1. Layout and test of silicon pad detectors for the PHOBOS experiment at RHIC Heinz Pernegger for the Phobos collaboration Massachusetts Institute of Technology February 26, 1998

2. February 26,1998, ViennaWire Chamber Conference 1998 Heinz PerneggerPage 2 Outline l Brief introduction of the experiment l Layout of silicon pad detectors l Measurements on the wafer » detector capacitances l Measurement of the signal response » signal/noise » signal uniformity » cross talk l Test of a fully assembled Phobos Detector Module

3. February 26,1998, ViennaWire Chamber Conference 1998 Heinz PerneggerPage 3 The PHOBOS Collaboration A “small” experiment with about 60 collaborators from: Argonne National Laboratory Brookhaven National Laboratory Case Western Reserve University Institute of Nuclear Physics Krakow Jagiellonian University Krakow Massachusetts Institute of Technology National Central University, Taiwan Oak Ridge National Laboratory University of Rochester University of Illinois Chicago University of Maryland Yale University

4. February 26,1998, ViennaWire Chamber Conference 1998 Heinz PerneggerPage 4 l Aim of Phobos: Search for Quark-Gluon Plasma at highest CM energies ever! l Phobos searches for (rare?) events with very high charged multiplicity and/or unusual multiplicity fluctuations » particle multiplicity can be high (>10000?) » interesting events may be rare record up to 300 events/s » a (relatively) simple detector with flexibility » reconstruct tracks in mid-rapidity range with low Pt threshold 1.) Phobos at RHIC Au 100 GeV/n

5. February 26,1998, ViennaWire Chamber Conference 1998 Heinz PerneggerPage 5 Layout of the Experiment l 1 layer Silicon multiplicity & Vertex Detector (~20,000 readout channels) l 14 layer Silicon Spectrometer Arms (~60,000 readout channels/arm) l Time of Flight Wall 1m Magnet (top half not shown)

6. February 26,1998, ViennaWire Chamber Conference 1998 Heinz PerneggerPage 6 l Full track reconstruction and particle identification in mid rapidity l reconstruction efficiency 85% Pt Threshold 50MeV for  and 200 MeV p 2 Silicon detectors with different aims Multiplicity Detector - Spectrometer Measure charged multiplicity in 4  l study event with high multliplicity and/or unusual fluctuations l up to 200 Tracks/wafer dE/dx650 MeV/c  /K 1200 MeV/c K/p TOF1200 MeV/c  /K 2000 MeV/c K/p SiTOF Single event multiplicity

7. February 26,1998, ViennaWire Chamber Conference 1998 Heinz PerneggerPage 7 2.) Layout the silicon pad detectors l Use larger pads for the multiplicity measurement (2.6x9 mm 2 ) l Smaller pads for better spatial resolution and lower occupancy in the spectrometer (1x1, 0,0.67x19,… mm 2 ) The challenge: Find a common readout scheme for different pad geometries 17 mm Single Technology for the entire experiment: Silicon Pad Detectors: - provide good multiplicity measurement - can cope with high particle density - provide 2-dimensional position resolution

8. February 26,1998, ViennaWire Chamber Conference 1998 Heinz PerneggerPage 8 Double metal layer for readout of pad detectors l Use a metal 1 layer as electrode and the metal 2 layer to route signals to the detector edge: Advantages of this readout scheme: + readout on detector edge: minimizes multiple scattering (no extra material in active area) + simplifies the readout: different pad geometries can be routed to a single type bond pad array + can use conventional Si-strip detector readout chips on pad detectors Disadvantages: - double metal structure adds to the total detector capacitance - increases capacitance between pads AC coupled Pad (p-implant + metal 1pad) polisilicon bias resistor metal 2 readout line contact hole metal 1- metal 2

9. February 26,1998, ViennaWire Chamber Conference 1998 Heinz PerneggerPage 9 3.) Test results with prototype detectors l Requirements to the detector: total of 462 wafers » total of 9 different pad geometries for entire experiment » leakage current < 5  A in active area » polysilicon resistor >5M  l Si-pad detectors produced by Miracle Technology Co, Taiwan l Will present two different pad geometries: l Type 1 Type 5 Pad size:1x1mm 2 0.667x19mm 2 Pads/detector:22 rows, 70 columns 4 rows, 64 columns Readout line length:7 to 22 mm 2 to 60 mm

10. February 26,1998, ViennaWire Chamber Conference 1998 Heinz PerneggerPage 10 Measurement of detector capacitances Metal 1 to Metal 2 capacitance (1.2  m oxide/nitride insulator layer) l Backplane capacitance of a Type 5 pad Neighbour columns grounded 1 MHz source frequency line width = 10  m line length = 6cm Metal 1-Metal 2 capacitance: from test structure: 4.5pF/cm from detector: 4.7pF/cm Neighbour pads grounded 1 MHz source frequency pad width = 0.667mm pad length = 19 mm Backplane capacitance: from p-n diode: 5.3pF/pad from detector: 5.4pF/pad V fd =105V

11. February 26,1998, ViennaWire Chamber Conference 1998 Heinz PerneggerPage 11 Readout line quality 22 mm 70 mm l Detect broken readout lines by measuring C back-plane l Other typical detector parameter » leakage currents active area @ V fd = 3-5  A » polisilicon resistors = 5M  » depletion voltage = 100-110V n+ p+ M1 “Cb” Broken readout line Currently typical 5% broken readout lines - work on improvement to <2%

12. February 26,1998, ViennaWire Chamber Conference 1998 Heinz PerneggerPage 12 4.) Measurement of Signal response l PHOBOS Electronics: VA-HDR1 chip manufactured by IDE AS, Norway » “Viking”-type sample/hold » high dynamic range of +/- 100 MIPs » peaking time 1-3  s » noise ENC = 660e- + 5e-/pF*C det @  =1.5  s l Setup for testbeam measurement (100GeV pions) » 4 reference x/y detectors » type 1 detector with VAHDR-1 @  =1.2  s l Setup for source test measurement » 90 Sr source with trigger scintilator below test detector » type 5 detector with VAHDR-1 @  =1.0  s

13. February 26,1998, ViennaWire Chamber Conference 1998 Heinz PerneggerPage 13 Signal / Noise performance Differences in S/N mainly due to - larger detector capacitance for Type 5 - larger leakage current/pad - fast shaping during test S/N on both detectors high enough for reliable operation in PHOBOS Pad signal-to-noise Type 1 Type 5

14. February 26,1998, ViennaWire Chamber Conference 1998 Heinz PerneggerPage 14 Measurement of cross talk on Type 1 detector l Use reference system to predict hit position on Type 1 detector l plot signal distribution for predicted pad and all neighbouring pads (Detector related) cross talk less than 0.6% on Type 1 detector top bot center leftright Pad signal (ADC) C= /S center cross talk %: top: <0.1 bot: 0.6* left: <0.1 right: <0.1 top hit bot leftright * crosstalk in analog readout chain 0 200 -200 +20 -200 +20 -200 +20 -200 +20

15. February 26,1998, ViennaWire Chamber Conference 1998 Heinz PerneggerPage 15 Measurement of cross talk on Type 5 detector l Expect largest cross talk of all Phobos detector types due to readout line to pad capacitance (9.4 pF) Cross talk less than 1% on Type 5 detector Pad signal (ADC) C= /S center cross talk %: row 0: 0.9 row 1: 0.6 row 3: 0.5 Row 0 Row 1 Hit in Row 2 Row 3 0 100 -50+5 -50+5 -50+5

16. February 26,1998, ViennaWire Chamber Conference 1998 Heinz PerneggerPage 16 Signal uniformity l readout line length changes with the row number l measure peak signal as function of the row number (relative to average peak) Small dependence on trace line length for Type 1 Signal response uniformity better than 3 % Type 1 Type 5 +2.5% -2.5% +2.5% -2.5%

17. February 26,1998, ViennaWire Chamber Conference 1998 Heinz PerneggerPage 17 5.) The final Phobos Detector Module l Up to 16 VA-HDR1 chips/module l 2, 3 or 4 detectors / module l analog readout of all pads (2-5MHz) l digitization next to detector l data transferred from FEC to the counting house via optical fiber l online signal correction and zero suppression in processor farm

18. February 26,1998, ViennaWire Chamber Conference 1998 Heinz PerneggerPage 18 Assembly and testing stations ready for production l Wafer tested on fully automated probe station (2 @ MIT, 1 NCU, 1 UIC) l hybrids and detectors bonded on Hughes 2450-V bonding station l 2 full lines for hybrid assembly and tests in place l finished modules tested and calibrated with 2-3 station

19. February 26,1998, ViennaWire Chamber Conference 1998 Heinz PerneggerPage 19 First test results of a full Phobos module l Module consists of 16 VAHDR-1 chips and 4 Type 5 sensors l test done with 90 Sr source Source profile on all 4 detectors Sensor 1 Sensor 2 Sensor 3 Sensor 4

20. February 26,1998, ViennaWire Chamber Conference 1998 Heinz PerneggerPage 20 Signal distribution on Phobos module Uniform signal on all 4 detectors Signal / Noise = 16:1 Pad signal (ADC) Sensor 1 S peak = 25.5 Sensor 2 S peak = 25.9 Sensor 3 S peak = 25.8 Sensor 4 S peak = 25.5

21. February 26,1998, ViennaWire Chamber Conference 1998 Heinz PerneggerPage 21 Status and plans for the Phobos Si-Detector l Silicon detectors: » Spectrometer detector Type 1, 2, 3, 4 and 5 are in production » Multiplicity detector (4 layouts) : layout in progress and will run prototype detectors during spring l Readout chip » received already 300 functional VA-HDR1 chips from IDE AS, Norway » additional 1300 ordered and will be delivered during spring and summer l Assembly and Test » automated wafer test operational » developed an assembly procedure for modules » successfully assembled and tested the first spectrometer module » module production has started

22. February 26,1998, ViennaWire Chamber Conference 1998 Heinz PerneggerPage 22 Conclusion l Phobos uses silicon pad detectors for » measurements of high multiplicity events in 4  » reconstruction of low momentum proton and pions in a 14 layer spectrometer » particle identification with dE/dx measurements l Use double metal structure to route signals from pads to the pre-amp » can use same electronics for detectors with different pad configuration » minimizes multiple scattering » the measured cross talk less than 1% » signal uniformity better than 3 % » measured Signal / Noise 15:1 to 25:1 l We assembled and tested a full Phobos Module » fully functional » uniform signal across the module