Giovanni Cervelli

Radiation-induced edge effects in deep submicron CMOS transistors

The study of the TID response of transistors and isolation test structures in a 130 nm commercial CMOS technology has demonstrated its increased radiation tolerance with respect to older technology nodes. While the thin gate oxide of the transistors is extremely tolerant to dose, charge trapping at the edge of the transistor still leads to leakage currents and, for the narrow channel transistors, to significant threshold voltage shift-an effect that we call Radiation Induced Narrow Channel Effect (RINCE).

Optical readout and control systems for the CMS tracker

The Compact Muon Solenoid (CMS) Experiment will be installed at the CERN Large Hadron Collider (LHC) in 2007. The readout system for the CMS Tracker consists of /spl sim/10 million individual detector channels that are time-multiplexed onto /spl sim/40000 uni-directional analogue (40MS/s) optical links for transmission between the detector and the /spl sim/65m distant counting room. The corresponding control system consists of /spl sim/2500 bi-directional digital (40Mb/s) optical links based upon the same components as far as possible. The on-detector elements (lasers and photodiodes) of both readout and control links will be distributed throughout the detector volume in close proximity to the silicon detector elements. For this reason, strict requirements are placed on minimal package size, mass, power dissipation, immunity to magnetic field and radiation hardness. It has been possible to meet the requirements with the extensive use of commercially available components with a minimum of customization. The project has now entered its volume production phase after successful completion of technical feasibility. Components have been identified that meet both the stringent analogue performance targets and are sufficiently radiation-hard for use in the CMS Tracker, where lifetime radiation exposure is expected to reach /spl sim/3.4/spl times/10/sup 14//cm/sup 2/ fluence and /spl sim/150kGy dose. Analogue and digital system performance, as well as the component radiation hardness and quality assurance procedures, are reviewed this paper.

G-link and gigabit Ethernet compliant serializer for LHC data transmission

Gbit/s data transmission links will be used in several LHC detectors in trigger and data acquisition systems. In these experiments, the transmitters will be subject to high radiation doses over the lifetime of the experiments. In this work, a radiation tolerant transmitter ASIC is described. The IC supports two standard protocols, the G-link and the Gbit-Ethernet, and sustains transmission of data at both 800 Mbit/s and 1.6 Gbit/s. The ASIC was implemented in a mainstream 0.25 /spl mu/m CMOS technology employing radiation tolerant layout practices. A 1.2 Gbit/s prototype with reduced functionality was tested. The ASIC behavior under total dose irradiation as well as its susceptibility to single event upsets was studied and the results are reported here.

A Radiation Tolerant Laser Driver Array for Optical Transmission in the LHC Experiments

A 3-way Laser Driver ASIC has been implemented in deep-submicron CMOS technology, according to the CMS Tracker performance and rad-tolerance requirements. While being optimised for analogue operation, the full-custom IC is also compatible with LVDS digital signalling. It will be deployed for analogue and digital transmission in the 50.000 fibre link of the Tracker. A combination of linearization methods allows achieving good analogue performance (8-bit equivalent dynamic range, with 250 MHz bandwidth), while maintaining wide input common-mode range (±350 mV) and power dissipation of 10 mW/channel. The linearly amplified signals are superposed to a DC-current, programmable over a wide range (0-55 mA). The latter capability allows tracking of changes in laser threshold due to ageing or radiation damage. The driver gain and laser bias-current are programmable via a SEU-robust serial interface. The results of ASIC qualification are discussed in the paper.

A 0.13-/spl mu/m CMOS serializer for data and trigger optical links in particle physics experiments

A 3.2-Gbit/s serializer prototype has been fabricated in a 0.13-/spl mu/m CMOS technology to demonstrate its applicability within future Large Hadron Collider (LHC) data readout and trigger systems. The IC includes a clock-multiplying phase-locked-loop (PLL), a 50-/spl Omega/ line driver, internal self-testing features, and data pattern generation. The serial output stream is 8 B/10 B encoded for compatibility with commercial receivers. Radiation hardening layout techniques have been adopted, which guarantee radiation tolerant operation inside the innermost LHC detectors over more than 10 yr. This paper describes the circuit architecture and reports on the experimental results. Signal quality (jitter, noise floor, eye opening) and bit-error rate (BER) are measured at different transmission rates using laboratory instrumentation and dedicated test beds.

ANALOGUE OPTICAL LINKS FOR THE CMS TRACKER READOUT SYSTEM

The optical fibre links for the analogue readout of the CMS tracker are based on the direct modulation of edge-emitting lasers located inside the detector volume. The front-end signals are transmitted by single-mode optical fibres and detected in the counting room using PIN photodiodes. One channel link demonstrators consisting of commercially available optoelectronic devices have been fully characterized. The lasers, fibres, and PIN diodes are representative of the devices intended to be used in the final system. The link overall performance is discussed in terms of its static and dynamic responses and is shown to meet the technical specifications of the full readout chain .

Ageing tests of radiation damaged lasers and photodiodes for the CMS experiment at CERN

The effects of thermally accelerated ageing in irradiated and unirradiated 1310 nm InGaAsP edge-emitting lasers and InGaAs p-i-n photodiodes are presented. 40 lasers (20 irradiated) and 30 photodiodes (19 irradiated) were aged for 4000 hours at 80/spl deg/C. Periodic measurements were made of laser threshold and efficiency, and p-i-n leakage current and photocurrent. There were no sudden failures and there was very little wearout related degradation in either unirradiated or irradiated sample groups. The results suggest that the tested devices have a sufficiently long lifetime to operate for at least 10 years inside the Compact Muon Solenoid experiment despite being exposed to a harsh radiation environment.

Radiation damage studies of optical link components for applications in future high-energy physics experiments

Optical data links are being developed at CERN for use in the tracking system of the Compact Muon Solenoid (CMS) experiment to be operated at the future CERN Large Hadron Collider. The radiation environment will be severe in the CMS tracker; simulations predict hadronic fluences > 1014/cm2 over an experimental lifetime of ten years, consisting of a mixture of neutrons, pions and protons over a wide energy spectrum, plus an ionizing dose of approximately 100 kGy. Candidate optical link components must therefore be qualified for sufficient radiation hardness. Results are presented for commercially available InGaAsP lasers and InGaAs p-i-n photodiodes irradiated with 330 MeV pions up to 5.4 X 1014 (pi) /cm2. The evolution of the laser threshold and efficiency with fluence is presented, in addition to the leakage current and photocurrent in the photodiodes. Comparisons are drawn with previous irradiation tests on identical devices using 6 MeV neutrons and 24 GeV protons, and ionizing damage due to 60Co gamma rays.

A linear laser-driver array for optical transmission in the LHC experiments

A 4-way linear laser driver has been designed and implemented in a commercial 0.25 /spl mu/m CMOS technology. The full-custom IC is intended for analogue and digital data transmission as part of the 50 000 optical fibre links of the CMS particle tracking system. Intrinsic radiation tolerance and specific design methodologies enable the device to operate over 10 years in the harsh radiation environment of the innermost LHC detectors. Although optimised for analogue operation the driver is compatible with LVDS digital signalling. A combination of linearization methods achieves good analogue performance (8-bit equivalent dynamic range with a bandwidth of 100 MHz), while maintaining wide input common-mode range (/spl plusmn/350 mV) and limited power dissipation. The linearly amplified signal is added to a DC current, which can be set over a wide range (-60 mA to +60 mA). The latter capability allows tracking of changes in laser threshold due to ageing or radiation damage. The driver gain and bias current are set via a serial interface. Measurements have been performed on individual chips-both in isolation and in combination with prototype optical links that confirm the full functionality of the device.

Characterization of laser diodes for analog parallel optical links

In this paper results from the evaluation and comparison of the analog performance of laser transmitters from several different manufacturers will be reported. The bulk of the tested devices were commercially available InGaAsP edge- emitters (1- and 4-way packages). The evaluation of the lasers is based on a semiautomatic setup that characterizes static properties such as slope efficiency, noise and linearity. The measured data is visualized in a compact way with system pass/fail criteria that enables easy comparison and selection of different laser diodes with respect to system noise, deviation from linearity an operating range.