1. Vertex05, 8/11/05Jaap Velthuis, Bonn University DEPFET Status DEPFET Principle Readout modes Projects: –XEUS –WIMS –ILC ILC Testbeam results Summary & Outlook Univ. of Bonn: M.Karagounis, R.Kohrs, H.Krüger, M. Mathes, L.Reuen, C.Sandow, E.von Törne, M.Trimpl, J.Velthuis, N.Wermes Univ. of Mannheim: P.Fischer, F.Giesen, I.Peric Politecnico di Milano: M. Porro MPI Halbleiterlabor Munich: O Hälker, S. Herrmann, L.Andricek, G.Lutz, H.G. Moser, R.H.Richter, M.Schnecke, L.Strüder, J.Treis, P.Lechner, S. Wölfel THCA of Tsinghua Univ.: C. Zhang, S.N. Zhang

2. Vertex05, 8/11/05Jaap Velthuis, Bonn University DEPFET Principle A p-FET transistor is integrated in every pixel. By sidewards depletion potential minimum created below internal gate. Electrons, collected at internal gate, modulate transistor current ~1µm p+ n+ rear contact drainbulksource p s y m m e t r y a x i s n+ n internal gate top gateclear n - n+ p+ - - + + + + - 50 µm - - -- -- MIP

3. Vertex05, 8/11/05Jaap Velthuis, Bonn University DEPFET Principle Advantages: –Fast signal collection due to fully depleted bulk –Low noise due to small capacitance and amplification in pixel –Transistor can be switched off by external gate – charge collection is then still active ! –Non-destructive readout Disadvantages: –Need to clear internal gate. This still requires high voltages. 2 readout modes: –Source follower mode readout. Signal is voltage (XEUS) –Drain readout. Signal is current (WIMS&ILC) required

4. Vertex05, 8/11/05Jaap Velthuis, Bonn University SOURCE FOLLOWER Constant bias current I Bias provided Charge at internal gate translates into source voltage node change Speed depends on overall load capacitance Slow (t≈C L /g m ≈3µs), but excellent noise Clear Clear- gate DrainSource Gate DEPMOS device I bias Buffer / amplifier I bias

5. Vertex05, 8/11/05Jaap Velthuis, Bonn University DRAIN readout Measure I drain directly Fast response: limited by RC time of input resistance CURO and C load (~ns) Clear Clear- gate SourceDrain Gate DEPMOS device V out CURO: current amplifier transimpedence amplifier

6. Vertex05, 8/11/05Jaap Velthuis, Bonn University DEPFET Applications DEPFET under study for: –XEUS Exploring the early universe by imaging spectroscopy in the X- ray band Need noise < 4e - Source follower mode –WIMS Wide-band Imaging and Multi-band Spectrometer, part of China’s spacelab mission Drain readout –ILC Need row rates of 20MHz Drain readout

7. Vertex05, 8/11/05Jaap Velthuis, Bonn University XEUS Exploring the early universe by imaging spectroscopy in the X- ray band Detector: –Device active area 7.68 x 7.68 cm 2 –Monolithic sensor integrated onto a single 6“ wafer –Device thickness 450 µm –Pixel size 75 x 75 µm 2 –Position resolution ca. 30 µm –Total 1024 x 1024 pixel cells –Total readout time / frame 1.25 ms –Processing time per detector row 2.5 µs

8. Vertex05, 8/11/05Jaap Velthuis, Bonn University Excellent noise Single pixel device 10 µs shaping Room temperature (22° C)

9. Vertex05, 8/11/05Jaap Velthuis, Bonn University Excellent noise Large structure (64x64): –75 x 75 µm 2 pixel size –45 µm gate circumference / 5 µm gate length –Drain in center of pixel –Cut gate geometry –Curved edge –Double metal Operated at: –Pixel current 30 µA –Line processing time 25 µs Energy resolution: 126 eV FWHM @ Mn-Ka Line corresponding to 4.9 e - ENC Noise dependence  Pixel readout noise: 63 – 14eV (17 – 3.6 e - ENC)

10. Vertex05, 8/11/05Jaap Velthuis, Bonn University WIMS Wide-band Imaging and Multi-band Spectrometer (WIMS) is part of China’s spacelab mission. Observe high-energy bursts, transients and fast-varying sources over a broad spectral range simultaneously Using Macro pixels –Pixel size 0.5x0.5 mm 2 –“Si-drift chamber readout using DEPFET” Room temperature Back side illuminates, fast drain readout Shaping time: 3μs Clear pulse period 1 ms with width 3 μs

11. Vertex05, 8/11/05Jaap Velthuis, Bonn University DEPFET for ILC Basic system Clearing ILC requirements Ladder proposal Power consumption Thinning Radiation hardness Testbeam results

12. Vertex05, 8/11/05Jaap Velthuis, Bonn University Basic system Select and Clear signals provided by SWITCHER –64 x 2 outputs –Max ΔV = 25V Read out row-wise: CURO –current based read out –128 channels –CDS –real time hit finding & zero-suppression –row rate up to 24 MHz Gate Switcher Clear Switcher Current Readout CUROII DEPFET Matrix 64x128 pixels, 36 x 28.5µm 2

13. Vertex05, 8/11/05Jaap Velthuis, Bonn University HighE vs non-HighE HighE extra n-type implant –Moves internal gate deeper into bulk –Clearing takes places deeper in the bulk –Lower signals, but easier clearing clear Internal gate channel Optional HighE implant

14. Vertex05, 8/11/05Jaap Velthuis, Bonn University Clearing CURO measures: I sig,i +I ped,i & I ped,i+1 Need to remove all charge such that I ped,i+1 =I ped,i COMPLETE CLEAR possible for HighE with low voltages (~7V) ⇒ possible to make radhard SWITCHER in standard CMOS HighE

15. Vertex05, 8/11/05Jaap Velthuis, Bonn University ILC requirements Time structure: 1 train of 2820 crossings in ~1 ms every ~200ms –Hit density: for r = 15 mm: ~ 100 tracks / mm 2 / train –Row readout rate: > 20 MHz –Occupany < 0.5 % Radiation length: ~0.1% X 0 per layer –thinned sensors (50 μm) –low power consumption Radiation tolerance:  200 krad (for 5 years operation) Resolution: few µm (  pixel size ≤ 25 x 25 µm 2 )

16. Vertex05, 8/11/05Jaap Velthuis, Bonn University Ladder proposal Modules have active area ~13 x 100 mm 2 Read out on both sides. Detectors 50µm thick, with 300µm thick frame yields 0.11% X 0 SWITCHER & CURO chips connected by bump bonding SWITCHER CURO

17. Vertex05, 8/11/05Jaap Velthuis, Bonn University ILC Power Measured Power Dissipation: –Switcher: 6.3 mW per active channel at 50MHz –CURO: 2.8 mW / channel Assumed Power Dissipation of DEPFET Sensor: –0.5 mW per active pixel –duty cycle: 1/200 Only active pixel dissipate power –1024 active pixels per module –8 modules in Layer 1 => 8192 active pixels Expected Power Dissipation in Layer 1 –Sensor: 8192 x 0.5 mW / 200 = 20 mW –Switcher: 16 x 6.3 mW / 200 = 0.5 mW –Curo: 8192 x 2.8 mW / 200 = 114 mW For Layer 1 Sum: 135 mW For 5 Layer DEPFET Vertex Detector: Total ~ 3.6 W  no active cooling

18. Vertex05, 8/11/05Jaap Velthuis, Bonn University Thinning sensor wafer handle wafer 1. implant backside on sensor wafer 2. bond wafers with SiO 2 in between 3. thin sensor side to desired thick. 4. process DEPFETs on top side 5. etch backside up to oxide/implant first ‘dummy’ samples: 50µm silicon with 350µm frame thinned diode structures: leakage current: <1nA /cm 2 Thinning technology for active area established

19. Vertex05, 8/11/05Jaap Velthuis, Bonn University Radiation hardness Irradiations with 60 Co and X-rays (~17keV) up to ~1Mrad (SiO 2 ) Threshold shift of the MOSFET (~4V) can be compensated by bias voltage shift 60 Co

20. Vertex05, 8/11/05Jaap Velthuis, Bonn University Testbeam DESY test beam with 6 GeV e- Bonn ATLAS telescope system: –double sided strip detectors –pitch 50 µm (no intermediate strips) –readout rate 4.5 kHz (telescope only) DEPFET: – 128x64 (28.5x36 µm 2 ) –450 µm thick –Frame time 1.8 ms DEPFET beam 1234 Scintillator 3 x 3 mm²

21. Vertex05, 8/11/05Jaap Velthuis, Bonn University Pedestal & Noise Pedestal: average signal after hit removal Noise: standard deviation after pedestal, common mode and hit removal

22. Vertex05, 8/11/05Jaap Velthuis, Bonn University Clustering Look for clusters: –Seed pixel largest signal seed cut >5σ –Neighbours Neighbour cut >2σ Combine signals seed & neighbors S/N 3x3 =125.9±0.2 –Noise higher than expected –Next generation expect to reduce noise by factor 2

23. Vertex05, 8/11/05Jaap Velthuis, Bonn University Position resolution Hit positions reconstructed using the CoG algorithm Note: pixelsize X=36µm Y=28.5µm Terrible, but … due to multiple scattering

24. Vertex05, 8/11/05Jaap Velthuis, Bonn University Multiple scattering E electron only 6GeV Telescope planes 10cm apart Minimize effect scattering by selecting hard tracks using  2 cut Price: lose statistics

25. Vertex05, 8/11/05Jaap Velthuis, Bonn University Multiple scattering (II) Performed simulation. Using Fraction remaining tracks, telescope uncertainty can be estimated. From CERN testbeam know that σ intrinsic ~5-6µm, but not compared S/N tel σ X =9.71±0.02µm, σ Y =9.31±0.02µm σ intrinsic XY 5µm5.95.2 6µm3.92.7

26. Vertex05, 8/11/05Jaap Velthuis, Bonn University HighE matrix HighE implant moves internal gate into bulk –Lower signal –Easier clearing Results: –S/N 3x3 =99.5±0.1 –σ X =9.11±0.03µm, σ Y =8.80±0.03µm –Somewhat larger clusters yield better position resolution Poor stats & fit σ intrinsic XY 5µm4.84.3 6µm1.9--

27. Vertex05, 8/11/05Jaap Velthuis, Bonn University Summary DEPFET integrates MOSFET in fully depleted bulk. Developed towards: –XEUS mission: Slow readout(source follower mode) Excellent noise (~2.2e - ) –WIMS mission Very large pixels (0.5x0.5mm 2 ) Si-drift chamber readout by DEPFET Fast(er) readout (noise=19e - )

28. Vertex05, 8/11/05Jaap Velthuis, Bonn University Summary (II) Developed towards ILC. Meets already demands on –Radiation length (0.11 X 0 ) –Radiation hardness (ΔVth shift~4V@1Mrad) –Power consumption (<5W full detector) –Position resolution ( ≲ 5µm) Excellent S/N: –S/N=126 without HighE –S/N=100 with HighE –⇒ can thin detector to 50µm with still good S/N

29. Vertex05, 8/11/05Jaap Velthuis, Bonn University Outlook Improving the system to increase readout speed. –Individual parts already function well at ILC speed Testbeam at DESY (6GeV electrons) with better mechanics and at CERN. Goals: –Improve S/N –Test zero suppression Build 512x512 matrix

30. Vertex05, 8/11/05Jaap Velthuis, Bonn University Author list Univ. of Bonn: M.Karagounis, R.Kohrs, H.Krüger, M. Mathes, L.Reuen, C.Sandow, E.von Törne, M.Trimpl, J.Velthuis, N.Wermes Univ. of Mannheim: P.Fischer, F.Giesen, I.Peric Politecnico di Milano: M. Porro MPI Halbleiterlabor Munich: O Hälker, S. Herrmann, L.Andricek, G.Lutz, H.G. Moser, R.H.Richter, M.Schnecke, L.Strüder, J.Treis, P.Lechner, S. Wölfel THCA of Tsinghua Univ.: C. Zhang, S.N. Zhang