Investigation of the effects of thickness, pitch and manufacturer on charge multiplication properties of highly irradiated n-in-p FZ silicon strips A. Affolder, P. Allport, G. Casse University of Liverpool

Charge Multiplication A. Affolder – 5th Trento Workshop, Feb 2010, Manchester, UK 2 MICRON RD50 n + -p FZ detectors Highest voltage limited by breakdown  More than 100% CCE seen The differences in Liverpool and Ljubljana measurements are due to annealing state 300 µm Blue empty symbols: Liverpool Black filled symbols: Ljubljana full charge collection (300  m) full charge collection (140  m) With thinner detectors, it is much easier to obtain more than 100% CCE Collected more than 2× deposited charge What more can be done experimentally to understand the phenomena? Strips

Studies shown so far Thickness –75/140/300  m Temperature –-10 C/-25 C/-50 C Standard TCT Edge-TCT Annealing Charge Depth A. Affolder – 5th Trento Workshop, Feb 2010, Manchester, UK 3 G. Casse, et. al., 14 th RD50 Workshop J. Lange, et. al., 15 th RD50 Workshop Expected bulk current for fully depleted detector G.Kramberger, et. al., 15 th RD50 Workshop Φ = 5·10 15 n/cm 2 I. Mandic, et. al., 15 th RD50 Workshop M.Milovanovic, et. al., 15 th RD50 Workshop penetration depth J. Lange, et.al., 14 th RD50 Workshop

Potential New Studies New submission with Micron to study effects of pitch, intermediate strips, etc. on multiplication underway What can we add now with what we have in hand? –Additional thickness available (500  m) from ATLAS UK MCMd studies –Different pitches (74.5/100 mm) available from ATLAS07 miniatures A. Affolder – 5th Trento Workshop, Feb 2010, Manchester, UK 4

Miniature Silicon Micro-strip Sensors A. Affolder – 5th Trento Workshop, Feb 2010, Manchester, UK 5 Micron/RD50 (4” wafers) Detector designed and produced within RD50 framework RD50 mask (see: n-in-p FZ, 80  m pitch, p-spray isolation 140  m, 300  m, 500  m thick HPK/ATLAS07 miniatures Detectors designed and produced within ATLAS Upgrade Silicon Detector Collaboration n-in-p FZ (V FD ~160V), ~320  m thick 74.5  m, 100  m pitch p-spray, p-stop isolation

Irradiation Sources & Doses Measurements from 26 MeV protons –Minimizes annealing –Charged particles dominant for inner layers of SLHC Studied three thickness between ×10 13 n eq cm -2 Focused manufacturer/isolation comparisons where we are most sensitive to multiplication –20-100×10 14 n eq cm -2 A. Affolder – 5th Trento Workshop, Feb 2010, Manchester, UK 6 Irradiation and dosimetry (26 MeV Protons): Compact Cyclotron, Karlsruhe, Germany: W. de Boer, A. Dierlamm, et. al.

7 Experimental Setup Charge collection efficiency (CCE) measured using an analogue electronics chip (SCT128) clocked at LHC speed (40MHz clock, 25ns shaping time). –Measurements performed in chest freezer at a temperature of ~-25 °C with N 2 flush 90 Sr fast electron source triggered with scintillators in coincidence used to generate signal. The system is calibrated to the most probable value of the MIP energy loss in a non-irradiated 300µm thick detector (~23000 e - ). A. Affolder – 5th Trento Workshop, Feb 2010, Manchester, UK Update picture with newest setup

Manufacturer Comparisons A. Affolder – 5th Trento Workshop, Feb 2010, Manchester, UK 8

2×10 15 n eq cm -2 A. Affolder – 5th Trento Workshop, Feb 2010, Manchester, UK 9 Slightly different response by Micron piece. Most likely due to differences in irradiation, normalization of SCT128.

5×10 15 n eq cm -2 A. Affolder – 5th Trento Workshop, Feb 2010, Manchester, UK 10 No significant difference between manufacturer, pitch or isolation technique

1×10 16 n eq cm -2 A. Affolder – 5th Trento Workshop, Feb 2010, Manchester, UK 11 No significant difference between manufacturer, pitch or isolation technique

500 V Manufacturer Comparisons At the lowest fluence, there may be some differences between Micron and Hamamatsu –Most likely systematic error At higher fluence, no trend seen A. Affolder – 5th Trento Workshop, Feb 2010, Manchester, UK V Appears once multiplication dominates, no strong differences between manufacturer, isolation and pitch’s tested. Weird!!

Thickness Comparison A. Affolder – 5th Trento Workshop, Feb 2010, Manchester, UK 13

Results with BCB Measured two pieces each with fluences of 1,10,100,1000×10 13 n eq cm -2 Everything as expected up to 1100 V max. tested –We still would like to check for changes in mechanical properties and breakdown voltage of BCB As far as we can tell, no negative effects from shield or BCB –Only expected increase in load capacitance A. Affolder – 5th Trento Workshop, Feb 2010, Manchester, UK 14

1×10 14 n eq cm -2 A. Affolder – 5th Trento Workshop, Feb 2010, Manchester, UK 15 Behaves completely as expected. V dep is roughly 3x higher with Sqrt(V) shape of CCE

1×10 15 n eq cm -2 A. Affolder – 5th Trento Workshop, Feb 2010, Manchester, UK 16 The collected charge and reverse current at consistent for all three thickness within experimental uncertainties

1×10 16 n eq cm -2 A. Affolder – 5th Trento Workshop, Feb 2010, Manchester, UK 17 Collected charge and reserve current is correlated as expected from other previous measurements of sensors in multiplication. Collected charge at a given voltage is larger as the device is thinned, but the current increases

Thickness Overview A. Affolder – 5th Trento Workshop, Feb 2010, Manchester, UK 18 Below 5×10 14 n eq cm -2, charge advantage to being thicker Above 3×10 15 n eq cm -2, charge advantage to being thinner

Conclusions (My Opinion) Multiplication effects do not appear to be strongly dependent on manufacturer’s parameters, interstrip isolation techniques, bulk silicon type, etc. –I don’t really understood why??? The effect does seem to scale smoothly with detector thickness over range studied with multiplication become dominant effect around 2-5×10 15 n eq cm -2 A. Affolder – 5th Trento Workshop, Feb 2010, Manchester, UK 19

What’s Next RD50 submission with Micron to study effects of junction geometry –6” wafer with 80 1×1 cm 2 sensors A. Affolder – 5th Trento Workshop, Feb 2010, Manchester, UK 20 LabelNumber per wafer Strip pitch Implant width NI8W88060 NI8M88025 NI8N8806 NI10W NI10M NI10N NI4W44027 NI4M44015 NI4N4406 Label# per Wafer Strip pitch Implan t width Intermediat e strip width I8N I8W I10N I10W I5N45015 I5W650156

A. Affolder – 5th Trento Workshop, Feb 2010, Manchester, UK 21 Technology description – MCM-D on Si wafers Dielectric layers: Benzocyclobutene (BCB) –Deposited in layers of 3-15 µm thickness –Dielectric constant of 2.65 Conducting layers: sputtered Cu/Ti –Standard thickness 1 µm Connecting vias: etched through BCB before curing –To the sensor –Between metal layers Feature sizes –Lithographic resolution: 10 µm –Good yield at 30 µm track width/spacing –Minimal via size at 15 µm thickness: 65 µm