Abstract: A method of making an improved aluminum oxide (sapphire) gate field effect transistor wherein the capacitance-voltage characteristic of the transistor is improved by annealing the aluminum oxide at a temperature less than the growth temperature of the aluminum oxide. A transistor annealed at a temperature less than the growth temperature is provided wherein the threshold voltage is the same as if the transistor were annealed at a temperature greater than the growth temperature; the capacitance-voltage characteristic of the transistor exhibiting markedly diminished hysteresis by annealing at a temperature less than the growth temperature.

Abstract: A method is provided for the manufacture of a semi-planar silicon-on-sapphire composite comprising a sapphire substrate, an epitaxial monocrystalline silicon mesa formed adjacent the substrate and an epitaxial deposition of monocrystalline aluminum oxide surrounding the mesa. An essential step in the method is deposition of the aluminum oxide simultaneously adjacent the sapphire substrate and the monocrystalline silicon mesa whereby aluminum oxide formed adjacent the silicon mesa is polycrystalline and aluminum oxide deposited adjacent the sapphire substrate is monocrystalline. This enables the selective removal of the polycrystalline aluminum oxide adjacent the surface of the monocrystalline silicon mesa, thereby forming the composite.

Abstract: A method for making an apertured aluminum oxide substrate by selectively masking a sapphire wafer, depositing aluminum oxide adjacent the wafer and the mask, and removing the aluminum oxide deposited adjacent the mask and the mask, whereby an aperture is formed in the aluminum oxide. A composite is thus formed of an insulating substrate of monocrystalline sapphire with an insulating epitaxial layer of aluminum oxide apposed thereto, the epitaxial layer having an aperture therein which may be filled with an island of epitaxial silicon.