Nonvolatile floating gate transistor structure

摘要

A field effect transistor includes a source region, a drain region, and a channel region formed in a semiconductor substrate and a floating gate and a control gate formed over the substrate. An opaque cover (typically aluminum) is formed over but electrically insulated from the transistor to prevent light from striking and affecting the electrical charge on the floating gate. The periphery of the opaque cover ohmically contacts the semiconductor substrate, thereby limiting the amount of light reaching the floating gate, except where the source and drain extend inwardly beyond the periphery of the opaque cover. The control gate extends over a portion of the substrate surrounding the transistor, and helps hinder light from reaching the floating gate. In addition, semiconductor material formed concurrently with the control gate extends over the source and drain regions, thereby providing additional shading.