Generalized MEMS lot monitoring using fully-integrated material and structure mechanical analysis

Abstract Industrialization of MEMS devices requires specific tools to verify that their mechanical properties and motions obey the designer’s intent. Accordingly, the following work investigates new on-chip mechanical laboratories that will allow systematic MEMS manufacturing lot monitoring. The first part of the paper investigates mechanical properties of micrometer thick polysilicon films deposited by low pressure chemical vapor deposition (LPCVD). A new standard method allowing direct and immediate measurement of polycrystalline silicon mechanical properties is introduced. Micrometer size polysilicon samples are actuated on the wafer level using electrostatic probing of high driving force electrostatic actuation cells that are monolithically connected to the head of the specimens. Polysilicon fracture strength ranging from 1800 up to 2000 MPa is preliminary observed using parallel actuation of distributed bending test units. Very first micrometer size self-actuated tensile test units are introduced afterwards using arrays of 50 μm ×50  μm electrostatic actuation cells that recently pointed driving forces as high as 1260 μN (e.g. 400,000 μN/mm 2 ). Experiments show that high-efficiency microactuator arrays, such as proposed in this paper, allow crack propagation to be initiated for a first time within tensile polysilicon specimens having a cross-section 1000 times smaller than that of a hair (e.g. 3 μm 2 ). Self-actuated tensile fracture of the order of 1800 MPa is reported using 0.075 mm 2 tensile units, leading to ideal testing configurations down to the micrometer scale, without human handling. The second part of the paper similarly investigates fully-integrated test units dedicated to the mechanical characterization of Φ 500 μm MEMS-based microactuators. Very first acquisition of torque/speed characteristics showing a locking torque on the order of 1.2 μN m with a maximal output mechanical power of 130 nW is also discussed as an illustration of the proposed monitoring methodology.