GaN HEMT CHARACTERIZATION AND MODELLING Student name: Yang Jiang Student number: 1013631

1. INTRODUCTION The GaN HEMT has many advantages that makes it suitable for high-power, high-temperature applications. The aim of this project is to do the DC and RF characterization of the GaN HEMT by using VNA and to extract the small signal equivalent circuit model and optimized by using AWR to fit measured S-parameters 2. CHARACTERIZATION of GaN HEMT Semiconductor analyzer is used for DC measurement. Vector network analyzer (VNA) is used to measure small-signal S-parameters of GaN HEMT fabricated by PhD student from Glasgow University.

Figure.3-4 shows measured S-parameters from 0.01GHz to 65GHz under DC biases (Vds=5V, Vgs=-2V and Vds=5V, Vgs=-3V). It can be seen that there are similar plot under these DC biases. 3. MODELING of GaN HEMT The frequency range is set from 1GHz to 20GHz. The S-parameters of GaN HEMT is measured by VNA under the DC bias of Vds=5V and Vgs=-3V. As shown in Figure.7, it can be seen that there is a relatively good result for both phase response and magnitude response of S21. Even though, there is a slight difference at lower frequency. REFERENCES [1] Fan Ren and John C Zolper, Wide Energy Bandgap Electronic Devices, World Scientific Publishing (2003). [2] Teng Ma, Yue Hao, Chi Chen and Xiaohua Ma, A new small-signal model for asymmetrical AlGaN/GaN HEMTs, Journal of Semiconductors, 31, 1-5 (2010). University of Glasgow, charity number SC004401

0 1 2 3 4 5 6 7 8 9 10

0

0.05

0.1

0.15

0.2

Vds (V)

Ids

(A)

Vgs=0V

Vgs=−1V

Vgs=−2V

Vgs=−4V

Vgs=−5V

Vgs=−6V

Vgs=−7V

Vgs=−3V

Figure.2 The result of DC measurement

After DC measurement, the IV curve can be provided as shown in Figure.2. The range of Vgs is from -7V to 0V, step is 1V. It can be seen that when gate-source voltage Vgs is lower than -6V, the drain-source voltage Vds is very small and close to zero.

Figure.4 Measured S21 (phase and magnitude) by using VNA

Figure.3 Measured S11 and S22 by using VNA

As shown in Figure.6, the result for both S11 and S22 are good, which they are almost overlap the measured S11 and S22. Even through modeled S22 is slightly different to measured S22, in general, the equivalent circuit can accurately reflect S11 and S22 from real device.

Figure.7 Modeled S21 and measured S21 (phase and magnitude)

Ri (Ω)

Rds (Ω)

Cgs (pF)

Cds (pF)

Cgd (pF)

gm (mS)

τ (ns)

Cgsi (pF)

Cgdi (pF)

4.8 33.97 1.596 0.169 0.224 404.8 0.014 0.467 0.036 Cdsi (pF)

Ls (nH)

Ld (nH)

Lg (nH)

Rs (Ω)

Rd (Ω)

Rg (Ω)

Cpg (pF)

Cpd (pF)

0.003 0.045 0.016 0.104 19.9 89.4 4.15 0.154 0.121

Table.1 The components values of small signal equivalent circuit

Figure.6 Modeled S11, S22 and measured S11, S22

Figure.1 the strucure of GaN HEMT

As shown in Figure.1, there is the GaN HEMT that used for this project. It can be seen that it is a Al0.25Ga0.75N/GaN HEMT. 2DEG is the channel that current can flow between drain and source.

Figure.5 Physical basis of HEMT

As shown in Figure.5, there is the physical basis of HEMT small-signal equivalent circuit model. Both intrinsic and extrinsic components are included in this equivalent circuit. Extraction is based on this circuit and tuned to suitable components values.