2005 Breaking News in Organic and Molecular Electronics
11.05.05 Spintronics: the End of the Transistor Era?
This article is not directly related to organic electronic materials. We make this exception because the information presented in a Science review paper "Magnetic Domain-Wall Logic" by a group of researches from United Kingdom, 2005, 309, page 1688 is extraordinary in it's possible affect on entire microelectronic industry in the future. Ultimately, the new developments in "spintronics", described in the article, may eliminate the need for the transistor (no matter - organic or inorganic) as a class of microelectronic logic devices. "Spintronics" is a new field of science and engineering that involves not only electric charge of the electron for operating of electronic devices (conventional integrated circuits), but both electric charge and spin of the electron. As it is well known from quantum mechanics, the "spin can have two directions, conventionally known as "up" and "down", permitting alternate representation of binary digits". The authors describe two different approaches used in spintronics: the semiconductor approach and the magnetic approach. The semiconductor approach operates with spin-polarized electrons in a semiconductor, but has limited development at this time due to "the lack of a suitable room-temperature ferromagnetic semiconductors". The magnetic approach uses magnetization of small elements made of a ferromagnetic metal. A number of devices have already been developed using this approach, such as magnetic tunnel junction (MTJ) and magnetic random access memory (MRAM). In the current Science paper, a development of a complete set of logic circuit elements: fan out junction, cross over junction, logical NOT, and logical AND based on magnetic domain wall approach is reported. The elements are made of tiny flat wire (nanowire) of magnetic material - Permalloy (Ni80Fe20), and the domain wall is a "mobile interface between regions" of the nanowire element with "oppositely aligned magnetization". To simplify, the domain wall is a border between small magnets that are formed in sections of wire and constantly (and logically) change their location, size, and direction of magnetization under the action of a rotating external magnetic field. The elements can be easily assembled into circuits of different complexity. The authors have fabricated even a 5-bit magnetic shift register and demonstrated one hour memory of the device. The logic output was measured using magneto-optical Kerr effect (MOKE). A scheme of operation of the magnetic nanowire logic NOT device is shown below.
1. Very little heat caused by data switching. 2. Extraordinary potential for a nonvolatile, high-density and high-speed memory technology. 3. Logical NAND function uses only two domain wall elements, whereas four transistors are required for the same operation in conventional circuits. 4. Logical AND function uses only one domain wall element, whereas six transistors are required for the same operation in conventional circuits. 10.24.05 Universal Display Corporation develops a blue phosphorescent OLED with practical operational lifetime Universal Display Corporation, one of the leading developers of OLED technology, has announced an invention of a blue phosphorescent OLED with operational lifetime of 15000 hours. This is a 'last linkage', long time needed for the development of practical, full color OLED display technology.
There are plenty of stable inorganic and organic LED materials emitting light of two of three major colors, red and green, however the blue ones are sparse.
Moreover, among known blue fluorescent and phosphorescent OLEDs, no one with operational lifetime exceeding 1000 hours has been reported to date.
The progress in this area was so slow that "the 1,000 hour lifetime barrier - a challenge that some people thought might be insurmountable" - UDC press release says. The present UDC development offers possibility for creation of OLED technology as efficient as never before.
Fujitsu announces developing of 'electronics paper', world's first efficient material with flexible display properties
Fujitsu company has released information on the development of a flexible display material, which possesses a number of marvelous characteristics: 1. Preserving the image in 'off' mode (no electricity necessary for the image's continuous display); 2. Very low energy consumption for the display operation (image change); 3. Preserving of color and all other image characteristics in bended state; 4. No image flickering. The company does not clearly reveal scientific background for the technology used, though mentions the display to be composed of as few as three colored layers (in comparison, modern liquid crystalline flat displays (LCDs) are composed of about 20 layers including different color filters, polarizers etc.).
300 GB of data on one disc are coming in our life An article "A New Dimension in Storage" published in PC magazine June 28, 2005, page 23 describes a break through achievement of InPhase Technologies in the development of three-dimensional holographic storage medium based on use of unique photopolymer. The invention will allow "to store as much as 20GB of data on a clear piece of plastic the size of a postage stamp". The main idea of dramatic increase in storage is distributing of the information in three dimensions using holographic technique instead of two dimensions (flat surface) as in 'conventional' CD and DVD discs. For continuation of the story click here.
Switching a single molecule conductivity
The researches prepared rows of molecules of a styrene derivative covalently bound to a silicon plate. At the 'tip' of each row they arranged a charged atom with 'free' valency they call 'dangling bond'. The charge of each charged atom could be altered using special 'doping' technique. Using a scanning tunneling microscope, the researches detected behavior of the row of styrene molecules depending on the charge. They found that at the charge of the sample bias of -2.4V, all molecules in the row were activated, e.g. electroconductive. At -1.8V only about half, and at -1.6 only closest to the charged spot were still active. Finally, the researches put 'caps' on the charged spots, using special compound - bulky amine, just closed the charged spots and observed that all molecules in the row weren't active any more. After stripping off the 'caps' using special reagent, the recovery of the conductivity was observed.
To summarize, the use of 'dangling bonds' method and voltage allows to detect, measure, and control the conductivity of a single organic molecule. The authors stress the effect to be very pronounced even at room temperature, which is extremely important in practice.
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