HFT Technology and Mechanical Design

1. HFT Technology and Mechanical Design Wieman RNC LBNL TAC Review Wed. 11:30 – 12:05 15-Mar-2006

2. Topics • Requirements and features • CMOS APS Detector Technology • APS Introduction • Basis for Technology Choice • Development history • Efficiency vs Accidentals based on electron beam measurements • R&D plan, a 4 ms chip followed by a 0.2 ms chip • Detector Verification in STAR Environment • Mechanical Concept • Minimum mass ladders • Single end support • Stable reproducible spatial alignment • Rapid insertion and removal • Thin beam pipe system • Conclude with summary of R&D issues

3. Requirement Detect low momentum D’s in the environment of high multiplicity heavy ion collisions and high luminosity at RHIC in the most effective manner consistent with available resources

4. Some HFT features

6. MIMOSTAR APS uses forward biased diode Pixel signal read every 4 ms Correlated double sample (CDS) – the difference between each sample Decay time is long compared to sample period ~100 ms

7. Basis for CMOS APS Technology Choice • Hybrid technology (silicon pixels bump bonded to ASIC readout) • Advantages: • Very fast, short integration time, no pileup • Potential for trigger generation • Rad hard • Well established technology, ATLAS etc • Disadvantages: • Too thick for optimum pointing accuracy required for low momentum D meson reconstruction • Additional mass required for cooling • Requires establishing complicated partnerships for production and testing (can’t just buy units)

8. Basis for CMOS APS Technology Choice • CCD technology • Advantage: • Successfully used in high precision vertex detector, VXD3 of SLD • Disadvantages: • Limited radiation tolerance • Sufficient readout speed pushes technology boundaries • Limited industry access • DEPFET technology • Advantages: • Excellent signal to noise • Sophisticated thin ladder structures • High speed • Probably RAD hard • Disadvantages: • Single foundry • Highly specialized one of a kind technology • No currently installed systems

9. Basis for CMOS Technology Choice • CMOS APS technology • Advantages: • Relatively RAD hard • Available through multiple standard CMOS foundries • Inexpensive commercial thinning • Good success rate making working detectors by many institutions • Excellent position resolution and fine granularity • Partnered with the leading institution, IReS (now IPHC) in Strasburg • Young technology, can expect considerable growth in capability • Disadvantages: • Young technology for vertex detectors, currently no installed systems • Limited signal to noise • Current designs have relatively long integration times, i.e. potential pileup at highest luminosities

10. Si Pixel Developments in Strasbourg • Mimosa – 1 • 4k array of 20 m pixels with thick epi layer • Mimosa – 4 • Introduce Forward Biased Diode • Mimosa – 5 • 1M array of pixels, 17 m pixels using AMS 0.6 process • Used at LBNL for ladder development • Mimosa – 8 • Fast parallel column readout with internal data sparsification • MimoSTAR – 1 128x128 pixels using TSMC 0.25 • MimoSTAR – 2 128x128 pixels using AMS 0.35 • Duct tape these to the STAR Beam Pipe for 07 run • MimoSTAR – 3 320x640 pixels using AMS 0.35 • MimoSTAR – 4 640x640 pixels production run • Ultra – 1 • Ultra – 2

11. IReS MIMOSTAR chips • MIMOSTAR1 (0.25 m TSMC) • Reduced size prototype but sophisticated chip with complete functions for operation in a real detector system • Everything operating except pixel signal because of 0.25 m TSMC feature: Unexpected short signal decay time compared to theory and AMS experience. • MIMOSTAR2(0.35 m AMS optical process) • Tested in beam • 700-800 e most probable for Min-I • 10-12 e-rms, noise. • Signal decay time 100 ms

12. MIMOSTAR2, features • Parallel voltage out - for readout chip (abandoned) • Serial current loop out – for off ladder ADC up to 80 MHz • 128 X 128 • ½ Standard forward bias design • ½ Rad Hard forward bias design, reduced oxide • Leakage Current 3-5 fA at room temperature, shot noise adds 4 e-rms for 4 ms integration (total noise 16 e-rms) • Min-I cluster signal 700-800 e • Successful radiation test, 20 Krad OK

13. Ultimate (fast APS detector) - good for high luminosity at RHIC Technology MIMOSA8 • Submitted requirements list to IReS. In discussion

14. Ultimate Chip • 640X640 30 m pixels • 200 sec integration time, a factor 20 improvement, will work at the highest luminosities • Digital readout, 3 bit ADCs, i.e. CDS plus two threshold levels • 4 parallel LVDS lines • 1 ms readout and dead time • Feasibility of this concept proven with MIMOSA8 • Multiple analogue storage on the pixel for reduced dead time? Not clear that this option is possible. 640 640 4ch LVDS

15. Efficiency vs Accidentals • A critical issue with thin APS CMOS detectors • Can data sparcification be achieved without loss of efficiency? • Following study shows that planned simple high speed algorithm will work

16. Accidental vs Efficiency Test based on Measured charge spectrum • APS measured signal spectrum in ALS electron beam agrees with Bichsel theory • To find efficiency add large measured signals scaled to distribution to empty APS noise frames and apply filter algorithm • Find accidental rate by using filter algorithm on empty noise frames noise contribution

17. Test of two threshold algorithm • Require > 98% efficiency • # of accidentals • Limit set by outer layer background rate • < 5 hits/cm2 • Data shows stable region of good efficiency and low noise

18. Event size and data rate, data reduction crucial Raw data rate: 31 GBytes/sec Some numbers: Only the hit addresses generate significant data volume. The totals are: Reduction 1/340,000 The HFT event size is significantly smaller than the TPC which has an event size of 2 MBytes for central Au+Au

19. R&D Plans, Scope change • R&D phase for technology verification using MIMOSTAR2 (4 ms integration) technology • Install n 4 ladder modules • Verify mechanical insertion technology and stability control • Verify DAQ and data reduction technology • Final phase MIMOSTAR-Ultimate (200 s integration) • Full 24 ladder, 2, installation • Multiple backup copies for rapid repair • The full luminosity solution

20. Main R&D effort this year • Build two ladders with two MIMOSTAR2 chips each • ( each chip 4 mm x 4 mm) • Install chip to chip (for coincidence) at an intersection region, preferably STAR • Operate with DAQ 1000 ALTERA/NIOS/SIU-RORC based system and STAR trigger interface • Gain operating experience and obtain track density numbers at small radius

21. Mechanical • Mechanical support • Beam pipe

22. HFT Mechanical requirements Full self consistent spatial mapping prior to installation Installation and removal does not disturb mapping Rapid replacement 10 Micron stability (mapping of BarBar with visual coordinate machine)

23. Conceptual mechanical design

26. Kinematic mounts

27. Beam pipe • Meetings and discussions with • Wolfram Fisher • Dick Hseuh • Robert Pak • Dan Weiss • Our beam radius OK for accelerator, but we are a limiting aperture • Accelerator can live with 10-5 (we expect 10-9, but what can we live with?) • PHENIX has adopted our 1.5 cm radius, 0.5mm wall. • Preferred bake out 200-250 C to activate NEG coating

28. Important R&D Issues - Electronics

29. Important R&D Issues - Mechanical

30. Conclusion