ATLAS: Minutes of the LARG electronics meeting on November 8th 19958. E delagnes (Saclay) : Non rad hard CMOS up to 50 krad; SCA in DMILL
In the crack between barrel and end-cap where we would like to have some electronics, the radiation is not totally negligible (about 25 krad/10years).
Standard AMS MOS transistors were irradiated up to 27 krad. Characteristics of PMOS transistors are not too much affected while an important (1 muA) leakage current develop in NMOS. Some annealing is observed. Such leakage currents would affect the operation of SCA.
Leakage currents are absent in the DMILL radhard technology even at doses as high as 10 Mrad. The PSALM SCA developed by Orsay/Saclay has been ported to DMILL. Interesting results are obtained : dynamic range stays at 11.8 bit for doses below 100 krad and only drops to 10.8 bit for a 10 Mrad dose.
A new chip with several improvements has been submitted and should be available for testing end april 96.
Conclusion: till about 50 krad safe with 'normal' electronics, above that radhard electronics should be considered
H1 expected about 15 krad/year. In 10 years of running that amounts to 150 krad in total. Non radhard electronics is used in their analog front-end on basis of that assumption. Measurements were made after Co60 irradiation. The chips were still functioning after a dose up to 160 krad, while after 250 krad large internal leakage currents were observed.
Hera-B requires a radiation hardness on their electronics of better than 100 krad. They expect less than 200 krad for R>7cm.
Sofar the knowledge on the radiation background is rather limited. The Status Report of 1993 quotes for the background radiation at the position of the VXD for nominal currents:
The total is <125 Gy/y=12 krad/y.
Radiation doses have been measured near the BPC (so far from the IP) as a function of distance. At 5 cm the dose was in 1994 about 1000 Gy=100 krad or more. The radiation is mainly coming from injection and dumping of the beam.
At the collaboration meeting of June 1996 numbers have been quoted for the synchroton radiation in the CTD of 2*10**8 gammas/s through the CTD after the luminosity upgrade. This would mean for the microvertex detector: 1 Gy/y; a minimal background from this source .
In case of the luminosity upgrade we could expect a factor 20 more radiation than presently or twice that for the nominal currents, so for an estimate based on the Status Report background <24 krad/y. This means that on basis of that number and a detector lifetime of 10 years radhard electronics would be required.
Placing of additional radiation minotors at several positions ,but especially at the vertex position, or installation of a Si-strip detector there, is essential to understand the radiation background better..
Please mail suggestion/corrections/updates to Leo Wiggers (wiggers.nikhef.nl)