* Corresponding author. Tel.: #39 49 827 7236; e-mail: darold@mxsld2.pd.infn.it. Nuclear Instruments and Methods in Physics Research A 409 (1998) 139 — 141 High-voltage operation of silicon devices for LHC experiments N. Bacchetta, D. Bisello, A. Candelori, M. Cavone, G.-F. Dalla Betta, M. Da Rold*, G. De Liso, R. Dell’Orso, P.G. Fuochi, A. Messineo, A. Mihul, O. Militaru, A. Paccagnella, G. Tonelli, P.G. Verdini, G. Verzellesi, R Wheadon  Universita % di Padova, Dipartimento di Fisica and INFN, Sezione di Padova, I-3 5131 Padova, Italy  Universita % di Padova, Dipartimento di Elettronica e Informatica and INFN Sezione di Padova, Padova, Italy  Microelectronics Laboratory Tecnopolis Csata N.O., Valenzano, Bari, Italy  Universita % di Trento, Dipartimento di Ingegneria dei Materiali, Trento, Italy  Universita % di Pisa, Dipartimento di Fisica and INFN, Sezione di Pisa, Pisa, Italy  CNR-FRAE, Bologna, Italy  IFA and University of Bucharest, Bucharest, Romania  INFN Sezione di Trieste, Trieste, Italy Abstract High-voltage operation can be a solution to obtain full charge collection in strongly irradiated silicon detectors. The maximum bias voltage which can be applied is limited by the breakdown point of the junction. We show how multiguard structures can enhance the breakdown voltage in p—n silicon devices designed for applications in the LHC environ- ment.  1998 Elsevier Science B.V. All rights reserved. 1. Introduction Silicon microstrip detectors equipping the inner layers of the LHC trackers will be subject to severe bulk damage leading to type inversion and change of the depletion voltage with time. In p—n devices this may lead to loss of charge collection efficiency due to partial depletion of the detectors and to effects related to the low fields at the microstrip side after type inversion. On the other hand p—n detectors are much more simple with respect to non-conventional n—n devices and very convenient in terms of cost and fabrication reliability. For these reasons CMS has chosen the p—n approach as baseline option. High-voltage operation may be used to over- come the problems induced by irradiation in p—n devices. It has been already shown that, by ap- plying high bias voltage, full charge collection can be achieved in heavily irradiated devices [1]. The results may be further improved by the use of guard ring structures which can limit the occurrence of critical fields and increase the breakdown voltage. Detectors reaching breakdown voltage above 500 V could be fully operational in the inner layers of CMS for fluences up to 2—310 part/cm. Multiguard structures appear to be very promis- ing to enhance the breakdown performance of 0168-9002/97/$19.00  1998 Elsevier Science B.V. All rights reserved PII S0168-9002(97)01252-7 II. TRACKING (SOLID STATE)