| Summary: | 碩士 === 國立中央大學 === 電機工程研究所 === 97 === Wide bandgap AlGaN/GaN heterostructures have been widely used in high electron mobility transistors (HEMTs) for high temperature, high frequency, and high power applications. For high power devices, ohmic contacts with low contact resistance, smooth surface and clear edge definition are essential as they are closely related to the performance, reliability and reproducibility of the devices.
We carry out a comparative study on the specific contact resistivity and surface morphology of Ti/Al/Ni/Au, Ti/Al/Mo/Au, Ti/Cr/Ni/Au, Ti/Cr/Mo/Au, and Ti/Al/Cr/Mo/Au metal contact stacks on AlGaN/GaN heterostructure. Compared to the conventional Ti/Al/Ni/Au contact, the Ti/Al/Cr/Mo/Au contact has a much smoother surface and keeps its specific contact resistivity (ρc) as low as 1.1×10-6 ohm-cm2. This contact maintains its low contact resistivity after storing at 200 oC for 100 hours in nitrogen ambient. These results are attributed to the Cr interlayer, which suppresses inter-diffusion and reaction between the Au and Al layers in the contact stack.
Moreover, we apply Ti/Al/Cr/Mo/Au ohmic contact to AlGaN/GaN HEMTs (Lg =2μm, Lds =6μm) and obtain fT and fMax of 5.95GHz and 17.85GHz respectively. These results suggest that the proposed Ti/Al/Cr/Mo/Au contact is a good ohmic electrode for high power and high frequency AlGaN/GaN HEMTs.
|
|---|
