1. TILC08, Sendai, March 2008 1 DEPFET Active Pixel Sensors for the ILC Marcel Vos for the DEPFET Collaboration (www.depfet.org)

2. TILC08, Sendai, March 2008 2 The DEPFET ILC VTX Project DEPFET in a nutshell Summary of the current achievements New r/o chip DCD2 News on thinning/ladder design See DEPFET Backup Document at www.depfet.org

3. TILC08, Sendai, March 2008 3 DEPFET Principle Drain Source Gate  fully depleted sensitive volume, charge collection by drift  internal amplification  q-I conversion: 0.5 nA/e, scales with gate length and bias current  Charge collection in "off" state, read out on demand J. Kemmer & G. Lutz, 1987 DEpleted P-channel FET

4. TILC08, Sendai, March 2008 4 DEPFET Array - read-out at the ILC Row wise read-out ("rolling shutter")  select row with external gate, read current, clear DEPFET, read current again  the difference is the signal  Low power consumption  two different auxiliary ASICs needed  limited frame rate  cap. load at the f/e adds noise Drain read out

5. TILC08, Sendai, March 2008 5 ILC VXD baseline design Just as a starting point for the R&D!  5 layer, old TESLA layout  10 and 25 cm long ladders read out at the ends  24 micron pixel  design goal 0.1% X 0 per layer in the sens. region Strategy to cope with the background:  read ~20 times per train  store data on ladder  transfer the data off ladder in the train pause  row rate of 40 MHz  read two rows in parallel, doubles # r/o channels but:  row rate 20 MHz

6. TILC08, Sendai, March 2008 6 ILC Prototype System 2 analog MUX outputs with 64 channels each Can switch up to 25 V 0.8µm AMS HV technology Clear Switcher Gate Switcher DEPFET Matrix 64x128 pixels, 33 x 23.75µm 2 current based 128 channel readout chip 50 MHz band width in the f/e On-chip pedestal subtraction by switched current technique (CDS) Current Readout CUROII

7. TILC08, Sendai, March 2008 7 New rad. hard Switcher3 chips tested and functional Production of 2nd iteration of DEPFETs under test New r/o chips DCD designed for read-out of large matrices are under test Prototype System with DEPFETs (450µm), CURO and Switcher test beam @ CERN: S/N≈110 @ 450 µm  goal S/N ≈ 20-40 @ 50 µm sample-clear-sample 320 ns  goal 50 ns s.p. res. 1.3 µm @ 450 µm  goal ≈ 4 µm @ 50 µm Thinning technology established, thickness can be adjusted to the needs of the experiment (~20 µm … ~100 µm) radiation tolerance tested with single pixel structures up to 1 Mrad and ~10 12 n eq /cm 2 Simulations show that the present DEPFET concept can meet the challenging requirements at the ILC VXD. In Summary: Achievements and status

8. TILC08, Sendai, March 2008 8 New DEPFET Generation ‘PXD5’  Mostly use ‘baseline’ linear DEPFET geometry  Build larger matrices Long matrices (full ILC drain length) Wide matrices (full Load for Switcher Gate / Clear chips)  Try new DEPFET variants: reduce clear voltages Very small pixels (20µm x 20µm)  Increase internal amplification (g q ) 512x512 matrix  Production finished  Currently under test and evaluation  beam test in July and August a PS and SPS (stand-alone and EUDET)  expect first results from Lab test at the Warsaw meeting

9. TILC08, Sendai, March 2008 9 A new r/o chip - DCD2 DCD: Drain Current Digitizer -: improved input cascode (regulated) and current memory cells -: digital hit processing done with 2nd chip/FPGA -: designed for 40 pF load at the input (1 st layer ILC VTX) -: f/e noise: 34nA@40pF, 17nA@10pF, add 37nA for memory cells  50nA@40pF  at 40pF with g q =500pA/e  100 e- ENC in total -: 2 current based ADCs per pixel, 8 bit -: layout for bump bonding, rad. hard design -: UMC 0.18µm, 1.8V technology -: 144 channels -: outer dimensions 3.2x1.5 mm 2

10. TILC08, Sendai, March 2008 10 DCD2 - first test results Pixel Control Registers ok DACs & DAC Control registers ok Current consumption ok Regulated cascode ok ADCs of top row ok LVDS in and out ok Output multiplexer not tested yet  extremely good news!!!  next step is to test the chip with mini matrices of the PXD5 DEPFET production………

11. TILC08, Sendai, March 2008 11 Thinning Technology Compatibility with the main production line tested So far: -: mechanical samples -: test structures (diodes) on SOI wafers The technology found its way into other projects: -: production of thin (75 and 150 μm) ATLAS pixel sensors for sLHC -: first production of Geiger-mode APDs on 70 μm top layer Top Wafer Handle Wafer a) oxidation and back side implant of top wafer b) wafer bonding and grinding/polishing of top wafer c) process  passivation open backside passivation d) anisotropic deep etching opens "windows" in handle wafer

12. TILC08, Sendai, March 2008 12 Thinning : mechanical samples

13. TILC08, Sendai, March 2008 13 Bow under gravity Bill Cooper, Fermilab

14. TILC08, Sendai, March 2008 14 Flatness!!!??  "all-Silicon" module? - Not really.. MaterialSiSiO 2 Si 3 N 4 Al Thickness (µm)500.1.. 1≈ 0.11.. 2 CTE (ppm/K)2.6≈ 0.5≈ 2.8 - 3.624  Build-in stress due to high temperature processes!  Wafer/Sensor bow! 1. Does it change with temperature (∆T ≈ 40 K) after processing/dicing? 2. If it's stable, is it of concern at all? (3. Can the build-in stress (and bow) be adjusted with additional single sided layers?)  First assesment: -: 1 st layer ladder with single sided double metal (Al-600nm SiO 2 -Al on front side) diced!  Measure bow and temp. dependence at RAL (Erik Johnson)

15. TILC08, Sendai, March 2008 15 Bow vs. Temperature (at RAL) measure flatness down to -24 degC: -: max. +/- 12 µm at ∆T=44K -: small effect at 20degC  -10degC -: these are just first results, more tests underway (many thanks to Erik and RAL!) double metal sample, 1st layer ILD ladder, 50µm thick

16. TILC08, Sendai, March 2008 16 Summary Preparations for the new DEPFET generation are in full swing: New Sensors, larger matrices, with improved gain under test New r/o chip operational Thinning technology at the door step to migrate to the production line. Excellent results using a commercial supplier for the engineered SOI wafers.... It remains a challenging task but we don't see any show stoppers and are on schedule for a thin "full size" demonstrator by ~2010!