WO2019011572A1

WO2019011572A1 - Assembly of carbon nanotubes and a method for production thereof

Info

Publication number: WO2019011572A1
Application number: PCT/EP2018/065762
Authority: WO
Inventors: Oktay Yilmazoglu; Sandeep Yadav; Deniz Cicek; Jörg J. SCHNEIDER
Original assignee: Technische Universität Darmstadt
Priority date: 2017-07-10
Filing date: 2018-06-14
Publication date: 2019-01-17
Also published as: DE102017115330A1

Abstract

The invention relates to an assembly of carbon nanotubes for a sensor or an actuator, comprising: a plurality of high-density stacks (110) arranged in layers, at least one low-density stack (120) arranged in layers, and at least two electrical contact elements (130). The high-density stacks (110) and the low-density stack(s) (120) each comprise a plurality of carbon nanotubes and the at least one low-density stack (120) is in contact on each of its two sides with one of the high-density stacks (110) so as to hold these at a variable distance (A) from one another. The at least two electrical contact elements (130) contact various high-density stacks (110) electrically so as to detect a change in the variable distance (A) in the form of an electrical sensor signal or so as to modify the variable distance (A) by applying an electrical voltage between the at least two electrical contact elements (130).

Description

ARRANGEMENT OF CARBON NANOTUBES AND A METHOD FOR THE PRODUCTION THEREOF

The present invention relates to an assembly of carbon nanotubes (CNT) and a method for their production. Embodiments relate in particular to nanostructured electromechanical multi-layered carbon-based spring elements with integrated resistance sensor as well as multilayer CNT blocks as a platform for a variety of mechanical sensors and actuators.

background

MEMS-based sensors (MEMS = microelectromechanical systems) are becoming increasingly interesting for many applications. One of these is, for example, spring mass systems, which are of interest for many applications with increasing stable deflection and deformation due to the applied tensile strains. This group of sensors also includes the so-called cantilever-based sensors, which are to have a high stability and are often to protect against high accelerations. In such sensors, a sensor for reading out the sensor data is required in addition to the spring element. This additional sensor is often in addition to integrate, which is a high cost, but is unavoidable if a desired response of the actual sensor element to a deflection of the spring element to be obtained.

The additional sensor is for example a capacitive, a magnetoresistive or a resistive sensor. Capacitive sensors typically exhibit a very small change in sensor size (for example in the femtofarad range), requiring additional on-chip signal processing. On the other hand, magnetoresistive sensors require magnetization with a defined polarity. The simplest way is to use resistive sensors such as Well-known strain gauges (DMS), however, have the following inherent disadvantages: a time-consuming application of the strain gauges in the manufacturing process, fatigue over the lifetime (limited for example to 10 million cycles, but can be significantly lower), a very strong sensitivity to mechanical overstressing (eg overstretching leads to irreversible damage or failure of the strain gages),

Detaching the strain gages from the wearer.

A class of pressure, vibration or biomechanical sensors are based on the unique properties of CNTs (carbon nanotubes), which can often provide the desired functionality. CNTs are one-dimensional carbon structures with a high aspect ratio (length / radius) that can be made in different orientations, dimensions and thicknesses. CNT-based nanoelectromechanical systems (NEMS) have excellent electrical and mechanical properties such as high electrical conductivity, high compressibility, flexural elasticity, structural flexibility, high aspect ratio, and high chemical resistance to a variety of media.

Fundamental studies of the mechanical properties and pressure sensitivities of CNTs or composites with stochastically distributed CNTs have been performed in several documents (see, for example, C. Hierold et al .: Nano electromechanical sensors based on carbon nanotubes, sensors and actuators A136, 51-61 (2007 ), N. Hu et al .: "Investigation on the sensitivity of a polymer / carbon nanotube composite strain sensor", carbon 48, issue 3, 680-687 (2010)). The mechanical properties of the CNT arrays with dense vertical alignment (3D-CNT structures) have also been studied (see AY Cao et al., "Super-Compressible Foam-Like Carbon Nanotube Films", 310, 1307-1310, November 2005, VL Pushparaj et al .: "Effects of compressive strains on electrical conductivities of a macroscale carbon nanotube block", Appl. Phys. Lett. 91,153,116, 2007).

However, selective positioning of individual CNTs is a complex and costly process. The use of disordered CNTs, however, is limited because of their uneven length, diameter and density. The micro-nanointegration of the vertically aligned CNT structures also poses a special technological challenge.

Therefore, there is a need for other sensor generations which on the one hand show high spatial resolution (for example for force measurements on biological cells) and on the other hand offer high sensitivity and high flexibility (for example, to apply to curved surfaces) as well as direct signal processing allow an integrated sensor.

Summary of the invention

At least part of the above problems are solved by an arrangement of carbon nanotubes according to claim 1 and a method of manufacturing CNT arrangement according to claim 13. The dependent claims define further advantageous embodiments for the subject matters of the independent claims.

The present invention relates to an arrangement of carbon nanotubes for a sensor or an actuator. The arrangement comprises a plurality of layers arranged in a stack of high density, at least one layered stack of low density and at least two electrical contact elements. The high-density stacks and the low-density stacks each have a plurality of carbon nanotubes and the at least one low-density stack is in contact with a high-density stack on both sides to keep them at a variable distance from each other. The at least two electrical contact elements electrically contact various high-density stacks in order to detect a change in the variable distance as an electric current. to detect the sensor signal or to change the variable distance by applying an electrical voltage between the at least two electrical contact elements (for example, to effect an actuator force).

The present invention also relates to an arrangement of carbon nanotubes for a sensor or an actuator, which differs from the aforementioned one in that only a high-density stack and a low-density stack are formed. In this arrangement, the electrical contact elements are optionally in contact with the high density stack, but may also contact only the one low density stack (on one side or even on both sides). The variable distance in this case corresponds to the thickness of the (at least one) low density stack.

For example, the electrical contact elements contact: either the two outermost stacks of high density (in arrangements from 3 stacks) or the two outermost stacks of low density (in arrangements of 3 stacks), or one outer high density stack and one outer low stack Density (in arrangements of 2 or more stacks).

The terms "high density stack" and "low density stack" should be understood to mean that the "high density stacks" have a higher density than the "low density stacks". The low density stacks may comprise fewer nanotubes than the high density stacks in a cross section perpendicular to the nanotube extension per unit area. The stacks of high and / or low density may comprise single-walled but also multi-walled nanotubes. Furthermore, it should be understood that the shape of the stacks may be any, i. the high or low density stacks may not necessarily be rectangular. These may for example have the shape of a half ring or circular or oval or any other shape.

The carbon nanotubes need not be rectilinear. Rather, it is usually the case that in the high density stacks the carbon nanotubes have a higher straightness than in the low density stacks. In the case of the low-density stacks, it is possible in particular to create frizzy structures come, which represent a nearly arbitrarily shaped tube structure. As a result of these frizzy structures, the low density stacks can be more deformed than the high density stacks. This, in turn, causes the individual carbon nanotubes to come into greater contact with one another when compressed, and thus the electrical resistance at a current flow, for example perpendicular to the tube extension, is significantly reduced (due to the additional contacts between the individual nanotubes).

It should be understood that the carbon nanotubes in the high density, low density stacks may be substantially the same length and may collectively form a membranous structure or block which may be of any desired shape and may also be of any thickness. Furthermore, it is possible that the pressure effect also acts in the direction of the tube extension and thus leads to a compression of the individual tubes. This, in turn, causes several tubes to come into contact with each other, thereby changing the electrical resistance, which can be detected as a sensor size. The sensor signal can also be purely capacitive, since the capacitance changes with a change in the distance of the electrical contact elements.

Optionally, the at least one low density stack comprises a plurality of low density stacks alternately arranged with the high density stacks. Between the electrical contact elements then a plurality of low-density stacks are arranged.

Optionally, the thicknesses of the high density stack (s) and / or the low density stack (s) may be different or the same.

Optionally, the assembly includes at least one metallization interconnecting the carbon nanotubes in the at least one low density stack at one end, the metallization being configured to effect growth of the carbon nanotubes at a reduced density. The metallization can have tantalum, so that an electrical connection between see the nanotubes being made in the low density stack.

Optionally, at least some of the high density stacks form, in part, spacers that extend at least partially into the low density stacks to define a variable distance stop. The spacers are therefore themselves formed from nanotubes. For example, the spacers may have a rectangular, a dome-shaped, a round or a triangular-shaped cross-section perpendicular to the extension of the nanotubes. The spacers are formed, for example, to allow changing the variable distance between adjacent high-density stacks only in a predetermined range.

Optionally, the assembly comprises a flexible substrate having a substrate surface with carbon nanotubes disposed on the substrate surface, not necessarily having direct contact between the substrate and the carbon nanotubes.

The high-density stacks and the low-density stacks may all be arranged between the at least two electrical contact elements on the substrate surface in such a way that one of the electrical contact elements is formed on a substrate-facing side and another of the electrical contact elements is formed on a substrate-remote side is.

On the substrate surface, a plurality of high-density stacks may be laterally offset from one another (eg lying) and may each be electrically contacted with an electrical contact element on a substrate-facing side. The plurality of laterally offset high-density stacks can be bridged on their side facing away from the substrate, at least by a stack of low density. In addition, it is also possible to arrange a stack of high density on the side of the low-density stack facing away from the substrate. For example, in the lateral arrangement of the stacks, the orientation of the CNTs in the high and low density stacks is parallel to the substrate surface and may be in any direction. Thus, the laterally offset high density stacks may be stacked with a low density stack, for example parallel to the CNT orientation or perpendicular to the CNT orientation. to be bound.

Optionally, all low density stacks are disposed between two outer high density stacks contacted by the electrical contact elements. The assembly may further include: at least one electrical insulation layer formed between at least one of the electrical contact elements and one of the high density outer stacks to electrically isolate the carbon nanotubes from the at least one electrical contact element.

The insulating layer may also be disposed on the substrate-remote side on the outer stack of high density and the at least one electrical contact element may comprise a plurality of laterally offset electrical contact elements.

The assembly may also include two or more insulating layers isolating all electrical contact elements from the high and low density stacks. As external stacks those stacks can be defined, between which all other stacks are arranged.

Since the insulating layers provide passivation or isolation of the individual nanotubes, it becomes possible to use the (block-like) arrangement of nanotubes as actuators, so that the high-density and low-density stacks formed within the passivation act as a variable capacitor which, when applied contracting a corresponding voltage or pressed apart, whereby locally changing layer thicknesses are formed, which in turn can then be used as nanopumps or simply be used as linear actuators. For example, as a pump, a wall may have this linear actuator, which is additionally passivated on the surface, and an opposite wall may have a solid substrate such as silicon. The liquid or gas can flow between these two walls. The actuator force is generated by the static electric field.

Optionally, the at least two electrical contact elements may extend in a planar manner parallel or perpendicular to the nanotubes. The present invention also relates to a sensor arrangement and / or an actuator with a previously described arrangement of carbon nanotubes.

The present invention further relates to a method of arranging carbon nanotubes for a sensor or an actuator. The method comprises:

- Forming a plurality of layered stack high density

Forming at least one layered stack of low density, the high density stack and the low density stack each having a plurality of carbon nanotubes and the at least one low density stack in contact with each of the high density stack on both sides thereof to keep at a variable distance from each other; and

- Forming of at least two electrical contact elements that electrically contact different high-density stack to

(i) detect a change in the variable distance as an electrical sensor signal, or

(Ii) to change the variable distance by applying an electrical voltage between the at least two electrical contact elements.

When forming the at least one layered stack of low density, at least one structured metallization can be used as the growth layer, the growth layer in particular having tantalum.

Embodiments of the present invention solve at least part of the above-mentioned problems of conventional MEMS or NEMS based sensors by CNT based multilayer blocks (= arrangement of high and low density stacks) and provide an alternative to previously established sensors based on semiconductor beam or membrane structures represents.

Embodiments of CNT-based multilayer blocks with integrated Resistance sensors offer the following advantages:

Multi-layered structures of dense and less dense CNTs can be formed to form a stable vertically oriented block.

The modulus of elasticity (modulus of elasticity) is greatly variable with the density, thickness and number of less dense CNT layers in the overall block.

Smallest moduli of elasticity are possible and therefore allow a simple deflection.

The modulus of elasticity is adaptable for different applications.

The stability is ensured with the dense CNT layers.

There are spring elements without mass possible (massless bending). The less dense CNT layer (low density stack) can greatly change the resistance when compressed to provide an integrated electrical resistance sensor with large sensor response. The CNT block structures used need no defined orientation and need not be arranged exactly vertically.

Small sensor dimensions are possible (for example, edge lengths of less than 10 μιτι can be achieved).

Direct lithography processes and subsequent CNT growth steps enable simple and cost-effective production.

Resolutions in the sensitivity in the μιη range of the sensor deflection allow a variety of one-dimensional, 2D and ßD applications, the CNT blocks can be lD, 2D and ßD arrangements.

Stable deflections are possible, in particular, deflections can be achieved up to almost 90 ⁰ , depending for example on the substrate and the length of the CNTs.

In a lateral arrangement, a transfer of the vertical blocks to a flexible foreign substrate allows a modified second platform technology, so that flexible portable sensors and detectors can be achieved. Freestanding films with vertically oriented carbon nanotubes have a maximum compressibility of up to 85%. In addition, CNTs show extreme structural flexibility and can alternately be bent over large angles and stretched without failing.

These properties make these sensor materials an attractive material for pressure, vibration and tactile sensors.

Micro-nano-integration of the vertically oriented CNT structures will provide a technologically novel approach and significant performance improvement over currently used pressure sensors based on nano-electromechanical systems (NEMS).

Brief description of the figures

The embodiments of the present invention will be better understood from the following detailed description and the accompanying drawings of the different embodiments, which should not, however, be construed as limiting the disclosure to the specific embodiments, but for explanation and understanding only.

Fig. 1 shows an arrangement of CNTs according to an embodiment of the present invention.

FIGS. 2A, B show a growth process of CNTs and resulting effective electrical resistances.

3 shows a plan view of a CNT arrangement according to an exemplary embodiment.

4A-4D show, by way of example, top views of schematic representations of the vertical arrangement of the multilayer CNT block with lateral contacts at the sensor ends according to further embodiments. Fig. 5 shows a schematic representation of an embodiment for a lateral arrangement of the multilayer CNT block with contacts from above and from below.

FIGS. 6A, B show schematic representations of embodiments for a lateral arrangement of the multilayer CNT block with direct lateral contacting at the sensor ends from below.

FIG. 7 shows schematically a representation of an actuator for the production of functional surfaces, such as nanopumps according to further embodiments.

Detailed description

1 shows an exemplary embodiment of an arrangement of carbon nanotubes (CNT arrangement) for a sensor or an actuator. By way of example, the CNT arrangement includes two high density stacked layers noa, nob, a low density layered stack 120 and two electrical contact elements 130a, 130b. The high density stacks 110a, 110b and the low density stack 120 each have a plurality of carbon nanotubes (CNTs) stacked at different densities. In the high-density stacks 110a, 110b, the CNTs are packed more densely than in the low-density stack 120.

The high-density stacks 110a, 110b are disposed on opposite sides of the low-density stack 120 and are thus held at a variable distance A from each other. The distance A is changed by deformation of the low density stack 120.

In addition, a first electrical contact element 130a contacts a first high-density stack 110a and a second electrical contact element 130b contacts a second high-density stack 110b such that all of the stacks are disposed between the electrical contact elements 130a, 130b. This will make it possible (i) detect a change in the variable distance A as an electrical sensor signal, or

(ii) to change the variable distance A by applying an electric voltage between the two electrical contact elements 130a, 130b to effect an actuator force.

Thus, the CNT assembly forms a multilayer block of (alternating) stacks of CNTs of different densities.

The CNTs may be arranged both horizontally (as shown in FIG. 1) and vertically. In the horizontal arrangement of the electrical contact elements 130a, 130b, at least a portion of the electrical contact elements extend parallel to the CNTs (i.e., in the direction of their longitudinal extent). In the vertical arrangement, the CNTs extend perpendicular to the electrical contact elements 130a, 130b. For example, the tubes extend vertically upward (or vertically downwards) from the electrical contact elements 130a, 130b so that the multi-layered CNT (CNT) blocks are laterally staggered and with direct lateral contact with the CNTs Sensor ends are contacted electrically.

Figure 2A illustrates a growth process of CNTs on an underlying substrate 200, wherein a vertical arrangement of the multilayer CNT block is made with a direct lateral contact at the sensor ends.

The CNTs are again arranged in different high and low density stacks. For this purpose, an intermediate layer 210 is optionally initially formed on a substrate 200 on which, opposite one another, two lateral metal contacts (a first electrical contact element 130a and a second contact element 130b) are formed. In addition, on the intermediate layer 210, by way of example, three metallizations 220a, 220b, 220c are arranged laterally offset from one another. The CNTs 120, 110 are grown on the structure thus obtained. On the three metallizations 220a, 220b, 220c, the carbon nanotubes 120a, 120b, 120c grow at a lower density than the CNTs 110a, 110c, iiod, 110b that exist between the metallizations 220a, 220b, 220c and the first and second electrical contact elements 130a, 130b (ie not on the three metallizations 220a, 220b, 220c) are arranged. To achieve this effect of lower density in the growth of CNTs, the three metallizations 220a, 220b, 220c include, for example, a metal (eg tantalum) which provides the dilute growth of the CNTs. For example, the interlayer 210 may include silicon oxide and the substrate 200 may be silicon.

As a result of this manufacturing process, an array of CNTs alternately having high density stacks 110a, 110c, iiod, 110b and low density stacks 120a, 120b, 120c is formed. The width and number of the low-density stacks 120 can be adjusted via the metallization 220, because on each metallization 220 the CNTs grow at a lower density than on the other regions of the intermediate layer 210 or on the electrical contact elements 130a, 130b.

FIG. 2B shows an equivalent circuit diagram for a current path between the first electrical contact element 130a and the second electrical contact element 130b. The current path passes through the high-density stacks 110 and the low-density stacks 120. The high-density stacks 110 have effective resistors 310 (Rdicht) and the low-density stacks 120 effective resistors 320 (thin). In addition, contact resistances (Ricontakt) are effective between the high-density stacks 110 and the low-density stacks. The current path between the first electrical contact element 130a and the second electrical contact element 130b is thus alternately exposed to the effective resistances Rdicht and Rdünn, wherein in each case a contact resistance acts Ricic contact.

Thus, there is effectively a lateral total resistance consisting of a sum of the lateral resistances of the dense CNT (CNT) stack, (n + i) times, the thin CNT layers, n times, and the contact resistances between the resistances. and the thin layers, 2n times. Thus, the resistance change or the sensor response multiplies in a deformation or bending with the number of layers. The greater resistance change takes place in the stack of low density 120, which corresponds to a resistance Rdünn, and the corresponding contact resistances Ri ontakt.

It is understood that the thicknesses of the stack need not be the same, but can be chosen arbitrarily. This can be done, for example, by a corresponding structuring of the metallizations 220, which define the areas in which thin and thick stacks are formed.

FIG. 3 shows a top view of the arrangement of CNTs, wherein at the lateral boundaries, the first contact element 130a and the second contact element 130b are formed, between which alternately low density stack 120 and high density stack 110 are located. The first contact element 130a contacts a first high-density stack 110a, and the second contact element 130b contacts a second high-density stack 110b. The first high density stack 110a is in contact with a first low density stack 120a, which in turn is in contact with a third high density stack 110c which, in turn, is in contact with a second low density stack 120b, which in turn is in contact with one fourth high-density stack iiod which, in turn, is in contact with a third low-density stack 120c, which is finally in contact with the second high-density stack 110b.

The first contact element 130a and the second contact element 130b may, for example, be formed as in FIG. 2A and extend approximately at right angles to the tube extension of the carbon nanotubes and serve for the electrical contacting.

4A-4D show various embodiments in which the high-density stacks 110 have or define spacers 115, 116, the spacers 115, 116 differing in their geometric shape. The spacers 115, 116 are formed such that they have a minimum is limited between two adjacent high-density stacks 110 and allows only a limited range of lateral movements.

For example, FIG. 4A shows spacers 115 having a rectangular shape perpendicular to the tube extension in the plan view (or cross-sectional view) shown. For example, the first high density stack 110a may include two spacers 115a extending along the tube direction and formed on the first high density stack 110a at opposite ends. Between the spacers 115a and the third high-density stack 110c there is still a portion 125a of the first low-density stack 120a that can be compressed upon deformation (for example, horizontal compression). However, the spacer 115a defines a maximum possible relative displacement direction between the first and third high density stacks 110a, 110c. Likewise, the third high density stack 110c again comprises two, e.g. spacers 115b formed at the ends (perpendicular to the tube extension) which extend towards the fourth high-density stack nod, which likewise comprises two spacers.

The electrical contact elements 130a, 130b are formed, for example, in the same manner as can be seen in FIG. 3 or in FIG. 2A.

FIG. 4B shows a further possibility of forming spacers 115. In the embodiment of FIG. 4B, the spacers 115 have a dome shape in the cross-sectional view shown perpendicular to the tube extension. As in Fig. 4A, two spacers are again formed at opposite ends of the respective high-density regions. The spacers may extend linearly or curved perpendicular to the plane of the drawing.

Fig. 4C shows an embodiment of another possible form of the spacers 115, which in this example are triangular in cross-sectional view. All other features are formed in the same manner as in Fig. 4A or Fig. 4B. A repeated description is not required.

FIG. 4D shows an embodiment in which spacers 115 are not only formed on one side of the high-density stacks 110. Rows of high density 110 rather have spacers 116, 115 on both sides. For example, the third high density stack 110c on both sides, i. toward the first contact element 130a and toward the second electrical contact element 130b, spacers 115, 116. Likewise, the fourth high-density stack nod has spacers 115 toward the second electrical contact element 130b and spacers 116 that are directed toward the first electrical contact element 130a.

An advantage of this approach is that the two-sided spacers provide a stronger stop, which can withstand greater force effects than is the case in the embodiments previously shown. Thus, in comparison to the exemplary embodiments of FIGS. 4A to 4C, twice as many spacers 115, 116 may be formed, which extend both in the direction of the first contact element 130a and in the direction of the second contact element 130b.

It should be understood that the shape of the spacers 115, 116 in the embodiment of FIG. 4D is not intended to be limited to the triangular shape shown in FIG. 4D. There are also the other forms possible. For example, both or some of the spacers 115, 116 of FIG. 4D may also have the rectangular shape (see FIG. 4A), the domed shape (see FIG. 4B), as well as any other suitable shape Restrict spacing between the high density stacks 110.

It is also possible for the spacers to extend between the high-density stacks 110 in a punctiform manner or only in sections in certain areas.

Thus, according to embodiments manifold spacers 115, 116th possible, which, as I said, can consist of the carbon nanotubes of the high density stack 110.

These structures can be easily fabricated with the metallization 220 on the substrate 200 to increase the stability in compression and the reproducibility of the resistance change.

5 shows a further embodiment of the present invention, in which an optional intermediate layer 210a is formed on the substrate 200. On the optional intermediate layer 210a or directly on the substrate 200, the second electrical contact element 130b is formed. The second electrical contact element 130b is followed by the second high-density stack 110b, on which a low-density stack 120 is arranged. On the low density stack 120, the first high density stack 110a is finally formed. Finally, on the first stack of high density 110a, the first electrical contact element 130a has a planar design.

The substrate 200 may in turn comprise a flexible material and the intermediate layer 210a may serve for isolation and may comprise silicon oxide by way of example. Likewise, the second contact element 130b may comprise a flexible material, and the first contact element 130a may also comprise a flexible material. Thus, the entire layer structure is flexible and can represent a membrane. This sensor signals can be generated, for example, depend on a pressure on the thus-shaped membrane or layer.

FIG. 6A shows a further exemplary embodiment, which differs from the exemplary embodiment shown in FIG. 5 in that, on the substrate 200 or on the optional intermediate layer 210a, the first electrical contact element 130a and the second electrical contact element 130b each have a stack of high Density 110a, 110b are laterally offset from one another. The two high-density stacks 110 a, 110 b are bridged by a low-density stack 120. Finally, another stack 110c of high density is optionally formed on the low density stack 120. The optional Intermediate layer 210a may in turn serve for electrical isolation. The first electrical contact element 130a and the second electrical contact element 130b are not in direct electrical contact with each other.

In the lateral arrangement of the stacks, the orientation of the CNTs in the high and low density stacks is parallel to the substrate surface, but may be in any direction. In Fig. 6A, the laterally offset high density stack having a low density stack is arranged, for example, parallel to the CNT orientation. The orientation of the CNTs is parallel to the displacement direction of the high-density stacks 110a, 110b.

Fig. 6B shows another embodiment which differs only in the embodiment shown in Fig. 6A in that the orientation of the CNTs in the stacks has been changed. The orientation of the CNTs in this embodiment is perpendicular to the displacement direction or the laterally offset high-density stack are connected to a stack of low density perpendicular to the CNT orientation. The arrows show exemplary current flow through the various stacks: a first high density stack 110a, the low density stack 120, a third high density stack 110c, the low density stack 120c, and finally a second high density stack 110b.

It should be understood that the illustrated two electrical contact elements 130a, 130b and the high density stacks 110a, 110b formed thereon are only an example. In further embodiments, a plurality of contact elements (in principle any number in any shape) may be formed on the substrate 200, all of which are bridged by the low density stack 120c and the final high density stack 110c (or even further layers) by way of example.

The overall resistance change, in turn, results from the sum of the vertical resistance changes in the individual stacks and the contact resistance between the high density stacks 110 and the stacks Density 120. Thus, in turn, the resistance change (sensor response) multiplies in a deformation with the number of layers. The larger change in resistance takes place again in the stack of low density (ie for thin) and in the contact area (ie for Ri ontakt).

The arrangements shown can be made on a variety of substrates 200. In addition, active layers can be made very thin (for example a few μιτι) and passivated, e.g. to achieve biocompatibility. Again, it should be understood that the thicknesses of the individual stacks (layer thicknesses), although shown the same, need not be equal.

FIG. 7 shows a further exemplary embodiment, which differs from the exemplary embodiment of FIG. 5 in that the first electrical contact element 130a is not formed as a layer, but rather by a multiplicity of contact elements 130a, 130b, 130c, i3od, ... was replaced. Otherwise, all other elements are formed in the same way as in the embodiment of FIG. 5.

As a result, different voltage values can be formed between the individual first contact elements 130a, 130b,... And the second electrical contact element 130b. In addition, in the exemplary embodiment shown, between the first electrical contact elements 130a, 130c, i3od,... And the first high-density stack 110a, a further intermediate layer 210b is formed, which in turn may comprise a flexible material and forms an electrical insulation. Thus, in the embodiment of FIG. 7, a plurality of capacitors are formed between the second electrical contact element 130b and the plurality of first electrical contact elements 130a, 130c,.

This embodiment allows shaping of the block shown. Thus, by the applied voltages, the high-density upper stack 110a in any shape (eg, a waveform) may be deformed. For example, voltage values can be applied periodically (also with different polarity) to the individual first contact elements 130a, 130b, 130c,.... The second electrical contact element 130b is for example at a reference potential (eg ground). As a result, the first contact elements 130a, 130b, 130c, ... are pulled to different degrees from the substrate 200 (depending on the polarity and the voltage values). A temporal change of the corresponding voltage values on the first electrical contact elements 130a, 130c,... Can achieve a wave-like movement of the block, which can be used, for example, for a micropump.

In addition, the low density stack 120 may reduce the modulus of elasticity to such an extent that only very low operating voltages are needed between the electrical contact elements 130 to electrostatically modulate the layer thicknesses. This arrangement can also be made on a variety of substrates 200. The active layers can in turn be made very thin (few μιτι) and passivated to achieve biocompatibility.

The platform technology of Figs. 5-7 enables a simple flexible membrane structure with a dense CNT layer 110 on a less dense (thin) CNT layer 120. For example, the dense CNT layer 110 may have high thermal resistance the thin CNT layer 120 insulates heat transfer to the substrate. In addition, this arrangement can be used as a thermoelectric material for the detection of micro, millimeter or THz waves and optical signals (such as infrared light). It is also possible to absorb the room heat to generate a thermoelectric current (for example, for energy harvesting). Also possible is a coating, such as the thin CNT layer 120, with piezoelectric materials such as zinc oxide (ZnO) to generate power (energy harvesting).

The CNT membrane can also be used as a support for a variety of 2D materials (such as graphenes, metal sulfides such as M0S2, SnS2, etc.). Also possible is chemical functionalization to create pn junctions in the multilayer blocks. For example, the dense CNT layer 110 may be made n-type and a thin CNT layer 120 may be formed as p-type. These pn layers have versatile applications as detectors. The said lateral arrangement can then be passivated (insulated) and coated with another thin electrode in order to build up electrostatic actuators. Functional surfaces (such as application-specific curved surfaces) as well as simple nanopumps with low operating voltages are also made possible.

The embodiments shown in particular offer the following solutions to the problems mentioned at the outset:

A. Mechanical stability

Properties such as the modulus of elasticity or the mechanical stability of the multi-layered CNT blocks of dense and less densely vertically oriented CNTs can be adapted process-specifically. Thus, the bending properties and the bending elasticity can be adjusted to a desired application. For example, multi-layered CNT blocks can be made for this purpose, each layer representing a stack of high density CNTs no or a low density stack 120. The modulus of elasticity is greatly variable with the density, thickness and number of the less dense CNT layer 120 in the overall block. Furthermore, the dimensions (for example, the length, thickness and width) of the CNT blocks can be varied in an application-specific manner and smallest moduli of less than 200 kPa can be set.

B. Simple contacting

Via a micro-nano-integration, it is further possible to enable a simple contacting of the vertically or laterally arranged CNT block. For example, can serve to lateral nickel contacts (or contact layers).

The growth of the CNTs can be achieved, for example, via a local (lithographically produced) structured thin metal layer 220 (for example from tantalum). be enough. Other layers or other materials may also be used to alter a growth density of the CNTs. The vertical single- or multi-walled CNT arrays (stacks of CNTs), for example, are arranged less densely vertically above the tantalum metallization 220. They grow there in a lower density. For example, to achieve the exemplary tantalum metallization (s) 220 in a multilayer CNT block with dense and less dense CNT layers, a stripe mask can be used that can be easily and inexpensively varied in number and thickness. Process specific, the diameters of the individual CNTs (for example, from 2 to 8 nm) can also be changed. It is also possible to change the CNT length. It can be varied, for example, in a range of 10 to 1500 μιτι. The height of the CNT blocks (eg the lengths of the individual CNTs) can be adjusted by adjusting the growth time in the manufacturing process.

These blocks are particularly useful for applications where mechanical deformation is being studied or measured.

C. Integrated resistance sensor

The less dense CNT layer 120 can greatly change the electrical resistance upon compression (by multiplying the contact points). Thus, there is an integrated resistance sensor with a large sensor response. Depending on the density, thickness and number of this less dense CNT layer 120, the sensor response may also be significantly increased and / or customized.

A βD-CNT device (ie, the multilayer CNT block) averages the electrical properties of the individual CNTs. A large number of CNTs (for example, several million per mm ² ) creates a high degree of redundancy. This makes it possible in particular to facilitate the fabrication of sensors with similar properties significantly. Upon compression or deformation of the less dense layer 120 of CNTs, the individual CNTs have one increased interaction with their respective adjacent CNTs (touching more or more frequently). Highly sensitive piezoresistive sensors with a reproducible lateral resistance decrease thereby become possible (see FIG. 2B). The stability of the CNT block is ensured with the dense CNT layers 110.

The piezoresistance of the contacted CNT blocks results in several effects:

A first effect is the modification of the resistance of the CNT layers 110, 120 in the block structure. The less dense layers 120 may have a greater change in resistance. Displacement of the CNT block under a compressive load increases the current through the lower lateral contacts (contact elements 130) of the CNT blocks on the substrate 200 (see FIG. 2A). The unique properties of these nanostructures enable the measurement of pressures, excursions and accelerations with high spatial resolution. In this case, for example, the transverse conductivity of the individual CNTs is utilized in the 3D CNT sensor arrangement.

The compressive stress causes a mechanical deformation of the CNT block structures and thus of the CNT layers with different CNT densities 110, 120. All thin 120 and dense 110 CNT layers have a resistance change dR_layer (see FIG. 2B). When deformed CNTs touch adjacent CNT tubes in the same layer, additional current paths are formed and the conductance increases. The lateral resistance change is particularly great when additional conduction paths arise in the CNT block near the substrate 200. Another sensor effect is to change the contact resistance between the individual CNT layers having different CNT density (for example, between the low-density stack 120 and a high-density stack 110), and the respective contact resistances for deformation / deflection of the entire CNT block Change R_contact (decrease or increase, see Fig. 2B). A measurement of the smallest deformations with high spatial resolution becomes possible. Their ease of fabrication and additional chemical functionalization enable cost-effective and versatile applications.

D. Lateral Arrangement

Especially the lateral arrangement allows flexible and portable sensors and detectors, which is not possible with the aforementioned conventional sensors. In the lateral arrangement, the vertical block is transferred (arranged) to a (flexible) foreign substrate 200. This very shallow sensors are possible, for example, have dimensions of a few micrometers. This lateral arrangement enables a very simple lateral and vertical contact (see FIGS. 5 and 6). This arrangement can then be passivated and coated with another (thin) electrode to achieve simple electrostatic actuators. Functional surfaces (for example application-specific curved surfaces) and simple nanopumps with low operating voltages are thereby possible (see FIGS. 5-7).

The CNT-based multilayer spring element with integrated resistance sensor has the following advantages in particular:

Direct lithography processes and CNT growth enable easy and cost-effective production.

The high local resolution (for example in the μιη range) and high sensitivity in the case of deformation enable a variety of ID, 2D and βD applications in sensor / actuator technology with ID, 2D and 3D arrangements of the multilayer CNT blocks. Among others, the following quantities can be measured: force, acceleration, angular velocity, pressure, tactile, vibration, flow (gas or liquid) and more.

A lateral arrangement by transferring the vertical blocks to a foreign substrate 200 is also possible.

The lateral arrangement may also be considered as a simple electrostatic actuator. serve. For this purpose, the surface can be passivated and coated with another electrode. Functional (application-specific curved) surfaces and simple nanopumps with low operating voltages are possible.

Small modulus of elasticity (<200 kPa) is possible (simple deflection).

The modulus of elasticity is adaptable for different applications.

Spring elements without mass are possible (massless bending).

Integrated resistance sensor with large sensor response.

Used CNT block structures do not require a defined orientation, need not be exactly vertical.

Small sensor dimensions are possible, for example, edge lengths of less than 10 μιτι.

Characterization of individual cells (~ 6o μιτι) is possible.

Measurement of force changes exerted by individual cells when exposed to drugs can be measured.

Stable deflections are achieved, bending up to almost 90 ⁰ , substrate and length-dependent.

The CNT block structures were integrated process-specifically into an adaptive microstructure. This is in particular characterized in that a simple contacting (micro-nanointegration) of the CNT block is achieved with, for example, laterally arranged nickel contacts. In addition, embodiments solve the above-mentioned problems by an integrated resistance sensor with a high sensor response, that is a high sensitivity that can be easily contacted both laterally and vertically. Furthermore, embodiments solve the problems by a 3D CNT sensor arrangement, which offers in the vertical and the lateral arrangement each a platform for a variety of mechanical and other applications. Flexible and portable sensors and actuators as well as detectors are possible.

The vertical arrangement, as can be seen for example in FIGS. 2-4, can be contacted laterally, for example, in a very simple manner. A For example, lateral placement may be achieved by transferring the vertical blocks to a (flexible) foreign substrate and providing a modified second platform technology. Here, for example, very flat sensors are possible, for example, have a height or an extension of a few μιτι. This lateral arrangement allows a very simple lateral and vertical contacting, as can be seen for example in Figs. 5, 6.

The features of the invention disclosed in the description, the claims and the figures may be essential for the realization of the invention either individually or in any combination.

LIST OF REFERENCE NUMBERS

110 stacks of high density carbon nanotubes

120 stacks of low density carbon nanotubes

130 electrical contact elements

115, 116 spacers

200 substrate

210a, 210b, ... intermediate layers

22oa, 22ob, ... metallization

310, 315, 320 Effective resistances

Claims

claims

An array of carbon nanotubes for a sensor or actuator, comprising: one or more high density stacked laminates (110); at least one layered low density stack (120), the high density stack (110) and the at least one low density stack (120) each having a plurality of carbon nanotubes and the at least one low density stack (120) unilaterally or on both sides in contact with the one or more high density stacks (110) to vary a distance (A) corresponding to a thickness of the at least one low density stack (120); and at least two electrical contact elements (130a, 130b) electrically contacting at least one of the high and low density stacks (110, 120)

(i) detect a change in the variable distance (A) as an electrical sensor signal, and / or

(Ii) to change the variable distance (A) by applying an electrical voltage between the at least two electrical contact elements (130a, 130b).

2. Arrangement according to claim 1, wherein the at least one low density stack (120) comprises a plurality of low density stacks (120a, 120b, ...) arranged alternately with the high density stacks (110), wherein between the electrical contact elements (130) a plurality of low-density stacks (120) are arranged, and wherein thicknesses of the high-density stacks (110) and the low-density stacks (120) are the same or different.

3. Arrangement according to claim 1 or claim 2, further comprising: at least one metallization (220a, 220b, ...) interconnecting the carbon nanotubes in the at least one low density stack (120) at one end, wherein the metallization (220a, 220b, ...) is formed to to cause a growth of the carbon nanotubes in a reduced density.

An assembly according to any one of the preceding claims, wherein at least some of the high density stacks (110) partially form spacers (115, 116) extending at least partially into the low density stacks (120) to form a variable distance stop (A ) define.

Arrangement according to claim 4, wherein the spacers (115, 116) perpendicular to the extension of the nanotubes have a rectangular, a dome-shaped, a round or a triangular cross-section.

The assembly of any one of the preceding claims, further comprising: a flexible substrate (200) having a substrate surface, wherein carbon nanotubes are disposed on the substrate surface. The assembly of claim 6, wherein between the at least two electrical contact elements (130a, 130b), the high density (110) and low density (120) stacks are disposed on the substrate surface such that one of the electrical contact elements (130b) on a submount - Strat-facing side and another of the electrical contact elements (130a) is formed on a side facing away from the substrate.

Arrangement according to claim 6 or claim 7, wherein on the substrate surface a plurality of high-density stacks (110) are arranged laterally offset from each other and each with an electrical contact element (130a, 130b) on a substrate-facing side electrically contacted, and the plurality of laterally offset high density stacks (110) are bridged on their substrate-opposite side by at least one low density stack (120), the carbon nanotubes being parallel, perpendicular or in another orientation relative to the lateral offset direction are arranged.

The assembly of any one of claims 6 to 8, wherein all of the low density stacks (120) are disposed between two outer high density stacks (110) contacted by the electrical contact members (130a, 130b) and the assembly further comprises: at least an electrical insulation layer (210) formed between at least one of the electrical contact elements (130a, 130b) and one of the high density outer stacks (110) to electrically connect the carbon nanotubes of the at least one electrical contact element (130a, 130b) isolate.

Arrangement according to claim 9, wherein the insulating layer (210b) on the substrate-remote side on the outer high-density stack (110) is arranged and the at least one electrical contact element (130) a plurality of laterally offset electrical contact elements (130a, 130c, i3od,. ..).

Sensor arrangement with an arrangement of carbon nanotubes according to one of claims 1 to 10.

An actuator with an array of carbon nanotubes according to any one of claims 1 to 10.

Method for arranging carbon nanotubes for a sensor or an actuator, comprising the following steps:

Forming a plurality of stacked high density stacks (110);

Forming at least one layered low density stack (120), the high density (110) and low density (120) stacks each having a plurality of carbon nanotubes and the at least one low density stack (120) in contact on both sides is in each case one of the stack of high density (110) to keep them at a variable distance (A) from each other; and

Forming at least two electrical contact elements (130) that electrically contact different high density stacks (110) to (iii) change the variable distance (A) as an electrical one

To detect sensor signal, and / or

(iv) to change the variable distance (A) by applying an electrical voltage between the at least two electrical contact elements (130)

The method of claim 13, wherein at least one patterned metallization is used as the growth layer in forming the at least one layered low density stack (120), wherein the growth layer comprises tantalum in particular.