. . "Preferentially, it consists of an SOI (Silicon On Insulator) substrate 10; the top layer 14 made of SI is for example between 2 ??m and 200 ??m thick, for example 60 ??m, and the intermediate oxide layer 16 is for example between 0.4 ??m and 2 ??m thick, for example 1 ??m; it may also consist of other substrates, possibly produced specifically on an individual base wafer 12; preferentially, the to" . .