Manufacturing Bits: April 22

Detecting counterfeit goods
Rare earths are chemical elements found in the Earth’s crust. They are critical for use in the production of cars, consumer electronics, computers, communications, clean energy, health care, national defense systems and others.

Researchers are looking for new ways to integrate rare earths into potential chips and other applications. For example, the Massachusetts Institute of Technology (MIT) has devised tiny particles using rare earth elements. The particles themselves could be used to detect counterfeit goods.

engineers hope smartphone-readable microparticles could crack down on counterfeiting. (Source: MIT).

Some 2% to 5% of all international trade involves counterfeit goods, according to MIT, citing a 2013 United Nations report as its source. To solve the problem, MIT has devised tiny particles that are invisible to the naked eye. They contain colored stripes of rare earth nanocrystals, which glow when lit up with near-infrared light, according to MIT.

Measuring about 200 microns long, the crystals are doped with rare earth elements, such as ytterbium, gadolinium, erbium and thulium. To manufacture the particles, MIT uses a technology called stop-flow or continuous flow lithography (CFL).

“CFL builds on the well-known technique of photolithography but its novelty lies in the fact that it is performed in a laminar (not turbulent) flowing stream as opposed to the traditionally used stationary film,” according to MIT. “Wherever pulses of ultraviolet light strike the flowing stream of small building blocks, or oligomers, a reaction is set off that forms a solid polymeric particle in a process known as photopolymerization.”

Using CFL, researchers can generate vast quantities of tiny ID tags for various goods. “The ability to tailor the tag’s material properties without impacting the coding strategy is really powerful,” said Paul Bisso of MIT on the university’s Web site. “What separates our system from other anti-counterfeiting technologies is this ability to rapidly and inexpensively tailor material properties to meet the needs of very different and challenging requirements, without impacting smartphone readout or requiring a complete redesign of the system.”

Rare earth chips
Using one type of rare earth, the University of California at Santa Barbara (UCSB) has devised a new compound semiconductor device that manipulates light in the invisible infrared/terahertz range.

The device consists of embedded nanostructures containing ordered lines of atoms. Researchers combined erbium (Er) with antimony (Sb), resulting in an embedded compound called erbium antimonide (ErSb). The ErSB-based semi-metallic nanostructures were also used in conjunction within the semiconducting matrix of gallium antimonide (GaSb).

Erbium is a rare earth that can be found in neutron-absorbing control rods. It is a key component in fiber optic communications systems. ErSb is an ideal material to match with GaSb, according to researchers.

The format and orientation of the rare earth element can be controlled during the epitaxial growth process. As a result, a surface plasmon arises within the semiconductor bandgap due to the semimetallic nanostructures.

All told, the conductive nanowires perform like a broadband polarizer in the infrared and terahertz frequency ranges, according to researchers. Applications include solar cells, medical systems and plasmonics.

“The nanostructures are coherently embedded, without introducing noticeable defects, through the growth process by molecular beam epitaxy,” said Hong Lu, researcher in UCSB’s Department of Materials and Department of Electrical and Computer Engineering, on the university’s Web site. “Secondly, we can control the size, the shape and the orientation of the nanostructures.”

In yet another application, the University of Cornell and Brookhaven National Laboratory have demonstrated the ability to switch a transition metal oxide, a lanthanum nickelate (LaNiO3), from a metal to an insulator by making the material less than a nanometer thick.

An artist’s rendering of the thickness-driven, metal-insulator transition in sub-nanometer films of a lanthanum nickelate. (Source: Cornell).

These types of oxides have high carrier densities. Lanthanum itself is a silver-white metal, which is one of the most reactive rare earth elements. It is used to make special optical glasses, such as infrared absorbing glass, telescope lenses, among other products.

Researchers used molecular beam epitaxy (MBE) to synthesize thin samples of the lanthanum nickelate. Using MBE with a technique called angle-resolved photoemission spectroscopy (ARPES), researchers were able to see how the interactions of the electrons in the material changed across this threshold.

Cornell and Brookhaven discovered that when the films were less than three nickel atoms thick, the electrons looked like a checkerboard. Researchers discovered a destruction of Fermi liquid-like quasiparticles in the correlated metal LaNiO3 when confined to a critical film thickness of two unit cells.

“This is accompanied by the onset of an insulating phase as measured by electrical transport,” according to researchers. “We show how this is driven by an instability to an incipient order of the underlying quantum many-body system, demonstrating the power of artificial confinement to harness control over competing phases in complex oxides with atomic-scale precision.”

Paper RAMs and other chips from Symposia on VLSI Technology & Circuits
Here’s an advance look at some of the papers to be presented at the 2014 Symposia on VLSI Technology & Circuits, which will be held in Hawaii on June 9-12, 2014 (Technology Symposium) and June 10-13, 2014 (Circuits Symposium).

*National Taiwan University will report on the first paper-based nonvolatile memories – resistive random access devices – made with an all printing approach using a sequence of inkjet- and screen-printing techniques. The printed paper-based memory devices (PPMDs) can be applied as labels on electronics or on living objects for multi-functional, wearable, on-skin, and biocompatible applications.

*Japan’s Low Power Electronics Association & Project (LEAP) consortium will reveal a critical redox-control technology to enable conducting bridge devices. Fast (10ns) and low voltage (2 V) programming of copper atom switches are demonstrated in a 1Mb switch array for the first time.

*Micron Technology will describe a monolithic silicon photonics–on-bulk-CMOS process flow for devices that would interconnect distant and distributed memories. Features include deep-trench isolation, polysilicon waveguides, grating couplers, filters, modulators, and detectors. With the addition of an external 1280-nm light source, a fully functional optical link (5 Gb/s with 2.8 pJ/b), capable of WDM (wavelength division multiplexing), has been demonstrated.

*In a demonstration of finFET technology suitable for 10nm CMOS manufacturing, Samsung, IBM, ST, GlobalFoundries and UMC will jointly showcase a platform technology for low-power and high-performance applications. It offers a contacted poly pitch (64nm) and metallization pitch (48nm) on both bulk and SOI substrates. A 0.053 μm2 SRAM bit-cell is reported with a low corresponding static noise margin of 140 mV at 0.75 V.

*CEA-LETI and others will present for the first time high-performance nanowire (NW) TFETs built with a CMOS-compatible process flow. The devices feature compressively strained Si1-xGex (x=0, 0.2, 0.25) nanowires, Si0.7Ge00.3 source/drain, and high-κ metal gate.