# GaN-on-Si: Monolithically Integrated All-GaN Drivers for High-Voltage DC-DC Power Conversion
## 1 Introduction  
Gallium nitride (GaN) is considered the most promising semiconductor technology for high frequency and high power applications [1; 2; 3; 4; 5]. The unique properties of GaN materials with high breakdown electric field (4 MV/cm), large band gap (3.4 eV), and low parasitics enable the fabrication of higher speed and larger voltage swing devices, which are a great advantage for designing power converters. For example, most buck converters use a half-bridge topology due to their simple and practical design structure. Many commercial DC-DC converters use silicon (Si) power devices as switching elements, but the switching frequency is limited to a few hundred kilohertz [6; 7; 8; 9; 10]. As the switching frequency increases, the losses associated with the output capacitance of the Si device increase and reduce efficiency. On the other hand, the demand to reduce the size of the overall converter system, especially the miniaturization of passive components, requires the system to operate at higher switching frequencies. The use of fully integrated GaN power transistors and their drivers greatly addresses this challenge. In addition to exploiting the low parasitics of GaN to enable high-speed switching and improve the response speed of the system, the increase in power density has resulted in a more reliable solution compared to traditional silicon-based or other compound semiconductors [11; 12; 13]. In much of the past work, silicon-based drivers for high-speed GaN power transistors were widely designedto implement high-speed and high-voltage power converters [14; 15; 16; 17; 18]. Since GaN devices and drivers are based on different processing technologies, packaging becomes a challenge. Each type of package will have leads that introduce parasitic inductance. These parasitics can cause switching losses, ringing, and reliability issues when power transistors are switched at high slew-rates of tens to hundreds of volts per nanosecond. Specially treated package types can also limit the switching performance of GaN FETs [17; 18]. However, integrating GaN power transistors and drivers for a half bridge in a single chip still poses many difficulties [19]. One of the main challenges is the implementation of high-side gate drivers. The high-side gate driver must turn on and off efficiently when its source switches at the full input voltage swing. Furthermore, short propagation delays and good matching are necessary for half-bridge operation at high frequencies to control gate slew rate, limit overshoot voltage and shoot-through current of power transistors. Meeting these conditions enables a high-performance integrated driver with electromagnetic interference (EMI) compliance. Various integrated gate driver designs have been reported in the literature. Normally-off or E-mode power transistors are preferred power stages for power converter applications as they provide a safe startup mode to reduce energy consumption in the driver stage. However, the design of integrated drivers using only E-mode transistors is challenging. Since there are no mature complementary devices in the existing GaN process, E-mode transistors must be designed in conjunction with on-chip resistors or diodes, which not only increases the area but also has greater uncertainty in the design results. Currently, the design of combined D-mode and E-mode GaN devices has, therefore, become a common solution [20; 21; 22]. However, while combining these two devices in the driver stage, one must pay special attention to leakage and overdrive design issues to ensure robust and efficient operation of high-voltage GaN power switches. A high switching frequency of 10 MHz and high-efficiency integrated drivers have been demonstrated for D-mode power switches [23]. Integrated E-mode gate drivers with GaN-HEMTs for MHz switching operation on more expensive GaN-on-SOI substrates have been validated for low-side drivers [24; 25; 26]. For the GaN-on-Si process, there are currently no economical integrated high-side drivers for DC-DC converter applications.