A millinewton microloading device

We present a new microelectromechanical device that can apply a compressive or tensile force on the order of a millinewton quasistatically by electrically actuating a set of comb capacitors. The same capacitors can be used to sense the displacement of the device by recording the change of capacitance. The device is fabricated using the SCREAM (single-crystal reactive etching and metallization) process developed at Cornell. The functionality of the device is demonstrated by compressing two slender bars and buckling them. The buckling experiment is then used to calibrate the load generated by the device and the spring constant. The device can be applied to the characterization of materials as their size is reduced to the sub-micron scale. An assortment of test samples can be patterned, cofabricated, and attached to the device, including 20 nm diameter tips, composite beams of thin films, thin-film plates (e.g., polysilicon) and other more complex micromechanical structures. It can also be coupled with other devices to improve their performance, such as tuning resonance frequencies by applying tension or compression. The material samples or other devices can be integrated, i.e., designed, patterned, and cofabricated with the loading device, thus avoiding the problem of attachment and alignment. The device's 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.