Manufacturing Bits: Aug. 8

Ferroelectric films; 1-Gbit spin torque MRAM.


Ferroelectric films
Ferroelectric RAM (FRAM) is creating a buzz again. For years, FRAMs have been shipping for embedded applications, although the technology has taken a backseat to MRAM, phase-change and ReRAM.

Using a ferroelectric capacitor to store data, FRAM is a nonvolatile memory with unlimited endurance. FRAM is faster than EEPROM and flash. FRAM performs an over-write function in the memory cell without an erase operation.

FRAM has some minuses, however. It is difficult to scale. To solve these and other problems, NaMLab and a spin-off company, Ferroelectric Memory (FMC), are pioneering the development of a next-generation FRAM, dubbed a ferroelectric FET (FeFET). Imec is also developing the technology.

There are other efforts as well. The Chinese Academy of Sciences, for example, is exploring the flux-closure domain (FCD) structures and other properties in ferroelectric thin films.

FCDs are microscopic topological phenomena found in these films, which have various electric polarization properties. Potentially, with FCDs, the industry could develop new types of ferroelectric devices, such as spintronic tunnel junctions and ultra-thin capacitors.

The problem? The use of most oxide electrodes limits the ability to form FCDs.

The Chinese Academy of Sciences, however, has made a breakthrough in the arena. For this, researchers have used two types of oxide electrodes–strontium ruthenate and lanthanum strontium manganite. Both oxide electrodes have similar perovskite structures.

Then, researchers looked at how these electrodes enabled FCD formation in PbTiO3 (PTO) perovskite-oxide-based thin films deposited on gadolinium scandium oxide (GSO) substrates. Researchers found that periodic FCD arrays can be stabilized in PTO films.

a) FCD domains in the PTO layer with symmetric oxide electrodes.
(b) (b) Alternating current domains in the PTO layer with asymmetric oxide electrodes.

(CREDIT: Shuang Li and Yinlian Zhu)

“The general thinking has been that oxide electrodes would destabilize flux-closure domains. However, our work has shown that this is no longer true when the top and bottom electrodes are symmetric, which physically makes sense,” said Yinlian Zhu, a professor at the Institute of Metal Research at the Chinese Academy of Sciences, on the organization’s Web site.

“We successfully grew ferroelectric thin films with symmetric oxide electrodes in which flux-closure domains and their periodic arrays clearly do exist,” Zhu said. “Our work sheds light on understanding the nature of flux-closure domains in ferroelectrics. We expect that it will open research possibilities in the evolution of these structures under external electric fields.”

1-Gbit spin torque MRAM
Everspin Technologies has begun sampling the world’s first 1-gigabit spin torque magnetoresistive random access memory (ST-MRAM).

The 1-Gbit ST-MRAM from Everspin is based on a perpendicular magnetic tunnel junction (pMTJ) technology. The device is made on GlobalFoundries’ 28nm process technology using 300mm wafers.

The device, dubbed the EMD4E001G, delivers persistent memory with a DDR4- compatible interface. In one application, Everspin’s ST-MRAM can be incorporated in the write-buffer socket in a solid-state storage (SSD) and RAID systems. It allows storage system vendors to protect against power loss without the use of supercapacitors or batteries.

In addition, Everspin has also rolled out its nvNITRO line of storage accelerators. Everspin is launching the initial nvNITRO acclerators with 1- and 2-GB capacities, based on 256Mb DDR3 ST-MRAM. The nvNITRO accelerators operate at 1.5 million IOPS with 6μs end-to-end latency.

The new devices and accelerators are part of a plan to “to build the ecosystem with our partners to make spin torque MRAM a reality for today’s storage market,” said Phill LoPresti, Everspin’s president and chief executive.

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