Preparation and evaluation of temperature-sensitive magnetic film with low Curie temperature

Up to now, only bulk materials and thick films were available for use as temperature-sensitive substances. However, due to the high heat capacity of these substances, their sensitivity is too low for the detection of minute temperature variations. General trends toward the miniaturization and weight reduction of electronic equipment necessitate development of thin films having magnetic properties. No technology for the preparation of temperature-sensitive magnetic thin: films (TMF) has existed so far because of difficulties related to the adjustment of the mixture ratio of TMF materials composed of Fe, Mn, and Zn oxides. The authors investigated a method of fabrication of TMF by annealing of the film formed by the sputtering of a target consisting of temperature-sensitive ferrites with low Curie temperature. This method involves a two-step processing: depositing the metal components of temperature-sensitive ferrites on a substrate by sputtering and a high-temperature annealing treatment performed in a flow of argon gas in a tank containing oxygen. As a result, a ferrite thin film (thickness 1.5 mu m) with spinel structure can be fabricated. The TMF characteristics closely reproduce parameters of the temperature-sensitive ferrites used in the target. The TMF so obtained also have an exceptional temperature dependence and a low heat capacity, thus providing for a prompt response to minute temperature variations of the order of 10(-1) degrees C. Therefore, the TMF are expected to find use in such applications as pyromagnetic sensors, optimized artificial sensors, and biosensors. (C) 1999 Scripta Technica, Elects Eng Jpn, 129(4): 17-23, 1999.