E.H.M. Heijne

Radiation tolerant VLSI circuits in standard deep submicron CMOS technologies for the LHC experiments: practical design aspects

We discuss design issues related to the extensive use of Enclosed Layout Transistors (ELTs) and guard rings in deep submicron CMOS technologies in order to improve radiation tolerance of ASICs designed for the LHC experiments (the Large Hadron Collider at present under construction at CERN). We present novel aspects related to the use of ELTs: noise measured before and after irradiation up to 100 Mrad (SiO/sub 2/), a model to calculate the W/L ratio and matching properties of these devices. Some conclusions concerning the density and the speed of ICs conceived with this design approach are finally drawn.

A readout chip for a 64 x 64 pixel matrix with 15-bit single photon counting

A single Photon Counting pixel detector readout Chip (PCC) has been derived from previous work in the CERN RD19 collaboration for particle physics tracking devices, recently developed for high energy physics experiments. The readout chip is a 64 x 64 matrix of identical 170 {micro}m x 170 {micro}m cells. It is to be bump-bonded to an equally segmented 1 cm{sup 2} matrix of semiconductor sensors, e.g. Si or GaAs. Each readout cell comprises a preamplifier, a discriminator and a 15-bit counter. The input noise is 170 e{sup {minus}} rms. At the lowest nominal threshold of 1,400 e{sup {minus}} (5.1 keV in Si) the cells exhibit a threshold distribution with a spread before adjustment of 350 e{sup {minus}} rms. Each cell has a 5-bit register which allows masking, test-enable and 3-bit individual threshold adjust. After adjustment the threshold spread is reduced to 80 e{sup {minus}} rms. Absolute calibration of the electrically measured equivalent charge can be done once the readout chip is bump-bonded to a detector.

The Medipix3RX: a high resolution, zero dead-time pixel detector readout chip allowing spectroscopic imaging

The Medipix3 chips have been designed to permit spectroscopic imaging in highly segmented hybrid pixel detectors. Spectral degradation due to charge sharing in the sensor has been addressed by means of an architecture in which adjacent pixels communicate in the analog and digital domains on an event-by-event basis to reconstruct the deposited charge in a neighbourhood prior to the assignation of the hit to a single pixel. The Medipix3RX chip architecture is presented. The first results for the characterization of the chip with 300 μm thick Si sensors are given. ~ 72e− r.m.s. noise and ~ 40e− r.m.s. of threshold dispersion after chip equalization have been measured in Single Pixel Mode of operation. The homogeneity of the image in Charge Summing mode is comparable to the Single Pixel Mode image. This demonstrates both modes are suitable for X-ray imaging applications.

ICON, a current mode preamplifier in CMOS technology for use with high rate particle detectors

A current mode preamplifier named ICON is intended for use in experiments at high-rate hadron colliders. The transient response and noise performance have been analyzed. One chip has been made using an ICON circuit with resistive feedback to produce a preamplifier with a peaking time below 10 ns. This fast preamplifier has a gain of 870 mV/pC and a power dissipation of around 1 mW. Another chip was made which uses the ICON circuit as the front-end to a dual port analog memory. The noise measured is between 2500 e/sup -/ and 3000 e/sup -/. An important characteristic of ICON is that it can tolerate a detector leakage current of 10 mu A at the DC coupled input. Therefore, it is very suitable for silicon detector systems under several radiation conditions.<<ETX>>

First operation of a 72-k element hybrid silicon micropattern pixel detector array

Abstract We have constructed and tested silicon pixel detector arrays of 96 × 378 (36 288) sensor elements with 75 μm × 500 μm area. The low-noise signal processing circuit associated with each element occupies an identical area on a bump-bonded readout chip. The pixel cell response for ionizing particles is binary with an adjustable threshold between 4000 e − and 15 000 e − . Single chips, the array of 6 ladders and a double array have been characterized in particle test beams and in the Omega experiment WA97 at CERN. The two arrays together, staggered by ∼ 4 mm cover hermetically a 53 mm × 55 mm area with 72 576 pixels. The proportion of properly functioning pixels was 98% in the first 36 k pixel array and 80% in the second one. The ∼ 1% “always-on” pixels could be masked electronically. After masking the rate of “spurious noise hits” was −8 of the identified particle hits while with beam off no hits at all were recorded With a beam trigger most events consisted of a single cluster with a single hit. At the 8000 e − threshold an efficiency > 99% was measured. Tracks were reconstructed with a precision of 22 μm. The proportion of double hits (∼ 11%) depends only slightly on threshold and detector bias voltage, and for these double hits a precision of 10 μm on the particle position was obtained.

Study of characteristics of silicon detectors irradiated with 24 GeV/c protons between −20°C and +20°C

High resistivity ion-implanted silicon pad detectors have been irradiated at +20°C, +10°C, 0°C and −20°C with 24 GeV/c protons at a flux of ∼ 5 × 109cm−2s−1, up to fluences of ∼ 1.1 × 1014cm−2, and maintained at these temperatures during several months after the end of irradiation. The change of the diode reverse current, full depletion voltage and collection efficiency of the charge, deposited by relativistic electrons, are presented as a function of the proton fluence and of annealing time. It is found that operating the detectors below +10°C limits the diode reverse current and the bias voltage necessary to achieve full depletion. Moreover, at these temperatures, the charge collection efficiency for an integration time of 20 ns (typical of LHC operation) is better than 90% for 300 μm detectors irradiated to a fluence of 1014 cm−2 and biased at 160 V.

Imaging properties of the Medipix2 system exploiting single and dual energy thresholds

Low noise, high resolution, and high dose efficiency are the common requirements for most X-ray imaging applications. The dose efficiency is especially important for medical imaging systems. We present the imaging performance of the Medipix2 readout chip bump bonded to a 300 mum thick Si detector as a function of the detection threshold, a free parameter not available in conventional charge integrating imaging systems. Spatial resolution has been measured using the modulation transfer function (MTF) and it varies between 8.2 line-pairs/mm and 11.0 line pairs/mm at an MTF value of 70%. An associated measurement of noise power spectrum (NPS) permits us to derive the detective quantum efficiency (DQE) which can be as a high as 25.5% for a broadband incoming spectrum. The influence of charge diffusion in the sensor together with threshold variation in the readout chip is discussed. Although the Medipix2 system is used in photon counting mode with a single threshold in energy, the system is also capable of counting within a given energy window as narrow as ~1.4 keV. First measurements and images using this feature reveal capabilities that allow identifying fluorescence and other sources of disturbance

Pixel readout electronics development for the ALICE pixel vertex and LHCb RICH detector

The ALICE1LHCB pixel readout chip emerged from previous experience at CERN. The RD-19 collaboration provided the basis for the installation of a pixel system in the WA97 and NA57 experiments. Operation in these experiments was key in the understanding of the system issues. In parallel the RD-49 collaboration provided the basis to obtain radiation tolerance in commercial submicron CMOS through special circuit layout. The new ALICE1LHB chip was developed to serve two different applications: particle tracking in the ALICE Silicon Pixel Detector and particle identification in the LHCb Ring Imaging Cherenkov detector. To satisfy the different needs for these two experiments, the chip can be operated in two different modes. In tracking mode all the 50 μm×425 μm pixel cells in the 256×32 array are read out individually, whilst in particle identification mode they are combined in groups of 8 to form a 32×32 array of 400 μm×425 μm cells. The circuit is currently being manufactured in a commercial 0.25 μm CMOS technology.

Deep submicron CMOS technologies for the LHC experiments

Abstract The harsh radiation environment at the Large Hadron Collider (LHC) requires radiation hard ASICs. This paper presents how a high tolerance for total ionizing dose can be obtained in commercial deep submicron technologies by using enclosed NMOS devices and guard rings. The method is explained, demonstrated on transistor and circuit level, and design implications are discussed. A model for the effective W/L of an enclosed transistor is given, a radiation-tolerant standard cell library is presented, and single event effects are discussed.

X-ray imaging using single photon processing with semiconductor pixel detectors

More than 10 years experience with semiconductor pixel detectors for vertex detection in high energy physics experiments together with the steady progress in CMOS technology opened the way for the development of single photon processing pixel detectors for various applications including medical X-ray imaging. The state of the art of such pixel devices consists of pixel dimensions as small as 55 55 m 2 , electronic noise per pixel <100 e rms, signal-to-noise discrimination levels around 1000 e with a spread <50 e and a dynamic range up to 32 bits per pixel. Moreover, the high granularity of hybrid pixel detectors makes it possible to probe inhomogeneities of the attached semiconductor sensor.