That face of the non-epitaxied substrate of high resistivity which supports the junction 3 formed by the planar method is treated by a mesa attack in such a way that it is smaller than the opposite face 7. An insulating ring 4 covers the periphery of the junction and projects beyond the substrate. This...http://www.google.de/patents/US4315275?utm_source=gb-gplus-sharePatent US4315275 - Acoustic storage device intended in particular for the correlation of two high-frequency signals
