Coactive stresses in MEMS and NEMS based on periodically bent crystals

A variety of MEMS and NEMS are base on chemical film deposition onto a ceramic substrate. Generally, the substrate consists of a Si (silicon) or Ge (germanium) plate. One of the most used chemical processes is low-pressure chemical vapor deposition (LPCVD). Through such a technology a wide class of MEMS/NEMS can be realized, with particular reference to crystalline undulators (CU)s [1]. CUs (Figure 1) are devices to generate intense coherent and collimated electromagnetic radiation across the UV and X-ray ranges. Electrical charges are forced to oscillate in the electromagnetic field of the crystalline lattice thus emitting electromagnetic radiation.The present study concerns the effects induced by coactive stresses on displacement and stress fields induced in the system by thermal loading due to the LPCVD process. The aim of the study is to find the optimum geometrical parameters (a, p, hf) suitable to obtain a CU. By imposing equilibrium conditions and perfect adhesion between the thin films and the substrate, a singular integral equation is derived. A closed-form solution is achieved by expanding the unknown interfacial shear stress fields in Chebyshev series. This leads to an algebraic system which solution allows assessing the stress, strain and displacement fields in the CU. REFERENCES: [1] Guidi V, Lanzoni L, Mazzolari A, et al. Design of a crystalline undulator based on patterning by tensile Si3N4 strips on a Si crystal. Appl Phys Lett 2007; 90(11): 114107