Methods of forming floating-gate ffram devices

Abstract

Methods of forming floating-gate ferroelectric random-access-memory (FFRAM) devices include the steps of forming vertically integrated FFRAM unit cells having floating-gate transistors and access transistors positioned at different levels on a semiconductor substrate to increase the density at which the unit cells may be integrated. Preferred methods include the steps of forming a first transistor having opposing floating and control gate electrodes, at a surface of a semiconductor substrate, and then forming a first insulating layer having a first contact hole therein, on the first transistor. The first transistor comprises a layer of ferroelectric material between the floating and control gate electrodes, which can be polarized in respective first and second states to retain logic 1 and logic 0 data. Steps are then performed to form a first electrical interconnect (e.g., conductive plug) in the first contact hole and electrically coupled to the control gate electrode. Then, a series of steps are performed to form a vertically integrated second transistor on the first insulating layer. Here, the second transistor is formed as a field effect transistor having a drain region electrically coupled to the control gate of the first transistor by the first electrical interconnect. The steps of forming a second transistor may include the steps of forming a silicon-on-insulator (SOI) substrate on the first insulating layer, forming a gate electrode on the silicon portion of the SOI substrate, and then forming source, drain and channel regions in the silicon portion of the SOI substrate.