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Vertex 2002, Kona, Hawaii
A vertex detector for the next linear collider
Stefania Xella
on behalf of the LCFI collaboration: Bristol Univ., Lancaster Univ., Liverpool Univ., Oxford
Univ., Rutherford Appleton Laboratory, Queen Mary University London
hep.ph.liv.ac.uk/~green/lcfi/home.html
Vertex 2002, Kona, Hawaii
Next Linear Collider: a challenging environment for a
vertex detector
Main goal of the next linear collider is to measure PRECISELY the Higgs boson and possibly physics beyond the SM. This requires:
• High energy and luminosity, which might mean high beam background: Tesla: 50 s = 4 backgr hits/mm2 at 15 mm radius => fast detector readout • Optimal jet/flavour reconstruction due to event topology ee->tt : 6 jets, 2 b and 2 c flavoured ee->HA : 12 jets, 4 b flavoured => very granular, low material budget detector
Vertex 2002, Kona, Hawaii
Importance of the right design
5 layers, 0.1%X0
optimal vertex detector design is most important, to reach final physics goal !
PRELIMINARY tagging purity vs efficiencyPRELIMINARY tagging purity vs efficiency
4 layers, 0.2%X0
Vertex 2002, Kona, Hawaii
LCFI collaboration
Linear Collider Flavour Identification collaboration R&D work concentrates on a CCD pixel device :
designoptimizationfrom physics(see T.Kuhl talk) (RAL PPD/Bristol/Lancaster)
CCD developmentdesign/test(RAL PPD/E2V/Liverpool)
Readout IC,Driver IC, …(RAL ME/Oxford)
Mechanicalsupport(RAL PPD/Oxford)
Vertex 2002, Kona, Hawaii
Current design (I)
•Small pixels (20x20 m2) -> precise point resolution• thin detector(<0.1%X0) -> less multiple scattering• close to the IP (15 mm) -> smaller extrapolation error• large polar angle coverage |cos()|<0.90 with 5 hits |cos()|<0.96 with 3 hits
Vertex 2002, Kona, Hawaii
Current design (II)
• 5 layers -> higher resolution -> robust local alignment -> effective gamma conversion• fast readout (50s/layer) -> sustain high integrated background• gas cooled, low mass foam cryostat• minimal electronics (power + few optical fibres) -> little material at low angles
Vertex 2002, Kona, Hawaii
Very challenging !
Detector SLD Future LC
CCDs 96 120
CCD active area (cm2) 12.8 27.5
n. of pixels (106) 307 799
n. of layers 3 5
inner layer radius(mm) 28 15
layer thickness (%Xo) 0.4 0.1
cos() max 0.90 (2 hits)
0.96 (3 hits)
readout time (1 layer) 216 ms 50 s (8 ms NLC)
Vertex 2002, Kona, Hawaii
Column Parallel CCD (CPCCD)
Fast readout speed only with Column parallel readout new design!• Serial register omitted• 50 Mpixels/sec from each column• Image section clocked at high frequency• Each column has its own ADC/amplifier
“Classic CCD”Readout time
NM/Fout
N
M
N
Column Parallel CCDReadout time = N/Fout
Vertex 2002, Kona, Hawaii
Readout chip (CPR)
CMOS circuit bump bonded to the CCD
• Each column has amplifier and ADC
• Correlated double sampling for low noise
• Sparsification done in the chip
• Buffer memory and I/O interface
Vertex 2002, Kona, Hawaii
Ladder end
• Bump bonding CPCCD-CPR
• Driver IC provides high frequency (50MHz), low voltage (1.5V pp) clocks
• 2-phase driven CCD• Low inductance
connections and layout• Small clock and digital
feedthrough
Vertex 2002, Kona, Hawaii
Device simulations
ISE-TCAD software used at RAL. Mostly important: • To check feasibility of current design • Foresee show-stoppers• Test new ideas
Vertex 2002, Kona, Hawaii
Status of R&D program
• 5 or 6 stage R&D program in collaboration with E2V (former Marconi Applied Technology) company in the UK
• Test for high speed CCD readout (up to 50MPix/sec) successfully carried out on standard CCD58 device, in serial register
• Test for radiation damage at different temperatures/RO frequency being carried out
• CPCCD-1 and CPR-0,1 are (being) produced. Testing during end2002/beg2003• Several options for mechanical support design currently
investigated (unsupported/semi-supported)
Vertex 2002, Kona, Hawaii
First CPCCD-CPR
• 2 different charge transfer regions
• 3 types of output circuitry
• Independent CPCCD and CPR test possible
• Designed to work in almost any case!
Standard 2-phaseimplant
Metallised gates(high speed)
Metallised gates(high speed)
Field-enhanced 2-phase implant (high speed)
Sourcefollowers
Sourcefollowers DirectDirect
2-stagesource
followers
To pre-amps
ReadoutASIC
ReadoutASIC
Vertex 2002, Kona, Hawaii
First CPR tests
• 0.25 m CMOS • Charge transfer amplifier (CTA) in each ADC comparator• Designed to work up to 50 MHz• First CPR produced: small chip (2x6mm), testing flash ADC
and voltage amplifiers. Very promising results.• Next CPR contains CTA,ADC,FIFO memory in 20 m pitch
Vertex 2002, Kona, Hawaii
Tests of high speed CCD
E2V CCD58
• 3-phase driven CCD
• Classical readout
(serial register)• 12 m 2 pixels• 2 outputs• 2x106 pixels in
two sections
Vertex 2002, Kona, Hawaii
Tests of high speed CCD
55Fe X-ray spectrum at 50 Mpix/s
• MIP-like signal (5.9 keV X-rays generate 1620 electrons)
• Low noise 50 electrons at 50 MHz clocks
• CCD58 is designed to work with large signals at 10 Vpp clocks
• No performance deterioration down to 5 Vpp clocks
• Still good even at 3 Vpp clocks
Vertex 2002, Kona, Hawaii
low drive voltage/CTI
Clock traces and 55Fe spectrumfor low drive voltagesat 50 Mpix/sec
Radiation damage effects:• beam background expected about 50krad/year (neutron 5x109/cm2/year)• CTI should improve at fast readout : to be verified• CCD58 can be flexibly clocked from 1 to 50 MHZ, so it should be possible to obtain good results for CTE
Vertex 2002, Kona, Hawaii
Mechanical support R&D
Final goal is to design a CCD support structure with
• Low mass (< 0.1% Xo)• Stable shape under repeated temperature
cycles down to –100oC• Minimum metastability and hysteresis effects• Compatible with bump bonding• Robust assembly• Able to undergo gentle gas cooling
Vertex 2002, Kona, Hawaii
Thin ladder options
• Unsupported CCD : thinned to 50 m and held under tension. Tested experimentally:
* sagitta stability found better than 2 m at T>2N, but
* large differential contraction at CCD surface causes lateral curling + design is difficult to handle
• Semi-supported CCD :thinned to 20 m and attached to thin (not rigid) Be support, held under tension. Tested in ANSYS simulation:
* CCD surface may become dimpled: under study * may need fine pitched matrix of glue: difficult? => still lots of work to do and ideas to test
Vertex 2002, Kona, Hawaii
Thin ladder options
Be substrate
~300µm(0.12% X
0)
CCD
Recessed NuSil adhesive pads
CCDBe
substrate
1mm
CCD (20 μm thin) bonded with adhesive pads to 250 μm Be substrate
On cooling adhesive contracts more than Be pulls Si down on to Be surface
Layer thickness 0.12% Xo
1 mm diameter adhesive columns inside 2 mm diameter wells 200 μm deep in Be substrate
Vertex 2002, Kona, Hawaii
Summary
The LCFI collaboration R&D program is vast, and very challenging. Its aim is to provide a fast and low material budget CCD based pixel
detector to maximize the physics potential of the next
linearcollider
We are only at the first stage of a long R&D program, so stay tuned to hear more !
Vertex 2002, Kona, Hawaii
Backup slides
Vertex 2002, Kona, Hawaii
Backgrounds at the nlc
Vertex 2002, Kona, Hawaii
CPR-1
FIFO
250 5-bit flash ADCs
Charge Amplifiers Voltage Amplifiers
Wire/bump bond pads
Bump bond pads
In CPR-1:
Voltage amplifiers – for source follower outputs from the CPCCD
Charge amplifiers – for the direct connections to the CPCCD output nodes
Amplifier gain in both cases: 100 mV for 2000 e- signal
Noise below 100 e- RMS (simulated)
Direct connection and charge amplifier have many advantages:
Eliminate source followers in the CCD
Reduce power 5 times to 1 mW/channel
Programmable decay time constant (baseline restoration)
ADC full range: 100 mV, AC coupled, Correlated Double Sampling built-in (CTA does it)
Vertex 2002, Kona, Hawaii
Semi-supported silicon
~1mm(0.12% X
0)
20µm Si
CCD
Aerogel
Carbon fibre: CTE is tunable, layers can have optimal orientation and fibre diameter, difficult to simulate
Aerogel support: chemically bonds to Si, aerogel in compression
Many other ideas: CVD diamond, vacuum retention, etc…
Carbon fibre support
Aerogel support