Carbon nanotubes transistor

[0002] This application is a Continuation of application Ser. No. 09/270,825 filed Mar. 18, 1999 now U.S. Pat. No. 6,465,813.

[0003] 1. Field of the Invention

[0004] The present invention relates to a transistor, and more particularly, to a junction type transistor of carbon nanotubes.

[0005] 2. Discussion of the Background Art

[0006] There are a horizontal, and vertical types in background art junction type transistors. The background art junction transistor will be explained with reference to the attached drawings. FIG. 1aillustrates a plane view of the background art junction transistor and FIG. 1billustrates a sectional view of the background art junction transistor.

[0007] Referring to FIGS. 2aand 2b,there is a background art PNP junction transistor having an n type epitaxial layer 2 isolated by a silicon oxide film 3 formed on a substrate 1. There are p type impurity regions 4 and 5 at fixed intervals in the n type epitaxial layer 2, wherein the p type impurity region 4 serves as a collector of a transistor and the p type impurity region 5 serves as an emitter of the transistor.

[0008] The aforementioned background art junction transistor has the following problems.

[0009] The limitation in fabrication of the background art transistor that an NPN transistor fabrication as well as circuit integration should be done on the same time, a geometry of the background art transistor is not optimal for preventing electron-hole couplings and collecting holes at collectors in a base.

[0010] Second, the comparatively high doping concentration in the collector with a thick depletion layer in the base degrades a performance, and conduction of additional diffusion in an effort to overcome such demerit results in a complicated fabrication process.

[0011] Third, even though the vertical type junction transistor fabricated in an effort for solving the aforementioned background art problems of the transistor may more or less help in an improvement of the performance, the fabrication of vertical type junction transistor requires significant cost increase and effort since it requires totally different fabrication process.

[0012] Accordingly, the present invention is directed a transistor that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.

[0013] An object of the present invention is to provide a transistor having carbon nanotubes which has improved performances and simple fabrication process.

[0014] Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.

[0015] To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the transistor of carbon nanotubes includes a base having a bundle of (n,n) carbon nanotubes, and an emitter and a collector having (n,m, n−m≠3 l) nanotubes connected to opposite sides of the base respectively.

[0016] A single carbon nanotube has a diameter not greater than approximately 1 nm, is metallic or semiconductive depending on atomic array of the carbon in the tube, and can be doped with p type impurities, but not with n type impurities.

[0017] A bundle of a few tens of metallic carbon nanotubes forms a so called pseudo gap with an electron and a hole present on the same time. Upon application of a bias to such a nanotube bundle, electrons or holes are caused to enter more or to enter less even if not doped with impurities.

[0018] Accordingly, in the transistor of carbon nanotubes of the present invention, a bundle of carbon nanotube is used as a base part of the transistor, one single line or a few lines of carbon nanotubes are used as the emitter and the collector, respectively.

[0019] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.

[0020] The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention:

[0021] In the drawings:

[0022] FIG. 1aillustrates a plane view of the background art junction transistor;

[0023] FIG. 1billustrates a sectional view of the background art junction transistor;

[0024] FIG. 2 illustrates an atomic array of a metallic carbon nanotube of the present invention;

[0025] FIG. 3 illustrates an atomic array of a semiconductive carbon nanotube of the present invention; and,

[0026] FIG. 4 illustrates a transistor of carbon nanotubes in accordance with a preferred embodiment of the present invention.

[0027] Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. FIG. 2 illustrates an atomic array of a metallic carbon nanotube of the present invention, FIG. 3 illustrates an atomic array of a semiconductive carbon nanotube of the present invention, and FIG. 4 illustrates a PNP junction type transistor of carbon nanotubes in accordance with a preferred embodiment of the present invention.

[0028] The carbon nanotubes are classified into metallic carbon nanotubes and semiconductive carbon nanotubes according to an atomic array in the carbon nanotube. As shown in FIG. 2, a single line of the metallic carbon nanotube has a hexagonal pattern of an atomic array of the carbons at a 90° to a tube axis. That is, the metallic carbon nanotube is, in technical term, called as (n,n) nanotube or armchair nanotube. The “n” represents an integer denoting a size, and the two characters are the same, the tubes have the same properties with only difference in their diameters. In general, the (n,n) carbon nanotubes are (10,10) carbon nanotubes.

[0029] And, as shown in FIG. 3, a semiconductive carbon nanotube has a hexagonal pattern of an atomic array of the carbons at, not a 90°, but slightly sloped (smaller than 90°), to a tube axis. The aforementioned semiconductive carbon nanotube is called in technical term as (n,m) (n−m≠3 l) carbon nanotubes. That is, the “n” and “m” should not be a multiple of 3, for example (10,0) or (11,0) carbon nanotube is a specific example, with an energy gap of 1 eV.

[0030] The transistor in accordance with one preferred embodiment of the present invention, of carbon nanotubes having the aforementioned properties is shown in FIG. 4. That is, as explained, a base part in the transistor includes a bundle of metallic carbon nanotube. The bundle has diameter×width at least 5 nm×6 nm. An emitter part in the transistor includes one single line or a few lines of semiconductive carbon nanotubes of large energy gap doped with “p” type impurity (for example, boron). Finally, a collector in the transistor includes one single line or a few lines of semiconductive carbon nanotubes of large energy gap doped with “p” type impurity (for example, boron) at a concentration lighter than the emitter. And, an electrode of a metal or metallic carbon nanotube is formed at a middle of a base region, the one bundle of carbon nanotubes, and, electrodes are also formed at ends of the emitter and the collector. In the aforementioned transistor of the present invention formed thus, unlike the background art transistor, the base region has no depletion region because the base region is not formed by an artificial doping, and, instead, acts similar to a kind of battery because an energy level of the base region either rises or drops depending on a net charge of entire base region.

[0031] The operation of the aforementioned transistor of carbon nanotube of the present invention will be explained.

[0032] Basic operation of the transistor of carbon nanotube of the present invention is the same with the background art transistor. However, the transistor of carbon nanotube of the present invention differs slightly due to unusual electric properties of the carbon nanotube bundle in the base. When an orderly direction operation is explained, though a background art transistor can provide a good performance (reducing a leakage current and having a high gain) only when a voltage V_EBbetween the emitter and the base is a little bit positive (for example, 0.7 volt), the transistor of carbon nanotube of the present invention can provide a good performance only when the voltage V_EBbetween the emitter and the base is a little bit negative, because, as an energy gap in the base is actually approximately “0”, the little bit negative voltage V_EBshould be applied to the emitter and the base for setting up an energy level positively when holes enter into the base. In this instance, a slight reduction of an absolute value of the voltage V_EBbetween the emitter and the base, which has a negative value, has an effect identical to a slight increase of a voltage V_EBof an orderly direction between an emitter and a base in the background art transistor. When the absolute value of the voltage V_EBbetween the emitter and the base, which has a negative value, is reduced slightly, a number of holes in the base is reduced slightly. This is identical to a slight provision of electrons to the base through a terminal connected to the base, with a consequential attraction of holes in the emitter toward the base, which produces a current gain. Alike the background art transistor, a strong reverse bias is applied between the base and the collector. If this is taken for a case when the emitter and the base are connected in common, since holes in the emitter is strongly attracted toward the collector, an emitter current IE and a collector current IC are almost the same like the background art transistor. Therefore, a resistance between the base and the collector is significantly higher than a resistance between the emitter and the base, producing a voltage gain and a power gain.

[0033] The aforementioned transistor of carbon nanotube of the present invention has the following advantages.

[0034] First, though the impossibility of n type doping into a carbon nanotube impede fabrication of transistor of carbon nanotube, the present invention embodies a PNP transistor using an unusual electric properties of carbon nanotube bundle.

[0035] Second, as the transistor of carbon nanotube has a size not greater than approx. 1 nanometer, a size of a device can be reduced to about {fraction (1/100)} in length and about {fraction (1/10,000)} in an occupied area.

[0036] Third, the formation of a transistor of carbon nanotubes having a thermal conductivity significantly higher than silicon can improve operation speed.

[0037] Fourth, the operation voltage of the transistor of carbon nanotube much lower than a silicon transistor can reduce a power consumption.

[0038] Fifth, the possibility of utilizing a metallic carbon nanotube as an electrode for applying a power to a transistor can reduce the fabrication process.

[0039] It will be apparent to those skilled in the art that various modifications and variations can be made in the transistor of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.