Connected Lead Zirconate Titanate Nanodot Arrays for Perspective Functional Materials

We describe the fabrication of lead zirconate titanate (PZT) nanodisc arrays isolated by a polymer layer and contacted with a top electrode. PZT thin films were deposited by multitarget sputtering onto a platinum/titanium bottom electrode and structured by means of nanosphere lithography. To guarantee short-circuit-free deposition of a top electrode, the space between the nanostructures was filled by a polymer. Two approaches for the filling are demonstrated: (a) imprinting and (b) skim coating. Single nanodiscs embedded in a flexible polymer matrix have two major advantages. First, taking into account the flexibility of the matrix, they can vibrate in lateral direction and, second, due to shrinking to the nanoscale, predominant directions of the polarization form, such as vortex- or bubble-like domain patterns. Piezoresponse force microscopy was performed on patterned and nonpatterned samples with and without a top electrode to check the local piezoresponse. Comparison of the different samples revealed an increase in lateral piezoactivity for patterned samples with Ni/Cr electrode while the out-of-plane piezoresponse remained constant. Gold electrodes limit the piezoresponse in both measured directions. 1. Introduction Ferroelectric thin films are of important interest in micro-electromechanical systems (MEMS). Especially PZT films combined with a standard CMOS process result in novel sensor and actuator devices like accelerometers [1], pressure sensors [2], motors [3], and ultrasonic transducers [4]. For further improvement of these devices, current research looks for novel functional materials with enhanced sensitivity or additional properties like flexibility and elasticity. Therefore, nanopatterning is an ideal technique to improve properties of ferroelectric materials. Enhanced material coefficients in ferroelectric nanopowders were already found in the 1950s [5]. But still today the reasons for the increase in pyro- and piezoelectric coefficients are under discussion. Taking advantage of this effect offers a large variety of perspective applications. Recently, remarkable increases in the local piezoresponse of nanopatterned PZT films were observed, both in the plane as well as out of the plane. This effect is mainly driven by the aspect ratio of the nanostructures [6]. More precisely, the enhancement is caused by the breakup of grains in order to compensate the stress induced by the polarization field and depends on the lateral dimensions and aspect ratio of the structures. By connecting such nanostructures equal in polarization and piezoresponse