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Looking at embedded trends: Non-volatile memory (Part 1)

Posted: 06 Jan 2010     Print Version  Bookmark and Share

Keywords:non volatile memory  embedded systems  electronic systems 

The level of innovation in companies throughout the supply chain has increased significantly in the past few months. Engineers are now turning their attention away from marginal improvements that were designed to keep products coming out in the pipeline to more long-term achievements that can bring a new paradigm to the market.

Many end equipment manufacturers look to chip manufacturers for the basic technological leaps that will enable the next generation of products. This series of articles will look at three significant trends emerging in one of the most critical and competitive sockets in modern electronic systems, including: nonvolatilve memory, hyperintegration and new packaging approaches. First we'll look at non-volatile memory.

In short, it's memory that does not require power in order to retain stored data. In the past decade, the market for this capability has been limited to a few applications, mostly in automotive, smartcard, medical and space applications, and companies have been willing to pay a premium because the fabrication processes have not been efficient or cheap.

However, there are larger emerging trends like energy harvesting, mesh networked wireless sensors, building automation and security, product durability, and deeply embedded applications (where manual maintenance would be near impossible) driving many existing and new end equipments to require memory with low power, high endurance and radiation resistance.

With existing memory technologies in the embedded processing/SOC market, there are two persistent problems. First, the processor speed, efficiency and size have outpaced the available memory technology, thus forcing designers to implement complicated modules in the architecture and workarounds in the hardware. Second, many processors today run at a very low voltage (1-3V), yet

Flash-based memory (most common memory used today) needs more than 10V to write to memory. This pains engineers as they have to design in large charge pump architectures that are costly in terms of the space on the die, which in turn increases costs of the chip.

As shown in Figure 1, several different technologies have emerged, including, Phase Change Memory, Magnetoresistive RAM, Ferroelectric RAM and SONOS Flash, and the next few years will determine which will be successful and which will fail. Each type has its pros and cons, and they are all one small step away from an explosion of market acceptance in the embedded market.

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Figure 1: Here�s an overview of non-volatile memory types.

Phase-change memory
Phase change memory (PCM or PRAM) technology emerged from research done in the sixties, and most people have probably interacted with PCM thousands of times in a more familiar form like rewriteable CD-RWs or DVD-RWs.

The basic principle is an amorphous substance (chiefly made using an element in the Oxygen/Sulfur family on the periodic table known as chalcogenide glass) that transforms into an organized crystal structure when heated (through current injection for chip memory and lasers for optical memory).

When the materials change from amorphous to crystalline, the resistivity and reflectivity change drastically. Today, companies are developing chip memory using the resistivity change in the material. PCM or PRAM chips are available today (although cost prohibits all but the most necessary applications), but due to the temperature instability and cost, no one has developed an embedded PCM on a processor.

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