MOSFETs on (111) Highly Oriented Polycrystalline 1-Inch Diamond Substrate

We fabricated 2DHG diamond MOSFETs on a (111) highly oriented polycrystalline 1-inch diamond substrate and confirmed that the devices correctly functioned as a FET. The area of the 1-inch substrate is about 55 times larger than that of conventional 3mm square substrate. In this work, we fabricated 220 devices on the 1-inch diamond substrate, and the yield rate was about 95 percent. We found that the yield rate on the 1inch substrate tends to be much higher than that on the 3mm square substrate.<br/>Diamond has outstanding characteristics as a semiconductor, such as wide band gap (5.5 eV), high thermal conductivity (22 W/cmK), and high breakdown field (10 MV/cm). Therefore, diamond is expected to be applied to the next generation’s RF amplifier and power device. However, a problem in fabricating diamond devices is the low yield rate due to the small substrate size. In this work, we fabricated 2DHG diamond MOSFETs on the polycrystalline 1-inch diamond substrate, and we found that the yield rate was greatly improved.<br/>The highly oriented (111) polycrystalline substrate was fabricated by Sumitomo Electric Industries, Ltd. All the devices on the 1-inch substrate are double-finger structure. Firstly, source and drain electrodes were deposited Ti/Pt/Au (20 nm/ 30 nm/ 90 nm). After H-termination and isolation, 200 nm of Al₂O₃ was deposited as the gate insulator. After that, 300 nm of Al was deposited as the gate electrode. 80 percent of all the devices have the gate length L_G= 5 µm and the others have L_G= 2 µm. There are 3 kinds of source-drain length L_SD, 10 µm, 15 µm, and 20 µm. Also, there are 3 kinds of total gate width W_GT, 1 mm, 2 mm, and 3 mm.<br/>The highest maximum drain current density was obtained from the device of L_G= 2 µm, L_SD = 10 µm, and W_GT = 1 mm at V_GS = -40 V and V_DS = -40 V, and the result was 151 mA/mm. For all the devices that correctly functioned as a FET, the drain current density was in the range of 100 mA/mm to 150 mA/ mm. The decrease in current density was observed as the gate width expanded, but it is assumed that the effect of the grain boundary on the devices is not serious. About 95 percent of yield rate was achieved in this work, and the distribution of the devices that did not function were impartial on the 1-inch substrate. This is because, thanks to the substrate size, photoresists uniformly coated the whole substrate in the fabricating process.<br/>In this work, we fabricated 2DHG diamond MOSFETs on a (111) highly oriented polycrystalline 1-inch diamond substrate and confirmed that the devices correctly functioned as a FET. The highest maximum drain current density was 151 mA/mm, and the yield rate of devices on the 1-inch substrate was greatly improved. Fabricating 2DHG diamond MOSFETs on polycrystalline 1-inch diamond substrate is possible and it contributes to the yield rate improvement.