A static random access memory cell based on a thin capacitively coupled thyristor device.

摘要

During the past two decades, processing speeds have increased by three to four orders of magnitude while DRAM random access speed has increased by less than an order of magnitude. The huge gap between the speed of processors and memory can be addressed by faster technologies such as SRAM, but the use of conventional SRAM is limited by the fact that it is an order of magnitude less dense than DRAM. The processor-memory performance gap has become the critical bottleneck in many applications, and the speed-density trade-off between SRAM and DRAM poses a significant quandary faced by chip and system architects.; In this work, a novel negative differential resistance (NDR) based SRAM cell (called T-RAM) is introduced. T-RAM addresses the memory bottleneck by providing DRAM-like densities at SRAM-like speeds. The area of a T-RAM cell is less than one tenth the area of a conventional SRAM cell and equal to the area of a DRAM cell. The speed of a T-RAM cell is comparable to state-of-the-art SRAMs. Furthermore, the fabrication process for T-RAM is fundamentally compatible with mainstream CMOS.; A T-RAM cell is based on a thin capacitively coupled thyristor (TCCT) structure that uses a novel gate-assisted switching mechanism. In this thesis, the basic concept and the characteristics (both DC and transient) of a TCCT device are discussed. The fabrication of experimental prototypes of TCCT devices with planar NMOSFETs (the two components of T-RAM cells) are also presented. Our experimental results for T-RAM cells show a record-low standby current among NDR-based SRAMs that is less than 10pA/cell and a switching speed of about 5ns. The proposed Read/Write operations of a T-RAM cell and its gate-assisted switching mechanism are experimentally verified. The thermal stability of a T-RAM cell is also discussed via device simulations and experimental measurements. Compared to other types of NDR-based memories, T-RAM shows a much better thermal stability that can be further improved by sacrificing the cell standby current.