Semiconductor device manufacturing: process – Having biomaterial component or integrated with living organism
Reexamination Certificate
2001-09-21
2003-10-21
Kielin, Erik (Department: 2813)
Semiconductor device manufacturing: process
Having biomaterial component or integrated with living organism
C438S479000, C438S939000, C438S945000, C438S962000
Reexamination Certificate
active
06635494
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a quantum device wherein quantum dots are arrayed in two-dimensional configuration. The quantum dots arrayed on the quantum device can be preferably used as a single-electron transistor, doping diode, doping transistor, doping transistor array and semiconductor light emitting device.
2. Description of Related Art
Devices that utilize single-electron tunnel effect such as single-electron transistors and single-electron memories are attracting much attention. The single-electron transistor, for example, is a promising candidate that can replace MOSFETs to satisfy the requirements of miniaturization of devices to the order of sub-micron for which improvements on the MOSFETs, the mainstream technology in the field of semiconductor transistors, are reaching limitations thereof.
A fine particle surrounded by thin insulation layer receives electrons from an external electrode by the tunnel effect. Because the particle has a capacitance C with respect to the outside, electrostatic energy of the particle changes by e
2
/2C when an electron enters therein. This prohibits subsequent electron from entering the fine particle by the tunnel effect. Therefore, in order to fabricate the device utilizing the single-electron tunnel effect, it is inevitable to arrange quantum dots on an insulator, the quantum dots being formed from microscopic metal particles having electrostatic energy higher than energy &Dgr;E (approximately 25 mV) required for thermal excitation of an electron at room temperature. In case e
2
/2C has a low value, it is inevitable to make an array of quantum dots having energy just above the Fermi level of a microscopic dot higher than the thermal excitation level of electron. Although single-electron operation is lost in this case, transistor operation can still be achieved. Also microscopic lead wires must be formed even when a quantum device can be achieved, because the tunnel effect does not occur with wide lead wires of conventional circuits due to parasitic capacitance accompanying the lead wires.
As a single-electron memory, a prototype device was made as a fine line (100 nm wide) of polycrystal Si film having an extremely small thickness of 3.4 nm and a gate electrode (100 nm) crossing each other via an oxide film gate of 150 nm by depositing a-Si in a depressurized CVD process and crystallizing it at 750° C. (Japanese Journal of Applied Physics: Vol. 63, No. 12, pp. 1248, 1994). This device operates at a room temperature and has a potential for the use as an nonvolatile memory which operates at a speed exceeding the limitation of the conventional flash memory. Also an aluminum-based single-electron transistor having an island electrode measuring 20 nm was fabricated by means of electron beam lithography and triangular shadow evaporation technologies (Jpn. J. Appl. Phys., Vol. 35, 1996, pp. L1465-L1467). This single-electron transistor has advantages which are not found in silicon-based devices, for example, a periodical gate modulation characteristic wherein background current does not depend on the gate voltage.
However, the single-electron memory based on the polycrystal Si film is unstable because there are variations in the Si film thickness. Also the Al-based single-electron transistor operates at 100 K, far below the room temperature, and is not of practical use.
SUMMARY OF THE INVENTION
Thus, an object of the present invention is to provide a quantum device which operates stably at the normal temperature and is applicable for commercial production of single-electron transistors and single-electron memories.
Another object of the present invention is to provide extremely small devices such as diode, transistor and semiconductor light emitting devices doped with extremely small amounts of impurities, not experienced in the prior art, by utilizing microscopic dots arranged in the quantum device.
In order to achieve the above and other objects, the quantum device of the present invention is constituted from a two-dimensional array of quantum dots formed from metal atom aggregates contained in a metalloprotein complex arranged on the surface of a substrate having an insulation layer at least on the surface thereof with a pitch of the size of the metalloprotein complex.
The metal which constitutes the metal atom aggregates used in the quantum device is preferably one that can ionize in an aqueous solution. For example, the metal may be iron Fe, aluminum Al, phosphorus P, germanium Ge, zinc Zn, manganese Mn, arsenic As, gold Au, silver Ag, tungsten W or the like, while Fe is preferable.
The diameter of the metal atom aggregates used in the quantum device is 7 nm or smaller, preferably 5 nm or smaller, and the pitch of the metalloprotein complex is preferably from 11 to 14 nm.
In a method appropriate for manufacturing the quantum device of the present invention, first the metalloprotein complex is let to be absorbed onto a denatured protein membrane, polypeptide membrane or LB membrane developed on a surface of an aqueous solution. The membrane is then placed on a substrate which is durable to temperatures beyond a burn-out temperature of the protein and has an insulating property on the surface thereof, to burn out the protein component in a gas atmosphere which does not react with the substrate. The metalloprotein complex is turned into a metal oxide and remains on the substrate in a pattern of dots spaced by a pitch of the size of the protein molecule. Then the metal oxide is heated in a reducing atmosphere to be reduced. The metal oxide is thus reduced into metal atom aggregates which are arranged in a two-dimensional array on the substrate.
The metalloprotein complex used in the quantum device of the present invention is preferably ferritin, but the protein may also be one derived from phage or virus.
As the substrate used in the quantum device of the present invention, silicon substrate has wide applicability, but a glass substrate or a ceramic substrate may also be used.
A single-electron transistor of the present invention is constituted from quantum dots which are formed from metal atom aggregates contained in metalloprotein complex and arrayed in a two-dimensional configuration with a pitch of the size of the metalloprotein complex on the surface of a substrate which is durable to temperatures beyond the burn-out temperatures of the protein and has an insulation layer on the surface thereof, and comprises a quantum well made of a first quantum dot, an electrode section made from at least three quantum dots located around the quantum well and a wiring section which connects the quantum dots other than those around the quantum well and the electrode section, wherein the electrode section has a source and a drain comprising second quantum dots and third quantum dots, respectively, which oppose each other, and a control gate comprising fourth quantum dots that remain.
The metal used in the metal atom aggregates, the metalloprotein complex and the substrate of the single-electron transistor may be the same as those used in the quantum device described above.
The diameter of the metal atom aggregate used in the single-electron transistor is 7 nm or smaller, or preferably 5 nm or smaller, which means that one aggregate normally comprises several thousands of atoms, depending on the metal element. As a consequence, the transition level nearest to the Fermi level of the aggregate is higher than the thermal excitation level of electron at room temperature. The quantum well and the electrode section are separated by a distance of 11 to 14 nm which allows the tunnel effect to occur. Therefore, the tunnel effect can be observed in the single-electron transistor at the room temperature or at around the temperature of liquid nitrogen.
An appropriate method for manufacturing the quantum transistor of the present invention comprises, in addition to the steps of manufacturing the quantum device described above, a step of irradiating the metal atom aggregates with an electron beam of a scanni
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