Study On In-Situ TEM Tensile Tests On SCS Nanostructures

Being the most important material in micro-electronics and microelectromechanical systems, the single crystalline silicon (SCS) is still the research hot in nano-electronics and nano-electromechanical systems, as the trend pushes technology to nanoscale (1nm-100nm). It is necessary to understand the mechanical behavior of nanoscaled SCS structure. While the experimental studies are not easy to carry on due to three main difficulties in: 1.nano-manipulating on nano-sturctures; 2.force performing and measuring on nano Newton scale; 3.measuring nano-scale strain.This work is the first try on in-situ tensile tests on SCS nano-sturctures in TEM, by combining MEMS and TEM. The method of combining MEMS and TEM realize TEM observation of the nano-structures during the on-chip tensile tests. The nano-scaled morphology and atomic figure can be observed real time. The SAD will give useful informations on material structures when they are under tension.In this work, a new MEMS tensile-testing chip and its TEM holder with electrodes are designed and manufactured. The MEMS chip includes a SCS nano-beam (sample), a force sensor beam, comb drives, electron window and etc. It is processed by bonding a SOI wafer and a standard wafer, the SOI wafer side being 0.1mm thick and with SCS nanobeam, combdrives and force sensor beam on it, the standard wafer side being 0.4mm thick and with the electron window in it. The processing is of bulk silicon process method. The chip is fixed into a recess in an electric ceramic plate. The electrodes on them are connected by wire-bonding. The ceramic plate is fastened on the metal structures at TEM holder head. Wires go through a feedthrough into TEM holder head and are solded to the electrodes on ceramic plate to ensure power supply to MEMS chip.During in-situ tensile tests in TEM, the combdrives pull the SCS nanobeam, whose movements are observed real time through the electron window in TEM. The tensile force can be calculated by observing the bending of the force sensor beam. Tests on a 90nm-thick, 9.3μm-board and 33μm-long SCS nanobeam show its Young’s modulus along <110> to be 180GPa and the experimental error is of 9.3%, with the greatest one being from the processing on force sensor beam and SCS nanobeam.A simple modal on surfaces effects shows that for the nanobeam with thickness much greater than that of its surface layers, the Young’s modulus measured by tensile testing and resonating/bending testing are same as that of the bulk value. While as the thickness decreases, the value measured by resonating/bending tests will show its tendency of decreasing more quickly. The surfaces influences are not same for tensile testing and resonating/bending testing. That is the reason why the Young’s modulus measured here shows no size effect by tensile testing on a 90nm-thick SCS nanobeam.