A New Package of High-Voltage Cascode Gallium Nitride Device for Megahertz Operation

Lateral gallium nitride (GaN)-based high-electron-mobility transistor (HEMT) power devices have high current density, high switching speed, and low on-resistance in comparison to the established silicon (Si)-based semiconductor devices. These superior characteristics make GaN HEMTs ideal for high-frequency, high-efficiency power conversion. Using efficient GaN HEMT devices switched at high frequency in power electronic systems could lead to an increase in power density as well as a reduction in the weight, size, and cost of the system. However, conventional packaging configurations often compromise the benefits provided by high-performance GaN HEMT devices, for example, by increasing the parasitic inductance and resistance in the current loops of the device. This undesirable package-induced performance degradation is prominent in the cascode GaN device, where the combination of a high-voltage depletion-mode GaN semiconductor and low-voltage enhancement-mode Si semiconductor is needed. In this study, a new package is introduced for high-voltage cascode GaN devices and is successfully demonstrated to make the device more suitable for megahertz operation. This packaging prototype for cascode GaN devices is fabricated in a power quad flat no-lead format with the new features of a stack-die structure, embedded external capacitor, and flip-chip configuration. The parasitic ringing in hard-switching turn-off and switching losses in soft-switching transitions are both effectively reduced for this newly packaged device compared with a traditional package using the same GaN and Si devices. Improved thermal dissipation capability is also realized using this new package for better reliability.