Ultra-low voltage ferroelectric electron emission from lead zirconate titanate thin films with nanostructured top electrodes

Electron emission from thin ferroelectric Pb( Zr 0 . 4 Ti 0 . 6 ) O 3 films is demonstrated reaching emission current densities of up to 3 × 10 - 8 A cm - 2 for pulsed excitation voltages of 60 V. Nevertheless, the emission process sets in at voltages as low as 10 V. Thin lead zirconate titanate (PZT) films were prepared with a structured top electrode, which exhibits nanometer-sized regularly arranged apertures. The emission current was measured under UHV conditions by both a single electron detector for small emission currents and an amperemeter for larger currents. The voltage dependent polarization state within the emission apertures was imaged using piezoresponse force microscopy and revealed that an increased fraction of the free surface area is switched by an increased applied voltage. This shows that the emission process is strongly correlated to the switching of ferroelectric polarization. Moreover, with the help of a metal grid in front of the detector, the maximum kinetic energy of emitted electrons was investigated and found to be limited by the excitation voltage, only.