Modification of the Drain Current on a Metal-Oxide-Semiconductor Field-Effect Transistor with Ferrite Gate Oxide

(Mn0.24Zn0.09Fe0.67)Fe2O4 (MZF) thin films were grown on Si substrates without and with MOSFETs by pulsed laser deposition (PLD). The deposition of MZF films was carried out by the following two procedures: (1) “1-step deposition,” in which 300-nm-thick MZF film was deposited at 800°C, and (2) “2-step deposition,” in which 10-nm-thick MZF film was deposited at 800°C and 300-nm-thick MZF film was deposited at 27°C followed by post–deposition annealing at 800°C for 1 h under an O2 pressure of 1.3 × 10-3 Pa. For both preparation procedures, epitaxial growth of MZF thin film with (111)-orientation was observed. The saturation and remanent magnetization of MZF thin film depends on the preparation procedure, and the highest magnetization was obtained for film prepared by 1-step deposition. A microfabrication process in which preparation of MZF thin film was limited to the gate areas of Si-MOSFETs was attempted, using a combination of the abovementioned processes and etching processes: (1) 1-step deposition followed by wet chemical etching, and (2) 2-step deposition. In the 2–step deposition, a lift-off process was inserted before 27°C deposition. ID-VDS characteristics before and after magnetization of the MZF thin film was measured. As a result, modification of the drain current was observed. The modification was brought about by the Lorentz force, which was caused by the magnetic field induced by remanent magnetization. For MZF/Si-MOSFETs fabricated by 1-step deposition, the modification of the drain current was on the order of several μA when the gate voltage was 5 V. For MZF/Si-MOSFETs fabricated by 2–step deposition, the modification of the drain current was on the order of a few dozen pA when the gate voltage was 0.8 V. It was also clarified that the degree of modification increases with decreasing gate length. These results suggest that this principle could be used in a novel nonvolatile memory application.