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Status of CCD Vertex Detector R_D for GLC

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					 Status of CCD Vertex
Detector R&D for GLC
                   Yasuhiro Sugimoto
                                KEK
 KEK/Niigata/Tohoku/Toyama Collaboration
   @Vertex Phone-meeting, Dec. 14, 2003




               Status of CCD Vertex Detector R&D for GLC   1
Outline
l   Introduction
l   R&D for thin wafer
l   Study of radiation tolerance
    l   Expected beam background
    l   Electron damage study -- H.E. beam/beta ray
l   Study of charge spread
l   Possible design of Vertex Detector for GLC
l   Summary and outlook

                     Status of CCD Vertex Detector R&D for GLC   2
Introduction
l       To get the excellent vertex resolution
    1. High spatial resolution of the sensor
    2. Thin material to minimize the multiple scattering
    3. Put the detector as close to the IP as possible
           è Radiation tolerance
l       CCD
    l    1. è Excellent resolution by charge sharing : σ < 3 µm
    l    2. è Sensitive layer ~20 µm, Mechanical Strength?
    l    3. è Not clear. Need R&D.
    l    Other R&D item : Readout Speed
    l    CCD: simple structure è Large size wafer with high yield

                        Status of CCD Vertex Detector R&D for GLC   3
R&D for thin wafer
l   Structure of CCD
    l   p+ substrate : ~300µm
    l   Epitaxial p layer : ~20µm
    l   n layer : few µm

    è We need only ~20µm for
      charged particle detection




                        Status of CCD Vertex Detector R&D for GLC   4
R&D for thin wafer
l   How to support thin
    wafer?
    l   Backing
    l   Stretching
    l   Partial thinning
        l Large area thinning
          brings non-flatness
        l Ordered several
          wafers with different
          cell sizes
        l Aim average thickness
          < 100µm

                        Status of CCD Vertex Detector R&D for GLC   5
Study of radiation tolerance
l   Expected Beam Background at GLC
    l   Neutron : Mainly from downstream of the beam line
        108~109 /cm2 y (depends on beam line design)
    l   Electron/Positron : Pair background through beam-beam
        interaction -- Strongly depends on B and R

                          B=3T,                     B=3T,              B=4T,
                          R=24mm                    R=15mm             R=15mm
        Hits/train
                                 0.3                            2           1
        ( /mm2)
        Hits/y (107sec)
                            0.5x1011                        3x1011       1.5x1011
        ( /cm2)
                           Status of CCD Vertex Detector R&D for GLC                6
Study of radiation tolerance
l   NIEL Hypothesis
    l   Bulk damage is thought to be proportional to non-
        ionizing energy loss (NIEL)
    l   NIEL of electrons has strong energy dependence
    l   e+/e- pair background hitting the inner-most layer of
        VTX at LC peaks at ~20MeV
        è High energy electron beam irradiation test
    l   NIEL of neutrons is ~x10 than that of H.E. electrons,
        but expected b.g. rate is 1/100~1/1000
        è Not so serious



                          Status of CCD Vertex Detector R&D for GLC   7
Study of radiation tolerance
       Sr-90             GLC b.g.




               Status of CCD Vertex Detector R&D for GLC   8
Electron Damage Study
l   Test Sample CCDs
    l   256x256 pixels
    l   Made by Hamamatsu
    l   Readout Freq : 250kHz
    l   Readout Cycle : 2 sec
    l   Irradiation:
        l At room temperature

        l Without bias/clock

        l Sr-90: 0.6, 1.0, 2.0 x 10 11/cm 2

        l 150 MeV beam: 0.5, 1.0, 2.0, 5.0 x 1011/cm2



                         Status of CCD Vertex Detector R&D for GLC   9
Electron Damage Study
l   Measurement of CCD characteristics
    l   Dark current
    l   Spurious dark current
    l   Flat-band voltage shift
    l   Charge transfer inefficiency (CTI)




                      Status of CCD Vertex Detector R&D for GLC   10
Electron Damage Study
l   Hot Pixels
    l   Observed only in beam-irradiated CCDs
    l   Presumably due to cluster defects which cannot
        be created by low energy electrons

                 Measured at +10 °C, Cycle time: 2 sec

                                                                   150MeV Beam
                 Sr-90                                             •Before Irradiation
                 •1x1011/cm2                                       •1x1011/cm2
                 •2x1011/cm2



                       Status of CCD Vertex Detector R&D for GLC                         11
Electron Damage Study
l   Charge Transfer
    Inefficiency (CTI)
    l   Derived from position
                                                                     Beam
        dependence of Fe-55
        X-ray(5.9keV) peak                                           Sr-90
    l   CTI induced by 150MeV
        beam is x2~3 larger
        than Sr-90 induced CTI
    l   CTI suppression by fat-
        zero charge injection
        was observed



                         Status of CCD Vertex Detector R&D for GLC           12
Electron Damage Study




          Status of CCD Vertex Detector R&D for GLC   13
Electron Damage Study




          Status of CCD Vertex Detector R&D for GLC   14
Electron Damage Study
l   CTI improvements
    ü Notch channel : è1/3
    ü Fat-zero charge injection
    l Fast readout speed

    l Wide vertical clock

    l Reduction of # of transfer

      è Multi-port CCD




                       Status of CCD Vertex Detector R&D for GLC   15
Study of charge spread in CCD
l   Diffusion of electrons in
    epitaxial layer
    l   Key of excellent spatial
        resolution for CCD ( and
        CMOS )
    l   Takes time to diffuse :
        How long do we have to
        wait for the charge
        collection ?
        è Measurement with
           IR LASER pulse

                       Status of CCD Vertex Detector R&D for GLC   16
Possible design of the CCD
vertex detector for GLC
l   Standard CCD
    l   >100MHz speed is needed
        for 6.3ms readout time of
        GLC
l   Multi-port CCD
    l   Wide vertical clock cannot
        be used
l   Multi-thread CCD
    l   Optimum in terms of
        radiation tolerance
    l   R&D necessary
                         Status of CCD Vertex Detector R&D for GLC   17
Possible design of the CCD
vertex detector for GLC
l   Baseline design
    l R=24, 36, 48, 60 mm
    l |cosθ| < 0.9
    l σ = 4 µm
    l Wafer thickness = 300 µm
    l B = 3T
      è σb = 7 ⊕ 20/(pβsin3/2θ) µm
l   R&D milestone
    l R=15, 24, 36, 48, 60 mm
    l |cosθ| < 0.9
    l σ = 4 µm
    l Wafer thickness = 100 µm
    l B = 4T
      è σb = 5 ⊕ 10/(pβsin3/2θ) µm
                       Status of CCD Vertex Detector R&D for GLC   18
Possible design of the CCD
vertex detector for GLC
l   Expected signal loss by CTI
    l   Assume 32(V)x2000(H) pixels at R=15mm, B=4T
    l   Measured CTI: 3x10-4 (V), <5x10-5 (H) for 1x1011e/cm2
        @-70 °C w/o fat-zero charge injection
    l   Simulated pair b.g. in 1 year (107s): 1.5x1011e/cm2
        è Signal loss: 1.5% (V), < 15% (H)
    l   With notch channel: 0.5% (V), < 5% (H)
    l   Fat-zero charge injection, wider V-clock, faster H-clock will
        improve the CTI still more
    l   Even room temperature operation might be possible

                         Status of CCD Vertex Detector R&D for GLC   19
Summary and outlook
l   R&D status for CCD vertex detector for GLC:
    l   Study of partially thinned wafer: Sample wafers
        ordered
    l   Radiation damage study: 150MeV beam
        irradiation test was carried out, and we found
        l   Hot pixel generation
        l   x2~3 larger CTI than 90Sr irradiated CCDs
        l   CTI suppression by fat-zero charge injection
    l   Charge spread in CCDs is being studied

                         Status of CCD Vertex Detector R&D for GLC   20
Summary and outlook (cont.)
l   Future plan
    l   Extend the present R&D :
        l   Optimize the design of partially thinned wafer
        l   CTI study as a function of clock width, speed, and
            amplitude
    l   Study the feasibility of Multi-thread CCD and try
        to make the prototype CCD + readout ASIC




                         Status of CCD Vertex Detector R&D for GLC   21

				
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posted:10/21/2011
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