A team of researchers at Aalto University in cooperation with Okmetic Oy and the Polish ITME, have studied the application of SOI (Silicon On Insulator) wafers, which are used as a platform for manufacturing different microelectronics components, as a substrate for producing gallium nitride crystals. They compared the characteristics of gallium nitride (GaN) layers grown on SOI wafers to those grown on silicon substrates more commonly used for the process. In addition to high-performance silicon wafers, Okmetic also manufactures SOI wafers, in which a layer of silicon dioxide insulator is sandwiched between two silicon layers. The objective of the SOI technology is to improve the capacitive and insulating characteristics of the wafer.
The Researchers used a standardized manufacturing process for comparing the wafer characteristics. GaN growth on SOI wafers produced a higher crystalline quality layer than on silicon wafers. In addition, the insulating layer in the SOI wafer improves breakdown characteristics, enabling the use of clearly higher voltages in power electronics. Similarly, in high frequency applications, the losses and crosstalk can be reduced. GaN based components are becoming more common in power electronics and radio applications. The performance of GaN based devices can be improved by using a SOI wafer as the substrate.
Growth of GaN on a silicon substrate is challenging. GaN layers and devices can be grown on substrate material using metalorganic vapor phase epitaxy (MOVPE). When using silicon as a substrate the grown compound semiconductor materials have different coefficients of thermal expansion and lattice constants than a silicon wafer. These differences in their characteristics limit the crystalline quality that can be achieved and the maximum possible thickness of the produced layer.
The research showed that the layered structure of an SOI wafer can act as a compliant substrate during gallium nitride layer growth and thus reduce defects and strain in the grown layers.
GaN based components have a wide range of applications from LED's to RF Applications in Radars and Wireless Infrastructure. Enhancing GaN Performance will very useful for all these applications.
