Thyristor volatile random access memory and methods of manufacture

A method of making a volatile memory array having row lines, column lines, and an array of thyristors having anodes coupled to one of the row and column lines and having cathodes coupled to the other of the row and column lines, the method comprising:

• implanting opposite conductivity type dopant into a first conductivity type semiconductor substrate to thereby provide a buried layer and the cathode for each of the thyristors;
• forming a first conductivity type epitaxial layer on the buried layer;
• removing all of the epitaxial layer and the buried layer to expose portions of the substrate from a first plurality of parallel regions extending in a first direction of the memory array to thereby form a first plurality of deep trenches;
• filling the first plurality of deep trenches with insulating material;
• removing all of the epitaxial layer to expose portions of the buried layer from a second plurality of parallel regions extending in a second direction of the memory array to thereby form a second plurality of shallow trenches;
• filling the second plurality of shallow trenches with insulating material;
• forming a further epitaxial layer on an upper surface of the epitaxial layer;
• implanting opposite conductivity type dopant into an upper portion of the further epitaxial layer to form upper opposite conductivity type regions separated from the buried layer by the epitaxial layer;
• implanting first conductivity type dopant into a top portion of the further epitaxial layer to form the anode for each of the thyristors;
• and
• providing electrical connections to the further epitaxial layer to provide connections to the anodes of the thyristors.