Marc Weber Rutherford Appleton Laboratory Bob Ely, Sergio Zimmermann, Paul Lujan LBNL Rong-Shyang Lu Academia Sinica Taiwan Shielding and Electrical Performance of Silicon Sensor Supermodules developed for the CDF Run IIb detector upgrade

What is a supermodule ? highly integrated mechanical, electrical and thermal structure; single-sided silicon strip sensors on top and bottom; 66 cm long; 3072 channels; low mass: 150 g; 1.7% of a radiation length 4-chip hybrids silicon sensors front side back side

How to use a supermodule ?  supermodules supported by bulkheads only => minimizes material  services at one end only => 1.2 m long 2-barrel construction Interesting design also for future hadron colliders Supermodules or staves Barrel Bulkhead 2 barrels with 192 supermodules around beampipe (+ Layer 0) for CDF Run IIb: Services

A closer look: schematic side view “simple” layer structure: SVX4 chip on BeO hybrid on single- sided sensor on bus cable on carbon fiber/foam core  hybrid is wire-bonded to bus cable through 3 mm gap between pairs of sensors  bus cable copper traces stop after reaching 3. hybrid  25/50 μm thick aluminum shields under each sensor pair, connected to hybrid ground (AG=DG=HG)  top and bottom side nearly symmetric, but typically axial strips on top and 1.2  stereo strips on bottom

Advantages  compact, light weight, radiation hard components  “easy” to build => fast construction, cheap, reliable  ideal for assembly: integrated services, modular detector  proximity of sensors and bus cable can cause systematic pedestal shifts (“pick-up”) => “fake hits”, noise occupancy, etc.  CDF runs in deadtime-less mode (data acquisition during “noisy” digitize and readout) to increase trigger bandwidth  requires understanding and suppression of conductive and capacitive interference mechanisms (see IEEE Trans. Sci., vol. 51, no. 3, pp , June 2004) Challenges

 single 18 μm thick copper layer (minimize material)  25 μm or 50 μm thick aluminum shield between copper and silicon sensors  wide power traces; joint digital grounds; etc. to minimize IR drops Layout of a low-tech component crucial for system performance Bus cable layout

Electrical Performance plot shows pedestal of arbitrary channels as a function of time/ chip mode every channel with “signal” above average pedestal by “2-3” x noise will be read out and used in tracking algorithms BE_CLK :______________________________ COMP_RST:XXXXXXXXXXXXXXXX___________ RREF_SEL:XXXXXXXXXXXXXXXXXXX________ FE_MODE :87XXXXXXXXXXXXXXXXXXX90XXX FE_CLK :T______T______T______T______T_ L1A :XXXXXXXXXXXXXXXXXXXXXXXXXX PRD1 :_____XXXXX________________XXXX  Excellent performance ! but one puzzle remained … a bucket bits of a control pattern Noise: ~2ADC counts/1000 e

Electrical Performance plot shows pedestal of all channels at arbitrary time (front-side, 25 μm shield, 3 hybrids superimposed) every channel with “signal” above average pedestal by “2-3” x noise will be read out and used in tracking algorithms What is this structure ? ( 50 ADC = 1 MIP) Pick-up above FE clock line !

Different experimental setups plot shows pedestal of all channels at an arbitrary time no pick-up if:  1.2  stereo strips (at supermodule bottom side)  no clock lines under sensor (at 3. sensor pair)  50 μm thick aluminum shield (final layout) => CDF supermodule design OK, but What is the interference mechanism ? ( 50 ADC = 1 MIP)

Transverse supermodule X-section (strips and clock traces run into slide plane, not to scale !) layer thicknesses: Sensor: 320 μm Adhesive: 25 μm Kapton: 25 μm Adhesive: 25 μm Aluminum: 25/50 μm Adhesive: 25 μm Copper: 18 μm Kapton: 25 μm … Would like to understand width and size of pick-up CLOCKCLOCK_B Sensor p-implants, AC coupling, ~40 μm pitch, every 2. strip is read out 75 μm width/ 100 μm space

 front-end clock signal => time-dependent magnetic fields => Eddy currents in aluminum shield => current produces magnetic field seen by the silicon strips  adjacent strips form loop (through preamplifier ground and interstrip capacitance) => time-dependent magnetic flux perpendicular to loop leads to emf => net current into preamplifier: “pick-up” Interference mechanism L/2 Strip Z axis X Axis - L/2 Interstrip capacitance 

Calculation of B Analytical approach following Smythe: Eddy currents in infinite plane sheet by image method x is coordinate perpendicular to shield and strips; z is coordinate along strips z Numerical approach using Maxwell 2D program from Ansoft: decent agreement of results Various approximations: only 10 Fourier harmonics to parameterize time- dependence of fields; consider only 19 adjacent strips; use only dominant pole to describe SVX4 preamp rise times; >10% uncertainty in clock driver currents; 2D model; ignored carbon fiber at supermodule core; etc.

Comparison with simulation  data averaged over 180 events, excellent data quality  here “extreme” scenario chosen to maximize effect: thin aluminum shield ( 25 μm); max. driver current ( ~20 mA); min. rise time  width and size of simulation ~30% too small (in our approximations), but Main effect reproduced by simulation Data Simulation

What influences size of interference ?  Clock driver currents: pick-up proportional to driver current; reduction by factor 2 for minimum current  Aluminum shield thickness (50 μm and 25 μm) : Simulation: reduction by factor ~5 with 50 μm shield Data: no pick-up for thick shield (in standard clock pattern)  Preamp bandwidth/rise times: pick-up reduced with increasing preamp rise time in data and simulation (by > factor 2)  [ Clock frequencies: little variation in data when reducing clock frequency from 50 MHz by factor 4.5 ] Huge collection of data, so far always consistent with simulation

Given a quantitative model of typical interference effects:  less prototyping needed  can optimize system components ( transceivers, readout chips, bus cable) at early design stages  simple design choices can have big effect: e.g. small 1.2  angle between strips and clock traces (rotate strips or rotate traces !)

Summary/Conclusions  local pedestal fluctuations in strips above a clock trace observed in prototype supermodules  Time-dependent magnetic fields, associated with clock signals, induce an emf in adjacent strips, which leads to a net charge flow into preamp  Numerical and analytical calculations of this effect agree with the data  the fields can be suppressed efficiently by a thin aluminum shield Quantitative estimate of interference effects possible, gives superior system design Electrical performance of CDF Run IIb supermodules is excellent Compact packaging can be combined with deadtime-less operation

Electrical Performance: prototype plot shows pedestal of arbitrary channel as a function of time/ chip mode every channel with “signal” above average pedestal by “2-3” x noise will be read out and used in tracking algorithms BE_CLK :______________________________ COMP_RST:XXXXXXXXXXXXXXXX___________ RREF_SEL:XXXXXXXXXXXXXXXXXXX________ FE_MODE :87XXXXXXXXXXXXXXXXXXX90XXX FE_CLK :T______T______T______T______T_ L1A :XXXXXXXXXXXXXXXXXXXXXXXXXX PRD1 :_____XXXXX________________XXXX Fair performance (if RTPS), but final design is much better ! a bucket bits of a control pattern

Interstrip capacitance L/2 Strip Z axis X Axis - L/2 