Trench and compact structures for dRAMs

There have been a large variety of trench based dRAM cells proposed in the last few years. This paper attempts to establish the requirements of a 4Megabit cell and classify the various trench based approaches. The original trench capacitor and its limitations are described and three classes of trench capacitors that attempt to overcome these limits are described. The first is the inside out capacitor where the roles of the storage electrode and the cell plate are interchanged. In the second class the trench serves to isolate as well as increase the available storage area. The third type builds a two concentric plates inside the trench. These can be attached to a planer transistor or a trench transistor to form a large number of combinations. These concepts are graded according to probability of success.