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July 14 2003 C Damerell LC technologies Cornell U 1 LC vertex detector technology options Chris Damerell The transition from microstrips to pixels, for.

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Presentation on theme: "July 14 2003 C Damerell LC technologies Cornell U 1 LC vertex detector technology options Chris Damerell The transition from microstrips to pixels, for."— Presentation transcript:

1 July C Damerell LC technologies Cornell U 1 LC vertex detector technology options Chris Damerell The transition from microstrips to pixels, for vertex detectors Detector requirements Detector architectures CCDs Monolithic APS (including FAPS) DEPFET Hybrid APS SOI-inspired RF pickup suppression Correlated double sampling The route to convergence Synergy with other science

2 July C Damerell LC technologies Cornell U 2 Since late70s, successful vertex detectors (for heavy flavour tagging) were mainly based on silicon microstrips Interesting paradigm shift is under way. Within 5 years, will mostly be based on silicon pixels Why is this? highest performance b and charm tagging in dense track environments has come from a series of pixel-based detectors, NA32 in 80s, SLD in 90s extreme radiation environments in the inferno close to IP at future hadron colliders high track density in core of jets at future e + e - colliders The disparate requirements at hadron and e + e - colliders have very different solutions, and are supported by contrasting R&D programmes The transition to pixels implies valuable synergies for other areas of science, where images taken with IR, visible, UV, X-rays benefit from the technologies being developed for HEP vertex detectors, and vice versa

3 July C Damerell LC technologies Cornell U 3 Of course, it will definitely be silicon pixels at the LC, or will it?

4 July C Damerell LC technologies Cornell U 4 Detector requirements Most were mentioned in LCFI talk: concentric barrels, thinnest possible layers, micron-level precision and stability Budget of inactive material (eg in endcaps) is also extremely important With ~10 9 channels, suppression of noise and pickup may be decisive

5 July C Damerell LC technologies Cornell U 5 Historically, some vertex detectors have diminished the capability of their experiments for leading edge physics: the possible top signal at 40 GeV in UA1 (early 80s) the possible Higgs signal in LEP (late 90s) Success at the LC should not be taken for granted. R bp could strike again … Intensive R&D in several technologies will surely be justified (cost effective) in terms of LC physics reach This is an area in which there is a distinct technical advantage (hence enhanced physics potential) wrt the inferno at the heart of LHC

6 July C Damerell LC technologies Cornell U 6 Detector architectures

7 July C Damerell LC technologies Cornell U 7

8 July C Damerell LC technologies Cornell U 8 MAPS Standard CMOS process so signal charge is collected from undepleted bulk or epitaxial layer However this isnt obligatory – early S Parker developments with 300 µm fully depleted devices were highly successful Early results have been based on few mm 2 devices and minimal in- pixel logic Recently, using 0.35 µm CMOS, increasing functionality is being implemented at the periphery of the chip by the Strasbourg group Flexible active pixel idea (Renato Turchetta at RAL) could lead the way to a TESLA-compatible architecture

9 July C Damerell LC technologies Cornell U 9 DEPFET Based on detector-grade high resistivity silicon, fully depleted Requirement of supporting CMOS chips on 2 sides may be a significant limitation Has advantage (wrt current MAPS) of fast CDS, given promise of pulsed clear of entire signal charge after each row readout, so equivalent noise performance and pickup suppression to CCD option HAPS (incl new SoI-inspired) Read 1 in N pixels, by analogy with capacitive charge division in strip detectors Resolution tends to be somewhat unstable Implications for 2-track resolution? SoI approach could reduce material, but looks pretty complex (?)

10 July C Damerell LC technologies Cornell U 10 MIMOSA-5 Strasbourg group

11 July C Damerell LC technologies Cornell U 11 MIMOSA-6 incorporates rolling shutter CDS in pixel device size 3.6x0.84 mm: plan to extend to sideways columns on ladder Discriminators, but not yet ADCs or data sparsification, on chip periphery

12 July C Damerell LC technologies Cornell U 12 FAPS could be extended to a full 20 samples per train, stored in pixel Again, limited to rolling shutter CDS Idea is to relax the requirement for fast, precise, signal transmission to chip periphery during train, and so render long columns feasible, with all processing logic out of the detector active volume, as for the CCD architecture FAPS RAL group

13 July C Damerell LC technologies Cornell U 13 MOS transistor instead of JFET A pixel size of ca. 20 x 20 µm² is achievable using 3µm minimum feature size. DEPFET Bonn/Munich group

14 July C Damerell LC technologies Cornell U 14 thin detector-area down to 50µm frame for mechanical stability carries readout- and steering-chips first thinned samples: [L.Andricek, MPI Munich] matrix is read out row-wise

15 July C Damerell LC technologies Cornell U 15 DEPFET pixel matrix - Read filled cells of a row - Clear the internal gates of the row - Read empty cells Low power consumption Fast random access to specific array regions

16 July C Damerell LC technologies Cornell U 16 Hybrid Pixel Detector with Interleaved Pixels Charge carriers generated underneath one of the interleaved pixel cells induce a signal on the capacitively coupled read-out pixels, leading to a spatial accuracy improvement by a proper signal interpolation. readout pitch = n x pixel pitch Large enough to house the VLSI front-end cell Small enough for an effective sampling HAPS Insubria/Krakow group

17 July C Damerell LC technologies Cornell U 17 Charge Sharing Studies – Resolution Resolution: –Interleaved pixels (efficient charge sharing): 3 m parameterization allows a coordinate reconstruction and resolution measurement function Average resolutionResolution vs. spot position

18 July C Damerell LC technologies Cornell U 18 SOI Imager – Main Concept Detector handlable wafer –High resistivity –300 m thick Electronics active layer –Low resistivity –1.5 m thick –Readout pixels (min charge sharing): 10 m Detector: conventional p + -n, DC-coupled Electronics: preliminary solution – conventional bulk MOS technology on the thick SOI substrate Insubria/Krakow group

19 July C Damerell LC technologies Cornell U 19 RF pickup suppression Beam-associated RF radiation penetrating the beam-pipe (even 0.25 mm Be) is presumably negligible (provided it isnt CF as tried in UA1) However, flanges, BPM cables, etc can permit RF radiation to leak out SLD experience: analogue signals stored securely in CCD buried channel Digital logic (PLL in optical links) was disrupted – fortunately could be restored within some s of end of bunch train) NLC/JLC: could envisage similar settling/restoration before readout TESLA: need to read detector repeatedly during train, to internal storage of sparsified data each internal frame readout spans ~150 BX, so electronics is hit repeatedly by whatever RF is present For SLD VTX, this would have been fatal As part of the verification procedure of any prototype ladder, suggest testing in a final focus lab where machine bunches are simulated by current pulses down wires in the beam-pipe, and all other FF equipment is in and running – needed as part of the GAN

20 July C Damerell LC technologies Cornell U 20 Correlated double sampling? CDS is the term invented circa 1972 for the form of pedestal subtraction used to suppress reset noise in CCD front-end circuits Simplest CDS involves: Reset***measure V-out***transfer signal charge***re-measure V-out Used to reduce the system noise from tens of e - to ~1 e - by suppressing the fluctuations in post-reset V-out DEPFET shares robust CDS capability with CCD, in LC application: read pedestal+signal***reset – ie remove signal Q***read pedestal alone However, MAPS CDS involves subtraction over full frame period of 50 s or whatever could in principle be resolved by incorporating 1-pixel CCD, or DEPFET structure, within the CMOS pixel CDS with = 50 s? SLD was OK in inter-train period with 200 s CDS sampling period might get away with it at NLC, after some settling time might not work at TESLA due to RF activity within train

21 July C Damerell LC technologies Cornell U 21 Extended row filter, SLD

22 July C Damerell LC technologies Cornell U 22 Effectiveness of ERF in suppressing noise hits (including pickup in operational conditions)

23 July C Damerell LC technologies Cornell U 23 Route to convergence Preferred technology(ies) to be selected on basis of full-size, fully operational prototype ladders (around 2010?) Choice probably time dependent: what can be ready for startup could well be superseded later [eg at SLC: silicon microstrips were replaced by CCDs in 1990] Convenient access to IR is an essential requirement (for the entire inner detector system) R&D groups should resist pressure from funding agencies to pick the winner Premature choice of technology could seriously degrade the physics potential Good world-wide communication is building a proto-collaboration for the VTX (eg phone conference at time of Arlington LC workshop)

24 July C Damerell LC technologies Cornell U 24 Construction, commissioning, operation and physics When choice is made, some groups (technically oriented) will prefer to develop their technology for other applications or possible upgrades Others (particle physics oriented) will wish to contribute to the construction of the first detector(s) The detector construction should be encouraged as a world-wide endeavour, in spirit of GDN SLD ladders (via UPS) SanJose SLAC e2V Brunel SLAC Yale MIT SLAC Make mbds Test mbds Fit CCDs Mech QC Functional test Fit blocks Opt survey Intstall Exploration of this new continent is at an early stage: dont jump to premature conclusions

25 July C Damerell LC technologies Cornell U 25 Synergy with other science Pixel detectors are uniquely inter-disciplinary Example from fall of the wall in structural biology (J Hajdu, TESLA colloquium) 120 Hz frame rate needed at LCLS (with 14 bit dynamic range) SNAP (600 Mpixels), XEUS, biological cell imaging, … Fast Gigapixel-scale imaging systems are widely needed, and the LC vertex detector community is making a strong contribution to their development


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