to fig4 a it will be better understood how the different parts are defined with great precision by virtue of the method of the invention if a half gauge is considered for example the half gauge j 3 it comprises a sensing zone of width c and of length l these dimensions were defined with precision during the etching of the layer 20 of polysilicon the half gauge j 3 also comprises two connection zones of width b this width also being defined with great precision during the etching of the polysilicon each connection zone has a length e which is also defined with great precision for the following reason during the creation of the windows 62 and 64 see fig3 their extremities were created with great precision at the distance e from the extremities of the sensing zone 32 and the polysilicon in the windows 62 and 64 is directly in contact with the metallization layer 80 from the point of view of electric current flow since the metal has an electrical conductivity very much higher than that of the polysilicon all the current flows in the metal as if there were no polysilicon underneath it the zones of polysilicon directly covered by the.