GaN MIS-HEMT PA MMICs for 5G Mobile Devices

As the data transfer rates in various mobile systems increase, the needs for 5G wireless communication systems have also been correspondingly increased. For the enhancement of data transfer rates, 28 GHz, one of the high frequency bands proposed by Korea for global standards, was chosen for 5G systems. While GaN-based high-electron-mobility transistors (HEMTs) are very promising candidates for 5G network applications due to their usage in high output power amplifiers, typical GaN HEMTs only operate in a normally-on state. However, for successful operations of mobile handsets of 5G systems, a normally-off device operating under positive gate bias is required, which provides advantages of decreased circuit complexity and system cost, as well as potential for use in the domain of digital circuits. For positive gate bias operation, metal-insulator-semiconductor (MIS)-HEMT devices were fabricated by using the ETRI GaN MIS-HEMT process. We designed and fabricated MIS-HEMTs and characterized their performances. In addition to the adaptation of a gate recess technique, we employed an Al₂O₃ gate insulator to shift the threshold voltage in GaN MIS-HEMTs. The power amplifier (PA) monolithic microwave integrated circuit (MMIC) was designed and operated under a positive gate bias for 5G mobile handsets and exhibited a maximum output power of 29.5 dBm, a power gain of 11 dB, and a power added efficiency (PAE) of 11% at frequencies of 26 and 28 GHz.