薄膜与小尺度材料及力学性能研究组

Analysis, simulation and fabrication of MEMS springs for a micro-tensile system

Rui Liu, Hong Wang, Xueping Li, Jun Tang, Shengping Mao and Guifu Ding
Key Laboratory for Thin Film and Microfabrication Technology of Ministry of Education, National Key Laboratory of Micro/Nano Fabrication Technology, Research Institute of Micro/Nano Science and Technology, Shanghai Jiao Tong University, Shanghai 200240, People's Republic of China
E-mail: wanghongsjtu@yahoo.com.cn

Characterization of Deformation Behaviors and Elastic Moduli of Multilayered Films in Piezoelectric Inkjet Head

Seong-Gu Hong   Minho Kim   Soon-Bok Lee   Chong Soo Lee

Dept. of Mater. Sci. & Eng., Pohang Univ. of Sci. & Technol., Pohan

Abstract

A bulge testing system was developed to mechanically characterize the deformation behaviors and elastic moduli of multilayered films, mainly composed of polycrystalline silicon (polysilicon) and lead zirconate titanate (PZT), used in a multilayer actuator of a piezoelectric inkjet head. In the tests, commercial inkjet heads including a few tens of multilayer actuators were directly pressurized by air, and the corresponding deflections were measured via full-field optical measurement techniques. An analytic solution derived from a thin-plate theory and finite-element analysis were used to describe pressure-deflection behaviors of films, and the results were compared with the experimental data to evaluate the elastic modulus of individual film. The results showed that the elastic moduli of polysilicon and PZT films are ~110 and ~49 GPa, respectively. These values were consistent with the nanoindentation results. For polysilicon films, about 30% reduction in elastic modulus, compared with that calculated from single-crystal elastic constants, was observed, and this was most likely attributed to the presence of microdefects like voids and microcracks at grain boundaries between columnar grains.

Keywords: Bulge test   full-field optical measurement   multilayered films   piezoelectric inkjet head

Micron-Scale Friction and Sliding Wear of Polycrystalline Silicon Thin Structural Films in Ambient Air

Alsem, D. H.   Dugger, M. T.   Stach, E. A.   Ritchie, R. O.

Abstract

Micron-scale static friction and wear coefficients, surface roughness, and resulting wear debris have been studied for sliding wear in polycrystalline silicon in ambient air at micro-Newton normal loads using on-chip sidewall test specimens, fabricated with the Sandia SUMMiT V$^{rm TM}$ process. With increasing number of wear cycles friction coefficients increased by a factor of two up to a steady-state regime, concomitant with a decay (after an initial sharp increase) in the wear coefficients and roughness. Wear coefficients were orders of magnitude smaller than reported macroscale values, suggesting that the wear resistance is higher at micrometer dimensions. Based on our observations, a sequence of micron-scale wear mechanisms is proposed involving: 1) a short adhesive wear regime ( $≪ 10^{4}$ cycles), where the oxide is worn away and the first silicon debris particles form and 2) a regime dominated by abrasive wear, where silicon particles (50–100 nm) are created by fracture through the grains ( $sim$500 nm). These particles subsequently oxidize and agglomerate into larger debris clusters, while “ploughing” by this debris leads to abrasive grooves associated with local cracking events rather than plastic deformation.

Keywords: Friction   microelectromechanical systems (MEMS)   silicon   thin films   wear