For the last few decades, the material of choice for high-frequency wireless applications has been the Gallium-Arsenide (GaAs) field effect transistor (FET). Next Generation technologies on the imminent horizon – self-driving cars, AI, IoT, Augmented Reality, and other low-latency-requiring applications – have pushed the development of new device technologies. At first, Silicon-Carbide (SiC) showed much promise, but today as both the laws of physics and economy guide the path the evolution follows, gallium-nitride (GaN) is beginning to emerge as the rising star for the next wave of technological development.
The new challenge in the field of electronics is to provide cost-effective Solid State Power Amplifiers (SSPAs) robust enough to operate reliably at high frequencies and under harsher conditions. By briefly analyzing some primary performance metrics of the three SSPA materials (GaAs, SiC and GaN), it is easy to see why GaN is rapidly positioning itself as the leader in this arena.
Band Gap Width Drives Chip Performance
The molecular properties of substrate materials have a dramatic effect on how well an SSPA operates at high frequencies (>>10Ghz). When two substances with very different properties are layered together, the “looseness” of the molecular bond between the two creates a pathway through which electrons can freely flow. The pathway, or heterojunction, determines how fast the chip operates under various conditions.
Devices designed using wide-bandgap (WBG) substances like GaN, maintain a very loose molecular bond pathway. Bandgap measured at 300°C is significantly higher in GaN (3.4 eV) than it is in both GaAs (1.4 eV) and SiC (2.9 eV).
This property gives GaN a distinct advantage over GaAs and SiC for applications requiring semiconductors to perform well at extremely high voltages, frequencies and temperatures.
GaN technology can incorporate complex geometries to realize higher carrier mobility and higher electron peak velocity. Consequently, GaN devices exhibit higher saturation velocity values than GaAs or SiC. Higher saturation velocity means the power-density levels and power-switching properties of a GaN device do not degrade as rapidly under high voltage or temperature conditions that would substantially reduce the efficiency of GaAs and SiC devices.
GaN Development Building on the Shoulders of Giants
No new technology evolves in a vacuum. The slow development and perfecting of design and testing methodologies that brought GaAs to the forefront can be incorporated into the realization of affordable and reliable SiC and GaN chips as well. Dictated mainly by market forces, perfecting any new technology takes time, money and expertise. If "necessity is truly the mother of invention," the need for the unique properties of GaN transistors signals the birth and acceptance of this new generation of super transistors.
