1EE241 - Spring 2005Advanced Digital Integrated CircuitsLecture 20:Thermal designGuest Lecturer: Prof. Mircea StanECE Dept., University of Virginia2Thermal DesignWhy should you care about thermals?What do we mean by thermals?How do you model thermals?What can you do about thermals?Temperature-aware circuit designThermal sensorsReferences: - Intel® Technology Journal: http://developer.intel.com/technology/itj/- IBM Journal of Research and Development: http://www.research.ibm.com/journal/rd/- IEEE Transactions on Components and Packaging Technologies- IEEE Transactions on VLSI Systems- IEEE Journal on Solid-State Circuits23Why should you care about thermals?Temperature affects:Circuit performanceCircuit power (especially leakage)System reliabilityIC and system packaging cost“Environment”4Circuit Performance vs. TemperatureTemperature  => Performance?Temperature => Performance?Source: E Long, WR Daasch, R Madge, B Benware, “Detection of Temperature Sensitive Defects Using ZTC” VLSI Test Symposium, 2004Temperature  => Transistor threshold  and carrier mobility Temperature => Transistor threshold and carrier mobility ( )α−µ=ThGSoxDSVVCLWI235Leakage vs. Temperature − µ=−−qkTVdsqkTmThVgVdseeqkTLWI 12[Taur, Ning] EECS241 Lecture 3-9-8-7-6-5-4-30 0.2 0.4 0.6 0.8 1 1.2VGS [V]log IDS [log A]Subthreshold slope S>ln10 kT/qk = 1.38x10^-23q = 1.6x10^-19kT/q = 25.9mV at 27C= 23.5mV at 0C (273K)= 32mV at 100C (373K)S = kT/q ln10 (1+Cd/Ci)6Leakage PowerFraction of leakage power increasing:exponentially with each generationexponentially dependent on temperatureIncreasingratio for newtechnology nodesSource: Sankaranarayanan et al, University of VirginiaStatic power/ Dynamic Power010203040506070298303308313318323328333338343348353358363368373Temperature(K)Percentage180nm 130nm 100nm 90nm 80nm 70nm47ReliabilityThe Arrhenius Equation: MTF=A*exp(Ea/k*T)MTF: mean time to failure at TA: empirical constantEa: activation energy k: Boltzmann’s constantT: absolute temperatureFailure mechanisms:Die metalization (Corrosion, Electromigration, Contact spiking)Oxide (charge trapping, oxide breakdown, hot electrons)Device (ionic contamination, second breakdown, surface-charge)Die attach (fracture, thermal breakdown, adhesion fatigue)Interconnect (wirebond failure, flip-chip joint failure)Package (cracking, whisker and dendritic growth, lid seal failure)8System Packaging CostToday…Grid computing: power plants co-located near compute farmsIBM S/390:refrigerationSource: R. R. Schmidt, B. D. Notohardjono “High-end server low temperature cooling”IBM Journal of R&D59IC Packaging CostIBM S/390 processor subassembly: complex!C4: Controlled Collapse Chip Connection (flip-chip)Source: R. R. Schmidt, B. D. Notohardjono “High-end server low temperature cooling”IBM Journal of R&D10Desktop processor, simpler, but still…Pentium 4, ItaniumSource: Intel web site611“Environment”Environment Protection Agency (EPA): computers consume 10% of commercial electricity consumptionThis includes peripherals, possibly also manufacturingA DOE report suggested this percentage is much lowerNo consensus, but it’s still a lotEquivalent power (with only 30% efficiency) for ACCFCs used for refrigerationLap burnFan noise12Ultimate Effect: Thermal RunawayTemperature  => Leakage power  => Temperature …“Loop gain” > 1 trouble! Source: Tom’s Hardware Guidehttp://www6.tomshardware.com/cpu/01q3/010917/heatvideo-01.html713Thermal DesignWhy should you care about thermals?What do we mean by thermals?How do you model thermals?What can you do about thermals?Temperature-aware circuit designThermal sensors14What do we mean by thermals?Anything that has to do with heat/temperatureHeat is a form of energy transferTemperature is a measure of entropy and determines heat flowSource: http://www.iun.edu/~cpanhd/C101webnotes/matter-and-energy/specificheat.html815Heat mechanismsHeat Conduction: phonons, vibrationsHeat Convection: fluid molecules movementHeat Radiation: photons, EM wavesPhase change: boiling, sublimation, condensation, etc.Heat storage: specific heatRefrigeration: move heat “backwards”Other many mechanisms…16Conduction“Similar” to electrical conduction (e.g. metals are good conductors)Heat flow from high temperature to low temperatureMicroscopic (vibration, adjacent molecules, electron transport)In a material: typically in solids (fluids: distance between mol)Typical example: thermal “slug”, spreader, heatsinkSource: CRC Press, R. Remsburg Ed. “Thermal Design of Electronic Equipment”, 2001 A917ConvectionMacroscopic (bulk transport, mix of hot and cold, energy storage)Need material (typically in fluids, liquid, gas)Natural vs. forced (air or liquid)Typical example: heatsink (fan), liquid coolingSource: CRC Press, R. Remsburg Ed. “Thermal Design of Electronic Equipment”, 200118Simplistic Thermal ModelMost thermal transfers: R = k/APower density matters!Ohm’s law for thermals (steady-state)∆∆∆∆V = I · R -> ∆∆∆∆T = P · R T_hot = P · Rth + T_ambWays to reduce T_hot:- reduce P (power-aware)- reduce Rth (packaging)- reduce T_amb (move to Alaska?)- maybe also take advantage of transients (Cth) 1019Simplistic Dynamic ModelElectrical-thermal dualityV ≅≅≅≅ temp (T)I ≅≅≅≅ power (P)R ≅≅≅≅ thermal resistance (Rth)C ≅≅≅≅ thermal capacitance (Cth)RC ≅≅≅≅ time constantKCLdifferential eq. I = C · dV/dt + V/Rdifference eq. ∆∆∆∆V = I/C · ∆∆∆∆t + V/RC · ∆∆∆∆tthermal domain ∆∆∆∆T = P/C · ∆∆∆∆t + T/RC · ∆∆∆∆t(T = T_hot – T_amb)One can compute stepwise changes in temperature for any granularity at which one can get P, T, R, C 20IC with die, package, heatsinkR = T/QR = V/IRja = Rjc + Rcs + Rsa = (Tj - Ta)/QRsa = ((Ts - Ta)/Q) - Rjc - Rcs1121Hot spots in Power4Temperature “landscape”: space and timeHow to estimate early in the design cycle?22Trends in Power DensityWatts/cm211010010001.5µ1.5µ1.5µ1.5µ 1µ1µ1µ1µ 0.7µ0.7µ0.7µ0.7µ 0.5µ0.5µ0.5µ0.5µ 0.35µ0.35µ0.35µ0.35µ 0.25µ0.25µ0.25µ0.25µ 0.18µ0.18µ0.18µ0.18µ 0.13µ0.13µ0.13µ0.13µ 0.1µ0.1µ0.1µ0.1µ 0.07µ0.07µ0.07µ0.07µi386i386i486i486Pentium® Pentium® Pentium® ProPentium® ProPentium® IIPentium® IIPentium® IIIPentium® IIIHot plateHot plateNuclear ReactorNuclear ReactorNuclear