One of rational way to measure a force is sensing a elastic deformation. If you need to measure the more micro force, you have to use springs having the lower spring constant. However, the limitation on measuring the micro force will arise from the vibration by external noise. Vibration isolators are often used to reduce the mechanical noise. Another effective way to reduce the mechanical noise is increasing resonance frequency by miniaturization as shown in Fig. 1. When the resonance frequency increases it becomes easier to dump the vibration. Therefore, microdevices are key to enhancing micro/nano science.
Fig. 1 Relation between resonance frequency and displacement
An FIB was used to create silicon cantilevers used for tribology testing. To make the springs, we started with a rectangular single-crystal silicon beam (about 25 um x 50 um x 300 um), and made two types of silicon cantilevers: parallel leaf spring (Fig. 2), and double parallel leaf spring (Fig. 3). Each leaf spring had a block at one end of the spring, and the sliding surface of each block contacting with the asperity was a plane. The block for the parallel leaf spring by a pair of parallel plates. Thus, each plate structure could deform perpendicular to the sliding plane (Fig. 4). For the double parallel leaf spring, we created some mounds on the backside of the block, where the laser beam is reflected. When the friction force acts on the block during scanning, the spot where the laser beam strikes the spring moves on the mound and the angle of the reflected laser beam changes. This lateral motion of the block can thus be detected by an AFM system. We then calculated the friction force by using the spring constant and the detection sensitivity of the AFM. We could change the sensitivity by selecting mounds of different radius of curvature (Fig. 5).
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Fig. 4 Schematic of deformation of parallel leaf spring. |
Fig. 5 Schematic of detecting friction force by double parallel leaf spring. |
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We have designed and developed z-stage driven by comb actuators. The stage consists of a traveling table, suspensions and a comb actuators (Fig. 6). The stage lift up the traveling table without a lateral displacement. The key to realizing three-dimensional motions in the stages is in the geometry of the suspensions, which incorporate a pair of leaf springs inclined at 45 degrees against the substrate. The stage was fabricated on an SOI (silicon on insulator) wafer (Fig. 7). The relation between the motion of the traveling table and driving voltage was examined for the stage. The lift-up amount increased with higher driving voltage. The maximum lift-up amount was 1.9 mm when the tilting angle was less than 0.1 degree (Fig. 8). The resonance frequency was 20 kHz (Fig. 9).
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last update October. 10.
2001 |
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Primal Scientist: Yasuhisa ANDO |