# An Improved Large Signal Model for 0.1 μm AlGaN/GaN High Electron Mobility Transistors (HEMTs) Process and Its Applications in Practical Monolithic Microwave Integrated Circuit (MMIC) Design in W band

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## Abstract

**:**

## 1. Introduction

## 2. Model Description

#### 2.1. Short Channel Effects

_{gs}refers to the gate-source voltage. V

_{pkn}(n = 1, 2, 3) are fitting parameters. P

_{n}(n = 1, 2, 3) are fitting coefficients of the ψ polynomial.

_{ds}has been included in P

_{n}(n = 1, 2, 3) to take the modulation effect of V

_{ds}into consideration, as shown in Equation (2).

_{n}

_{0}, P

_{n}

_{1}, P

_{n}

_{2}and α are all fitting parameters.

_{gs}is from −6 V to −3 V and the drain source voltage V

_{ds}is from 0 V to 20 V.

_{gs}is close to the pinch-off voltage. The DIBL effect can be successfully modeled by using proposed model.

_{ds}to V

_{ds}is not equal to zero due to channel length modulation. The channel length effect is mainly induced by expanding of the depletion region towards the source. The effective channel is then shortened. This phenomenon is shown in Figure 4.

#### 2.2. Large Signal Model up to W Band

_{gs}and C

_{gd}mentioned in [21], is employed in this work. The improvement for accurate characterization of short channel effect, which is mentioned in the previous section, has also been included in the nonlinear current model. In order to accurately characterize the self-heating effect in AlGaN/GaN HEMT. The three-pole thermal network in [25] is used. Thermal resistances as well as the thermal capacitances are extracted by a method based on FEM simulation in ANSYS. The trapping effect is modeled by the equivalent voltage method in [26]. The scalability of the model parameters, including the I

_{pk}

_{0}, R

_{th}, and C

_{th}has been realized with the method that is mentioned in [22] for practical monolithic microwave integrated circuit design. With the help of MATLAB coding, model parameters, except the coefficients in Equation (2), are all extracted with the method in [27]. In terms of parameters in Equation (2), they are all extracted by fitting the transfer characteristics curve with the least square method.

## 3. Model Validation

#### 3.1. Small Signal Characterization

_{T}of the 0.1 μm GaN process is 90 GHz, while f

_{max}is 220 GHz. The peak power density for a specific device can reach up to 3.46 W/mm. The photography of devices is shown in Figure 7.

#### 3.2. The Large Signal Model Validation

_{gs}is investigated from −6 V to 0 V, while the drain-source voltage V

_{ds}is from 0 V to 20 V for these two devices.

_{gs}= −2.6 V, V

_{ds}= 15 V, which is at deep class AB working state. The quiescent drain current is 82 mA at this bias. The optimum source and load resistance for the maximum output power are Z

_{S}= (13.44 + 12.41 × j) Ω and Z

_{L}= (27.19 + 27.44 × j) Ω. The power sweep was then performed based on the optimum resistance with the input power ranging from −4 dBm to 22 dBm. The comparison between the simulated and measured results, including output power (Pout), gain, and power added efficiency (PAE) are shown in Figure 11. Also, the influence that is brought by the DIBL effect has also been investigated in Figure 11. Results show that the DIBL effect will lead to the reduction of Pout, gain, and PAE. This can be explained by the variation of static bias point due to the DIBL effect.

## 4. W Band MMIC Power Amplifier Design

_{ds}= 15 V and V

_{gs}= −2 V.

## 5. Conclusions

## Author Contributions

## Funding

## Conflicts of Interest

## References

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**Figure 1.**Drain induced barrier lowering (DIBL) effect in Static IV curves of 0.1 μm AlGaN/GaN high electron mobility transistor (HEMT) with different gate width: (

**a**) 4 × 20 μm and (

**b**) 4 × 50 μm.

**Figure 2.**Comparison between simulated and measured results when V

_{gs}is close to pinch-off voltage.

**Figure 3.**Channel length modulation effect in Static IV curves of 0.1 μm AlGaN/GaN HEMT with different gate width: (

**a**) 4 × 20 μm and (

**b**) 4 × 50 μm.

**Figure 8.**Comparison of simulated and measured S-parameters: (

**a**) 4 × 20 μm at Vgs = −2 V, Vds = 10 V and (

**b**) 4 × 50 μm at Vgs = −1 V, Vds = 15 V.

**Figure 9.**Comparison of simulated and measured DC characteristics of 0.1 μm AlGaN/GaN HEMTs: (

**a**) 4 × 20 μm and (

**b**) 4 × 50 μm.

**Figure 12.**Comparison between simulated impedance chart and measured one: (

**a**) maximum Pout and (

**b**) maximum power added efficiency (PAE).

**Figure 14.**Photograph of a W-band Gallium Nitride (GaN) monolithic microwave integrated circuits (MMIC) amplifer.

**Figure 17.**Measured (Symbol) and simulated (solid) large-signal characteristics of the W-band MMIC PA.

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**MDPI and ACS Style**

Li, J.; Mao, S.; Xu, Y.; Zhao, X.; Wang, W.; Guo, F.; Zhang, Q.; Wu, Y.; Zhang, B.; Chen, T.;
et al. An Improved Large Signal Model for 0.1 μm AlGaN/GaN High Electron Mobility Transistors (HEMTs) Process and Its Applications in Practical Monolithic Microwave Integrated Circuit (MMIC) Design in W band. *Micromachines* **2018**, *9*, 396.
https://doi.org/10.3390/mi9080396

**AMA Style**

Li J, Mao S, Xu Y, Zhao X, Wang W, Guo F, Zhang Q, Wu Y, Zhang B, Chen T,
et al. An Improved Large Signal Model for 0.1 μm AlGaN/GaN High Electron Mobility Transistors (HEMTs) Process and Its Applications in Practical Monolithic Microwave Integrated Circuit (MMIC) Design in W band. *Micromachines*. 2018; 9(8):396.
https://doi.org/10.3390/mi9080396

**Chicago/Turabian Style**

Li, Junfeng, Shuman Mao, Yuehang Xu, Xiaodong Zhao, Weibo Wang, Fangjing Guo, Qingfeng Zhang, Yunqiu Wu, Bing Zhang, Tangsheng Chen,
and et al. 2018. "An Improved Large Signal Model for 0.1 μm AlGaN/GaN High Electron Mobility Transistors (HEMTs) Process and Its Applications in Practical Monolithic Microwave Integrated Circuit (MMIC) Design in W band" *Micromachines* 9, no. 8: 396.
https://doi.org/10.3390/mi9080396