Future Memories(2)

MRAM is closer to production than most other experimental memories, and IBM and Freescale Semiconductor Inc. are the leading MRAM developers. Researchers call the technology “magnetic storage on a chip” because it adapts the magnetic polarization techniques used in disk drives to silicon. The fast, nonvolatile memory offers a nice combination of high speed, high endurance and reasonable density.

Chip samples can be produced at about the same density and cost per bit as flash. But while promoted as universal memory, the density of MRAM doesn’t approach that of DRAM or SRAM. Most interest today is focused on embedded applications.

Several other challengers to conventional memory technologies look promising but are much earlier in their development cycles than FRAM or MRAM.

Phase-change memory (PCM) is a fast, nonvolatile memory that proponents claim could become a universal memory. IBM and Intel have each partnered with other companies to develop the technology.

A transistor in a PCM cell applies energy to either heat or cool the material, forcing it to change between an amorphous (high-resistance) and a crystalline (low-resistance) form. A current is then applied to measure the resistance and establish the state of the memory cell as a 0 or 1.

While PCM technology is much faster than flash, it’s slower than SRAM. To be competitive with DRAM, it would also have to support unlimited writes. IBM’s research shows that PCM can match flash’s 100,000-write limit, but endurance beyond that hasn’t been proved. Ovonyx Inc. in Santa Clara, Calif., however, claims that its technology, called Ovonics, can be written to 10 trillion times.

Carbon nanotubes—hollow, tube-shaped lattices of carbon atoms—can be used to make a mechanical memory that works by bending the carbon filament up or down to make or break a connection between two electrodes.

The technology can theoretically scale as small as 5 nanometers and has achieved speeds a few times faster than today’s DRAM chips. Nanotube chips could be 10 to 15 times smaller than today’s DRAM and could offer a tenfold reduction in power consumption. Initial products are still two to five years away.

Molecular memory, developed by ZettaCore Inc., uses a chemical process to create DRAM memory cells with a molecular capacitor. The “chemically self-assembling” molecules work by adding and removing electrons. This changes the voltage, which is then measured to determine the state (0 or 1). The technique supports four states and can store 2 bits per memory cell. Molecular memories also require 70% less power than a standard DRAM memory cell because the capacitor can hold 100 times the charge and therefore needs to refresh memory less frequently.

Molecular memory will allow manufacturers to double or quadruple capacity without increasing costs. Initial products may be available by 2007 or 2008.

Axon Technologies Inc.’s Programmable Metallization Cell memory (PMCm) is a DRAM alternative that’s nonvolatile, uses less power and offers higher density than DRAM. In it, tiny quantities of metal self-assemble into a filament as electrons are added to the metal ions. Resistance is then detected to determine the state of the memory cell.

Ultimately, the ability to cost-effectively manufacture new memory technologies using existing fabrication facilities may separate the winners from the losers. To succeed, emerging technology vendors will initially focus on niche markets where they can coexist, rather than compete, with established vendors, and thereby continue to evolve. (The end)

未來(lái)的存儲(chǔ)器(2)

MRAM比其他多數(shù)技術(shù)更接近生產(chǎn)。IBM和Freescale半導(dǎo)體公司是MRAM開(kāi)發(fā)者。研究人員將此技術(shù)叫做“芯片上的磁存儲(chǔ)”，是因?yàn)樗鼘⒋疟P(pán)機(jī)中的磁極化技術(shù)用到硅片上。這種快速的非易失性存儲(chǔ)器將高速度、(存儲(chǔ)的)高耐久性與合理的集成度很好地結(jié)合起來(lái)了。

(FRAM的)芯片樣品可以做到集成度和每位成本與閃存相同。但如果將它作為通用存儲(chǔ)器進(jìn)行推銷(xiāo)，那它的集成度還達(dá)不到DRAM或SRAM的水平。今天，它的最大用處集中在嵌入式應(yīng)用。

其他幾種對(duì)常規(guī)存儲(chǔ)器技術(shù)的挑戰(zhàn)看上去有希望，但比起FRAM或MRAM更是處于開(kāi)發(fā)的前期。

相變存儲(chǔ)器(PCM)是一種快速的非易失性存儲(chǔ)器，其支持者稱(chēng)它能成為通用存儲(chǔ)器。IBM和Intel各自都在與其他公司進(jìn)行合作，開(kāi)發(fā)此項(xiàng)技術(shù)。

PCM單元中的晶體管運(yùn)用能量加熱或冷卻材料，強(qiáng)迫它在非晶體(高電阻)和晶體(低電阻)形式之間轉(zhuǎn)換。然后加上電流，測(cè)量電阻以建立存儲(chǔ)單元的狀態(tài): 0或1。

雖然PCM技術(shù)比閃存快得多，但仍比SRAM慢。為了能與DRAM競(jìng)爭(zhēng)，它必須支持無(wú)次數(shù)限制的寫(xiě)。IBM的研究表明，PCM能達(dá)到閃存10萬(wàn)次寫(xiě)的極限，但超過(guò)閃存耐久力的能力未得到證明。然而，加州Santa Clara市的Ovonyx公司聲稱(chēng)其Oyonics技術(shù)能寫(xiě)10萬(wàn)億次。

碳納米管(中空的管狀碳原子晶格)能用于制造機(jī)械的存儲(chǔ)器，它通過(guò)上下彎曲碳絲從而接通或斷開(kāi)兩個(gè)電極之間的連接而工作。

理論上，此技術(shù)能做到5納米的尺寸，并已獲得比今天DRAM芯片快若干倍的速度。將來(lái)，納管芯片可能比目前的DRAM芯片小10至15倍，功耗降低10倍。最早的產(chǎn)品還需2至5年的時(shí)間。

ZettaCore公司開(kāi)發(fā)的分子存儲(chǔ)器利用一種化學(xué)工藝，制造帶分子電容器的DRAM存儲(chǔ)單元。這種“化學(xué)自我裝配”分子是通過(guò)加入和去掉電子而進(jìn)行工作的。這會(huì)改變電壓，然后測(cè)量電壓以確定狀態(tài)(0或1)。此技術(shù)支持4個(gè)狀態(tài)，每個(gè)存儲(chǔ)單元能儲(chǔ)存2位。分子存儲(chǔ)器的耗電比標(biāo)準(zhǔn)的DRAM單元少70%，因?yàn)殡娙荼４媪?00倍的電荷，故而不需要頻繁刷新存儲(chǔ)器。

分子存儲(chǔ)器允許制造商在不增加成本的情況下，將存儲(chǔ)容量翻一番或者翻兩番。2007年或2008年，第一批產(chǎn)品有可能面市。

Axon技術(shù)公司的可編程金屬化單元存儲(chǔ)器(PMCm)是DRAM的替代品，它是非易失的，耗電比DRAM少但密度更高。在這種存儲(chǔ)器內(nèi)，能自我組配成細(xì)絲的微型金屬作為電子，加到金屬離子上。隨后測(cè)量電阻，以確定存儲(chǔ)單元的狀態(tài)。

歸根結(jié)底，利用現(xiàn)有制造設(shè)備能低成本高效率地制造新穎的存儲(chǔ)器之能力，將起到優(yōu)勝劣汰的作用。為了能成功，新技術(shù)公司最初將把注意力集中在專(zhuān)業(yè)市場(chǎng)，在這些市場(chǎng)上，他們能與已有的公司共存，而不是競(jìng)爭(zhēng)，從而繼續(xù)發(fā)展。(全文結(jié)束)