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Deep N-well CMOS MAPS and Hybrid Pixels in Vertical Integration Technology for the SuperB SVT

This paper discusses the use of deep N-well CMOS MAPS and hybrid pixels in vertical integration technology for the SuperB Silicon Vertex Tracker (SVT). It covers the working principle, features, and expected performance of these technologies.

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Deep N-well CMOS MAPS and Hybrid Pixels in Vertical Integration Technology for the SuperB SVT

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  1. Deep N-well CMOS MAPS and hybrid pixels in vertical integration technology for the SuperB SVT L. Rattia for the VIPIX collaboration Pixel systems for thin charged particle trackers based on vertical integration technologies aUniversità degli Studi di Pavia and INFN Pavia SuperB Workshop IX June 16-20 2009 Perugia, Italy

  2. SVT layer0 options for SuperB Design of the SVT layer0 at SuperB has to comply with severe requirements large background, >5 MHz, small thickness, <0.5X0 Striplets Hybrid pixel detectors presently the baseline solution for the TDR submission of a 130 nm CMOS front-end chip planned for September (see talk by G. Traversi) fine pitch (50 μm) bump bonding (IZM, Munich) with a 200 μm thick pixel detector (FBK-irst, Trento) Deep N-well CMOS monolithic sensors (DNW-MAPS) extensive R&D ongoing in a 130 nm CMOS process (Apsel and SDR families), Apsel4D tested on the PS beam at CERN in September 2008 can be easily made compatible with low material budget requirements innovative approach (deep N-well sensor) proposed to enable fast readout through pixel-level sparsification and time stamping

  3. 3DIC Consortium Includes FNAL and Italian and French Institutions (also Bonn and AGH Universities, see http://3dic.fnal.gov) aiming to work together on a MPW run using the Tezzaron 3D IC fabrication process The collaborating institutions are willing to share information on design tools and design rule implementation, cell libraries, circuit blocks (besides costs) The Consortium has made a considerable effort to meet the deadline of end of May ’09 for a multiproject run in the Tezzaron/Chartered 130 nm technology As far as the Italian contribution is concerned, this first submission, funded in the frame of the P-ILC experiment (INFN), includes 3D MAPS sensors mainly for applications to the ILC, but also some vertically integrated structures aimed at vtx applications to the SuperB Factory

  4. Outline Deep N-well (DNW) MAPS working principle and features Vertical integration (or 3D) technologies and the Tezzaron/Chartered process DNW MAPS in 3D CMOS technology: Apsel MAPS 3D version From 2D to 3D Analog FE design features and expected performance Charge collection efficiency improvement through 3D processes Hybrid pixels with 3D FE chip (3D hybrid pixels) 3D FE for a pixel detector in XFAB technology Conclusion and future plans

  5. + + + + - - - - Deep N-well MAPS PMOS NMOS In triple-well CMOS processes a deep N-well is used to isolate N-channelMOSFETs from substrate noise P-well Buried N-type layer Standard N-well Deep N-well structure These features were exploited in the development of deep N-well (DNW) MAPS devices P-substrate ADNW is used to collect the charge released in the substrate A classical readout channel for capacitive detectors is used for Q-V conversion  gain decoupled from electrode capacitance Using a large detector area, PMOS devices may be included in the front-end design  charge collection inefficiency depending on the relative weight of the DNW area with respect to the area of all the N-wells (deep and standard) NMOS devices of the analog section are built in the deep N-well

  6. Vertical integration (3D) technologies WB/BB pad In wafer-level, three-dimensional processes, multiple strata of planar devices are stacked and interconnected using through silicon vias (TSV) TSV 3D processes rely upon the following enabling technologies 2nd wafer Fabrication of electrically isolated connections through the silicon substrate (TSV formation) Inter-tier bond pads Substrate thinning (below 50 μm) Inter-layer alignment and mechanical/electrical bonding 1st wafer Tezzaron Semiconductor technology (via first approach) can be used to vertically integrate two layers specifically processed by Chartered Semiconductor (130 nm CMOS, 1 poly, 6 metal layers, 2 top metals, dual gate option, N- and PMOS available with different Vth)

  7. From 2D to 3D MAPS Separate analog from digital section to minimize cross-talk between digital blocks and sensor/analog circuits less PMOS in the sensor layer  improved collection efficiency more room for both analog and digital power and signal routing (in planar CMOS MAPS scaling to suitably large matrices is forbidden by the need for point-to-point lines from macropixels to periphery) Digital section Digital section Analog section P-well NMOS N-well PMOS DNW sensor Analog section DNW sensor Tier 1: collecting electrode and analog front-end and part of the discriminator Tier 2: part of the discriminator, digital front-end and peripheral digital readout electronics

  8. Analog FE and discriminator Analog design aimed at minimizing the number and size of PMOS devices in the sensor layer shaperless FE (SFE) discriminator AVDD AVDD DVDD Inter-tier bond pads IFB Vt DGND CF AGND Only preamplifier PMOS devices are kept in the analog layer (TIER 1) TIER 1 (BOTTOM) TIER 2 (TOP)

  9. Analog FE Main design features and simulation results W/L=30/0.3 ID=20 μA, power dissipation=35 mW CD=250 fF ~1 ms peaking time Charge sensitivity (GQ): 750 mV/fC Equivalent noise charge (ENC): 33 e- Threshold dispersion (DQt): 40 e- (34 e- from the SFE, 22 e- from the discriminator)

  10. 40 mm 40 mm Collecting electrode layout Adoption of a three-dimensional technology makes it possible to significantly reduce the area covered by charge stealing N-wells  significant improvement in charge collection efficiency expected Collecting electrode Parasitic N-wells Apsel5T cell (planar CMOS technology) Apsel_3D cell (vertical integration CMOS technology)

  11. Test structures chip layout: bottom and top tiers Small test structures (3x3 matrices, analog tier) 8x32 matrix with data driven readout (analog tier) 8x32 matrix with data driven readout (digital tier) Small test structures (3x3 matrices, digital tier) 5.5 mm 6.3 mm 6.3 mm

  12. Small test structures Analog (bottom) tier 3x3 matrix with all the analog outputs available, injection capacitance for the central pixel Digital (top) tier 3x3 matrix with all the analog outputs available, injection capacitance for the central pixel, enclosed layout transistors as input devices of the analog FE

  13. 8x32 matrix with data driven readout Analog (bottom) tier Sensor and pixel-level analog front end Digital (top) tier Pixel-level digital front end Digital readout electronics

  14. 3D hybrid pixels Development of a 3D front-end chip to be vertically integrated with fully depleted detectors through some more (bump bonding) or less (direct bonding) standard technique Digital section 1st layer 1st layer Direct bonding (e.g. Ziptronix) Bump bonding (e.g. IZM) Analog section 2nd layer 2nd layer detector layer detector layer Larger signal available from the detector More advantageous trade-off between S/N and dissipated power

  15. 3D FE for the XFAB detector (W. Dulinski and coworkers, IPHC Strasbourg) If~1 nA Gx1-x10 Cf~10 fF Cc~200 fF σoff~10 mV Dff~ 40 µm2 Cd~10-20 fF Qmin~100-200 el Shaperlessfront-endtpeak ~1µs 14 μm high res epilayer, fully depleted at 5V Low offset, continuousdiscriminator Latch (memory) and readout logic Designed by Pavia group XFAB 0.6µm PIN (Tier_0) Chartered Tier_1 (analog) and Tier_2 (digital) Ziptronix (metal-metal fusion)

  16. Chip to XFAB wafer bonding Direct bonding (through Ziptronix DBI technology) between the Tezzaron/Chartered 3D wafer and the XFAB wafer Bonding pads Bonding pads Bumps TSVs Tezzaron/Chartered Tezzaron/Chartered + Ziptronix+XFAB

  17. Conclusion and future plans Two different 3D solutions are being investigated for the SVT layer0 at SuperB through extensive R&D programs, namely hybrid pixel detectors and DNW MAPS, both in 130 nm CMOS technology Both MAPS and hybrid pixels can gain significant benefits from going 3D increase in charge collection efficiency immunity from (or reduction of) cross-talk phenomena between digital blocks and sensor/analog circuits scalability to large sensor matrices better trade-off between point resolution and functional density The hybrid pixel approach is expected to guarantee superior performance as far as the trade-off between S/N and power dissipation is concerned Test of the first 3D MAPS sensors expected to start next September Design of a vertically integrated large (~256x256) DNW MAPS detector with data driven readout architecture and of a 3D FE chip for hybrid pixels is planned for the beginning of next year

  18. Backup slides

  19. Tezzaron vertical integration process Tezzaron uses a “via first” approach for the fabrication of 3D chip  through silicon vias (TSV) is done either before or after CMOS devices processing (to be compared to the “via last” approach, where TSV are done after wafer fabrication and either before or after wafer bonding) IBM, NEC, Elpida, OKI, Tohoku, DALSA…. Ziptronix Chartered, TSMC, RPI, IMEC……..

  20. Oxide Silicon Dielectric(SiO2/SiN) Gate Poly STI (Shallow Trench Isolation) “Super-Contact” W (Tungsten contact & via) Cu (M1 – M5) Cu (M6, Top Metal) Tezzaron vertical integration process Complete transistor fabrication on all wafer to be stacked Form super via (TSV) on all wafer to be stacked Fill super via at the same time connections are made to transistors

  21. Oxide Silicon Dielectric(SiO2/SiN) Gate Poly STI (Shallow Trench Isolation) “Super-Contact” W (Tungsten contact & via) Cu (M1 – M5) Cu (M6, Top Metal) Tezzaron vertical integration process Complete back end of line (BEOL) processing by adding Cu metal layers and top Cu metal

  22. Tezzaron vertical integration process Bond first layer to second layer using Cu-Cu thermo-compression bond

  23. Tezzaron vertical integration process Thin the second wafer to about 12 μm total thickness to expose super via Add Cu to back of second wafer to bond second wafer to third wafer OR add metallization on back of second wafer for bump bond or wire bond

  24. Tezzaron vertical integration process 3σ alignment=1 μm, missing bond connections=0.1 PPM Via size plays an important role in high density pixel arrays Tezzaron can place vias very close together

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