1T-SRAM
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1T-SRAM is MoSys's implementation of embedded-DRAM on a conventional digital-logic (standard-cell) ASIC process.
Conventional DRAM devices (ICs) are designed and built for foundry production lines tweaked to maximize bit density, rendering traditional DRAM-cell layout incompatible with nearly all commercial digital-logic CMOS foundry processes. Embedded-DRAM is essentially the same RAM-cell ported to a CMOS digital-logic foundry process, allowing a designer to pair a digital-logic circuit with a sizable quantity of embedded-RAM.
In development since the early 1990s, MoSys's 1T-SRAM combines the high speed of SRAM with the high bit-density and lower-power consumption of embedded DRAM. MoSyS markets 1T-SRAM as physical IP for embedded (on-die) use in System-on-a-chip (SOC) applications. It is available on a variety of foundry processes, including (but not limited to) NEC, TSMC, and UMC. In common industry parlance, many engineers use the terms 1T-SRAM and "embedded DRAM" interchangeably, as some foundry processes only provide Mosys's offering in lieu of e-DRAM. However, other foundries list the two as clearly distinct offerings.
[edit] Comparison with other embedded memory technologies
In the context of SOC design (wireless processors, graphics controllers, media player chipset, etc.), MoSys 1T-SRAM is a compelling alternative to traditional e-DRAM. 1T-SRAM boasts faster speed than e-DRAM (though not as fast as 6T-SRAM), and delivers nearly the same bit/area density. On most of the foundry processes, designs with e-DRAM require additional masking-steps, adding to per/wafer cost. MoSys's 1T-SRAM does not require additional processing steps, offsetting 1T-SRAM's lower bit/density (in terms of cost per memory bit.)
1T-SRAM is also available in device (IC) form. The Nintendo GameCube was the first video game system to use 1T-SRAM as a primary (main) memory storage; the GameCube possesses several dedicated 1T-SRAM devices. 1T-SRAM is also used in the successor to the GameCube, Nintendo's Wii console.
It is important to point out that no single RAM fulfills the requirements of all applications. For extremely large (>1MB) on-chip RAM, e-DRAM is generally preferred. For high-speed applications, SRAM remains dominant. 1T-SRAM fits in between, overlapping quite well with e-DRAM.
[edit] Technology
For more information on the technology, see 1T DRAM. Below are the specifications retrieved from a year 2000 presentation by MoSys:
Size: 128 MB Speed: 600 MHz Channel Length: Dunga
In U.S. Patent 6,256,248, granted to MoSys under the name 'Monolithic System Technology, Inc.', the patent is applied to 1T-SRAM, but the document describes the memory device consists of DRAM array, indicating 1T-SRAM uses dynamic memory cell.
In U.S. Patent 6,487,135, 1T-SRAM is described as a dynamic memory cell including one transistor and one capacitor. Throughout the document, the term 1T DRAM is used to describe 1T-SRAM, to indicate the fact that 1T-SRAM does not use static memory cells.
