Nonlinear Electrical Transport Properties And Mobility In Colossal Magnetoresistance (CMR) Field-effect Transiators (FETs)

In recent years, the study on colossal magnetoresistance (CMR) materials, as well as their application becomes more and more popular in magnetism and magnetic materials fields. Up to now, CMR materials have previously been studied for various purposes, which were mainly focus on the colossal magnetoresistance decrease and magnetotransport properties caused by magnetic field. The full study on electric-field (ER) effects coupled with magnetic field (MR) effect and the charge carrier mobility in these materials at electric field seems to be lacking.The mobility becomes compromised with increased charge density. As the device size is reduced with the trend for higher device packing density following the Moore's law, the problem with the mobility becomes compounded. In particular when the size of the device goes down to a nano-meter level it is highly worthy of discussing if silicon is still the best choice as a semiconductor material.People are trying to fabricate functional apparatus using new semi-conductor materials with certain function in recent years. Perovskite oxide is one kind of these materials, which provides us so many physical pictures and fascinating properties. But strong reciprocity among electron- crystal lattice ,electron- electron and spin-spin in these materials leads great reduction of carrier mobility ,which blockes the applications of these materials in the field of electronic apparatus.Recently, the ferroelectric field effect transistor(FET)based on epitaxial La0.7Ca0.3MnO3 thin film heterostruture was reported. It was found the carrier density of the semiconductor varies widely with both the ratio of Ca︰Mn and oxygen stochiometry, and so the channel could be"tuned"by the ferroelectric gate.In order to study electric-field effects in La_0.8Ca_0.2MnO₃(LCMO) CMR film, an inverted metal-insulator-CMR field-effect transistor(CMR-FET) structure was chosen. This arrangement has an advantage that CMR film does not influence the structural and dielectric properties of the gate insulator-PZT, as would be the case if the PZT were grown on top of the CMR film. We carried out a quatitative investigation of carrier effective mobility and differential mobility under low and high electric field in La_0.8Ca_0.2MnO₃/PbZr_0.2Ti_0.8O₃ field-effect-transistors through the measurement of the current-voltage relationship and the capacitance-voltage relationship over a wide range of temperature. This result demonstrates, for the first time, that under a high reverse electric field that significantly narrows the thickness of the LCMO channel, a MOSFET with a material with MIT can operate with a very high mobility.