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EDITOR'S REPORT

Advances in Memory

Next Generation of Memory to Emerge from Smartphones

Getting low-power, dense, high-performance memory to work effectively in such a limited form factor requires a huge engineering effort. The results, however, may be not only a new generation of phones, but also a new modular character for embedded devices in general.

BY TOM WILLIAMS, EDITOR-IN-CHIEF

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There may have been a time when being a memory manufacturer seemed like a pretty straight line job of cramming as many bits onto a die as possible and trying to keep up with the ever-increasing clock speed of the day’s processors. Of course, there were also power and heat dissipation issues but they were not insurmountable and users were always happy to get more RAM into the system, be it in the form of additional boards plugged into the bus or denser packages or both.  Storage was, and to a large extent still is, provided in the form of rotating media of ever decreasing size and ever increasing density. 

This old scenario has been on the wane for some time now and is speeding on its way to entry into what we may soon call the “days of yore.” Semiconductor memory continues to march to the tune of Moore’s Law getting ever denser as geometries shrink, power consumption and heat dissipation continue to shrink, package height gets smaller and new technologies pack more bits into smaller spaces. This affects not only RAM but also nonvolatile storage like NAND flash, which is gradually but steadily replacing the mechanical rotating drive in much the way the quartz crystal watch has replaced large numbers of the old “clink-clank-clunk” mechanical watches. This development, which in now greatly accelerating, could have profound effects on the design and composition of embedded systems in wide areas of applications.

The most intense arena of development appears to be for smartphones and tablets, which of course represent the highest volume market (Figure 1). For a memory vendor to land a contract with a Samsung, an Apple or a large Chinese vendor can well reward the expense of devoting major effort to a detailed and optimized design. In the smartphone space, according to the Senior Product Marketing Manager for Micron Technology’s Mobile Business Unit, Ken Steck, “We try to develop not just the correct technology (low power, high throughput, etc.) but also the right density. We want to be sure that we’re not guessing—underguessing of overguessing.” 

Figure 1
Smartphones and their growing applications are now driving the memory demands for both high-speed, low-power RAM (LPDRAM) but also for storage in the form of NAND flash as well. Source: Micron Technology.

Thus, while the demand for memory density is certainly increasing, it is important to hit current needs while also looking to meet future demands. But at this point, says Steck, “There is now a need for low power, performance and density that has not yet been met.” It is not just an LPDRAM device. “We’re trying to create the perfect intersection of LPRAM with NAND density that meets the requirements for the customer including the height of the chip, the thermal level, throughput and everything. So we try to have the right density mixtures that intersect with the design requirements.”

Optimizing memory for a given customer’s design can entail a large amount of detailed work on that particular design including software such as fine tuning the firmware and the drivers and also often fine tuning the actual physical layout to make sure the processor can use the memory in the best way. According to Steck, this requires staying in lock step with the chip manufacturers to see where they are going and the type of memory architectures they will need. In fact, often it comes down to the literal proximity of the RAM to the processor given the speed of the CPU and the length of the traces involved. Increasingly, there are designs, such as that in the Apple watch, where processor and RAM are two separate dies, but in a single package that from the outside looks like a single device.

There is quite a bit of software work that goes along with making memory to make it work well, including tuning the drivers as well as the fact that on many memory devices there is a dedicated processor with its own firmware that must be matched with the processor so that everything operates optimally. Talk about embedded systems within embedded systems!

The pace of change and demands on memory in smartphones and tablets will of course continue. The design cycle has recently gone from three years to about six months. “There are things on the shelf now that our teams knew about eighteen months ago,” Steck says. The pace of the increase in demand for both RAM and storage memory (now NAND flash) can tell us something about the future of embedded designs in general.

Growth within Constraints

Make no mistake. The demands for memory capacity and performance trends in both RAM and storage in smartphones and tablets stand at a pretty high point today and are expected to expand significantly in the near future. But what else is new? The challenge is especially great in the case of phones because the form factor is completely limited. The days of Maxwell Smart’s shoe phone are long gone as are thoughts of anything more bulky or less sleek than what fits in our hands today. True, there are some size variants but they mostly serve different demands for screen size rather than making any compromises to accommodate performance.

So right now the sweet spot for storage appears to be about 32GBytes heading toward an optionally available high end of 65GBytes. New devices with only 8GBytes are hard to find today with 16GBytes still available for cheapskates. In the RAM side, it’s looking like 2 to 3GBytes with 4GBytes soon to become the norm. Within three years we should be looking at 4GBytes of RAM and 64 to 128GBytes of storage.

Driving these increasing demands are factors like larger and higher resolution screen size and higher camera resolution. In addition, operating systems are adding features such as the recent introduction of iOS 9, which supports split-screen multitasking and the appearance of bigger, more demanding apps like games, some of which now require a gigabyte of RAM (Figure 2). While operating systems now offer and encourage the storage of things like pictures, videos and music in the Cloud, many users prefer having them instantly available. According to Ken Steck, if his daughter is any indication—and we’re betting she is—the availability of Cloud storage from the phone is not wildly popular, so more NAND flash is needed as well.

Figure 2
The LPDRAM needs of smartphones are expected to increase something like 200% in response to display and camera performance as well as the sheer complexity of operating systems and their applications. Source: Micron Technology.

This, in turn, is leading to technical innovation. Intel and Micron have jointly introduced their 3D Crosspoint memory, which is expected to take NAND storage well beyond its current limits of both capacity and performance. In addition to significantly reducing latencies, it allows much more data to be stored close to the processor and accessed at speeds previously impossible for non-volatile storage. The new, transistor-less cross point architecture creates a three-dimensional checkerboard where memory cells sit at the intersection of word lines and bit lines, allowing the cells to be addressed individually. As a result, data can be written and read in small sizes, leading to faster and more efficient read/write processes.

Future Effects on Embedded?

The amount of intense design work going into smartphones is having the effect of creating optimized modules that consist of highly integrated SoCs, some including multicore CPUs, FPGAs, graphics and DSP functionality along with rich I/O capability on a single die. These are closely integrated with large amounts of memory—both volatile and nonvolatile—often in the same package. In other words, they are integrated and tested high-performance, low-power modules that can potentially be connected to all manner of external devices and loaded with specialized application software to perform all kinds of embedded tasks.

This is analogous to the evolution of embedded designs, which have inherited so much standard technology from the PC world. These include such things as USB and PCI/PCI Express, which came from the PC and therefore were produced in huge volumes bringing down the costs and making them attractive for niche applications in the embedded arena, which could never have justified the expense involved with creating their own interfaces.

The next generation of SoCs is a natural for use in demanding, often mobile, embedded applications and the expertise gained in matching memory and creating integrated modules will serve the industry in good stead. There may be proprietary issues involved with using the exact modules developed for phones, but the expertise is now there and the effort involved in adapting it for embedded applications is small compared to what would be needed to create such modules from scratch.

 

Micron Technology
Boise, ID
(208) 368-4000
www.micron.com