What is GaN power amplifier
-Gallium Nitride (GaN) belongs to the family of wide bandgap (WBG) materials. It is a binary compound whose molecule is formed from one atom of Gallium (III-group, Z=31) and one of Nitrogen (V-group, Z=7) with a basic hexagonal (wurtzite) structure.
- GaN technology has revolutionized wide-bandgap semiconductor industry through offering transistors with remarkably high breakdown voltages, e.g., exceeding 100 V. This enables the operation of GaN transistors with high supply voltages and, as a result, impressive output power densities. GaN technology has been primarily employed for high power generation where the GaN high-electron mobility transistor (HEMT) has emerged as the dominant force in solid-state power amplifiers (PAs).
Early developments in GaN HEMT started in 1990s, where a number of two-dimensional electron gas (2DEG) of GaN/AlGaN heterojunction implementations were reported .These preliminary processes used sapphire as the substrate, a material with low thermal conductivity (32 W/m⋅K at room temperature), which was not suited for high-power applications . This issue was later resolved by using silicon carbide (SiC) with excellent thermal conductivity (490 W/m⋅K at room temperature) as the substrate which allows high power densities be efficiently dissipated and avoids extremely high channel temperatures. The first GaN integrated circuits using flip-chip bonding for thermal management were reported in 1999. In a traveling-wave power amplifier (TWPA) was presented, where GaN HEMTs were grown on sapphire substrate with flip-chip bonding onto AlN substrate to improve the thermal management. The TWPA operated over 1–8 GHz bandwidth and delivered 4.5 W output power under 22 V supply voltage, while the power-added efficiency (PAE) was 15%. Other PAs using the same process but reactive output matching circuit architectures were presented in, which achieved 3–9 GHz bandwidth, 3.2 W output power, and 24% PAE. Using a similar process, later, a PA with 6–10 GHz bandwidth delivered a record output power of 14.1 W under 25 V supply voltage with 25% PAE. The first fully integrated, i.e., monolithic microwave integrated circuit (MMIC), GaN PA was presented in 2000, where a nonuniform distributed power amplifier (NDPA), realized using dual-gate transistors with 400-nm gate length on sapphire substrate, achieved 1.25 W peak output power and 25% peak PAE at 3 GHz under 15 V supply voltage.
The research and development activities on GaN integrated circuit technologies have been pursued on three main streams: material, device, and circuit. In the material level, different substrate materials have been investigated including sapphire, native GaN, diamond, SiC, silicon (Si), and silicon-on-insulator (SOI). The substrate materials are evaluated based on several factors mainly thermal conductivity, fabrication cost, electrical parasitic components, loss, and mechanical robustness. Currently, GaN-on-SiC is the most popular process used in many commercial products. Other than the substrate material, a number of materials have been explored in GaN processes for the fabrication of the gate electrode, drain/source contacts, metal layers, interlayer via, and through-silicon via (TSV).
In the device level, a number of GaN HEMT structures capable of operating under higher supply voltages or in higher frequency bands, e.g., T-gate structure, have been presented. Moreover, scaling of the minimum gate length of transistors down to sub-100 nm has enabled the operation of GaN circuits in mm-wave bands. An important challenge in the transistor level has been the development of accurate models for GaN HEMTs which include nonlinearities, high-frequency parasitic components, the charge trapping and memory effects, and the thermal heating impact on performance and reliability.
Finally, in the circuit level, major developments can be classified to low-loss power combining techniques, harmonic termination networks, integration of bandpass filter (BPF) into the PA circuit, linearization techniques for AM-AM and AM-PM distortions, and broadband uniform and nonuniform distributed PAs. The overall result of these progresses is the development of fully integrated GaN RF PAs with multi-hundred-watt output power, e.g., products by Qorvo and Wolfspeed, highly scaled GaN processes, e.g., 40-nm GaN-on-SiC double-heterostructure field-effect transistor (DHFET), 40-nm and 70-nm GaN-on-SiC HEMTs, and high-power mm-wave GaN PAs providing 34.8 dBm (3 W) at 84 GHz, 37.8 dBm (6 W) at 95 GHz, 26 dBm at 120 GHz, 15.8 dBm at 180 GHz, and 18.5 dBm at 205 GHz.
Although the main application of GaN technology is power amplifications, the high power handling capabilities, inherent high linearity, and low noise of the GaN HEMT devices have motivated other applications. GaN low-noise amplifiers (LNAs) can tolerate extremely high input power levels and can provide excellent linearity. Other circuits implemented using GaN technology are control components including switches, limiters, phase shifters, nonreciprocal circulator for full-duplex operation, and DC-DC converters. Moreover, single-chip GaN transceiver front-ends have been developed operating at 3 GHz, 5.4 GHz, 5.9 GHz , and 39 GHz .
- Gallium nitride (GaN) is a wide bandgap semiconductor which has rapidly transformed the world by enabling energy-efficient white light-emitting diodes and promising energy-efficient power electronic devices. Bulk crystal growth is actively being researched to enable inexpensive large-area substrates. Currently, bulk GaN substrates are commercially available using the hydride vapor phase epitaxy method, but they lack high structural quality and availability of arbitrarily oriented substrate orientations. The ammonothermal and sodium flux methods are the two most promising true bulk crystal growth techniques being explored to fill this void and enable large-area, arbitrarily oriented, low-cost substrates of high structural quality. While challenges remain for all three growth methods, considerable progress has occurred over the years. This chapter provides an overview of the three growth methods and current characteristics of state-of-the-art material after a brief introduction to GaN and general challenges for bulk GaN growth.l
What is the benefit if GaN power amplifier compare to traditional SiC transistor
- the higer power density of gallium nitride (GaN) means higher power in a small footprint, fewer components ,smaller systems, and less weight- contributing to more reliable and more eddicient system.
- Xinhang Zhiyuan’s breadth and depth of expertise in GaN device design and support combined with our deep domain knowledge make us the ideal partner of realing the benefits of GaN technology.
iable and more efficient systems.
