GaN Power Integration for High Frequency and High Efficiency Power Applications: A Review <s> B. CO-INTEGRATION OF GAN HEMTS FOR MMIC AND POWER SWITCHING <s> In this letter, we discuss a novel asymmetric field plate structure utilizing a slanted field plate (FP) engineered to appropriately distribute the electric field on GaN high-electron mobility transistors (HEMTs) scaled for low-loss, high-speed power switch applications. A uniform electric field distribution achieved with the slant FP enables an optimum device design, where a low-dynamic ON-resistance ( $\text{R}_{\textsf {on,dyn}}$ ) and high breakdown voltage are obtained simultaneously by minimizing the gate-drain distance. The optimized FP design demonstrated a low $\text{R}_{\textsf {on,dyn}}$ of 2.3 (2.1) $\Omega $ -mm at a quiescent drain voltage of 50V in $\mathsf {E}$ -mode ( $\mathsf {D}$ -mode) HEMTs with a breakdown voltage of 138 V (146 V). The corresponding high-frequency performance of E-mode (D-mode) HEMTs of peak $\text{f}_{\textsf {T}}/\text{f}_{\textsf {max}}= 41$ /100 GHz (53/100 GHz) yielded a decent $\text{R}_{\textsf {on,dyn}} \times \text{Q}_{\textsf {g}}$ product in the range of 31.0–34.5 (28.0–33.3) $\text{m}\Omega \vphantom {^{\int }}$ -nC. This new slant FP technology combined with scaled epitaxial structure (for short $\textsf {L}_{\textsf {g}}$ ) and reduced access resistances, using n+ GaN ohmic contacts, greatly enhances performance and design flexibility of high-speed, low-loss, GaN power switch devices. <s> BIB001 </s> GaN Power Integration for High Frequency and High Efficiency Power Applications: A Review <s> B. CO-INTEGRATION OF GAN HEMTS FOR MMIC AND POWER SWITCHING <s> Abstract In this paper, an innovative air-bridge recessed source field plate is implemented into the fabrication of high voltage mm-wave GaN high-electron-mobility transistors (HEMTs). The device integrates a metal field plate (FP) and an air-bridge FP that locate over the gate region and land between the gate and drain. The reduced peak electric field contributes to a three-terminal breakdown voltage of 144V for GaN HEMTs with L SD =2.4 μ m, which is 96V for the normal mm-wave device. One order of magnitude lower in off-state leakage currents and well suppressed current collapse are also achieved. Particularly, slight increase in C gs and C gd was obtained after applying the air-bridge field plate, keeping the high frequency characteristic of mm-wave devices. The technology might attract significant attention in mm-wave GaN HEMTs. <s> BIB002
Monolithic co-integration of the optimal GaN HEMTs for MMIC and power switching can be the promising solution of multi-function GaN ICs. In GaN devices, the drain-side access region with length of L GD bears most breakdown voltage (BV). The L GD of the power devices is relatively large to obtain a high breakdown voltage; however, the GaN HEMTs for MMIC have very high channel carrier concentration and shorter L GD (typically less than 1 µm) to improve operation frequency with the sacrifice of BV. In order to realize the trade-off between high frequency and high breakdown voltage in the co-integration, specially designed and optimized field plates (FPs) can be introduced as one of the possible solutions. The FPs connected with source and gate can modulate the distribution of surface electric field and alleviate the high electric filed at gate corner in drain side, which contributes to higher BV. The reported FP types in GaN HEMTs are summarized in Fig. 3 . Other than the conventional source FP and gate FP, novel FP structures have been developed. Table 1 listed the reported characteristics of GaN HEMTs with several FP types. The FP techniques can offer efficient solutions to improve BV of GaN HEMTs. Although adding FPs could improve BV, it brings additional parasitic capacitance which limits the operation frequency of GaN HMETs. Especially for the co-integration of GaN HEMTs for MMIC and power switching, it is essential to realize high BV without increasing parasitic capacitance. As shown in Fig. 4 (a) and (b), the recessed foot of FP reduce the distance between FP and 2DEG and the SiN dielectric is replaced by air-bridge with lower dielectric constant BIB002 , which all contributing to less increase in gate capacitance. The slant FP structure in Fig. 4 (c) can provide smoother electric field distribution without significant increase in gate capacitance BIB001 . As for commercial GaN HEMTs, Fig. 5 shows the cross-sectional SEM images of EPC 2045, Panasonic-PGA26E19BA and GaN Systems GS61004B GaN transistors, where the source and discrete FPs are adopted. The possible reason can be intention of limiting the introduction of additional gate capacitance and leaving gate intact for reliability concern in commercial GaN HEMTs. With the help of field plates, the GaN HEMTs for MMIC can have BV up to hundreds of volt with acceptable high frequency operation capability. The optimal GaN HEMTs for MMIC and power switching can probably be co-integrated.