Fabrication and characterization of micromachined quartz-crystal cantilever for force sensing

A highly sensitive thin rectangle cantilevered resonator of AT-cut quartz crystal with the capability of self-sensing using the piezoelectric effect has been developed for force and nanometric sensing. The fabrication and characterization of quartz crystal cantilever-shape resonators are reported. The thin cantilevers along the electrical axis (the x-axis) of the quartz crystal have metal electrodes at both sides and were fabricated by deep reactive ion etching using a Ni mask pattern with thicknesses of 15-27 νm. Its force sensing principle using the quartz cantilever is based on the resonant frequency changes in the case that an external force is applied. Shear vibration in the direction of the electrical axis can be piezoelectrically excited, which was characterized by impedance measurements. Despite the weak electromechanical coupling, flexural and torsional vibrations can be excited and piezoelectrically detected. The detectable minimum noise of the piezoelectric detection was about 0.08 nm Hz^-0.5 and a sensitivity of 8 mV nm^-1 of the third flexural mode was achieved.