First and second wells are formed in a semiconductor substrate. First and second trenches in the first second wells, respectively, each extend vertically and include a central conductor insulated by a first insulating layer. A second insulating layer is formed on a top surface of the semiconductor substrate. The second insulating layer is selectively thinned over the second trench. A polysilicon layer is deposited on the second insulating layer and then lithographically patterned to form: a first polysilicon portion over the first well that is electrically connected to the central conductor of the first trench to form a first capacitor plate, a second capacitor plate formed by the first well; and a second polysilicon portion over the second well forming a floating gate electrode of a floating gate transistor of a memory cell having an access transistor whose control gate is formed by the central conductor of the second trench.