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Nanolithography in the Large

Reviews of graphene

January 6th, 2012

An experimental review of graphene has appeared on the arXiv in late October. Its arrival prompted me to seek out other review articles on this material which have appeared in the last few years. I list them here in reverse chronological order:

Happy reading!

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Photonic wire bonding

November 17th, 2011

Karlsruhe Institute of Technology has demonstrated photonic wire bonding between two SOI chips. They have demonstrated an aggregate data transmission rate of 5.25 Tbit/s over one photonic wire. Assuming a linear wire bond pitch of 5 microns, they conclude that a transmission rate of 1 Pbit/s/mm from a chip is within reach.

The photonic wire bonds are manufactured by two-photon lithography in SU-8 resist. One can easily envision taking this technology into manufacturing. It should enable very high speed chip-chip communication.

For details, see arXiv:1111.0651v1.

Posted in Nanophotonics | No Comments »

Mechanical systems in the quantum regime

October 20th, 2011

The title is taken from a recent review posted to the arXiv.

When we speak of quantum mechanical systems, what usually comes to mind are optical, electrical, and magnetic phenomena associated with atoms, molecules or solids. Rarely do we think of mechanical systems per se.

The review discusses progress in cooling nanoscale mechanical systems to the ground state, and then measuring position and momentum. Remembering the peculiarities of quantum mechanics, it is evident that measuring location of such an object, for example, disturbs the very location being measured. Nevertheless, the ground state motion of nanomechanical systems has been observed.

Interesting reading.

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BACUS musings, 2011 edition

October 6th, 2011

The SPIE Photomask Conference (a.k.a. BACUS) for 2011 recently concluded. Conference attendance was up by 10% over last year. We were pleased to host ten of the papers from the unfortunately cancelled Photomask Japan Conference. All PMJ papers are posted to the web, BTW. The abstracts can be found here.

Highlights:

NuFlare announced specifications for the EBM-8000 mask writer, targeting the 22 nm node. They have coaxed the lanthanum hexaboride source up to a current density of 400 A/cm² and reduced the maximum flash size to 0.35 micron. The field sizes are also reduced, the main field now being 180 microns and the sub-field 10 microns max. They anticipate achieving 2 nm overlay (sparse patterns).

IMS continues to meet their multi-beam development milestones. We were treated to linearity measurements over features from 24 nm to 90 nm (±0.5 nm). So they are able to do quite good multi-e-beam exposures with a fixed stage. The schedule calls for integrating the full sized (512 X 512) blanker array this month, a moving stage and data-path in December, and first mask printing in March 2012.

Lowlights:

In the 1980′s 1X X-ray was the “lithography of the future” and, as one wag put it, “always will be”. EUV looks increasingly like the “lithography of the future”. This conference we were asked to believe that the source vendors are going to leap from < 10W to > 100W by this time next year. I found no believers among the audience. Defects of all manner continue to bedevil mask blank production. It turns out that even a 2 nm bump (or dig) on the base silicon shows up as a defect to EUV radiation. Needless to say, any 2 nm anomaly in any of the 85 or so layers stacked on top also shows up as a defect. To cap it off, the V.P. of Rapid (K-T’s photomask inspection division) decidedly did not commit to fund an inspection tool at this time. (He also subtly hinted that such a tool would be frightfully expensive.)

Oddities:

The squeegee is back. Out of the Insitute for Microelectronics, Stuttgart comes news of an organic 6-bit DAC fabricated by stencil printing. A nice graphic can be found here.

Conference abstracts may be found here for a limited time.

Posted in Photomask | No Comments »

Atomic resolution 3D electron tomography

August 30th, 2011

Electron tomography is now able to resolve atomic scale structure in three dimensions. The novelty of yesterday’s preprint lies in absence of a requirement for a priori information about the structure. Further, while conventional electron tomography achieves ~ 1 nm resolution, this paper demonstrates 2.4 Å resolution.

arXiv:1108.5350v1 [cond-mat.mtrl-sci]

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Status of Patterned Media Development

July 29th, 2011

Ricardo Ruiz of Hitachi GST gave a short lecture on the status of patterned media development, to the local section of the IEEE Magnetics Society yesterday. I summarize by pointing to four publications listed below. R Ruiz, et al. (Hitachi GST, U Wisc, Hitachi) gives a compact, readable overview of patterned media development circa 2008. Figure 2 is particularly noteworthy; in order to become commercially interesting, one needs a bit density above 1Tb/in^2. Since the read/write head design constrains one to a 2:1 or (better) 4:1 aspect ratio, the dot pitch has to be below 20 nm. [SST 51(9)(2008)]

For reliable operation, every bit on a hard disk should switch in the same way. Happily, electron-beam directed assembly yields tighter switching field distributions than either e-beam lithography or block copolymer self-assembly alone. [Appl. Phys. Lett. 96, 052511 (2010), doi:10.1063/1.3293301]

Recently, Hitachi GST has also reported on an integrated thermally-assisted recording head and its operation on patterned media. Going under the moniker of “BP-TAR”, the authors have achieved 1Tb/in^2 on a 24 nm track pitch. This represents a solid advance over writing on continuous media, even with thermal assist. [Nature Photonics 4, 484 - 488 (2010), doi:10.1038/nphoton.2010.90]

By means of orthogonal double patterning, Hitachi is able to show 27 nm full pitch dots of arbitrary aspect ratio. This is achieved by using e-beam directed self-assembly in the radial direction of the media, and then cutting the resulting long (radial) lines into tracks with EBL. Directed self-assembly can accomodate small (~5%) variations from the block-copolymer’s preferred lattice period, thereby making equi-angular spacing feasible. [ACS Nano, 2011, 5 (1), pp 79–84, doi:10.1021/nn101561p]

In summary, patterned media development appears to be on track. Like anything complex, a lot of engineering and learning remains to be done.

Posted in Nanoimprint | No Comments »

Graphene Update

June 17th, 2011

Apart from the buzz generated by IBM’s paper in Science , graphene research continues apace. Here I will bring your attention to two sub-topics: graphene on boron nitride, and patterning of graphene.

Experimental research led by the LeRoy group at the University of Arizona has shown that graphene lays down nearly flat on boron nitride substrate. This is in contrast to the wrinkling that occurs when graphene is placed onto silicon dioxide. Consequently the electronic properties of graphene on BN are much closer to those properties for free-standing graphene, but the material is much more robust and therefore more accessible to experiment. [Nature Materials, also found at arXiv:1102.2642]

From the Kavli Institute of Nanoscience in Delft comes a report that multi-layer graphene can be sculpted by high-energy e-beam without defects. If one irradiates graphene at room temperature, one finds that the graphene rapidly converts to amorphous carbon. The Kavli Institute has discovered that raising the temperature to 600C allows the graphene to heal while being irradiated, so that patterning is possible. [arXiv:1102.0971]

Finally, work at the Cavendish Laboratory, Cambridge, shows that apparent scanning probe nanolithography on graphene may be deceptive. A voltage is applied between tip and substrate during contact mode scanning. One then inspects the sample in tapping mode, and finds indentations wherever the tip was dragged. However, it seems that current flow through the probe tip causes oxidation of the graphene substrate only if the current flowing through the tip drops to (near) zero. This current drop depends on setting the tip voltage high enough to drive the oxidation to completion. The authors do not report what atomic state the “pseudo-cut” (that is, indented) graphene remains in. [arXiv: 1102.2781]

Posted in Materials, Research | No Comments »

PPM-II

June 16th, 2011

In March I wrote about Point Projection Microscopy (PPM), in which electrons are emitted from a single-atom tip and accelerated to (and through) a target with very high coherence. The spatial resolution is quite high. I found that the same research group had earlier calculated that PPM should be able to distinguish atoms of differing atomic number one from another. This would imply analytical applications of the technique in addition to image formation. See arXiv:1101.5135.

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Boron nitride nanotubes

March 25th, 2011

Marvin Cohen and Alex Zettl have published a small review of boron nitride nanotubes [Physics Today 63 (11), 34-38 (2010)]. Two potential applications loom. The authors point out that these nanotubes (abbreviated BNNT) show field emission that is unusually stable compared to carbon nanotube field emission. Also, BNNT field emission closely follows the Fowler-Nordheim law. The implications to cold field emission device construction are obvious.

Furthermore, the BNNT bandgap can be tuned by application of an electric field transverse to the tube axis. At zero applied voltage, the gap is around 5 eV. At sufficiently large applied voltage, the band gap collapses to 0 eV. Perhaps one may use a BNNT as a transistor channel based on this giant Stark effect.

Other electronic applications may arise from the peculiar spatial localization of the lowest conduction band. It is physically situated in the tube, leading lightly doped BNNTs to act like plumbing for nearly a free electron gas.

Posted in Devices, Materials | No Comments »

Point Projection Microscopy

March 18th, 2011

Mutus et al. at the University of Alberta have recently examined a suspended graphene film by low energy electron point projection microscopy (LEEPPM). [arXiv:1102.1758] Even though the electron energy was only 100-200 eV, approximately 75% of the electrons get through the film. With an effective source size of < 5Å, imaging resolution is quite good. The authors claim that the low beam energy does not result in sample contamination in the way higher voltage techniques such as STEM do. (I find this claim puzzling, since it is the secondary electrons which are largely responsible for chemical reactions induced by high voltage e-beams.) They speculate that a graphene film could be used as the ultimate microscope slide for imaging thin objects by PPM.

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