Microinstruments for submicron material studies
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Microinstruments for submicron material studies M. T. A. Saif a) and N. C. MacDonald School of Electrical Engineering and The Cornell Nanofabrication Facility, Cornell University, Phillips Hall, Ithaca, New York 14853 (Received 1 July 1997; accepted 13 May 1998)
We present two microinstruments for submicron scale material characterization. One of the instruments applies torsion on two single crystal silicon bars with square cross sections, 1 and 2.25 mm2 , until fracture. The maximum shear stress prior to fracture is found to be 5.6 and 2.6 GPa, respectively. The second instrument applies tension on a composite (aluminum-silicon dioxide) beam, 1 3 1.5 mm2 in cross section. The beam fails at 220 mN. In both the experiments, the samples are designed, patterned, and cofabricated with the instruments. The microinstruments’ small size, low thermal mass, vacuum compatibility, and built-in vibration isolation allow material characterization to be performed over a wide range of environmental conditions: high vacuum (electron microscopy and surface analysis), high humidity, high pressure, and high and low temperatures.
Ever decreasing size of microelectronic components has prompted considerable interest in mechanical characterization of materials at submicron scale. The scope of such characterization is, however, limited by the available instruments which are primarily macroscopic. The use of macroinstruments limits the minimum size scale of the samples, and poses difficulties in aligning and attaching samples to the instruments. Here, we develop, fabricate, and test microinstruments for submicron scale material studies. We provide two examples of such microinstruments: (1) a microinstrument that applies torsion on single crystal silicon (SCS) bars with 1 and 2.25 mm2 square cross sections, until fracture. Two identical instruments are used for the two torsion bars; (2) a microinstrument that applies tension on an aluminum-silicon dioxide composite beam, 1 mm wide and 1.5 mm thick. Figure 1 shows the microinstrument for torsion test and its schematic (top view). The instrument consists of two actuators, L and R, and the torsion test sample. Each actuator generates force by actuating 2000 interdigitated comb capacitors.1 It spans an area of 2 3 1 mm2 and is 10 mm deep. It is released from the substrate. It consists of a rigid backbone, supported by beams (springs) which originate from supports attached to the substrate. The backbone supports cantilever beams from which originate the movable comb capacitors. The fixed combs are attached to the substrate. When a voltage is applied between them, the fixed combs attract the movable ones. The actuator thus moves toward the fixed combs by bending the supporting beams, and applies force on the sample. The instrument is made by the SCREAM (single crystal reactive etching and metallization) process.2,3 a)
Current address: Mechanical and Industrial Engineering, University of Illinois, Urbana, Illinois 61801. J. Mater. Res., Vol. 13, No.
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