GaN Power Integration for High Frequency and High Efficiency Power Applications: A Review <s> V. GAN POWER INTEGRATION ROAD AHEAD <s> SUMMARY Gallium nitride high electron mobility transistors (GaN HEMTs) were developed for millimeter-wave high power amplifier applications. The device with a gate length of 80 nm and an InAlN barrier layer exhibited high drain current of more than 1.2 A/ mm and high breakdown voltage of 73V. A cut-off frequency fT of 113GHz and maximum oscillation frequency fmax of 230GHz were achieved. The output power density reached 1 W/ mm with a linear gain of 6.4dB at load-pull measurements at 90GHz. And we extracted equivalent circuit model parameters of the millimeter-wave InAlN/ GaN HEMT and showed that the model was useful in simulating the millimeter-wave power performance. Also, we report a preliminary constant bias stress test result. <s> BIB001 </s> GaN Power Integration for High Frequency and High Efficiency Power Applications: A Review <s> V. GAN POWER INTEGRATION ROAD AHEAD <s> This paper presents a 40-MHz hybrid CMOS/GaN integrated multiphase dc–dc switched-inductor buck converter with a maximum 20-V input voltage. The half-bridge switches are realized using lateral AlGaN/GaN HEMTs, while the drivers and other circuitry are implemented in standard 180-nm CMOS. The interface between the CMOS and GaN dice is achieved through face-to-face bonding, reducing inductive parasitics for the connection to less than 15 pH. A capacitively coupled level shifter provides the gate drive for the high-side GaN switch using 5-V CMOS devices. The converter demonstrates 76% efficiency for 8:1 V conversion and over 60% efficiency for conversion ratios up to 16:1. <s> BIB002 </s> GaN Power Integration for High Frequency and High Efficiency Power Applications: A Review <s> V. GAN POWER INTEGRATION ROAD AHEAD <s> This letter presents a novel technology for the integration of gallium nitride (GaN) power devices with silicon control circuits. It comprises stacked GaN power transistors and bipolar-CMOS-double-diffused metal-oxide-semiconductor (DMOS) (BCD) circuits. It leverages on both advantages of the high-voltage low-loss GaN devices and the high-integration BCD circuits. Using conventional manufacturing, packaging, and assembly techniques and equipment, the proposed technology is technology transferrable and applicable for commercial power electronic applications. To validate the concept, a 3.3–70 V dc–dc boost converter is designed, implemented, and verified experimentally. It features a conversion efficiency of 70.3%, output power of 1.68 W, and compact size of ${\text{0.32}}\times {\text{0.18}}\,{\text{cm}}^{2}$ . <s> BIB003 </s> GaN Power Integration for High Frequency and High Efficiency Power Applications: A Review <s> V. GAN POWER INTEGRATION ROAD AHEAD <s> Light-emitting diodes (LEDs) are solid-state devices that are highly energy efficient, fast switching, have a small form factor, and can emit a specific wavelength of light. The ability to precisely control the wavelength of light emitted with the fabrication process enables LEDs to not only provide illumination, but also find applications in biology and life science research. To enable the new generation of LED devices, methods to improve the energy efficiency for possible battery operation and integration level for miniaturized lighting devices should be explored. This paper presents the first case of the heterogeneous integration of gallium nitride (GaN) power devices, both GaN LED and GaN transistor, with bipolar CMOS DMOS (BCD) circuits that can achieve this. To validate this concept, an LED driver was designed, implemented and verified experimentally. It features an output electrical power of 1.36 W and compact size of 2.4 × 4.4 mm2. The designed fully integrated LED lighting device emits visible light at a wavelength of approximately 454 nm and can therefore be adopted for biology research and life science applications. <s> BIB004
GaN integration can take the power conversion to where silicon power cannot go  . More technologies in Si electronics have been applied on the GaN integration. The dedicated Si CMOS gate drivers can be packaged in the same case or directly bonded with GaN in 3-dimension. The heterogeneous integration of GaN and Bipolar-CMOS-DMOS (BCD) has been shown by GLOBALFOUNDRIES ''GaN2BCD'' technology in BIB003 , BIB004 . The driver circuits can be dedicatedly designed and fabricated in BCD process, and then integrated with GaN power devices using the die-towafer transfer (D2W) as shown in the schematic in Fig. 19 . Another novel approach is the CMOS gate driver flip-chip assembled with GaN devices together on the IPD substrate, which minimizes the parasitic effects caused by bonding wires BIB001 . The PCB embedded inductor is also a solution to low parasitic IPDs  . Die bonding between CMOS and GaN ICs to form the integrated converter is one of the solutions provided by BIB002 . The half-bridge switches are AlGaN/GaN HEMTs, while the drivers and other functional circuits are implemented in a 0.18 µm CMOS platform. The GaN and CMOS dies are faceto-face bonded to reduce inductive parasitics. Fig. 20 shows the optical images of silicon die (top), GaN die (middle), and the face-to-face bonding illustration (bottom). The converter demonstrates the 8-to-1 V, 40 MHz and 76 % efficiency opeartion BIB002 . The integration on Direct Bonded Copper (DBC) has the GaN power device bonded and other components soldered in the way as shown in Fig. 21 by Fraunhofer IAF in 2019  . A prototype 200-to-100 V, 500 kHz, 100 W, 97% efficiency converter is designed and characterized. More approaches are being proposed. However, the GaN integration firstly should be established on a stable platform with well calibrated and modelled active and passive components. So the performance of the GaN power ICs can be reliably predicted. The technology of discrete GaN devices is improving fast and the GaN power integration should be updated simultaneously. In order to exploit the most of theoretical GaN performance, GaN power integration road follows the path of Si power IC, but on a fast lane.