JPH11266007A - Molecular single electron transistor and integrated circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make feasible direct connection of tunneling junction molecules to a fullerene, by forming a coupling of cyclopropane ring in a single electron transistor structure including quantum dot. SOLUTION: A molecular single electron transistor is composed of a quantun dot 11 made of a fullerene, insulating molecules 12, 13 displaying tunneling junction characteristics, conductive molecules 14, 15 displaying conductive characteristics, a gate insulating body 16 consisting of an insulate molecule forming an insulating gate and a gate 17 comprising conductive molecules. The conductive molecule 14 and the conductive molecule 15 respectively function as a source and a drain. In such a constitution, when a potential is impressed to the gate 17, the potential of the quantum dot 11 made of the fullerene is fluctuated by the potential fluctuation, and as a resultant, the channel current flowing between the source 14 and the drain 15 changes corresponding to the gate potential. Furthermore, the width of the tunnel junction and the barrier height, etc., can be controlled by changing the insulator molecular structure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel structure of an ultra-high performance transistor used for information processing, and more specifically, to a quantum dot made of organic molecules, a source,
In a single-electron transistor structure having a drain, a gate, a tunnel junction, and the like, the quantum dot is composed of fullerene having an organic three-dimensional structure, or a higher fullerene and a derivative thereof, and relates to a structure of an ultra-high-performance transistor. Things.

[0002]

2. Description of the Related Art A conventional information processing device has mainly used a transistor using a silicon semiconductor. The improvement in performance has been achieved by reducing the processing dimensions of gates and the like. For example, Wada et al., Journal of
Applied Physics, Vol. 74, No. 12, p. 7321
(1993) (Y. Wada, et. Al., J. Appl. Phys., 7.
4 (12), 7321 (1993).), The minimum feature size has been reduced for almost 30 years at a very fast pace of 70% in 3 years, and is now 0%. A working dimension of .25 microns (μm) has been used. However, 50 years after its birth, size reduction is approaching its limit, and a device with higher performance is required.

[0003] In order to solve this problem, single-electron transistors have been devised and studied. For example, Likarev,
IBM Journal, Vol. 32, p. 144 (1989)
Year) (KK Likharev, IBM J. Res. Develop, 32, 144
As described in detail in (1989).), A typical example is a single electron transistor consisting of a minute quantum dot and a source, drain region and gate region separated by a tunnel junction. It is stated that by setting the size to about 30 nm, an operation speed of 1 tera (10 ¹² ) hertz can be realized, and the speed can be increased by several orders of magnitude as compared with a conventional field-effect transistor made of silicon. Have been.

[0004] However, his performance estimation is not always accurate, and our research has revealed that it is necessary to make the size of the quantum dot very small in order to exhibit sufficient performance as an information processing device. Was. Ratovich et al., Journal of Applied Physics, 7
Vol. 5, No. 7, p. 3654 (1994) (M. Lutwyche, e
As described in detail in t. al., J. Appl. Phys., 75 (7), 3654 (1994)), in order to operate a single-electron transistor at an ultra-high speed of 1 terahertz or more, a diagram must be obtained. As shown in FIG. 6, the relationship between the size of the quantum dot and the operation speed is 10 nm or less, and it is necessary to set the size of the quantum dot to 1 nm or less in order to realize higher-performance device operation. On the other hand, the variation of the quantum dot size, which is very important when a device is integrated on a large scale, needs to be 5% or less.
Quantum dot size required for future ultra-high-speed devices 1
Ultra-fine and ultra-high-precision processing technology such as nm cannot be realized.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem of the single-electron transistor technology. It is intended to realize a device with high performance. In other words, the present invention realizes a novel device that makes maximum use of the characteristics of molecules, such as precise control of structural dimensions and simultaneous mass production of molecules having the same structure. This point will be described in more detail. By using a molecule composed of fullerene or higher fullerene or a derivative thereof for the quantum dot, the size of the quantum dot can be extremely reduced to 1 nm or less, which will be described later. As described above, the dimensional control of the tunnel junction portion where the dimensional control is particularly important can be performed very accurately by using molecules. Regarding single-electron transistors composed of organic molecules, see Wada, Atomic and Molecular Wires, Kruwer Publishing 19
1997 p. 193 (Atomic and Molecular Wires, C. Jo
achim and S. Roth (Eds.), Kluwer Academic Publishe
rs (1997) pp193). However, in a planar quantum dot structure as disclosed in this document,
Due to the limitation that a molecular bond must be formed between the tunnel junction and the gate insulator in the quantum dot, the space in which the molecule is to be placed is small, and the gate is large enough to enable high device performance. Cannot achieve capacity. For this reason, in order to realize higher performance device characteristics, it is desirable that the quantum dots have a three-dimensional structure so that an appropriate molecular arrangement is possible.

[0006] Although not particularly taken up in the prior art, it is necessary that two tunnel junctions provided adjacent to the quantum dot have substantially the same tunnel resistance. This cannot be controlled sufficiently simply by using conventional physical techniques. The reason is that the tunnel resistance (R) roughly depends on the film thickness (t) of the insulating film acting as a tunnel junction in a relationship such as R = k exp (−t) (1), so that only 0. This is because even if there is a difference in the tunnel junction width of 1 nm, the resistance value differs by about one digit. Here, k is a constant. With molecules,
The dimensional difference, that is, the difference in the bonding distance between the molecules is almost completely negligible. If the molecular structures are the same, almost the same tunnel resistance value can always be obtained.
Therefore, good operation characteristics can be realized even when many devices are integrated.

In addition, it is very difficult to connect a molecule to be a tunnel junction directly to fullerene with the conventional technology, and a high-performance molecular single-electron transistor having a structure using fullerene or a similar molecule for a quantum dot has been realized. To do so was technically impossible. In the present invention, a technique for connecting a direct tunnel junction molecule to fullerene has been made possible by forming a bond of a cyclopropane ring. Therefore, a very high-performance single-electron transistor having an operation speed of several terahertz or more can be realized, and the technical effect of the present invention is great.

[0008]

The basic structure of a single-electron transistor is a quantum dot, a tunnel junction, a conductive electrode, an insulated gate, and a gate. FIG. 1 schematically illustrates the structure of a single-electron transistor according to the present invention, in which a quantum dot 101, tunnel junctions 102 and 103, and a conductive electrode 10 are formed.
4, 105, insulated gate 106, and gate electrode 10
7 shows a structure consisting of The operating principle is that the gate electrode 107
The potential of the quantum dot 101 is changed by the applied potential, and the number of electrons passing through the quantum dot 101 is controlled.

Therefore, in order to form these structures with molecules, the quantum dots 101, the conductive electrodes 104,
105 and the gate electrode 107 must be formed of conductive molecules, the tunnel junctions 102 and 103 must be formed of a tunnel insulating molecule thin enough for electrons to tunnel, and the insulating gate 106 must be formed of an insulating molecule.

The quantum dot 101 has a size that satisfies the relationship between the quantum dot size and the operation speed shown in FIG. 6, that is, at least 10 nm or less, and about 1 nm or less for achieving higher performance. It is necessary. Fullerene or higher-order fullerenes and derivatives thereof have a double bond between carbons that gives conductivity and a diameter of about 0.7 nm, which satisfies all the conditions required for quantum dots in high-performance single-electron transistors. And is a very suitable material. Because its derivatives have various dimensions,
It is possible to select an appropriate molecule as the quantum dot according to the required device characteristics. Tunnel junction 102,
The molecule forming 103 needs to be an insulating molecule having a length of about 0.2 to 4 nm in order to combine with fullerene and exhibit tunneling characteristics. It is possible to design an insulator molecule having an appropriate length from FIG. 6 so as to show particularly good tunneling characteristics. In the case where fullerene is used for a quantum dot, about 0.3 to 1 nm is most suitable. Length. As the molecules 104 and 105 forming the conductive electrode, a conductive molecule having a conjugated electron such as a benzene ring, thiophene, or polyacetylene is preferably used. Generally, linear molecules such as polyacetylene are
It does not take a linear structure as it is, it curls in a ring,
Because of the strong tendency to have a spatially controlled structure, it is difficult to use it as a device that needs to place the corresponding part of the molecule in an appropriate location. Therefore,
Similarly, it is desirable to arrange a molecular group having a linear structure, such as a conjugated molecule such as a benzene ring and thiophene, appropriately in the molecule to obtain a linear structure.

The insulated gate 106 must have at least higher resistance than the molecules 102 and 103 forming the tunnel junction. Therefore, its length needs to be longer than at least the tunnel junction molecules 102 and 103. It is also desirable that the capacitance is larger than the tunnel junction. The gate electrode 107 is preferably formed using a conductive molecule having a conjugated electron, including a group such as a benzene ring, thiophene, and polyacetylene, similarly to the molecules 104 and 105 forming the conductive electrode.

The molecular single electron transistor shown in FIG.
This can be realized by adopting a molecular configuration in which conductive and insulating molecules are appropriately arranged. In addition, by using a quantum dot composed of fullerene and a derivative thereof, the size of the quantum dot can be reduced to 1 nm or less, so that the operation speed is very high, several terahertz or more. In addition, by using a tunnel junction made of an insulating molecule, it is possible to form a tunnel resistance with extremely high accuracy, so that a device with accurate characteristics and good controllability can be realized.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (Implementation of Single-Electron Device Structure) This embodiment discloses a structure of a molecular single-electron transistor provided with quantum dots made of fullerene or a derivative thereof. The most basic structure of a single-electron transistor is a structure that can be called a single-electron device, and includes a quantum dot, a tunnel junction, and a conductive electrode. Needless to say, a single-electron transistor has a gate connected thereto. Therefore, realizing a single-electron device structure is the most important technical issue for realizing a single-electron transistor.

FIG. 2 shows a basic structure of a molecular single electron device according to the present invention. In the figure, the molecular single-electron device is based on a quantum dot 1 made of fullerene or a derivative thereof, tunnel junctions 2 and 3 made of insulating molecules connected to the quantum dot by chemical bonding, and tunnel junctions 2 and 3 Are formed of conductive portions 4 and 5 made of conductive molecules that come into contact with the conductive portions. In such a basic structure, by connecting both ends of the conductor portions 4 and 5 made of the conductive molecules to external electrodes, the conductivity characteristics of the single-electron device can be measured.

[60] fullerene polyam as shown in FIG.
In the ide, quantum dots 1 made of fullerene, tunnel junctions 2 and 3 made of an insulating molecule whose main part is formed by a cyclopropane ring, and conductive molecules mainly made of a benzene ring in contact with the tunnel junction It is shown to consist of conductor parts 4,5. The molecules 2 and 3 forming the tunnel junction and the conductive molecules 4 and 5 forming the conductor do not necessarily have to have the structure shown in this example. For example, the former can form a tunnel junction having a relatively high resistance value by further bonding an insulating molecule such as an alkyl group or an ethoxy group to a cyclopropane ring. The structure of the latter is not particularly limited as long as it is a conductive molecule having a conjugated multiple bond as a skeleton of the molecule, such as a phenyl group, an alkene, an alkyne, and a thiophene group. In general, it is extremely difficult to form an insulating molecule bond directly on fullerene, and the molecular structure of cyclopropane disclosed in this example is very stable, which is excellent in device fabrication.

Using such molecules, the conductor portions at both ends are connected to the outside, and the current-voltage characteristics are measured so as to pass through the quantum dots. A known Coulomb steer case is observed, and it can be seen from the results that the magnitude of the Coulomb gap caused by the quantum dots made of fullerene is about 1V.

Therefore, the structure shown in FIG. 2 can be used as a basic structure of a molecular single electron device capable of operating at room temperature. That is, if the fullerene 1 used as the quantum dot is provided with a gate electrode for controlling the potential of the fullerene 1, it becomes a molecular single electron transistor.

Of course, since the size of the Coulomb gap is determined by the total capacity of the quantum dots, it is needless to say that the value may vary greatly depending on the molecule bound to the fullerene.

An example of the configuration of the above-described single-electron device structure will now be described. In this example, a tunnel junction made of insulating molecules,
An example in which a conductor portion made of a conductive molecule which is in contact with the tunnel junction reacts and is synthesized. Figure 4 depicts the reaction in molecular formula, [60] fullereneobisacetic acid
[60] fullerene polyami from 4,4'-Diaminobenzophenone
This is to synthesize de. [60] An insulator consisting of a cyclopropane cyclic bond is formed across a fullerene such as fullerene polyamide, and the structure connected to the conductor is used to realize the molecular single-electron device described above. Is the basic structure of This synthesis reaction,
The reaction is carried out via a catalyst such as pyridine or lithium chloride. The main synthesis conditions are as follows. This is Lee,
Chemistry Letters, 1037, 1997 (J. Li, et.
al., Chemistry Letters, 1037 (1997).).

Catalyst: lithium chloride Reaction temperature: 110 degrees Reaction atmosphere: nitrogen Reaction solvent: pyridine [60] fullerene polyamid by the reaction shown in FIG.
The yield of e is about 90-95%, which is high enough for practical use. Further, the desired reaction product can be easily purified.

The most important point of the gist of the present invention is that it comprises fullerenes or higher fullerenes and derivatives thereof as quantum dots. However, it is very difficult to directly form a tunnel junction in fullerene by the conventional method. This has been made possible by providing the molecule to be a tunnel junction disclosed in the present example with a structure having a cyclopropane cyclic bond as shown in FIG. In addition, the conductor molecules disclosed in this example are not limited to the materials described in this example, but may be phenyl groups, alkene, alkyne, thiophene groups, and the like, as described above, and generally have a conjugated multiple bond having a skeleton of a molecule. Can be used.
In addition, it is possible to connect a molecule to be a tunnel junction to a cyclopropane ring to have an appropriate tunnel resistance.

(Embodiment 1) In this embodiment, the [60] fuller
Disclosed is a method of forming a molecular single-electron transistor by connecting a gate portion to a fullerene portion to be an ene polyamide quantum dot with an insulating layer interposed therebetween. Figure 5 shows the [60] full
This shows a structure in which a conductive molecule selectively reacted with the 6-membered ring portion of erene polyamide is used as a gate. In the figure, a molecular single-electron transistor is composed of a quantum dot 11 made of fullerene, insulating molecules 12 and 13 having a tunnel junction characteristic, conductive molecules 14 and 15 having a conductive characteristic, and an insulating molecule serving as an insulating gate. Composed gate insulator 1
6. It comprises a gate 17 composed of conductive molecules. The conductive molecule 14 functions as a source, and the conductive molecule 15 functions as a drain.

When a potential is applied to the gate 17, the potential change causes the potential of the fullerene quantum dot 11 to change. As a result, the channel current flowing between the source 14 and the drain 15 changes the potential of the gate. Changes in response to In this manner, the potential of the gate changes the conductance of the transistor and performs a predetermined transistor function. Further, in the device structure of the present embodiment, by changing the structure of the insulator molecule, device parameters such as the width of the tunnel junction and the barrier height can be controlled to predetermined values. Also, the dimensions of the quantum dots can be varied by using appropriate derivatives of fullerenes, and by proper selection and arrangement of molecules, devices with the required properties can be manufactured. Thus, an organic single-electron transistor having appropriate operation characteristics can be realized.

In the molecular single-electron transistor disclosed in this embodiment, the size of the quantum dots is 10 nm or less, particularly 1 nm or less when the structure is selected. Operation at a speed of terahertz or higher, which is twice as high, is possible. In addition, since the tunnel junction is also formed of insulating molecules with sufficiently controlled parameters such as structure and length, it is possible to control the resistance with extremely high precision, and it is highly controllable and has almost perfect characteristics. A single-electron transistor can be realized. Therefore, the technical effect of the present invention is very large.

(Embodiment 2) FIG. 7 shows an example of a structure for developing the molecular single electron transistor prepared in Embodiment 1 into an integrated circuit. The concept of bonding a structure mainly composed of molecules to a solid surface or bonding molecular elements themselves to each other is described in, for example, Japanese Patent Application Laid-Open No. 9-30 / 1990.
7157 or Japanese Unexamined Patent Application Publication No. 6-302807. This idea can be applied. In this embodiment, each conductive terminal and gate electrode terminal have a structure in which a specific metal is bonded. It is. Therefore, selenium group Se and thiol group
It binds S and carboxylic acid groups COO and binds them to specific atoms arranged on the integrated circuit substrate.

FIGS. 8A and 8B show the molecular single-electron transistor shown schematically in FIG. 1 and the selenium groups Se provided at the ends of the conductive terminals and the gate terminal of the single-electron transistor.
Thiol group S, carboxylic acid group COO are specific atoms arranged on an integrated circuit substrate, such as silver Ag, gold Au and silicon S
It is a figure which shows typically the state couple | bonded with i. 101
Is a fullerene to be a quantum dot, and the selenium group Se of each conductive terminal chemically bonded to the
2 shows a situation where the thiol group S is selectively bonded to the gold 111 and the carboxylic acid group COO is selectively bonded to the silicon 112.

FIG. 9 is a schematic diagram of an example in which the molecular single electron transistor shown in FIG. 8 is integrated on a substrate. Reference numeral 201 denotes a substrate on which a large number of connection pads are arranged on the periphery.
Shows a state in which a part thereof is enlarged and a molecular single electron transistor is connected. Fullerene 1 as a quantum dot
Selenium group Se, thiol group S, carboxylic acid group COO of each conductive terminal of molecular single-electron transistor 20 centered on 01, silver 113, gold 111,
And silicon 112, which are sequentially coupled according to a desired circuit configuration. These connection points are silver 113, gold 111, and silicon 112.
Are connected by a connection conductor or a wiring made of molecules.

For example, STM can be used to arrange the connection points silver 113, gold 111, and silicon 112 at desired positions on the substrate. In this case, when the substrate is made of an insulator, for example, STM may be used by a method as disclosed in JP-A-6-216395 proposed by the present inventors.

[0029]

As is clear from the above embodiments, according to the present invention, the operation speed is much higher than that of a conventional transistor made of a silicon semiconductor by about 1000 times,
Since the ultra-high-performance molecular single-electron transistor having a high integration density due to the extremely small size of about 1000 can be realized, the technical effect of the present invention is great.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a structure of a single-electron transistor of the present invention.

FIG. 2 is a diagram showing a basic structure of a molecular single electron device according to the present invention.

FIG. 3 is a view showing current-voltage characteristics obtained by a structure serving as a basis of a molecular single electron device according to the present invention.

FIG. 4 is a diagram showing an example in which a tunnel junction made of an insulating molecule and a conductor portion made of a conductive molecule in contact with the tunnel junction are reacted with fullerene used as a quantum dot and synthesized by a molecular formula.

FIG. 5 is a diagram showing an embodiment of a molecular single-electron transistor employing [60] fullerene polyamide for quantum dots.

FIG. 6 illustrates performance of a single-electron transistor.

FIG. 7 is a diagram showing an embodiment for arranging molecular single-electron transistors employing [60] fullerene polyamide for quantum dots on a substrate.

FIG. 8 is a schematic diagram for explaining that each connection point of a molecular single-electron transistor employing [60] fullerene polyamide as a quantum dot selectively bonds to atoms.

FIG. 9 is a diagram schematically showing an embodiment of an integrated molecular single-electron transistor.

[Explanation of symbols]

1, 11, 101... Quantum dots, 2, 3, 12, 13,
102, 103 ... Tunnel junction, 4, 5, 14, 15,
104, 105 conductor, 16, 106 ... gate insulator,
17, 107: gate, 111: gold, 112: silicon, 113: silver, 20: molecular single electron transistor, 20
1. Integrated molecular single-electron transistor.

[Procedure amendment]

[Submission date] February 12, 1999

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

1. A one fullerene or fullerene derivative molecules and derivatives thereof comprising as a quantum dot to form Ri insulated gate by molecules to the quantum dot binding
Form at least two tunnel junctions with the drawer
A lead portion of the bound ingredients Bei, further each of
It is formed by chemically bonding a molecule to be a portion from which a bond is drawn and a conductive molecule to form the insulated gate.
A tunnel junction is formed by using the side that includes the
The side containing the bond to be connected is the source terminal and drain terminal
Molecular single-electron transistor, characterized in that.

Wherein to is 0.2 length of the molecule to serve as the tunnel junction 4n m der Ru claim 1 molecule single electron transistor according.

Wherein tonnes from molecular to be the the quantity child dots
Molecular single electron transistor according to claim 1 Symbol mounting lead portion of the bonds forming the channel junction is obtained by via cyclo propane annular bond.

4. A quantum dot comprising one of fullerene or higher fullerene molecule and its derivative, and at least two tunnel junctions are formed with a portion from which a molecule to become the quantum dot leads to a bond forming an insulated gate. A connection extraction part, and further comprising a chemical bond between a molecule to be a connection extraction part and a conductive molecule, and a side including the bond forming the insulated gate as a gate terminal, and a tunnel junction. A source including a bond including a bond forming a source terminal and a drain terminal, wherein one of a carboxylic acid group, a selenium group, and a thiol group is bonded to an end of each terminal. Molecular single electron transistor.

5. A fullerene or higher fullerene molecule or a derivative thereof as a quantum dot, and at least two tunnel junctions are formed from a molecule forming an insulated gate from a molecule to be a quantum dot. A connection extraction part, and further comprising a chemical bond between a molecule to be a connection extraction part and a conductive molecule, and a side including the bond forming the insulated gate as a gate terminal, and a tunnel junction. The side including the bond forming the is a source terminal and a drain terminal,
And a plurality of molecular single-electron transistors in which any one of a carboxylic acid group, a selenium group and a thiol group is bonded to an end of each terminal, and a silicon atom, a silver atom and a gold atom at a predetermined position on the surface. An insulating substrate provided with a plurality of sets of connection points comprising silicon atoms, silver atoms and gold atoms at the connection points on the substrate and carbon atoms bonded to the ends of the respective terminals of the molecular single electron transistor. An acid group, a selenium group, and a thiol group are bonded to each other, and connection points between terminals of the molecular single-electron transistor are connected so as to have a predetermined function by the molecular single-electron transistor. An integrated circuit characterized by the above.

Claims (7)

[Claims] 1. A molecular single-electron transistor comprising one of a fullerene or a higher fullerene and a derivative thereof as a quantum dot. 2. The method according to claim 1, wherein the fullerene or higher-order fullerene molecules and derivatives thereof are provided as quantum dots, and one or more, more preferably two or more, molecules exhibiting particularly good characteristics than the molecules to be quantum dots. 2. The structure according to claim 1, wherein a portion where the above-mentioned number of bonds are drawn is provided as a tunnel junction, and the molecule to be the tunnel junction is chemically bonded to another molecule having a conjugated double bond chain. Molecular single-electron transistor. 3. The molecular single-electron transistor according to claim 2, wherein the length of the molecule to be the tunnel junction is about 0.2 to 4 nm, and 0.3 to 1 nm in order to exhibit particularly good tunneling characteristics. . 4. A quantum dot comprising one of fullerene or higher fullerene molecules and derivatives thereof as a quantum dot, and one or more, more preferably two or more molecules, exhibiting particularly good properties than the molecule to be a quantum dot. The molecular single-electron transistor according to claim 1, wherein the molecular single-electron transistor is chemically bonded to another molecule having a conjugated double bond chain through the above-mentioned number of cyclopropane cyclic bonds. 5. A molecular single-electron transistor comprising a fullerene or higher fullerene or a derivative thereof as a quantum dot, wherein a gate made of a conductive molecule is formed of the fullerene or higher fullerene or a derivative thereof. A molecular single-electron transistor characterized by being connected by an insulating organic molecule. 6. A gate made of the conductive molecule is connected to the fullerene or higher fullerene or a derivative thereof by an insulating organic molecule, and the length of the molecule to be the tunnel junction is 0.2 to 4 nm. 5. The molecular single-electron transistor according to claim 4, wherein the thickness is 0.3 to 1 nm in order to exhibit a good degree of tunneling characteristics. 7. A quantum dot comprising any one of a fullerene or higher fullerene molecule and a derivative thereof, and two or more of the molecules to exhibit one or more, particularly better characteristics than the molecule to be a quantum dot. In the molecular single-electron transistor, which is chemically bonded to another molecule through the above-mentioned cyclopropane cyclic bond, the gate made of a conductive molecule has an insulating property with the fullerene or higher fullerene and its derivative. 5. The molecular single-electron transistor according to claim 4, which is connected by an organic molecule.