Presentation on theme: "Radiation Tolerance D. C. Christian, J. A. Appel, G. Chiodini,"— Presentation transcript:
Radiation Tolerance D. C. Christian, J. A. Appel, G. Chiodini,
Tests of a Prototype B. Hall, J. Hoff, S. Kwan, A. Mekkaoui,
Pixel Readout Chip R. Yarema, W. Wester, S. Zimmermann,
For BTeV Fermilab
1TeV p Luminosity= 2x10 32 cm -2 s -1 ( interactions each 132 ns)
FPIX Roadmap Pixel size = 50 x 400 (matches ATLAS n + on n test sensors) Target rad-hard technology = Honeywell 0.5 CMOS (SOI) (3 metal, 3.3V) (1 metal layer used for shield between sensor & R/O chip) FPIX0 (1997) HP 0.8 CMOS Close to final analog front end R/O pixel includes a peak sensor – digitized off chip Array size = 12 x 64 Bench tests and beam tests FPIX1 (1998) HP 0.5 CMOS Optimized front end 4 comparators per cell (2-bit FADC) New fast R/O architecture, allows both self-triggered and externally-triggered operation Array size = 18 x 160 Bench tests and beam tests Then (Dec, 1998), a change of plans Try to use deep-submicron CMOS All subsequent prototypes should be rad-hard.
FPIX2 Roadmap 0.25 CMOS (5 metal [6 possible], 2.5V) Design for 2 vendors (“lowest common denominator” design rules): “CERN” – Very favorable contract, but problems with US Gov. restrictions Taiwan Semiconductor Manufacturing Corp (TSMC) – Available through MOSIS PreFPIX2T (1999) TSMC 0.25 CMOS New analog front end, with new leakage current compensation strategy 8 comparators per cell (3-bit FADC); no EOC logic included Array size = 2 x 160 Bench tests ( radiation exposure) PreFPIX2I (2000) “CERN” 0.25 CMOS Same front end Complete “core” – including new, simplified EOC & R/O (self-triggered only) Array size = 18 x 32 Bench tests (proton exposure) PreFPIX2Tb (2000) TSMC 0.25 CMOS New programming interface Internal DAC’s – no external currents required; only external voltages are 2.5V & ground. Array size = 18 x 64 Bench tests (proton exposure) FPIX2 (2001) 0.25 CMOS - Final BTeV R/O chip!!??
Total Dose Tolerance Threshold shifts – and hadrons. –Small as expected. Surface leakage currents – and hadrons. –Negligible by design (gate all around NFET’s and guard rings). Bulk damage – hadrons. –Small, manageable, increase in leakage due to parasitic device formation.
Single Event Effect Tolerance Catastrophic events – gate rupture, latch up. –None observed rate guaranteed to be acceptable to BTeV. Soft errors – single event upset. –Small cross sections measured: (1 – 6 x /cm 2 ) no need for redundant logic or other design measures.
Positive charge trapped in the oxide layer effectively biases the transistors. Gate oxide n+ Source (normally connected to gnd) Drain Conductive channel is induced by positive voltage applied to the gate Gate p bulk “Threshold voltage” shifts with exposure to radiation BUT, the effect gets smaller as the oxide gets thinner (with smaller feature size) … by 0.25 the threshold shifts are small enough to be “benign.” Radiation damage to CMOS transistors
Trapped charge in the field oxide also causes leakage current in nmos devices by inducing an n-channel in the p-bulk. source drain pmos leakage current does not increase (glass charges +; doesn’t induce a p-channel). Radiation induced leakage current
Rad-hard nfet layout (very schematic!) Or, impossible! Large W/L is “easy” Small W/L is hard “gate all around” layout (guard rings to prevent current between devices (can cause latchup) not shown)
Irradiation Tests Irradiation ( 60 Co at Argonne National Lab) – individual transistors and FE prototype: 58 MRad, preFPIX2T: 33 MRad. 200 MeV proton irradiation (Indiana University Cyclotron Facility) – preFPIX2I: 26 MRad (4.4x10 14 /cm 2 ), preFPIX2Tb: 43 MRad (7.4x10 14 /cm 2 ).
Front end response, before and after 33 MRad 60 Co
Front end response, before and after 26 MRad 200 MeV p DC shift believed to result from increased leakage to bulk.
preFPIX2I noise, before and after 26 MRad proton irradiation
PreFPIX2Tb DAC Response
Total Dose: Effect on FPIX Small increase in gain = decrease in dynamic range. Small increase in DAC nonlinearity. Small decrease in front end noise. Small decrease in discriminator threshold dispersion. Design verified to be sufficiently radiation tolerant.
200 MeV proton irradiation tests 2.5V Power Supplies LVDS driver board Laptop LVDS driver board PCI- PTA Card GPIB 100 foot twist-n-flat to PTA card 200 MeV Protons Concrete walls Devices Under Test SEU Test Procedure: download pattern, wait 1 minute, read back & check for errors, repeat. Irradiation done in air at room temperature. No low energy particle or neutron filter. Nominal flux 2 x protons/(cm 2 s). 1.5 cm beam spot diameter measured with a sensitive film (flux 90% center value). Laser spot alignment and remote video monitoring. Dosimetry : Faraday cup + SEM.
FF in DAC (112 in chip) FF in SR (1152 in chip) Due to the symmetric configuration: 0 1 and 1 0 are expected to be equally likely. Due to asymmetric configuration: 1 0 SEU is expected to be two times more likely than 0 1. Single Event Upset Expectations
Single Event Upset Cross Sections TimeBoardFluence [cm -2 ] Bit errors in SR [2x576 bits] Bit errors in DAC [8x14 bits] Apr E14 53=18 +35 10=8 +2 Aug E14 74=22 +52 19=9 +10 Aug E14 86=27 +59 19=8 +11 Aug E14 80=23 +57 20=8 +12 Aug.014 (45 0 ) 3.65E14 77=14 +63 31=19 +12 April 01 April 01 +Aug 01 = transition from 0 to 1. = transition from 1 to 0.
Estimated SEU Rate in BTeV Ch.Had. E>10MeV Neutrons E>14MeV Neutrons E<14MeV e, E>0.1MeV Flux per plane [Hz] 1.4E80.15E80.20E8 3E7, 1.4E8 Pixel Kill SR [SEU/hr] 10< 1< 1.40 DAC [SEU/hr]2< 0.2< bit Data Output Serializer [SEU/hr]