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Static and Dynamic Characterization of a GaN-on- GaN 600 V, 2 A Vertical Transistor

Vertical GaN transistor
Fig. 1. Image of the 1mm2 vertical GaN transistor after being mounted onto a PCB, wirebonded and encapsulated.
Most gallium-nitride (GaN) power transistors have a lateral device structure because this structure can be fabricated using silicon (Si) and silicon carbide (SiC) substrates, which are less expensive than GaN substrates. This means the fabrication process can be carried out more simply. While lateral GaN transistors have demonstrated high efficiency and fast switching speeds, their current-carrying capability and breakdown voltage are limited by this lateral device structure. Several challenges have hindered the development of vertical GaN transistors, including the relative immaturity of GaN substrates and the need to create a new fabrication process. Recent advances have overcome these barriers, and now more vertical GaN devices are being developed.

Fig. 1 shows the vertical GaN transistor developed by HRL Laboratories, which is overcoming these barriers. This paper describes the vertical GaN fabrication process and the circuit developed to test this device. The vertical GaN transistor is demonstrated to have a threshold voltage of 3.3 V, a static breakdown voltage of 600 V, and an on-resistance of 880 m&Omega. For the dynamic characterization, the device is shown to have switching speeds up to 97 V/ns, and turn-on and turn-off switching losses of 8.12 µJ and 3.04 µJ, respectively, demonstrating the great potential of this device. It is the first vertical GaN transistor reported to have a dynamic breakdown voltage of up to 450 V. The waveform for this voltage level is shown in Fig. 2. The results illustrate the immense potential of developing this technology further.

Switching waveforms
Fig. 2. Switching waveforms of the vertical GaN transistor at 450 V, 2 A.
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