GaN-based Semiconductor Devices for Future Power Switching Systems Hidetoshi Ishida, Ryo Kajitani, Yusuke Kinoshita, Hidekazu Umeda, Shinji Ujita, Masahiro Ogawa, Kenichiro Tanaka, Tatsuo Morita, Satoshi Tamura, Masahiro Ishida and Tetsuzo Ueda Panasonic Corporation 3-1-1 Yagumo-nakamachi Moriguchi-shi, Osaka 570-8501, Japan email: ishida.hi@jp.panasonic.com Abstract— GaN-based natural superjunction diodes and Gate Injection Transistors (GITs) with p-type gate on AlGaN/GaN hetero structure are promising power devices with lower on- state resistance and higher breakdown voltage for power switching applications. In this paper, the current status of the devices for integrated circuits and their application to power switching systems are reviewed, after explaining the basic technologies for decreasing on-resistance, increasing breakdown voltage, and suppressing current collapse. In addition, a solution to increase switching frequency of GITs for smaller system size is described. The effects of integrated circuit of DC/DC converter consisted of gate driver, high-side GIT and low-side GIT with short gate length are also examined. I. INTRODUCTION GaN-based materials are very promising semiconductors for power switching devices taking advantages of the superior material properties such as higher breakdown field and higher sheet carrier density of two dimensional electron gas (2DEG) at hetero interface between AlGaN/GaN. Although higher sheet carrier density of 2DEG is attractive to decrease channel resistance of GaN-based transistors, normally-off operation of the transistors is difficult. Thus much effort has been devoted to achieve GaN-based transistors with normally-off operation together with decreasing channel resistance and increasing breakdown voltage. GaN-based Gate Injection Transistor (GIT) with p-type gate on AlGaN/GaN hetero structure is a solution to overcome them. In this paper, the current status of the GITs with normally- off operation for integrated circuits and their application to power switching systems are reviewed after describing material aspects of nitride semiconductors to achieve higher sheet carrier density of 2DEG by polarization and higher breakdown voltage. The demonstrated performances of the GITs with the breakdown voltage of 600V are superior to those of Si-based power devices such as IGBTs and MOSFETs. A methodology for suppression of current collapse which has been a crucial issue of GaN-based power devices is also described. Moreover, GITs with shorter gate length to reduce RonQg are also examined to extend the application field of GITs. These GITs can be used to reduce the system size with keeping high conversion efficiency of electrical power conversion systems such as DC/DC converters. A DC/DC converter IC with high speed gate driver is also reviewed. II. TECHNOLOGIES OF GAN-BASED DEVICES FOR POWER SWITCHNG SYSTEMS Thick GaN layer can be grown on Si substrate with buffer layer in which the mismatch of lattice constant and thermal expansion coefficient between GaN and Si are relaxed [1]. Fig.1 shows a photograph of epitaxial wafer of GaN on Si substrate. The mismatch between GaN and Si is relaxed in the buffer layer shown in Fig.2. The size of epitaxial wafer can be increased up to 8 inch. The variation of Hall mobility and sheet carrier density of 2DEG at AlGaN/GaN on 6 inch Si substrate are quite small as shown in Fig.3 [2]. A unique feature of the nitride semiconductors is a large amount of 2DEG induced at heterojunction such as AlGaN/GaN without any intentional doping. Although InAlN- based HFETs have been researched in which higher sheet carrier density of 2DEG owing to larger spontaneous polarization can be realized [3], more sheet carrier can be induced by introducing piezoelectric polarization additionally as shown in Fig.4. The comparison of induced charge density of 2DEG is shown in Fig.5. The hetero structure of InAlGaN/GaN is applied to access region of GIT to decrease on-resistance. As a result, the fabricated device with InAlGaN/GaN shows lower Ron than that of conventional GIT [4]. Although the threshold voltage of GaAs-based HFETs often depends on the gate direction due to the piezoelectric charge induced under the gate of HFET, GaN-based HFET on c-face do not depend on their gate direction, because the elastic stiffness tensor [C] and piezoelectric tensor [e] are not changed by coordinate transformation with respect to the c- axis at any rotation as shown in Fig.6 [5], where [a] and [M] are matrices for coordinate transformation. This feature is advantageous to realize GaN-based ICs in which FETs with various gate directions are integrated in a chip. Breakdown mechanism of GaN-based devices has been researched because it seems to be different from that of Si- based devices in which the breakdown voltage is saturated in a certain electrode distance. By contrast, breakdown voltage of GaN-based devices looks like to be limitlessly increased by longer electrode distance. This characteristic is partially IEDM16-540 20.4.1 978-1-5090-3902-9/16/$31.00 ©2016 IEEE