Silicon Carbide Electrical and

Thermal Modeling, Characterization

and Device/Module Fabrication

Akin Akturk, Neil Goldsman,

James McGarrity, Siddharth Potbhare

Ronald Green and Aivars Lelis

1 11/4/2014

Silicon Carbide Modeling:

Device, Module, System Simulations

2

CoolSPICE Circuit Simulator 1- SiC Power System Design

11/4/2014

Student version is available online

~1.5 months =>

~2500 total downloads (last year)

~6000 total this year

http://coolcadelectronics.com/coolspice/

2- SiC IC Design

Other Silicon Carbide Areas of Interest: Photodiodes

Power Converters

Ionizing Dose / Neutron / Heavy Ion Radiation Characterization

3 11/4/2014

Deep UV Sensors Co60, Ions, Neutrons

Converters

CoolSPICE: SiC SPICE Simulator

11/4/2014 4

Transient Simulations:

Capacitance Modeling Previously: IV DC fits / modeling : Main DC IV models have been determined, and

these models are used to fit measured data.

Currently: We are working on improving our CV models for power MOSFETs.

– Ciss, Coss and Crss capacitance models

– 0oC, 25oC, 75oC and 125oC exps

– Drain voltage up to 200V exps

5 11/4/2014

BSIM Transient / Capacitance Model

11/4/2014 6

BSIM capacitance model is based on charge conservation =>

Qg(Vd,Vg,Vs,Vb) =>

Cgd = dQg / dVd

Cgs = dQg / dVs

Cgg = dQg / dVg

Cgb = dQg / dVb

Qd(Vd,Vg,Vs,Vb) =>

Cdd = dQd / dVd

Cds = dQd / dVs

Cdg = dQd / dVg

Cdb = dQd / dVb

Qs(Vd,Vg,Vs,Vb) =>

Csd = dQs / dVd

Css = dQs / dVs

Csg = dQs / dVg

Csb = dQs / dVb

Qb(Vd,Vg,Vs,Vb) =>

Cbd = dQb / dVd

Cbs = dQb / dVs

Cbg = dQb / dVg

Cbb = dQb / dVb

Qg(Vd,Vg,Vs,Vb) + Qd(Vd,Vg,Vs,Vb) + Qs(Vd,Vg,Vs,Vb) + Qb(Vd,Vg,Vs,Vb) = 0

BSIM Transient / Capacitance Model

11/4/2014 7

http://en.wikipedia.org/wiki/Power_MOSFET

Standard Methods to Model Power

MOSFET Capacitances - 1

11/4/2014 8

1 – Wheatley Model : Uses voltage controlled switches to change terminal caps

Similar to behavioral cap models.

Pro: Can be run by any SPICE engine.

Con: Switches may lead to numerical instability.

Standard Methods to Model Power

MOSFET Capacitances - 1

11/4/2014 9

.options trtol=1 chgtol=1e-16 abstol=1e-6

SPICE does not converge without relaxed

convergence criteria.

Standard Methods to Model Power

MOSFET Capacitances - 2

11/4/2014 10

2 – Franz / Scott Model : Uses PMOSCAP to model CGD

SiC Power MOSFET SPICE Model

11/4/2014 11

X

X

X

1- Remove CDX terms from BSIM while preserving charge neutrality.

3- Optional: Use small correction term for CGS

2- Use behavioral cap for CGD – If

necessary, can modify BSIM to incorporate

this as part of the model -

SiC Power MOSFET SPICE Model

11/4/2014 12

Coupled-Thermal-Electrical Simulation

11/4/2014 13

Previously: DC / steady state electrical-thermal analysis for single power device.

Currently:

1- DC / steady state electrical-thermal analysis for multiple power devices.

2- Framework for transient electrical-thermal simulations is being developed.

Coupled-Thermal-Electrical Simulation

11/4/2014 14

1- Fabricated module / Design 2- 3D CAD drawing 3- Define bodies and boundaries

4- Thermal mesh generation 5- Solving for heatflow and possibly flow equations

Coupled-Thermal-Electrical Simulation

11/4/2014 15

CoolSPICE provides:

SPICE load line: P = As × ΔT + Bs

Thermal simulator provides:

Thermal load line: ΔT = At × P

In a linear world !, the self-consistent temperatures are:

P = As × At × P + Bs

[ I - As × At ] × P = Bs

ΔT = At × P

Example: Thermal-Electrical Simulation

11/4/2014 16

MN3 N2b N4 0 0 CMF10120

RBrcN3 N2b N2 0.08 myres dtemp=0

MN1 N2c N4 0 0 CMF10120

RBrcN1 N2c N22 0.08 myres dtemp=0

MN2 N2a N4 N22 N22 CMF10120

RBrcN2 N2a N2 0.08 myres dtemp=0

- The drain-to-source currents of MN1, MN2 and MN3 are 0.64, 0.64 and 1.49A, respectively,

when we consider self-heating.

- In the case of no self-heating the drain-to-source currents of MN1, MN2 and MN3 are 0.57, 0.57

and 1.29A, respectively.

- Even in the case of lower biases quoted here, the error in current and power is as much as 15%.

Coupled Electrical-Thermal Transients

11/4/2014 17

What is the power input for the

thermal simulator?

Coupled Electrical-Thermal Transients

11/4/2014 18

1- Instantaneous power, Pi, is calculated.

2- Energy consumed for the last D time is

calculated: Pi is integrated over the current

time t to t-D

Implemented pointer tree in CoolSPICE

to keep track of averages.

3- Energy is averaged over time.

Many time steps are computed for the electrical analysis.

Thermal transients are slower, and therefore tracked

using larger time steps.

SiC IC Development

11/4/2014 19

1- Overview of CoolSPICE Development

for SiC IC Applications

This is in collaboration with Auburn Univ. and USCi. 20 11/4/2014

Type Size (Width [m]/Length [m])

LARGE 400/400

SMALL 5/5

SHORT 400/5

NARROW 5/400

L-Scaled 400/10, 400/20, 400/100, 400/200

W-Scaled 10/400, 20/400, 100/400, 200/400

LW-Scaled

10/5, 20/5, 100/5, 200/5, 5/10, 10/10, 20/10, 100/10, 200/10, 5/20, 10/20, 20/20, 100/20, 200/20, 5/100, 10/100, 20/100, 100/100, 200/100, 5/200, 10/200, 20/200, 100/200, 200/200

Layout and parameter extraction for SiC IC components.

~250C probe

CoolSPICE Development for SiC IC

Applications

This is in collaboration with Auburn Univ. and USCi. 21 11/4/2014

5/5

10/5

400/400

Room Temp

CoolSPICE Development for SiC IC

Applications

This is in collaboration with Auburn Univ. and USCi. 22 11/4/2014

20/5

10/5

400/5

200C

CoolSPICE Development for SiC IC

Applications

This is in collaboration with Auburn Univ. and USCi. 23 11/4/2014

High temperature nmos-

only op-amp design.

Terrestrial Neutron Induced Failure

in Silicon Carbide Power MOSFETs

11/4/2014 24

CoolCAD Electronics and Prairie View A&M Univ.

Presented at 2014 Nuclear and Space Radiation Effects Conference (NSREC):

“Terrestrial Neutron Induced Failure in Silicon Carbide Power MOSFETs”

Richard T. Wilkins, Kazi Rashed, Ramesh Dwivedi, Brad Gersey, Prairie View A&M

University; Akin Akturk, CoolCAD Electronics LLC

Brief Explanation of Neutron Effects

in SiC Power MOSFETs

11/4/2014 25

Earth Radii

Trapped Proton Belt

4

ABB report on “Failure Rates of HiPak Modules Due to Cosmic Rays”

Low energy neutron flux as a function of altitude.

High energy neutron flux as a function of altitude.

High Energy Neutrons Create High Energy

Knock-On Atoms in SiC Devices

11/4/2014 26

Knock-on atoms in SiC due to

atmospheric neutrons

Los Alamos Neutron Experiments

11/4/2014 27

Atmospheric neutron spectrum at Los Alamos.

SiC CMF10120D Failure Cross Sections

11/4/2014 28

< Pre and post

IV curves of a

“surviving”

MOSFET biased

at 1000V during

irradiation.

< Example IDS-VGS curve

of a failed SiC device.

Similar cross sections

were measured for silicon

carbide diodes as well!

SiC CMF10120D Failure Predictions

11/4/2014 29

Failures / Year = N x λ x σ x t x d [fail/yr]

where

N = # devices in application

λ = neutron flux at location [n/cm2/hr]

σ = failure cross section at Vds [cm2/n/fail]

t = operating hours per year [hr/yr]

d = duty cycle [hr/hr]

Army:

100 devices/veh x 20 n/cm2/hr x 5 x 10-8 @ 1200V x 400

hr/yr x 0.5 = 2 x 10-2 / yr

=> 1 Failure / 50 yrs per vehicle

(x thousands of vehicles ?)

Wind turbine (low altitude):

50 devices/turbine x 20 n/cm2/ hr x 5 x 10-8 @ 1200V x 9000

hr/yr x 0.5 = 2.25 x 10-1 / yr

=> 2 Failures / 10 yrs per wind turbine

(100s of turbines ?)

Air Force:

100 devices/aircraft x 6000 n/cm2/hr x 5 x 10-8 @ 1200V x

1000 hr/yr x 0.5 = 15

=> 15 Failures /1 yr per aircraft

(100s of aircraft ?)