Piezoelectric measurements using an atomic force microscope

This study explores the use of an atomic force microscope (AFM) to measure the piezoelectric effect in thin films. One advantage of this piezoelectric measurement method is its high lateral resolution. A large potential source of error in AFM piezoelectric measurements is an electrostatic interaction between the tip and sample. The effects due to the electrostatic interaction were quantified, and a new measurement approach was developed that minimizes this effect. This new approach involves measurements with conducting diamond-coated AFM tips which are in contact with a top electrode. Single point measurements of the piezoelectric constant were performed on thin film ZnO, nonpiezoelectric SiO₂, single crystal quartz, and thin film Pb(Zr_x,Ti _1-x)O₃ (PZT).; This new AFM piezoelectric measurement technique was used to examine the ferroelectric properties of PZT thin films. Both the phase and magnitude of the piezoelectric constant were imaged, and local piezoelectric hysteresis loops were measured. The shapes of the hysteresis loops of several PZT compositions provided further evidence that the AFM system was measuring the piezoelectric effect.; Piezoelectric images of PZT films revealed a micron-scale variation in the ferroelectric properties which was not observable by macroscopic polarization measurements. The AFM piezoelectric measurements were correlated with measurements using a double-beam interferometer system. An in-depth study was undertaken of polarization fatigue in tetragonal PZT films. A spatial variation in the fatigue properties was reflected in the piezoelectric images. In fatigued PZT, regions were measured with hysteresis loops shifted upward, some so much that both remnant polarization points exhibited a positive polarization. Measurement of the piezoelectric effect by AFM has been shown to be a valuable microscopic technique for characterizing thin films.