CN101692461A - Nanometer electronic device based on semiconductor nano materials and preparation method thereof - Google Patents

Abstract

The invention discloses a nanoelectronic device based on semiconductor nanomaterials and a preparation method thereof. Metal yttrium with low work function is used as the contact electrode material, and the metal yttrium can directly form ohmic contact with the conduction band of the one-dimensional semiconductor nanomaterial through micro-processing technology, so that high-performance electronic field effect transistors and other semiconductor nanomaterials can be obtained. Material-based nanoelectronic devices, including diodes, biological and chemical sensor devices, etc. The invention greatly reduces the processing cost of n-type devices and circuits, improves the performance of the devices, has very important significance for promoting the practical process of nanoelectronic devices, and has broad application prospects.

Description

A nanoelectronic device based on semiconductor nanomaterials and its preparation method

technical field

The invention relates to the field of nanoelectronic devices, in particular to a nanoelectronic device based on semiconductor nanomaterials, especially carbon nanotubes, and a method for realizing high-performance n-type contact between semiconductor nanomaterials and metal electrodes.

Background technique

The research of nanoelectronic devices is the most important field in today's nanotechnology. One-dimensional or quasi-one-dimensional semiconductor nanomaterials have unique electrical and optical properties, especially semiconductor nanomaterials represented by carbon nanotubes are considered to be one of the most promising building materials for nanoelectronic devices due to their unique electrical properties. one. So far, various nanoelectronic devices such as field-effect transistors (FETs), diodes, logic operation circuits, oscillators, decoders, infrared light-emitting devices, photodetectors, biological and chemical sensors, etc. have been constructed with semiconductor nanomaterials such as carbon nanotubes. etc. have been successfully developed, and the performance of a single device has surpassed the current silicon-based microelectronic devices in many aspects. The application prospects of nanoelectronic devices represented by carbon nanotubes are very optimistic. In particular, the increased investment in research by the world's top large companies such as IBM and Intel has further promoted the practical process of nanoelectronic devices.

Different from silicon-based devices, the source and drain electrodes used in contact with nanomaterials in various nanoelectronic devices based on one-dimensional or quasi-one-dimensional nanomaterials, including carbon nanotubes, are all metal electrodes. determined by the one-dimensional properties of nanomaterials. Therefore, the processing of carbon nanotube devices inevitably involves the connection between carbon nanotubes and external electrodes, and between carbon nanotubes. At present, it is widely used to connect metal electrodes with different work functions, that is, to use various micromachining methods to select appropriate metal materials to connect carbon nanotubes to build nanoelectronic devices. At present, metal palladium (Palladium, Pd) has been used to realize the p-type high-performance contact with carbon nanotubes [A.Javey, J.Guo, Q.Wang, M.Lundstrom, H.Dai, Nature, 424, 654 (2003 )]. The carbon nanotube field effect transistor using Pd as the contact electrode can not only obtain ohmic contact, but also realize the ballistic transport of carriers, and some performances have far exceeded the current p-type metal oxide semiconductor FET based on silicon technology. As we all know, CMOS as the basic unit of logic circuits requires both p-type and n-type FETs. Although ballistically transported p-type carbon nanotube FETs have been successfully realized, research on n-type carbon nanotube FETs lags far behind p-type FETs. There are two main methods for preparing n-type carbon nanotube FETs at present, one is to use metals with low work function (such as Al, Mg, Ca) [Y.Nosho, Y.Ohno, S.Kishimoto, T.Mizutani , Nanotechnology, 17, 3412 (2006), Ali Javey, Qian Wang, Woong Kim, and Hongjie Dai, IEEEIEDM2003] as an electrode material to realize the n-type contact between metal and carbon nanotubes, and the other is to conduct n-type contact on carbon nanotubes themselves Electron-type doping to realize n-type devices [A.Javey, R.Tu, D.B.Farmer, J.Guo, R.G.Gordon, and H.Dai, Nano Lett, 5, 345 (2005)]. However, the performance of n-type devices reported by the first method is generally poor, and the on-off current ratio and on-state current value are relatively small, mainly because the metals with low work function used do not form well with carbon nanotubes. On the one hand, it may be that the wettability between the metal and the carbon nanotubes is not good, and the metal coating cannot form a good physical contact with the carbon nanotubes. On the other hand, most low work function metals have high chemical activity. It is easy to form an oxide layer on the surface (generally, the work function is higher), and these metal targets with oxides are easy to form compound-doped metal contacts in the coating process, or the vacuum degree is not high during the coating process. Oxidation of metal atoms also makes it difficult to form high-performance n-type contacts. Therefore, it is generally believed that it is difficult to use a metal with a low work function as a contact electrode to realize an n-type device with ohmic contact of carbon nanotubes. Although the second method can obtain n-type devices with better performance, because carbon tubes do not have dangling bonds, and doping with high chemical activity such as potassium is not stable, the device must be in a certain chemical environment. When the environment (such as When the temperature, atmosphere) changes, the performance of the device changes accordingly, and the practicability is poor. Therefore, how to realize the high-performance n-type contact between carbon nanotubes and metal electrodes has become an important factor limiting the practical application of nanoelectronic devices. Chinese invention patent ZL 200710090362.4 uses metal scandium (Scandium, Sc) as an electrode material to prepare a carbon nanotube n-type field effect transistor whose performance is close to the theoretical limit. However, due to the relatively low output of metal scandium, the cost is high, which is about 5 times the price of gold, and it is difficult to apply it on a large scale in the industry. Therefore, it is necessary to seek metal materials that can form high-performance n-type contacts with carbon nanotubes and are relatively low in price.

Contents of the invention

The purpose of the present invention is to provide a nanoelectronic device based on semiconductor nanomaterials and its preparation method. On the one hand, it will be possible to form a high-performance n-type contact between the nanomaterial and the metal electrode, and on the other hand, the fabrication of the device will Reduce costs.

To achieve the above object, the present invention adopts the following technical solutions:

A nanoelectronic device based on a semiconductor nanomaterial, comprising a one-dimensional semiconductor nanomaterial and a metal electrode in direct contact with it, characterized in that the metal electrode is a Yttrium (Yttrium, Y) electrode.

Using metal yttrium as the contact electrode can form ohmic contact with the conduction band of the one-dimensional semiconductor nanomaterial, so that the performance of the device can be optimized.

In the above nanoelectronic device, the one-dimensional semiconductor nanomaterial is preferably carbon nanotube.

The nanoelectronic device can be an electronic field effect transistor (n-type FET device), or various other high-performance nanoelectronic devices, including diodes, light emitting devices, photodetectors, biological and chemical sensing devices, and the like. Among them, the n-type FET uses a one-dimensional semiconductor nanomaterial as a conductive channel, and uses low work function yttrium metal as a source-drain electrode material to establish an ohmic contact electrode connection with the one-dimensional semiconductor nanomaterial.

The preparation method of the nanoelectronic device of the present invention is simple and easy, using metal yttrium as the contact electrode material, through various micro-machining techniques, an electrode connection is established between the metal yttrium and the one-dimensional semiconductor nanomaterial, and the direct connection between the two can be realized High performance n-type contacts. Commonly used micromachining techniques such as:

By photolithography (electron beam or optical lithography), the pattern shape of the required electrode is formed on the one-dimensional semiconductor nanomaterial, and then a layer of metal Y is evaporated, and then the unnecessary metal layer is removed by peeling off, that is, between the metal yttrium and the semiconductor nanometer An electrode connection is established between the materials.

When the above-mentioned vapor deposition method is used to fabricate the Y electrode, it is preferable to carry out the vapor deposition in a high vacuum environment, for example, vacuuming to a pressure of ≤3×10 ^-8 Torr, more preferably a pressure of <1×10 ^-8 Torr.

Further, the surface of the metal Y target is treated with acid before evaporation to remove the oxide on the metal surface, or the oxide layer on the metal surface is evaporated first during the metal evaporation process, and then the formal sample is evaporated. Plating, the electrode of the device can be made of relatively pure metal Y.

Below, the characteristics and principle of the present invention will mainly be described by n-type FET devices based on carbon nanotubes, but its application scope is not limited to carbon nanotubes, and the basic working principle is applicable to other n-type FET devices based on one-dimensional semiconductor nanomaterials. Devices are also applicable.

The conduction channel of the nanoelectronic device involved in the present invention is an intrinsic carbon nanotube or other one-dimensional semiconductor nanomaterials, and the realization of n-type ohmic contact does not need to dope the conduction channel. In theory, metals with low work functions can form n-type devices. The mechanism for achieving n-type ohmic contact is: due to the one-dimensional nature of carbon nanotubes, there is no Fermi surface pinning effect when metals and semiconducting carbon nanotubes are in contact, so the height of the Schottky barrier formed by the contact between the two is mainly determined by the carbon nanotubes. It is determined by the difference in work function with the metal material. The Fermi level of carbon nanotubes is 4.5eV, and the energy gap of single-walled carbon nanotubes with a diameter of 1.5nm is about 0.6eV, so the conduction band bottom of carbon nanotubes is about 4.2eV. In order to realize the n-type contact, a metal material with a work function lower than 4.5eV must be selected as the electrode. For most low work function metals, although the work function is low, such as Al (4.3eV), Mg (3.60eV) and Ca (2.87eV), they are easily oxidized in air. Generally, low work function metals The work function of the oxide will be significantly higher than that of the metal itself, resulting in an increase in the Schottky barrier. In addition, many low work function metals have poor wettability with carbon nanotubes, which makes it difficult for them to form high-performance n-type contacts with carbon nanotubes.

For metal yttrium (Y), its work function is 3.1eV (<4.2eV), and it is relatively stable in the air. At the same time, the wetting performance of Y and carbon nanotubes is also relatively good, and metal Y can be deposited on the surface of carbon nanotubes. Forming a complete package ensures good physical contact between Y and carbon nanotubes. At the same time, in order to ensure that the Y electrode can maintain the original characteristics during the preparation process to obtain high-performance n-type contact, the Y electrode needs to be prepared under high vacuum conditions (such as vacuuming to an air pressure of ≤3×10 ^-8 Torr) carried out. Generally, we use bulk metal Y to evaporate in a high vacuum environment (pressure ≤ 3×10 ^-8 Torr) to reduce the oxidation of metal Y atoms that may be caused by insufficient vacuum under high temperature conditions during the evaporation process. Further, the surface of the metal target is treated with acid before evaporation to remove the oxide on the metal surface, or the oxide layer on the metal surface is evaporated first during the metal evaporation process, and then the formal sample is evaporated , so as to ensure that the electrodes of the device are composed of relatively pure metal Y.

Using Y as the metal electrode material to establish an ohmic contact electrode connection with carbon nanotubes can not only obtain n-type devices with stable performance, but also realize ballistic transport of electrons in carbon nanotubes. The switching current ratio of carbon nanotube field effect transistors with Y electrodes can exceed 10 ⁶ , the on-state current can reach more than 25 μA, the mobility of electrons can exceed 5100 cm ² /Vs, and the mean free path of electrons can reach 0.7 μm. From the comparison of field effect devices with scandium and yttrium as contact electrodes on the same carbon tube, the n-type device with yttrium as the electrode even surpasses scandium in some device performance indicators.

The present invention proposes the idea of using Y as a metal electrode material to form a high-performance n-type contact with a one-dimensional semiconductor nanomaterial, which can not only be used to prepare high-performance n-type FETs, but also can be used to prepare other materials based on semiconductor nanomaterials. Various high-performance nanoelectronic devices, including carbon nanotube diodes, as well as light-emitting devices, photodetectors, biological and chemical sensing devices. According to the above mechanism analysis, and the data of the appended examples of the present invention show, the carbon nanotube nanoelectronic device (comprising field-effect transistor, diode, biological and chemical sensing device etc.) prepared by using Y as electrode material not only has excellent performance, Stable, and the preparation method is simple and easy. Although the metal scandium electrode in the previous patent can also form a good n-type ohmic contact with carbon nanotubes, the cost of yttrium itself is much lower than that of the scandium electrode, and the current market price is about 1000 times different. For large-scale applications, yttrium electrodes are more advantageous. The invention has very important significance for promoting the practical process of nanoelectronic devices, and has broad application prospects.

Description of drawings

Figure 1 is a schematic diagram of the structure of a carbon nanotube field effect transistor with _SiO2 as the bottom gate structure.

Fig. 2 is a transfer characteristic diagram of a single-walled carbon nanotube (diameter is 2nm) field effect transistor with a bottom gate structure of yttrium as the source and drain electrodes.

Fig. 3 is an output characteristic diagram of a single-walled carbon nanotube (2nm in diameter) field effect transistor with a bottom gate structure of yttrium as the source and drain electrodes.

4 is a schematic structural view of a carbon nanotube field effect transistor with a top-gate structure in which the source (S), drain (D) electrode material is yttrium, and the gate (G) electrode material is Ti.

Fig. 5 is a transfer characteristic diagram of a single-walled carbon nanotube (3nm in diameter) field effect transistor with a top-gate structure using yttrium as the source-drain electrode.

FIG. 6 is an output characteristic diagram of a single-walled carbon nanotube (3nm in diameter) field effect transistor with a top-gate structure of yttrium as the source and drain electrodes.

Detailed ways

Below in conjunction with the accompanying drawings, the present invention will be further described in detail through examples, but the present invention is not limited in any way.

Embodiment 1: A single-walled carbon nanotube field-effect transistor with a bottom-gate structure using yttrium (Y) as the source-drain electrode and its preparation

As shown in Figure 1, with _SiO2 as the gate dielectric 4 and Si as the single-walled carbon nanotube field effect transistor with the back gate 5 structure, its source (S) 2 and drain (D) 3 electrode materials are yttrium (Y) , located at both ends of the single-walled carbon nanotube 1 . Concrete preparation steps are as follows:

1) Obtain carbon nanotubes located on Si/ _SiO2 substrates by positioning growth or dropping the dispersed carbon tube solution onto the substrate;

2) Observing with a scanning electron microscope or an atomic force microscope, and recording the specific position of the carbon nanotubes;

3) Coating photoresist on the carbon nanotube and forming the shape of the electrode by optical exposure or electron beam lithography;

4) Put the photolithographic sample into the electron beam evaporation system, evacuate to about 3×10 ^-8 Torr, and evaporate a layer of metal Y with a thickness of 50nm at a rate of 1A/s;

5) The sample is put into acetone and peeled off, and the unnecessary metal layer is removed to obtain a carbon nanotube n-type field effect transistor with _SiO2 as the substrate and Si as the back gate structure.

The performance of the device prepared by the above method is shown in Figure 2 and Figure 3:

When the diameter of single-walled carbon nanotubes is 2nm, the transfer characteristics and output characteristics of the prepared single-walled carbon nanotube field effect transistor with yttrium (Y) as the source and drain electrodes and the bottom gate structure are shown in Figure 2 and Figure 3, respectively. As shown, Figure 2 shows that the on-state resistance of the device at room temperature is about 32kΩ, which is an n-type ohmic contact, and Figure 3 shows that the saturation current of the device can exceed 20μA.

The above results show that the use of yttrium (Y) as the metal electrode material in nanomaterial field effect transistors can indeed form ohmic contacts with carbon nanotubes and obtain high-performance n-type devices.

Example 2: Carbon nanotube field effect transistor with Y as the top gate structure and its preparation

As shown in Figure 4, the carbon nanotube field effect transistor with Y as the top gate structure, its source (S) 8, drain (D) 10 electrode materials are all yttrium (Y), and the electrode material of the gate (G) 6 is Ti, single-walled carbon nanotubes 11 are located under the HfO ₂ gate dielectric layer 7 and on the substrate composed of SiO ₂ 9 and Si12. Concrete preparation comprises the following steps:

1) Obtain carbon nanotubes located on Si/ _SiO2 substrates by positioning growth or dropping the dispersed carbon tube solution onto the substrate;

2) Observing and recording the specific position of the carbon nanotubes through a scanning electron microscope or an atomic force microscope;

3) Apply photoresist and form the shape of source and drain electrodes by optical exposure or electron beam lithography;

4) Put the photolithographic sample into the electron beam evaporation system, evacuate to about 3×10 ^-8 Torr, and evaporate a layer of metal Y with a thickness of 50nm at a rate of 1A/s;

5) Coating photoresist on the carbon nanotubes and forming the shape of the gate dielectric by optical exposure or electron beam lithography;

6) Put the sample into the atomic layer deposition system to grow a gate dielectric layer (ZrO ₂ , Al ₂ O ₃ or HfO ₂ );

7) Put the sample into acetone and peel it off to remove the unnecessary medium layer;

8) Coating photoresist on the carbon nanotubes and forming the shape of the grid dielectric by optical exposure or electron beam lithography;

9) Put the photolithographic sample into the electron beam evaporation system, evacuate to about 3×10 ^-8 Torr, and evaporate a layer of metal Ti with a thickness of 10nm at a rate of 1A/s;

10) Put the sample into acetone and peel it off, remove the unnecessary metal layer to obtain a carbon nanotube n-type field effect transistor with a top-gate structure with Y as the source-drain electrode.

When the diameter of single-walled carbon nanotubes is 3nm, the transfer characteristics and output characteristics of the single-walled carbon nanotube field-effect transistors with yttrium (Y) as source and drain electrodes prepared by the above method are shown in Fig. 5 and output respectively. As shown in Figure 6, Figure 5 shows that the switching ratio of the top-gate structure device at room temperature reaches 5 orders of magnitude, the on-state resistance is about 19kΩ, and it is an n-type ohmic contact, and the subthreshold slope of the device is about 73mV/Dec, Figure 6 It indicates that the device saturation current exceeds 30μA.

The above-mentioned embodiments are all set forth by using carbon nanotubes as the device structure of the conductive channel, but the method of the present invention is not limited to carbon nanotube electronic field effect transistor devices, and can be used to prepare semiconductor nanowires, tubes, and strips based on other semiconductor nanotubes. One-dimensional and quasi-one-dimensional electronic field effect transistor devices, and diode rectifier devices. The present invention is not limited to certain device structures, and any device technology modified based on the essence of the present invention belongs to the scope of the present invention.

Claims (10)

1. A nanoelectronic device based on a semiconductor nanomaterial, comprising a one-dimensional semiconductor nanomaterial and a metal electrode in direct contact with it, characterized in that the metal electrode is an yttrium electrode. 2. The nanoelectronic device according to claim 1, wherein the one-dimensional semiconductor nanomaterial is carbon nanotube. 3. The nanoelectronic device according to claim 1, wherein the nanoelectronic device is an electronic field effect transistor, its conduction channel is a one-dimensional semiconductor nanomaterial, and the source and drain electrodes are yttrium electrodes. 4. A preparation method of a nanoelectronic device based on semiconductor nanomaterials, using one-dimensional semiconductor nanomaterials as a conductive channel, using metal yttrium as a contact electrode material, and establishing an electrode connection between metal yttrium and semiconductor nanomaterials through micromachining technology . 5. preparation method as claimed in claim 4 is characterized in that, the concrete method of establishing electrode connection between metal yttrium and semiconductor nanomaterial is: form the pattern shape of required electrode on one-dimensional semiconductor nanomaterial by photolithography , and then vapor-deposit a layer of metal yttrium, and then peel off to remove the unnecessary metal layer. 6. The preparation method according to claim 5, characterized in that yttrium metal is evaporated in a high vacuum environment. 7. The preparation method according to claim 6, characterized in that, the high vacuum environment is evacuated to an air pressure of ≤3×10 ^-8 Torr. 8. The preparation method according to claim 5, characterized in that bulk metal yttrium is used for vapor deposition. 9 . The preparation method according to claim 5 , wherein the surface of the metal yttrium target is treated with acid to remove oxides on the surface before evaporation. 10. The preparation method according to claim 5, characterized in that, during vapor deposition, the oxide layer on the surface of metal yttrium is evaporated first, and then the formal sample is vapor deposited.

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