Sumitomo Electric Industries, Ltd. has developed a gallium nitride transistor (GaN-HEMT) that uses N-polar GaN and, for the gate insulating layer, the first hafnium (Hf)-based, highly heat-resistant, high dielectric material, setting its sights on the post-5G era, which will realize even greater capacity and high speed communications.

GaN HEMTs are widely used in high frequency amplifier applications, including 5G. In the future post-5G era, the transistors used in communication devices will be required to support higher power and higher frequencies for an increased volume of data transmission.

Fig. 1 Comparison of Ga-polar and N-polar HEMT

Conventionally, Ga-polar (0001 orientation) GaN has been widely used. Along with the demand for further higher power and higher frequencies, however, attention is being focused on the improvement of characteristics with N-polarity (000-1 orientation) (the crystal orientation is different from that of the Ga-polarity), which enables an inverted HEMT structure that increases the degree of freedom in device design and can reduce leakage current (Fig. 1). Meanwhile, N-polar crystals have the problem of being prone to irregularities caused by abnormal growth called hillocks. In addition, in terms of device design, the realization of an inverted HEMT structure required the development of a high-quality gate insulating layer that would serve as a barrier against the gate electrode in place of the conventional semiconductor barrier layer.

Fig. 2 Improved quality of N-polar GaN

Therefore, Sumitomo Electric has utilized its years of experience in crystal growth technology to realize high-quality N-polar crystals without hillocks (Fig. 2). In addition, by applying a type of Hf-based highly heat-resistant and high dielectric material, used in state-of-the-art Si transistors, to the challenging gate insulating layer for the first time in the world, the company completed an N-polar crystal transistor incorporating a high dielectric material and achieved excellent high frequency characteristics (Fig. 3).

Fig. 3 High-frequency characteristics of N-polar crystal transistor using high-dielectric material

This achievement is the result of the "Research and Development Project for Strengthening Post-5G Telecommunication System Infrastructure" commissioned by the New Energy and Industrial Technology Development Organization. The details were announced on October 17, 2022 at the 2022 IEEE BiCMOS and Compound Semiconductor Integrated Circuits and Technology Symposium held in Phoenix, Ariz.

GaN HEMTs, which excel in high frequency characteristics and low power consumption, are essential for the post-5G era. Therefore, expectations are placed on further improvement of their characteristics. Sumitomo Electric will continue to develop technology and contribute to further sophistication of high frequency communications, energy saving and decarbonization of society.

HEMT is the abbreviation of high electron mobility transistor. As the name suggests, it is a type of transistor. HEMTs were first used in satellite broadcasting receivers in many countries. Since then, they have become devices indispensable for various apparatuses in the microwave and millimeter-wave ranges, such as mobile phones and base stations, satellite navigation receivers and mmWave radar sensors for preventing collision of vehicles. To date, HEMTs have served as the fundamental technology underpinning the telecommunications society. Based on its years of experience in HEMT technology, Sumitomo Electric commercialized GaN HEMTs ahead of our competitors in the world by combining the technological achievement of HEMTs with GaN, characterized by superior material properties.