Surface wave sensor device

Abstract

The invention relates to a sensor device which has a carrier material, in particular a piezoelectric carrier material. The sensor device also comprises: at least one interdigital transducer which is designed as a transmitter (IDTs) and as a receiver (IDTe) and is positioned on the carrier material; or at least one interdigital transducer which is designed as a transmitter (IDTs) and at least one interdigital transducer which is designed as a receiver (IDTe) and is also positioned on the carrier material. The sensor device also comprises at least one mechanical resonator (MR) which is positioned on the carrier material at a distance (A) from the IDTs and at a distance (B) from the IDTe, wherein the sensor device is designed so that a surface wave emitted by the IDTs as a transmission signal causes the MR to vibrate mechanically and a surface wave emitted by the vibrating MR travels in the direction of the IDTe as a received signal and triggers a measurement signal in said IDTe.

Description

SURFACE WAVE SENSOR DEVICE

[0001] In the field of micro- and nanotechnology, nanoelectromechanical resonators (NEMS = nanoelectromechanical systems) are increasingly being used as sensors. The increased interest in NEMS-based sensors is based, among other things, on the fact that it is possible to manufacture the mechanical resonator of a NEMS in such a way that the sensor exhibits specific properties for a measurement task and can also be tailored to this purpose. However, this requires a high degree of control over the mechanical properties of the resonator. These include, for example, the coherent control of the mechanical oscillations, the fine-tuning of the coupling properties with other mechanical systems or with other physical degrees of freedom, or the control of dissipative and nonlinear effects.

[0002] Current areas of application include the highly sensitive measurement of forces, masses, gas concentrations and temperature.

[0003] Although the high sensitivity of NEMS is important in the field of mass spectrometry, its application is limited, particularly in this area. This is due to the fact that NEMS cannot effectively capture the particles under investigation due to their small spatial extent. One approach to solving this problem is to use several individual mechanical resonators in a smaller space. Such an arrangement of mechanical resonators on the NEMS substrate is referred to as a two-dimensional array. Bargatin et al. describes an array in which thousands of individual mechanical resonators are arranged on a NEMS substrate (“Large-Scale Integration of Nanoelectromechanical Systems for Gas Sensing Applications”, Nano Lett. 2012 March 14; 12(3): DOI: 10.1021 / nl2037479). A system consisting of twenty resonators The array formed is described by Sage et al. in “Single-particle mass spectrometry with arrays of frequency-addressed nanomechanical resonators”, Nat Commun 9, 3283 (2018): DOI: 10.1038 / s41467-018-05783-4

[0004] The excitation of the mechanical resonators isolated on the substrate surface of a NEMS can be achieved by surface acoustic waves (SAWs), which propagate through the substrate surface and whose motion is transferred to the resonators, causing them to oscillate mechanically. The spatial distribution of the elastic energy of the surface waves at the surface of the substrate is influenced by the resonators. The elastic wave source can be implemented in the form of an acoustic interdigital transducer. A corresponding NEMS with an array formed from seven different geometric mechanical resonators, which are driven by one of two wave sources arranged around the array, is described by S. Benchabane et al. in "Surface-Wave Coupling to Single Phononic Subwavelength Resonators", https: / / doi.org / 10.1103 / PhysRevApplied.8.034016.

[0005] Acoustic transducers are used here as a wave source, i.e., to generate surface waves. A transducer is a converter that converts an electrical wave received as an input signal into an acoustic wave and then outputs this wave, e.g., into the surface of the substrate on which the transducer is arranged. An interdigital transducer (IDT) is an acoustic transducer that has finger-like structures. These finger-like structures are called interdigital electrodes. They look like the teeth of two combs that interlock without touching each other. The finger-like structures are usually made of metal and are arranged on a piezoelectric substrate. If an electrical voltage is applied between the combs, the generated mechanical force (piezoelectric effect) causes a change in the length of the substrate between each two teeth. If a When an alternating voltage is applied, the substrate material is caused to vibrate by this mechanical force. As a result, surface waves are generated that propagate across the substrate material.

[0006] The mechanical resonators are often formed as cylindrical columns, which are grown individually, for example, by focused ion beam-induced deposition on a piezoelectric substrate and exhibit different geometric parameters. The columns can be excited by a long-wavelength elastic surface wave. The mechanical deflection of the resonators induced by the surface waves can be significantly stronger than the displacement fields of the surface waves due to resonance. In this context, Benchabane et al. reported a tenfold amplification of the deflection compared to the oscillation at the surface.

[0007] The displacement of the resonators is detected using laser scanning interferometry. This measurement method has two particular disadvantages. Firstly, due to the required optical setup, it is difficult to integrate, for example, for the production of an integrated NEMS-based sensor, which should have a small spatial extent. Secondly, the optical detection method cannot measure or read the displacements of several resonators simultaneously, which is necessary for applications such as mass spectrometry. In contrast to the approach of Benchabane et al., the sensors of Bargatin and Sage do not have these disadvantages. Both use purely electrical methods to drive and read the resonators.However, their purely electrical methods prevent the formation of dense arrays of resonators, as the electrical wires that must be placed close to the resonators and are necessary for reading the resonators leave very little space for an array. The current state of the art therefore has the disadvantage that the density of a two-dimensional array, or rather, the number of resonators and their spacing, is limited to array arrangements. few resonators. However, to increase the efficiency of a NEMS-based mass sensor, for example, several resonators would have to be used in a small space. It would therefore be advantageous if the density of the two-dimensional array could be increased by a larger number of resonators. A dense two-dimensional array of mechanical resonators is understood in particular to be an array in which the resonators are spaced from one another by less than 20 pm, e.g. from resonator center to resonator center or from resonator outer wall to resonator outer wall. For example, the resonators are spaced from one another by less than 10 pm and / or less than 1 pm.

[0008] It is therefore an object of the invention to provide a sensor device that enables the formation of dense two-dimensional arrays of mechanical resonators. Furthermore, it is an object of the invention to provide a sensor device in which multiple mechanical resonators can be read individually and / or together.

[0009] The problem is solved by the subject matter of the independent claims. Preferred embodiments are the subject matter of the subclaims.

[0010] The sensor device according to the invention comprises a, in particular piezoelectric, carrier material; according to the first IDT arrangement, at least one interdigital transducer, which is configured as a transmitter (IDTs) and as a receiver (IDTe) and is arranged on the, in particular piezoelectric, carrier material; at least one, in particular micro or nanomechanical resonator (MR), which is arranged on the, in particular piezoelectric, carrier material at a distance A from the IDTs and at a distance B from the IDTe, wherein the sensor device is configured such that a surface wave emitted by the IDTs, as a transmission signal, causes the MR to oscillate mechanically and a The surface wave emitted by the oscillating MR runs as a received signal towards the IDTe and triggers a measurement signal in it.

[0011] Alternatively, a sensor device according to the invention comprises: a, in particular piezoelectric, carrier material; according to the second IDT arrangement, at least one interdigital transducer, which is configured as a transmitter (IDTs) and at least one interdigital transducer, which is configured as a receiver (IDTe) and is arranged on the, in particular piezoelectric, carrier material; at least one, in particular micro-mechanical resonator (MR), which is arranged on the, in particular piezoelectric, carrier material at a distance A from the IDTs and at a distance B from the IDTe, wherein the sensor device is configured such that a surface wave emitted by the IDTs causes the MR to oscillate mechanically as a transmission signal and a surface wave emitted by the oscillating MR travels as a reception signal towards the IDTe and triggers a measurement signal therein.

[0012] A sensor device is understood, in particular, to be a sensor. A sensor, also referred to as a detector, (measured variable or measuring) transducer, or (measured) probe, is a technical component that can detect certain physical or chemical properties (physical, e.g., mass, temperature, humidity, pressure, sound field variables, acceleration, or chemical, e.g., pH value, ionic strength, electrochemical potential) and / or the material properties of its environment qualitatively or quantitatively as a measured variable. These variables are detected by means of physical, chemical, or biological effects and converted into a further processable, particularly electrical, signal. A NEMS can be understood to be a sensor device according to the invention.

[0013] In measurement technology, the term transducer (measured quantity transducer) is used and defined as the part of a measuring device that responds directly to a measured quantity. The transducer is therefore the first element of a measuring chain. Sensors belong to the measuring transducers, and if the physical size at the input and output is the same, they also belong to the measuring transformers.

[0014] The definition of the terms sensor and transducer, measuring probe, measuring device, measuring equipment, etc. is fluid, since in addition to the actual transducer, other elements of the measuring chain can sometimes be assigned to the sensor.

[0015] A carrier material is understood to be a substrate on which the NEMS is at least partially structurally constructed. The substrate preferably provides the sensor device with a dimensionally stable structure, allowing the sensor device to be used as a single component. A piezoelectric material is particularly preferred as the carrier material and / or exhibits piezoelectric behavior. The carrier material can be constructed from several different materials, in particular functional materials. Functional materials in this context are materials that are necessary for the function of the sensor device or have a positive effect on it, in the sense of improved mechanical strength of the component, sensitivity, efficiency, or reproducibility of the measurement.For example, piezoelectric materials, thermally insulating materials, electrically conductive and / or electrically insulating materials, and acoustically damping materials. Particularly preferably, an interdigital transducer structure can be applied, in particular directly, to the piezoelectric material of the carrier material.

[0016] An interdigital transducer (IDT) is an acoustic transducer that has finger-like structures. An acoustic transducer is a converter that converts an electrical wave received as an input signal into an acoustic wave and outputs it. The finger-like structures are called interdigital electrodes. They look like fingers or like the teeth of two combs that interlock without touching each other. The finger-like structures are usually made of metal and are arranged on a carrier material, especially a piezoelectric one. If an electrical voltage is applied between the combs, the resulting mechanical force (piezoelectric effect) causes a change in the length of the carrier material between each pair of prongs or fingers. If an alternating voltage is applied, this mechanical force causes the carrier material to vibrate. As a result, surface waves are generated that propagate across the carrier material. The piezoelectric effect describes the change in electrical polarization and thus the occurrence of an electrical voltage in solids, such as the carrier material, when they are elastically deformed. Conversely, materials deform when an electrical voltage is applied.

[0017] In this context, a transmitter is understood to be an acoustic transducer configured to emit a transmission signal in the form of a surface wave. The transmitter's radiated power or transmission power is configured to propagate the signal as a surface wave at least over a predetermined area of ​​the carrier material and is further configured to excite the mechanical resonators to oscillate.

[0018] In this context, a receiver is understood to be an acoustic transducer configured to receive a surface acoustic wave as a received signal. The sensitivity of the receiver is configured to receive a surface acoustic wave emitted by the transmitter, which has propagated at least over a predetermined area of ​​the carrier material, thereby triggering a measurement signal. Furthermore, the sensitivity of the receiver is configured to receive a surface acoustic wave emitted by a mechanical resonator, thereby triggering a measurement signal.

[0019] A mechanical resonator, particularly a micro- and / or nano-mechanical resonator, is understood here to be a mechanical resonator dimensioned in the micro- and / or nanometer range. A resonator is an oscillatory device or an oscillatory system that exhibits resonance or shows resonance behavior. This means that the resonator oscillates at certain frequencies, the so-called resonance frequencies, with a greater amplitude than at other frequencies. The oscillations in a resonator are in this case mechanical, including acoustic, but can also, in particular additionally, be electromagnetic. The resonator can be tuned to one or more of the specific frequencies, so-called natural frequencies, in such a way that the resonator oscillates essentially only at these frequencies, particularly with broadband excitation. A mechanical resonator in this case is a resonator that preferentially oscillates acoustically, i.e. a solid whose atoms are collectively excited to oscillate and is also referred to as a phononic resonator. A solid, in the sense of matter in the solid state, can be a body composed of several solid bodies.The vibration modes of the body are at least partially predetermined, so that they can be set into vibration via predetermined excitation frequencies, in particular by means of surface waves. Preferably, a mechanical resonator is set into vibration by the mere mechanical contact between the resonator and the carrier material on which the surface wave propagates. The mechanical resonators can be designed in a wide variety of geometries. Preferred geometries are cylindrical, columnar, or rod-shaped, or hybrids thereof. The mechanical resonators can be assembled by stacking several cylindrical, columnar, or rod-shaped resonators on top of one another, thus forming an oscillatory system that, as a mechanical resonator, can be excited to vibrations by means of surface waves.The mechanical resonators can be constructed and / or assembled from one material or from several different materials.

[0020] In this context, a distance is understood to mean a spatial distance, in particular the spatial distance between an interdigital transducer and a mechanical resonator, measured from a point of the interdigital structure of the transducer, for example to the center of the resonator or to its Outer wall. If several mechanical resonators are positioned in one area, i.e. within a geometrically definable surface, e.g. within a circle or an oval, on the carrier material, the distance between an interdigital transducer and a mechanical resonator is to be understood as the distance that exists between the interdigital transducer and a center point of the area. The center point does not have to be the geometric center of the area, but can be a point that essentially coincides with this center point. For example, a point that roughly corresponds to the center of the circle in a circular area. In this context, an array refers to the two-dimensional arrangement of the mechanical resonators on the carrier material, whereby the arrangement of the resonators does not have to be regular in the sense of equal distances between the resonators or symmetries.The distance can be determined, for example, by measuring from a finger of the interdigital structure to the outer wall or to the center or point of symmetry of the mechanical resonator.

[0021] A surface wave is generally understood to be a mechanical deformation of a surface in the form of a wave. In this context, a surface wave is specifically understood to be a surface acoustic wave (SAW). A surface acoustic wave is an acoustic wave that propagates along the surface of an elastic material and whose amplitude generally decreases exponentially with the depth of the material, so that it is limited to a depth of approximately one wavelength. Also known as Rayleigh waves, surface waves have a longitudinal and a transverse shear component that can couple with any media, such as additional layers that are in contact with the surface of the material in which the surface wave propagates. This coupling has a strong effect on the amplitude and speed of the wave. Surface waves also include acoustic surface waves, such as:Love waves that are polarized in the plane of the surface and not longitudinally and vertically polarized. Similar to a Rayleigh wave, Lamb waves in plates also generate a longitudinal and a vertical deflection at the plate surfaces, which is why surface waves also include applications in which Lamb waves are generated.

[0022] In this case, a transmission signal is understood to be the surface wave emitted by the transmitter, in particular to the carrier material.

[0023] In this case, a received signal is understood to be a surface wave which is emitted, i.e. given off, in particular by an oscillating resonator and is suitable for triggering a measurement signal in an acoustic transducer.

[0024] A measurement signal is the further processable electrical signal converted by the sensor device.

[0025] In this context, a mechanical vibration is preferably understood to mean the lattice vibration of a solid. The solid is designed as a mechanical resonator and is set into vibration by a surface wave.

[0026] An emitted surface wave is a surface wave that has been emitted, for example, by an acoustic transducer. Alternatively, an emitted surface wave can also be emitted by a mechanical resonator if it has been set into vibration, for example, by an acoustic surface wave.

[0027] The sensor device according to the invention offers the advantage that a surface wave emitted by the IDTs causes the MR to oscillate mechanically, and a surface wave emitted by the oscillating MR travels toward the IDT as a received signal, triggering a measurement signal therein. This eliminates the need for optical measurement technology, such as laser scanning interferometry, to detect a displacement field at the mechanical resonator. There are no restrictions on the spatial arrangement of a plurality of mechanical resonators within a region on the carrier material, in particular not due to electrical lines. The density of the array of resonators can thus advantageously be increased in order to achieve, for example, greater efficiency of the sensor device. The sensor device according to the invention further has the advantage, particularly in comparison to optical measurement techniques such as laser scanning interferometry, that a plurality of mechanical resonators can be measured or read out simultaneously, ie with one another or jointly, and / or that a plurality of mechanical resonators can be measured or read out individually, ie individually.

[0028] In a sensor device according to the invention, at least one interdigital transducer is used as a transmitter and at least one further, spatially separated interdigital transducer is used as a receiver. The distances A, B between the transmitters (IDTs) and / or receivers (IDTs) are arranged such that a surface wave transmitted by the IDT causes at least one mechanical resonator to oscillate mechanically, causing it to emit a surface wave and transmit it in the direction of the at least one IDT, so that the IDT receives a received signal. The sensor device can comprise several identical mechanical resonators, or the sensor device can comprise several different mechanical resonators, or hybrids of identical and different mechanical resonators. In the case of different resonators, the resonators oscillate at different frequencies, so that they can be distinguished from one another.For example, if an IDT emits a surface wave with frequencies f1 and f2, essentially only these two resonators are excited, which can oscillate at frequencies f1 and f2.

[0029] As an alternative sensor device according to the invention, the sensor device can comprise at least one interdigital transducer that functions as a transmitter and a receiver. The term bipolar transducer is used synonymously for a transducer that functions as a transmitter and a receiver. Acoustic transducers first act as transmitters, sending a surface wave toward the at least one mechanical resonator, thereby causing the at least one resonator to oscillate mechanically. This causes a surface wave to be generated by the resonator and travel back toward the transmitter. Since the transmitter is also configured to function as a receiver, the returning surface wave then acts as a received signal and causes the interdigital structure of the bipolar transducer to oscillate, thereby triggering an electrical voltage as a measurement signal at this bipolar transducer. The sensor device can have several identical mechanical resonators, or the sensor device can have several different mechanical resonators, or hybrids of identical and different mechanical resonators.In the case of different resonators, the resonators oscillate at different frequencies, so they can be distinguished from each other.

[0030] Further alternative sensor devices according to the invention are those that comprise hybrids of bipolar transducers and unipolar transducers. For example, an NEMS according to the invention can comprise at least one bipolar and at least one unipolar transducer, wherein the at least one unipolar transducer can operate as a transmitter (IDTs) or as a receiver (IDTs). Furthermore, an NEMS according to the invention comprises at least one bipolar transducer. The sensor device can comprise several identical mechanical resonators, or the sensor device can comprise several different mechanical resonators, or hybrids of identical and different mechanical resonators. In the case of different resonators, the resonators oscillate at different frequencies, so that they can be distinguished from one another.

[0031] In a preferred embodiment, the distance A between an IDT and the at least one mechanical resonator can be greater or smaller than the distance B between an IDT. This geometric arrangement of the transducer distances has the advantage that anisotropies in the carrier material can be taken into account, which leads to an improved signal.

[0032] In a preferred embodiment, the IDT is arranged on the carrier material (2) at an angle of 10-360 degrees, preferably at an angle of 70-110 degrees, more preferably at an angle of 170-210 degrees, more preferably at an angle of 250-290 degrees, more preferably at an angle of 300-350 degrees, relative to the propagation direction of the surface wave emitted by the IDT. In a preferred embodiment, the IDT is arranged on the carrier material (2) at an angle of approximately 90 degrees relative to the propagation direction of the surface wave emitted by the IDT. The propagation direction of the surface wave corresponds to the direction in which the surface wave travels to excite the resonator. The propagation direction can be described by a straight line or a straight section between the at least one resonator and the IDT, both of which are arranged on the carrier material.The line can extend from a freely selectable point on the interdigital structure of the IDT, for example, to the center of the mechanical resonator. The propagation direction can be determined by a line between the IDT and the region in which the plurality of mechanical resonators are arranged on the carrier material. The line can extend from a freely selectable point on the interdigital structure of the IDT, for example, to the center of the region in which the mechanical resonators are arranged. In particular, the propagation direction can be the smallest distance between the IDT and the at least one mechanical resonator and / or the region in which the plurality of mechanical resonators are arranged on the carrier material.

[0033] An angular range is understood as follows: If you define two arbitrary points on a circle at which an IDTs and an IDTe are to be arranged on the substrate and connect them by stretching them to the center of the circle, with a mechanical resonator arranged in the center, then the two parts of the Circular areas separated from each other by these lines represent circular sections (also called circular sectors). In this arrangement, the distance from the IDTs to the circle center corresponds to the propagation direction of the SAW. A circular section is thus, as it were, "cut out" of a circle by two radii. The part of the circular line belonging to a circular sector is called the circular arc, and the angle between the two radii is called the angular range (also called the central angle). Instead of a circle, the two arbitrary points can also be defined on an essentially circular, e.g., an oval geometry. For example, the claim wording "in an angular range of 70 - 110 degrees" can mean that the actual central angle of the IDT arrangement to the propagation direction lies within the range of 70 and 110 degrees.A possible arrangement of the IDTe to the propagation direction can therefore have a specific value of the center angle of 80, 90 or 100 degrees in order to be within the angular range of 70 - 110 degrees.

[0034] The 90-degree arrangement has the advantage that a SAW that runs directly from the IDTs into the IDTe generates only a minimal signal there, since the finger structure of the IDTe is perpendicular or largely perpendicular to the SAW wavefront.

[0035] In a particularly preferred embodiment, the mechanical resonator is columnar. Other geometries, such as rectangular, cylindrical, conical, a stack of disc-shaped segments, or hybrids of the aforementioned geometries, which are connected to one another in a vibration-capable manner by layering or stacking, are also possible. A columnar geometry, also known as a columnar resonator, has the advantage of being the easiest to manufacture and can be mathematically described as a point source.

[0036] In a preferred embodiment, the columnar resonator has a diameter between 1 nm and 10 pm, preferably between 25 nm and 1 pm, particularly preferably between 50 nm and 200 nm. The diameter D is measured in the plane of the support material. For a cylindrical or columnar resonator geometry, the diameter corresponds to the geometric diameter of a cylinder, measured in the plane of the support material on which the resonator is arranged.

[0037] In a preferred embodiment, the columnar resonator has a height between 10 nm and 10 pm, preferably between 50 nm and 5 pm, particularly preferably between 200 nm and 2 pm. The height H corresponds to the extension of the resonator in the direction perpendicular to the carrier material on which the resonator is arranged.

[0038] In a preferred embodiment, the carrier material comprises a piezoelectric material or the carrier material consists of a piezoelectric material, in particular lithium niobate (LiNbO3) or quartz (SiO2) or zinc oxide (ZnO) or aluminum nitride (AIN), or zirconate titanate (PZT), or lithium tantalate (LiTaO3), or mixtures thereof. Lithium niobate (LiNbO3) has the advantage of having a high piezoelectric coupling constant compared to other piezoelectric materials and therefore leads to good signal quality.

[0039] In a preferred embodiment, the IDTs and / or the IDTe are designed as focusing, in particular interdigital, transducers. In this case, the transducer can have an at least partially conical or arrow-shaped geometry, in particular the transducer can be conical or arrow-shaped in its entirety. In particular, the interdigital structure of the transducer is arc-shaped at least in sections. However, the transducer can also have a rectangular geometry. A conical, in particular focusing, geometry has the advantage that the surface waves propagate with a higher intensity in a preferred direction, e.g., in the direction of the resonators. Further preferably, the at least one transducer configured as a transmitter can be a focusing transducer. Further preferably, the one or more Transducers configured as transmitters can be configured as focusing transducers, and the at least one transducer configured as receivers can be configured as non-focusing transducers. Further preferably, the one or more transducers configured as receivers can be configured as focusing transducers, and the at least one transducer configured as transmitters can be configured as non-focusing transducers.

[0040] In a preferred embodiment, the IDTs and / or the IDTe have a finger width between 50 nm and 20 pm, preferably between 200 nm and 10 pm, particularly preferably between 1 pm and 5 pm. A finger width is the width of one finger of the interdigital structure, measured in a direction parallel to the carrier material on which the interdigital structure is arranged.

[0041] In a preferred embodiment, at least one interdigital transducer comprises or consists of aluminum, or silver, or gold, or platinum, or copper, or nickel, or titanium, or niobium, or mixtures thereof, for forming the interdigital structure.

[0042] In a preferred embodiment, A has a value between 50 pm and 2000 pm and B has a value between 50 pm and 2000 pm, preferably A has a value between 150 pm and 1500 pm and B has a value between 150 pm and 1500 pm, more preferably A has a value between 300 pm and 1000 pm and B has a value between 300 pm and 1000 pm. The values ​​of A and B should also be able to lie within the defined ranges. For example, A can have a value of 50 pm or 200 pm and thus lies within the specified range between 50 pm and 2000 pm.

[0043] In a preferred embodiment of the sensor device, at least one electrode is arranged on the carrier material next to an interdigital transducer. The term "next to" is to be understood as meaning that if two transducers are arranged next to each other or adjacent to each other, no further transducer is arranged between them. In particular, between adjacent interdigital transducers At least one electrode must be arranged on the carrier material. Due to the interdigital structure of the transducers, they act as antennas, which is why electrical signals from outside the sensor device are also received by it, resulting in signal noise. Arranging the electrodes between adjacent transducers has the advantage of at least partially suppressing the resulting signal noise, thus improving the signal-to-noise ratio of the sensor device.

[0044] The invention further relates to a system having a sensor device according to the invention. The system according to the invention comprises a control unit for controlling at least one IDT and an evaluation unit for evaluating a measurement signal from the at least one IDT. The control unit preferably outputs an electrical signal to at least one IDT to generate a surface acoustic wave as a transmission signal, the transmission signal causing the at least one mechanical resonator to oscillate, and a surface acoustic wave emitted by the at least one oscillating MR to travel toward the at least one IDT as a reception signal, triggering the measurement signal therein. The measurement signal is preferably processed by the evaluation unit, in particular the measurement signal from the at least one IDT is tracked for a change in an amplitude signal (17) at a resonance frequency (14) predetermined by the at least one mechanical resonator (5).The control unit and the evaluation unit can be separate devices or combined in the same device. Such combined devices are typically lock-in amplifiers or network analyzers.

[0045] In a preferred embodiment of the system, the system is configured to perform the tracking of the frequency, in particular the resonant frequency and the amplitude, using an oscillator circuit, such as a phase-locked loop (PLL) or self-sustaining oscillator (SSO). The PLL and the SSO are closed-loop circuits that drive individual resonators coherently at a defined resonant frequency and with a defined amplitude, thus causing them to oscillate. The oscillation frequency of this NEMS circuit is identical to the resonant frequency of the resonator, allowing real-time tracking of changes in the resonant frequency and amplitude. Such circuits can be operated simultaneously for multiple resonators.

[0046] Furthermore, the invention relates to a method for producing a sensor device according to the invention, the method comprising the following steps: A) Providing a carrier material, in particular a piezoelectric one; B) applying the first IDT arrangement or the second IDT arrangement to the carrier material; C) Applying at least one mechanical resonator to the carrier material, wherein step B can optionally be carried out by at least the following steps: a. Applying a metal layer to the carrier material to form an interdigital structure of at least one interdigital transducer, which serves as a transmitter (IDTs) and as a receiver (IDTe), according to the first IDT arrangement; OR Applying a metal layer to the carrier material to form an interdigital structure of at least one interdigital transducer serving as a transmitter (IDTs) and at least one interdigital transducer serving as a receiver (IDTe), according to the second IDT arrangement; b. Forming the interdigital structure of the at least one IDT on the carrier material, preferably by means of: - Photolithography and etching process; or - by means of photolithography and lift-off process, whereby step C can optionally be carried out by at least one of the following steps: - Focused Electron Beam Induced Deposition (FEBID), or - Photolithography and physical vapor deposition (PVD), or - Photolithography and chemical vapor deposition (CVD), or - Photolithography and vapor deposition or sputtering process, or - Ion-Beam Induced Deposition (IBID), or - Wet or dry etching into the substrate, or - Structuring of photoresists, in particular structuring of SU-8, or - Metal-Organic Vapor Phase Epitaxy.

[0047] Further preferred embodiments of the sensor device according to the invention and the method for its production, as well as of the system of the invention, will become apparent from the following description of the exemplary embodiments in conjunction with the figures and their description. Identical components are essentially identified by identical reference numerals unless otherwise stated or apparent from the context.

[0048] Fig. 1 shows a first embodiment of the sensor device 1 according to the invention.

[0049] Fig. 2 shows a second embodiment of the sensor device 1 according to the invention.

[0050] Fig. 3 shows an electron micrograph of an embodiment of a mechanical resonator 5 of the sensor device 1 according to the invention.

[0051] Fig. 4 a - c schematically shows embodiments of the sensor device 1 according to the invention.

[0052] Fig. 5 shows schematically an embodiment of the system 10 according to the invention.

[0053] Fig. 1 shows a first embodiment of the sensor device 1 according to the invention on a carrier material 2, using the first IDT arrangement. In Fig. 1, starting from the upper left edge of the image, an interdigital structure 6, 18 of an acoustic transducer (IDT) 3, 4 is shown. The interdigital structure of the transducer 3, 4 is arc-shaped, resulting in a conical shape of the transducer that is oriented in the direction of the mechanical resonator 5, so that a surface wave emitted as a transmission signal 7 is focused onto the mechanical resonator 5. In addition, Fig. 1 shows an electron microscopic view of a cylindrical mechanical resonator 5 next to the sensor device 1 shown. The mechanical resonator 5, as well as the transducer 3, 4 serving as transmitter and receiver in Fig. 1, are arranged on the substrate 2.A surface wave emitted by the mechanical resonator 5 as a received signal 8 is also shown. In this particularly preferred embodiment shown in Fig. 1, only one bipolar transducer 3, 4 is necessary to generate and detect a mechanical oscillation of the resonator 5 shown. The sensor device further comprises two electrodes 11. The electrodes 11 are arranged on the substrate 2 and positioned directly adjacent to the transducer 3, 4. The electrodes 11 have the task of coupling, in particular high-frequency, electrical signals from external sources into the sensor device 1. This has the advantage of improving signal quality, since electrical coupling can negatively affect the noise-to-signal ratio of the measurement signal 9.

[0054] Fig. 2 shows a second embodiment of the sensor device 1 according to the invention, wherein Fig. 2 differs from Fig. 1 essentially in that two unipolar transducers (IDTs) 3, 4 are arranged on the substrate 2, i.e. the second IDT arrangement is used. In Fig. 2, a dashed line is also shown. This line runs centrally between the transducer 3 acting as transmitter and the mechanical resonator 5. The receiver transducer 4 is positioned at an angle (not shown) of approximately 90 degrees to this dashed line, so that a surface wave as received signal 8, which is emitted by the oscillating resonator 5, travels towards the receiver 4 and triggers a measurement signal 9 there. The sensor device further has three electrodes 11. The electrodes 11 are arranged on the substrate 2 and are positioned adjacent to the two transducers 3, 4.The electrodes 11 are designed to prevent electrical coupling, particularly of high-frequency, from external sources into the sensor device 1, as well as crosstalk from the transducer (IDTs) acting as transmitter 3 to the receiver transducer 4 (IDTs). Electrical coupling or crosstalk can negatively impact the noise-to-signal ratio of the measurement signal 9. The use of electrodes 11 has the advantage of enabling improved signal quality.

[0055] Fig. 3 shows an electron micrograph of an embodiment of a mechanical resonator 5 of the sensor device 1 according to the invention. The resonator 5 is columnar here, or as a columnar resonator. The resonator 5 is applied in a vibratable manner directly to the substrate surface of the substrate 2. The columnar resonator shown has a height H measured perpendicular to the surface of the substrate 2 (longitudinal dimension) of approximately 1.9 pm and a diameter D or a width, measured horizontally to the surface of the substrate 2 of 702.4 nm. The height H and the diameter D are shown in Fig. 3 by dashed lines.

[0056] Fig. 4 a - c schematically show embodiments of the sensor device 1 according to the invention. Fig. 4a shows the embodiment illustrated in Fig. 1, in which a single bipolar transducer (IDT) 3, 4, i.e. the first IDT arrangement, is used. A plurality of mechanical resonators 5 with a uniform geometry are shown arranged within a region to form an array. A transmitted signal 7 is emitted in the direction of the resonators 5 and causes them to oscillate mechanically. A received signal 8 is emitted by the oscillating resonators 5. The resonators 5 can have different geometries. In particular, the resonators can have different geometries that are configured to realize different resonant frequencies of the individual resonators 5.

[0057] Fig. 4b shows a schematic representation of the embodiment shown in Fig. 2. Two unipolar transducers are used as receiver 4 or as transmitter 3. Furthermore, a number of resonators 5 with the same, i.e. uniform geometry are shown, which are arranged as an array within a circular area shown in dashed lines. These resonators 5 can have either the same resonance behavior, i.e. essentially the same resonance frequencies, or different resonance behavior, i.e. essentially different resonance frequencies. The transmitter 3 is positioned at a distance A from the center of the circular area. The receiver 4 is positioned at a distance B from the center of the circular area. If the distances are different, as shown in Fig. 4b, i.e. A is greater than B, the result is an oval contour, which is shown in dashed lines in Fig. 4b.Transmitter 3 and receiver 4 are positioned along this contour. With such an arrangement, the signal strength of the surface waves picked up by the receiver is particularly high. The angle a of 90 degrees within the angular range of 70-110 degrees is indicated by a dashed line with arrows. indicated on the left in Fig. 3b, perpendicular to the propagation direction of the SAW of the ITD 3, which is shown in dash-dotted lines and coincides with the direction of the transmission signal 7.

[0058] Fig. 4c schematically shows an embodiment in which a bipolar 3, 4 and a unipolar 4 transducer are used. A surface wave emitted by the transmitter 3 in the direction of the resonators 5 as a transmission signal 5 is received both by the bipolar transducer 3, 4 and by the unipolar receiver arranged at 90 degrees to it. This makes it possible to output a first and a second measurement signal 9. In such an embodiment, the bipolar transducer 3, 4 can additionally be designed as a focusing transducer, i.e., conically. The unipolar transducer 4 can have a rectangular outer geometry or can also be focusing, in particular conically. Mixed arrangements of focusing and non-focusing transducers on the carrier material 2 are also possible.

[0059] Fig. 5 schematically shows an embodiment of the system 10 according to the invention. The system has a sensor device 1, a control unit 12 and an evaluation unit 13. The control unit 12 outputs an electrical signal 15 to the bipolar transducer 3, 4 of the sensor device 1, which signal is also sent to the evaluation unit 13 as a reference signal. The bipolar transducer 3, 4 then outputs a surface wave radiated as a transmission signal 7 in the direction of the resonator 5. The resonator is set into resonance by the transmission signal 7 and then emits a surface wave as a reception signal 8 in the direction of the bipolar transducer 3, 4. The transducer 3, 4 receives the reception signal 8 and converts it into a measurement signal 9. The measurement signal 9 is transmitted to the evaluation unit 13 via the transducer 3, 4. The evaluation unit 13 determines the amplitude and phase of the measuring signal 9 as a function of frequency.The relevant frequency range is determined by the natural frequency of resonator 5. If resonator 5 is excited by the emitted surface waves in its natural frequency range, this results in: Amplitude signal 16, which exhibits a resonance peak. If no excitation occurred, the noisy amplitude signal 17 shown in Fig. 5 results, without a resonance peak. The amplitude signal 14 shown in dashed lines corresponds to a fit based on the model of a one-dimensional and driven linear resonator. The resonator's natural frequency can be predetermined by its geometric shape, allowing the sensor device 1, i.e., its resonance behavior, to be specifically tuned to a specific measurement task. LIST OF REFERENCE SYMBOLS Sensor device Carrier material Interdigital transducer as transmitter Interdigital transducer as receiver Mechanical resonator Interdigital structure Surface wave as transmission signal Surface wave as received signal measurement signal system Electrodes Control unit Evaluation unit Theoretical amplitude signal at resonance frequency Electrical transmission signal Amplitude signal at resonance Amplitude signal without resonance effect Finger width of the interdigital structure

Claims

CLAIMS Sensor device (1) for measuring acoustic surface waves, comprising a, in particular piezoelectric, carrier material (2), with at least one first interdigital transducer (IDT) arrangement or a second IDT arrangement, wherein the first IDT arrangement has at least one interdigital transducer which is configured as an IDT transmitter (IDTs) (3) and as an IDT receiver (IDTe) (4) and which is arranged on the carrier material (2), and wherein the second IDT arrangement has at least one interdigital transducer which is configured as an IDT transmitter (3) and at least one interdigital transducer which is configured as an IDT receiver (4), and which are arranged on the carrier material (2), wherein the sensor device has at least one mechanical resonator (MR) (5) which is arranged on the carrier material (2) at a distance A from the IDTs (3) and at a distance B from the IDTe (4). is,The sensor device (1) is configured such that an acoustic surface wave emitted by the IDT (3) causes the MR (5) to mechanically vibrate as a transmission signal (7), and a surface wave emitted by the vibrating MR (5) travels toward the IDT (4) as a reception signal (8) and generates a measurement signal (9) therein. The sensor device according to claim 1, wherein the distance A is greater or smaller than the distance B. Sensor device according to claim 1 or 2, wherein the IDT (4) is arranged on the carrier material (2) in an angular range of 10-360 degrees, preferably in an angular range of 70-110 degrees, more preferably in an angular range of 170-210 degrees, more preferably in an angular range of 250-290 degrees, more preferably in an angular range of 300-350 degrees to the propagation direction of the surface wave emitted by the IDT (3). Sensor device according to one of the preceding claims, wherein the MR (5) is columnar. Sensor device according to claim 4, wherein the columnar MR (5) has a diameter between 1 nm and 10 pm, preferably between 25 nm and 1 pm, particularly preferably between 50 nm and 200 nm. Sensor device according to claim 4 or 5, wherein the columnar MR (5) has a height between 10 nm and 10 pm, preferably between 50 nm and 5 pm, particularly preferably between 200 nm and 2 pm.Sensor device according to one of the preceding claims, wherein the carrier material (2) comprises a piezoelectric material, in particular lithium niobate (LiNbO3) or quartz (SiO2) or zinc oxide (ZnO) or aluminum nitride (AIN), or zirconate titanate (PZT), or lithium tantalate (LiTaO3), or mixed forms thereof. Sensor device according to one of the preceding claims, wherein the IDTs (3) and / or the IDTe (4) are designed as focusing interdigital transducers. Sensor device according to one of the preceding claims, wherein the IDTs (3) and / or the IDTe (4) have a finger width (18) between 50 nm and 20 pm, preferably between 200 nm and 10 pm, particularly preferably between 1 pm and 5 pm. Sensor device according to one of the preceding claims, wherein the interdigital transducer (3, 4) comprises aluminum, or silver, or gold, or platinum, or copper, or nickel, or titanium, or niobium or mixtures thereof, for forming the interdigital structure (6). Sensor device according to one of the preceding claims, wherein A has a value between 50 pm and 2000 pm and B has a value between 50 pm and 2000 pm, preferably A has a value between 150 pm and 1500 pm and B has a value between 150 pm and 1500 pm, further preferably A has a value between 300 pm and 1000 pm and B has a value between 300 pm and 1000 pm. Sensor device according to one of the preceding claims, wherein in addition to an interdigital transducer (3, 4), at least one electrode (11) is arranged on the carrier material (2).System (10) comprising a sensor device according to one of claims 1 to 12, a control unit (12) for controlling at least one IDT (3) and an evaluation unit (13) for evaluating a measurement signal (9) of the at least one IDT (4), wherein the control unit (12) outputs an electrical signal (15) to at least one IDT (3) for generating the surface wave serving as the transmission signal (7), and the transmission signal (7) causes the at least one mechanical resonator (5) to oscillate, and wherein the measurement signal (9) of the at least one IDT (4) is processed by the evaluation unit (13). System according to claim 13, wherein the system (10) is configured to track the frequency and the amplitude of the measurement signal (9) and wherein in particular this tracking of the change in the amplitude and the frequency of the measurement signal (9) is carried out according to a phase-locked loop (PLL) method or according to a self-sustaining oscillator method (SSO). A method for producing a sensor device according to any one of claims 1 to 12, comprising the following steps: A) Providing a carrier material, in particular a piezoelectric one; B) applying the first IDT arrangement or the second IDT arrangement to the carrier material; C) Applying at least one mechanical resonator to the carrier material (2), wherein step B can optionally be carried out by at least the following steps: a. Applying a metal layer to the carrier material (2) to form an interdigital structure (6, 18) of at least one interdigital transducer (3, 4), which serves as a transmitter (IDTs) (3) and as a receiver (IDTe) (4), according to the first IDT arrangement; OR Applying a metal layer to the carrier material (2) to form an interdigital structure (6, 18) of at least one interdigital transducer (3) serving as a transmitter (IDTs) (3) and at least one interdigital transducer (4) serving as a receiver (IDTe) (4), according to the second IDT arrangement; b. Forming the interdigital structure (6, 18) of the at least one IDT (3, 4) on the carrier material (2), preferably by means of: - Photolithography and etching process; or - by means of photolithography and lift-off process, whereby step C can optionally be carried out by at least one of the following steps: - Focused Electron Beam Induced Deposition (FEBID), or - Photolithography and physical vapor deposition (PVD), or - Photolithography and chemical vapor deposition (CVD), or - atomization process (sputtering), or - Ion-Beam Induced Deposition (IBID), or - Wet or dry etching into the substrate (2), or - Structuring of photoresists, in particular structuring of SU-8, or - Metal-Organic Vapor Phase Epitaxy.

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