Ferroelectric field effect studies at low temperatures

Abstract

The ferroelectric field effect has been studied experimentally at low temperatures (300°K > T > 78°K) using n type tin oxide films deposited on polished ferroelectric ceramic (PZT) substrates. It is shown that the film, in its enhanced state, possesses the characteristics of a degenerate semiconductor with the Fermi level 0.60 eV above the conduction band edge. In the depleted state (high resistance) the Fermi level can be as much as 0.28 eV below the conduction band edge. There is evidence of a trapping state that degrades the field effect transition at temperatures below ∼183°K and at 78°K there is only a very small field effect transition even though the substrate switches more polarization charge than at room temperature. The depleted state instability is shown to be due to a thermally activated process with the high resistance being relatively stable with time for temperatures below 253°K.