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PPE S/C detector lecturesDr R. Bates1 Semiconductor detectors An introduction to semiconductor detector physics as applied to particle physics.

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Presentation on theme: "PPE S/C detector lecturesDr R. Bates1 Semiconductor detectors An introduction to semiconductor detector physics as applied to particle physics."— Presentation transcript:

1 PPE S/C detector lecturesDr R. Bates1 Semiconductor detectors An introduction to semiconductor detector physics as applied to particle physics

2 PPE S/C detector lecturesDr R. Bates2 Contents 4 lectures – cant cover much of a huge field Introduction Fundamentals of operation The micro-strip detector Radiation hardness issues

3 PPE S/C detector lecturesDr R. Bates3 Lecture 1 - Introduction What do we want to do Past, present and near future Why use semiconductor detectors

4 PPE S/C detector lecturesDr R. Bates4 What we want to do - Just PPE Track particles without disturbing them Determined position of primary interaction vertex and secondary decays Superb position resolution Highly segmented high resolution Large signal Small amount of energy to crate signal quanta Thin Close to interaction point Low mass Minimise multiple scattering Detector Readout Cooling / support

5 PPE S/C detector lecturesDr R. Bates5 Ages of silicon - the birth J. Kemmer Fixed target experiment with a planar diode * Later strip devices Larger devices with huge ancillary components * J. Kemmer: Fabrication of a low-noise silicon radiation detector by the planar process, NIM A169, pp499, 1980

6 PPE S/C detector lecturesDr R. Bates6 Ages of Silicon - vertex detectors LEP and SLAC ASICs at end of ladders Minimise the mass inside tracking volume Minimise the mass between interaction point and detectors Minimise the distance between interaction point and the detectors Enabled heavy flavour physics i.e. short lived particles

7 PPE S/C detector lecturesDr R. Bates7 ALEPH

8 PPE S/C detector lecturesDr R. Bates8 ALPEH – VDET (the upgrade) 2 silicon layers, 40cm long, inner radius 6.3cm, outer radius 11cm 300 m Silicon wafers giving thickness of only 0.015X 0 S/N r = 28:1; z = 17:1 r = 12 m; z = 14 m

9 PPE S/C detector lecturesDr R. Bates9 Ages of silicon - tracking paradigm CDF/D0 & LHC Emphasis shifted to tracking + vertexing Only possible as increased energy of particles Cover large area with many silicon layers Detector modules including ASICs and services INSIDE the tracking volume Module size limited by electronic noise due to fast shaping time of electronics (bunch crossing rate determined)

10 PPE S/C detector lecturesDr R. Bates10 ATLAS A monster !

11 PPE S/C detector lecturesDr R. Bates11 ATLAS barrel 2112 Barrel modules mounted on 4 carbon fibre concentric Barrels, 12 in each row 1976 End-cap modules mounted on 9 disks at each end of the barrel region

12 PPE S/C detector lecturesDr R. Bates12 What is measured Measure space points Deduce Vertex location Decay lengths Impact parameters

13 PPE S/C detector lecturesDr R. Bates13 Signature of Heavy Flovours Stable particles > sc n2.66km 658m Very long lived particles > s, K ±, K L x m K S 0, E ±, x cm Long lived particles > s ± 0.3 x m B d 0, B s 0, b 1.2 x m Short lived particles 0, x m, 4 x m!!

14 PPE S/C detector lecturesDr R. Bates14 Decay lengths By measuring the decay length, L, and the momentum, p, the lifetime of the particle can be determined Need accuracy on both production and decay point L Primary vertex Secondary vertex L = p/m c E.g. B J/ K s 0

15 PPE S/C detector lecturesDr R. Bates15 Impact parameter (b) b beam b = distance of closest approach of a reconstructed track to the true interaction point

16 PPE S/C detector lecturesDr R. Bates16 Impact parameter Error in impact parameter for 2 precision measurements at R 1 and R 2 measured in two detector planes: a=f(R 1 & R 2 ) and function of intrinsic resolution of vertex detector b due to multiple scattering in detector c due to detector alignment and stability

17 PPE S/C detector lecturesDr R. Bates17 Impact parameter b = f( vertex layers, distance from main vertex, spatial resolution of each detector, material before precision measurement, alignment, stability ) Requirements for best measurement Close as possible to interaction point Maximum lever arm R 2 – R 1 Maximum number of space points High spatial resolution Smallest amount of material between interaction point and 1 st layer Good stability and alignment – continuously measured and correct for 100% detection efficiency Fast readout to reduce pile up in high flux environments

18 Impact parameter * Effect of extra mass and distance from the interaction point Blue = 5mm Black = 1mm (baseline) Green = 0.5 mm Red = 0.1 mm GR WidthFlux increase(%) to siliconImprovement of the IPres. wrt 1mm(%) 5mm mm mm Lower P t * Guard Ring Width Impact on d0 Performances and Structure Simulations. A Gouldwell, C Parkes, M Rahman, R Bates, M Wemyss, G Murphy, P Turner and S Biagi. LHCb Note, LHCb

19 PPE S/C detector lecturesDr R. Bates19 Why Silicon Semiconductor with moderate bandgap (1.12eV) Thermal energy = 1/40eV Little cooling required Energy to create e/h pair (signal quanta)= 3.6eV c.f Argon gas = 15eV High carrier yield better stats and lower Poisson stats noise Better energy resolution and high signal no gain stage required

20 PPE S/C detector lecturesDr R. Bates20 Why silicon High density and atomic number Higher specific energy loss Thinner detectors Reduced range of secondary particles Better spatial resolution High carrier mobility Fast! Less than 30ns to collect entire signal Industrial fabrication techniques Advanced simulation packages Processing developments Optimisation of geometry Limiting high voltage breakdown Understanding radiation damage

21 PPE S/C detector lecturesDr R. Bates21 Disadvantages Cost Area covered Detector material could be cheap – standard Si Most cost in readout channels Material budget Radiation length can be significant Effects calorimeters Tracking due to multiple scattering Radiation damage Replace often or design very well – see lecture 4

22 PPE S/C detector lecturesDr R. Bates22 Radiation length X 0 High-energy electrons predominantly lose energy in matter by bremsstrahlung High-energy photons by e + e - pair production The characteristic amount of matter traversed for these related interactions is called the radiation length X 0, usually measured in g cm -2. It is both: the mean distance over which a high-energy electron loses all but 1=e of its energy by bremsstrahlung the mean free path for pair production by a high-energy photon

23 PPE S/C detector lecturesDr R. Bates23 Lecture 2 – lots of details Simple diode theory Fabrication Energy deposition Signal formation

24 PPE S/C detector lecturesDr R. Bates24 Detector = p-i-n diode Near intrinsic bulk Highly doped contacts Apply bias (-ve on p + contact) Deplete bulk High electric field Radiation creates carriers signal quanta Carriers swept out by field Induce current in external circuit signal N D ~10 12 cm -3 n+ contact N D =10 18 cm -3 p+ contact N A =10 18 cm -3

25 PPE S/C detector lecturesDr R. Bates25 Why a diode? Signal from MIP = 23k e/h pairs for 300 m device Intrinsic carrier concentration n i = 1.5 x cm -3 Si area = 1cm 2, thickness=300 m 4.5x10 8 electrons 4 orders > signal Need to deplete device of free carriers Want large thickness (300 m) and low bias But no current! Use v.v. low doped material p + rectifying (blocking) contact

26 PPE S/C detector lecturesDr R. Bates26 p-n junction p+p+ n Dopant concentration Space charge density Carrier density Electric field Electric potential (1) (2) (3) (4) (5) (6) (7)

27 PPE S/C detector lecturesDr R. Bates27 p-n junction 1) take your samples – these are neutral but doped samples: p + and n - 2) bring together – free carriers move o two forces drift and diffusion o In stable state J diffusion (concentration density) = J drift (e-field) 3) p + area has higher doping concentration (in this case) than the n region

28 PPE S/C detector lecturesDr R. Bates28 p-n junction 4) Fixed charge region 5) Depleted of free carriers o Called space charge region or depletion region o Total charge in p side = charge in n side o Due to different doping levels physical depth of space charge region larger in n side than p side o Use n- (near intrinsic) very asymmetric junction 6) Electric field due to fixed charge 7) Potential difference across device o Constant in neutral regions.

29 PPE S/C detector lecturesDr R. Bates29 Resistivity and mobility Carrier DRIFT velocity and E-field: n = 1350cm 2 V -1 s -1 : p = 480cm 2 V -1 s -1 Resistivity p-type material n-type material

30 PPE S/C detector lecturesDr R. Bates30 Depletion width Depletion Width depends upon Doping Density: For a given thickness, Full Depletion Voltage is: W = 300 m, N D 5x10 12 cm -3 : V fd = 100V

31 PPE S/C detector lecturesDr R. Bates31 Reverse Current Diffusion current From generation at edge of depletion region Negligible for a fully depleted detector Generation current From generation in the depletion region Reduced by using material pure and defect free high lifetime Must keep temperature low & controlled

32 PPE S/C detector lecturesDr R. Bates32 Capacitance Capacitance is due to movement of charge in the junction Fully depleted detector capacitance defined by geometric capacitance Strip detector more complex Inter-strip capacitance dominates

33 PPE S/C detector lecturesDr R. Bates33 Noise Depends upon detector capacitance and reverse current Depends upon electronics design Function of signal shaping time Lower capacitance lower noise Faster electronics noise contribution from reverse current less significant

34 PPE S/C detector lecturesDr R. Bates34 Fabrication Use very pure material High resistivity Low bias to deplete device Easy of operation, away from breakdown, charge spreading for better position resolution Low defect concentration No extra current sources No trapping of charge carriers Planar fabrication techniques Make p-i-n diode pattern of implants define type of detector (pixel/strip) extra guard rings used to control surface leakage currents metallisation structure effects E-field mag limits max bias

35 PPE S/C detector lecturesDr R. Bates35 Fabrication stages Starting material Usually n- Phosphorous diffusion P doped poly n+ Si Stages dopants to create p- & n-type regions passivation to end surface dangling bonds and protect semiconductor surface metallisation to make electrical contact n - Si

36 PPE S/C detector lecturesDr R. Bates36 Fabrication stages Deposit SiO 2 Grow thermal oxide on top layer Photolithography + etching of SiO 2 Define eventual electrode pattern

37 PPE S/C detector lecturesDr R. Bates37 Fabrication stages Form p + implants Boron doping thermal anneal/Activation Removal of back SiO 2 Al metallisation + patterning to form contacts

38 PPE S/C detector lecturesDr R. Bates38 Fabrication Tricks for low leakage currents low temperature processing simple, cheap marginal activation of implants, cant use IC tech gettering very effective at removal of contaminants complex

39 PPE S/C detector lecturesDr R. Bates39 Energy Deposition Charge particles Bethe-Bloch Bragg Peak Not covered Neutrons Gamma Rays Rayleigh scattering, Photo-electric effect, Compton scattering, Pair production

40 PPE S/C detector lecturesDr R. Bates40 At 3 dE/dx minimum independent of absorber (mip) Electrons 1 MeV E>50 MeV radiative energy loss dominates Momentum transferred to a free electron at rest when a charged particle passes at its closest distance, d. integrate over all possible values of d Charge particles - concentrating on electrons

41 PPE S/C detector lecturesDr R. Bates41 at end of range specific energy loss increases particle slows down deposit even more energy per unit distance Bragg Peak Useful when estimating properties of a device E = 5 MeV in Si: (increasing charge ) R ( m) p O4.3 Well defined range

42 PPE S/C detector lecturesDr R. Bates42 Energy Fluctuation Electron range of individual particle has large fluctuation Energy loss can vary greatly - Landau distribution Close collisions (with bound electrons) rare energy transfer large ejected electron initiates secondary ionisation Delta rays - large spatial extent beyond particle track Enhanced cross-section for K-, L- shells Distance collisions common M shell electrons - free electron gas

43 PPE S/C detector lecturesDr R. Bates43 e/h pair creation Create electron density oscillation - plasmon requires 17 eV in Si De-excite almost 100% to electron hole pair creation Hot carriers thermal scattering optical phonon scattering ionisation scattering (if E > 3/4 eV) Mean energy to create an e/h pair (W) is 3.6 eV in Si (E g = 1.12 eV 3 x E g ) W depends on E g therefore temperature dependent

44 PPE S/C detector lecturesDr R. Bates44 Delta rays a)Proability of ejecting an electron with E T as a function of T b) Range of electron as a function of energy in silicon

45 PPE S/C detector lecturesDr R. Bates45 Displacement from -electrons Estimate the error Assume 20k e/h from track 50keV -electron produced perpendicular to track Range 16 m, produces 14k e/h Assume ALL charge created locally 8 m from particles track

46 PPE S/C detector lecturesDr R. Bates46 Consequences of d-electrons Centroid displacement Resolution as function of pulse height

47 PPE S/C detector lecturesDr R. Bates47 Consequence of -electrons 45º 15 m E.g. CCD E.g. Microstrip 45º 300 m Most probable E loss = 3.6keV 10% prob y of 5keV pulls track up by 4 m Most probable E loss = 72keV 10% prob y of 100keV pulls track up by 87 m

48 PPE S/C detector lecturesDr R. Bates48 Signal formation Signal due to the motion of charge carriers inside the detector volume & the carriers crossing the electrode Displacement current due to change in electrostatics (c.f. Maxwells equations) Material polarised due to charge introduction Induced current due to motion of the charge carriers See a signal as soon as carriers move

49 PPE S/C detector lecturesDr R. Bates49 Signal Simple diode Signal generated equally from movement through entire thickness Strip/pixel detector Almost all signal due to carrier movement near the sense electrode (strips/pixels) Make sure device is depleted under strips/pixels If not: Signal small Spread over many strips

50 PPE S/C detector lecturesDr R. Bates50 Lecture 3 – Microstrip detector Description of device Carrier diffusion Why is it (sometimes) good Charge sharing Cap coupling Floating strips Off line analysis Performance in magnetic field Details AC coupling Bias resistors Double sides devices

51 PPE S/C detector lecturesDr R. Bates51 What is a microstrip detector? p-i-n diode Patterned implants as strips One or both sides Connect readout electronics to strips Radiation induced signal on a strip due to passage under/close to strip Determine position from strip hit info

52 PPE S/C detector lecturesDr R. Bates52 What does it look like? P+ contact on front of n- bulk Implants covered with thin thermal oxide (100nm) Forms capacitor ~ 10pF/cm Al strip on oxide overlapping implant Wirebond to amplifier Strips surrounded by a continuous p+ ring The guard ring Connected to ground Shields against surface currents Implants DC connected to bias rail Use polysilicon resistors M Bias rail DC to ground HV

53 PPE S/C detector lecturesDr R. Bates53 Resolution Delta electrons See lecture 2 Diffusion Strip pitch Capacitive coupling Read all strips Floating strips

54 PPE S/C detector lecturesDr R. Bates54 Carrier collection Carriers created around track Φ 1 m Drift under E-field p + strips on n - bulk p + -ve bias Holes to p + strips, electrons to n+ back-plane Typical bias conditions 100V, W=300 m E=3.3kVcm -1 Drift velocity: e= 4.45x10 6 cms -1 & h=1.6x10 6 cm -1 Collection time: e=7ns, h=19ns

55 PPE S/C detector lecturesDr R. Bates55 Carrier diffusion Diffuse due to conc. gradient dN/dx Gaussian Diffusion coefficient: RMS of the distribution: Since D & t coll 1/ Width of distribution is the same for e & h As charge created along a strip Superposition of Gaussian distribution

56 PPE S/C detector lecturesDr R. Bates56 Diffusion Example for electrons: tcoll = 7ns; T=20 o C = 7 m Lower bias wider distribution For given readout pitch wider distribution more events over >1 strip Find centre of gravity of hits better position resolution Want to fully deplete detector at low bias High Resistivity silicon required

57 PPE S/C detector lecturesDr R. Bates57 Resolution as a f(V) V<50V charge created in undeleted region lost, higher noise V>50V reduced drift time and diffusion width less charge sharing more single strips Spatial resolution as a function of bias V fd = 50V

58 PPE S/C detector lecturesDr R. Bates58 Resolution due to detector design Strip pitch Very dense Share charge over many strips Reconstruct shape of charge and find centre Signal over too many strips lost signal (low S/N) BUT FWHM ~ 10 m Limited to strip pitch 20 m Signal on 1 or 2 strips

59 PPE S/C detector lecturesDr R. Bates59 Two strip events Track between strips Find position from signal on 2 strips Use centre of gravity or Algorithm takes into account shape of charge cloud (eta, ) Track mid way Q on both strips best accuracy Close to one strip Small signal on far strip Lost in noise

60 PPE S/C detector lecturesDr R. Bates60 Capacitive coupling Strip detector is a C/R network C strip to blackplace = 10x C interstrip C sb || C is ignore C sb Fraction of charge on B due to track at A: A B C

61 PPE S/C detector lecturesDr R. Bates61 Floating strips Large Pitch (60 m) Intermediate strip 1/3 tracks on both strips Assume = 2.2 m 2/3 on single strips = 40/ 12 = 11.5 m Overall: = 1/3 x /3 x 11.5 = 8.4 m 60 m 20 m Capacitive charge coupling 2/3 tracks on both strips NO noise losses due to cap coupling 1/3 tracks on single strips = 2/3 x /3 x 20/ 12 = 3.4 m 20 m strip pitch =2.2 m

62 PPE S/C detector lecturesDr R. Bates62 Off line analysis Binary readout No information on the signal size Large pitch and high noise Get a signal on one strip only -½ pitch ½ pitch P(x) = 0

63 PPE S/C detector lecturesDr R. Bates63 Have signal on each strip Assume linear charge sharing between strips Centre of Gravity PH L PH R P x Q on 2 strips & x = 0 at left strip e.g. PH L = 1/3PH R

64 PPE S/C detector lecturesDr R. Bates64 Eta function Non linear charge sharing due to Gaussian charge cloud shape PH L PH R P x More signal on RH strip than predicted with uniform charge cloud shape Non-linear function to determine track position from relative pulse heights on strips

65 PPE S/C detector lecturesDr R. Bates65 Eta function Measured tracks as a function of incident particle flux Measured and predicted particle position

66 PPE S/C detector lecturesDr R. Bates66 Lorentz force Force on carriers due to magnetic force Perturbation in drift direction Charge cloud centre drifts from track position Asymmetric charge cloud No charge loss is observed Can correct for if thickness & B-field known EH L vhvh veve

67 PPE S/C detector lecturesDr R. Bates67 Details Modern detectors have integrated capacitors Thin 100nm oxide on top of implant Metallise over this Readout via second layer Integrated resistors Realise via polysilicon Complex Punch through biasing Not radiation hard Back to back diodes – depleted region has high R

68 PPE S/C detector lecturesDr R. Bates68 Details Double sided detectors Both p- and n-side pattern Surface charge build up on n-side Trapped +ve charge in SiO Attracts electrons in silicon near surface Shorts strips together p+ spray to increase inter-strip resistance

69 PPE S/C detector lecturesDr R. Bates69 Lecture 4 – Radiation Damage Effects of radiation Microscopic Macroscopic Annealing What can we do? Detector Design Material Engineering Cold Operation Thin detectors/Electrode Structure – 3-D device

70 PPE S/C detector lecturesDr R. Bates70 Effects of Radiation Long Term Ionisation Effects Trapped charge (holes) in SiO 2 interface states at SiO 2 - Si interface Cant use CCDs in high radiation environment Displacement Damage in the Si bulk 4 stage process Displacement of Silicon atoms from lattice Formation of long lived point defects & clusters

71 PPE S/C detector lecturesDr R. Bates71 Displacement Damage Incoming particle undergoes collision with lattice knocks out atom = Primary knock on atom PKA moves through the lattice produces vacancy interstitial pairs (Frenkel Pair) PKA slows, reduces mean distance between collisions clusters formed Thermal motion 98% lattice defects anneal defect/impurity reactions Stable defects influence device properties

72 PPE S/C detector lecturesDr R. Bates72 PKA Clusters formed when energy of PKA< 5keV Strong mutual interactions in clusters Defects outside of cluster diffuse + form impurity related defects (VO, VV, VP) e & dont produce clusters

73 PPE S/C detector lecturesDr R. Bates73 Effects of Defects GenerationRecombinationTrappingCompensation e h e e hh Leakage Current Charge Collection Effective Doping Density e ECEC EVEV

74 PPE S/C detector lecturesDr R. Bates74 Reverse Current I = Volume Material independent linked to defect clusters Annealing material independent Scales with NIEL Temp dependence = x Acm -1 after 80minutes annealing at 60 C

75 PPE S/C detector lecturesDr R. Bates75 Effective Doping Density Donor removal and acceptor generation type inversion: n p depletion width grows from n + contact Increase in full depletion voltage V N eff = 0.025cm -1 measured after beneficial anneal

76 PPE S/C detector lecturesDr R. Bates76 Effective Doping Density Short-term beneficial annealing Long-term reverse annealing temperature dependent stops below -10 C

77 PPE S/C detector lecturesDr R. Bates77 Signal speed from a detector Duration of signal = carrier collection time Speed mobility & field Speed 1/device thickness PROBLEMS Post irradiation mobility & lifetime reduced lower longer signals and lower Q s Thick devices have longer signals

78 PPE S/C detector lecturesDr R. Bates78 Signal with low lifetime material Lifetime,, packet of charge Q 0 decays In E field charge drifts Time required to drift distance x: Remaining charge: Drift length, L is a figure of merit.

79 PPE S/C detector lecturesDr R. Bates79 Parallel plate detector: In high quality silicon detectors: 10ms, e = 1350cm 2 V -1 s -1, E = 10 4 Vcm -1 L 10 4 cm (d ~ cm) Amorphous silicon, L 10 m (short lifetime, low mobility) Diamond, L m (despite high mobility) CdZnTe, at 1kVcm-1, L 3cm for electrons, 0.1cm for holes Induced charge

80 PPE S/C detector lecturesDr R. Bates80 What can we do? Detector Design Material Engineering Cold Operation Electrode Structure – 3-D device

81 PPE S/C detector lecturesDr R. Bates81 Detector Design n-type readout strips on n-type substrate post type inversion substrate p type depletion now from strip side high spatial resolution even if not fully depleted Single Sided Polysilicon resistors W<300 m thick limit max depletion V Max strip length 12cm lower cap. noise

82 PPE S/C detector lecturesDr R. Bates82 Multiguard rings Enhance high voltage operation Smoothly decrease electric field at detectors edge Poly Guard rings V strip bias back plane bias

83 PPE S/C detector lecturesDr R. Bates83 Substrate Choice Minimise interface states Substrate orientation not Lower capacitive load Independent of ionising radiation has less dangling surface bonds

84 PPE S/C detector lecturesDr R. Bates84 Metal Overhang Used to avoid breakdown performance deterioration after irradiation Breakdown Voltage (V) Strip Width/Pitch (1)(2) m 0.6 m p+p+ p+p+ n+n+ SiO 2 n after 4 x p/cm 2

85 PPE S/C detector lecturesDr R. Bates85 Material Engineering Do impurities influence characteristics? Leakage current independent of impurities N eff depends upon [O 2 ] and [C]

86 PPE S/C detector lecturesDr R. Bates86 O 2 works for charged hadrons N eff unaffected by O 2 content for neutrons Believed that charge particle irradiation produces more isolated V and I V + O VO V + VO V 2 O V 2 O reverse annealing High [O] suppresses V 2 O formation

87 PPE S/C detector lecturesDr R. Bates87 Charge collection efficiency Oxygenated Si enhanced due to lower depletion voltage CCI ~ 5% at 300V after 3x10 14 p/cm 2 CCE of MICRON ATLAS prototype strip detectors irradiated with p/cm 2

88 PPE S/C detector lecturesDr R. Bates88 ATLAS operation Damage for ATLAS barrel layer 1 Use lower resistivity Si to increase lifetime in neutron field Use oxygenated Si to increase lifetime in charge hadron field

89 PPE S/C detector lecturesDr R. Bates89 Cold Operation Know as theLazarus effect Recovery of heavily irradiated silicon detectors operated at cryogenic temps observed for both diodes and microstrip detectors

90 PPE S/C detector lecturesDr R. Bates90 The Lazarus Effect For an undepleted heavily irradiated detector: Traps are filled traps are neutralized N eff compensation (confirmed by experiment) B. Dezillie et al., IEEE Transactions on Nuclear Science, 46 (1999) 221 d D undepleted region active region where

91 PPE S/C detector lecturesDr R. Bates91 Reverse Bias Measured at 130K - maximum CCE CCE falls with time to a stable value

92 PPE S/C detector lecturesDr R. Bates92 Cryogenic Results CCE recovery at cryogenic temperatures CCE is max at T ~ 130 K for all samples CCE decreases with time till it reaches a stable value Reverse Bias operation MPV ~5000 electrons for 300 m thick standard silicon detectors irradiated with n/cm 2 at 250 V reverse bias and T~77 K very low noise Forward bias is possible at cryogenic temperatures No time degradation of CCE in operation with forward bias or in presence of short wavelength light same conditions: MPV ~13000 electrons

93 PPE S/C detector lecturesDr R. Bates93 Electrode Structure Increasing fluence Reducing carrier lifetime Increasing N eff Higher bias voltage Operation with detector under-depleted Reduce electrode separation Thinner detector Reduced signal/noise ratio Close packed electrodes through wafer

94 PPE S/C detector lecturesDr R. Bates94 The 3-D device Co-axial detector Arrayed together Micron scale USE Latest MEM techniques Pixel device Readout each p+ column Strip device Connect columns together

95 PPE S/C detector lecturesDr R. Bates95 Proposed by S.Parker, Nucl. Instr. And Meth. A 395 pp (1997). Equal detectors thickness W 2D >>W 3D h + e - -ve +ve SiO 2 W 3D E Bulk h + e - +ve E p + n n + Operation Carriers drift total thickness of material Carriers swept horizontally Travers short distance between electrodes W 2D +ve -ve

96 PPE S/C detector lecturesDr R. Bates96 Advantages If electrodes are close Low full depletion bias Low collection distances Thickness NOT related to collection distance No charge spreading Fast charge sweep out

97 PPE S/C detector lecturesDr R. Bates97 A 3-D device Form an array of holes Fill them with poly-silicon Add contacts Can make pixel or strip devices Bias up and collect charge

98 PPE S/C detector lecturesDr R. Bates98 Real spectra At 15V Plateau in Q collection Fully active Very good energy resolution

99 PPE S/C detector lecturesDr R. Bates99 3-D V fd in ATLAS time [years] V d e p ( m ) [ V ] standard silicon oxygenated silicon operation voltage: 600 V 6000 e for B-layer 6000 e for B-layer Damage projection for the ATLAS B-layer (3 rd RD48 STATUS REPORT CERN LHCC , LEB Status Report/RD48, 31 December 1999). 3D detector!

100 PPE S/C detector lecturesDr R. Bates100 Summary Tackle reverse current Cold operation, -20 C Substrate orientation Multiguard rings Overcome limited carrier lifetime and increasing effective doping density Change material Increase carrier lifetime Reduce electrode spacing

101 PPE S/C detector lecturesDr R. Bates101 Final Slide Why? Where? How? A major type A major worry

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