The layer in a CCD chip that contains the electron gates is the:

• A. Polysilicon layer
• B. Silicon dioxide layer
• C. Metal layer
• D. Glass layer

Answer: (A)

In a CCD, the gates that control how charge is moved are made as a polysilicon layer. This polysilicon is patterned into the individual gate electrodes and sits atop a thin silicon dioxide insulating layer on the silicon substrate. By applying voltages to this polysilicon gate layer, the electric potential wells that trap and move electrons are created and steered along the device. The silicon dioxide layer is simply the insulating layer beneath the gates, metal layers, if present, are usually for wiring, and a glass layer isn’t part of the CCD gate structure. So the layer that contains the electron gates is the polysilicon layer.