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Semiconductor Device Modeling and Characterization – EE5342 Lecture 16 – Spring 2011 Professor Ronald L. Carter

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©rlc L16-07Mar20112 SPICE Diode Temp. Eqs. 1

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©rlc L16-07Mar20113 Corrections in some versions of SPICE

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©rlc L16-07Mar20114 PARAMETER definition and units default value XTI IS temperature exponent 3.0 TIKF ikf temperature coefficient (linear) °C TRS1 rs temperature coefficient (linear) °C TRS2 rs temperature coefficient (quadratic) °C TBV1 bv temperature coefficient (linear) °C TBV2 bv temperature coefficient (quadratic) °C T_ABS absolute temperature °C T_MEASURED measured temperature °C T_REL_GLOBAL relative to current temperature °C T_REL_LOCAL Relative to AKO model temperature °C SPICE Diode Temp. Pars. 1

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©rlc L16-07Mar20115 Thermal Resistance

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©rlc L16-07Mar20116 Self-Heating Effects V d,ext = Vd + Id*RS Id (A) 348K < TNOM < 300K 10 mW 20 mW 30 mW 40 mW 50 mW 60 mW 70 mW 80 mW Rth = 0 K/W, RS = 0.32 Rth = 600 K/W, RS = 1

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©rlc L16-07Mar20117 Self-Heating Effects SPICE models the IS, etc. the same for all power dissipations. The effect of diode self-heating is to increase the current at all voltages. In this case, an Rth of 600K/W gave nearly the same simulation as re- setting RS from 1 Ohm to 0.32 Ohm. The diode T j is different at all curr.

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©rlc L16-07Mar20118 PiN Diode PiN: N a >> N int (= N - ) & N int << N d W i = Intrinsic region (metall.) width E m,P-T = Peak field mag. when x n = W i V bi = i = V t ln(N a N d /n i 2 ) V bi,int = i,int = V t ln(N a N int /n i 2 ) V HL = V t ln(N d /N int ), the offset at N + N - V bi = V bi,int + V HL V PT = applied voltage when x n = W i

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©rlc L16-07Mar20119 PiN Diode Depletion Fields Normalized Position, x’ = x/Wi Normalized Field, E/E m,P-T x’ p x’ n x’ n -x’ p

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©rlc L16-07Mar PiN Diode Depletion Conditions

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©rlc L16-07Mar CV data and N(x) calculation

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©rlc L16-07Mar Diode Switching Consider the charging and discharging of a Pn diode –(N a > N d ) –W d << Lp –For t < 0, apply the Thevenin pair V F and R F, so that in steady state I F = (V F - V a )/R F, V F >> V a, so current source –For t > 0, apply V R and R R I R = (V R + V a )/R R, V R >> V a, so current source

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©rlc L16-07Mar Diode switching (cont.) + + VFVF VRVR D R RFRF Sw R: t > 0 F: t < 0 V F,V R >> V a

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©rlc L16-07Mar Diode charge for t < 0 xnxn x nc x pnpn p no

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©rlc L16-07Mar Diode charge for t >>> 0 (long times) xnxn x nc x pnpn p no

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©rlc L16-07Mar Equation summary

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©rlc L16-07Mar Snapshot for t barely > 0 xnxn x nc x pnpn p no Total charge removed, Q dis =I R t

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©rlc L16-07Mar I(t) for diode switching IDID t IFIF -I R tsts t s +t rr I R

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©rlc L16-07Mar References 1 Semiconductor Device Modeling with SPICE, 2nd ed., by Massobrio and Antognetti, McGraw Hill, NY, **OrCAD Pspice A/D Reference Guide, Copyright 1999, OrCAD, Inc. ***MicroSim OnLine Manual, MicroSim Corporation, 1996.

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