A vertex detector for the next linear collider

1. 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 S.Xella – Rutherford Appleton Laboratory

2. 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 ms = 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 S.Xella – Rutherford Appleton Laboratory

3. Importance of the right design optimal vertex detector design is most important, to reach final physics goal ! PRELIMINARY tagging purity vs efficiency 5 layers, 0.1%X0 4 layers, 0.2%X0 S.Xella – Rutherford Appleton Laboratory

4. LCFI collaboration • Linear Collider Flavour Identification collaboration R&D work concentrates on a CCD pixel device : Mechanical support (RAL PPD/Oxford) CCD development design/test (RAL PPD/E2V/ Liverpool) design optimization from physics (see T.Kuhl talk) (RAL PPD/Bristol/Lancaster) Readout IC, Driver IC, … (RAL ME/Oxford) S.Xella – Rutherford Appleton Laboratory

5. Current design (I) • Small pixels (20x20 mm2) • -> 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 S.Xella – Rutherford Appleton Laboratory

6. Current design (II) • 5 layers • -> higher resolution • -> robust local alignment • -> effective gamma conversion • fast readout (50s/layer) • -> sustain high integrated • background • gas cooled, low mass foam • cryostat • minimal electronics (power + • few optical fibres) • -> little material at low angles S.Xella – Rutherford Appleton Laboratory

7. Detector VXD2 VXD3 Future LC 480 96 120 1.2 12.8 27.5 120 307 799 CCDs 2 3 5 28 28 15 1.1 0.4 0.06 CCD active area 0.75 0.90 0.96 Number of pixels 160 ms 216 ms 50/250 (8 ms for NLC) Effective no. of layers Inner layer radius (mm) Layer thickness () (2-hit) Imp. param resoln. Readout time Very challenging ! S.Xella – Rutherford Appleton Laboratory

8. N N “Classic CCD” Readout time  NM/Fout Column Parallel CCD Readout time = N/Fout 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 M S.Xella – Rutherford Appleton Laboratory

9. 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 S.Xella – Rutherford Appleton Laboratory

10. 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 S.Xella – Rutherford Appleton Laboratory

11. Device simulations • ISE-TCAD software used at RAL. Mostly important: • To check feasibility of current design • Foresee show-stoppers • Test new ideas S.Xella – Rutherford Appleton Laboratory

12. 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) S.Xella – Rutherford Appleton Laboratory

13. Standard 2-phase implant Field-enhanced 2-phase implant (high speed) Metallised gates (high speed) Metallised gates (high speed) 2-stage source followers Source followers Source followers Direct Direct Readout ASIC Readout ASIC To pre-amps 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! S.Xella – Rutherford Appleton Laboratory

14. First CPR tests • 0.25 mm 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 mm pitch S.Xella – Rutherford Appleton Laboratory

15. 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 S.Xella – Rutherford Appleton Laboratory

16. 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 S.Xella – Rutherford Appleton Laboratory

17. low drive voltage/CTI Clock traces and 55Fe spectrum for low drive voltages at 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 S.Xella – Rutherford Appleton Laboratory

18. 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 S.Xella – Rutherford Appleton Laboratory

19. Thin ladder options • Unsupported CCD : thinned to 50 mm and held under tension. Tested experimentally: • * sagitta stability found better than 2 mm at T>2N, but • * large differential contraction at CCD surface causes lateral curling + design is difficult to handle • Semi-supported CCD :thinned to 20 mm 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 S.Xella – Rutherford Appleton Laboratory

20. Thin ladder options 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 S.Xella – Rutherford Appleton Laboratory

21. 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 linear • collider • We are only at the first stage of a long R&D program, so stay tuned to hear more ! S.Xella – Rutherford Appleton Laboratory

22. Backup slides S.Xella – Rutherford Appleton Laboratory

23. Backgrounds at the nlc S.Xella – Rutherford Appleton Laboratory

24. Wire/bump bond pads Charge Amplifiers Voltage Amplifiers 250 5-bit flash ADCs FIFO Bump bond pads CPR-1 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) S.Xella – Rutherford Appleton Laboratory

25. Semi-supported silicon Carbon fibre support Aerogel support 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… S.Xella – Rutherford Appleton Laboratory