Abstract
Copper-metallized gallium nitride (GaN) high-electron-mobility transistors (HEMTs) using a Ti/Pt/Ti diffusion barrier layer are fabricated and characterized for Ka-band applications. With a thick copper metallization layer of 6.8 μm adopted, the device exhibited a high output power density of 8.2 W/mm and a power-added efficiency (PAE) of 26% at 38 GHz. Such superior performance is mainly attributed to the substantial reduction of the source and drain resistance of the device. In addition to improvement in the Radio Frequency (RF) performance, the successful integration of the thick copper metallization in the device technology further reduces the manufacturing cost, making it extremely promising for future fifth-generation mobile communication system applications at millimeter-wave frequencies.
Highlights
Gallium nitride (GaN) high-electron-mobility transistors (HEMTs) have become one of the most popular devices for high-frequency and high-power applications in recent years
The objective of this study focuses on the investigation of the effect of thick copper metallization on device performance at millimeter-wave frequencies
The device mesa isolation was performed, which defined the active region by lithography; an inductively coupled plasma (ICP) machine was used with Cl2 in an Ar ambient to etch the AlGaN and GaN layer for around 180 nm
Summary
Gallium nitride (GaN) high-electron-mobility transistors (HEMTs) have become one of the most popular devices for high-frequency and high-power applications in recent years. Compared to traditional silicon devices, GaN material has several remarkable properties, such as better electron mobility at high electric field, wider energy bandgap (3.4 eV), higher breakdown electric field and higher saturation electron drift velocity [1–3] Such excellent material properties have made AlGaN/GaN devices the streamline technology for high-frequency and high-power applications for next-generation wireless communication systems at millimeter-wave frequencies [4–6]. Device performance is strongly affected by the skin effect at high operating frequencies since the parasitic resistance tends to increase due to the limited cross-sectional area for current flow Such parasitic resistance could possibly be minimized through thick metal deposition for interconnects at the device level. The price of the material makes production cost inevitably high, making commercialization difficult To address this issue, Au-free process technology was developed [7], which demonstrated CMOS-compatible AlGaN/GaN Metal-Insulator-Semiconductor HEMT (MIS-HEMT) device configuration for power electronics applications. In order to quantize the effect of the thick copper metallization, we have extracted the corresponding parameters of the small-signal equivalent circuit for comparison purposes
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