Science Daily — Chemistry researchers at Eindhoven University of Technology (TUE), funded by NWO's Chemical Sciences Council, recently discovered a way to determine the chemical composition of chips or coatings which are only a few nanometers across. This technique makes a major contribution to further miniaturisation in the field of micro-electronics and semiconductors, in which the smallest structural details are about 200 nanometers in size.
The method which the Eindhoven have developed is based on the radiation emitted by an object when it is irradiated by a beam of electrons. The measurable phenomenon occurs because the electrons in the beam collide with electrons in the atoms making up the object so that they enter an excited state. When the electrons return to the free state, with lower energy, X-rays are emitted. The wavelength of this radiation is characteristic of the chemical element, while the intensity of the radiation depends on the overall composition of the material.
The Dutch researchers combined a model for determining the chemical composition on the basis of the measured intensity with the use of a high resolution electron microscope. The beam of electrons which the microscope produces irradiates a minimum area of 10 by 10 nanometers. Using the X-rays emitted from this area, it is possible to determine precisely which chemical elements occur at that location and in what quantity.
Using this technique, research is now being carried out on a new type of electrical contact within chips constructed of a thin layer of cobalt deposited on a semiconductor. The cobalt forms an electrical connection for the semiconductor. When heat is applied, a chemical reaction takes place between the cobalt and the semiconductor, improving the mechanical strength and the electrical conductivity of the contact. The new chemical technique allowed the researchers to determine accurately where chemical changes had developed as a result of the heat-treatment.
In industry, micro-electronics or semiconductor components with a diameter of less than 1 micrometre are now commonplace. Further miniaturisation of the smallest structures within equipment, such as electrical connections and junctions within a chip, will only be possible if researchers are in a position to measure the chemical composition of the smallest details of the new materials.
http://www.sciencedaily.com/releases/2000/01/000127082008.htm
Thursday, May 24, 2007
How "Micro" Can We Go?
Science Daily — Microelectronics may be a growth industry, but the devices it produces are getting smaller every year. Just how "micro" can electronic devices go?
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Weizmann Institute scientists have provided one of the answers to this question. Making simple and elegant use of a chemical theory of liquids, they developed a way to predict the minimal possible size of bipolar transistors, one of the major types of transistors commonly used in microelectronics. They then managed to manufacture such a tiny structure using the experimental semiconductor copper indium diselenide. With an inner core of just 20 nanometers (billionths of a meter) and total width of 50 nanometers -- less than one-thousandth the width of a human hair -- the device is five times smaller than today's smallest standard transistors of this type.
This research, reported recently in Applied Physics Letters, was performed by doctoral student Shachar Richter, working with Prof. David Cahen of the Materials and Interfaces Department, Dr. Yishay Manassen, formerly of Weizmann's Chemical Physics Department and now a professor of physics at Ben-Gurion University of the Negev, and Dr. Sidney Cohen, head of Weizmann's Surface Analysis Unit.
In his research, Richter used atomic force microscopy -- a technique in which a phonograph-like stylus probes the surface of a material -- to manipulate atoms in a semiconductor. Normally, such microscopes can only shift atoms on the surface of a material, but Richter, building on earlier research by Prof. Cahen, managed to move these atoms around inside the semiconductor.
Richter achieved his results by applying a voltage to the semiconductor and passing a current through the material. Aided by the slight heating produced by the current, the voltage caused atoms called dopants, which determine the material's conductivity, to be propelled in a particular direction. Even though only 100 to 200 dopants were moved in this manner, this sufficed to produce a tiny transistor. It consisted of a hemispherical layer of relatively high conductivity containing the redistributed dopants, flanked on both sides by material with different conductivity.
Next, Richter used the same microscope stylus -- at low voltage -- to map the conductivity of this miniature structure. Richter's new mapping method, called scanning spreading resistance, reveals the precise path that would be taken by an electric current flowing through a transistor of this type. This new type of measurement, developed independently by Belgian researchers around the time of Richter's study, promises to become an important tool for evaluating miniature electronic devices.
These findings don't necessarily mean that microelectronic devices will eventually get as small as Richter's transistor. His device, however, can serve as a valuable research tool for studying the limits of miniaturization.
Funding for this research was provided by the Israel Science Foundation and the Minerva Foundation, Munich, Germany.
http://www.sciencedaily.com/releases/1998/12/981204074905.htm
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Nanotechnology
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Weizmann Institute scientists have provided one of the answers to this question. Making simple and elegant use of a chemical theory of liquids, they developed a way to predict the minimal possible size of bipolar transistors, one of the major types of transistors commonly used in microelectronics. They then managed to manufacture such a tiny structure using the experimental semiconductor copper indium diselenide. With an inner core of just 20 nanometers (billionths of a meter) and total width of 50 nanometers -- less than one-thousandth the width of a human hair -- the device is five times smaller than today's smallest standard transistors of this type.
This research, reported recently in Applied Physics Letters, was performed by doctoral student Shachar Richter, working with Prof. David Cahen of the Materials and Interfaces Department, Dr. Yishay Manassen, formerly of Weizmann's Chemical Physics Department and now a professor of physics at Ben-Gurion University of the Negev, and Dr. Sidney Cohen, head of Weizmann's Surface Analysis Unit.
In his research, Richter used atomic force microscopy -- a technique in which a phonograph-like stylus probes the surface of a material -- to manipulate atoms in a semiconductor. Normally, such microscopes can only shift atoms on the surface of a material, but Richter, building on earlier research by Prof. Cahen, managed to move these atoms around inside the semiconductor.
Richter achieved his results by applying a voltage to the semiconductor and passing a current through the material. Aided by the slight heating produced by the current, the voltage caused atoms called dopants, which determine the material's conductivity, to be propelled in a particular direction. Even though only 100 to 200 dopants were moved in this manner, this sufficed to produce a tiny transistor. It consisted of a hemispherical layer of relatively high conductivity containing the redistributed dopants, flanked on both sides by material with different conductivity.
Next, Richter used the same microscope stylus -- at low voltage -- to map the conductivity of this miniature structure. Richter's new mapping method, called scanning spreading resistance, reveals the precise path that would be taken by an electric current flowing through a transistor of this type. This new type of measurement, developed independently by Belgian researchers around the time of Richter's study, promises to become an important tool for evaluating miniature electronic devices.
These findings don't necessarily mean that microelectronic devices will eventually get as small as Richter's transistor. His device, however, can serve as a valuable research tool for studying the limits of miniaturization.
Funding for this research was provided by the Israel Science Foundation and the Minerva Foundation, Munich, Germany.
http://www.sciencedaily.com/releases/1998/12/981204074905.htm
Delft University Of Technology Discovers How To Control Nanowires
Science Daily — Jorden van Dam, researcher at the Kavli Institute of Nanoscience Delft, has succeeded in largely controlling the transportation of electrons in semiconductor nanowires. Van Dam moreover discovered how to observe a divergent type of supercurrent in these wires. Nanowires have superior electronic properties which in time could improve the quality of our electronics. On Tuesday, June 13, Van Dam will receive his PhD degree at Delft University of Technology based on this research.
During his PhD research, Jorden van Dam focused on semiconductor nanowires. These are extremely thin wires (1-100 nanometers thick) made of, for example, the material indiumarsenide, which has superior electronic properties. The integration of these high quality nanowires with the now commonly used silicium technology offers intriguing possibilities for improving our electronics in future. According to Van Dam, in recent years many possible applications for semiconductor nanowires have emerged, such as in lasers, transistors, LEDs and bio-chemical sensors. Philips is one of the companies that is conducting intensive research into the possibilities for semiconductor nanowires in specific applications.
Van Dam - who during his PhD research co-authored articles that were published in Nature and Science - was able to make a so-called quantum dot in a semiconductor nanowire (this is done at extremely low temperatures). These quantum dots can be regarded as artificial atoms and in the distant future will serve as building blocks for super-fast quantum computers. In a quantum dot, a number of electrons can be 'confined'. The magnificence of Van Dam's research is the total control he has managed to gain over the number of electrons that can be confined in a quantum dot. He can control this number by means of an externally introduced charge. A crucial factor for the extreme degree of control that Van Dam has achieved is the quality (for example the purity) of the nanowires, which were supplied by Philips. It is above all the quality of the material used (wires and electrodes) that was greatly improved during Van Dam's research.
The research also produced new physical observations. In the improved nanowires, Van Dam achieved for the first time the realisation and observation of a (theoretically already predicted) divergent type of supercurrent (a supercurrent is the current that occurs in superconductivity). In a quantum dot, the electrons normally pass through one by one. In superconductivity, the passage of electrons occurs in pairs. Van Dam, with the help of superconductor electrodes, has now achieved a supercurrent in the quantum dot, whereby the pairs of electrons pass through one by one.
Van Dam has also - under specific conditions - achieved a reversal in the direction of the supercurrent. He is able to control this reversal by varying the number of electrons confined in the quantum dot. With this, the Delft University of Technology researcher has achieved a largely controllable superconductor connection in semiconductor nanowires.
http://www.sciencedaily.com/releases/2006/06/060615075247.htm
During his PhD research, Jorden van Dam focused on semiconductor nanowires. These are extremely thin wires (1-100 nanometers thick) made of, for example, the material indiumarsenide, which has superior electronic properties. The integration of these high quality nanowires with the now commonly used silicium technology offers intriguing possibilities for improving our electronics in future. According to Van Dam, in recent years many possible applications for semiconductor nanowires have emerged, such as in lasers, transistors, LEDs and bio-chemical sensors. Philips is one of the companies that is conducting intensive research into the possibilities for semiconductor nanowires in specific applications.
Van Dam - who during his PhD research co-authored articles that were published in Nature and Science - was able to make a so-called quantum dot in a semiconductor nanowire (this is done at extremely low temperatures). These quantum dots can be regarded as artificial atoms and in the distant future will serve as building blocks for super-fast quantum computers. In a quantum dot, a number of electrons can be 'confined'. The magnificence of Van Dam's research is the total control he has managed to gain over the number of electrons that can be confined in a quantum dot. He can control this number by means of an externally introduced charge. A crucial factor for the extreme degree of control that Van Dam has achieved is the quality (for example the purity) of the nanowires, which were supplied by Philips. It is above all the quality of the material used (wires and electrodes) that was greatly improved during Van Dam's research.
The research also produced new physical observations. In the improved nanowires, Van Dam achieved for the first time the realisation and observation of a (theoretically already predicted) divergent type of supercurrent (a supercurrent is the current that occurs in superconductivity). In a quantum dot, the electrons normally pass through one by one. In superconductivity, the passage of electrons occurs in pairs. Van Dam, with the help of superconductor electrodes, has now achieved a supercurrent in the quantum dot, whereby the pairs of electrons pass through one by one.
Van Dam has also - under specific conditions - achieved a reversal in the direction of the supercurrent. He is able to control this reversal by varying the number of electrons confined in the quantum dot. With this, the Delft University of Technology researcher has achieved a largely controllable superconductor connection in semiconductor nanowires.
http://www.sciencedaily.com/releases/2006/06/060615075247.htm
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