be carried out.

.

(3)Tony Weidberg reported that the CERN order for 89km of 12-way ribbon fibre had gone out.
Japan will order the remaining 30km of fibre.

(4)Ingrid-Maria Gregor prsented results on the 5 new GEC VCSEL packages.
Visual inspection by Pedja Jovanovic showed that the silicon v-grooves
were very poorly made. All 5 packages had at least one working VCSEL but the
spread in output power was large. This is understood to be due to the poor fibre
alignment as a result of the poor quality v-grooves. This problem is understood by
GEC and they believe it can be fixed by correct calibration of the etching process and
by addition of sacrificial features such that the correct length v-grooves will be
present at the end of the processing. Stable operation of the VCSELs was possible and
no serious problems of modal instability were found (as seen by the Bern group with
Sandia VCSELs). A very large noise margin was obtained from a Bit Error rate
measurement.
Oxford will insert fibres into the spare lids and check the reproducibilty of the lid to
base connection. Assuming these tests are successful it was agreed to proceed with
phase 2 of the GEC programme, production of 60 VCSEL/PIN packages. It was
agreed to ask GEC to make 50 pig-tailed pacakges:
10 for the pixel detector
20 for the forward SCT modules
20 for the barrel SCT modules
GEC will also make 10 bases and 50 lids for us to use to learn more about how to put
fibres into lids.

(5)
Roy Wastie reported that the BPM chip has been submitted. Roy agreed to make
up more BiLED boards.
Roy reported on behalf of Dave White that the layout has been done for a 4 channel
DRX chip. Two additional channels wih hysteresis have been added to test the use of
hsyeteresis in DORIC.
The BPM status transparencies are available here.
The DRX status transparencies are available here.

(6)Ingrid-Maria Gregor prsented results on further studies of DORIC4.
It was
found that the addition of SMD filter network improved the performance of the
system significantly. The following changes are proposed to DORIC4
(a) improve the on-chip PIN bias filter.
(b) Change the frequency range for the lock in circuitry to avoid the possibility of
DORIC4 locking to 20 MHz.
(c) Change the fixed offset in the discriminator to hysteresis. This will remove the
problem of “two families” of recovered clocks at low optical power.
Ingrid Maria Gregor reported results on SEU studies of the PIN and DORIC4. No
significant rate of BER was observed with a source giving a flux of electrons a factor
two higher than the MIP rate in the B-layer of the pixel detector.
ACTION on John Dowell and John Wilson: investigate the use of the Birmingham
cyclotron for repeating these studies with heavy particles.
.

(7) X-talk measurements.

The measurement system and a summary of the results obtained with the Liverpool forward opto-modul test set-up are desribed here.
Tony Smith discussed the significance of the results for his design of the forward
modules. It was agreed to perform further tests with the grounding scheme and by
exchanging opto-packages. If these tests were not successful then it will probably be
necessary to increase the separation between and the number of ground pins between
the PIN and the VCSEL lines.
Zdenek Dolezal showed the results of the cross-talk measurements with his design for
the forward opto-modules. Significant cross-talk was observed. The layout was not
optimal from the point of view of cross-talk. An optimised test board will be made
and tested.
The transparencies are available here.

(8) DORIC4 radiation tests plan.

Tony Weidberg reported on the probe card tests of DORIC4 and ouelined the proposed radiation testing programme. The transparencies are available here.

(9)Ingrid-Maria Gregor prsented result on the first tests of VDC.
The chip was fully functional. The transparencies are available here.
.

(10) Alan Rudge reported results on the tests of the MITEL 4 channel PIN array.
The transparencies are avaialable here. We will try to obtain more channels of PIN array so that Alan can
make receiver boards with the MITEL PIN arrays.

(11) Ingrid-Maria Gregor prsented results on tests of the MITEL 4 channel VCSEL array.

The results were very encouraging. However we would like to change from a common cathode to common anode connection. Other users have requested this. Mark Pearce will discuss the timescale for this change with MITEL. If this not practical then we will have to change the driver cicruitry in BPM to use CMOS transistors.

(12)
Maurice Goodrick reported on discussions with MITEL for the VCSEL and PIN
packaging. See Maurcie's web site for details.

(13)
Roy Wastie reported on the status of the cavern cable. The cable would contain a
number (probably 8) 12 way ribbons. The cable would comply with CERN safety
regulations. A prototype cable is being developed by ERICSON. The development is
common between ATLAS and CMS. A problem that has emerged is that ERICSON
do not want to put in single fibres for laser safety monitoring. Mark Peaece will
discuss whether they can use 4 way ribbons for the safety fibre.
Roy will also discuss this cable with Fujikura to see if they could produce a suitable
cable.
The transparencies are avaialble here.

(14) Tony Weidberg showed examples of dog-leg (double sided copper on kapton)to

low mass (single sided Aluminium on kapton) tape solder connections.

The transparencies are available here.

(15) Other sources of on-detector opto-packaging.
Tony Weidberg reported on other sources (i.e. apart from GEC) for the on-detector
pacakges. A common development between CMS and ATLAS has started with
Honeywell. Discussions with Truelight are continuing. KK Gan (Ohio State University)
will produce some prototype ceramic packages to mount VCSELs.

The transparencies are available here