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Detector Research & Development for Particle Physics at Liverpool

Detector Research & Development for Particle Physics at Liverpool.  Improving Radiation Hardness  Monolithic Active Pixels  Detectors for Very Large Area Arrays  Future Directions. Segmented Semiconductor Devices For Charged Particle Detection. Semiconductor detectors

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Detector Research & Development for Particle Physics at Liverpool

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  1. Detector Research & Development for Particle Physics at Liverpool  Improving Radiation Hardness  Monolithic Active Pixels  Detectors for Very Large Area Arrays  Future Directions

  2. Segmented Semiconductor Devices For Charged Particle Detection Semiconductor detectors are based on segmented diodes which collect charges produced by ionising radiation The position resolution comes primarily from the granularity which exploits standard microchip processing technology

  3. Improving Radiation Hardness  Radiation damage to silicon detectors increases reverse currents, creates interface trapped charge, introduces traps reducing charge collection efficiencies changes the effective doping concentrations  Studies of the latter effect have shown significant improvements under charged hadron irradiation when high concentrations of interstitial oxygen are introduced  However, unlike in the case of n-side read-out detectors, the charge collection efficiencies for p-side read-out detectors do not plateau with voltage until well above the depletion voltage This is usually assigned to the effect of trapping

  4. Detectors Studied at Liverpool The following were carried out with miniature ATLAS p-side strip detectors using a fast current amplifier Also extensively studied are diodes and full-size devices (p-side and n-side strips), the latter using LHC speed 128 channel analogue read-out.

  5. Evaluation of Trapping Effects  Capacitance – Voltage Derived Depletion Voltage 1.90.11014p/cm2 Oxygenated Miniature Micro-strip Detector VFD = 100  7 V from fitting C(V)

  6. Evaluation of Trapping Effects  Corresponding Charge Collection Efficiency vs Voltage 100 V

  7. Old ATLAS Irradiated n-in-n Results 21014p/cm2

  8. Trapping and Ballistic Deficit The trapping probability is expected to depend on the carrier velocity and hence the field. At the LHC, electronics response times are close to charge collection times. Therefore signal loss due to incomplete charge integration must also be considered. (Also velocity / field dependent.) Non-irradiated p-strip Detector

  9. Influence of Ballistic Deficit Miniature detectors irradiated to 1.91014p/cm2 Non-Oxygenated Oxygenated

  10. Influence of Ballistic Deficit Miniature detectors irradiated to 2.91014p/cm2 Non-Oxygenated Oxygenated

  11. Influence of Ballistic Deficit Miniature detectors irradiated to 5.11014p/cm2 Non-Oxygenated Oxygenated

  12. Non-Oxygenated Detectors: Relative Ballistic Deficit Non-irradiated 1.91014 p/cm2 2.91014 p/cm2 5.11014 p/cm2 Oxygenated

  13. Oxygenated Detectors: Relative Ballistic Deficit 1.91014 p/cm2 2.91014 p/cm2 5.11014 p/cm2

  14. Fits to the Charge Collection Efficiency The above results suggest that, particularly at high doses, the ballistic deficit is not a major factor for LHC speed operation In the following fits, sufficient integration time has anyway been allowed such that the only charge loss is due to trapping Free parameters: attenuation length , depletion voltage VFD total generated charge Q0 1.91014 p/cm2

  15. Fits to the Charge Collection Efficiency 2.91014 p/cm2 5.11014 p/cm2

  16. Detector label Fluence [p cm-2] Oxygen enrichment VFD [V] (From C-V) VFD [V] (From CCE) l [m] NI Non irr. No 49  2 50  2 SO1 1.90.1 · 1014 Yes 100  7 90  2 1338  15 SN1 1.90.1· 1014 No 150  8 137  2 1407  220 SO2 2.90.2· 1014 Yes 121 7 130  2 1224  138 SN2 2.90.2· 1014 No 218  15 214  4 1313  122 SO3 5.1 0.4· 1014 Yes 181  15 196  3 731  84 SN3 5.10.4· 1014 No 320  20 348  7 781  55 Fits to the Charge Collection Efficiency

  17. Fits to the Charge Collection Efficiency The fitted values of VFD agree with each other and with other oxygenated data (taking account of the relative neutron to proton damage factor) The fitted values of Q0: 18.10.3, 18.20.3, 17.70.3, 18.10.6, 18.20.4 and 18.30.4 are all consistent and agree with the pre-irradiation value 17.90.3

  18. Fits to the Charge Collection Efficiency The dependence of Q/Q0 and therefore  on  leads to a value of eff = 5.60.610-16cm2/ns (1/ = eff ) Assuming this value allows extrapolation of CCE to high 

  19. Improving Radiation Hardness Because for p-strip read-out, the trapping significantly affects the CCE(V), the improvements in VFD due to oxygenation do not give correspondingly large effects in terms of CCE The trapping dependence on the field leads to CCE(VFD) being higher for non-oxygenated than oxygenated detectors by ~5% Read-out from the high-field n-side gives less dependence on trapping leading to the CCE(V)  V behaviour below VFD This would imply that for high doses, n-side readout should benefit more from oxygenation of the substrate

  20. Consequences for LHC-b The LHC-b vertex detector is proposed to use oxygenated n-strip detectors for which the first prototypes have just been delivered to Liverpool and have very recently been irradiated in the CERN PS

  21. Proposed LHC-b Detectors LHC-b uses back-to-back thinned disks for r and  plus double-metal routing

  22. Consequences for ATLAS LHC-b and the pixel systems of ATLAS and CMS need to maximise their survival; n-side readout oxygenated detectors look to offer the best possibilities Super-LHC with factor of 10 increased luminosity would also need such technology

  23. The Use of p-type Silicon Detectors produced with n-side read-out do suffer from the disadvantage of requiring potentially expensive double-sided processing Use of p-type substrates does provide a viable alternative where cost is of paramount importance Comparison of p-type and n-type detectors after 31014 p/cm2

  24. Monolithic Active Pixel Sensors CCDs have been used at SLAC to achieve excellent spatial resolution for b, c and  tagging. The future Linear Collider would be an excellent environment to use this technology. However, MAPS may prove to be a more radiation tolerant, faster, cheaper alternative with greater built-in functionality. SLD 300 million pixel array

  25. Monolithic Active Pixel Sensors MAPS use standard very fine lithography (deep sub-micron) processing such that each pixel (20m20m) contains its own diode contact to the substrate, amplifier, read-out switches and possibly simple signal processing. The very low input capacitance means that, even at room temperature, the input noise is only a few electrons, so the typically 10m epitaxial layer is still thick enough for signals of up to thirty times the noise to be produced. The use of standard processing allows integration of all read-out features onto the same silicon die (‘camera on a chip’)

  26. Monolithic Active Pixel Sensors Liverpool has helped initiate the ‘PRIMA’ proposal to the Technology Fund (with CLRC, Royal Marsden, LMB Cambridge, Marconi, Surrey and Glasgow) for £3M which was one of the 26 out of 230 proposal to go to full application. Liverpool is part of the international collaboration looking to explore use of such technology at TESLA.

  27. Detectors for Very Large Area Arrays Liverpool, with Cambridge and QMW initiated the use of 150mm wafers within ATLAS with Micron processing 2 detectors on a single wafer to Liverpool mask designs For NASA’s Gamma-ray Large Area Space Telescope, we designed masks for 10cm10cm strip detectors which have been processed and delivered to the collaboration

  28. Detectors for Very Large Area Arrays Silicon detectors have dropped a factor of ten in price in the last decade. However, substrate costs are now a significant fraction of the total for high purity material. Conjugate polymers are being actively developed as semiconductor materials suitable for large area flat display screens. If devices can be produced which are sensitive to ionising radiation then very large area (several thousand square metre) solid-state high spatial resolution detectors may be achievable. MAPS technology could also eventually prove cost effective for very large areas.

  29. Future Directions Semiconductor detectors will continue to improve in radiation hardness with charge collection efficiency finally limiting performance (1015 n/cm2). Fine lithography allows very radiation hard circuits to be designed which, if integrated onto appropriate substrate structures, could give low mass pixel detectors of 100MRad, many 1015 n/cm2radiation hardness. Very large areas could be affordably instrumented with very high spatial resolution detectors in the future using the Moores Law extrapolation of conventional circuitry costs plus MAPS technology or new, much cheaper, substrate materials such as conjugate polymer diodes.

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