Depletion Mode MOSFETs for Monolithic Digital Integrated Circuits in 6H-SiC S.Ryu, K.T. Kornegay, J.A.Cooper, Jr.

Digital circuits in 6H-SiC has been implemented using enhancement mode transistors configured as non-saturated load devices[1,2]. However, due to their reduced voltage swing, degraded noise margins, and the need for large Beta ratios, their performance is far from optimal. To overcome these limitations, we propose to use depletion mode MOSFETs configured as saturated load devices which will yield a significant performance improvement. Two types of depletion mode MOSFETs are being considered: 1) buried channel and 2) surface channel. They are both fabricated by implanting nitrogen ions into an Al doped p-type SiC substrate to form a channel. The two devices only differ by their ion implantation energy and dose. The buried channel MOSFET [3], which is controlled by the width of its surface depletion region like JFETs or MESFETs, is fabricated using deep implantations at heavy doses while the surface channel MOSFET requires shallow implantations at lighter doses. For better control of th..