An oven is disclosed having a first food preparation apparatus in the form of a convection heat source andor a steam production assembly andor a radiating heat source, and a second food preparation apparatus in the form of a smoking assembly. Each of the plurality of filaments includes scintillating particles dispersed within a thermoplastic polymer. A crystalline oxide semiconductor film is formed over and in contact with an insulating film whose surface roughness is reduced, whereby the oxide semiconductor film can have stable electric characteristics.