Radiation Damage Tests at 1GRad Dose on 65nm CMOS transistors Marlon Barbero – CPPM GrezgorzDeptuch–FNAL - The RD53 collaboration
Plan • RD53 & CERN upgrades. • Effect of radiation on CMOS. • Few results on test transistors. • Few results on ICs and blocks. • Conclusion.
RD53 collaboration • “Development of pixel readout IC for extreme rate and radiation” : ATLAS-CMS-CLIC working group on small feature size electronics (focus on one 65nm techno so far). • Goal: • Small pixels. • Very high hit rates. • Very high radiation levels. • Started with 1st meetings mid-2013. • 6 working groups, among which one working group on radiation effects (Bergamo-Pavia, CERN, CPPM, Fermilab, LPNHE, New Mexico, Padova, but also others). • The work presented here essentially done in this framework. See Valerio Re’s talk, Tuesday 20th
Pixel detectors upgrades ATLAS IBL CMS Phase I ATLAS / CMS phase II Nominal: 1-2 GHz.cm-2, 1GRad, 1016 neutrons.cm-2, typ 50×50μm2, billion transistor 2×2 cm2 IC Main goal of this R&D!
Classical view of radiation effects in MOS • Focus here on the sensitive oxide (thin gate and FOX). • Reminder: • gate thickness 2.6nm. • hole mobility is << than e- mobility. • 1st step: Radiation e-/hole pair creation in oxide. Depending on biasing, electrons swept out in ~ps. Still fraction e- / holes recombine. • 2nd step: Hopping hole transport to Si/SiO2 interface. • 3rd step: Holes at interface long-lived trap states. • 4th step: Interface traps build-up. Typical values (room T): ref: Oldham (ionizing radiation effects in MOS oxides)
Notes on defect generation (I) • Which hole fraction recombines initially = fn (density -particle energy, particle type- and magnitude of field applied). • Deep hole trapping (in transition region where oxidation is incomplete). Annealing depends again on thickness, time, temperature and applied field. Annealing process == either tunneling (at ~ room temperature or below, neutralization by electron to Si+) or thermal excitation (higher temp.). ΔVFB shift / Mrad dose Flat-Band Shift / Mrad dose function of oxide thickness in MOS cap oxide thickness [nm]
Notes on defect generation (II) • Radiation-induced traps: Trivalent Si is passivated when oxide is grown by H. But radiation (or other type of stress) depassivation (holes free proton reach interface and form H2 centers)== electrically active. • Annealing (in particular in thin oxides) might cure deep hole trapping component but not radiation-induced interface traps. ΔDit shift / Mrad dose Interface Traps Density Increase / Mrad dose function of oxide thickness Vth vs annealing oxide thickness [nm] ref: Schwank (physical mechanisms contributing to device rebound)
Effect on drain current when radiation in MOS structure particle metal ionization pos. charge trapped in oxide e-/hole creation fixed charge oxide surface states surface states silicon due to deep hole trapped + interface states due to interface states
Radiation Induced Narrow Channel Effect -RINCE- • Trapping in STI of rad-induced positive charges opens inversion channel / parasitic transistor. • Strong dependence on width of transistor: for narrow transistors, influence of parasitic channels strong competitor to main channel. ref: Faccio (radiation induced edge effect in deep submicron CMOS transistors)
A word from the past • CMS / ATLAS current Front-End: • 250 nm technology. • ~50 MRad. • Use of enclosed layout + guard rings. Custom libraries!!! If so, safe! • ATLAS IBL (FE-I4): • 130nm. • ~250 MRad. • Minimum W imposed. If so, safe!
XRay irradiation at CERN • XRay irradiation, 10 keV, 150 kRad.min-1 T = -25°C T = 25°C T=100°C T = -25°C T = 25°C T=100°C First day : T=25°C Mohsine Menouni et al, CPPM
NMOS threshold shift • A little decrease of the threshold for low dose level • -20 mV shift for the minimum width device • For levels of dose > 200 Mrad, the absolute value of Vth increases • At 1000 Mrad, the Vth shift is between 150mV to 320 mV depending on the device width (maximum for 240nm/60nm) • The Vth recovery at room temperature is very slow • Except at the beginning of annealing period and only for the narrowest devices (W=120nm and W=240nm) • High Temperature annealing (100 °C for 7 days) : • The Vth recovery is accelerated • The global Vth shift is < 200 mV • Reverse annealing behavior for the device with W=120nm (Vth first decreases and increases after)
Proton irradiation • 3MeV proton -1016 neq.cm-2-, 3.6 - 36 MRad.min-1 , Lili Ding et al, Padova.
nmos transconductance variation • After 1000 Mrad : KPN loss is between 20% and 40% • The GM recovery at room temperature is very slow • 100°C annealing : KPN loss decreases to reach a values between 25% and 8% • The loss is still higher for narrower devices T = -25°C T = 25°C T=100°C Menouni, CPPM
Notes on NMOS results • Note 3MeV p (Padova) -1016 neq.cm-2- vs 10 keV Xray (CPPM). • Note very different dose rate: • 3.6 MRad.min-1 to 36 MRad.min-1 for Padova. • 150 kRad.min-1 for CPPM / Xray box at CERN. • Different time cst for building of Q in oxide vs interface Does this translate in much stronger influence of Qox contribution in Padova’s case (compensating interface charges)? annealing studies!
pmos transconductance variation • For high level of dose (1000 Mrad), KPP decrease reaches 100% for 120 nm and 240nm devices • With annealing, devices recover the most part of GM loss • Wider devices recovers practically the pre-irradiation GM value • For the narrowest device, KPN variation is only 32% compared to the pre-irradiation value T = -25°C T = 25°C T=100°C Menouni, CPPM
pmos threshold shift • Vth increases rapidly from a dose levels of 200 Mrad • Vth shift is < 120 mV for 1000 Mrad for wider devices and cannot be computed for narrower devices. • Vth is still increasing with annealing (reverse annealing) T = -25°C T = 25°C T=100°C Menouni, CPPM
CPPM test of LBNL’s IC • When CPPM tested SEU in LBNL-dvp’ed 65nm proto (CERN PS) Observed localized bits stuck in shift register used for pixel config. loading. • Hypothesis: TID effect / Bit leaking. • Narrow pmos dose effect? 390 MRad to 420 MRad 260 MRad to 310 MRad Pattern 1111 Pattern 1111 Rows 0-255 Rows 0-255 Tests with 24 GeV proton beam Columns 0-15 Columns 0-15 CPPM / LBNL
Test IC dvped by CERN • chip with digital logic blocks • Assembled with foundry standard cells, pads and IP blocks • Packaged, functional tests & irradiation measurements run on a custom test board • Shift-register • 64 kbit, “DFQD1” • MinW=150nm for both p and n • Ring oscillator • 1025 inverters “INVD0” • Wn=195nm, Wp=260nm • SRAM (from foundry compiler) • 56 kbit • MinW = 90nm Ring oscillator Shift-register SRAM Sandro Bonacini, CERN
Low temp / high temp influence? Bonacini, CERN 2011, @25C 2014, @ –25C • Ring oscillator 2014 test at –25C • For same sized inverter: • -10% @200Mrad • -35% @1Grad • Ring oscillator 2011 test at 25C • -22% after irradiation 200Mrad • -13.8% after annealing
CLICpix TID / biasing effects in PMOS • XRay irradiation performed to 800 MRads. • DACs use PMOS switches to control a current mirror for each bit. • At high rates switches irradiated while they are ON (their control voltage is GND) degrade more quickly than the ones irradiated while they are OFF. • Above 200MRad, damaged switches are unable to let the nominal current pass (their driving current becomes too low). 400nm/1u VDD IDAC >600 mV A A ~200 mV Iout Iout Above 200 MRad. Pierpaolo Valerio, CERN
BUT… • All I/O interfaces and digital structures did not show any significant degradation during irradiation, even after the analog front-end stopped working • The chips regained some functionality after two week of annealing at room temperature (the total power consuption went back to pre-rad value). Analog performances of the measured chip were found to be considerably degraded. • The measurement was performed at a dose rate of ~150 krad/minute (~75 krad/minute for the first 10 Mrads). The high dose rate could have an effect on the radiation damage and needs to be explored Pierpaolo Valerio, CERN
Summary • Unexplored territory in terms of process and radiation level. • Studies done so far on one 65nm technology mainly. • Gate effects / STI effects not clearly disentangled so-far. • NMOS: shift of Vth, drive capability loss… steep increase above 200 MRads. Still, provided one could handle degradation, depending on application, hint that devices might be operated to close to ~1GRad TID down to small W. • PMOS: Strong drive loss, narrowest devices completely off above few 100 MRads. Indication that narrowest devices will not work at close to 1GRad. • Effects seeing in test IC too.
Outlook • Still studies too preliminary and more work to be done in well-controlled conditions: Biasing for PMOS? Influence of temperature? Annealing scenario? • Then: Other damages type (Xray / neutron/ proton … investigate if DD becomes an issue). LDR vs HDR? • Relation to other stresses: NBTI, HCI… • If it is confirmed that damage is unacceptable, 2 ways out: • Other technologies (work starts on that topic, with limited momentum so far). • Rules for design to be established to allow intermediate dose level to be reached and replacement strategy. • Still to come later: SEE studies / Statistical spread after irrad / Modelling after irrad /etc…
BACKUP • BACKUP
Core NMOS radiation performance • Up to ~20mV shift for 200 Mrad • Some rebound effect visible for narrow devices • in 130nm: was 150mV • At high doses Vth shift is positive for wide devices, negative for narrow devices • STI edge oxide traps considerable charge (RINCE) • Subtreshold slope does not change significantly • Less than 10× increase in leakage for wide devices (W > 360nm) • Narrow devices have up to 2.5 orders of magnitude increase • In 130nm: • All devices are peaking at ~100nA • Narrow devices increase leakage by 3 orders of magnitude • Ileak is ~1nA @136 Mrad Threshold voltage shift Leakage current Sandro Bonacini - PH/ESE - firstname.lastname@example.org
Core PMOS: Vth shift and gm loss • PMOS Vth shift limited to 60 mV • trapped charge and interface states sum up • More evident for narrow devices • Less than 10mV for transistors with W>1um • Compared to other technologies • Better performance than 130 nm • had up to 90mV @136Mrad • 30mV for wide devices • In a 90 nm tech we observed a similar effect: 70mV @ 200Mrad gm,max • Radiation kills maximum gm,max (strong inversion) • ...but not gm in weak inversion region Sandro Bonacini - PH/ESE - email@example.com