Microelectronic assemblies with improved isolation voltage performance

A microelectronic assembly comprising:

• first and second semiconductor devices formed over a substrate having a first dopant type at a first concentration;
• first and second buried regions having a second dopant type respectively below the first and second semiconductor devices with a gap between the first and second buried regions, the first and second buried regions each having first ends adjacent to the gap and second ends opposing the gap, the first ends extending a first depth from the first and second semiconductor devices;
• an epitaxial layer having the first dopant type over the substrate;
• at least one well region over the substrate and between the first and second semiconductor devices;
• and
• a barrier region having the first dopant type at a second concentration between and adjacent to the first ends of the first and second buried regions such that at least a portion of the barrier region extends a second depth from the first and second semiconductor devices, the second concentration being greater than the first concentration and the second depth being greater than or equal to the first depth.

A microelectronic assembly comprising:

• first and second buried layers formed in a semiconductor substrate having a first dopant type at a first concentration with a gap between the first and second buried layers, the first and second buried layers having a second dopant type and each having a first end adjacent to the gap and a second end opposing the gap;
• a barrier region within the gap and adjacent to the first ends of the first and second buried layers, the barrier region having the first dopant type at a second concentration, the second concentration being higher than the first concentration;
• an epitaxial layer having the first dopant type over the semiconductor substrate;
• first and second semiconductor devices over the epitaxial layer above the respective first and second buried layers;
• and
• first and second well regions having the second dopant type within the epitaxial layer respectively above the first ends of the first and second buried layers.