GaN Power Integration for High Frequency and High Efficiency Power Applications: A Review <s> 2) NORMALLY-OFF HEMT TECHNOLOGY <s> In this paper, we present a state-of-the-art integrated GaN power IC capable of operating in a high frequency (MHz) regime. This realizes system size reduction, 60% maximum, of a power IC. The IC consists of two output power transistors (PT) and two gate drivers (GD). The key devices in the IC are normally-off gate injection transistors (GITs) for PT and GD and a normally-on hetero-junction field effect transistor (HFET) for GD. Novel local control of carrier concentration of an identical 2 dimensional electron gas (2DEG) at an AlGaN/GaN interface which made integration of the transistors with such a large threshold voltage difference possible is described. A specially developed post-passivation interconnection process giving low parasitic components is also described. The IC applied to a 12V–1.8V DC-DC converter shows high frequency switching operation well beyond the limit of Si pointing to future improvement in consumer electronics power supply systems. <s> BIB001 </s> GaN Power Integration for High Frequency and High Efficiency Power Applications: A Review <s> 2) NORMALLY-OFF HEMT TECHNOLOGY <s> This paper presents switching operation of a monolithically integrated half-bridge stage in a 600 V-class GaN-on-Si technology. The integrated power chip includes two high performance GaN-HEMTs with integrated freewheeling Schottky diodes, on a total chip area of 4×4 mm2. Operation of the half-bridge chip is demonstrated in a soft-switching buck converter at switching frequencies up to 3 MHz, input voltages up to 400 V, and output power up to 250 W. <s> BIB002 </s> GaN Power Integration for High Frequency and High Efficiency Power Applications: A Review <s> 2) NORMALLY-OFF HEMT TECHNOLOGY <s> This study presents monolithically integrated power circuits, fabricated in a high-voltage GaN-on-Si heterojunction technology. Different advanced concepts are presented and compared with solutions found in the literature. High switching transition slew rates are demonstrated by means of a monolithic power circuit with integrated gate driver. A highly linear temperature sensor is integrated in a GaN-high-electron-mobility transistor (HEMT) power device for the 600 V class and on-state resistance of 53 mΩ. An area-efficient HEMT structure with integrated freewheeling diodes is presented. This structure is applied in a monolithic multilevel converter chip, as well as in a 600 V class half-bridge chip. The multilevel chip is integrated by an advanced printed circuit board embedding technology and tested in inverter operation with a mains voltage output of 120 V ::: RMS ::: . The performance of the half-bridge is demonstrated in a synchronous buck converter operation from 400 to 200 V and with a switching frequency of 3 MHz. <s> BIB003
The conventional normally-OFF technologies which are feasible for device integration have been discussed in Fig. 13 . The normally-OFF devices provide fault-safe operation and ease the design of gate driver. Additionally the gate dielectric can be included in devices to form MIS-HEMTs, which can reduce the gate leakage and enlarge the gate voltage swing. Table 4 lists the publications with integrated converters using normally-OFF technologies. Normally-OFF technology is promising to assist GaN integrated converters to work at MHz range with efficiency up to nighty percent. The output power at current stage is less than VOLUME 8, 2020 DC-DC converters with discrete GaN power switches, which could be due to the limited total gate width of integrated power stages. Larger power stages are integrated on 200-mm GaN IC platforms now. Ujita et al. has designed a fully integrated GaN-based power IC including gate drivers for highefficiency DC-DC conversion BIB001 . The 12-1.8 V DC-DC converter IC demonstrates a maximum 3 MHz frequency, which is far beyond the limit of Si and can reduce 60% of system volume. Fraunhofer IAF has realized an integrated half-bridge converter as shown in Fig. 18 , which can be switched at 3 MHz with a input/output of 400/200 V, and a current 1.15 A BIB003 , BIB002 . In the aspects of GaN integration in companies, Navitas and Dialog have lunched the GaN power IC products. Both of these two companies cooperated with TSMC on the practical fabrication. The high-frequency operation of GaN based circuit induces excessive parasitic from wire bonding, which has been reduced by TSMC's integration of peripheral circuits with low-voltage devices into CMOS-compatible 100/650 V enhancement GaN device platform. Functional blocks including control, clock, pre-gate driver, ESD protection circuits have been demonstrated using 12 V E/D-HEMTs, rectifiers. 2DEG resistors and capacitors  . Now Navitas' NV6115 can offer high-efficiency 650 V, 160 m power switches with integrated gate drive and logic circuits, which can enable high switching speed, power efficiency and power density. Dialog's DA8801 can offer a half bridge of 650 V, 500 m power switches with integrated analog, logic, and protection.