having the shape of a frusto pyramid in fig7 only spring elements 17 a are visible which correspond to the spring elements 17 a of fig2 additional spring elements corresponding to 17 b of fig2 are not shown but extend perpendicular to the drawing plane the second wafer 52 comprises a substrate 56 in which electronic components are integrated belonging to the control circuitry and a protection layer 63 for instance a silicon dioxide layer in which a cavity or depression 57 is present the third wafer 58 forms a plate 60 similar to the plate 27 of fig3 and supported by a frame 61 similar to the frame 30 and spring elements similar to the spring elements 28 and 31 of which spring elements 62 may be seen only in part the plate 60 has an underside 60 a facing the cavity 57 and a top side 60 b facing the platform 53 mobile electrodes 70 are arranged on the underside 60 a of the plate 60 face the fixed electrodes 71 arranged on the bottom of the cavity 57 and form with the mobile electrodes 70 actuation electrodes in a known way in practice the plate 60 together with the frame 61 the spring elements 62 and the electrodes 70 71 forms a linear actuator 65 two engagement springs 73 are formed on the top side 60 b of the plate 60 each engagement spring 73 is formed by a metal plate having an elongated arched shape fig8 with the concavity upwards in detail each engagement spring 73 has a first end 73 a fixed to the plate 60 and a second end 73 b.