System and method for in situ electrical characterisation of carbon nanotubes, and method for adapting a chip for growing nanotubes for characterisation purposes

Abstract

The invention relates to a method for the in situ electrical characterisation of a grown carbon nanotube connecting two neighbouring cantilevers within a cantilever chip (2) and forming a low-temperature quantum dot, comprising the steps of 1) applying a voltage between two electrically conductive areas provided respectively on the two cantilevers close to the respective ends of the nanotube, the end conductive areas of the cantilevers acting respectively as drain and source of a field-effect transistor, 2) applying a gate potential to the field-effect transistor, between a gate (220) placed close to the carbon nanotube and the end conductive area acting as source, 3) measuring the current flowing between the end conductive areas of the cantilevers, and 4) processing the current measurements and the applied gate potential.

Description

System and method for in situ electrical characterization of carbon nanotubes, and method for adapting a nanotube culture chip for characterization purposes FIELD OF THE INVENTION

[0001] The present invention relates to a system for in situ electrical characterization of grown carbon nanotubes, in particular on the growth substrate. It also relates to an in situ electrical characterization method implemented in this system, as well as a method for adapting a nanotube culture chip for characterization purposes.

[0002] The field of invention is that of quantum components and computers, and more generally nano-electronics. STATE OF THE ART

[0003] There are already techniques for electrical characterization, for example in the form of IV curves, of carbon nanotubes in electronic devices, such as field-effect transistors.

[0004] When growing carbon nanotubes directly on integrated circuit chips (e.g., on Single Quantum Dot or Double Quantum Dot devices), it is easy to characterize the nanotube immediately after growth.

[0005] But we will more specifically consider the case where carbon nanotubes, called CNTs, are grown on Cantilever Array Dies (CAD), referred to hereinafter as cantilever chips, and then these nanotubes are transferred via a nanoassembly technique called "stapling" onto devices. The advantage of this method is well known in the literature, as it allows for cleaner nanotubes to be obtained.

[0006] But the problem associated with this fabrication method is that many events occur in a nanotube after the growth step, before it is fully electrically detected on a device after nano-assembly or "stapling":

[0007] The CAD leaves the growth setup in a quartz "boat." The CAD is picked up with forceps and placed in a gel box (a standard technique in the field). The CAD could then be transferred to an optical spectroscopy setup (such as a Raman setup) where it is optically characterized. The CAD is then transferred to the "stapler" device, during which it is in contact with the atmosphere and adsorbs hydrocarbons. The CAD is then removed again from the gel box with forceps. The CAD is then placed in the stapler and assembled on the device.

[0008] Only after its assembly and detection by resistance measurement can we then electrically characterize the tube on the device.

[0009] For example, the paper Taechang an et al: "Nitrophenol detection using suspended SWNT films for environmental monitoring" proposes an a posteriori characterization of nanotubes and further dispersed in solution.

[0010] All of these steps can alter the integrity and electrical properties of the nanotube.

[0011] The objective of the present invention is to be able to carry out an electrical characterization of the nanotube immediately after its growth on the growth substrate, to really know if it is worth assembling it on a device. For example, one might want a so-called "narrow band gap" nanotube, but it is ultimately a semiconductor tube with a huge band gap.

[0012] This objective is achieved with a method for electrically characterizing in situ a grown carbon nanotube connecting two neighboring cantilevers within a cantilever chip and producing a quantum dot at low temperature, comprising the following steps: an application of a voltage between two electrically conductive zones provided respectively on the two cantilevers near the respective ends of said nanotube, said end conductive zones of the cantilevers acting respectively as drain and source of a field effect transistor, an application of a gate potential for said field effect transistor, between a gate arranged near said carbon nanotube and a ground reference for said cantilever chip, a measurement of the current flowing between the end conductive zones of the cantilevers, and a processing of the current measurements, the drain-source voltage and the gate voltage.

[0013] The potential is applied to the gate electrode so that it radiates an electric field that changes the potential felt by the conduction electrons, which are subject to a source-drain voltage. The gate electrode is the end of an open circuit

[0014] The steps of applying drain-source voltage and gate voltage may implement a set of conductive tracks previously produced on the surface of the cantilever chip, each of said conductive tracks comprising a proximal end located at the end of a cantilever in proximity to a carbon nanotube and a distal end located on the substrate of the cantilever chip and provided with an electrical contact pad, said electrical contact pads being designed to each receive an application and / or measurement probe tip.

[0015] The characterization method according to the invention further comprises a switching process providing a series of electrical characterizations of a grown nanotube bridging between two cantilevers among a set of grown nanotubes present on pairs of cantilevers of the cantilever chip.

[0016] The electrical characterization method according to the invention is implemented to detect a first contact that a nanotube establishes between a first electrode and a second electrode of a receiving chip during a nano-assembly process, by applying a voltage difference between said first and second electrodes and measuring the current passing between said first and second electrodes.

[0017] According to another aspect of the invention, there is provided a system for electrically characterizing in situ a grown carbon nanotube connecting two neighboring cantilevers of a cantilever chip and producing a quantum dot at low temperature, implementing the characterization method according to any one of the preceding claims, characterized in that it comprises: means for applying a voltage between two electrically conductive zones provided respectively on the two cantilevers near the respective ends of said nanotube, said end conductive zones of the cantilevers acting respectively as drain and source of a field effect transistor, means for applying a gate voltage for said field effect transistor, between a gate arranged near said carbon nanotube and the end conductive zone acting as source,means for measuring a current flowing between the end conductive zones of the cantilevers, and means for processing the current measurements and the drain-source and gate-source voltages applied to the ends of the cantilevers.,

[0018] The cantilever chip comprises on its substrate at least one set of conductive tracks, each of said conductive tracks comprising a proximal end located at the end of a cantilever in proximity to the carbon nanotube and a distal end located on the substrate of the cantilever chip and provided with an electrical contact pad, said electrical contact pads being designed to each receive an application and / or measurement probe tip.

[0019] The characterization system according to the invention further comprises a grid common to all pairs of cantilevers of the cantilever chip. This common grid can be mobile and independent of the cantilever chip.

[0020] The characterization system according to the invention further comprises means for selectively connecting the drain-source voltage application and drain-source current measurement means to a given carbon nanotube-based field effect transistor device from among a set of carbon nanotube-based field effect transistor devices existing on the cantilevers of the cantilever chip.

[0021] The selective linking means may comprise a switching matrix.

[0022] According to yet another aspect of the invention, there is provided a method for adapting a cantilever chip intended for the cultivation of carbon nanotubes, for the implementation of the in situ electrical characterization method according to the invention, comprising the following steps:patterning tracks on a substrate of the cantilever chip, said tracks each being arranged to connect one end of a cantilever of said cantilever chip near a contact zone of one end of a cultivated carbon nanotube, to a contact pad intended to receive a probe tip connected to measuring equipment;metallizing the contact pads and said tracks thus patterned to make them conductive so as to apply a voltage between two cantilevers ensuring drain and source functions of a nanotube-based field effect transistor and measuring a current flowing between said drain and source.

[0023] For the above and for the remainder of the description, the term "patterning" means the action of making or drawing or designing or arranging or creating a pattern of an electronic circuit, according to techniques known to those skilled in the art.

[0024] The track patterning step may include a Kapton masking step.

[0025] The metallization step includes an evaporation and / or spraying step, also called sputtering.

[0026] The tracks or electrodes can be modeled using different methods well known in the industry: Shadow masking, Kapton masking, Lithography, allowing the wafer scale to be reached.

[0027] The tracks or electrodes can then be metallized using various methods well known in the industry, for example by evaporation or by spraying, also known as sputtering.

[0028] A measuring station is then used to induce a voltage in the electrodes (source, drain, gate)

[0029] The technical characterization solution has several advantages.

[0030] Rapid feedback on nanotube growth can be obtained (e.g., resistance measurement, gate voltage dependence of current or conductance).

[0031] We have a way to detect the first contact that the nanotube makes with an electrode during the stapling or nano-assembly process. Indeed, we can set a voltage difference between any electrode of the receiving chip (electrode E), and any of the two electrodes present on the two neighboring cantilevers (electrode C), so that if the nanotube touches electrode E, a current will flow between electrode E and electrode C. This facilitates the stapling process. DESCRIPTION OF FIGURES

[0032] illustrates a carbon nanotube bridging two cantilevers of a cantilever chip,

[0033] illustrates a patterned cantilever chip for implementing the in situ electrical characterization method according to the invention;

[0034] Diagrammatically illustrates an example of practical implementation of an in situ electrical characterization system according to the invention;

[0035] Schematically illustrates the connections of measurement probe tips to measurement pads of a cantilever chip implemented in an in situ electrical characterization system according to the invention;

[0036] Schematically illustrates a bridge configuration made by a carbon nanotube grown between two cantilevers;

[0037] The figure represents an example of the implementation of a pipetting system implemented to prepare a cantilever chip dedicated to the culture of carbon nanotubes;

[0038] La represents a curve of variation of the drain-source current as a function of the drain-source voltage at the terminals of a field effect transistor device implementing a carbon nanotube;

[0039] La represents a curve of variation of the drain-source current as a function of the gate-source voltage, for a drain-source voltage of 0.5 V at the terminals of a field-effect transistor device implementing a carbon nanotube;

[0040] The figure includes Figures 9A and 9B showing the surface of a cantilever chip, respectively after a Kapton masking step and after a puttering step;

[0041] This is a functional diagram of an exemplary embodiment of an in situ electrical characterization system according to the invention. DETAILED DESCRIPTION

[0042] As illustrated in Figures 1 and 2, a carbon nanotube 1 provides a bridge 10 between two adjacent cantilevers 13, 14 among sets 21-25 of cantilevers of a cantilever chip 2. The two ends 11, 12 of the carbon nanotube 1 which is arranged in close proximity to a set of electrodes 15, are respectively in contact with conductive tracks 131, 141 deposited on the two cantilevers 13, 14.

[0043] The cantilever chip 2 is provided with an in situ electrical characterization system according to the invention comprising sets of electrical conductors 250 of which a proximal end is arranged on a cantilever in close proximity to a carbon nanotube and a distal end is connected to a pad 200 provided to receive a measuring tip.

[0044] With reference to the, an in situ electrical characterization assembly 3 comprises a cantilever chip 3 arranged on a PDMS (PolyDiMethylSiloxane) support 34, which has been patterned to receive a set of electrically conductive tracks 250 each provided with pads 200 provided to provide electrical contacts to measuring tips or probes 46 connected to a multi-probe assembly 30 of probes 31 which is connected to characterization measurement equipment (not shown) described below with reference to the.

[0045] The cantilevers 14 of the cantilever chip 2 are arranged against or in the immediate vicinity of a conductive part 220 acting as a field effect transistor gate. This gate part 220 is secured to a control arm 35 and connected to a voltage source unit (not shown) intended to apply a gate potential, described below with reference to the.

[0046] This setup 3 allows electrical characterization of carbon nanotubes immediately after their growth process. This characterization is non-destructive. The carbon nanotubes can thus be selected and transferred to a Qubit chip.

[0047] The gating effect is achieved at long distances, typically about 10 µm from the carbon nanotube, which allows rapid detection and avoids the risk of carbon nanotube collapse. The multi-probe 30 allows the electrical characterization of 8 carbon nanotubes in parallel.

[0048] As illustrated, probe tips 4, 40-46 are placed in contact on the pads 200 of the conductive tracks 250. These probe tips are connected to electronic equipment (not shown) provided for processing the electrical signals measurable from these probe tips and for delivering electrical characterization information according to processing techniques already known in the state of the art of field effect transistor measurements.

[0049] This in situ electrical characterization method is particularly suitable for detecting the state of a carbon nanotube 1 grown from a catalysis zone 51,50 previously produced on a cantilever 13 using a micropipetting technique described below, this carbon nanotube 1 having been grown until it reaches a neighboring cantilever 14.

[0050] We will now describe, with reference to the, an exemplary embodiment of a system 6 for depositing droplets on a cantilever chip, implemented to prepare these chips for the carbon nanotube growth process. This deposition system 6 comprises a first micrometric control device 65 provided to carry a support of a cantilever chip 60, a second micrometric control device 64 provided to carry a micropipette 62 containing a catalyst solution and having a diameter greater than 1 µm, a microscope objective 63 provided for controlling the deposition of droplets, and a light source 62. The substrate of the cantilever chip is placed at an angle of 45° with respect to the objective. The light source 62 is placed at an angle of 90° for reflection on the cantilever chip 60. This system allows a rapid deposition process, typically lasting 8 minutes per cantilever chip.

[0051] It is possible to carry out, with reference to figures 7 and 8, an electrical characterization of a field effect transistor made at the ends of a set of electrical conductors arranged on neighboring cantilevers between which a carbon nanotube forms a bridge. By long-distance “gating” effect, we can detect the electrical impedance of this carbon nanotube and deduce its state and several of its physical characteristics.

[0052] We can thus obtain () curves of variation of the source-drain current (in nA) and of the resistance (in MΩ) as a function of the Vsd voltage (in mV) on the field effect transistor near the carbon nanotube being characterized, as well as a curve of variation of the source-drain current (in nA) as a function of the gate voltage (in mV) for a drain-source voltage of 0.5 V.

[0053] The cantilever chip 2 shown is subjected to several treatments to be equipped with the sets of electrically conductive tracks which will allow the electrical connections between the probe tips and the ends on the cantilevers in the immediate vicinity of the carbon nanotubes. Thus, Figure 9A represents a Kapton masking to produce the conductive tracks, while Figure 9B represents the blued surface of the cantilever chip after a “sputtering” step.

[0054] With reference to which schematically represents the measurement assembly illustrated in, the system 100 for electrical characterization in situ of carbon nanotubes grown on cantilevers 211 of the cantilever chip 2, is structured to characterize carbon nanotube devices 201, 202, .. 20N acting as a field effect transistor each associated with a pair of cantilevers. This characterization system 100 comprises: a voltage source unit 101 provided to deliver a gate voltage applied via a conductor 221 to a gate 220 common to all the field effect transistor devices 201, 202,…20N, a source measurement unit 102 provided to apply a drain-source voltage to the terminals of a field effect transistor device 201, 202,…20N, via a switching matrix 103 and pairs of conductors 231, 232, and to measure the current flowing between the drain and the source of the field effect transistor device thus powered.

[0055] The in situ characterization method according to the invention which has just been described can operate under ambient temperature and pressure conditions. But it can also be implemented in an enclosure subjected to a high vacuum, for example of the order of 10 -6 mbar, and at a temperature of 4K.

[0056] Of course, the present invention is not limited to the examples which have just been described and many other embodiments can be envisaged without departing from the scope of the present invention. In particular, the number of cantilevers provided on a cantilever chip can vary and is only limited by dimensional constraints. The same applies to the number of culture pads per cantilever or the number of conductive tracks and contact pads provided on a cantilever chip prepared according to the invention.

Claims

A method for electrically characterizing in situ a grown carbon nanotube (1) connecting two neighboring cantilevers (13,14) within a cantilever chip (2) and producing a quantum dot at low temperature, comprising the following steps: - applying a voltage between two electrically conductive zones provided respectively on the two cantilevers (13,14) near the respective ends (11,12) of said nanotube (1), said end conductive zones of the cantilevers acting respectively as drain and source of a field effect transistor, - applying a gate potential for said field effect transistor, between a gate (220) arranged near said carbon nanotube (1) and a ground reference for said cantilever chip (2), - measuring the current flowing between the end conductive zones of the cantilevers (13,14), and - processing the current measurements,and the applied drain-source voltage and gate potential., Characterization method according to the preceding claim, characterized in that the steps of applying drain-source voltage and gate potential implement a set of conductive tracks (250) previously produced on the surface of the cantilever chip (2), each of said conductive tracks (250) comprising a proximal end located at the end of a cantilever in proximity to a carbon nanotube (1) and a distal end located on the substrate of the cantilever chip and provided with an electrical contact pad (200), said electrical contact pads (200) being designed to each receive a probe tip (40-46) for application and / or measurement. Characterization method according to the preceding claim, characterized in that it further comprises a switching process providing a series of electrical characterizations of a grown nanotube (1) bridging between two cantilevers (13, 14) among a set of grown nanotubes present on pairs of cantilevers of the cantilever chip (2). Electrical characterization method according to any one of the preceding claims, characterized in that it is implemented to detect a first contact that a nanotube (1) establishes between a first electrode and a second electrode of a receiving chip during a nano-assembly process, by applying a voltage difference between said first and second electrodes and measuring the current passing between said first and second electrodes. System (100) for electrically characterizing in situ a grown carbon nanotube (1) connecting two neighboring cantilevers (13,14) of a cantilever chip (2) and producing a quantum dot at low temperature, implementing the characterization method according to any one of the preceding claims, characterized in that it comprises: - means (102) for applying a voltage between two electrically conductive zones provided respectively on the two cantilevers (13,14) near the respective ends of said nanotube (1), said end conductive zones of the cantilevers acting respectively as drain and source of a field effect transistor, - means (101) for applying a gate potential for said field effect transistor, between a gate (220) arranged near said carbon nanotube (1) and the end conductive zone acting as source,- means (102) for measuring a current flowing between the end conductive zones of the cantilevers, and - means for processing the current measurements, the drain-source voltages and the gate potential., Characterization system (100) according to the preceding claim, characterized in that the cantilever chip (2) comprises on its substrate at least one set of conductive tracks (250), each of said conductive tracks (250) comprising a proximal end located at the end of a cantilever in proximity to the carbon nanotube (1) and a distal end located on the substrate of the cantilever chip (2) and provided with an electrical contact pad (200), said electrical contact pads (200) being designed to each receive a probe tip (40-46) for application and / or measurement. Characterization system (100) according to the preceding claim, characterized in that it further comprises a grid (220) common to all the pairs of cantilevers of the cantilever chip (2). Characterization system (100) according to the preceding claim, characterized in that the common grid (220) is mobile and independent of the cantilever chip. Characterization system (100) according to any one of claims 5 to 8, characterized in that it further comprises means (103) for selectively connecting the means (102) for applying drain-source voltage and measuring drain-source current to a given carbon nanotube-based field effect transistor device from among a set of carbon nanotube-based field effect transistor devices existing on the cantilevers of the cantilever chip (2). Characterization system (100) according to the preceding claim, characterized in that the selective connection means comprise a switching matrix (103). Method for adapting a cantilever chip (2) intended for the cultivation of carbon nanotubes (1), for the implementation of the in situ electrical characterization method according to any one of claims 1 to 4, comprising the following steps:- patterning tracks (250) on a substrate of the cantilever chip (2), said tracks (250) each being arranged to connect one end of a cantilever of said cantilever chip (2) near a contact zone of one end of a cultivated carbon nanotube (1), to a contact pad (200) intended to receive a probe tip (40-46) connected to measuring equipment;- metallizing the contact pads (200) and said tracks (250) thus patterned to make them conductive so as to apply a voltage between two cantilevers (13, 14) ensuring drain and source functions of a nanotube-based field effect transistor and measuring a current flowing between said drain and source. Adaptation method according to the preceding claim, characterized in that the step of patterning the tracks (250) comprises a Kapton masking step (90). Adaptation method according to one of the two preceding claims, characterized in that the metallization step comprises an evaporation and / or spraying step (91). Adaptation method according to one of the three preceding claims, implemented to characterize carbon nanotubes (1) grown on a cantilever of a cantilever chip (2), from a base on which a catalyst has been previously deposited by micropipetting.

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