Seeking a solution to reliability issues with the mesa
transistor (1958 Milestone), Fairchild physicist Jean Hoerni
recalled an idea he had recorded in December 1957 - a new
process in which the oxide layer is left in place on the silicon
wafer to protect the sensitive p-n junctions underneath. Focused
on getting its first devices into production, the company did
not pursue the approach at that time. Due to concerns about
possible contaminants, conventional wisdom required removing
this layer after completion of oxide masking, thus exposing the
junctions. Hoerni viewed the oxide instead as a possible
solution - his "planar" approach, named after the flat
topography of the finished device, would protect these
junctions. After writing a patent disclosure in January 1959, he
demonstrated a working planar transistor that March. The oxide
layer was indeed found to protect the junctions, as Hoerni had
predicted. Planar devices also proved to have better electrical
characteristics - particularly far lower leakage cu