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An Introduction to Gallium Nitride (GaN) Device Characterization

Steve Dudkiewicz, Eng

Your Complete Measurement & Modeling Solutions Partner

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- Introduction to GaN

- Pulsed IV Measurements

- Introduction to Load Pull

- Pulsed-Bias Pulsed-RF Harmonic Load Pull

- Thermal Infrared Load Pull

Agenda

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Viable enabling technology for high power amplifiers: -material maturity-yield improvement-expansion to 4” wafers-and inclusion of lower cost substrates

GaN offers several advantages over other technologies:-higher operating voltage (over 100V breakdown)-higher operating temperature (over 150oC channel temperature)-higher power density (5-30W/mm)

GaN Technology

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Problems associated with GaN:-the large output power capability → heat dissipation-trapping-self-heating-electrical performance degradation over time (threshold voltage, gate leakage current)

Partial solution:-Pulsing bias minimizes self-heating-Choosing proper quiescent voltage minimizes trapping

GaN Technology

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Pulsed Measurements – System 1

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Pulsed Measurements – System 2

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0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0 5 10 15 20 25 30Drain Voltage (V)

Dra

in C

urr

ent

(A)

Non Pulsed IV Curves (for various Vg) Pulsed IV Curves (for various Vg)

DC- and Pulsed-IV Measurements

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Impedance Control

,,

,

( )( )

( )x n n

x n nx n n

a ff

b f

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Y

X

Airline

X YProbe

Airline

Probe

The slide-screw tuner approach

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Open loop active tuner approachb2

a2

2

2L

a

b

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x = source (s) or load (l) n = frequency band, e.g. baseband (0), fundamental (1) and harmonic (2 and up) = user defined reflection coefficient vs. frequency

The wideband open loop active load-pull approach

, , ,( ) ( ) ( )x n n x n n x n na f b f f , ( )x n nf

,,

,

( )( )

( )x n n

x n nx n n

a ff

b f

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Many higher-power GaN devices have source impedances around or below 1-5Ω because of their large peripheries

Pulsed Source/Load Pull

Load impedances are higher than source impedances, in the range of 3-15Ω

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The following is an example of a 10W-linear power GaN device operating under compression at 25W where the fundamental impedance was kept constant at ZFo= 3Ω and the second harmonic impedance Z2Fo was swept across the entire Smith Chart. A variation of ~25% drain efficiency was observed while tuning 2Fo

PAE=60%

PAE=35%

Harmonic Load Pull

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Maury’s solution makes use of the triggering that is native to the pulsed-IV controller to trigger both the signal generator and power meter for accurate

and reliable results.

Pulsed Considerations

1) Bias Tees

2) Power Meter Average VS Peak

3) Triggering

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Thermal IR Load Pull

Max Pout

Thot_spot=212°CMax PAE

Thot_spot=188.25°C

- Compromise between Pout and PAE, using Temp to decide

- Effect of poor match on temperature

- Operating temperature in real-life conditions due to poor match

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VSWR 3:1 in CW mode

Pin_avail 28 dBmPout 32.57 dBmGt 4.57 dBVq_out 40 VIq_out 1.99 mAVq_in 3.55 mAVout 40VIout 351 mAEff 8.39 %

Thot_spot=284°C

Pin_avail 28 dBmPout 38.95 dBmGt 10.95 dBVq_out 40 VIq_out 6.21 mAVq_in 3.55 mAVout 40VIout 362 mAEff 49.89 %

Thot_spot=181.5°CPin_avail 28 dBmPout 34.48 dBmGt 6.48 dBVq_out 40 VIq_out 9.06 mAVq_in 3.55 mAVout 40VIout 415 mAEff 13.06 %

Thot_spot=301°C

Thot_spot=350°C

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VSWR 3:1 in Pulse mode

130.4°C

124.5°C

114.6°C

109.6°C109.3°C110°C

122.6°C

139°C

148°C

151°C

153°C

152.81°C151°C

147.8°C144.73°C

134.6°C