11 a small quantity a drop for example of an hsq solution filtered at 0 45 u03bcm is deposited on the plate 11 in turn placed on a spinner the hsq solution is filtered to avoid any dust harmful to adhesion the hsq layer 12 is obtained by centrifugation at 5 000 rpm for 30 seconds fixed acceleration at 2 000 rpm the thickness of the layer 12 obtained is generally between 100 nm and 10 u03bcm typically less than a micrometer for example between 300 nm and 400 nm the plate 11 connected to the layer 12 hsq is annealed at 150 u00b0 c for two minutes on a heating plate with respect to step e 2 chemical activation of the upper surface of the layer 12 is obtained by immersion of the plate 11 connected to the layer 12 in oxygen rich plasma 300 mtorr for 30 seconds the cap 13 is as such chemically activated due to immersion in a bath nh 3 28 h 2 o 2 h 2 o 1 1 5 for around one hour at 80 u00b0 c then rinsed in deionised water for two minutes the cap can also be dipped in a bath of sulphuric acid for example once step e.