Current Affairs in the Non-Volatile Memory Market

Non-volatile memory (NVM) technology has revolutionized information storage and enabled new categories of mobile consumer electronics, from smartphones and tablet computers to digital cameras and GPS navigation devices. This has created a shift to a higher ratio of NVM to logic content in mobile devices, making the cost structure of NVM more important in achieving acceptable and competitive end product cost. To compete globally, an important implication for NVM manufacturers is the need to invest in electrical test tools that allow them to rapidly and accurately characterize NVM devices in both R&D and production.

NVM Technology. Flash memory, which has been around since the 1980s is probably the best-known form of NVM. However, to keep up with the consumer demands placed on today’s mobile products, new NVM technologies are needed to drive down the cost per megabyte. An important part of the solution is T&M technology that cost-effectively increases the speed and accuracy with which NVM devices are characterized. Electrical test technology has been an integral part of the Moore’s Law legacy, which was just as applicable to flash memory device scaling as it was to logic device scaling. Still, at high device densities, traditional flash memory processes today face several problems, including higher gate leakage due to thinner oxides thickness and a decrease in retention time. This is accompanied by a limited number of electrons in the floating gate, increasing threshold voltage variations, and requiring more process complexity that increases production cost.

As a result, the NVM industry has been considering a variety of alternatives to traditional flash memory that allow higher density, including so-called 3D Flash, which uses the device’s vertical dimension instead of scaling. Although 3D Flash solves some problems (leakage, proximity effects, etc.), it presents some new ones, including a complicated manufacturing process.

In response, some manufacturers are exploring technologies intended to replace flash memory altogether, including PRAM or PCRAM (Phase or Phase Change RAM), RRAM (Resistive RAM) and FRAM (Ferroelectric RAM). It’s not yet clear which, if any, of these technologies is destined to replace flash storage, but it’s likely several of them will survive to address the differing needs of different memory applications. For example, PCRAM may someday replace flash memory because it is not only much faster and scaleable to smaller dimensions than flash memory, but it’s also more resilient, offering up to 100 million write cycles.

Electrical Test Needs. From a T&M perspective, all these NVM technologies have some things in common. They all require parametric testing for material and device characterization during development, such as threshold voltage/drain current testing for flash memory, PUND (pulse mode) testing for FRAM, or resistance-current (RI) testing for PRAM structures. Tests of cycling endurance, data retention, read disturbance, etc. are equally essential. All of them require tightly integrated source and measurement hardware with programmable timing, such as that found in Keithley ultra-fast pulse I-V modules. Such modules are part of an integrated semiconductor device characterization system designed to solve T&M challenges in NVM device development, such as materials research and product development testing. Once a new NVM technology goes into production, the same pulse mode testing technology can be used there as well.

Conclusions. NVM plays an ever-increasing role in the performance of today’s mobile consumer products. The growing influence of social media means that products which don’t live up to users’ performance expectations have nowhere to hide—a bad review from an unhappy customer can reach millions of potential buyers virtually instantaneously and impact sales dramatically. For manufacturers, the ability to characterize and test NVM devices quickly, accurately, and economically could make the difference between a successful product and one that loses money.

References. More information on NVM testing is contained in the following online seminars:

Phase Change Memory: Fundamentals and Measurement Techniques, and New Methods for Testing Flash Memory.