Development of Large-area GaN High Electron Mobility Transistors and the Applications to Power Electronics
Date Issued
2014
Date
2014
Author(s)
Lee, Finella
Abstract
Silicon is the most widely used material for power devices. However, Si-based power devices are approaching their material limits. Gallium nitride (GaN) high electron mobility transistors (HEMTs) have great potential for high-frequency and high-power applications because of their excellent characteristics, such as high breakdown voltage, high output power and low on-resistance. Nonetheless, the inherent normally-on behavior excludes GaN HEMTs from most power electronic applications for reduced circuit complexity and fail-safe operation.
In this thesis, p-GaN cap layer was utilized to raise the conduction band energy underneath the gate contact in order to achieve enhancement-mode (E-mode) operation. The effects of p-GaN etching depth and alloy temperature on the characteristics of the E-mode GaN HEMTs were investigated in order to improve the device performances. By adjusting the process methods, a noticeably high breakdown voltage of 1630V was achieved for the p-GaN cap HEMTs with LGD = 16μm.
Although Ni/Au is commonly used as a gate metal for the commercial GaN HEMTs, many metals can be chosen as the gate contact metal of p-GaN cap HEMTs because most of the metals have adequate work function difference comparing to p-GaN. In this thesis, different gate metals including Ni/Au-, Ti/Au-, and Mo/Ti/Au-gate GaN HEMTs were demonstrated to study the impacts of gate metals on the device performances, such as VTHs, saturated output currents, and breakdown voltages of GaN HEMTs. Compared to Ni/Au-gate HEMTs, the devices with a Mo/Ti/Au gate can improve 32% of the breakdown voltage with a trade-off of reducing 11% of operating current at LGD = 6um.
Moreover, multi-finger large-area power devices were demonstrated. Two kinds of methods were employed to realize E-mode power devices whose operating currents are higher than 6A. One is using a Si MOSFET in series to drive the depletion-mode (D-mode) GaN HEMTs, the other one is using p-GaN cap E-mode HEMTs.
Subjects
高電子遷移率電晶體
氮化鎵
增強型
p型氮化鎵覆蓋層
多指型功率元件
Type
thesis
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