Dresden 2009 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 37: ZnO: devices

HL 37.6: Vortrag

Mittwoch, 25. März 2009, 17:45–18:00, POT 51

Ferroelectric thin film transistors based on ZnO/BaTiO₃ heterojunctions — •Brandt Matthias, Heiko Frenzel, Holger Hochmuth, Michael Lorenz, and Marius Grundmann — Universität Leipzig, Institut für ExperimentellePhysik II, Leipzig, Germany

ZnO and BaTiO₃ (BTO) are transparent oxide materials. ZnO is a semiconductor showing a spontaneous electric polarization and is very easily doped n–type. BTO is an insulating ferroelectric at room temperature. The ability to control the free carrier concentration in the ZnO by the polarization of the BTO can be used to develop ZnO/BTO based ferroelectric field effect transistors, thus demonstrating fully transparent non–volatile memory elements.
We have grown epitaxial BTO/ZnO heterostructures by pulsed laser deposition on lattice matched SrTiO₃ and SrTiO₃:Nb substrates. The electrical properties of ZnO/BTO heterostructures have been investigated by current-voltage measurements, showing that the BTO layer is highly insulating (I_l<10⁻⁹ A/cm² at 5V). Field effect transistors were fabricated with an on–current of up to 6× 10 ⁻⁵ A and an on/off ratio of 10⁶. The FETs are normally on. The structures could be programmed by a positive gate voltage pulse and erased by a negative gate voltage. The ratio in the source–drain currents in both states could be as high as 1000, depending on the gate voltage at read–out. The effect was reproducible in repeated switching cycles, showing the suitability of the structure as a memory device.