Citterio, M

Kierstead, J A

Rescia, S

CERN Document Server

THE ATLAS CALORIMETER PREAMPLIFIER: PERFORMANCE,RADIATION DAMAGE, ELECTROSTATIC DISCHARGE RESISTANCE,RELIABILITY AND MANUFACTURING ISSUES*M. Citterio, J. Kierstead, and S. Rescia (email: citterio@bnl.gov)Brookhaven National Laboratory, Upton, NY 11973-5000AbstractThe requirements, design, measured specification ofthe ATLAS liquid argon (LAr) calorimeter preamplifiersare reviewed. The experience gained so far inproduction, the quality assurance and testing, as well asthe reliability estimate according to MILSTRESSstandard will be discussed.1.  INTRODUCTIONThe preamplifiers are the first amplification stage inthe LAr readout architecture, which set the noiseperformance of the calorimeter. They amplify the analogsignal generated at the calorimeter electrodes.Figure 1 shows a picture of the liquid argon Front-EndBoard (FEB). The preamplifiers are at the input of theboard and are connected via a transmission line to thedetector electrodes. The space allocated on the FEB forthe preamplifiers have dictated the aspect ratio of thecircuits and, up to certain extent, the technology adoptedfor the production.Figure 1. Photograph of a FEB board. The inputsignals come into the board from the two externalconnectors at the bottom. The preamplifiers areimmediately above the input connectors. Eight hybridsare encircled in the picture.*The U.S. Department of Energy supports this work: ContractNo. DE-AC02-98CH10886.Each FEB contains 128 channels of amplification, 64channels on each side of the card grouped in two blockof 32 channels each. The preamplifiers are moreovergrouped in block of four channels and have been realisedin a hybrid package the dimension of which are 53.3 mmin length and 23.0 mm in width. The preamplifierhybrids are independent units that plug into the FEB.About 190,000 read-out channels or about ~ 47,500hybrids are needed for the LAr calorimeter.More than one type of preamplifier/hybrid is requiredto accommodate the different characteristics of thedetector. The detector structure (impedance, capacitance,etc.), the estimated maximum energy deposited perreadout cell as a function of rapidity, together with theneed of a maximum output signal of about 3 to 4 Volt,determine that three types of preamplifiers must be used.These three type of preamplifiers share a same generalcircuit diagram which has been properly “optimised” forthe different sections of the calorimeter.2. PREAMPLIFIER DESIGN2.1  Requirements and SpecificationThe preamplifier requirements and specification aredescribed in detail in the ATLAS LAr Technical DesignReport (TDR) [1].The most important ones can be summarised asfollow:- Noise: as low as possible with respect to pile-up,Rnoise = 10 Ω, typical Equivalent Noise Current (ENI)values are in Table 1.- Uniformity: TDR: < 5 % in amplitude for triggersums (< 1 % meas.), TDR: < +/- 2 ns timing (< +/- 1 nsmeas.).- Power dissipation: TDR: < 100 mW/ch.- Environment: must tolerate 20 Gy/year (2 krad/year)and 1012 n/cm2year.- Reliability: < 0.5 % missing channel per year.- ESD discharge: must withstand 4 mJ multipledischarge without damage (i.e. 2 KV on 2 nF typical).- Stability: must be stable even in case of presence offaults in the signal chain (short, open).- Output impedance: must be able to drive a 50 Ω load(i.e. the shaper input impedance).- Dynamic range: up to 10 mA, depending onrapidity range.Table 1: Typical noise valuesPreamp type ENI [nA]50 Ω / 1mA 50 @ CD = 330 pF, tp = 46 ns25 Ω / 5mA 125 @ CD = 1500 pF, tp = 53 ns25 Ω / 10 mA 270 @ CD = 2200 pF, tp = 40 ns2.2  Preamplifier circuitThe LAr preamplifiers are coupled to the detector by atransmission line. As the signal duration is longcompared to the shaping time, current preamplifiers areused which provide a voltage output directlyproportional to the input current.The main characteristic of the ATLAS preamplifier isthe use of a local feedback in the input stage to attributethe functions of low noise and high dynamic range totwo different transistors. This circuit configurationallows to improve the linearity and to reduce the noisewhile reducing the power dissipation by a factor of three(to about 50 mW) with respect of the first generationRD3 preamplifier [4]. The gain (i.e., the transresistance)and the input impedance can be chosen independentlywithout changing the power supply voltages and powerdissipation.The principle of coupling a preamplifier to a highcapacitance detector and a detailed description of theATLAS implementation are described in ref. [2, 3]. Thecircuit schematic is shown in Figure 2.Figure 2. Preamplifier schematic.Figure 3. Hybrid Layout.2.3  Preamplifier TechnologyThe preamplifiers have been manufactured by meansof thick film hybrid technology. This technology is awell-known technology with predictable time schedulefor production and high reliability, as proven in manyhigh-energy physics experiments. Moreover each devicecan be chosen to optimise its function (e.g. low noise)and many different type of devices (NPN, PNP,decoupling capacitors, etc.) are available.Use of a more advanced monolithic technology wasrejected because of the higher development costs (acomplementary bipolar process featuring low noise,radiation resistant transistors was necessary) and higherrisks associated with the research and development, bothin terms of performance and schedule.The hybrid design has been carried out with veryconservative design rules (10 mils line, 10 milsseparation) to both expand the pool of manufacturers andto improve the production yield. The layout is shown inFig. 2.3.  PREAMPLIFIER CHARACTERISTICSThe hybrid preamplifier design has been tested andverified through the productions of 200 prototypes firstand 1600 hybrids to equip LAr Mod0, subsequently.The information gathered during these preliminaryphases would be used to optimise the final production.Gain, peaking time, noise and input impedance werethe main parameters of interest. Radiation tolerances toionising radiation and to neutrons were also measured.23 mm53 mmDesign Rules:Lines: 10 milSpaces:  10 milCeramic Thickness: 40 milPins:No: 20Grid: 100 milPower Supply:+ 10 V+   3 V -   3 VThe results obtained are summarised in the followingsections.Finally stability analysis was performed. Thepreamplifiers were found stable for any value of cablelength and detector capacitance foreseen for the LArcalorimeter [5].3.1 Parameter DistributionThe preamplifier characteristics meet and exceed thespecification. Figure 3 illustrates peaking time,amplitude and noise distribution for the preamplifiertype Zin/Imax = 50Ω / 1mA.All the preamplifiers are within +/- 3σ from theaverage value. Similar results were obtained for theother preamplifier types.The preamplifier input impedance for each hybridtype is summarised in Table 2.Table 2: Input impedancePreamp Type Zin Tolerance50 Ω / 1 mA 51.4 Ω +/- 2.9 %25 Ω / 5 mA 25.8 Ω +/- 1.8 %25 Ω / 10 mA 26.3 Ω +/- 1.7 %3.2  Preamplifier Radiation ToleranceExpected gamma doses over the life of thepreamplifiers is estimated to be approximately2 x 104 rad silicon. It is expected that the total possibledose would be no more than five times this number or105 rad. Two hybrid preamplifiers under power wereexposed to a total of 105 rad. One was a 50 Ω impedancedevice and the other was a 25 Ω impedance device. Bothhybrids were measured for gain, peaking time, ENI, andinput impedance before irradiation and after total dosesof 5 x 104 and 105 rad of 60Co gamma radiation. Gain,peaking time, and ENI changed by less than themeasuring error for both hybrids after 10 5 rad.Average input impedance (of 4 channels) at selecteddoses for the two devices is shown in Table 3.Table 3: Input impedance versus doseunirradiated 5 x 104 rad60Co105 rad 60Co51.3 Ω 50.1 Ω(2.3% change)48.8 Ω(4.9% change)25.4 Ω 25.3 Ω(0.4% change)25.2 Ω(0.8% change)Preamplifier hybrids were irradiated with fast neutronsat the SARA facility, Grenoble [6].No noise degradation was measured till a fluence of5 x 1013 n/cm2. The neutrons induce a degradation of theforward-gain β of the NEC856 (NPN) transistors used inthe circuit. The β degradation follows theMessenger-Sprat relation and, at first order, is inverselyproportional to fT.The impact of the β degradation of transistors on thepreamplifier gain is very small. The 25Ω preamplifiersexhibit about 3% of gain loss after 1.1 x 1014 n/cm2,while the 50Ω preamplifier, has about 7% gain loss afterthe same fluence.The measurement of input impedance of all irradiatedpreamplifiers indicated that there is no stability problemwith irradiation. All of them have positive real part ofinput impedance in a frequency range 1-200 MHz.45020406080100frequency45 4020406080100120140frequencyFigure preamplifThe metd_line = 960 962010203040506070frequencya)<tpeak>=46 nsrms = 0.14 ns45.1 45.2 45.3 45.4 45.5 45.6 45.7 45.8 45.9 46. 46.1 46.2 46.3 46.4 46.5peaking time [ns]5.5 46. 46.5 47. 47.5 48. 48.5 49. 49.5 50. 50.5 51. 51.5 52. 52.5 53.ENI rms [nA]4. Parameter distributions for 50 Ω / 1 mAiers: a) peaking time, b) amplitude and c) ENI.asurements conditions are CD = 330 pF,16 ns (RG174), tp_tr ~ 46ns (τshaper = 30 ns).964 966 968 970 972 974 976 978 980 982 984 986 988 990 992 994 996 998 1000Peak Amplitude [mV]<ENI> = 49.3rms = 0.5b)c)<Vpeak> = 981 mVrms = 2.98 mV4. QUALITY ASSURANCE4.1  Burn-in studyThe first series of hybrid produced (200 units) afterbeing tested for electrical functionality was subjected to168 hours of an environmental stress screening (or burn-in) at ambient temperature to identify and eliminatedeficiencies and early failures. Moreover few hybrids(eight units randomly chosen) were fully characterised interm of gain, peaking time and noise before and afterburn-in to detect any possible variation of performancesdue to ageing effects.At the conclusion of the burn-in only one channelfailed to meet specification. The unit failed because aPNP transistor (Q4) in the white follower broke duringburn-in. After replacing the transistor the channel wastested again and it met specification.The hybrids that were fully characterised beforeburn-in did not show any performance variation due tothe environmental stress.The burn-in results brought to the conclusion that theenvironmental conditions adopted for the test were notsufficient to rule out all the early failure mechanisms. Amore extensive burn-in study was adopted for the batchof hybrids produced for Mod0. The temperature waselevated to ~ 70 oC and the time were extended up to 432hours. The combination of elevated temperature andextended time did not increase the number of failures.The only source of failures for thick-film hybrids was a“cold solder joint”.Under the assumption that the same failuremechanism dominates in the ATLAS hybrids, wasconcluded that a burn-in of 168 hours at an elevatedtemperature of 70-80 oC, will be used to eliminate allcauses of infant mortality. A higher burn-intemperature/shorter time is not achievable because someof the components used in the preamplifiers are not ratedfor temperatures higher than 100 oC, namely theinductors.4.2  Reliability EvaluationThe reliability of the hybrids has been evaluated basedon the internationally recognised method of calculatingelectronic equipment reliability given in “MilitaryHandbook MIL-HDBK-217” (published by the USDepartment of Defense). This standard uses a series ofmodels for various categories of electronic componentsto predict failure rates that are affected by environmentalconditions, quality levels, stress conditions and variousother parameters. These models are fully detailed inMIL-HDBK-217.Most of the models in MIL-HDBK-217 use ten ormore parameters for the calculation of the componentfailure rate. Commercially available programs, such as“Milstress” from ITEM software have been written tofacilitate the calculation of failure rates. The calculationwas performed using the Milstress software package.The TDR specification for channel failure rate is “0.5missing channel per year” or “868 missing channel peryear”. If the worse case condition is taken, i.e. onechannel missing means a full hybrid missing, themaximum tolerable failure rate per hybrid is “217missing hybrid per year” or 0.57 frmh (where frmhstands for failure per million hours of operation) or1.75 106 hours “mean time between failure” (MTBF).N x Failure RatePart Number0.000.020.040.060.08NE856 Q5 BF660 Q4 NE856 Q2 C4 c1NE856 Q1 BF660 Q6 NE856 Q3 c6 c5Figure 5. Significant component failure ratesThe technology/component/design adopted for thehybrids has to be evaluated against this benchmark.The reliability prediction presented in this section isfor guidance, the purpose of this calculation is toestablish, by means of a consistent and uniform method,the reliability of what has to be considered a “maturedesign”. The calculation is based on the two methodsknown as “Part Count” and “Part Stress Analysis” andthe following assumptions have been made:- Most of the details used in the project are known, interm of material and components.- In a hybrid package, resistors and inductors areconsidered to contribute insignificantly to the overallhybrid failure rate and for this reason are assumed tohave a failure rate of zero.- The hybrid temperature has been assumed to be knowand equal to 35 degree centigrade.- The power dissipation of each hybrid component hasbeen estimated from an actual hybrid sample and fromdesign analysis. It has been compared with the maximumpower from the component data sheet to obtain the“stress factor” for each individual hybrid component.The stress factor has been always rounded up to thesecond figure.- The hybrid quality has been chosen equal to “class Bmicroelectronic” as defined in Mil883-C screeningprocedure method 5004.9.- The quality of the individual component used for themanufacturing has been set to “industrial grade, RE”.- The environment has been set to “ground benign”Based on this information a failure rate of 0.48 frmhhas been calculated. This result shows that the solutionadopted has a predicted reliability similar to the onerequested by ATLAS TDR.Figure 4 shows the significant component failure ratesof a hybrid. The transistor Q5 (the NPN NE856) used inthe white follower is the single largest contributor to thehybrid failure rate.The failure rate is also temperature dependent asshown in Table 4.Table 4: Failure as a function of temperatureTemperature (oC) frmh20 0.4430 0.4840 0.5950 0.7060 0.7670 0.934.3  Highly Accelerated Life TestsAs an aid in testing the reliability and design limits ofthe preamplifier a Highly Accelerated Life Test (HALT)of a selected group of preamplifiers was performed at aQualmark Corporation facility in Marlborough,Massachusetts. The purpose of this testing process wasto induce failure in the tested product(s) in a non-destructive way so as to expose weaknesses in design ormanufacture.  This information then can be used toimprove the devices and to select the manufacturingprocesses used in producing the devices.Twelve preamplifiers, six 50Ω / 1mA and six25Ω / 5mA, were mounted on a board with power andsignal input/output lines so that the response could bemonitored during the test. The board with the mountedpreamplifiers was inserted in a computer controlledenvironmental chamber and tightened to a “platform”which can be vibrated by simultaneous triaxial shakersin a frequency range of 0 to 2 kHz.The testing process was divided into 3 stages. Theinitial stage consisted of varying the temperature of thepreamplifiers, first gradually and then in rapidtemperature cycling (between - 100 °C and 100 °C). Thesecond stage involved accelerating the preamplifiers at afixed temperature (30 °C) starting at 5 Grms (Gravitiesroot mean square) and increasing the acceleration insteps of 5 Grms up to a maximum of 50 Grms. In thefinal stage, both acceleration and rapid thermal cyclingwere combined.The only preamplifier failure during the test wasobserved after many thermal cycles and at a vibration~ 50 Grms, where all four channels of one hybridbecame intermittent.  The failure was caused by thefailure of the + 3 Volt power pin. The edge pin solderjoint broke due to the “fatigue” accumulated in the test.At the conclusion of the test the pin was replaced andthe hybrid was found working in specification.A visual inspection identified that some of the hybridpower pins (the four pins on the longest side of thehybrid) were not centred into the pad and they weresoldered to an angle in respect to the ceramic substrate.The pins were the last components to be assembledwere hand-soldered in place. The input/output pins onthe contrary were assembled through “dipping andflowing” in one step operation. The pin assembly is theless automated part of the manufacturing process. Amore stringent inspection will be required for the finalproduction.5.  CONCLUSIONSThe design and technology used for the constructionof the LAr calorimeter preamplifier have beenextensively tested on 1,800 hybrids. These devices havemet all physics requirements. No changes in design areexpected. The hybrid quality has been successfullyinspected. The final hybrid production is in progress.6. ACKNOWLEDGMENTSThe authors wish to thank F. Densing for therealisation of the hybrid layout and QualmarkCorporation personnel for the assistance during the testsof the preamplifiers.7.  REFERENCES1. Technical Design Report [Sec. 10, 401-410].2. R.L. Chase, C. de La Taille, S. Rescia and N.Seguin, “Transmission Line Connections BetweenDetector and Front End Electronics in Liquid ArgonCalorimetry”, Nucl. Instrum. & Meth., A330,(1993), pp. 228-242.3. R. L. Chase and S. Rescia; A Linear Low PowerRemote Preamplifier for the ATLAS Liquid ArgonEM Calorimeter; BNL 63745; IEEE Trans. Nucl.Sci. Vol. 44, No. 3, June (1997), 1028.4. R.L. Chase, C. de La Taille and N. Seguin,“Experimental results on cable-coupledpreamplifiers (0T)”, Nucl. Instrum. & Meth., A343(1994), pp. 598-605.5. G. Battistoni, D.V. Camin, N.Fedyakin, P. Ramaioliand R. Shuvalov, “Stability of a line receiver (0-T)preamplifier, connected to a capacitive detector viaa transmission line”, Nucl. Instrum. & Meth., A424(1999), pp. 533-544.6. G. Battistoni et al., ATLAS internal Note LARG-NO-083.

The ATLAS calorimeter preamplifier: performance, radiation damage, electrostatic discharge resistance, reliability and manufacturing issues

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