Editor’s Note
This article highlights a significant domestic breakthrough in semiconductor materials, with RFHIC successfully depositing a polycrystalline synthetic diamond layer on a 4-inch wafer. This development of GaN-on-Diamond technology promises enhanced performance for next-generation wireless communication devices due to superior heat dissipation.
A domestic company has developed, for the first time in the country, a deposition technology for Gallium Nitride-on-Diamond (GaN-on-Diamond), a next-generation material for wireless communication (RF) semiconductors.
Gallium Nitride-on-Diamond is exceptionally suitable for high-performance, high-temperature, and high-voltage mobile communication equipment due to its superior heat dissipation characteristics. The company plans to develop the entire production process and equipment for each step to launch RF components based on GaN-on-Diamond.
RFHIC (CEO Cho Deok-soo) announced on the 2nd that it has recently developed a 4-inch GaN-on-Diamond wafer manufacturing technology.
RF semiconductors must operate at faster speeds than other semiconductors and withstand high voltage and high temperatures. This company, which manufactures RF components, modules, and systems, began developing GaN-on-Diamond technology because the poor heat dissipation performance of RF components used in high-frequency systems was causing malfunctions and failures.
The methods for depositing diamond on gallium nitride are broadly divided into two: fusing the two under high pressure and high temperature (HPHT), or growing diamond via Chemical Vapor Deposition (CVD) and then forming a gallium nitride layer.
RFHIC chose the latter. This is because HPHT can cause various problems in subsequent processes.
The company seeded the substrate with nano-sized diamond particles and grew them in a Microplasma Chemical Vapor Deposition (MPCVD) process to create a polycrystalline diamond layer. A buffer layer was then placed on top, and gallium nitride was grown to create the wafer.
To achieve this, RFHIC acquired Element Six’s (E6) GaN-on-Diamond technology in 2017. Element Six is a subsidiary of De Beers, the world’s largest diamond producer, and specializes in the design and manufacture of synthetic diamonds.
This company is the first in Korea to secure GaN-on-Diamond wafer fabrication technology. Overseas, Qorvo has created transistors based on GaN-on-Diamond with support from the U.S. Defense Advanced Research Projects Agency (DARPA).
Currently, Gallium Arsenide (GaAs), Gallium Nitride-on-Silicon (GaN-on-Si), and Gallium Nitride-on-Silicon Carbide (GaN-on-SiC) are primarily used as RF semiconductor materials.
In particular, demand for GaN began to increase with the start of 5th generation (5G) mobile communication infrastructure construction. This is because higher frequency bands than before are utilized, requiring faster signal switching speeds and higher energy efficiency. GaN has high electron mobility and low leakage current. It can also be used at medium voltages up to 600V.
The problem is heat. As power density increases, surface temperature rises and substrate resistance increases, impairing the performance of the entire device.
Diamond has higher thermal conductivity than Si or SiC, which are the substrate materials for conventional GaN devices. GaN-on-Diamond based transistors dissipate heat 4 to 6 times faster than GaN-on-SiC.
This means that the chip size can be reduced, allowing operation even with a correspondingly higher power density. A GaN device using a diamond substrate can be reduced to one-third the size of one made with an SiC substrate while maintaining performance. It can be utilized in frequency bands up to 400 GHz, and its RF output reaches 1000W, which is more than 5 times higher than GaAs.
Of course, there are still issues to resolve. Since the diamond layer is formed as polycrystalline, subsequent processes are relatively difficult. When developing the process, the difference in thermal expansion coefficients between diamond and GaN must also be considered. The thermal expansion coefficients of the two materials differ by almost three times.
The global RF transistor market is dominated by five companies—NXP Semiconductors, Ampleon, Infineon, Sumitomo Electric, and RFHIC—which hold 90% of the market. NXP, Ampleon, and Infineon manufacture silicon-based LDMOS (Lateral Diffused MOS) transistors, while Sumitomo and RFHIC manufacture GaN transistors.
RFHIC has been involved in GaN-related business for over 20 years, from device design to modularization and systems. It started generating sales in 2006. At the time of the company’s founding, GaN was expensive relative to demand, and most RF companies were focused on existing silicon-based LDMOS.
The company judged that higher frequency bands would require low-loss, high-speed RF semiconductors. After R&D, it secured its own design and back-end process technology and launched GaN-based devices faster than its competitors. Initially, products began to be used in mobile communication infrastructure, and from 2014, they also gained traction in the defense market.
Its main clients are communication equipment companies like Samsung Electronics, Huawei, and Ericsson, as well as defense contractors.
Currently, the company entrusts wafer and foundry work to Cree and handles the back-end processes itself to manufacture GaN products. For GaN-on-Diamond, it has secured everything from design to wafer manufacturing technology.