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Outline Semiconductor equations Examples pnCCD Depleted Field Effect Transistor (DEPFET)

Semiconductor device simulation of silicon radiation detectors R. H. Richter for the MPI Semiconductor Lab. Outline Semiconductor equations Examples pnCCD Depleted Field Effect Transistor (DEPFET) Pixel detectors: field distribution in heavily irradiated silicon Summary.

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Outline Semiconductor equations Examples pnCCD Depleted Field Effect Transistor (DEPFET)

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  1. Semiconductor device simulation of silicon radiation detectorsR. H. Richter for the MPI Semiconductor Lab Outline Semiconductor equations Examples pnCCD Depleted Field Effect Transistor (DEPFET) Pixel detectors: field distribution in heavily irradiated silicon Summary

  2. Continuity equations Equations • Simultaneous consideration of • Generation • Recombination • Drift • Diffusion • Drift due to electric field derived from Poisson Equation • Numerical simulation: simultaneous solution of diffusion and Poisson equation with boundary conditions R. H. Richter, 6th Hiroshima Symposium - STD6, Carmel, September 12th 2006

  3. Boundary conditions and features • Neumann b.c. (termination and symmetric continuation) • Direchlet b.c. (Ohmic contacts) • Gate b.c. • Schottky contacts • Simple networks with R,C,L possible • Sophisticated mobility models • Parametrization of impact ionization (avalanche) R. H. Richter, 6th Hiroshima Symposium - STD6, Carmel, September 12th 2006

  4. Concept of PN-CCD with frame store(Google-> pnCCD, XMM) PN-CCD different from MOS-CCDs anode + JFET on chip per channel pn-junctions instead of MOS gates p n p transfer “deep” in bulk fully depleted  0.5 mm pn-junction (homogeneous) backside illumination R. H. Richter, 6th Hiroshima Symposium - STD6, Carmel, September 12th 2006

  5. pnCCD – simulation tasks • WIAS-TeSCA • 2D-Simulation • charge transfer • barriers to surface • Transfer region + anode • charge transfer to anode • Channel separation (perpendicular to transfer region) • Technology compatibility with on chip amplifiers (JFETs). • Challenges: large domain (50000 triangles), depletion state - electrons • How to verify? R. H. Richter, 6th Hiroshima Symposium - STD6, Carmel, September 12th 2006

  6. Meshing • Triangulated grid (2D) often taken from the • technolgy simulator but additional programs • are also used (Gridgen, B. Heinemann) 20.000 – 40.000 points R. H. Richter, 6th Hiroshima Symposium - STD6, Carmel, September 12th 2006

  7. potential log(n) Localized generation of e/h pairs simulate particle tracks or converted photons.

  8. pn-CCD performance • largest monolithic CCD • 6 x 6 cm² • 384 x 400 pixel • 150 µm pixel • fast, parallel readout • 5 msec full frame • low noise • 4 el. rms • high quantum efficiency • 90 % • radiation hard • 400 Mp/cm²

  9. XMM-Newton – first light (January 2000) large Magellanic cloud supernova remnant 1987A

  10. Getting insight into a CCD - Mesh Analysis of the charge collection process Mesh experiment (Tsunemi, Yoshita, Kitamoto, Jpn J. Appl. Physics 36, 2906 N. Kimmel et al, Analysis of the charge collection process in pnCCDs , Proceedings of SPIE vol. 6276, p. R. H. Richter, 6th Hiroshima Symposium - STD6, Carmel, September 12th 2006

  11. Mesh-results vs Simulation Charge distribution over the pixel Simulation: charge generation in steps of 5µm scanning the transfer direction R. H. Richter, 6th Hiroshima Symposium - STD6, Carmel, September 12th 2006

  12. CTE degradation due to traps • You can’t predict the real life completely. Even if you create ‘perfect’ transfer potential with a lot of headroom. • N. Krause et al, NIM A439, p228 • Contamination in epitaxial layers (gas delivery, stainless steel) • Titanium contamination (ET about 0.26eV, several 1010cm-3) during epitaxy (also measured with DLTS) • Replace the epitaxial layer High energy implantation (P 20MeV) R. H. Richter, 6th Hiroshima Symposium - STD6, Carmel, September 12th 2006

  13. pn-CCD – charge transfer efficency Replacing the epitaxial layer by a 20MeV HE P-impl. R. H. Richter, 6th Hiroshima Symposium - STD6, Carmel, September 12th 2006

  14. DEPFET-Principle of Operation MIP source top gate drain clear bulk n+ p+ p+ n+ n+ p n s i internal gate x a + - - y - - - r t - - e + m - m y s + - n + - p+ rear contact Potential distribution: internal Gate ~1µm Backcontact Drain 50 µm Source [TeSCA-Simulation] FET-Transistor integrated in every pixel (first amplification) Electrons are collected in „internal gate“ and modulate the transistor-current Signal charge removed via clear contact R. H. Richter, 6th Hiroshima Symposium - STD6, Carmel, September 12th 2006

  15. DEPFET-Principle of Operation +15V source top gate drain clear bulk 0V 0V n+ p+ p+ n+ n+ p n s i internal gate x a - - y - - - r t - e m m y s - n p+ rear contact Potential distribution: internal Gate ~1µm Backcontact Drain 50 µm Source [TeSCA-Simulation] FET-Transistor integrated in every pixel (first amplification) Electrons are collected in „internal gate“ and modulate the transistor-current Signal charge removed via clear contact R. H. Richter, 6th Hiroshima Symposium - STD6, Carmel, September 12th 2006

  16. DEPMOS Technology on high ohmic 6” wafer(DIOS-ISETCAD-Simulation) • DEPMOS pixel array cuts through one cell Clear Gclear Channnel Metal 2 Metal 1 Oxyd Poly 2 Metal 2 Metal 1 Poly 2 Poly 1 p n+ Deep n Deep p Along the channel Perpendicular to the channel Double poly / double aluminum process on high ohmic n- substrate Low leakage current level: < 200pA/cm² (fully depleted – 450µm) R. H. Richter, 6th Hiroshima Symposium - STD6, Carmel, September 12th 2006

  17. Potential of the empty Internal Gate L = 4 (3) µm L= 5 (4) µm L = 6 (5) µm L = 7 (6) µm L = 10 (9) µm ToSCA – 2D device simulation R. H. Richter, 6th Hiroshima Symposium - STD6, Carmel, September 12th 2006

  18. Comparison with simulation – internal amplification vs channel length • Simulation @ 50µA drain current • Assuming an under-etching of 1.2µm • Measured by S. Rummel measured at 100µA measured at 50µA nice illustration of the DEPFET scaling potential R. H. Richter, 6th Hiroshima Symposium - STD6, Carmel, September 12th 2006

  19. DEPFET 3D-Simulation K. Gärtner, R.R., DEPFET sensor design using an experimental 3d device simulator, accepted for publication in NIM ILC layout R. H. Richter, 6th Hiroshima Symposium - STD6, Carmel, September 12th 2006

  20. Simulated signal response Introduction of: buried channel implantation lateral drift fields by inclined deep p implantations Charge reaches the interface -> slow diffusion In reality: charge loss due to trapping and small potential barriers R. H. Richter, 6th Hiroshima Symposium - STD6, Carmel, September 12th 2006

  21. Bias Bias Bias Gate #1 Gate #2 Gate #1 Gate #1 Gate #2 Gate #2 Auslese- knoten #1 Clear #1 Clear #2 Auslese- knoten #2 Auslese- knoten #1 Auslese- knoten #1 Clear #1 Clear #1 Clear #2 Clear #2 Auslese- knoten #2 Auslese- knoten #2 Transfer- gate Transfer- gate Transfer- gate Bias Gate #1 Gate #2 Bias Bias Gate #1 Gate #1 Gate #2 Gate #2 Auslese- knoten #1 Clear #1 Clear #2 Auslese- knoten #2 Transfer- gate Auslese- knoten #1 Auslese- knoten #1 Clear #1 Clear #1 Clear #2 Clear #2 Auslese- knoten #2 Auslese- knoten #2 Transfer- gate Transfer- gate RNDR principle(repetitive non destructive readout ) • By measuring the charge multiple (n) time the noise can be reduced by 1/ sqrt(n) • Because the collected charge is stored during readout in the DEPFET-RNDR, the very same charge can be measured multiple times. R. H. Richter, 6th Hiroshima Symposium - STD6, Carmel, September 12th 2006

  22. Investigated Structure: 4x4 Minimatrix(G. Lutz) • ILC-Type RNDR • Realised as a four by four Minimatrix R. H. Richter, 6th Hiroshima Symposium - STD6, Carmel, September 12th 2006

  23. Laser spectra (S. Wölfel) • Measurement: • Charge injection with laser during integration time • 180 Loops for the readout (duration: 9.18 ms) -45 °C • Measured leakage current: • ca. 0,4 e- in 180 loops Noise Limit 0,25 e- R. H. Richter, 6th Hiroshima Symposium - STD6, Carmel, September 12th 2006

  24. Double trap model for heavily irradiated silicon • V. Chiocia et al (accepted for Proceedings of Wildbad Kreuth (NIM A)) see also Eremin, Verbitskaja, Li, NIM A476, p.556 R. H. Richter, 6th Hiroshima Symposium - STD6, Carmel, September 12th 2006

  25. Charge collection profile by grazing angle techniqueon a CMS pixel detector (testbeam measurement) R. H. Richter, 6th Hiroshima Symposium - STD6, Carmel, September 12th 2006

  26. Simulated and measured charge 10V 15V 20V 0.5 x 1014 neq 2 x 1014 neq 25V 150V 50V 100V R. H. Richter, 6th Hiroshima Symposium - STD6, Carmel, September 12th 2006

  27. Electric fields 0.5 x 1014 neq 2 x 1014 neq unirradiated R. H. Richter, 6th Hiroshima Symposium - STD6, Carmel, September 12th 2006

  28. Summary • Developing state of the art detectors there is no way around a thorough • numerical simulation. • Primary task: Prediction of the device behavior and finding optimal operation states and process parameters • Provides insight into the potential and limits of a device concept. • For a full understanding of complicated pixel detectors 3D-simulation is a must! • Investigation of radiation induced defects by the ‘grazing angle technique’ together with simulations is a promising way. R. H. Richter, 6th Hiroshima Symposium - STD6, Carmel, September 12th 2006

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