Professor Takahiro Shinada of the Consolidated Research Institute for Advanced Science and Medical Care, Waseda University (ASMeW)(Japanese Only) and Professor Iwao Ohdomari, et al. of the Ohdomari Laboratory have discovered that the systematic placement of impurity (dopant) atoms one-by-one in a silicon semiconductor results in fewer (large) variations in threshold voltage for the operation of a semiconductor device, and furthermore they discovered that threshold voltage decreases by approximately 0.2 volts. This has raised hopes for the development of a dependable, highly functionalized semiconductor device which runs on low-voltage and is also highly integrated and miniaturized. The possibility is also being raised of the creation of a quantum device from silicon, something which has been a source of frustration up until now. Work will now be done to apply this new method to cutting-edge measurement technologies for medical treatments which utilize the DNA and proteins of cells and organic molecules
The results of Professors Shinada, Ohdomari, et al. are published in the October 20th edition of the British journal ”Nature”. (Title: “Enhancing semiconductor device performance using ordered dopant arrays”)
ASMeW was chosen for the 2004 Ministry of Education Culture, Sports, Science and Technology’s program for fostering strategic research centers (Super COE); ASMeW contributes to the expansion and development of research into maintaining and promoting public health.(Japanese Only) The present research results are part of basic research being done into semiconductor devices with the hope that they will aid in the development of new therapeutic technologies. Waseda University receives funding from the Ministry of Education, Culture, Sports, Science and Technology to further its special research (ustilizing the established single-ion implantation technique) at its (COE Program) “Molecular Nano-Engineering Research Center”.
Note:
Single-ion implantation is the penultimate nanotechnology used in the research of various fields from semiconductors to Biotech where atoms are ionized and placed one at a time in specific locations.
In the present research, phosphorous atoms – needed in the making of n-type semiconductors – were ionized and systematically arranged on a silicon substrate. For highly integrated and miniaturized semiconductors, it has been shown that large variations in the distribution of impurity atoms cannot be ignored. The research group has been making semiconductor devices where the number and position of impurity atoms is strictly controlled, and they have succeeded in lowering the fluctuation in electrical conductivity which is caused by large variations in the number of impurity atoms from 63% to 13%. Analysis revealed that large variations in the positions of impurity atoms (not just number) also had a great effect on the properties of the semiconductor.
In the present research, the threshold values for semiconductors with even more strictly numbered and placed impurity atoms were compared with semiconductors whose impurity atom placement was by-and-large random. The result was less fluctuation in threshold voltage and, furthermore, an average threshold voltage value 0.2V less for the semiconductors with systematically placed impurity atoms. This is attributed to the uniformity of coulomb potential in the conducting channel region due to the ordered distribution of impurity atoms.
The results, as they apply to high integration through controlling number and placement of impurity atoms, is an increased trust in and improvement of the functionality of silicon (whose limits were being reached). It also means a reduction in inferior items. There is also hope for the realization of a quantum device made from the systematic arrangement of single atoms (silicon based), which has been quite difficult until now. Semiconductor physics and electrical engineering now have the notion of number and placement of impurity atoms, not just their average density, to consider when determining the electrical qualities of semiconductors.
At present, however, production via this method is low, so the question that must be tackled is how to develop manufacturing technologies for ion implantation and how to improve aiming precision.
Work will now commence on how to make a single-atom device from just one impurity atom in a nano-sized semiconductor device. Also, in order to put the results of the present research to work for society, researchers from many fields in the COE Program will work together to develop a way to use the systematic array of organic molecules and cells for the creation of a high function bio-chip to support basic research for medical treatment and examination.
（Improvement in the electric qualities of semiconductors through ordered arrays of dopant atoms.）
【 Explanation of Terminology 】
Single Ion Implantation
Discovered by the Ohdomari Laboratory, Waseda Science and Engineering. This technology is the only one in the world which is able to implant ions one by one using focused ion beam technology. As of October 2005, Be, B, Si, P, Fe, Ni, Cu, Ga, Ge, As, Pd, In, Sb, Pt, Au are able to be implanted. Aiming precision is 60nm.
Focused Ion Beam
A focused ion beam device scans the surface of a test material with a highly concentrated ion beam, detects the secondary electrons produced, and fabricates the test material surface using the microscopic images.
Silicon Semiconductor
Silicon: atomic number 14. One of the most common elements on earth. The interfusion of dopant atoms leads to the creation of p-type and n-type semiconductors. An extremely important element in electrical engineering.
Impurity Atoms (dopant atoms)
Xenogenic elements which affect the electrical conductivity, etc. of semiconductors when implanted in small amounts. Also known as dopant atoms.
Threshold Voltage
One parameter affecting the performance of transistors; the lowest voltage that can run between two electrodes (source – drain). The lowest amount of voltage for turning on the switch.
Quantum device
A device that applies the features of quantum physics where (in this case) electrons have both particle-like and wave-like properties.
Posted by: Public Relations Office, Public Relations Department
