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2001 December Review Detector Research & Development for Particle Physics at Liverpool Improving Radiation Hardness Monolithic Active Pixels Detectors.

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Presentation on theme: "2001 December Review Detector Research & Development for Particle Physics at Liverpool Improving Radiation Hardness Monolithic Active Pixels Detectors."— Presentation transcript:

1 2001 December Review Detector Research & Development for Particle Physics at Liverpool Improving Radiation Hardness Monolithic Active Pixels Detectors for Very Large Area Arrays Future Directions

2 2001 December Review 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 2001 December Review 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 2001 December Review 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 2001 December Review Evaluation of Trapping Effects Capacitance – Voltage Derived Depletion Voltage p/cm 2 Oxygenated Miniature Micro-strip Detector V FD = V from fitting C(V)

6 2001 December Review Evaluation of Trapping Effects Corresponding Charge Collection Efficiency vs Voltage 100 V

7 2001 December Review Old ATLAS Irradiated n-in-n Results p/cm 2

8 2001 December Review 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 2001 December Review Influence of Ballistic Deficit Miniature detectors irradiated to p/cm 2 Non-OxygenatedOxygenated

10 2001 December Review Influence of Ballistic Deficit Miniature detectors irradiated to p/cm 2 Non-OxygenatedOxygenated

11 2001 December Review Influence of Ballistic Deficit Miniature detectors irradiated to p/cm 2 Non-OxygenatedOxygenated

12 2001 December Review Non-Oxygenated Detectors: Relative Ballistic Deficit Oxygenated p/cm p/cm p / cm 2 Non-irradiated

13 2001 December Review Oxygenated Detectors: Relative Ballistic Deficit p/cm p/cm p/cm 2

14 2001 December Review 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 V FD total generated charge Q p/cm 2

15 2001 December Review Fits to the Charge Collection Efficiency p/cm p/cm 2

16 2001 December Review Fits to the Charge Collection Efficiency Detector label Fluence [p cm -2 ] Oxygen enrichment V FD [V] (From C-V) V FD [V] (From CCE) [ m] NI Non irr. No SO · Yes SN · No SO · Yes SN · No SO · Yes SN · No

17 2001 December Review Fits to the Charge Collection Efficiency The fitted values of V FD agree with each other and with other oxygenated data (taking account of the relative neutron to proton damage factor) The fitted values of Q 0 : , , , , and are all consistent and agree with the pre-irradiation value

18 2001 December Review Fits to the Charge Collection Efficiency The dependence of Q/Q 0 and therefore on leads to a value of eff = cm 2 /ns (1/ = eff ) Assuming this value allows extrapolation of CCE to high

19 2001 December Review Improving Radiation Hardness Because for p-strip read-out, the trapping significantly affects the CCE(V), the improvements in V FD due to oxygenation do not give correspondingly large effects in terms of CCE The trapping dependence on the field leads to CCE(V FD ) 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 V FD This would imply that for high doses, n-side readout should benefit more from oxygenation of the substrate

20 2001 December Review 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 2001 December Review Proposed LHC-b Detectors LHC-b uses back-to-back thinned disks for r and plus double-metal routing

22 2001 December Review 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 2001 December Review 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 p/cm 2

24 2001 December Review 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 2001 December Review 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 2001 December Review 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 2001 December Review 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 NASAs Gamma-ray Large Area Space Telescope, we designed masks for 10cm 10cm strip detectors which have been processed and delivered to the collaboration

28 2001 December Review 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 2001 December Review Future Directions Semiconductor detectors will continue to improve in radiation hardness with charge collection efficiency finally limiting performance (10 15 n/cm 2 ). 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 n/cm 2 radiation 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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