Semiconductor structure incorporating thin film transistors with undoped cap oxide layers

A field effect transistor (FET) structure, comprising:

• a) a first insulator layer containing at least one primary level stud extending through the layer;
• b) an undoped cap oxide layer disposed over the insulator layer, and abutting the upper region of each stud;
• c) a primary level thin film transistor (TFT) disposed over the undoped cap oxide layer, said TFT itself comprising:
• c1) doped polysilicon source and drain regions disposed over a portion of the cap oxide layer and over the exposed upper surface of the stud, wherein the source and drain regions are separated from each other by a channel;
• c2) a second insulator layer disposed over the channel, source, and drain regions;
• and
• c3) a transistor gate electrode disposed over a portion of the second insulator layer, and substantially self-aligned with the channel,
• wherein a protective, interfacial layer of doped polysilicon is disposed between the lower surface of the source and drain regions and the upper surface of the primary level stud, covering the surface of the stud;
• and
• d) a planarized dielectric layer disposed over the TFT.