Case studies

July 2020

Step change thermal management of RF devices using CVD diamond

2

Simple introduction – a stack of thermal resistors

• Heat spreader reduces peak device temperature by reducing heat flux density

• In an RF circuit there are two components with high power density:• Thermal management of active device: CVD diamond heat spreader for high power amplifiers (HEMPTs)• Thermal management of passive device: CVD diamond substrate for high power RF resistor

Device

CVD diamondheatspreader

Heat sink

Primary and secondary interfaces

3

CASE 1: Novel metallization scheme (Cr) compared with conventional (Ti-Pt) reduce Tj of PA by 25%

Tj of “Big” Device (High Power Amplifier) Tj of “Small” DeviceTi-Pt

Cr

Ti-Pt

Cr

• A new metallization scheme (Cr) has improved the thermal conductivity of the die-diamond attach by 3-4X – compared to using Ti-Pt.

• With Cr, channel temperature drops 25% (for big devices e.g. high-power PAs), and 13% (for small devices) compared to using Ti-Pt.

4

CASE 2 - CVD diamond for an RF (GaAs) package

Need to replace BeO for a combination of toxicity and thermal performance issues

28.147 30.072 31.998 33.924 35.849 37.775 39.701 41.627 43.552 45.478

CuMo flange

Heat spreader

5

CASE 2 - CVD diamond for an RF (GaAs) package

Thermal resistance of RF package

50%

60%

70%

80%

90%

100%

BeO 1mm BeO 0.3mm TM100 0.3mm TM180 0.3mm

Rel

ativ

e th

erm

al re

sist

ance

Significant thermal resistance reduction in moving todiamond heat spreader

Chart1

BeO 1mm

BeO 0.3mm

TM100 0.3mm

TM180 0.3mm

Relative thermal resistance

Thermal resistance of RF package

1

0.9476472037

0.7009320851

0.6322712217

Data

w_hsprTmaxRthSPartHeightConductivityTmaxRth

10046.6640.24562358280[mm][mil][W/m/K]250.2095013605

12045.47270.232116781.651Base1.6516517835.860.123132539759%

14044.60290.2222551021.654048Solder 20.0030480.122536.050.00214886621%

16043.96380.21500907031.659128Metal 30.005080.230836.080.00029115650%

18043.4780.20950113381.958848Heat spreader0.2997211.8180036.630.0063116783%

1.963928Metal 20.005080.230836.720.00099829930%

h_hsprTmaxRth1.966976Solder 10.0030480.128336.920.0022308391%

0.2543.8840.21410430841.977136Metal10.010160.43438.520.01816224499%

0.29943.4780.20950113382.104136Die0.127515043.230.053439569226%

0.3543.17020.20601133792.116836Source0.01270.515043.480.00278616781%

0.442.93450.2033390023

Heat spreader materialHeight [mm]Rth [K/W]Relative to BeO

BeO 1mm10.331100%Base cas 078_0

BeO 0.3mm0.2990.31495%ST_Z

TM100 0.3mm0.2990.23270%0.025.00

TM180 0.3mm0.2990.21063%0.225.95

0.326.91

0.527.88

0.728.87

0.829.90

1.030.96

1.232.07

1.333.24

1.534.52

1.736.05

1.736.10

1.736.14

1.736.18

1.836.22

1.836.28

1.836.34

1.936.41

1.936.48

1.936.57

2.036.92

2.038.18

2.038.73

2.039.01

2.039.30

2.039.59

2.039.88

2.040.18

2.040.47

2.040.77

2.041.06

2.141.28

2.141.49

2.141.70

2.141.92

2.142.14

2.142.35

2.142.57

2.142.79

2.143.01

2.143.23

2.143.28

2.143.32

2.143.36

2.143.39

2.143.42

2.143.44

2.143.46

2.143.47

2.143.48

2.143.48

6

CASE 2 - CVD diamond for an RF package

28.147 30.072 31.998 33.924 35.849 37.775 39.701 41.627 43.552 45.478

Result: Significant temperature drop from junction to base using diamond heat spreader

CuMo flange

Diamond heat

spreader

RF device

Rth reduced by 30% - giving improved reliability and device linearity

HSBeO heat spreader

7

CASE 3 – Continuous wave 160W 2 GHz InAlN/GaN

SiC with diamond heat spreader SiC - no diamond heat spreader

Assembly A(SiC =100 µm – Ti:Pt:Au: TM180: Ti:Pt:Au: Cu Sink )

Assembly B(SiC =400 µm – no heat spreader)

Max. temp. Measured at the top of the GaN die 173°C

Max. temp. Measured at the top of the GaN die 214°C

• SiC thinned with an E6 diamond metallized heat spreader • 41°C reduction in device surface temperature

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CASE 4 - RF thin film resistors

• At microwave frequencies resistors deviate from ideal behaviour due to parasitic capacitance and inductance → signal distortion

• Capacitive reactance usually dominates → minimise by reducing area of resistor• High dissipated power leads to high temperature → minimise by increasing area of resistor

High power RF applications also require passive components able to handle high power densities e.g. thin-film resistors

Ideal resistor Resistor at RF

9

CASE 4 - RF resistors – substrate materials

• Low permittivity desirable to minimise parasitic capacitances

• High thermal conductivity desirable for power handling

• Diamond has best combination of both• Objective: model performance of TiN thin

film RF resistors on AlN, BeO and CVD diamond substrates

• What power and frequency can be achieved consistent with• Peak temperature < 125 °C• Low distortion (VSWR

10

CASE 4 - RF resistors high power and frequency performance

• Frequency of operation before parasitic effects become significant:• 2.9 GHz on AlN (S-band)• 4.3 GHz on BeO (C-band)• 12 – 27 GHz on diamond (Ku to K band)

• Results for 50 Ω thin film resistor• For 100 W dissipated RF power, resistor

parasitic capacitance is• 0.9 pF on AlN substrate• 0.6 pF on BeO substrate• 0.1 - 0.2 pF on diamond substrate

depending on thermal grade used

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CASE 5 - CVD diamond handles a record 10KW/cm2using microfluidics

Diamond & microfluidics enables

• 10KW/cm2 power density handling &

• 75C Drop in Max Hotspot

Chips withHotspots

Diamond Heat Spreaders

12

Summary

• CVD diamond heat spreaders provide superior thermal management for high power RF applications

• Thermal conductivity can be engineered to suite the application• Need to consider the system as a whole for maximum benefits

• For active devices CVD diamond heat spreaders enable:• Higher power operation for a given maximum operating temperature• Reduced peak temperatures (~25%) for a given power

• RF resistors using CVD diamond substrates can operate at higher frequencies and powers before parasitic effects lead to signal distortion

• >100w & > 10 GHz

Contact us to find out moreE ustechnologies@e6.comT +1 408 986 2400W e6.com

Case studiesSimple introduction – a stack of thermal resistorsCASE 1: Novel metallization scheme (Cr) compared with conventional (Ti-Pt) reduce Tj of PA by 25%CASE 2 - CVD diamond for an RF (GaAs) packageCASE 2 - CVD diamond for an RF (GaAs) packageCASE 2 - CVD diamond for an RF packageCASE 3 – Continuous wave 160W 2 GHz InAlN/GaNCASE 4 - RF thin film resistorsCASE 4 - RF resistors – substrate materialsCASE 4 - RF resistors high power and frequency performanceCASE 5 - CVD diamond handles a record 10KW/cm2 �using microfluidicsSummaryContact us to find out more