Patent Grant
6960782
The present invention claims priority to European Application Number 02009742.4, “Electronic Devices”, filed on Apr. 30, 2002, now abandoned. The EP application is herein incorporated by reference in its entirety.
The present invention generally relates to electronic devices and particularly relates to electronic devices based on fullerenes and method of making such devices.
Ultra-small electronic devices on the nanometer have been the subject of considerable exploratory research. For example, U.S. Pat. No. 5,331,183 describes heterojunctions, diodes, photodiodes, and photovoltaic cells each based on a junction between a conjugated polymer and a fullerene, such as Buckminsterfullerene, C60. The polymer forms a p-type semiconductive donor layer and the fullerene forms an n-type semiconductive acceptor layer. Charge separation in the junction occurs on illumination of the junction.
In accordance with the present invention, there is now provided an electronic device comprising a junction formed between a first fullerene layer having a first doping concentration and a second fullerene layer having a second doping concentration different from the first doping concentration.
The first doping concentration may be zero. The second fullerene layer may be a monolayer. Similarly, the first fullerene layer may be a monolayer. The second fullerene layer may comprise an electron donor dopant such as an alkali metal. The second doping concentration may be in the region of 1021 per cm3. In a preferred embodiment of the present invention, the device is in the form of a diode wherein the first fullerene layer is connected to an anode and the second fullerene layer is connected to a cathode. In another preferred embodiment of the present invention, the device is in the form of a field effect transistor wherein the first fullerene layer serves as a gate region and the second fullerene layer serves as a channel region extending between a source terminal and a drain terminal. The second fullerene layer may alternatively comprise an electron acceptor dopant. At least one of the first and second fullerene layers may be formed from C60. It should be appreciated that at least one of the first and second fullerene layers may consist of a single bucky ball.
Viewing the present invention from another aspect, there is now provided, a method for fabricating an electronic device comprising forming a junction between a first fullerene layer having a first doping concentration and a second fullerene layer having a second doping concentration different from the first doping concentration.
In a preferred embodiment of the present invention, there is provided a semiconductor/metal combination. By varying the ratio between the semiconductor and the metal, the electrical properties of the device can be adjusted. No illumination is needed to render the device operable.
Preferred embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:
Preferred embodiments of the present invention to be described shortly include nanometer sized structures that operate as elements for electronic circuits on the nanometer scale. The structures described by way of example are based on combinations of fullerenes in pure form with fullerenes doped with a metal. In particularly preferred embodiments of the present invention, doped exohedral and endohedral fullerenes such as Li@C60 and La@C82 are employed. Other embodiments of the present invention may include both semiconducting and/or metallic carbon nanotubes. The present invention advantageously facilitates the fabrication of circuit elements on a 1 nm scale because the typical length scale in fullerenes is 0.7 nm, which is the diameter of a single bucky ball.
Referring first to
The doping of the fullerenes constituting the doped fullerene layer 3 is in the concentration of 1021 per cm3 or one Li atom per C60. Li@C60 is an n-type material. However, experimental results to be described shortly demonstrate that Li@C60 in the aforementioned concentration is surprisingly metallic in behavior. More surprisingly, experimental results to be described shortly demonstrate that the doped/undoped fullerene junction of the diode hereinbefore described exhibits an I/V curve which is characteristic of a diode. In operation, the undoped fullerene layer 2 is connected to the anode of the diode and the doped fullerene layer 3 is connected to the cathode of the diode. This demonstrates that electronic devices can be fabricated based on junctions between metal doped fullerenes and undoped fullerenes. The metal doped fullerenes alone exhibit metallic properties and the undoped fullerenes alone exhibit semiconductor properties.
In other embodiments of the present invention, the undoped fullerene layer 2 may also be a monolayer. Similarly, in other embodiments of the present invention, the undoped fullerene layer 2 may be more than two molecules thick. Likewise, in other embodiments of the present invention, the doped fullerene layer 3 may be more than one molecule thick. In alternative embodiments of the present invention, different fullerenes may be employed, such as C82, for example. As indicated earlier, the doping of the fullerenes constituting the doped fullerene layer 3 is in the concentration of 1 Li atom per C60. However, different concentrations of electron donors may be employed in other embodiments of the present invention. Doping with more than one atom per C60 is equally possible. Other metals may be employed together with or in place of Li. Group 1 elements such as sodium (Na), potassium (K), otherwise known as the alkali metals, and elements such as lanthanum (La) are examples of possible alternatives. It will be appreciated then that Fermi levels and other relevant energy levels can be tuned by choice of dopant. Different combinations of endohedral and exohedral fullerenes are also possible in the interests of tuning barrier heights, carrier concentrations and transport properties.
The metal substrate 1 may be replaced by a semiconducting substrate such as a silicon substrate or an insulating substrate such as silicon dioxide substrate, with appropriate conductive contacts made to the undoped fullerene layer 2. Examples of such contacts may be provided by intervening metal depositions, vias, or regions of degenerate semiconductor. The fullerenes can be located in step sites on such substrates. This advantageously permits self-assembly of devices. By surface relief patterning of the substrate, such devices can then be attached and interconnected at kinks, corners and steps in the pattern. As indicated earlier, Li@C60 is an n-type material. However, the present invention equally contemplates doping fullerenes with electron acceptors to produce p-type materials.
Such junctions as those described herein are important elements of nanoscale semiconductor technology. Possible applications of junctions such as those hereinbefore described include but are not limited to electronic and optoelectronic components such as diodes, photodiodes and the like on a nanometer scale. Such elements permit fabrication of many different well-known electronic devices, such as charge-coupled devices for example, at a much higher integration density than hitherto possible.
Referring now to
Referring now to
In the JFETs hereinbefore described with reference to
In other JFETs embodying the present invention, a different fullerene may be employed, such as C82, for example. Similarly, in other JFETs embodying the present invention, other dopant metals may be employed together with or place of Li. Group 1 elements such as Na, K, otherwise known as the alkali metals, and elements such as La, are examples of possible alternatives. Likewise, different concentrations of electron donors may be employed in other embodiments of the present invention. It should also be realized that, in other JFETs embodying the present invention, the gate region may be greater than one monolayer thick. Similarly, in other JFETs embodying the present invention, the gate region may have a different shape and dimensions to those hereinbefore described with reference
In particularly preferred examples of the JFETs hereinbefore described with reference to
Referring now to
In the embodiments of the present invention hereinbefore described, junctions are formed between metal-doped and undoped fullerenes. However, in other embodiments of the present invention, both similar and different devices may be produced by forming junctions between metal-doped fullerenes in which the dopants and/or doping concentrations differ. Accordingly, embodiments of the present invention include device structures involving n-n+, p-p+, and many other junctions. By combining p-type and n-type doped fullerene layers, n-p-n and p-n-p bipolar transistor structures with nanometer dimensions can be produced. Similarly, quantum well heterostructures can be made by stacking appropriately doped fullerene layers.
Examples of test junctions and their corresponding I/V characteristics will now be described with reference to
Referring first to
Referring now to
With reference again to
| Number | Date | Country | Kind |
|---|---|---|---|
| 02009742 | Apr 2002 | EP | regional |
| Number | Name | Date | Kind |
|---|---|---|---|
| 5171373 | Hebard et al. | Dec 1992 | A |
| 5331183 | Sariciftci et al. | Jul 1994 | A |
| 5391323 | Haddon et al. | Feb 1995 | A |
| 5454880 | Sariciftci et al. | Oct 1995 | A |
| 5637260 | Okuda et al. | Jun 1997 | A |
| 6750471 | Bethune et al. | Jun 2004 | B2 |
| Number | Date | Country | |
|---|---|---|---|
| 20040016922 A1 | Jan 2004 | US |
