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Quantum dots are semi conductor structures with dimensions 1.0 nanometer (1 nanometer = 10-9 meter) in length, width and height. These dimensions have large applications in futuristic electronic devices and precisely tuned lasers. We have tried to analyze the patent information in order to follow the technological development of the quantum dots. It was interesting to note that 37 patents presently exist on the fabrication methods and devices made out of quantum dots. The titles of all 37 patents are listed in Table 1.
The first patent on the method of forming quantum dot structures appeared way back in 1989 which was taken by Philips Electronic & Associated Industries Limited. This patent, granted by the European Patent Office (EPO), describes a method called the arrested precipitation technique. A suspension of particles of a semiconductor material for forming a quantum dot structure is formed a quantum dot structure is formed as a colloid by using the arrested precipitation technique and laser electromagnetic radiation of a wavelength which interacts resonantly with particles of a given size is directed through the suspension towards the substrate, so causing particles of the given size within the suspension to be deposited onto the substrate.
The next patent was granted by the United States Patent Office (USPTO) in 1992 which disclosed a new method for making highly integrated quantum wire arrays and quantum dot arrays in a single crystal compound semiconductor and Field Effect Transistors (FETs) of less than 0.1 micron gate length. Subsequently, other patents appeared on the basic technology for fabricating quantum dots and the concept of a "Quantum Dot Laser" was introduced.
In the following years, as the technology developed, the emergence of devices utilizing quantum dots was predominantly seen. This included the development of non-linear quantum dot optical devices, Shannon cell circuits, resonant electron transfer devices and quantum effect devices in which conduction between a plurality of quantum dots is achieved by terminal transition.
Quantum dots were further used for making a logic cell in 1995 (U.S. Patent No.5447873) and lateral resonant tunneling devices in 1996 a patent was issued on an invention which utilizes quantum dots for logic and memory elements of atomic scale which are used in computer central processing units. These elements consist of two quantum dots having opposite states and a third quantum dot situated between the two quantum dots and in physical contact with them. The third quantum dot is of a material which makes the opposite states of the first two quantum dots energetically favourable. In particular, there is provided by the invention a spin flip-flop suitable for use as electronic logic and memory in a quantum computer.
The spin flip-flop is designed to have two highly stable states, encoded entirely in the arrangement of electronic spins in the structure. Switching between the two states is accomplished by fast electromagnetic pulsing generally and by optical pulsing in the case of the spin flip-flop. The two stable states are the up-down and the down-up spin states of two single electros placed into two neighboring electronic quantum dots typically by doping or by a field effect. The operation of the device is facilitated and stabilized by the presence of a small particle or dot of an antiferromagnetic material placed between the two electronic dots.
It is also interesting to note that patents on the method of fabricating quantum dot structures with improved quality are being issued continuously and three such patents have been issued in 1996 by the USPTO. Another interesting feature is : an English company by the name of Isis Innovation Ltd. has obtained numerous patents on the making of quantum dots of uniform size from the EPO. On the other hand, the situation in India regarding quantum dots is rather bleak as no patents on this technology, have been granted until January 1997 and no application were filed in the last two years. It appears that India has not developed its competence in this area.
From the patent literature found in this area it appears that the major players in this technology are International Business Machines (IBM), Texas Instruments (TI), AT&T Corporation from U.S.A. and Sony Corporation, Nippon Telegraph & Telephone Corporation, Shimadzy Corporation, Matsushita Electric Inc. Co. Ltd. from Japan and Isis Innovation Limited from England.