front metal or at the bottom of the trench creates conditions for u201c active area u201d avalanche i e it forces the avalanche to occur at the edge of the cells an avalanche that will spread over the entire active area the top structure 22 is very similar to schottky barrier diodes sbd available from microsemi corporation but the epitaxial layers are designed for lower breakdown voltage and therefore the forward voltage of the part will be lower a thick substrate 15 mils or thicker and a thick heat sink soldered to the top metal will provide the required thermal capacitance of the device the n drift region 2 can have a graded doping profile as in fig5 with greater doping concentration towards the anode which provides an improved low series resistance both in forward mode and when in avalanche the process flow of the trench termination tvs is very similar to the one disclosed in previous paragraphs fig2 1 to 2 4 show the differences starting material in this case consists of a sic substrate 1 4h u2014 sic in our case but this invention is not restricted to the use of this polytype on which either a u201c flat u201d or a u201c graded u201d second epitaxial layer 2 is grown and on which the third epitaxial layer 21 is deposited the doping and the thickness of the epitaxial layer 21 are chosen to be consistent with the rated voltage of the tvs and in general terms its doping e g range 1e16 to 1e18 cm3 is about one order of magnitude higher than the doping of the first epitaxial layer 2 n type doping polarity of all three layers substrate first epitaxial layer and second epitaxial layer is described here but.