Nanoelectromechanical devices including carbon nanotubes and methods of fabrication

Abstract

This disclosure relates to a device including a substrate, a first electrode on the substrate configured as a source or drain of the device, and a second electrode on the substrate configured as the other of the source and drain of the device. The device further includes a carbon nanotube having a first end connected to the first electrode and a second end connected to the second electrode, with intermediate segments of the carbon nanotube suspended above a surface of the substrate. The carbon nanotube extends substantially longitudinally from the first electrode to the second electrode. The device also includes a plurality of third electrodes disposed above the carbon nanotube and configured as a plurality of top gates. The third electrodes are disposed at different locations along the longitudinal direction and along the intermediate segments of the carbon nanotube. A void exists between the top portions of the carbon nanotube and the bottom portions of one or more of the third electrodes. This disclosure further includes a method of fabricating such a device.

Description

Technical Field

[0001] This application claims the benefit of European Patent Application No. EP23383396.1, filed on December 28, 2023. This disclosure relates to nanoelectromechanical devices including carbon nanotubes and methods for manufacturing the same. Background Technology

[0002] Nanoelectromechanical systems (NEMS) are devices characterized by electrical and mechanical capabilities at the nanoscale. As technology advances towards greater miniaturization, NEMS devices represent a step from microelectromechanical systems (MEMS) devices into the nanoscale realm. Nanoscale physics differs from microscale physics, and quantum effects dominate the physical behavior of these devices. This opens up possibilities for new device concepts and applications, such as, for example, quantum computing and quantum simulation. However, selecting appropriate materials and fabricating devices at the nanoscale also present their own challenges. In particular, current fabrication techniques commonly exhibit problems of low yield and high device quality variability.

[0003] Carbon-based materials are among the preferred materials for fabricating NEMS devices because they exhibit mechanical, electrical, and electromechanical properties well-suited to the requirements of NEMS devices. Carbon can form a variety of allotropes, such as diamond, graphite, amorphous carbon, graphene, or carbon nanotubes (CNTs). Carbon nanotubes are particularly promising for fabricating various NEMS with a wide range of applications. Carbon nanotubes can be essentially understood as cylinders obtained by rolling up graphene sheets. On the one hand, single-walled carbon nanotubes (SWCNTs) consist of a single cylinder, which typically exhibits a diameter in the nanometer range. The length of SWCNTs can vary depending on, for example, the manufacturing technique, and can range from several nanometers to several micrometers (μm). On the other hand, multi-walled carbon nanotubes (MWCNTs) consist of multiple nested cylinders. Depending on how the graphene sheet is rolled up, CNTs exhibit different properties. Furthermore, depending on their electronic properties, CNTs can be classified as metallic or semiconductor.

[0004] Carbon nanotubes (CNTs) possess excellent crystallinity, which results in remarkable mechanical properties, such as extremely high tensile strength. Furthermore, the nanostructure of CNTs also contributes to excellent thermal and electronic conductivity. Based on these exceptional properties, carbon nanotube-based devices can be used in various applications, such as supercapacitors, field-effect transistors, sensors, or quantum bits (qubits).

[0005] Due to their nanoscale size, CNTs are one-dimensional (1D) objects, and they confine electrons within 1D. When electrons are confined to small regions within carbon nanotubes, CNT quantum dots (QDs) are formed. This is typically accomplished by connecting a single CNT between two electrodes by applying a voltage to several gate electrodes. In such cases, electrons can be confined in a zero-dimensional (0D) potential well with discrete energy levels. Alternatively, one or more quantum dots can be defined at one or more locations along the carbon nanotube by electrostatic gates, i.e., by arranging one or more gates capacitively coupled to the CNT at different locations, allowing fine-tuning of the electrostatic potential at these different locations to create single or multiple quantum dots.

[0006] As mentioned, structures including CNTs can be used as qubits in quantum computing applications. A qubit is a two-level quantum system that constitutes the basic unit of information in quantum computing. Various types of qubits can be defined by utilizing the different properties of carbon nanotubes and depending on the arrangement of the carbon nanotubes in the system. Therefore, a quantum dot (QD) can be created by connecting a single CNT between two electrodes and arranging one or more gate electrodes along the length of the CNT. The QD is then formed in the middle segment of the carbon nanotube, i.e., in the segment of the carbon nanotube between the two electrodes. Electrons can be physically confined within the quantum dot, and quantum information can be encoded, for example, in the spin of the confined electrons, thus creating a so-called spin qubit.

[0007] Charge-based qubits, including those based on carbon nanotubes, have also been proposed. Different types of charge-based qubits can be envisioned. For example, a system can be defined in which two quantum dots (QDs) are formed in a CNT arranged between two electrodes. For this purpose, multiple gate capacitors can be coupled to the CNT at different locations along its length. In particular, the number and arrangement of the gates can be chosen such that two QDs are formed and separated by a tunneling barrier. Therefore, charge-based qubits can be defined based on the excess or presence of electrons in one quantum dot relative to that in the other.

[0008] Further examples of CNT-based qubits include the use of carbon nanotubes in nanoelectromechanical qubits. Therefore, suspended CNTs can be used as nanoelectromechanical resonators with two or more quantized energy levels.

[0009] Quantum dots placed along vibrating nanotubes provide a quantum simulation platform that can directly address electron-phonon interactions.

[0010] Nanoelectromechanical systems (NEMS) including carbon nanotubes can also be used in other applications, such as sensors for small masses and forces or field-effect transistors. In the latter case, semiconducting carbon nanotubes can be used as transistor channels.

[0011] Regardless of the specific application, most NEMS devices involving the use of carbon nanotubes include connections from the ends of the carbon nanotubes to corresponding electrodes, as well as definitions for one or more gates capacitively coupled to the carbon nanotubes. The fabrication of such devices falls into three main categories: bottom gate, top gate, and mechanical transfer.

[0012] Bottom gate fabrication involves growing or depositing carbon nanotubes on electrodes prefabricated on a substrate. The prefabricated electrodes act as end contacts of the carbon nanotubes and also as the gate. This technique has several drawbacks. One of these drawbacks relates to the quality of the contacts, which is limited, so the carbon nanotubes are only located on top of the electrodes, and the contact area can be very small. More importantly, bottom gate fabrication processes typically exhibit very low yields because obtaining a working device depends on the chance of obtaining a single carbon nanotube with the desired properties located at a precise position. Specifically, this is where the carbon nanotube contacts the first and second electrodes, i.e., the source and drain, only at each of its ends.

[0013] Top-gate fabrication involves fabricating an electrode comprising one or more gate electrodes on top of a carbon nanotube previously provided on a substrate. An insulating material, such as an oxide, is typically disposed between the carbon nanotube and the gate in the region where they overlap. This enables capacitive coupling and prevents short circuits. However, the top-gate fabrication process also exhibits some limitations. In particular, patterning and etching steps are required to define the electrodes, i.e., the source, drain, and gate of the device. Doing so can damage the already deposited carbon nanotube. Additionally, top-gate devices retain the carbon nanotube buried in or at least in contact with the insulating material. This contact is known to affect the properties of the carbon nanotube due to charge fluctuations caused by charge traps present in the insulating material. Furthermore, the presence of insulating material in contact with the carbon nanotube is an obstacle for some applications, such as the use of flexural modes of carbon nanotubes in nanoelectromechanical quantum bits.

[0014] The third category of manufacturing processes involves mechanical transfer. In this case, individual carbon nanotubes are processed. The carbon nanotubes are then transferred to corresponding electrodes pre-defined on a substrate. Individual processing and transfer allow for highly controlled and precise placement. Furthermore, this method allows for the selection of specific carbon nanotubes and the production of clean structures. However, processing carbon nanotubes is challenging and can easily cause damage that may affect the electromechanical properties of the transferred carbon nanotubes.

[0015] In the examples of this disclosure, improved nanoelectromechanical (NEMS) devices incorporating carbon nanotubes are provided. Furthermore, in the examples of this disclosure, methods of fabrication that reduce at least some of the aforementioned disadvantages are provided. Summary of the Invention

[0016] In one aspect of this disclosure, a carbon nanotube-based nanoelectromechanical device is provided. The device includes a substrate, a first electrode, and a second electrode. The first electrode is on the substrate and is configured as either a source or a drain of the device. The second electrode is also on the substrate and is configured as the other of the source and drain of the device. The device further includes a carbon nanotube having a first end connected to the first electrode and a second end connected to the second electrode, at least a portion of an intermediate segment of the carbon nanotube being suspended above a surface of the substrate. One or more third electrodes are disposed above the carbon nanotube and are configured to be capacitively coupled to a top gate of the carbon nanotube. An empty space exists between the top portion of the carbon nanotube and the bottom portion of at least one of the top gates.

[0017] Based on this aspect, a device with improved capabilities is presented. Fully suspended carbon nanotubes (CNTs) can be provided when the entire intermediate segment is suspended above the surface of the substrate. In other words, the device can be configured such that the carbon nanotubes are suspended between the end contacts established with the first and second electrodes, without providing further support between the carbon nanotubes and the substrate. By preventing contact with the substrate, reduced uncertainty at the interface between the CNT and the substrate is achieved, thereby improving device performance. Furthermore, the effects on CNT characteristics caused by charge fluctuations in the substrate are avoided.

[0018] One or more top gates are arranged near the carbon nanotubes, such that they are capacitively coupled to the carbon nanotubes. Therefore, the top gates are configured to induce a controllable electrostatic potential in the carbon nanotubes. The arrangement (e.g., number and location) and controllability of the top gates provide enhanced flexibility to the device, allowing it to be configured for different applications.

[0019] Furthermore, top gates are disposed above the carbon nanotubes, but at least one of them is configured to have no physical contact. In other words, at least one top gate overlaps with an intermediate segment of the carbon nanotube (i.e., a segment of the carbon nanotube not connected to the first and second electrodes), but no direct or indirect physical contact is established between the carbon nanotube and this particular top gate. Therefore, an empty space exists between the top portion of the carbon nanotube and the bottom portion of this particular third electrode configured as a top gate, such that the corresponding top gate is in a floating configuration. This physical separation prevents charge fluctuations caused by charge traps in the material (e.g., oxides) between the carbon nanotube and the gate in a previously existing device. Therefore, the absence of any direct contact with the floating segment of the carbon nanotube can generate increased electron mobility and thus increased conductivity of the carbon nanotube.

[0020] Furthermore, the separation of the carbon nanotube from one or more top gates and the substrate allows for the utilization of the mechanical properties of the carbon nanotube. This separation enables the use of the flexural modes of the carbon nanotube, thereby opening up the possibility of storing quantum information and using the device as a nanoelectromechanical quantum bit.

[0021] Specifically, where an empty space is provided between the top portion of the carbon nanotube and the bottom portion of all the top gates, the flexure mode of the carbon nanotube can correspond to the flexure mode of the full length of the middle segment of the carbon nanotube. In other examples, as mentioned above, a physical contact can be established between the carbon nanotube and at least one of the one or more top gates. Such a physical contact can allow for the segmentation of the flexure modes of the carbon nanotube.

[0022] In a further aspect of this disclosure, a method of manufacturing a device according to a prior aspect is provided. The method includes providing a substrate and providing a first insulating layer on the substrate. A plurality of carbon nanotubes are provided on the first insulating layer. The method further includes detecting at least one of the plurality of carbon nanotubes and identifying a longitudinal end of the detected carbon nanotube. A second insulating layer is deposited on the first insulating layer and at least on the detected carbon nanotube. The method then includes exposing the longitudinal end of the detected carbon nanotube by etching the first and second insulating layers in regions surrounding each of the longitudinal ends. Conductors are deposited in the etched regions to define a first electrode and a second electrode, the conductors contacting the longitudinal end of the carbon nanotube. Conductors are also deposited on the second insulating layer in regions overlapping with intermediate segments of the carbon nanotube to form one or more third electrodes configured as a top gate. Finally, the method includes etching the first and second insulating layers in at least a portion of the region between the first and second electrodes and along the length of the carbon nanotube.

[0023] According to this further aspect of the disclosure, a method for manufacturing a MEMS device is provided, the MEMS device comprising gate-controlled, suspended, or fully suspended carbon nanotubes.

[0024] The method according to this further aspect enables the fabrication of electrodes after the detection of carbon nanotubes. In this way, individual carbon nanotubes with desired properties (e.g., length or shape) can be selected. Specific electrodes are then fabricated for the individually selected carbon nanotubes. This fabrication process offers high yields and eliminates reliance on chance, a characteristic of commonly used processes, particularly those involving bottom gates.

[0025] Furthermore, fabricating the top gate structure after providing the carbon nanotubes eliminates the need for them to endure the harsh conditions of carbon nanotube growth that might exist in other fabrication methods. In this way, the constraints on the gate material are relaxed compared to some of the previously existing methods.

[0026] A further advantage of this approach is that the manufacturing method offers greater scalability and automation than other manufacturing methods, such as those involving mechanical handling and transfer of individual carbon nanotubes. Therefore, the method according to this disclosure can be performed using automated nanotube positioning and automated etching and patterning procedures to form different electrodes.

[0027] Throughout this disclosure, the intermediate segment of a carbon nanotube should be understood as a segment of the carbon nanotube that is not connected to the first electrode and the second electrode. In other words, the intermediate segment refers to the portion of the carbon nanotube that extends between the first electrode and the second electrode.

[0028] Furthermore, throughout this disclosure, different electrodes are referred to, which are configured for different purposes. Therefore, the term "first electrode" refers to a contact electrode configured as the source or drain of a device, while the term "second electrode" refers to a contact electrode configured as the other of the source or drain of a device. Furthermore, the term "third electrode" refers to a top gate electrode configured as the top gate of a device, while the term "fourth electrode" refers to a bottom gate electrode configured as the bottom gate of a device. Attached Figure Description

[0029] Non-limiting examples of this disclosure will be described below with reference to the accompanying drawings, in which: Figure 1 A side view of a nanoelectromechanical device including carbon nanotubes according to an example of this disclosure is schematically illustrated. Figure 2 A flowchart illustrating an example method for fabricating nanoelectromechanical devices including carbon nanotubes is shown; Figures 3A to 3G Top and cross-sectional (A-A') views are schematically illustrated at different stages of an example method for fabricating nanoelectromechanical devices including carbon nanotubes; Figures 4A to 4E A side view of a nanoelectromechanical device including a carbon nanotube and a bottom gate, according to different examples of the present disclosure, is schematically illustrated. Figures 5A to 5B A side view schematically illustrates a nanoelectromechanical device comprising carbon nanotubes, wherein the carbon nanotubes are coupled to a top gate (Fig. 5a) or a bottom gate (Fig. 5a). Figure 5B Physical contact was provided between them. Detailed Implementation

[0030] Reference will now be made in detail to embodiments, one or more examples of which are illustrated in the accompanying drawings. Each example is provided by way of explanation only and is not intended to be limiting. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in this disclosure. This disclosure is intended to cover such modifications and variations within the scope of the appended claims and their equivalents. Furthermore, the drawings are intended to illustrate different examples and manufacturing processes. For clarity, the dimensions of different elements are not drawn to scale to facilitate the identification of different parts.

[0031] Figure 1 This is a side view of a nanoelectromechanical device 1 including carbon nanotubes 30, according to an example. Device 1 includes a substrate 10, a first electrode 50, and a second electrode 60. The first electrode 50 is disposed on the substrate 10 and is configured as either the source or drain of device 1. The second electrode 60 is also disposed on the substrate 10 and is configured as either the source or drain of device 1.

[0032] Device 1 includes a carbon nanotube 30 having a first end connected to a first electrode 50 and a second end connected to a second electrode 60, with a middle segment of the carbon nanotube 30 suspended above the surface of a substrate 10. One or more third electrodes 70 are disposed above the carbon nanotube 30, and the third electrodes 70 are configured to be capacitively coupled to a top gate of the carbon nanotube 30. An empty space exists between the top portion of the carbon nanotube 30 and the bottom portion of the third electrode 70.

[0033] Therefore, according to this example, the entire intermediate segment is suspended above the surface of the substrate 10. Furthermore, there is an empty space between the top portion of the carbon nanotube 30 and the bottom portions of all the third electrodes 70, and in this example, no physical contact is provided between the carbon nanotube 30 and any of the third electrodes 70 configured as the top gate. Therefore, a device 1 with a fully suspended carbon nanotube 30 can be provided, which can be positioned between the intermediate segment of the carbon nanotube 30 and the substrate 10 along the entire intermediate segment without support.

[0034] An empty space is provided between the top portion of the carbon nanotube 30 and the bottom portion of the third electrode 70, which is configured as the top gate of device 1, allowing the utilization of the mechanical properties of the carbon nanotube 30. Therefore, one or more top gates can be configured to induce vibrations in the carbon nanotube 30, such that device 1 can be configured as a nanoelectromechanical quantum bit. Specifically, in this example, vibrations can be induced along the entire middle segment of the carbon nanotube 30.

[0035] Furthermore, the physical separation of the middle segment of the carbon nanotube 30 from the substrate 10 and from the third electrode 70 prevents charge fluctuations that could result from interactions with charge traps at the substrate 10 and / or the third electrode 70. This floating top gate and the fully suspended position of the carbon nanotube 30 can also enhance electron mobility within the carbon nanotube 30. This aspect may be particularly useful in some applications. Therefore, the device 1 can be configured as a field-effect transistor, more specifically, wherein the carbon nanotube 30 can be configured as the channel of the field-effect transistor, and the top gate can be configured as the gate contact of the field-effect transistor.

[0036] In the examples of this disclosure, the carbon nanotube 30 may extend substantially longitudinally from the first electrode 50 to the second electrode 60. The device may include a plurality of third electrodes 70 disposed above the carbon nanotube 30, the plurality of third electrodes being configured as a plurality of top gates. The third electrodes 70 may be arranged at different locations along the longitudinal direction and along the middle segments of the carbon nanotube 30. Specifically, in the examples of this disclosure, three or more third electrodes 70 may be provided. More specifically, five third electrodes 70 may be provided.

[0037] Providing multiple third electrodes 70, i.e., multiple top gates, can facilitate certain applications by allowing control of the electrostatic field at selected locations (i.e., in this case, different longitudinal positions along the carbon nanotube) 30. Specifically, this controllability can allow different quantum dots (QDs) to be defined along the length of the carbon nanotube 30. Thus, QDs can be formed in the carbon nanotube 30 by the electrostatic potential generated by the multiple third electrodes 70. The position and size of the QDs can be modified by adjusting the voltage of the top gates. Therefore, device 1 can be configured as a qubit. Thus, one or more top gates can be configured to define one or more quantum dots in the carbon nanotube 30, and device 1 can be configured as a spin qubit and / or a charge qubit.

[0038] In one example of this disclosure, five top gates, i.e., five third electrodes 70, can be provided above the middle segment of the carbon nanotube 30 along the longitudinal direction of the carbon nanotube 30. In this way, dual quantum dots (DQDs) can be obtained. More specifically, the third electrode 70 (i.e., the top gate) arranged closest to the first electrode 50 can be used to control the voltage barrier between the corresponding first electrode 50 and the first quantum dot, while the third electrode 70 arranged closest to the second electrode 60 can be used to control the voltage barrier between the second electrode 60 and the second quantum dot of the DQD. Then, three third electrodes 70 arranged between the three electrodes 70 at the two ends (i.e., between the top gates at the two ends) can be used to control tunnel coupling between the quantum dots (QDs) in the DQD.

[0039] In the examples disclosed herein, an arrangement can be provided to prevent bending of the suspended carbon nanotubes 30. Therefore, a rigid configuration of the carbon nanotubes 30 may be preferred for some applications that do not depend on the flexural degrees of freedom of the carbon nanotubes 30. In particular, when using device 1 as, for example, a spin qubit or a charge qubit, a substantially rigid carbon nanotube 30 can be advantageous in preventing interference or undesirable coupling between different degrees of freedom. In this way, a cleaner or purer device 1 can be obtained. Furthermore, providing a rigid configuration can also be advantageous in enhancing the structural and mechanical stability of device 1. Different methods can be used to increase the stiffness of the carbon nanotubes 30. In one example, the device may include a coating material, specifically an oxide, arranged to encapsulate the intermediate segments of the carbon nanotubes 30.

[0040] Figure 1 Device 1 is depicted, wherein a single carbon nanotube 30 is disposed between a first electrode 50 and a second electrode 60. However, in the examples of this disclosure, multiple carbon nanotubes 30 may be arranged in parallel. They may be connected between the first electrode 50 and the second electrode 60, wherein intermediate segments of the multiple carbon nanotubes 30 are suspended above the surface of the substrate 10.

[0041] In some applications, it may be advantageous to use multiple carbon nanotubes 30. Therefore, when using device 1 as a field-effect transistor, the number of carbon nanotubes 30 can be modified to adjust the conductivity of the transistor channel.

[0042] The dimensions of device 1 and its different portions may be defined by the application and / or manufacturing method of device 1. In one example of this disclosure, the third electrode 70 may have a thickness between 1 nm and 100 μm and a width between 1 nm and 10 μm.

[0043] The dimensions of the third electrode 70 can be limited not only by considering the intended final functionality of device 1, but also by taking into account the mechanical and structural stability of device 1. More specifically, such as Figure 1 As shown, the third electrodes 70 can be arranged in a floating configuration, allowing them to be suspended, with the suspended segments positioned above the carbon nanotubes 30 but not in physical contact with them. To improve the mechanical stability of this suspended portion, a certain thickness of the material constituting the third electrode 70 may be desirable.

[0044] The length of the carbon nanotubes 30 provided on the substrate 10 is related to the main dimensions of the device 1, and the length can vary over a very wide range depending on the circumstances.

[0045] Therefore, in the examples of this disclosure, the distance between the first electrode 50 and the second electrode 60 can be between 3 nm and 100 μm. In practice, the length of the carbon nanotubes 30 used to fabricate the device 1 can be selected considering the anticipated applications or implementations. Furthermore, the length of the carbon nanotubes 30 may also be influenced by the method used to provide the carbon nanotubes 30.

[0046] In some applications, including when using device 1 as a nanoelectromechanical device, the vibration of the suspended carbon nanotubes 30 can be utilized, and the vibration mode of the carbon nanotubes 30 can be tuned based on their length. In other applications, such as when using device 1 as a field-effect transistor, a shorter length of the carbon nanotubes 30 may be preferred, as this corresponds to a shorter channel length of the field-effect transistor, thereby improving the performance of device 1, such as speed.

[0047] As already mentioned, Figure 1 The device 1 shown is characterized by a suspended carbon nanotube 30 and a plurality of third electrodes 70, which are capacitively coupled to the carbon nanotube 30 but not in physical contact (direct or indirect physical contact). Therefore, the third electrodes 70 are in a similar floating configuration. In the examples of this disclosure, the distances of the carbon nanotube 30 relative to the top surface of the substrate 10 and relative to the bottom portion of the third electrodes 70 can be designed to meet the specific needs of the intended application.

[0048] In one example, the distance between the middle segment of the carbon nanotube 30 and the substrate 10 can be between a few angstroms and 10 μm, more specifically between 1 nm and 5 μm. Variations in this distance can produce different effects. In particular, a larger distance can exhibit the advantage of preventing charge trapping on the carbon nanotube 30. In other cases, a bottom gate can be provided, in which case the spacing can be adjusted to optimize controllability.

[0049] Similarly, the distance between the carbon nanotube 30 and the third electrode 70, configured as the top gate, can also be adjusted. Therefore, in the example of this disclosure, the distance between the bottom portion of the third electrode 70 and the top portion of the carbon nanotube can be between a few angstroms and 1 μm, more specifically between 1 nm and 0.5 μm. This distance can depend on the intended application and the corresponding range of the applied gate voltage. This distance may affect the capacitive coupling between the carbon nanotube 30 and the third electrode 70, and therefore, it may affect the electrostatic field in the carbon nanotube 30. In the example, the electrostatic force caused by capacitive coupling may produce some vibrations. Contact between the carbon nanotube 30 and the third electrode 70 (i.e., the top gate) may need to be avoided to prevent short circuits in device 1. In other words, the distance can be designed as a trade-off between capacitive coupling and mitigating the risk of unwanted contact between the portions.

[0050] The first end of the carbon nanotube 30 can be embedded in the first electrode 50, and / or the second end of the carbon nanotube 30 can be embedded in the second electrode 60. Specifically, Figure 1 An example is shown in which both ends of the carbon nanotube 30 can be embedded in the material used for the first electrode 50 and the second electrode 60.

[0051] The electrical and mechanical contact between the ends of the carbon nanotubes 30 and the first electrode 50 and the second electrode 60 can be enhanced by embedding. Specifically, the contact resistance between the carbon nanotubes 30 and the respective first electrode 50 and second electrode 60 can be reduced using such an embedded arrangement compared to other contact arrangements such as clamping. Figure 2 and Figures 3A to 3G More details about the embedded contacts will be provided when discussing the fabrication of device 1.

[0052] As is known to those skilled in the art, carbon nanotubes (CNTs) can exhibit different configurations. Specifically, CNTs can be single-walled or multi-walled, and they can exhibit different electronic properties, such as metallic or semiconducting. In the examples of this disclosure, carbon nanotube 30 can be a single-walled carbon nanotube (SWCNT). More specifically, carbon nanotube 30 can be a (narrow bandgap) semiconducting carbon nanotube 30.

[0053] Different materials can be used to manufacture different components of device 1. Therefore, in the examples of this disclosure, at least one of palladium (Pd), platinum (Pt), chromium (Cr), titanium (Ti), aluminum (Al), or gold (Au) can be used for at least one of the first electrode 50, the second electrode 60, or the third electrode 70. Furthermore, binary metals such as titanium nitride (TiN) or tantalum nitride (TaN) can also be used. In further examples, conductive carbon nanotubes (CNTs) or two-dimensional conductors, such as graphene, can also be employed.

[0054] The choice of materials can depend on the materials possessing sufficient electronic properties (e.g., work function) to allow for proper connection between the carbon nanotubes 30 and the corresponding first and second electrodes 50. The application of device 1 may influence the electronic properties of the carbon nanotubes 30 selected for device 1. Therefore, this selection may affect the desired electronic properties of the materials used for the first and second electrodes 50. Furthermore, the choice of material for the third electrode 70 can also be based on its mechanical properties, particularly due to the suspended arrangement of a portion of the top gate.

[0055] In some examples, the first electrode 50 and the second electrode 60 may be made of different materials than those used for the third electrode 70. In some further examples, the material used for the first electrode 50 may be different from the material used for the second electrode 60. In even further examples, multiple different materials may be used for a single electrode. Therefore, combinations of, for example, chromium and gold (Cr / Au) or titanium and gold (Ti / Au) may be used for the first electrode 50 and / or the second electrode 60 to improve, for example, adhesion or electronic properties.

[0056] Materials can be deposited using various semiconductor manufacturing techniques, including chemical vapor deposition (CVD), atomic layer deposition (ALD), physical vapor deposition (PVD), or ink-based additive methods.

[0057] Similar to the electrodes, different materials can be used for the substrate 10. Therefore, in the examples of this disclosure, the substrate 10 of the device 1 may include one of a silicon substrate, a sapphire substrate, a diamond substrate, a quartz substrate, or a borosilicate substrate.

[0058] The choice of material for substrate 10 can depend on various factors. Specifically, the temperature requirements of the manufacturing process can be considered. In some examples, providing carbon nanotubes 30 on substrate 10 may require high temperatures (in the range of 900°C–1000°C). In such examples, a substrate 10 capable of supporting such high temperatures may be required.

[0059] In addition to the manufacturing process, the application and functional requirements of device 1 can also determine the material of substrate 10.

[0060] Now refer to Figure 2 and Figures 3A to 3G An example of a method for manufacturing device 1 according to this disclosure is provided. Figure 2 A flowchart of a method 100 for manufacturing a nanoelectromechanical device according to an example is shown.

[0061] At block 110, the method includes providing a substrate 10. In block 120 of method 100, a first insulating layer 20 is provided on the substrate 10, and block 130 includes providing a plurality of carbon nanotubes 30 (CNTs) on the first insulating layer 20. Block 140 includes detecting at least one of the plurality of carbon nanotubes 30 and identifying the longitudinal end of the detected carbon nanotube 30. In block 150, a second insulating layer 40 is deposited on the first insulating layer 20 and at least on the detected carbon nanotube 30. Block 160 includes exposing the longitudinal end of the detected carbon nanotube 30 by etching the first insulating layer 20 and the second insulating layer 40 in a region surrounding each of the longitudinal ends. In block 170, conductors are deposited in the etched region to define a first electrode 50 and a second electrode 60, such that the conductors contact the longitudinal end of the carbon nanotube. Block 180 of method 100 includes depositing a conductor on a second insulating layer 40 in a region overlapping with an intermediate segment of the carbon nanotube 30 to form one or more third electrodes 70 configured as a top gate structure. In block 190, a first insulating layer 20 and a second insulating layer 40 are etched. Specifically, the first and second insulating layers are etched in at least a portion of the region defined between the first electrode 50 and the second electrode 60 and along the length of the carbon nanotube 30.

[0062] according to Figure 2 Method 100 of the flowchart in the document can generate a flowchart with... Figure 1 The device depicted is similar to device 1. In particular, by exposing the longitudinal ends of the carbon nanotubes 30 in frame 160 and then depositing conductors in frame 170, embedded contacts can be created, i.e., the ends of the carbon nanotubes 30 can be embedded in the conductor material used for the first electrode 50 and the second electrode 60.

[0063] Even though a certain number of boxes are provided in method 100, it should be understood that there may be examples that include additional boxes and / or change the order of previously presented boxes. As an example, in the case where the design of device 1 includes different materials for each of the first and second electrodes, two different sequences of boxes 160 and 170 may be performed, one sequence for each of the first and second electrodes.

[0064] Furthermore, the method according to a further example may include, in the region between the first electrode 50 and the second electrode 60 and after etching the first insulating layer 20 and the second insulating layer 40 along the length of the carbon nanotube 30, growing an oxide to encapsulate at least the intermediate segments of the carbon nanotube 30. According to this example, a device 1 comprising a more rigid carbon nanotube 30 can be fabricated. This may be desirable for some applications that are independent of the flexural modes of the carbon nanotube 30. In this way, the effects of flexural modes can be prevented when the device 1 is operated as, for example, a spin qubit or a charge qubit. Different methods are conceivable for depositing coating materials, such as oxides, on the carbon nanotube 30. As an example, atomic layer deposition (ALD) can be used to conformally deposit thin coating materials on different surfaces of the device 1, and in particular, to encapsulate the intermediate segments of the carbon nanotube 30.

[0065] Now refer to Figures 3A to 3G These diagrams provide access to and Figure 1 Details of an example of a manufacturing method for a device similar to device 1, as presented. Specifically, Figures 3A to 3G The top view and cross-sectional (A-A') view at different stages of the example method are illustrated schematically.

[0066] Figure 3A The first step of this example is illustrated, which includes providing a first insulating layer 20 on the substrate 10. As mentioned above, this disclosure is not limited to any particular material used for the substrate 10. Depending on the substrate 10 and the intended application, different dielectric materials and different techniques can be used to provide the first insulating layer 20. Thus, in some examples, the layer can be deposited by, for example, chemical vapor deposition (CVD), physical vapor deposition (PVD), or atomic layer deposition (ALD). In other examples including silicon (Si) substrates, the first insulating layer 20 can be provided by thermal oxidation of silicon (Si). Furthermore, in different variations of this example, the first insulating layer may include a nitride or a high-k material.

[0067] Figure 3B This essentially corresponds to frame 130 of manufacturing method 100. As shown, a plurality of carbon nanotubes 30 are provided on the first insulating layer 20. For illustrative purposes, in Figure 3B Only two carbon nanotubes 30 are shown in the diagram. Different alternatives can be used to provide the carbon nanotubes 30. In one example of this disclosure, providing the carbon nanotubes 30 on the first insulating layer 20 may include growing the carbon nanotubes 30 directly on the first insulating layer 20. More specifically, the method may include growing the carbon nanotubes 30 by means of chemical vapor deposition (CVD).

[0068] To grow carbon nanotubes 30 on the first insulating layer 20 by means of CVD, a first step including the deposition of catalyst particles can be performed. The specific location of the catalyst particles can be defined by patterning using photolithography, followed by deposition of a solution containing the catalyst particles. The solvent can then be dried, and excess catalyst can be removed by a stripping process. After the catalyst particles are formed on the surface of the first insulating layer 20, the substrate can be placed in a CVD reactor. The CVD process can use hydrogen (H2), argon (Ar), and methane (CH4), and the carbon nanotube growth process can be carried out at high temperatures in the range of 900°C. Based on the parameters of this process, carbon nanotubes 30 with different characteristics (e.g., length) can be obtained.

[0069] In other examples, Figure 3B The provision of carbon nanotubes 30 may include depositing a solution of pre-formed carbon nanotubes 30 in a solvent and removing the solvent after deposition.

[0070] By using a solution containing pre-formed carbon nanotubes 30, the process temperature can be significantly lower than that used in CVD, allowing for the use of a wider variety of materials. More specifically, avoiding the high temperatures associated with the CVD process allows for the use of a wider range of materials for the substrate. Furthermore, the use of a solution containing pre-formed carbon nanotubes facilitates the use of carbon nanotubes with predetermined characteristics. In particular, depending on the intended application, metallic or semiconducting carbon nanotubes, or single-walled or multi-walled carbon nanotubes, can be selected to fabricate the device 1.

[0071] like Figure 3B As shown, the provided carbon nanotubes 30 do not necessarily need to be arranged in a known and predetermined manner. This may be particularly true when carbon nanotubes 30 are provided using a solution-based method, in which case the carbon nanotubes may be randomly distributed on the surface of the substrate 10. For this reason, the carbon nanotubes 30 can be inspected before proceeding to subsequent fabrication steps, and more specifically, the precise location of the ends of the carbon nanotubes 30 can be detected. Thus, in one example of this disclosure, detecting at least one deposited carbon nanotube 30 and identifying the longitudinal ends of the detected carbon nanotubes 30 may include using optical methods to detect the deposited carbon nanotubes, and / or using at least one of low-power scanning electron microscopy (SEM) and atomic force microscopy (AFM) to identify the longitudinal ends. In examples where the carbon nanotubes are grown at specific locations (rather than randomly distributed), prior knowledge about the location of the nanotubes can be used when detecting them.

[0072] The detection of carbon nanotubes 30 and the identification of their longitudinal ends can involve different methods and techniques, depending on the characteristics of the carbon nanotubes 30, such as their size. Therefore, when considering long carbon nanotubes, for example, with a longitudinal length exceeding 100 nanometers, optical microscopy can be used for both detection and end identification. For this purpose, advanced deep ultraviolet (DUV) optical systems can be employed. In other examples, a combination of optical detection methods and more advanced scanning techniques can be used. Specifically, optical microscopy can be used to detect carbon nanotubes 30, while subsequent steps, including scanning electron microscopy (SEM) or atomic force microscopy (AFM), can be utilized to precisely identify the longitudinal ends.

[0073] In a further example, specifically including very short carbon nanotubes 30, for example, with a length less than 10-20 nm, direct observation using SEM or AFM can be implemented. Markings can be defined on the surface of the substrate 10 to serve as references or guides for defining and recording the locations of the identified carbon nanotubes 30. As an example, markings can be defined at certain locations on the substrate 10 by means of, for example, photolithography or electron beam lithography.

[0074] In the examples of this disclosure, the detection of carbon nanotubes 30 may be accompanied by the selection or testing of carbon nanotubes 30. In this way, only carbon nanotubes 30 exhibiting the desired mechanical and / or electronic properties can be used to fabricate device 1. In fact, it is known that carbon nanotubes 30 can exhibit different electronic properties. More specifically, the band gap of semiconducting carbon nanotubes 30 can also exhibit different values. Therefore, for applications requiring the adjustment of the tunneling barrier by means of an electrostatic gate, narrow band gap semiconducting carbon nanotubes 30 may be preferred. In other cases, semiconducting carbon nanotubes 30 exhibiting a larger band gap or carbon nanotubes exhibiting metallic electronic behavior may be preferred.

[0075] Figure 3C Essentially corresponding to block 150 of method 100, this involves depositing a second insulating layer 40 on the first insulating layer 20 and on at least one detected carbon nanotube 30. The same or different material may be used as the material used for the first insulating layer 20. In fact, in the examples of this disclosure, at least one of the first insulating layer 20 and the second insulating layer 40 may comprise silicon dioxide (SiO2) or a high-k material. A deposition technique similar to that already referenced for the first insulating layer 20, such as CVD, PVD, or ALD, may be used for the second insulating layer 40.

[0076] Up to this stage of the manufacturing process, two insulating layers are provided on the substrate 10, and at least one carbon nanotube 30 is disposed between the first insulating layer 20 and the second insulating layer 40. As shown in more detail below, the thickness of the first insulating layer 20 affects the spacing between the carbon nanotube 30 and the substrate 10. Depending on the specific application, a certain spacing may be required. Similarly, the thickness of the second insulating layer 40 can define the spacing between the top portion of the carbon nanotube 30 and the bottom portion of the third electrode 70. This spacing, and therefore the thickness of the second insulating layer 40, can also be defined depending on the application of the device 1. In particular, the third electrode 70, configured as the top gate of the device 1, is capacitively coupled to the carbon nanotube 30. Therefore, a relatively short distance may be required to provide electrostatic coupling between the two components. However, especially if the mechanical properties of the carbon nanotube 30 (e.g., vibration) are relevant to the specific application, a minimum spacing, i.e., a minimum thickness of the second insulating layer 40, may also be specified.

[0077] Once the longitudinal end of the carbon nanotube 30 is identified, the next step involves exposing the longitudinal end by etching the first insulating layer 20 and the second insulating layer 40. Figure 3D The diagram schematically illustrates a stage of the manufacturing process following the patterning and etching of the insulating layer. Thus, the longitudinal ends of the carbon nanotubes 30 are exposed, while the middle segments of the carbon nanotubes 30 are sandwiched between the first insulating layer 20 and the second insulating layer 40.

[0078] Identification of the longitudinal ends of the carbon nanotubes 30 can be used to generate a corresponding mask for the photolithography process based on the positional data of the longitudinal ends. The mask can be used to etch the first insulating layer 20 and the second insulating layer 40 at precise locations. Therefore, the etching of the first insulating layer 20 and the second insulating layer 40 can include photolithographic patterning. In other examples, the patterning and etching of the first insulating layer 20 and the second insulating layer 40 can include the use of direct patterning techniques. For example, electron beam lithography (EBL), direct laser writing (DLP), or AFM lithography can be used.

[0079] The etching of the first insulating layer 20 and the second insulating layer 40 can be performed while ensuring compatibility with the carbon nanotubes 30. In practice, it may be desirable for the longitudinal ends of the carbon nanotubes 30 to remain substantially unaffected during the etching process. Different etching alternatives can be used in the examples of this disclosure. In one example, diluted (i.e., wet) hydrofluoric acid HF can be used. In other examples, etching the first insulating layer 20 and the second insulating layer 40 may include using a vapor or dry gas etching process. Specifically, etching may involve gas-phase HF etching or fluoride gas-based plasma etching. Gas-phase etching or dry etching can be chosen due to the lack of surface tension. This can facilitate the etching of the insulating layers without substantially affecting the longitudinal ends of the carbon nanotubes 30. In practice, the longitudinal ends of the carbon nanotubes 30 are cantilevered during etching, which may result in bending of the carbon nanotube structure. In examples using a vapor or dry gas etching process, this bending can be reduced or even eliminated.

[0080] The etching of the first insulating layer 20 and the second insulating layer 40 creates cavities or spaces for defining the first electrode 50 and the second electrode 60. Figure 3E The process is depicted following the deposition of conductors in regions at the two longitudinal ends of the carbon nanotube 30. As shown, the two longitudinal ends of the carbon nanotube 30 are embedded in their respective conductors. Therefore, a single step may be sufficient to embed the longitudinal ends. As mentioned earlier, providing embedded contacts between the longitudinal ends of the carbon nanotube 30 and the first electrode 50 and the second electrode 60 can provide improved mechanical and electrical properties at the interface.

[0081] As referenced above Figure 1 As mentioned, different materials can be used to provide conductors for the first electrode 50 and the second electrode 60. In one example of this disclosure, the materials for the first electrode 50 and the second electrode 60 can be deposited over the entire area of ​​the substrate using standard semiconductor manufacturing techniques including chemical vapor deposition (CVD), physical vapor deposition (PVD), and atomic layer deposition (ALD). After deposition, a chemical mechanical planarization (CMP) process can be used to obtain a smooth surface and remove unwanted material. In other examples of this disclosure, photolithography or electron beam lithography can be used to selectively deposit conductor materials at desired locations. Therefore, the location data for etching the first insulating layer 20 and the second insulating layer 40 can be used to selectively deposit conductor materials in the areas for the first electrode 50 and the second electrode 60 by means of photolithography.

[0082] If the same material is used for both the first electrode 50 and the second electrode 60, the previously mentioned example can be used. However, in a further example, different conductive materials can be used for both the first electrode 50 and the second electrode 60. In this case, etching the first insulating layer 20 and the second insulating layer 40 at the longitudinal ends of the carbon nanotube 30 is included. Figure 3D ) and the conductors deposited for electrodes 50 and 60 ( Figure 3E The sequence of consecutive steps can be performed individually for each of electrodes 50 and 60. In other words, a first etching step can be performed on the first electrode 50, and material for the first electrode 50 can be deposited in a corresponding space corresponding to one end of the carbon nanotube 30. Subsequently, the same steps can be repeated to define the second electrode 60 at the other end of the carbon nanotube 30. Alternatively, the etching of the first insulating layer 20 and the second insulating layer 40 can be performed in a single step, and subsequently, two separate photolithography steps can be performed to obtain the first electrode 50 and the second electrode 60.

[0083] Refer again Figures 3A to 3G For examples, refer to Figure 3F The next step in the manufacturing method is disclosed. Therefore, after defining the first electrode 50 and the second electrode 60, a plurality of third electrodes 70 are deposited on the second insulating layer 40. (As...) Figure 3F As shown, a plurality of third electrodes 70 can be provided, configured as the top gate of device 1. The third electrodes 70 are arranged in an overlapping configuration relative to the carbon nanotube 30, i.e., the third electrodes 70 are physically disposed above the middle segment of the carbon nanotube 30 and separated from the latter by the thickness of the second insulating layer 40. Similar to the definition of the first electrode 50 and the second electrode 60, the third electrodes 70 can be deposited using photolithography or electron beam lithography. Previously generated position data can be used to accurately position the third electrodes 70 relative to the carbon nanotube 30 and relative to the first electrode 50 and the second electrode 60.

[0084] exist Figure 3FIn the depicted example, a third electrode 70 is provided perpendicular to the longitudinal direction of the carbon nanotube 30. Other orientations can be used in alternative examples, provided that the third electrode 70, acting as a top gate, is capacitively coupled to the carbon nanotube 30. In this way, the electrostatic potential at the carbon nanotube 30 can be locally controlled, or an electrostatic force can be applied via the third electrode 70 (i.e., via the top gate) to induce vibration of the carbon nanotube 30. As mentioned above, different spacings between the carbon nanotube 30 and the top gate may be preferred depending on the specific application of device 1. For this purpose, different thicknesses can be deposited for the second insulating layer 40. Besides the spacing between the carbon nanotube 30 and the third electrode 70, other relevant parameters can be adjusted according to the application in the examples of this disclosure. Therefore, the number of third electrodes 70 and the spacing between them, i.e., the pitch, can also be adjusted.

[0085] Furthermore, the dimensions of each third electrode 70 can also be varied. More specifically, both the thickness and width of the deposited third electrode 70 can be selected to ensure appropriate mechanical stability.

[0086] Figure 3G The final stage of the manufacturing process is depicted. As shown, material from the first insulating layer 20 and the second insulating layer 40 is removed (i.e., etched) in the region between the first electrode 50 and the second electrode 60 and along the carbon nanotube 30. In this way, the carbon nanotube 30 becomes suspended or suspended, i.e., it is only contacted and supported at its two ends, while the middle segment of the carbon nanotube 30 is spaced apart from both the substrate 10 and the third electrode 70. Thus, each of the third electrodes 70 can define a bridge-like structure. The ends of the third electrode 70 can be supported on the second insulating layer 40, while the middle segment of the third electrode 70 spans a trench formed after the etching of the insulating layer. In other words, the third electrode 70 is suspended between the walls formed in the first insulating layer 20 and the second insulating layer 40. For this reason, the dimensions of the third electrode 70 can be adjusted, and more specifically, the thickness of the metal deposition performed to define the third electrode 70 can be adjusted to provide sufficient mechanical stability for such a suspended structure.

[0087] Similar to a reference Figure 3D The etching steps shown, including vapor or gas phase etching, can also be used in the examples of this disclosure to etch the region between the first electrode 50 and the second electrode 60. Such gas phase etching can prevent surface tension that would otherwise cause bending of the carbon nanotubes 30 and / or the third electrode 70.

[0088] In one example of this disclosure, not only the first insulating layer 20 and the second insulating layer 40 can be etched, but the substrate 10 can also be etched. Therefore, the method according to one example includes etching the substrate 10 after etching the first insulating layer 20 and the second insulating layer 40 to expose the longitudinal ends of the detected carbon nanotubes 30, and / or etching the substrate 10 after etching the first insulating layer 20 and the second insulating layer 40 in the region between the first electrode 50 and the second electrode 60 and along the length of the carbon nanotubes 30. In other words, it is possible to... Figure 3D The situation described or after Figure 3G The substrate 10 was then etched after the situation described.

[0089] Therefore, in the examples of this disclosure, the substrate 10 itself can be selectively etched to adjust the performance and functionality of the device 1. More specifically, after the patterning of the first electrode 50 and the second electrode 60, but before the deposition of the corresponding conductors (i.e., in... Figure 3D and Figure 3E (Between the stages schematically depicted in the diagram), etching of the substrate 10 can be used to improve the mechanical and electrical connection between the longitudinal ends of the carbon nanotube 30 and the corresponding first electrode 50 and second electrode 60. Similarly, forming grooves in the substrate 10 in the regions for the first electrode 50 and second electrode 60 before depositing the corresponding conductive material can also facilitate proper definition and fixation of the electrodes 50, 60 on the substrate 10, since the first electrode 50 and second electrode 60 can then be partially embedded in the substrate 10, thereby improving mechanical anchoring.

[0090] In another example of this disclosure, the substrate 10 can be etched at a later stage of the manufacturing process. Specifically, this can be done during the step of defining the suspended carbon nanotubes 30, i.e.... Figure 3F Following the presented stage, substrate 10 is etched. In this way, the distance between the intermediate segments of carbon nanotubes 30 and substrate 10 can be increased while keeping carbon nanotubes 30 suspended from their longitudinal ends. More generally, the ability to etch substrate 10 can provide additional flexibility in examples of the manufacturing process to better adjust the spacing between carbon nanotubes 30 and substrate 10. In one example, substrate 10 may comprise a silicon (Si) substrate, and xenon difluoride (XeF2) vapor etching or dry etching using fluorinated gases can be used for etching the substrate.

[0091] In the previously described examples, a device 1 comprising only a top gate has been considered. However, in the examples of this disclosure, device 1 may include one or more bottom gates. Therefore, in addition to the third electrode 70 defining one or more top gates, one or more bottom gates may be provided to enable further control of device 1. The voltage of the one or more bottom gates may be adjusted independently of the voltage of the top gates. This can provide additional parameters to control the electrostatic interaction with the carbon nanotubes 30. Such additional levels of control can be used in applications such as when device 1 is used to define one or more quantum dots (QDs) in the carbon nanotubes 30. Thus, both the top gate and the bottom gate can be used to tune the electronic properties of one or more quantum dots.

[0092] Different topologies can be used to provide, for example Figures 4A to 4D The bottom gate is shown. In Figure 4A The diagram schematically depicts a first variant of device 1 including a bottom gate. In this example, substrate 10 may include a top surface and a bottom surface, with a first electrode 50, a second electrode 60, and carbon nanotubes 30 disposed on the top surface. One or more fourth electrodes 80 (in...) Figure 4A In this example, only one fourth electrode (80) can be defined on the bottom surface, and the fourth electrode is configured as a bottom gate. In this example, the single bottom gate can be arranged to compensate for the voltage across the entire structure of device 1. In this example, the thickness of substrate 10 can range from a few nanometers to hundreds of nanometers, and it can behave like a gate oxide.

[0093] Figure 4B A further variation of device 1, including a bottom gate, is schematically depicted. In this example, a doped semiconductor (e.g., a doped silicon wafer) can be used as substrate 10, which can then be biased with a voltage so that it can operate as a bottom gate or "body bias". In this example, an insulator 20 can be provided between substrate 10 and the first electrode 50 and the second electrode 60. For this purpose, references can be made... Figures 3A to 3G The process described is similar to that described above. Specifically, after the deposition of the second insulating layer 40 (i.e., corresponding to...) Figure 3C Furthermore, patterning and etching steps can be performed on insulating layers 20 and 40 to define areas for the first electrode 50 and the second electrode 60 (i.e., similar to...). Figure 3D (The steps described).

[0094] However, in this example, a first insulating layer 20 of at least a certain thickness can be maintained in the electrode region to prevent direct contact between the doped substrate 10 and the first electrode 50 and the second electrode 60. In other words, with Figure 3DThe illustrated example differs in that the etching of insulating layers 20 and 40 can reach the surface of substrate 10, allowing for a more carefully controlled etching process. Therefore, the etching times of the first insulating layer 20 and the second insulating layer 40 can be carefully adjusted to control the depth of the etching process, such that the first insulating layer 20 can be partially etched to maintain a minimum distance between the doped substrate 10 and the electrodes 50 and 60.

[0095] The subsequent steps, namely, depositing conductors in the regions at the two longitudinal ends of the carbon nanotube 30 to define the first electrode 50 and the second electrode 60, depositing the third electrode 70, and etching insulating layers 20 and 40 in the region between the first electrode 50 and the second electrode 60, can be performed as follows: Figures 3E to 3G The equivalent method described is followed. As a result of this sequence of steps, the following can be obtained: Figure 4B The device depicted is similar to device 1, wherein the substrate 10 can act as a bottom gate to define a bias voltage, and the ends of the carbon nanotubes 30 can be embedded in the first electrode 50 and the second electrode 60, while the middle segments of the carbon nanotubes 30 can be suspended above the substrate 10.

[0096] Figure 4C A further variation of device 1 including a bottom gate is shown. In this example, a substrate 10 including a top surface and a bottom surface may be provided. Device 1 may include a fourth electrode 80 disposed on the top surface of substrate 10, the fourth electrode 80 being configured as a bottom gate. Device 1 may further include a first insulating layer 20 disposed between the fourth electrode 80 and the first electrode 50 and the second electrode 60 to prevent contact between the fourth electrode 80 and either the first electrode 50 or the second electrode 60. In this example, a further variation of device 1 including a bottom gate may be provided. Figure 3A The fourth electrode 80 is deposited prior to the corresponding steps described. Subsequently, procedures related to... Figures 3A to 3G And about Figure 4B The steps described in the example are similar to those in the previous example. Therefore, similar to the previous example, direct contact between the fourth electrode 80 and either the first electrode 50 or the second electrode 60 can be prevented by a first insulating layer 20 of at least a certain thickness. Therefore, controlled etching of the insulating layers 20, 40 can be performed such that the first insulating layer 20 can be etched only to a certain depth.

[0097] exist Figure 4D Another example of device 1, including a bottom gate, is described in the reference. This example is similar to the one in the reference. Figure 4CThe example shown also includes a fourth electrode 80 deposited on the substrate 10. However, in this variation, two different insulating materials can be used for the first insulating layer 20 and the second insulating layer 40. This allows for selective etching of the insulating layers 20 and 40. In fact, in this example, after the deposition of the second insulating layer 40, patterning and etching steps can be performed to define the electrode region by removing only the second insulating layer 40, while keeping the first insulating layer 20 substantially unaffected. Therefore, the ends of the carbon nanotubes 30 can be exposed, and they can be contacted by subsequent deposition of conductive materials for the first electrode 50 and the second electrode 60. Finally, similar to... Figure 3F and Figure 3G A third electrode 70 can be deposited, and an etching step can be performed, in which both the first insulating layer 20 and the second insulating layer 40 are etched. On the one hand, this example can facilitate the manufacturing process. On the other hand, in this variation, the ends of the carbon nanotubes 30 may not be fully embedded in the electrodes 50 and 60, such as... Figure 4D It is shown schematically in the diagram.

[0098] It should be noted that, reference Figure 4D The described manufacturing method (i.e., including the method of using different materials for the first insulating layer 20 and the second insulating layer 40, followed by selective etching of only the second insulating layer 40) can also be applied to any of the examples previously shown. Specifically, the method can be applied to other example devices 1 including a bottom gate ( Figures 4A to 4C (as depicted), and can also be applied to only include with Figure 2 and Figures 3A to 3G The depicted top gate is similar to that of device 1. As noted, the main difference when using this method is that the ends of the carbon nanotubes 30 may not be embedded in the first electrode 50 and the second electrode 60.

[0099] In some other examples, multiple fourth electrodes 80 may be arranged at different locations along the length of the intermediate segment of the carbon nanotube 30, instead of having a single bottom fourth electrode 80 extending over the entire region of device 1. By providing multiple fourth electrodes 80, these electrodes can act as multiple bottom gates, which can facilitate selective modulation of the voltage at specific portions of device 1 by, for example, synergistic excitation of the top and bottom gates. Figure 4E An example device 1 including multiple bottom gates is shown. In particular, three fourth electrodes 80 are depicted in this example.

[0100] Multiple fourth electrodes 80 of this type can be provided using different manufacturing methods. Therefore, in Figure 4EIn one example of this disclosure, parallel strips of conductive material can be pre-patterned on substrate 10. Subsequently, they can be patterned as follows: Figure 3A The first insulating layer 20 is deposited in the equivalent manner shown. Then, it can be deposited as follows: Figure 3B The equivalent method shown provides a plurality of carbon nanotubes 30 on the first insulating layer 20.

[0101] In this example, steps for detecting and identifying the carbon nanotubes 30 can also be provided. However, in this case, the identification of the carbon nanotubes 30 can also indicate their relative position to the pre-patterned conductor strips. Therefore, the carbon nanotubes 30 can be selected to intersect with several parallel strips, which will then be configured as the bottom gate of the device 1. Figure 4E In this case, a carbon nanotube 30 spanning five such pre-patterned strips (see dashed rectangle) is depicted, although only three of these pre-patterned strips are arranged in the portion of the carbon nanotube 30 intended for levitation. The conductor strip at the end of the dashed rectangle is located in the region intended for use with the first electrode 50 and the second electrode 60.

[0102] After selecting carbon nanotubes 30, it is possible to achieve the following: Figure 3C The equivalent method shown deposits the second insulating layer 40. Subsequently, it can be deposited in accordance with the reference... Figures 4B to 4D The process described above is similar to that used to define the first electrode 50, the second electrode 60, and the third electrode 70. Specifically, controlled etching of the first insulating layer 20 and the second insulating layer 40 can be performed to define the areas for the first electrode 50 and the second electrode 60, thereby preventing potential short circuits between either the first electrode 50 and the second electrode 60 and the pre-patterned strips, i.e., strips at the ends of the dashed rectangles that might overlap with the corresponding areas of the first electrode 50 and the second electrode 60.

[0103] exist Figure 4E The examples depicted can be implemented and referenced. Figure 4D The described solution is an equivalent solution, although it can also be used with reference to Figure 4C The solution explained is similar to the solution. Therefore, during the process steps used to define the regions of the first electrode 50 and the second electrode 60, selective etching of the second insulating layer 40 can be performed while leaving the first insulating layer 20 substantially unaffected. Subsequently, an etching step including etching the first insulating layer 20 and the second insulating layer 40 while leaving the conductor material of the fourth electrode 80 substantially unaffected can be performed as referenced. Figure 3G The equivalent method described above is used to leave suspended carbon nanotubes 30, in which case the carbon nanotubes can be capacitively coupled to both the third electrode 70 and the fourth electrode 80.

[0104] In one example of this disclosure, with Figure 4E The arrangement schematically depicted in the diagram allows for a larger spacing between the third electrodes 70, which can help prevent capacitive coupling between the top gates.

[0105] In the examples of this disclosure, in addition to the top gate and the bottom gate, device 1 may further include one or more side gates disposed on one or both sides of the carbon nanotube 30. Figure 1 (Not shown in the image).

[0106] Depending on the application of device 1, the side gate can be provided for different purposes. Thus, in some examples, the side gate can be arranged at a short distance from the carbon nanotube 30 to enable capacitive coupling between the side gate and the carbon nanotube 30. In this way, the side gate can be used as an electrostatic gate to, for example, fine-tune the electrostatic potential and / or induce electrostatic forces at certain locations on the carbon nanotube 30.

[0107] The examples described in the previous figures include device 1, in which the carbon nanotubes 30 are completely suspended, i.e., the entire middle segment of the carbon nanotubes 30 is spaced above the substrate 10. Furthermore, the previous examples relate to device 1 in which there is an empty space between the top portion of the carbon nanotubes 30 and all the third electrodes 70 or the top gate. However, this disclosure also contemplates examples of device 1 in which physical contact is established with the carbon nanotubes 30. Figure 5A and Figure 5B Two such examples are illustrated schematically.

[0108] Figure 5A Device 1 is schematically disclosed, which is related to... Figure 1 The devices shown share many similarities. However, in this example, an insulator 40G is disposed between the top portion of the carbon nanotube 30 and the bottom portion of one of the third electrodes 70, which acts as the top gate. More specifically, the insulator 40G can be configured as a gate oxide corresponding to the top gate. The insulator 40G can correspond to a portion of the second insulating layer 40 in the region where the corresponding third electrode 70 overlaps with the carbon nanotube 30. Photolithography or electron beam lithography steps, as well as selective etching processes, can be performed. Therefore, processes and techniques similar to those described for the previous examples can be used, and further details are considered unnecessary.

[0109] In a variation of this example, not only insulator 40G but also a portion of the first insulating layer 20 may be provided in the region below insulator 40G. Figure 5A (Not shown in the image). This may be beneficial for manufacturing and / or for functional purposes.

[0110] When using device 1 as a nanoelectromechanical system, it may be useful to provide physical contact with the carbon nanotube 30 at one or more locations along the length of the intermediate segment. Therefore, the flexural modes of the carbon nanotube 30 can be segmented. Specifically, as... Figure 5A As shown, a single insulator 40G can be arranged such that it can physically contact only one of the third electrodes 70. Therefore, the flexural modes of the carbon nanotube 30 can be segmented into two types. In other examples, the flexural modes of the carbon nanotube 30 can be further segmented by dividing the middle segments of the carbon nanotube 30 into more segments, by enabling more third electrodes 70 (i.e., the top gate) to establish physical contact with the carbon nanotube via the corresponding gate oxide.

[0111] exist Figure 5B A similar concept is illustrated in the example. In similar examples about... Figure 4E In this device 1 described, the third electrode 70 and the fourth electrode 80 can both be defined and configured as the top gate and bottom gate of device 1, respectively. In this example, an insulator 20G can be used to define a physical contact between one of the fourth electrodes 80 and the carbon nanotube 30. In this case, the insulator 20G can correspond to a portion of the first insulating layer 20. Similar to... Figure 5A In the example described, insulator 20G can serve as the gate oxide for the corresponding bottom gate. The fabrication of this device 1 may also include steps and techniques similar to those already described, therefore further details will not be provided.

[0112] Figure 5B Examples can be provided for reference. Figure 5A The advantages described are similar to those of other technologies. Therefore, providing such contacts can serve as dividing points for intermediate segments of the carbon nanotube 30, which can allow for the segmentation of the flexural modes of the carbon nanotube 30. Such segmentation may be useful when the device 1 is employed as a nanoelectromechanical device.

[0113] In further variations, combinations are possible. Figure 5A and Figure 5B For example, an insulator or gate oxide can be provided for one or more third electrodes 70 that act as top gates and one or more fourth electrodes 80 that act as bottom gates. In this way, physical contact with the carbon nanotubes 30 can be provided from both types of gates.

[0114] For the sake of completeness, various aspects of this disclosure are set forth in the following numbered clauses: Clause 1. A device comprising: Substrate; A first electrode, which is on a substrate and configured as the source or drain of a device; The second electrode, which is on the substrate, is configured as the other of the source and drain of the device; A carbon nanotube having a first end connected to a first electrode and a second end connected to a second electrode, wherein at least a portion of the middle segment of the carbon nanotube is suspended above the surface of a substrate. One or more third electrodes are disposed above the carbon nanotube and configured to be capacitively coupled to the top gate of the carbon nanotube; wherein there is an empty space between the top portion of the carbon nanotube and the bottom portion of at least one of the third electrodes.

[0115] Clause 2. The device according to Clause 1, wherein the carbon nanotube extends substantially longitudinally from the first electrode to the second electrode, the device including a plurality of third electrodes disposed above the carbon nanotube and configured as a plurality of top gates, the third electrodes being disposed at different locations along the longitudinal direction and along the middle segment of the carbon nanotube.

[0116] Clause 3. The device according to Clause 2, the device comprising three or more third electrodes, more specifically, comprising five third electrodes.

[0117] Clause 4. The device according to any of the preceding clauses, wherein the entire middle segment of the carbon nanotube is suspended above the surface of the substrate.

[0118] Clause 5. The device according to any of the preceding clauses, wherein there is an empty space between the top portion of the carbon nanotube and the bottom portion of all the third electrodes.

[0119] Clause 6. The device according to any one of Clauses 1 to 4, wherein an insulator, more specifically an oxide, is provided in the space between the top portion of the carbon nanotube and the bottom portion of at least one of the third electrodes, such that physical contact is established.

[0120] Clause 7. The device according to any of the preceding clauses further includes a coating material, specifically an oxide, arranged to encapsulate the intermediate segments of the carbon nanotubes.

[0121] Clause 8. The device according to any of the preceding clauses, wherein a plurality of carbon nanotubes are arranged in parallel and connected between a first electrode and a second electrode, and intermediate segments of the plurality of carbon nanotubes are suspended above the surface of a substrate.

[0122] Clause 9. The device according to any of the preceding clauses, wherein the device includes one or more bottom gates.

[0123] Clause 10. The device according to Clause 8, wherein the substrate includes a top surface and a bottom surface, a first electrode, a second electrode and a carbon nanotube are disposed on the top surface, and one or more fourth electrodes are defined on the bottom surface, the fourth electrodes being configured as a bottom gate.

[0124] Clause 11. The device according to Clause 8, wherein the substrate includes a top surface and a bottom surface, the device includes a fourth electrode disposed on the top surface of the substrate and configured as a bottom gate, and the device further includes a first insulating layer disposed between the fourth electrode and the first electrode and the second electrode to prevent contact between the fourth electrode and either the first electrode or the second electrode.

[0125] Clause 12. The device according to any of the preceding clauses further includes one or more side gates disposed on one or both sides of the carbon nanotube.

[0126] Clause 13. The device according to any of the preceding clauses, wherein the third electrode has a thickness between 1 nm and 100 μm and a width between 1 nm and 10 μm.

[0127] Clause 14. The device according to any of the preceding clauses, wherein the distance between the first electrode and the second electrode is between 3 nm and 100 μm.

[0128] Clause 15. The device according to any of the preceding clauses, wherein at least a portion of the intermediate segment suspended above the substrate is at a distance between itself and the substrate of a few angstroms and 10 μm, more specifically between 1 nm and 5 μm.

[0129] Clause 16. The device according to any of the preceding clauses, wherein the distance between the top portion of the carbon nanotube in which the empty space exists and the bottom portion of at least one of the third electrodes is between a few angstroms and 1 μm, more specifically between 1 nm and 0.5 μm.

[0130] Clause 17. The device according to any of the preceding clauses, wherein a first end of the carbon nanotube is embedded in a first electrode, and / or a second end of the carbon nanotube is embedded in a second electrode.

[0131] Clause 18. The device according to any of the preceding clauses, wherein the carbon nanotube is a single-walled carbon nanotube (SWCNT), and more specifically wherein the carbon nanotube is a semiconductor carbon nanotube.

[0132] Clause 19. The device according to any of the preceding clauses, wherein at least one of the following: Pd, Pt, Cr, Ti, Al, Au, a binary metal similar to TiN or TaN, or a two-dimensional conductor similar to graphene, is used for at least one of the first electrode, the second electrode, or the third electrode.

[0133] Clause 20. The device according to any of the preceding clauses, wherein the substrate comprises one of a silicon substrate, a sapphire substrate, a diamond substrate, a quartz substrate or a borosilicate substrate.

[0134] Clause 21. A method of manufacturing a device according to any one of Clauses 1 to 20, the method comprising: Provide substrate; A first insulating layer is provided on the substrate; Multiple carbon nanotubes are provided on the first insulating layer; Detect at least one carbon nanotube among multiple carbon nanotubes and identify the longitudinal end of the detected carbon nanotube; A second insulating layer is deposited on the first insulating layer and at least on the detected carbon nanotubes; The longitudinal ends of the detected carbon nanotubes are exposed by etching a first insulating layer and a second insulating layer in the region surrounding each longitudinal end. Conductors are deposited in the etched area to define the first and second electrodes, the conductors contacting the longitudinal ends of the carbon nanotubes; A conductor is deposited on a second insulating layer in a region that overlaps with the middle segment of a carbon nanotube to form one or more third electrodes configured as a top gate structure. The first and second insulating layers are etched in at least a portion of the region between the first and second electrodes and along the length of the carbon nanotubes.

[0135] Clause 22. The method of Clause 21, further comprising growing an oxide to encapsulate at least intermediate segments of the carbon nanotube after etching the first and second insulating layers in at least a portion of the region between the first and second electrodes and along the length of the carbon nanotube.

[0136] Clause 23. The method described in accordance with any one of Clauses 21 or 22, wherein providing carbon nanotubes on the first insulating layer comprises growing carbon nanotubes directly on the first insulating layer, and more specifically, growing carbon nanotubes by means of chemical vapor deposition (CVD).

[0137] Clause 24. The method according to any one of Clauses 21 or 22, wherein providing carbon nanotubes on the first insulating layer comprises depositing a solution of pre-formed carbon nanotubes in a solvent and removing the solvent after deposition.

[0138] Clause 25. The method according to any one of Clauses 21 to 25, wherein detecting at least one deposited carbon nanotube and identifying the longitudinal end of the detected carbon nanotube comprises using an optical method to detect the deposited carbon nanotube and / or using low-power scanning electron microscopy (SEM) or atomic force microscopy (AFM) to identify the longitudinal end.

[0139] Clause 26. The method described in any one of Clauses 21 to 25, wherein etching the first insulating layer and the second insulating layer comprises an etching process using vapor or dry gas.

[0140] Clause 27. The method described in any one of Clauses 21 to 26, wherein the patterning and etching of the first and second insulating layers includes the use of direct writing techniques, specifically electron beam lithography or laser direct writing.

[0141] Clause 28. The method according to any one of Clauses 21 to 27, wherein the substrate is etched after etching the first insulating layer and the second insulating layer to expose the longitudinal ends of the carbon nanotubes being detected, and / or wherein the substrate is etched after etching the first insulating layer and the second insulating layer in the region between the first electrode and the second electrode and along the length of the carbon nanotubes.

[0142] Clause 29. The method according to Clause 28, wherein the substrate comprises a silicon (Si) substrate, and is etched using XeF2 vapor or dry etching using fluorinated gas.

[0143] Clause 30. The method according to any one of Clauses 21 to 29, wherein at least one of the first insulating layer and the second insulating layer comprises silicon dioxide (SiO2) or a high-k material.

[0144] This written description uses examples to disclose teachings including preferred embodiments and also enables any person skilled in the art to practice the teachings, including making and using any apparatus or system and performing any combined methods. The scope of patentability is defined by the claims and may include other examples that would occur to a person skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that are not different from the literal language of the claims, or if they include equivalent structural elements that are not substantially different from the literal language of the claims. Based on the principles of this application, those skilled in the art can mix and match aspects of the various embodiments described, as well as other known equivalents of each such aspect, to construct additional embodiments and techniques. If reference numerals associated with the drawings are enclosed in parentheses in the claims, they are merely for the purpose of increasing the comprehensibility of the claims and should not be construed as limiting the scope of the claims.

Claims

1. A device, the device comprising: Substrate; A first electrode, which is located on the substrate and configured as the source or drain of the device; The second electrode, on the substrate, is configured as the other of the source and drain of the device; A carbon nanotube having a first end connected to a first electrode and a second end connected to a second electrode, at least a portion of a middle segment of the carbon nanotube being suspended above the surface of the substrate, the carbon nanotube extending substantially longitudinally from the first electrode to the second electrode; A plurality of third electrodes are disposed above the carbon nanotube and configured as a plurality of top gates, the third electrodes being disposed at different locations along the longitudinal direction and along the middle segment of the carbon nanotube; There is an empty space between the top portion of the carbon nanotube and the bottom portion of one or more of the third electrodes.

2. The device according to claim 1, the device further comprising a coating material, specifically an oxide, encapsulating at least a portion of the intermediate segment of the carbon nanotube.

3. The device according to claim 1 or 2, wherein, The device includes one or more bottom gates.

4. The device according to claim 3, wherein, The substrate includes a top surface and a bottom surface, the first electrode, the second electrode and the carbon nanotube are disposed on the top surface, and one or more fourth electrodes are defined on the bottom surface, the fourth electrodes being configured as the bottom gate.

5. The device according to claim 3, wherein, The substrate includes a top surface and a bottom surface, the device includes a fourth electrode disposed on the top surface of the substrate and configured as the bottom gate, and the device further includes a first insulating layer disposed between the fourth electrode and the first electrode and the second electrode to prevent contact between the fourth electrode and either the first electrode or the second electrode.

6. The device according to any one of claims 1 to 5, the device further comprising one or more side gates disposed on one or both sides of the carbon nanotube.

7. The device according to any one of claims 1 to 6, wherein, The first end of the carbon nanotube is embedded in the first electrode, and / or the second end of the carbon nanotube is embedded in the second electrode.

8. The device according to any one of claims 1 to 7, wherein, An insulator is provided in the space between the top portion of the carbon nanotube and the bottom portion of at least one of the third electrodes, so that physical contact is established.

9. A method for manufacturing a device according to any one of claims 1 to 8, the method comprising: Provide the substrate; A first insulating layer is provided on the substrate; Multiple carbon nanotubes are provided on the first insulating layer; Detect at least one carbon nanotube among the plurality of carbon nanotubes and identify the longitudinal end of the detected carbon nanotube; A second insulating layer is deposited on the first insulating layer and at least on the detected carbon nanotubes; The longitudinal ends of the detected carbon nanotubes are exposed by etching the first insulating layer and the second insulating layer in the region surrounding each of the longitudinal ends; A conductor is deposited in the etched area to define the first electrode and the second electrode, the conductor contacting the longitudinal end of the carbon nanotube; A conductor is deposited on the second insulating layer in the region overlapping with the intermediate segment of the carbon nanotube to form the one or more third electrodes configured as a top gate structure; The first insulating layer and the second insulating layer are etched in at least a portion of the region between the first electrode and the second electrode and along the length of the carbon nanotube.

10. The method of any one of claims 9, further comprising, after etching the first insulating layer and the second insulating layer in at least a portion of the region between the first electrode and the second electrode and along the length of the carbon nanotube, growing an oxide to encapsulate at least a portion of the intermediate segment of the carbon nanotube.

11. The method according to any one of claims 9 or 10, wherein, Providing carbon nanotubes on the first insulating layer includes growing carbon nanotubes directly on the first insulating layer, and more specifically, growing carbon nanotubes by means of chemical vapor deposition (CVD).

12. The method according to any one of claims 9 or 10, wherein, Providing carbon nanotubes on the first insulating layer includes depositing a solution containing pre-formed carbon nanotubes in a solvent and removing the solvent after deposition.

13. The method according to any one of claims 9 to 12, wherein, Detecting at least one deposited carbon nanotube and identifying the longitudinal end of the detected carbon nanotube includes using optical methods to detect the deposited carbon nanotube and / or using at least one of low-power scanning electron microscopy (SEM) and atomic force microscopy (AFM) to identify the longitudinal end.

14. The method according to any one of claims 9 to 13, wherein, Etching the first and second insulating layers includes a vapor or dry gas etching process.

15. The method according to any one of claims 9 to 14, wherein, The substrate is etched after the first insulating layer and the second insulating layer are etched to expose the longitudinal ends of the detected carbon nanotubes, and / or the substrate is etched after the first insulating layer and the second insulating layer are etched in the region between the first electrode and the second electrode and along the length of the carbon nanotubes.

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