Future Memories

Chip makers are searching for cheap, fast, “universal” memories to replace DRAM, SRAM and flash.

For 40 years, systems designers have seen memory densities double every 18 to 24 months while memory chip prices have remained essentially flat, cutting the cost per bit in half each time. As the technical challenges of building ever-smaller memory cells in silicon have increased, however, some memory manufacturers have predicted that the cost curve will start to swing the other way before the end of the decade.

Researchers are working on several alternate technologies that could eventually replace those in the three memory types commonly used today: low-cost dynamic RAM (DRAM), used in PCs and servers; fast static RAM (SRAM), used for processor caches and mobile devices; and nonvolatile flash memory, used in everything from computer BIOSs to cell phones.

Researchers at IBM, Intel Corp. and other companies envision the development of a universal memory technology that could someday replace all three.

A universal memory technology could change how computers are designed. For example, nonvolatile RAM could allow computers to boot up and power down instantly because stored information wouldn’t be lost when power was. But the emergence of a universal memory technology is probably at least 10 to 15 years away.

Others argue that a universal memory isn’t possible because one memory type can’t satisfy all needs. For example, nothing could be the fastest and cheapest at the same time.

Most research today is focused on addressing the limitations of one memory technology at a time, such as flash. But some attributes of today’s technologies will be hard to beat.

Most technologies will probably not be able to compete on lowest cost per bit against DRAM or with the fastest SRAM. So they will fall into that space in between. Ferroelectric RAM (FRAM) and magnetoresistive RAM (MRAM) are the best-funded and most-evolved of the emerging memory technologies. FRAM is a nonvolatile RAM that was developed by Ramtron International Corp. in Colorado Springs. It’s licensed by Texas Instruments Inc. and others. More than 30 million products have already shipped using FRAM, including metering, radio frequency identification and smart-card devices.

FRAM, which is based on nanoscale “quantum dots,” uses less power and writes faster than DRAM or flash, and it has a long life span. But the technology remains 20 to 50 times more expensive per bit than DRAM, and chip density is far lower. Ramtron is prototyping 1Mbit parts today and hopes to push the technology to 4Mbit or 8Mbit in 2006. Until MRAM is ready for the market, however, FRAM is the only game in town for nonvolatile DRAM. (To Be Continued)

未來的存儲器(1)

芯片制造商正在尋找廉價、快速、通用的存儲器來替代DRAM、SRAM和閃存。

四十年來，系統(tǒng)設(shè)計(jì)師看到了每18至24個月存儲器密度翻一番，而存儲器芯片的價格基本保持不變，每次每比特的成本會降低一半。然而，隨著在硅片上制造越來越小存儲單元的技術(shù)挑戰(zhàn)增加，有些存儲器制造商預(yù)測，到本十年末成本曲線將向另外一個方向擺動(即成本增大)。

研究人員正在研究幾種替代技術(shù)，最終替代今天常用的三類存儲器：低成本的用于PC機(jī)和服務(wù)器的動態(tài)RAM(DRAM)、用作處理器高速緩存和用于移動設(shè)備中的快速靜態(tài)RAM(SRAM)、以及用于從計(jì)算機(jī)BIOS到手機(jī)電話等各種設(shè)備中的非易失性閃存。

IBM、Intel和其他公司的研究人員設(shè)想開發(fā)一種通用的存儲器技術(shù)，有一天能把這三類存儲器統(tǒng)統(tǒng)替代掉。

通用的存儲器技術(shù)有可能改變計(jì)算機(jī)的設(shè)計(jì)。例如，非易失性RAM能讓計(jì)算機(jī)立即啟動和關(guān)機(jī)，因?yàn)榇鎯Φ男畔⒉粫跀嚯姇r丟失。但通用存儲器技術(shù)的出現(xiàn)可能至少還有十年之遙。

其他一些人則稱通用存儲器是不可能的，因?yàn)橐环N存儲器不可能滿足所有的需求。例如，沒有一樣?xùn)|西可以是最快同時又是最便宜的。

今天大多數(shù)的研究集中在一次解決一種存儲器技術(shù)(如閃存)的局限。但今天技術(shù)的有些屬性是很難克服的。

多數(shù)技術(shù)大概不可能在每位最低成本上與DRAM競爭，而在速度與最快的SRAM競爭。因此它們將處于這兩者之間的空間。鐵電RAM(FRAM)和磁阻RAM(MRAM)是存儲器新技術(shù)中投入最多、研究最深入的兩項(xiàng)技術(shù)。FRAM是非易失性RAM，它是由Ramtron國際公司開發(fā)的。德州儀器等公司已獲得了(該技術(shù)的)許可。已經(jīng)有3000多萬臺使用FRAM的設(shè)備交付使用，包括測量儀器、RFID和智能卡設(shè)備等。

基于納米級“量子點(diǎn)”的FRAM比起DRAM和閃存耗電更低、寫更快、有更長的生命周期，但這項(xiàng)技術(shù)的位成本要比DRAM貴20～50倍，而芯片的集成度低得多?，F(xiàn)在，Ramtron公司正在試生產(chǎn)1兆位的零件，希望在2006年將此技術(shù)提升到4兆位或8兆位。在MRAM能上市之前，F(xiàn)RAM將是市場上惟一的非易失性DRAM。(未完待續(xù))