NIL: AN ULTRA LOW COST, LARGE AREA WAY FOR NANOELECTRONICS FABRICATION

Nanoimprinting lithography (NIL) is a simple pattern transfer process that is emerging as an alternative nanopatterning technology to traditional photolithography. NIL allows the fabrication of two-dimensional or three-dimensional structures with submicrometer resolution and the patterning and modification of functional materials. A key benefit of nanoimprint lithography is its sheer simplicity. There is no need for complex optics or high-energy radiation sources with a nanoimprint tool. There is no need for finely tailored photoresists designed for both resolution and sensitivity at a given wavelength. The simplified requirements of the technology allow low-cost, high-throughput production processes of various nanostructures with operational ease. NIL already has been applied in various fields such as biological nanodevices, nanophotonic devices, organic electronics, and the patterning of magnetic materials.

Recently researchers have taken this process one step further by demonstrating that direct nanoimprinting of metal nanoparticles enables low temperature metal deposition as well as high-resolution patterning. This approach has substantial potential to take advantage of nanoimprinting for the application in ultralow cost, large area printed electronics.

In nanoimprinting, a mold with nanostructures is pressed to deform and shape a thin material film deposited on a substrate. That is why nanoprinting for metal is harder to achieve. Therefore, to achieve successful nanoimprinting, the material needs to have proper flow properties (viscosity and surface tension) adjustable for complete mold pattern replication within reasonable processing temperatures and pressures. Ideal materials usually are thermoplastics, thermoset polymers, or other deformable materials with the desired flow properties.

Metal nanoimprinting is typically an indirect process where a polymer (e.g., PMMA) pattern is first created by nanoimprinting, which is then used as mask for dry etching of a predeposited metal film or as part of the metal lift-off process. It is conventional metal nanoimprinting involves multiple steps and expensive processes, thereby increasing the cost of manufacturing and offsetting the advantages of the nanoimprinting process. Very few direct metal nanoimprinting processes have been demonstrated so far due to the high melting temperature of metals.

The advantage of this process is that it eliminates the need of intermediate polymer nanoimprinting steps for dry etching or vacuum deposition. Also metal nanoparticle solution is also there as a precursor to use the solution processable form of the metal component for the nanoimprinting process, thereby eliminating the need to exceed the bulk metal melting temperature. The nanoimprinted nanoparticles can be transformed into conductive and continuous metal films by low-temperature nanoparticle melting.

NANOTUBE = RAM + FLASH MEMORY

In the previous articles we have talked about memories, whose potentiality and functionality are rapidly increasing due to the advancement in nano technology. I this article we move forward to one upper level by introducing the duality of random access memory and flash memory.

We all know random access memories require constant power to offer their fast access speeds, but can't be scaled to as small a size as slower nonvolatile flash memories. Now researchers believe they can combine the high-speed of RAM with the nonvolatility of flash by using telescopic nanotubes.

Ultra-dense nano-electro-mechanical system (NEMS) arrays could offer molecular sized memory cells that are as fast as RAM but nonvolatile like flash by harnessing concentric nanotubes that turn bits on(1) and off(0) by running current through the tubes to make the inner one stick out or stay inside the outer nanotube.

A study has been going on aimed at replacing silicon-based memory technologies with carbon-based concentric telescopic nanotubes that measure only a few nanometers in diameter. This NEMS approach uses the mechanical movement of nanotube telescoping in and out of concentric tubes to either contact or break contact with a molecular-sized electrode, thus combining the speed of RAM with the non-volatility of flash memory.

To change a bit's state, current would be run through the nanotube, causing electrostatic forces to move the inner nanotube either into or out of the outer nanotube—depending on the direction of current flow. Once a bit has been flipped, power could be removed while the bit stays locked to retain its state indefinitely since van der Waals forces would attract the concentric tubes to each other.

Other potential applications of the telescopic nanotubes include drug delivery to individual cells and nano-sized thermometers which can differentiate between healthy and cancerous cells.

Ultra-Dense Memory Storage Devices: Water and Nanoelectronics Will Do The Trick!

We all know that excessive moisture can typically wreak havoc on electronic devices, but now researchers have demonstrated that a little water can help create ultra-dense storage systems for computers and electronics.

A team of experimentalists and theorists at the University of Pennsylvania, Drexel University and Harvard University has recently proposed a new and surprisingly effective means of stabilizing and controlling ferroelectricity in nanostructures: terminating their surfaces with fragments of water. Ferroelectrics are technologically important smart materials for many applications because they have local dipoles, which can switch up and down to encode and store information.

According to the researchers a single wire of even a few atoms across can act as a stable and switchable dipole memory element which is here the prime factor behind this ultra dense memory devices. The researchers have also successfully demonstrated the benefits of using water to stabilize memory bits in segments of oxide nanowires that are only about 3 billionths of a meter wide.

The question is how water helps to building this devices holding higher number of bits. The key is how water sticks to oxides. Here water is the key ingredient in making these wires hold their state.

But another question is why nanotechnology again as usual take its place here. The results show that ferroelectric surfaces with water fragments or other molecules can stabilize ferroelectricity in smaller structures than previously thought.

Though a scheme for the dense arrangement and addressing of these nanowires remains to be developed, such an approach would enable a storage density of more than 100,000 terabits per cubic centimeter. If this memory density can be realized commercially, a device the size of an iPod nano could hold enough MP3 music to play for 300,000 years without repeating a song or enough DVD quality video to play movies for 10,000 years without repetition.

GAME IS CHANGING IN SOLAR POWER!

Researchers at Rensselaer Polytechnic Institute have discovered and demonstrated a new method for overcoming two major hurdles facing solar energy. By developing a new antireflective coating that boosts the amount of sunlight captured by solar panels and allows those panels to absorb the entire solar spectrum from nearly any angle.

To get maximum efficiency when converting solar power into electricity, every single of photon of light should be absorbed by solar panel regardless of the sun’s position of the sky. New antireflective coating synthesized by the researchers makes it possible.

An untreated silicon solar cell only absorbs 67.4 percent of sunlight shone upon it — meaning that nearly one-third of that sunlight is reflected away and thus unharvestable. From an economic and efficiency perspective, this unharvested light is wasted potential and a major barrier hampering the proliferation and widespread adoption of solar power.

After a silicon surface was treated with new nano engineered reflective coating, however, the material absorbed 96.21 percent of sunlight shone upon it — meaning that only 3.79 percent of the sunlight was reflected and misutilised. This huge gain in absorption was consistent across the entire spectrum of sunlight, from UV to visible light and infrared, and moves solar power a significant step forward toward economic viability.

Typical antireflective coatings are engineered to transmit light of one particular wavelength. This new coating stacks seven of these layers, one on top of the other, in such a way that each layer enhances the antireflective properties of the layer below it. These additional layers also help to bend the flow of sunlight to an angle that augments the coating's antireflective properties. This means that each layer not only transmits sunlight, it also helps to capture any light that may have otherwise been reflected off of the layers below it.

The seven layers, each with a height of 50 nanometers to 100 nanometers, are made up of silicon dioxide and titanium dioxide nanorods positioned at an oblique angle — each layer looks and functions similar to a dense forest where sunlight is "captured" between the trees. The nanorods were attached to a silicon substrate via chemical vapor disposition.

The added advantage is that the new coating can be affixed to nearly any photovoltaic materials for use in solar cells, including III-V multi-junction and cadmium telluride.