A portion of the control gate could extend into a trench formed into the substrate, wherein the drain region is formed underneath the trench, and the channel region has a first portion extending along {TAIL ~ the trench sidewall} and a second portion extending along {HEAD ~ the substrate surface} 
A portion of the control gate could extend into a trench formed into the substrate , wherein the drain region is formed underneath the trench , and the channel region has a first portion extending along { TAIL ~ the trench sidewall } and a second portion extending along { HEAD ~ the substrate surface }
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