1

An Introduction to Gallium Nitride (GaN) Device Characterization

Steve Dudkiewicz, Eng

Your Complete Measurement & Modeling Solutions Partner

2

-  Introduction to GaN

-  Pulsed IV Measurements

-  Introduction to Load Pull

-  Pulsed-Bias Pulsed-RF Harmonic Load Pull

-  Thermal Infrared Load Pull

Agenda

3

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

4

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

5

Pulsed Measurements – System 1

6

Pulsed Measurements – System 2

7

DC- and Pulsed-IV Measurements

8

Impedance Control

9

The slide-screw tuner approach

10

Open loop active tuner approach

11

12

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

13

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

14

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

15

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

16

Thermal IR Load Pull

Max Pout

Thot_spot=212°C

Max 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

17

VSWR 3:1 in CW mode

Pin_avail 28 dBm Pout 32.57 dBm Gt 4.57 dB Vq_out 40 V Iq_out 1.99 mA Vq_in 3.55 mA Vout 40V Iout 351 mA Eff 8.39 %

Thot_spot=284°C

Pin_avail 28 dBm Pout 38.95 dBm Gt 10.95 dB Vq_out 40 V Iq_out 6.21 mA Vq_in 3.55 mA Vout 40V Iout 362 mA Eff 49.89 %

Thot_spot=181.5°C Pin_avail 28 dBm Pout 34.48 dBm Gt 6.48 dB Vq_out 40 V Iq_out 9.06 mA Vq_in 3.55 mA Vout 40V Iout 415 mA Eff 13.06 %

Thot_spot=301°C

Thot_spot=350°C

18

VSWR 3:1 in Pulse mode

130.4°C

124.5°C

114.6°C

109.6°C 109.3°C 110°C

122.6°C

139°C

148°C

151°C

153°C

152.81°C 151°C

147.8°C 144.73°C

134.6°C