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High Performance Analog Integrated Circuit Design: The Effect of Device SelfHeating on Design Optimization Ronald L. Carter, Professor Analog Integrated Circuit Design Lab Electrical Engineering Department The University of Texas at Arlington Analog IC Design with Self-Heating Heat Source/Temperature Effects Thermal Equations/Analogy Thermal Resistance Models Effect of Thermal Resistance on Device Biasing Effect of Thermal Resistance on the Circuit Performance RLCarter: Analog IC Conclusions/Future Work Design with Self Heating 2 Typical IC npn BJT Figure 9.2a, Semiconductor Physics & Devices, 2nd ed., by Neamen, Irwin, Chicago, 1997 RLCarter: Analog IC Design with Self Heating 3 EB and CB Heat Sources Figure 9.2a, Semiconductor Physics & Devices, 2nd ed., by Neamen, Irwin, Chicago, 1997 emitter contact collector base contact RLCarter: Analog IC Design with Self Heating EB Depletion Region, PE = iE*v BE EB Depletion Region, PC = iC*v BC 4 Temperature Increase Td-Ta=Ta{[1 + (n+1)(Dte+Dtc)/Ta)]1/(n+1)1} Dte and Dtc are pseudo-temperatures via the Kirchoff transformation, assuming k(T) = k(300K)[T/300]n Dte = RTh,EB|ievbe| Dtc = RTh,CB|icvbc| RTh,EB, RTh,CB are thermal res. at Ta. Following S. H. Whemple, and H. Huang, "Thermal Design of Power GaAs FETs", in GaAs FET Principles and RLCarter: Analog IC Technology, J. V. DiLorenzo and D. D. Khandelwal, eds., pp. 313-347, Artech House, 1982. Design with Self Heating 5 Circuit Simulation of Temperature Effects Typically TNOM (parameter spec. temperature) and TEMP (circuit operation temperature) only variables However, Td =Tdevice is a function of ie, vbe, ic and vbc. More flexibility with Vertical Bipolar Inter-Company model (VBIC) RLCarter: Analog IC Design with Self Heating 6 Gummel-Poon Static npn Circuit Model C B RBB B’ RC ILC IBR ILE IBF RLCarter: Analog IC Design with Self Heating E Intrinsic Transistor ICC - IEC = IS(exp(vBE/NFVt) exp(vBC/NRVt)/QB RE 7 VBIC Model Overview RLCarter: Analog IC Design with Self Heating Self-heating effects included Improved Early effect modeling Quasi-saturation modeling Parasitic substrate transistor modeling Parasitic fixed (oxide) capacitance modeling An avalanche multiplication model included Base current is decoupled from collector current 8 CAD Tools Support for VBIC Hspice Does not support PNP device Does not scale with “Area” and “M” terms Spectre [4] [5] Support both NPN and PNP devices scale with “Area” and “M” term HPADS No temperature nodes (“dt” and “tl”), so unable to simulate thermal coupling effects RLCarter: Analog IC Design with Self Heating 9 Temperature Designations for VBIC Parameters Description Spectre [4] Hspice [5] Name Default Name Default Temperature rise of the device from ambient trise 0 dtemp 0 Ambient temperature temp 27 temp 25 Parameters measurement temperature tnom 27 tnom 25 tref 27 RLCarter: Analog IC Design with Self Heating 10 Using VBIC in Spectre [5] Name c b e [s] [dt] [tl] ModelName parameter=value ... Selft=1 and Rth>0 to enable Self-heating 1 volt at the temperature nodes = 1 degree in temperature “tl” node represents the initial local temperature of device which always corresponds to trise+temp “dt” node represents the rise above trise+temp caused by thermal dissipation, whose value equals V(dt)-V(tl) Analog IC RLCarter: Device temperature=V(dt)-V(tl)+trise+temp Design with Self Heating 11 Using VBIC in Cadence Need explicit external temperature nodes in the symbol to model inter-device thermal coupling by Connecting thermal network between “dt” nodes, or Adding VCVS between “tl” and “tlr” node Customized VBIC 6-terminal (5-pin) symbol RLCarter: Analog IC Design with Self Heating 12 Model Conversion Most BJTs are defined with SGP model A conversion from SGP to VBIC is needed Only approximate conversion is possible Some parameters are unmapped such as Rth and Cth Two approaches are provided Manual conversion — done empirically and need Local Ratio Evaluation [2] Program conversion using program sgp_2_vbic [3] RLCarter: Analog IC Design with Self Heating 13 Parameter Mapping using sgp_2_vbic VBIC mapping VBIC Rcx Rc Mc Rci 0 Cjcp Rbx Rbm Ps Rbi Rb-Rbm Ms Re Re Nei Is Is Iben Nf Nf Nen Nr Nr Ibei Fc Fc Ibci Cje Cje Nci Pe Vje Ibcn Me Mje Ncn Cjc Cjc·Xcjc Ikf Cjep Cjc(1-Xcjc) Ikr Pc Vjc Tf RLCarter: Analog IC Design with Self Heating mapping Mjc Cjs Vjs Mjs Nf Ise Ne Is/Bf Is/Br Nr Isc Nc Ikf Ikr Tf VBIC Xtf Vtf Itf Tr Td Ea Eaie Eaic Eane Eanc Xis Xii Xin Kfn Afn mapping Xtf Vtf Itf Tr Tf·Ptf/180 Eg Eg Eg Eg Eg Xti Xti-Xtb Xti-Xtb Kf Af Early Effect model is different Need Vbe, Vbc to solve the 3 equations below g OF IC g oR Ie 1 / VAF 1 VbeF / VAR VbcF / VAF 1 / VAR 1 VbeR / VAR VbcR / VAF F CbcF 1 F q q be bc F g / I c o VEF 1 CbeR 1 1 R R qbe R qbc g o / I e VER 14 Analog IC Design with Self-Heating Heat Source/Temperature Effects Thermal Equations/Analogy Thermal Resistance Models Effect of Thermal Resistance on Device Biasing Effect of Thermal Resistance on the Circuit Performance RLCarter: Analog IC Conclusions/Future Work Design with Self Heating 15 Device Geometry and Boundary Conditions RLCarter: Analog IC Design with Self Heating 16 Static Heat Flow Equation and Poisson’s Equation T DT ( x, y, z ) g ( x, y, z ) V 2 DT = T-T0 (K) is the temperature rise above local ambient = Thermal conductivity (Wcm-1K-1) g= volumetric heat gen. rate (W cm-3) RLCarter: = charge dens., and = permittivity Analog IC Design with Self Heating 17 The Electrical Analogy The Kirchoff transformation factors the (T) Both equations become the Laplacian DV[Volt] is the analog of DT[K] I[Ampere] is the analog of P [Watts] V = IR is the analog of DT = P RTH RLCarter: Analog IC Design with Self Heating 18 Semiconductor Material Properties at 300K Parameter Name Si SiO2 Al Cu Conductivity (Wcm-1K-1) 1.412 0.014 2.37 3.98 Density (g cm-3) 2.328 2.648 2.7 8.96 Specific Heat CP(Jg-1K-1) 0.7 0.787 0.898 0.384 RLCarter: Analog IC Design with Self Heating 19 Applying the Analogy to Spreading Resistance The potential field due to a point current source on a wafer surface is V = I/(2r) The thermal analogy is T = P/(2r) For a cylindrical contact of radius r, the spreading resistance, Rsp = /4r The thermal analogy is Rth = 1/4r Dieter K.Analog Schroder, RLCarter: IC “Semiconductor material and device characterization, 2nd Ed., Wiley-Interscience in 1998, Self New York Pages 31-33. Design with Heating 20 Analog IC Design with Self-Heating Heat Source/Temperature Effects Thermal Equations/Analogy Thermal Resistance Models Effect of Thermal Resistance on Device Biasing Effect of Thermal Resistance on the Circuit Performance RLCarter: Analog IC Conclusions/Future Work Design with Self Heating 21 Thermal Resistance Model for square emitter For a square emitter of side w RTh,CB RTh, EB w RTh, F (Tnom ) w kSi,Tnom 1 tw w RTh, R (Tnom ) w kSi,Tnom 1 tw S. H. Whemple, RLCarter: Analogand IC H. Huang, op. cit. Design with Self Heating -1 -1 22 Image effect of Heat Sources Below Surface base contact emitter contact collector D RTH EB Depletion Region, PE = iE*v BE EB Depletion Region, PC = iC*v BC 1 4 lw D / 2 2 , where the emitter is l long and w wide, D below the surface and the wafer is thick, tw lw RLCarter: Analog IC Design with Self Heating 23 Dielectric Isolated BJT (DIBJT) kSi ~ 100 kSi02 Perimeter of “well” is approximately an isotherm Rtrench = Rwall + Rsurface Rbulk = Risolation + Rsubstrate RLCarter: Analog IC Design with Self Heating 24 DIBJT Rth Model RLCarter: Analog IC Design with Self Heating 25 Analogy Modeling of Device Thermal Resistance RLCarter: Analog IC Design with Self Heating 26 Analog IC Design with Self-Heating Heat Source/Temperature Effects Thermal Equations/Analogy Thermal Resistance Models Effect of Thermal Resistance on Device Biasing Effect of Thermal Resistance on the Circuit Performance RLCarter: Analog IC Conclusions/Future Work Design with Self Heating 27 Transient Analysis of a BJT with Multiple Thermal Paths Simulation circuit The thermal network consists of 3 poles t1=1us, t2=100us and t3=10ms Spectre is used as a simulator RLCarter: Analog IC Design with Self Heating 28 VBIC Model Parameters used for the BJT rcx re fc cjc cjcp iben nci ver xtf td eane xin 1 0.5 0.5 417.5fF 0 3.471pA 1.07 333.331V 120V 0 1.11 0.7 rci is cje cjep ps nen ibcn ikf vtf ea eanc kfn 0 4.479fA 910fF 417.5fF 0.7 3.66 0 1mA 0 1.11 1.11 rbx nf pe pc ms ibei ncn ikr itf eaie xis 36 1.07 0.661 1 0.5 0.0172269fA 1 0 0 1.11 3 0 afn 1 rbi nr me mc nei ibci vef tf tr eaic xii 0 1.07 0.294 0.28 1.07 4.479fA 195.325V 112ps 1ns 1.11 0.7 * Mapped from GP model RLCarter: Analog IC Design with Self Heating 29 Transient Thermal Response - JI BJT Current and Temperature Rise of a BJT with 3-Pole Thermal Network 20 Current Temperature Rise 10 t1 0 -10 10 RLCarter: Analog IC Design with Self Heating -8 10 -6 10 Time (s) t2 -4 10 Temperature Rise (Degree) Collector Current (mA) 1 t3 -2 0 10 30 Transient Thermal Response - DIBJT A DIBJT with 3-Pole Thermal Network 1.5 30 Current Temperature Rise RTH,epi=394 K/W CTH,epi=79.4p sW/K 1 20 0.5 10 Temperature Rise (Degree) Collector Current (mA) ( tepi 0 -10 10 RLCarter: -8 10 Analog IC Design with Self Heating tox tw -6 10 Time (s) -4 10 -2 10 0 ) RTH,ox=2742 K/W CTH,ox=39.75p sW/K ( tepi=31.3ns tox=109ns ) RTH,w=126 K/W CTH,w=11.9p sW/K ( tw=1.5ms ) 31 Build SDD BJT model in ADS SDD (Symbolic Defined Device) Combination of the classical GP model and the thermal network For static model, IS, BF, BR, ISE and ISC values changed by temperature rise RLCarter: Analog IC Design with Self Heating 32 SDD Model verification I-V Characteristics Comparison of Different Models 6 IB=100uA 5 IB=75uA Collector current (mA) 4 IB=50uA 3 IB=25uA 2 1 Spectre VBIC model ADS GP model ADS SDD model 0 -1 RLCarter: Analog IC 0 Design with Self Heating 1 2 3 Vce (v) 4 5 6 33 Current Mirror Driving BJT with 3 Emitter Fingers Simulation Circuit IC1 IC2 IC3 cme cee RLCarter: Analog IC Design with Self Heating The multiple finger BJT consists of 3 fingers, Q1, Q2 and Q3. They have the same geometrical size with Qref Q2 is the inner finger Thermal coupling occurs between 3 fingers. The coupling factor is Cme and Cee No thermal coupling between the multiply finger BJT and Qref 34 VCVS Thermal Coupling Model RLCarter: Analog IC Design with Self Heating 35 Model Parameters IS ISE ISC IKF IKR IRB BR 110-18 A BF -18 110 A NF 0 10mA 0.7371 NR NC NE VAF VAR 100 RE 1.07 RC 1.07 2 1.259 74.03V 500V RB RBM EG XTI XTB 5 5 10 10 1.11eV 3 1.5 * Typical values for 1um2um device RLCarter: Analog IC Design with Self Heating 36 Current Ratio (IC/Iref) for Different RTH 1um2um device W 1um L 2um S 3um cme 0.102 cee RLCarter: Analog IC Design with Self Heating 0.051 37 Temperature Rise for Different RTH 1um2um device W 1um L 2um S 3um cme 0.102 cee RLCarter: Analog IC Design with Self Heating 0.051 38 Current Ratio for Different Spacing 2.8 2.6 2.4 Inner emitter Outer emitter RTH=3000 K/W 3um L=2um W=1um 5um Current Ratio 2.2 7um 2 1.8 Cme Cee 3um 0.102 0.051 1.4 5um 0.073 0.036 1.2 7um 0.057 0.028 1.6 No thermal coupling 1 0.8 0 0.5 RLCarter: Analog1IC Design with Self Heating 1.5 2 Iref (mA) 2.5 3 3.5 4 39 Temperature Rise for Different Spacing 120 Inner emitter Outer emitter 100 Temperature Rise (Degree) 3um 5um 80 7um L=2um W=1um 60 RTH=3000 K/W 40 20 0 0 0.5Analog1IC RLCarter: Design with Self Heating Cme Cee 3um 0.102 0.051 5um 0.073 0.036 7um 0.057 0.028 No thermal coupling 1.5 2 Iref (mA) 2.5 3 3.5 4 40 Current Ratio (IC/Iref) for Different RTH 2.6 2.4 Inner emitter Outer emitter 2.2 1um5um device Current Ratio 2 1.8 1.6 1.4 Rth=2000K/W Rth=1000K/W 1.2 1 0.8 0 0.5 RLCarter: Analog1 IC 1.5 Design with Self Heating 3 L 5um S 3um cee Rth=200K/W 2.5 Iref (mA) 1um cme 0.100 2 W 3.5 4 4.5 0.050 5 41 Temperature Rise for Different RTH 100 90 Temperature Rise (Degree) 80 Inner emitter Outer emitter 1um5um device 70 60 50 40 W 1um 30 L 5um S 3um 20 Rth=1000K/W Rth=2000K/W 10 cme 0.100 Rth=200K/W 0 0 0.5 1 RLCarter: Analog IC Design with Self Heating 1.5 2 2.5 Iref (mA) 3 3.5 cee 4 4.5 0.050 5 42 Current Ratio for Different Spacing 2.6 2.4 Inner emitter Outer emitter 3um 2.2 L=5um W=1um 5um Current Ratio 2 7um 1.8 RTH=2000 K/W 1.6 1.4 No thermal coupling 1.2 1 0.8 0 0.5 Analog 1 1.5 RLCarter: IC Design with Self Heating Cme Cee 3um 0.100 0.050 5um 0.080 0.040 7um 0.067 0.033 2 2.5 Iref (mA) 3 3.5 4 4.5 5 43 Temperature Rise for Different Spacing 100 90 Inner emitter Outer emitter 3um Temperature Rise (Degree) 80 70 L=5um W=1um 5um 7um 60 RTH=2000 K/W 50 40 Cme Cee 3um 0.100 0.050 5um 0.080 0.040 7um 0.067 0.033 30 20 No thermal coupling 10 0 RLCarter: Analog IC 0 0.5 1 1.5 Design with Self Heating 2 2.5 Iref (mA) 3 3.5 4 4.5 5 44 Analog IC Design with Self-Heating Heat Source/Temperature Effects Thermal Equations/Analogy Thermal Resistance Models Effect of Thermal Resistance on Device Biasing Effect of Thermal Resistance on the Circuit Performance RLCarter: Analog IC Conclusions/Future Work Design with Self Heating 45 A741 Simulation Simulated by Spectre (Ver. 4.4.6.061301) Analog Waveform is used to obtain graphic output Use the circuit posted on WEB (http://wwwee.uta.edu/Online/adavis/analog/f_opamp.cir) Transistor models are mapped to VBIC model using sgp_2_vbic (only one npn and pnp model used) Area of Q13A is 0.25; Area of Q13B is 0.75 Areas of Q14 and Q20 are 3 Areas of other transistors are 1 Connect A741 with 15V voltage supplies RLCarter: Analog IC Design with Self Heating 46 μA741 Op-Amp Schematic RLCarter: Analog IC Design with Self Heating [1] 47 Relative Device Temperatures Configure A741 as a voltage 100 follower 80 DC analysis result 60 Rth for all npn transistors is 40 5000K/W 20 Rth for all pnp 0 transistors is 1000KW Transistor No load is connected RLCarter: Analog IC Q17 is 91 degrees higher than the ambient temperature! Design with Self Heating 23 21 19 17 15 13 11 9 7 5 3 1 Degree Temperature deflection 48 Temperature transitions of Q1 and Q13 (without Cth) Q1 Q13 7 RLCarter: Analog IC Design with Self th,npn Heating (R =5000 K/W;Rth,pnp=1000 K/W) 49 Temperature transition of Q17 (1) Rth,npn=5000K/W Cth,npn=1 sW/K Rth,pnp=1000K/W Cth,pnp=10 sW/K Need about 60ms to reach the stable temperature RLCarter: Analog IC Design with Self Heating 50 Temperature transition of Q13 (1) Rth,npn=5000K/W Cth,npn=1 sW/K Rth,pnp=1000K/W Cth,pnp=10 sW/K Need about 60ms to reach the stable temperature RLCarter: Analog IC Design with Self Heating 51 Temperature transition of Q17 (2) RLCarter: Analog IC Design with Self Heating Rth,npn=5000K/W Cth,npn=0.1sW/K Rth,pnp=1000K/W Cth,pnp=10 sW/K Need about 40ms to reach the stable temperature Temperature variation increases 52 Temperature transition of Q13 (2) RLCarter: Analog IC Design with Self Heating Rth,npn=5000K/W Cth,npn=1 sW/K Rth,pnp=1000K/W Cth,pnp=1 sW/K Need about 10ms to reach the stable temperature Temperature variations increase 53 Circuit used to measure the open loop gain[2] Simulation parameters: Use a feedback technique to determine the open loop gain DUT is the op amp to be tested Nulling op amp is connected in a feedback mode RLCarter: Analog IC Design with Self Heating R1=100 R2=1M R3=1K Vmid=0 VSRC1 sweeps from 0 to 1V 54 Typical simulation output RLCarter: Analog IC Design with Self Heating 55 Table of open loop gain Note: Each value times 104 RLCarter: Analog IC Design with Self Heating 56 Surface of open loop gain 5 x 10 12 Open Loop Gain 10 Interpolation used 8 6 4 2 1.8 Decreases about a factor of 60! 2 2.2 3.5 2.4 3 2.6 2.5 2 RLCarter: Analog IC log10(Rth,npn) Design with Self Heating 2.8 log10(Rth,pnp) 57 Surface of open loop gain (dB view) Open Loop Gain (dB) 120 110 100 Decreases about 36dB! 90 1.8 2 80 3.5 2.2 3 2.4 2.5 RLCarter: Analog IC log10(Rth,npn) Design with Self Heating 2.6 2 2.8 log10(Rth,pnp) 58 Slew rate (without Cth ) Voltage follower is used Input signal 5K pulse input rise and fall time: 1S RLCarter: Analog IC Design with Self Heating Voltage level: 0 and 10V Rising edge is measured Unit: V/S Only 2% variation 59 Slew rate (including Cth ) Set Rth,npn=5000 K/W and Rth,pnp=1000 K/W Only 0.4% variation when Cth changes Comparing with Cth=0 case (0.6751, circled value at previously table), only 1.5% variation Self-heating (isolated) has no significant effect RLCarter: Analog IC on slew rate Design with Self Heating 60 Thermal coupling effect on open-loop gain Use the same circuit discussed previously Set Rth,npn=4000 K/W and Rth,pnp=900 K/W and Cth,npn=Cth,pnp=0 The hottest transistor is Q17 The amplificatory transistors at 1st stage are Q3 and Q4 Temperature node of Q17 is connected with temperature node of Q3 and Q4 by two identical thermal resistors RC RLCarter: Analog IC Design with Self Heating 61 Open-loop gain reduced by thermal coupling 4 2.7 x 10 2.6 Open Loop Gain 2.5 2.4 2.3 2.2 2.1 2 1.9 1 10 2 10 RLCarter: Analog Design with Self Heating 3 4 10 10 IC Coupling Thermal Resistor 5 10 Interpolation is used to obtain this curve Decrease about 25.4%! 6 10 62 Analog IC Design with Self-Heating Heat Source/Temperature Effects Thermal Equations/Analogy Thermal Resistance Models Effect of Thermal Resistance on Device Biasing Effect of Thermal Resistance on the Circuit Performance RLCarter: Analog IC Conclusions/Future Work Design with Self Heating 63 Summary VBIC model used to analyze thermal effects Isolated self-heating in A741 Effect of individual device temperatures in a A741 Inter-device heating effects Isolated self-heating can reduce the open loop gain Not a significant change in slew rate Preliminary study on thermal coupling effect Open loop gain is reduced if significant thermal coupling exists between 1st and 2nd stage Current mirror temperature compensation schemes are more critical when coupling is not optimum. RLCarter: Analog IC Design with Self Heating 64 Acknowledgements: Support TheTexas Higher Education Coordinating Board (THECB) National Semiconductor Corporation (NSC) The National Science Foundation Industry/University Center for Electronic Materials, Devices and Systems (NSF/CEMDAS) RLCarter: Analog IC Design with Self Heating 65 Acknowledgements: Analog IC Research Group Professor W. Alan Davis Zhipeng Zhu Zheng Li Siddharth Nashiney Naveen Kumar Reddy Siddareddygari Shankaranarayanan Rajaraman Piyush Thacker Anurag Lakhlani RLCarter: Analog IC Design with Self Heating 66 References Paul R. Gray, Robert G. Meyer, et al, Analysis and design of analog integrated circuits, New York: Wiley, c2001 Fujiang Lin, et al, “Extraction Of VBIC Model for SiGe HBTs Made Easy by Going Through Gummel-Poon Model”, from http://eesof.tm.agilent.com/pdf/VBIC_Model_Extraction.pdf http://www.fht-esslingen.de/institute/iafgp/neu/VBIC/ Avanti Star-spice User Manual, 04, 2001. Affirma Spectre Circuit Simulator Device Model Equations Zweidinger, D.T.; Fox, R.M., et al, “Equivalent circuit modeling of static substrate thermal coupling using VCVS representation”, Solid-State Circuits, IEEE Journal of , Volume: 2 Issue: 9 , Sept. 2002, Page(s): 1198 -1206 Jonathan S. Brodsky, “Physics based impedance models for the simulation of self-heating in semiconductor devices and circuits”, PhD Dissertation, Dept of Electrical and Computer Engineering, University of Florida, Gainesville, Aug 1997. McAndrew, C., Seitchik, J. and etal, ” VBIC95: An improved vertical, IC bipolar transistor model”, Bipolar/BiCMOS Circuits and Technology Meeting, 1995., Proceedings of the 1995 Burns and Robert, An introduction to mixed-signal testing, Oxford University Press, 1999 Copyright Texas Instruments RLCarter: Analog IC Design with Self Heating 67