The New SOI-Based Memory Technology

In the electronics industry today there are two commonly used high-speed memory types: static RAM (SRAM) and dynamic RAM (DRAM). Traditionally, SRAM embedded memory has been the designer's choice for fast memory, but since a typical SRAM bitcell is comprised of six transistors, that benefit comes at the expense of cost and silicon area. Embedded DRAM (eDRAM), whose smaller bitcell is comprised of a single transistor and single capacitor, offers a much lower cost option, but has higher latency and is typically used further from the processor. While DRAM is fundamental to electronic systems, it does have its limit — namely, its inability to scale to accommodate the migration to smaller, and therefore more advanced, process geometries. This limitation is further complicated by the fact that new application areas for memory are fast appearing, fueled by the popularity of digital home appliances and next-generation mobile devices, the digital convergence of electronic goods and telecommunications, and ever evolving media content.

DRAM Scaling Issue

Given its current roadmap, DRAM will soon reach its scaling limit due to the difficulty in shrinking its capacitor. Traditional SRAM will also face problems due to its instability at smaller process geometries. There is another alternative though — ultra-dense Zero- Capacitor DRAM (Z-RAM) memory technology. Z-RAM is a true single-transistor memory technology that harnesses the floating body effect of silicon on insulator (SOI) semiconductor devices. The elegance and simplicity of Z-RAM provides a number of significant advantages versus standard memory technologies:

  • Simplified manufacturing: Z-RAM does not require exotic processing steps for forming a DRAM capacitor, which lowers manufacturing costs and enables faster technology node introduction.
  • Smaller product size: Z-RAM is up to twice the density of DRAM and up to four times the density of SRAM, enabling more memory in the same area footprint.
  • Scalability: The Z-RAM bitcell is a transistor — the most scalable element of any semiconductor process — and has been demonstrated on advance device types such as FinFETs and MUGFETs.

Because Z-RAM is implemented on a standard SOI logic process, it will logically migrate into the same application areas that SOI does. This graphic depicts some of the high-performance SOI applications that will evolve in the coming years.
According to Jim Feldhan, president of Semico, "With wafer yields and die size reductions slowing down at each lithography generation, Z-RAM gives memory manufacturers a way to stay on the Moore's Law slope, and perhaps even accelerate it." In other words, Z-RAM is a memory technology that not only benefits today's memory manufacturers but, unlike DRAM, is well poised to address their future needs as well.