2.3.3 Vertical Transistors

MOSFETs which are used as access transistors in DRAM cells need a particularly small footprint to allow high integration densities [29]. The DRAM capacitor, which requires a capacitance of approximately 50fF to allow practicable retention times, is usually built as a trench capacitor. One approach by which the footprint is reduced drastically is to turn the access transistor into the vertical direction directly above the trench capacitor [30,31,32,33,34,35].

A. Gehring: Simulation of Tunneling in Semiconductor Devices