The difference of the gates in FET

[Quhe]

I noticed that there are different types of gate in FET devices. one is the gate that locates only above or below the channel; the other one is the gate that locates over all the device (that is not only the channel but also source and drain).
Does anyone know the difference of these two? Or is there any paper about these topics?

[zh]

In real FET devices, the gate mostly locates above or below the channel.