layer 13 b and the structural layer 12 b in the guard ring 120 can form a tightly closed structure with other portions thereof the structural layer 12 b is preferably a dielectric layer or a layer with dielectric function so that the guard ring 120 is not short circuited to the conductive layer 17 but it should be formed by a material other than that for the dielectric layer 20 for example the dielectric layer 20 can be made of silicon dioxide and the structural layer 12 b can be made of silicon nitride silicon oxynitride etc in a preferable embodiment the structural layer 12 b is made of undoped polysilicon for better process integration in the microelectronic device area 200 the conductive layer 17 can be electrically connected to the microelectronic devices through interconnection formed by the contact layer 13 c the metal layer 14 etc fig4 illustrates the third embodiment of the present invention in this embodiment the contact layer 13 a is also used as the conducting wire in the mems device area 100 and the structural layer 12 a such as an undoped polysilicon layer or a layer made of any other material capable of providing electrical isolation is provided as the electrical isolation between the contact layer 13 a and the substrate 11 yet the cross area interconnection of the mems device and the microelectronic device is achieved by a well 18 in the substrate 11 the well 18 for example includes an n type well 18 a and a heavily doped n well 18 b above the n type well 18 a and the substrate 11 for example can be a p.