Abstract: The semiconductor substrate comprises a silicon substrate 10, a silicon germanium layer 12 formed on the silicon substrate; and a silicon layer 14 formed on the silicon germanium layer. At least one of an isotope composition ratio of one Si isotope and an isotope composition ratio of a Ge isotope of at least one of the silicon substrate, the silicon germanium layer and the silicon layer is above 95%. In at least one of the silicon substrate, the silicon germanium layer and the silicon layer, at lest one of an isotope composition ratio of one Si isotope and an isotope composition ratio of one Ge isotope is set higher, whereby the heat can be scattered in the direction horizontal to the substrate plane. Thus, the semiconductor substrate can have higher heat radiation.

Abstract: The present invention provides a highly reliable liquid bearing unit which can, by securely repelling a lubricant by an oil repelling film, prevent the lubricant from leaking and a magnetic disk device mounted therewith. In a case where the lubricant contains a constituent of at least one of a hydrocarbon-based oil and an ester-based oil and the oil repellent film is a film of at least one of a fluorine base and a silicone base, surface tension of the lubricant is made greater than the critical surface tension of the oil repellent film by 5 mN/m or more. Moreover, when the lubricant is a fluorine-based lubricant, surface tension of the lubricant is made greater than the critical surface tension of the oil repellent film by 8 mN/m or more.