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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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DC- and Pulsed-IV Measurements
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Impedance Control
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The slide-screw tuner approach
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Open loop active tuner approach
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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
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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°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
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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
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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