132 is removed in the region 134 such that a surface 136 of the first layer 106 a 1 with high acoustic impedance is exposed and the ridges 132 a 132 b of the planarization layer 132 only remain in the peripheral region the portion 134 includes at least the active region of the piezoelectric resonator with which the mirror to be produced is used wherein the region 134 is usually chosen slightly greater than the active region of the piezoelectric resonator actually resulting later due to the adjustment tolerances and the oblique etching flanks the structure shown in fig3 d is subjected to a planarization process leading to the removal of the ridges 132 a and 132 b for example by a cmp process the structure resulting after the planarization is shown in fig3 e in which the structure comprises a planar surface wherein the surface 136 of the first layer 106 a 1 is substantially flush with a surface 138 of the portions of the planarization layer 132 arranged on the first layer 106 b 1 with low acoustic impedance subsequently the steps illustrated on the basis of fig3 a to 3 e are repeated so that the structure shown in fig3 f with two layers with high acoustic impedance 106 a.