A carbon nanotube field effect transistor based on low work function metal and a method for realizing ohmic contact thereof

Abstract

The application belongs to the technical field of semiconductor device preparation, and relates to a carbon nanotube field effect transistor based on a low work function metal, which comprises a substrate, a carbon nanotube film, source and drain electrodes, an oxide dielectric layer and a metal particle layer; the carbon nanotube film is laid on the substrate, the source and drain electrodes are located on the carbon nanotube film, and the metal particle layer completely covers the surface area of the oxide dielectric layer; the source and drain electrodes are chromium gold electrodes, and the source and drain electrodes can realize ohmic contact with the carbon nanotube; when a voltage is applied to the drain end, the metal particles diffuse to the oxide dielectric layer, forming a layer of composite oxide rich in oxygen vacancies, which dopes the carbon nanotube channel with electrons, greatly lowers the Fermi level of the carbon nanotube so as to make the carbon nanotube closer to the conduction band, reduces the Schottky barrier, makes more electrons inject into the carbon nanotube channel, forms ohmic contact, and increases the saturated output current of the field effect transistor.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor device fabrication technology, and relates to a carbon nanotube field-effect transistor based on a low work function metal and a method for realizing its ohmic contact. Background Technology

[0002] One-dimensional semiconducting carbon nanotubes, with their nanoscale dimensions, exhibit carrier concentrations highly sensitive to the shift of the Fermi level relative to the conduction or valence band. This means that the conductance of carbon nanotube field-effect transistors (FETs) can be more easily modulated by gate voltage. Due to their unique structure and excellent properties, carbon nanotubes have been widely used to construct various nanodevices. The contact between the metal and carbon nanotube plays a crucial role in carbon nanotube FET devices, being a key factor affecting device performance. Therefore, strictly speaking, an undoped carbon nanotube FET is a Schottky barrier FET, and its electrical transport characteristics are primarily determined by the height of the Schottky barrier between the metal and the carbon nanotube conductive channel.

[0003] For electronic devices, the presence of a Schottky barrier not only prevents more charge carriers from being injected into the conductive channel but also increases contact resistance, leading to a decrease in the device's carrier transport efficiency and performance. When the Schottky barrier is very small or even zero, an ohmic contact is formed between the metal and the semiconductor, which is a relatively ideal contact method for fabricating high-performance devices. Due to the difference in work function of metals, when a metal contacts a carbon nanotube, the Fermi level of the metal is located at a different position relative to the conduction band and valence band of the carbon nanotube. Currently, many studies have shown that palladium, with its high work function, can achieve a barrier-free ohmic contact with the valence band of carbon nanotubes. However, palladium is expensive and has poor wettability with the surface of carbon nanotubes. Research shows that titanium, aluminum, and chromium all form Schottky contacts with carbon nanotube films, increasing contact resistance and leading to a decrease in the saturation output current of the transistor. Therefore, it is essential to focus on reducing the Schottky barrier height between the metal and carbon nanotube, or to achieve an ohmic contact. The contact characteristics between carbon nanotubes and metal source / drain electrodes depend not only on the ideal Fermi level difference before contact but also on the interfacial properties. However, because carbon nanotubes lack delocalized dangling bonds on their surface, it is difficult to form stable chemical doping compared to traditional silicon-based field-effect transistors that rely on doping to form stable contacts. Furthermore, metals with lower work functions, such as scandium, are easily oxidized at room temperature and are highly unstable.

[0004] In summary, it can be seen that using metals with lower work functions as electrodes results in poorer device performance and lower yield. Therefore, technicians in this industry generally do not use metals with lower work functions as electrodes. Summary of the Invention

[0005] The purpose of this invention is to provide a carbon nanotube field-effect transistor based on a low work function metal and a method for realizing its ohmic contact, thereby solving the problem of unstable device performance caused by using an even lower work function metal as the source and drain electrodes.

[0006] This invention is achieved through the following technical solution:

[0007] This invention discloses a carbon nanotube field-effect transistor based on a low work function metal. The carbon nanotube field-effect transistor includes a substrate, a carbon nanotube thin film, a source electrode, a drain electrode, an oxide dielectric layer, and a metal particle layer.

[0008] A carbon nanotube film is laid flat on a substrate, with the source electrode and drain electrode located on the carbon nanotube film, and the metal particle layer completely covering the upper surface region of the oxide dielectric layer.

[0009] The source and drain electrodes are chromium-gold electrodes, which can achieve ohmic contact with carbon nanotubes.

[0010] When a voltage is applied to the drain electrode, metal particles diffuse into the oxide dielectric layer to form a composite oxide layer rich in oxygen vacancies. This electron doping of the carbon nanotube channel allows more electrons to be injected into the carbon nanotube channel, forming an ohmic contact and increasing the saturation output current of the field-effect transistor.

[0011] Furthermore, the metal particle layer consists of 0.5-2 nm yttrium nanoparticles.

[0012] Furthermore, the thickness of the oxide dielectric layer is 10-20 nm.

[0013] Furthermore, an electron beam evaporation process is used to deposit a layer of metal particles.

[0014] Furthermore, the oxide dielectric layer is made of HfO2. When a voltage is applied to the drain terminal of the device, metal particles diffuse into the oxide dielectric layer, forming a composite oxide YHfO rich in oxygen vacancies. x .

[0015] Furthermore, in the source and drain electrodes, the chromium thickness is 20 nm and the gold thickness is 40 nm.

[0016] The present invention also discloses a method for realizing the ohmic contact of the carbon nanotube field-effect transistor. First, a carbon nanotube field-effect transistor is prepared. After preparation, a voltage is applied to the drain electrode, and metal particles diffuse into the oxide dielectric layer to form a composite oxide rich in oxygen vacancies. Electron doping is performed on the carbon nanotube channel to inject more electrons into the carbon nanotube channel, forming an ohmic contact and increasing the saturation output current of the field-effect transistor.

[0017] Furthermore, the fabrication method of the carbon nanotube field-effect transistor includes the following steps:

[0018] Step 1: Deposit a carbon nanotube film using the substrate as the growth surface;

[0019] Step 2: Perform homogenization on the surface of the carbon nanotube film, and then vapor deposit the source electrode and drain electrode.

[0020] Step 3: Etch the carbon nanotube film between the source electrode and the drain electrode to obtain the carbon nanotube channel layer.

[0021] Step 4: Perform spin coating and exposure again to prepare an oxide dielectric layer on the upper surface of the carbon nanotube channel layer;

[0022] Step 5: Partially vapor-deposit a metal particle layer on the upper surface of the oxide dielectric layer;

[0023] Step 6: Place the device prepared in step 5 under an inert atmosphere for annealing to obtain a carbon nanotube field-effect transistor.

[0024] Furthermore, after step 5, a top gate electrode is prepared by vapor deposition on the metal particle layer.

[0025] Compared with the prior art, the present invention has the following beneficial technical effects:

[0026] This invention discloses a carbon nanotube field-effect transistor based on a low work function metal. The source and drain metal electrodes are low work function chromium-gold electrodes. The upper surface region of the dielectric layer is completely covered with a yttrium metal particle layer. When a voltage is applied to the drain terminal of the device, the metal particles diffuse into the dielectric layer, forming a composite metal oxide with a large number of oxygen vacancies. This electron doping of the carbon nanotube channel significantly lowers the Fermi level of the carbon nanotube, bringing it closer to the conduction band, reducing the Schottky barrier, and allowing more electrons to be injected into the carbon nanotube channel, forming an ohmic contact and increasing the saturation output current of the field-effect transistor. By introducing a yttrium particle layer to achieve ohmic contact between the metal and the carbon nanotube, the contact resistance can be effectively reduced, the carrier transport rate can be improved, and the saturation output current can be increased.

[0027] Furthermore, the metal particle layer is designed as 0.5-2 nm yttrium nanoparticles. Increasing the thickness of the metal particle layer ensures that yttrium can diffuse into the oxide dielectric layer to form a composite oxide; however, an excessively thick metal particle layer not only increases the complexity of the process but also generates a dense metal layer, reducing transistor performance.

[0028] Furthermore, the thickness of the oxide dielectric layer is designed to be 10-20 nm. An excessively thin oxide dielectric layer will lead to an increase in transistor leakage current. A suitable oxide dielectric layer thickness is a necessary condition to ensure the formation of yttrium-doped composite oxides. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of a carbon nanotube field-effect transistor structure according to an exemplary embodiment of the present invention;

[0030] Figure 2 This is the present invention. Figure 1 A schematic diagram of the output curve of the carbon nanotube field-effect transistor in the embodiment;

[0031] Figure 3 This is the present invention. Figure 1 A schematic diagram of the output curve of the carbon nanotube field-effect transistor after the introduction of a yttrium particle layer in the embodiment;

[0032] Figure 4 This is the present invention. Figure 1 A schematic diagram illustrating the bandgap modulation principle of the metal-carbon nanotube field-effect transistor in the embodiment.

[0033] Figure 5 This is the present invention. Figure 1 A schematic diagram illustrating the bandgap modulation principle of the ohmic contact between metal and carbon nanotubes in the carbon nanotube field-effect transistor after the introduction of a yttrium particle layer in the embodiment.

[0034] Among them, 100 is a silicon substrate; 210 is a carbon nanotube channel layer; 300 is a drain electrode; 310 is a source electrode; 410 is an oxide dielectric layer; 500 is a metal particle layer; and 610 is a top gate electrode. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of the present invention clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention; that is, the described embodiments are only a part of the embodiments of the present invention, and not all of them.

[0036] The components described and illustrated in the accompanying drawings and embodiments of this invention can be arranged and designed in various different configurations. Therefore, the detailed description of the embodiments of the invention provided in the following drawings is not intended to limit the scope of the claimed invention, but merely to illustrate one selected embodiment of the invention. All other embodiments obtained by those skilled in the art based on the accompanying drawings and embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0037] It should be noted that the terms “comprising,” “including,” or any other variations are intended to cover non-exclusive inclusion, such that a process, element, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to the process, element, method, article, or apparatus.

[0038] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0039] Figure 1 This is a schematic diagram of a carbon nanotube field-effect transistor (FET), fabricated on a silicon substrate 100. It includes a carbon nanotube channel layer 210, a drain electrode 300, a source electrode 310, an oxide dielectric layer 410, a metal particle layer 500, and a top gate electrode 610. The fabrication process involves preparing the source electrode 310 and drain electrode 300 on the carbon nanotube thin film, and completely covering the metal particle layer 500 on the upper surface of the oxide dielectric layer 410.

[0040] The source electrode 310 and the drain electrode 300 are chromium-gold electrodes with thicknesses of 20 nm and 40 nm, respectively.

[0041] A yttrium metal particle layer 500 is deposited on the surface of the oxide dielectric layer 410 to reduce contact resistance and increase saturation output current.

[0042] When a voltage is applied to the drain terminal of the device, metal particles diffuse into the dielectric layer, and the oxide dielectric layer 410 forms a composite metal oxide YHfO rich in oxygen vacancies. x .

[0043] The metal particle layer 500 consists of 0.5-2 nm yttrium nanoparticles. Increasing the thickness of the metal particle layer ensures that yttrium can diffuse into the oxide dielectric layer to form a composite oxide; however, an excessively thick metal particle layer not only increases the complexity of the process but also generates a dense metal layer, reducing transistor performance.

[0044] The oxide dielectric layer 410 is designed to have a thickness of 10-20 nm. An excessively thin oxide dielectric layer will lead to an increase in transistor leakage current. A suitable oxide dielectric layer thickness is a necessary condition to ensure the formation of yttrium-doped composite oxide.

[0045] The method for fabricating the carbon nanotube field-effect transistor of the present invention includes the following steps:

[0046] Step 1: Deposit a carbon nanotube film using the substrate as the growth surface;

[0047] Step 2: The surface of the carbon nanotube film is homogenized, and the drain electrode 300 and the source electrode 310 are deposited by vapor deposition.

[0048] Step 3: Etch the carbon nanotube film between the drain electrode 300 and the source electrode 310 to obtain the carbon nanotube channel layer 210.

[0049] Step 4: Perform spin coating and exposure again to prepare an oxide dielectric layer 410 on the upper surface of the carbon nanotube channel layer 210;

[0050] Step 5: Deposit a metal particle layer 500 on the upper surface of the oxide dielectric layer 410 by partial vapor deposition;

[0051] Step 6: Place the device prepared in step 5 under an inert atmosphere for annealing to obtain a carbon nanotube field-effect transistor.

[0052] After step 5, the top gate electrode 610 is prepared by vapor deposition on the metal particle layer 500.

[0053] The method for realizing the ohmic contact of the carbon nanotube field-effect transistor involves first fabricating the carbon nanotube field-effect transistor. After fabrication, a voltage is applied to the drain electrode 300, and metal particles diffuse into the oxide dielectric layer 410 to form a composite oxide rich in oxygen vacancies. Electron doping is then performed on the carbon nanotube channel to inject more electrons into the carbon nanotube channel, forming an ohmic contact and increasing the saturation output current of the field-effect transistor.

[0054] Figure 2 This is a schematic diagram of the output curve of a carbon nanotube field-effect transistor (FET) without a yttrium granular layer. The drain voltage range is 0–2V, the gate voltage is 0–1V, and the source is grounded. Under low bias, the on-state current varies nonlinearly with the bias voltage. The surface electron barrier is relatively large, hindering the injection into the conduction band of the carbon nanotubes, thus forming a distinct Schottky contact between the chromium metal and the carbon nanotubes.

[0055] Figure 3 This is the present invention. Figure 1 The schematic diagram of the output curve of the carbon nanotube field-effect transistor after depositing a 1.5 nm yttrium particle layer in the embodiment. When the drain voltage of the device is in the range of 0-2V, the gate voltage is 0-0.5V, and the source is grounded, from... Figure 3 As can be seen, when the bias voltage is small, the on-state current changes linearly with the voltage. The carbon nanotube channel and the source electrode 310 and drain electrode 300 are typical ohmic contacts. When the gate voltage is changed, the drain current changes with the drain voltage in a clear linear region and a saturation region.

[0056] Figure 4 This is a schematic diagram illustrating the bandgap modulation principle of the metal-carbon nanotube contact in a carbon nanotube field-effect transistor without a yttrium metal particle layer. According to Schottky contact theory, the relative positions of the metal Fermi level and the semiconductor Fermi level can affect the Schottky barrier height at the contact interface. The electron affinity of the metal Fermi level and the carbon nanotube is relatively similar. When a positive voltage is applied, the conduction band and valence band of the carbon nanotube bend downwards, making it easier for n-type electron transport to occur when the two come into contact.

[0057] Figure 5 This is the present invention. Figure 1This embodiment illustrates the bandgap modulation principle of the carbon nanotube field-effect transistor after introducing a yttrium particle layer, demonstrating the contact between the metal and carbon nanotubes. When a voltage is applied to the drain terminal of the device, the metal particles diffuse into the dielectric layer, forming a composite metal oxide with a large number of oxygen vacancies. This electron doping of the carbon nanotube channel significantly lowers the Fermi level of the carbon nanotube, bringing it closer to the conduction band. This reduces the Schottky barrier, allowing more electrons to be injected into the carbon nanotube channel, forming an ohmic contact and increasing the saturation output current of the field-effect transistor.

[0058] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the claims of the present invention.

Claims

1. A carbon nanotube field-effect transistor based on a low work function metal, characterized in that, The carbon nanotube field-effect transistor includes a substrate, a carbon nanotube thin film, a source electrode (310), a drain electrode (300), an oxide dielectric layer (410), and a metal particle layer (500). A carbon nanotube film is laid flat on a substrate, and a source electrode (310) and a drain electrode (300) are located on the carbon nanotube film. A metal particle layer (500) is completely covered on the upper surface region of the oxide dielectric layer (410). The source electrode (310) and drain electrode (300) are chromium-gold electrodes, and the source electrode (310) and drain electrode (300) can achieve ohmic contact with carbon nanotubes; When a voltage is applied to the drain electrode (300), the metal particles diffuse into the oxide dielectric layer (410) to form a composite oxide layer rich in oxygen vacancies, which electron dopes the carbon nanotube channel, allowing more electrons to be injected into the carbon nanotube channel, forming an ohmic contact and increasing the saturation output current of the field-effect transistor. The metal particle layer (500) consists of 0.5-2 nm yttrium nanoparticles; The oxide dielectric layer (410) is HfO2. When a voltage is applied to the drain electrode of the device, yttrium nanoparticles diffuse perpendicularly into the oxide dielectric layer (410) to form a composite oxide dielectric layer YHfO rich in oxygen vacancies. x .

2. The carbon nanotube field-effect transistor based on a low work function metal according to claim 1, characterized in that, The thickness of the oxide dielectric layer (410) is 10-20 nm.

3. The carbon nanotube field-effect transistor based on a low work function metal according to claim 1, characterized in that, Electron beam evaporation was used to deposit a metal particle layer (500).

4. A carbon nanotube field-effect transistor based on a low work function metal according to claim 1, characterized in that, In the source electrode (310) and drain electrode (300), the chromium thickness is 20 nm and the gold thickness is 40 nm.

5. A method for implementing the ohmic contact of a carbon nanotube field-effect transistor according to any one of claims 1-4, characterized in that, First, a carbon nanotube field-effect transistor is prepared. After preparation, a voltage is applied to the drain electrode (300). Metal particles diffuse vertically into the oxide dielectric layer (410) to form a composite oxide rich in oxygen vacancies. Electron doping is performed on the carbon nanotube channel to inject more electrons into the carbon nanotube channel, forming an ohmic contact and increasing the saturation output current of the field-effect transistor.

6. The method for realizing the ohmic contact of a carbon nanotube field-effect transistor according to claim 5, characterized in that, The method for fabricating the carbon nanotube field-effect transistor includes the following steps: Step 1: Deposit a carbon nanotube film using the substrate as the growth surface; Step 2: The surface of the carbon nanotube film is homogenized, and the source electrode (310) and drain electrode (300) are deposited by vapor deposition. Step 3: Etch the carbon nanotube film between the source electrode (310) and the drain electrode (300) to obtain the carbon nanotube channel layer (210). Step 4: Perform spin coating and exposure again to prepare an oxide dielectric layer (410) on the upper surface of the carbon nanotube channel layer (210). Step 5: Deposit a metal particle layer (500) on the upper surface of the oxide dielectric layer (410). Step 6: Place the device prepared in step 5 under an inert atmosphere for annealing to obtain a carbon nanotube field-effect transistor.

7. The method for realizing the ohmic contact of a carbon nanotube field-effect transistor according to claim 6, characterized in that, After step 5, a top gate electrode (610) is prepared by vapor deposition on the metal particle layer (500).

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