T. A. Savas

Fabrication of patterned media for high density magnetic storage

Arrays of discrete, lithographically patterned magnetic elements have been proposed as a new generation of ultrahigh density patterned magnetic storage media. Interferometric lithography has been used to make prototype arrays over large areas with periods of 100–200 nm. Arrays of magnetic pillars, pyramids, and dots have been made by electrodeposition, evaporation and liftoff, and etching processes, and the magnetic properties of the particles and their mutual interactions have been measured.

Large‐area achromatic interferometric lithography for 100 nm period gratings and grids

Achromatic interferometric lithography is the preferred approach for producing large‐area, spatially coherent 100 nm period gratings and grids. We report on improvements to processes which have enabled exposure areas of ≊10 cm2. In addition, we report on the fabrication of 100 nm period free‐standing gold gratings.

Achromatic interferometric lithography for 100‐nm‐period gratings and grids

For the fabrication of periodic structures with spatial periods of 100 nm or less, achromatic interferometric lithography is preferred over other lithographic techniques. We report on processes we have developed, using achromatic interferometric lithography, to fabricate large‐area coherent gratings and grids with spatial periods of 100 nm.

Magnetic force microscopy study of interactions in 100 nm period nanomagnet arrays

The magnetic behavior of two different 100 nm period arrays of Ni pillars has been characterized using vibrating sample magnetometry and magnetic force microscopy. The samples have similar aspect ratios of approximately two but different particle dimensions, leading to differences in the strength of magnetostatic interactions. The experimental results were compared with a simulation based on an Ising-like simple interaction model.

Magnetic properties and interactions of single-domain nanomagnets in a periodic array

Macroscopic and microscopic switching characteristics are obtained for 100 nm period arrays of Ni nanomagnets with a mean switching field (coercive field) of 710 Oe. Magnetic force microscopy in combination with micromagnetic theory shows that inhomogeneities in the particle shapes result in an intrinsic standard deviation in switching fields of 105 Oe, while the interactions between neighboring nanomagnets broaden the distribution to 276 Oe, equivalent to a squareness of 0.8 in the bulk hysteresis loop. The switching field distribution is consistent with curling as the switching mechanism.

Zone-plate-array lithography in the deep ultraviolet

We describe initial steps we have taken in the development of zone-plate-array lithography (ZPAL), a proposed new paradigm for sub-100 nm lithography. The optimal implementation of ZPAL would employ an undulator emitting soft x rays of 4.5 nm wavelength. However, we have opted to concentrate initially on the major uncertainties associated with ZPAL: (1) fabrication of a large array of zone plates with a center-to-center spacing accuracy finer than the minimum zone width, (2) multiplexing of input beams to the individual zone plates, and (3) coordination of that multiplexing with precision motion of a substrate stage. We fabricated arrays of pure-phase zone plates suitable for the 193 nm output of an ArF laser, and conducted exposure tests using a modified Michelson configuration for focusing the zone plate array on the substrate. We also show the first example of simplistic writing. We show that the micromirror array manufactured by Texas Instruments, for use in projection displays, has dimensions and swi...

Modelling of hysteresis loops of arrays of 100 nm period nanomagnets

Magnetic hysteresis loops have been measured for a 100 nm period array of 35 nm diameter nickel pyramids formed by interferometric lithography. Results are compared with a computational model which describes a square array of Stoner-Wohlfarth particles. This allows the distribution of particle anisotropies and easy axis directions, and the switching mechanism, to be inferred.

A cluster size nanofilter with variable openings between 2 and 50 nm

A variable size nanoscale particle sieve with openings between 2 and 50 nm has been used for determining, selecting, and manipulating the size of large liquid helium clusters in the range from 7×103 to 3×106 atoms. The variable openings of the sieve are obtained by rotating a nanofabricated free-standing transmission grating with a 100 nm period and 50 nm wide slits around an axis parallel to the slits. The new nano-sieve can be applied to clusters of various species as well as to large molecules with sizes down to 2 nm.

Soft X-Rays for Deep Sub-100 Nm Lithography, with and Without Masks

The development of micro- and nanofabrication, their applications, and their dependent industries has progressed to a point where a bifurcation of technology development will likely occur. On the one hand, the semiconductor industry (at least in the USA) has decided to develop EUV and SCALPEL to meet its future needs. Even if the semiconductor industry is successful in this (which is by no means certain) such tools will not be useful in most other segments of industry and research that will employ nanolithography. As examples, MEMS, integrated optics, biological research, magnetic information storage, quantum-effect research, and multiple applications not yet envisioned will not employ the lithography tools of the semiconductor industry, either because they are too expensive, insufficiently flexible, or lacking in accuracy and spatial-phase coherence. Of course, direct-write electron-beam lithography can meet many of these non-semiconductor-industry needs, but in other cases a technique of higher throughput or broader process-latitude is necessary. Our experience at MIT in applying low-cost proximity x-ray nanolithography to a wide variety of applications leads us to conclude that this technology can provide an alternative path of a bifurcation. A new projection lithography technique, zone-plate-array lithography (ZPAL), does not require a mask, can operate from UV to EUV to x-rays, and has the potential to reach the limits of the lithographic process.