Piezoelectric coefficient measurement of AlN thin films at the nanometer scale by using piezoresponse force microscopy

In this research, aluminum nitride (AlN) thin films were fabricated on Au/Si3N4/Si structure by using a radio-frequency sputtering system. The film's properties were measured using high-resolution X-ray diffraction, atomic force microscopy, and piezoresponse force microscopy (PFM) with a lock-in-amplifier. The value of the full width at half maximum indicated that the AlN thin film was well formed along the c-direction and had a highly (002) preferred orientation. Through the PFM measurements, the images of the piezoelectric dynamics were confirmed, and the strain-electric field hysteresis loops for each indexed grain was measured using the conductive tip of the PFM without a top metallic electrode layer. From these loops and for each grain, the strain behavior and the effective piezoelectric coefficient d33eff were measured at the nanometer scale, and the real piezoelectric coefficient d33 was calculated from the d33eff. The d33 value was found to lie in the range 1.33 to 8.93 pm/V along the grain positions, and the average d33 value was calculated as 4.81 pm/V.