Nanometrology for New Spintronics
Mark Tondra, NVE Corp., Eden Prairie, MN 55344
1-25-04
The commercial driving forces of nanomagnetism are the hard disk drive industry, other discrete magnetic storage modes, and the MRAM development effort. The present track width on hard disks is now less than the feature size of standard silicon foundries (50 nm vs. 90 nm). The shrinking of hard disk bit size at the current rate of 100% / year will ensure that these efforts continue to lead the way in terms of smallest featured fabrication in magnetics.
MRAM is at the stage of rapid ramp-up to commercial production. It is expected that the bit density will approach the smallest feature size of standard silicon devices in the next 5 years or so.
Taking these two data storage applications to be the defining problems for the next decade, and using the present rate of density increase as a means of projection, one can see that commercial devices will have dimensions on the order of 1 - 10 nm in the year 2014.
Some key issues for hard disk media are: 1)The magnetic grain size of will need to be less than 10 nm, and be controllable on this length scale. The introduction of patterned media in commercial drives is a distinct possibility. 2) More sophisticated structures are needed (perpendicular media, AF-coupled media, etc.) to keep the density ramping up.
For hard disk read heads and MRAM, the challenges are in understanding the behavior of magnetoresistive devices on the 10 nm length scale. Specifically, there are issues of curling, vortex, layer-layer coupling, effects of defects and roughness, interfaces, temperature, etc.
In all cases, the relevant time scale will shrink below 1 ns. For MRAM in particular, reducing the energy required to switch and read bits will mean better control of switching sequences on the 100 ps time frame.
The need for new Spintronics devices in these industries will occur when the means of storing and reading information are not viable at the relevant dimensions. The most immediate hurdle appears to be the thermal stability of magnetic objects on the 10 nm scale. There are several development efforts to incorporate thermal action in the writing procedures. If these are successful, it is likely that the present modes of devices can be extended to the 10 nm scale.
At some point around 10 nm, new spintronics devices may become attractive if they can be designed to have stable states at room temperature. Some promising new areas are: spin momentum transfer, spin-wall interactions, internal spin structure manipulation, spin packets, time-dependent phenomena, high frequency magnetic excitations, quantized conductance, and magneto-thermal effects.
With this technology path in mind, here is a proposed NanoMetrology Challenge:
Measure the magnetic field with 0.25 nm spatial resolution
On-wafer if possible
Measure moment of 100 x 100 x 100 atoms
Predict internal moment orientation structure/s
Detect using scanning instrument
Measure these properties on 10 psecond time scale
As the hard disk industry and MRAM make 100 nm-sized features mundane over the next 10 years, new “spinoff” applications of nanomagnetismare likely to spring up. The most promising areas appear to be in Nano-Machinery (pumps, gears, motors, etc.) and biological devices (Biosensors, implanted electronics, artificial cells). The nanometrology tools developed for the data storage industry will likely be applied to a growing and fascinating field of new nano-devices. This, in turn, could inspire a new set of metrology requirements.