BENDING RESPONSE OF A 100nm THICK FREE STANDING ALUMINUM CANTILEVER BEAM M. Taher A. Saif and Aman Haque Mechanical and Industrial Engineering, University of Illinois 1206 West Green Street, Urbana, IL 61801, saiffuiuc.edu ABSTRACT A micro instrument is developed to apply force on free standing cantilever samples with suborm thickness. The objective is to study the effect of small thickness on the strength of materials when subjected to bending. The instrument consists of a MEMS actuator, 2mm x 3mm in size, and 20pm deep. It is employed to study an annealed Al cantilever sample, ll0nm thick, 2[im wide and 15tm long, fabricated by evaporation. The sample yields at 841MPa during the first cycle of loading. It is then unloaded and reloaded, when yielding occurs at 1200MPa. To the best of our knowledge, this is the first reported experiment on free standing submicron metal film subjected to bending. INTRODUCTION It is generally accepted that materials' behavior depends on its characteristic lengths, such as grain size and distance between obstacles for dislocation motion [1]. For example, yield strength of Al increases as the grain size decreases [2]. Materials strength may also depend on the size of the specimen, [3, 4], such as hardness increases with decreasing inden- ters size. Several models have been proposed to relate materials strength with characteristic size. For example, Hall-Petch equation relates yield strength with grain size [5, 6]. The effect of the sample size on strength has been accounted for by introducing a characteristic length and by relating stress with strain and the strain gradient [4, 7]. More recently, a mechanism based strain gradient plasticity theory has been proposed [8] to account for the size effect on strength. A major difficulty in exploring the dimensional effect on strength is experimentation with small samples, such as free standing thin films. The difficulty lies in the instrumentation that can treat small samples. Only a few of such experiments have been carried out. For example, strain gradient effects have been studied in [4] by twisting a copper wire 12-30pnm in diameter, in [9] by bending Ni foils, 12-50 pim thick, around a small diameter cylindrical mandril. These experiments, as well as nanoindentation experiments [10], reveal the strain gradients effects on strength. In this paper we develop microinstrumentation, based on MEMS (micro electro mechan- ical systems) technology, to study free standing films with thickness of micron to submicron dimension subjected to bending. The instrumentation is small and allows insitu experi- mentation in analytical chambers such as SEM and TEM under different environmental conditions to investigate the mechanisms of strengthening. The instrument is applied to study ll0nm thick free standing Al film. A significant increase in strength has been ob- served. MICRO INSTRUMENTATION Figure 1 shows the schematic of the microinstrument and the sample. The instrument consists of a MEMS electrostatic comb drive [11] actuator fabricated by the SCREAM process [12]. The structure of the device is made from single crystal silicon (SCS) coated by a thin layer (.25 tim) of silicon dioxide and Al. The actuator is 20PiM deep, and spans an area of 2mrm x 3mm. The interdigitated comb drives are 2 pim wide and have a gap of 2.5 frm between each other. The movable part of the actuator, consisting of a rigid 207 Mat. Res. Soc. Symp. Proc. Vol. 594 © 2000 Materials Research Society