Binary Readout Research Articles

The ATLAS SemiConductor Tracker operation and performance

The ATLAS SemiConductor Tracker (SCT) is a key precision tracking detector in the ATLAS experiment at CERN's Large Hadron Collider.The SCT is composed of 4088 planar p-in-n silicon micro-strip detectors. The signals from the strips are processed in the front-end ABCD3TA ASICs, which operate in binary readout mode; data are transferred to the off-detector readout electronics via optical fibres.The SCT was completed in 2007. An extensive commissioning phasefollowed, during which calibration data were collected and analysed todetermine the noise performance of the system, and further performanceparameters of the detector were determined using cosmic ray data, bothwith and without magnetic field. After the commissioning phase, theSCT was ready for the first LHC proton-proton collisions in December2009.From the beginning of data taking, the completed SCT has been in verygood shape with more than 99% of its 6.3 million strips operational;the detector is well timed-in and the operational channels are 99.9%efficient in data acquisition. The noise occupancy and hit efficiencyare better than the design specifications. The detector geometry ismonitored continuously with a laser-based alignment system and isstable to the few-micron level; the alignment accuracy as determinedby tracks is near specification and improving as statisticsincrease. The sensor behaviour in the 2T solenoidal magnetic fieldhas been studied by measuring the Lorentz angle. Radiation damage inthe silicon is monitored by periodic measurements of the leakagecurrent; these measurements are in reasonable agreement withpredictions.

Oil-sealed femtoliter fiber-optic arrays for single molecule analysis.

This paper describes a novel method for fabricating and sealing high-density arrays of femtoliter reaction chambers. We chemically etch one end of a 2.3 mm diameter glass optical fiber bundle to create an array of microwells. We then use a contact printing method to selectively modify the surface of the material between microwells with a hydrophobic silane. This modification makes it possible to fill the wells with aqueous solution and then seal them with a droplet of oil, forming an array of isolated reaction chambers. Individual β-galactosidase molecules trapped in these reaction chambers convert a substrate into a fluorescent product that can be readily detected because a high local concentration of product is achieved. This binary readout can be used for ultra-sensitive measurements of enzyme concentration. We observed that the percentage of wells showing enzyme activity was linearly dependent on the concentration of soluble β-galactosidase in the picomolar range. A similar response was also observed for streptavidin-β-galactosidase captured by biotinylated beads. These arrays are also suitable for performing single-molecule kinetics studies on hundreds to thousands of enzyme molecules simultaneously. We observed a broad distribution of catalytic rates for individual β-galactosidase molecules trapped in the microwells, in agreement with previous studies using similar arrays that were mechanically sealed. We have further demonstrated that this femtoliter fiber-optic array can be integrated into a PDMS microfluidic channel system and sealed with oil on-chip, creating an easy to use and high-throughput device for single-molecule analysis.

Bakelite RPCs for Digital Hadron Calorimeter

Abstract This paper presents the test results of Bakelite RPCs using readout pads with an area of 1 cm×1 cm and 1-bit resolution per pad (binary readout). The results include noise rate, detection efficiency and pad multiplicity as well as comparisons of different surface treatments for Bakelite plates. Pad multiplicity’s dependence on surface resistivity at the readout side is also reported. This study shows Bakelite RPCs can be used as the active elements of digital hadron calorimeter.

Design and performance of a CMOS study sensor for a binary readout electromagnetic calorimeter

We present a study of a CMOS test sensor which has been designed, fabricated and characterised toinvestigate the parameters required for a binary readoutelectromagnetic calorimeter.The sensors were fabricated with several enhancementsin addition to standard CMOS processing.Detailed simulations and experimental results of the performance of the sensor are presented. The sensor and pixels are shown to behave in accordance with expectations and the processing enhancementsare found to be essential to achieve the performance required.

The ATLAS silicon microstrip tracker. Operation and performance

In December 2009 the ATLAS experiment at the CERN Large Hadron Collider (LHC) recorded the first proton-proton collisions at a centre-of-mass energy of 900 GeV. This was followed by collisions at the unprecedented energy of 7 TeV in March 2010. The SemiConductor Tracker (SCT) is a precision tracking device in ATLAS made up from silicon microstrip detectors processed in the planar p-in-n technology. The signal from the strips is processed in the front-end ASICs working in binary readout mode. Data is transferred to the off-detector readout electronics via optical fibers. The completed SCT has been installed inside the ATLAS experiment. Since then the detector was operated for two years under realistic conditions. Calibration data has been taken and analysed to determine the performance of the system. In addition, extensive commissioning with cosmic ray events has been performed both with and without magnetic field. The sensor behaviour in magnetic field was studied by measurements of the Lorentz angle. After this commissioning phase it arrived to the first LHC pp collision runs in very good shape: 99% of the SCT strips are operational, noise occupancy and hit efficiency exceed the design specifications, the alignment is already close enough to the ideal one to allow online track reconstruction and invariant mass determination.

Particle pixel detectors in high-voltage CMOS technology—New achievements

Abstract Particle pixel detectors in standard high-voltage CMOS technology are a new detector family that allows implementation of low-cost radiation-tolerant detectors with good time resolution. In order to test the concept we have implemented three detector variants. The first variant uses simple four-transistor pixel electronics that allows the rolling-shutter readout. The second variant implements complex CMOS pixel electronics with particle hit detection on pixel level and binary readout. The third variant uses the readout based on the capacitive chip-to-chip signal transmission. In this paper we will present the recent experimental results.

Performance evaluation of 3D-DDTC detectors on p-type substrates

In this work, we report on the noise and signal properties of n-on-p, 3D Double-Side Double Type Column (3D-DDTC) detectors fabricated at FBK-irst (Trento, Italy). Compared to full 3D detectors, devices made with this approach allow for a simpler fabrication process, but the efficiency and speed of the charge collection process critically depend on the column overlap and should be carefully evaluated. Measurements were performed on detectors in the microstrip configuration coupled to the ATLAS ABCD3T binary read-out. Spatially resolved signal efficiency tests made with a pulsed infrared laser setup and charge collection efficiency tests made with a β source setup are here reported.

Environmental dependence of the performance of resistive plate chambers

This paper reports on the performance of Resistive Plate Chambers (RPCs) as function of the gas flow rate through the chambers and of environmental conditions, such as atmospheric pressure, ambient temperature and air humidity. The chambers are read out by pads with an area of 1 × 1 cm2 and 1-bit resolution per pad (binary readout). The performance measures include the noise rate as well as the detection efficiency and pad multiplicity for cosmic rays. The measurements extended over a period of almost one year and are sensitive to possible long-term aging effects.

A MAPS-based readout for a Tera-Pixel electromagnetic calorimeter at the ILC

The majority of the proposed detector concepts for the ILC are built around the particle flow algorithm (PFA) approach which requires a highly granular calorimeter. The leading proposed technology for a PFA electromagnetic calorimeter at the ILC is using silicon-tungsten. We have developed a monolithic active pixel sensor for silicon-tungsten calorimeters, which would have extremely fine granularity, allowing binary pixel readout and the usage of digital electromagnetic calorimetry. A first generation chip (TPAC 1.0) has been fabricated, which contains a 168 × 168 pixel array, consisting of 50 × 50 μ m 2 pixels with integrated charge pre-amplifier and comparator. TPAC 1.0 has been manufactured in the 180 nm CMOS INMAPS process which includes a deep p-well implant. We present recent results of the performance of the TPAC 1.0 chip and give an outlook on its successor TPAC 1.1.

Design of Time Invariant Analog Front-End Circuits for Deep N-Well CMOS MAPS

This work is concerned with the design of time invariant analog circuits for processing the signals from deep N-well monolithic CMOS sensors. As compared to the three-transistor front-end typically used in imaging applications, the schemes proposed here, which were conceived to be included in a binary readout channel, lend themselves to pixel-level sparsified readout and are expected to be capable of managing the large flow of data anticipated for the future high luminosity colliding machines while obeying quite severe material budget requirements. Various solutions complying with different power dissipation and point resolution constraints have been implemented in a 130 nm CMOS technology, paying particular attention to equivalent noise charge and threshold dispersion performance. This paper intends to describe and compare the features of the different approaches by means of simulations, experimental results and theoretical analysis.

Development of Binary Readout CMOS Monolithic Sensors for MIP Tracking

Recently, CMOS Monolithic Active Pixels Sensors (MAPS) have become strong candidates for pixel detectors used in high energy physics experiments. A very good spatial resolution lower than 5 mum can be obtained with these detectors. A recent fast MAPS chip, designed in AMS CMOS 0.35 mum Opto process and called MIMOSA16 (HiMAPS2), was submitted to foundry in June 2006. The chip is a 128times32 pixels array where 8 columns have analog test outputs and 24 columns have their outputs connected to offset compensated discriminator stages. The pixel array is addressed row-wise. The array is divided in four blocks of pixels with different charge-to-voltage conversion factors and is controlled by a serially programmable sequencer. The sequencer operates as a pattern generator which delivers control signals both to the pixels and to the column-level discriminators. Discriminators have a common adjustable threshold. This chip is the basis of the final sensor of the EUDET-JRA1 beam telescope which will be installed at DESY in 2009. In this paper, laboratory tests results using a <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">55</sup> Fe source together with beam tests results obtained at CERN using Minimum Ionizing Particles (MIPs) are presented.

Laser and beta source setup characterization of 3D-DDTC detectors fabricated at FBK-irst

We report on the functional characterization of the first batch of 3D Double-Sided Double Type Column (3D-DDTC) detectors fabricated at FBK, Trento. This detector concept represents the evolution of the previous 3D-STC detectors towards full 3D detectors, and is expected to achieve a performance which is comparable to standard 3D detectors, but with a simpler fabrication process. Measurements were performed on detectors in the microstrip configuration coupled to the ATLAS ABCD3T binary readout. This paper reports spatially resolved signal efficiency tests made with a pulsed infrared laser setup and charge collection efficiency tests made with a Beta source.

Design of fundamental building blocks for fast binary readout CMOS sensors used in high-energy physics experiments

In this paper, design details of key building blocks for fast binary readout CMOS monolithic active pixel sensors developed for charged particle detection are presented. Firstly, an all-NMOS pixel architecture with in-pixel amplification and reset noise suppression which allows fast readout is presented. This pixel achieves high charge-to-voltage conversion factors (CVF) using a few number of transistors inside the pixel. It uses a pre-amplifying stage close to the detector and a simple double sampling (DS) circuitry to store the reset level of the detector. The DS removes the offset mismatches of amplifiers and the reset noise of the detector. Offset mismatches of the source follower are also corrected by a second column-level DS stage. The second important building block of these sensors, a low-power auto-zeroed column-level discriminator, is also presented. These two blocks transform the charge of the impinging particle into binary data. Finally, some experimental results obtained on CMOS chips designed using these blocks are presented.

Hexagonal pixel detector with time encoded binary readout

The University of Hawaii is developing continuous acquisition pixel (CAP) detectors for vertexing applications in lepton colliding experiments such as SuperBelle or ILC. In parallel to the investigation of different technology options such as MAPS or SOI, both analog and binary readout concepts have been tested. First results with a binary readout scheme in which the hit information is time encoded by means of a signal shifting mechanism have recently been published. This paper explains the hit reconstruction for such a binary detector with an emphasis on fake hit reconstruction probabilities in order to evaluate the rate capability in a high background environment such as the planned SuperB factory at KEK. The results show that the binary concept is at least comparable to any analog readout strategy if not better in terms of occupancy. Furthermore, we present a completely new binary readout strategy in which the pixel cells are arranged in a hexagonal grid allowing the use of three independent output directions to reduce reconstruction ambiguities. The new concept uses the same signal shifting mechanism for time encoding, however, in dedicated transfer lines on the periphery of the detector, which enables higher shifting frequencies. Detailed Monte Carlo simulations of full size pixel matrices including hit and BG generation, signal generation, and data reconstruction show that by means of multiple signal transfer lines on the periphery the pixel can be made smaller (higher resolution), the number of output channels and the data volume per triggered event can be reduced dramatically, fake hit reconstruction is lowered to a minimum and the resulting effective occupancies are less than 10 - 4 . A prototype detector has been designed in the AMS 0.35 μ m Opto process and is currently under fabrication.

Detection of Single-Molecule DNA Hybridization Using Enzymatic Amplification in an Array of Femtoliter-Sized Reaction Vessels

Improving the sensitivity of DNA biosensors is extremely important in clinical diagnostics, gene therapy, and a variety of other biomedical studies. In this regard, we have developed a highly sensitive single molecule DNA assay platform with a 1fM experimental detection limit using enzymatic amplification in an array of femtoliter-sized reaction wells. To validate the utility of this technology in our study, we employed a fiber optic array to create thousands of femtoliter-sized reaction wells, each specifically functionalized with oligonucleotide probes capable of capturing biotinylated target DNA. After hybridization, the fiber was incubated with streptavidin-labeled enzyme solution. The bound single enzyme molecules were confined to individual reaction vessels containing excess fluorogenic substrate and catalyzed the production of a sufficient number of fluorescent product molecules to generate a detectable signal. At low target DNA concentrations with relatively short incubation times, only a small percentage of the capture sites bind target DNA, enabling a binary readout of target concentration from the high-density fiber array. This simple binary readout-based scheme is easy to perform and exhibits a high signal-to-noise ratio in the presence of trace amounts of DNA target. Furthermore, it also should be possible to extend this technology to protein detection by modifying the reaction wells with specific capture antibodies. We expect this assay to be useful in a number of biomedical applications where accurate and highly sensitive target analysis is critical.

Validation of Real-Time Methylation-Specific PCR to Determine O6-Methylguanine-DNA Methyltransferase Gene Promoter Methylation in Glioma

Epigenetic silencing of the DNA repair protein O(6)-methylguanine-DNA methyltransferase (MGMT) by promoter methylation predicts successful alkylating agent therapy, such as with temozolomide, in glioblastoma patients. Stratified therapy assignment of patients in prospective clinical trials according to tumor MGMT status requires a standardized diagnostic test, suitable for high-throughput analysis of small amounts of formalin-fixed, paraffin-embedded tumor tissue. A direct, real-time methylation-specific PCR (MSP) assay was developed to determine methylation status of the MGMT gene promoter. Assay specificity was obtained by selective amplification of methylated DNA sequences of sodium bisulfite-modified DNA. The copy number of the methylated MGMT promoter, normalized to the beta-actin gene, provides a quantitative test result. We analyzed 134 clinical glioma samples, comparing the new test with the previously validated nested gel-based MSP assay, which yields a binary readout. A cut-off value for the MGMT methylation status was suggested by fitting a bimodal normal mixture model to the real-time results, supporting the hypothesis that there are two distinct populations within the test samples. Comparison of the tests showed high concordance of the results (82/91 [90%]; Cohen's kappa = 0.80; 95% confidence interval, 0.82-0.95). The direct, real-time MSP assay was highly reproducible (Pearson correlation 0.996) and showed valid test results for 93% (125/134) of samples compared with 75% (94/125) for the nested, gel-based MSP assay. This high-throughput test provides an important pharmacogenomic tool for individualized management of alkylating agent chemotherapy.

Test Beam Characterization of 3-D Silicon Pixel Detectors

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Three-dimensional (3-D) silicon detectors are characterized by cylindrical electrodes perpendicular to the surface and penetrate into the bulk material in contrast to standard Si detectors with planar electrodes on the top and bottom. This geometry renders them particularly interesting to be used in environments where standard silicon detectors have limitations, such as, for example, the radiation environment expected in an upgrade to the Large Hadron Collider at CERN. For the first time, several 3-D sensors were assembled as hybrid pixel detectors using the ATLAS-pixel front-end chip and readout electronics. Devices with different electrode configurations have been characterized in a 100 GeV pion beam at the CERN SPS. Here, we report results on unirradiated devices with three 3–D electrodes per 50<formula formulatype="inline"> <tex Notation="TeX">$\,\times \,$</tex></formula>400 <formula formulatype="inline"> <tex Notation="TeX">$\mu {\rm m}^{2}$</tex></formula> pixel area. Full charge collection is obtained already with comparatively low bias voltages around 10 V. Spatial resolution with binary readout is obtained as expected from the cell dimensions. Efficiencies of 95.9%<formula formulatype="inline"><tex Notation="TeX">$ \pm$</tex></formula>0.1% for tracks incident parallel to the electrodes and of 99.9%<formula formulatype="inline"><tex Notation="TeX">$ \pm$</tex></formula>0.1% for tracks incident at 15<formula formulatype="inline"> <tex Notation="TeX">$^{\circ}$</tex></formula> are measured. The homogeneity and charge sharing of the efficiency over the pixel area are measured. </para>

A new class of cleavable fluorescent nucleotides: synthesis and optimization as reversible terminators for DNA sequencing by synthesis †

Fluorescent 2′-deoxynucleotides containing a protecting group at the 3′-O-position are reversible terminators enabling array-based DNA sequencing by synthesis (SBS) approaches. Herein, we describe the synthesis of a new family of 3′-OH unprotected cleavable fluorescent 2′-deoxynucleotides and their evaluation as reversible terminators for high-throughput DNA SBS strategies. In this first version, all four modified nucleotides bearing a cleavable disulfide Alexa Fluor® 594 dye were assayed for their ability to act as a reversible stop for the incorporation of the next labeled base. Their use in SBS leaded to a signal–no signal output after successive addition of each labeled nucleotide during the sequencing process (binary read-out). Solid-phase immobilized synthetic DNA target sequences were used to optimize the method that has been applied to DNA polymerized colonies or clusters obtained by in situ solid-phase amplification of fragments of genomic DNA templates.

Measurements of Matching and High Count Rate Performance of Multichannel ASIC for Digital X-Ray Imaging Systems

We present the measurements of matching and high count rate performance of a 64 channel readout ASIC called DEDIX for high count rate position-sensitive measurements using semiconductor detectors. The ASIC is designed in 0.35 mum CMOS process and its total area is 3900 times 5000 mum <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The DEDIX has a binary readout architecture. Each channel is built of a charge sensitive amplifier (CSA) with a pole-zero cancellation circuit, a shaper, two independent discriminators and two independent 20-bit counters. The size of the input device in CSA has been optimized for a detector capacitance in the range of 1-3 pF per strip. An equivalent noise charge of 110 el rms has been achieved for a total detector capacitance of 1 pF at the shaper peaking time of 160 ns. Internal correction DAC implemented in each channel independently ensures a low spread of discriminator effective threshold, namely 0.4 mV at one sigma level. The mean gain in the multichannel ASIC is 54 muV/el, with a good uniformity from channel-to-channel (sd/mean ap 0.8%). Low noise performance and high rate capability have been demonstrated by the measurement up to and above 1 MHz average rate of input signals.

Fast binary readout front-end electronics for silicon strip detectors for low energy x-ray imaging applications

A binary readout architecture of multichannel front-end electronics used in a position-sensitive measurement system provides fully parallel signal processing, including data storage, and is the best one to cope with high intensity x-ray radiation. However, for low x-ray energy applications, the noise and matching performance of multichannel ASIC impose contradictory requirements on the high rate capability of the front-end electronics. These important aspects of ASIC design are analysed in this paper for two different generations of multichannel ASICs produced in CMOS technology and dedicated to low energy x-ray imaging applications using a silicon strip detector.