Tensile-strained iii-nitride nano- and micromechanical resonators and methods for producing these resonators

Abstract

The present disclosure relates to a method for producing a mechanical resonator (100), the method (300) comprises providing (310) a crystalline substrate (151); growing (320) a III-N film (152) on the substrate (151), wherein the grown III-N film (152) is tensile-strained; forming (330) the resonator (100) of said III-N film (152) grown on the substrate (151), wherein forming the resonator (100) comprises applying (332) a resist (155), performing lithography (333), and etching (335) steps, and wherein the formed resonator (100) comprises a resonating part (110) arranged to maintain a vibration and at least two anchor parts (120); wherein the resonating part (110) is released from the substrate (151) by said etching (335), wherein the anchor parts (120) are in contact with the substrate (151), and wherein the resonating part (110) is attached to two or more of said anchor parts (120).

Description

[0001] Tensile-strained Ill-nitride nano- and micromechanical resonators and methods for producing these resonators.

[0002] TECHNICAL FIELD

[0003] Micro-electromechanical systems, micromechanical resonators, nanomechanical resonators, Ill-nitride resonators, microfabrication, nanofabrication, lithography, resonant mass sensors, inertial sensors, and electromechanical signal processing systems.

[0004] BACKGROUND ART

[0005] Mechanical resonators on a nano- to micro-scale are key components for nanoelectromechanical systems (NEMS) and micro-electromechanical systems (MEMS). NEMS and MEMS devices find wide applications, including but not limited to biological and chemical sensors, such as resonant mass sensors, inertial sensors, and pressure sensors, and in electromechanical signal processing systems and quantum technologies. Nano- and micromechanical resonators are mechanically vibrating elements that allow for the resonant enhancement of mechanical energy at specific resonant modes of the mechanical structure they are made of. The resonant modes depend on the mass, shape and stiffness of the resonator. For many applications of nano- and micromechanical resonators it is important to maintain a long storage time of vibrational energy, which can be quantified by the mechanical quality factor. The mechanical quality factor, as well, determines the sensitivity of a mechanical resonator to an external perturbation or signal. Furthermore, it determines, amongst other quantities, the thermal noise the resonator experiences. In these cases, it is beneficial to have larger mechanical quality factors. One can increase the mechanical quality factor using thin films with a large aspect ratio, low defect density, and large tensile strain. A low defect density increases the intrinsic mechanical quality factor of the material and a large tensile strain in the film can be exploited for diluting mechanical dissipation, which also relies on a large aspect ratio of the mechanical resonator (its length to thickness ratio). The concept of dissipation dilution entails a large fraction of the elastic energy in the resonator mode being stored in the lossless nonlinear strain, which dilutes the energy loss associated with the bending of the mechanical resonator.

[0006] Soft-clamping, which shields the modes of interest from radiation loss at the substrate clamping points, and local strain-engineering techniques, which focus the stress in an area of the resonator that is subject to large bending, can dilute the mechanical dissipation further. In practice, soft clamping can be realized in various ways. For instance, the resonator can be soft clamped by patterning the mechanical resonator such that a phononic bandgap around the mechanical mode frequency of interest is formed. Alternatively, the mechanical resonator can be connected to the substrate with long narrow and branched tethers, which enhances the stress in the tethers and, thus, leads to a reduction of both radiation and bending losses.

[0007] There is a need for new solutions in geometry, materials and fabrication processes to create nanomechanical and micromechanical resonators with high mechanical quality factors.

[0008] SUMMARY

[0009] The invention relates to nano- and micromechanical resonators. Typically, the mechanical resonator needs to be interfaced to another system to measure and control its displacement. This can be implemented by functionalizing the resonator, for example, by adding additional conductive layers, which, however, may reduce its mechanical quality factor. Nano- and micromechanical resonators fabricated from piezoelectric materials would thereby enable the engineering of the interaction between mechanical and electrical degrees of freedom directly. This, in turn, does not require introducing additional materials and, thus, avoids a potential decrease of the mechanical quality factor. At the same time, the in-built functionality to interface mechanical with electrical degrees of freedom leads to new phenomena and opportunities for applications in mechanical sensing, mechanical energy storage and transduction, and in mechanical-based quantum technologies. A solution is to create high quality factor nano- and micromechanical resonators from crystalline tensile-strained thin films, which offer in-built functionality via the material itself, such as piezoelectricity.

[0010] One object of the invention is to provide Ill-nitride nanomechanical and micromechanical resonators with a high-Q.

[0011] This has in accordance with the present disclosure been achieved by means of a method for producing a mechanical resonator. The method comprises

[0012] - providing a crystalline substrate;

[0013] - growing a lll-N film on the substrate, wherein the grown lll-N film is tensile-strained;

[0014] - forming the resonator of said lll-N film grown on the substrate, wherein forming the resonator comprises applying a resist, performing lithography, and etching steps, and wherein the formed resonator comprises a resonating part arranged to maintain a vibration and at least two anchor parts; wherein the resonating part is released from the substrate by said etching, wherein the anchor parts are in contact with the substrate, and wherein the resonating part is attached to two or more of said anchor parts. This has the advantage of allowing for a high mechanical quality factor nano- and micromechanical resonator out of crystalline piezoelectric aluminium nitride at room temperature or lower temperatures, and high vacuum conditions. This further has the advantage of allowing for improved sensing and metrology, such as allowing for novel types of nano- or micromechanical resonators usable in atomic force microscopy.

[0015] In some embodiments, forming the resonator comprises applying a hard mask to the lll-N film.

[0016] In some embodiments, the grown lll-N film and the resonating part comprises aluminium nitride and / or InAIGaN.

[0017] This has the advantage of allowing nano- or micromechanical transducers for microwave to optical conversion exploiting the piezoelectricity of the resonator material. This further has the advantage of allowing for modulators, such as electronic control via piezoelectricity of nanomechanical motion, which then modulates light coupled to the nanomechanical system. The use of aluminium nitride further allows for possible biomedical applications due to the biocompatibility of the material. AIN and GaN are known for their wide bandgap, large thermal conductivity, high pyro- and piezoelectric coefficients, mechanical stiffness, and high thermal stability.

[0018] In some embodiments, wherein said resonator is a nanomechanical resonator or micromechanical resonator that operates at pressures below 10'5mbar at room temperature and / or temperatures below.

[0019] In some embodiments, the crystalline substrate is a {111}-oriented Si substrate and / or a {110}- oriented Si substrate, and the crystalline lll-N film is grown on the {111}-oriented Si substrate and / or on the {110}-oriented Si substrate, respectively.

[0020] This allows us to form tensile-strained mechanical resonators.

[0021] In some embodiments, the resonating part is attached to three or more anchor parts, and the resonating part comprises at least one junction, wherein each junctions leads to at least three anchor part(s) and / or other junctions.

[0022] In some embodiments, the resonator part comprises a central pad that is attached to three or more junctions, wherein, from the central pad to the anchor parts, each junction is branched off into two at successive junctions in a hierarchical structure.

[0023] This has the advantage of allowing to form hierarchically clamped triangline resonators with quality factors above 107at room or lower temperatures and at pressure lower than 10'5mbar. The present disclosure further relates to a mechanical resonator comprising

[0024] - a resonating part comprising a strained lll-N film, and

[0025] - at least two anchor parts attached to the resonating part; wherein the resonating part is arranged to maintain a vibration, and wherein the anchor parts are in contact with a substrate.

[0026] In some embodiments, the resonating part comprises tensile-strained aluminium nitride, and / or InAIGaN.

[0027] In some embodiments, the substrate is a Si substrate.

[0028] BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Fig. 1a-b shows schematically a micro- or nanomechanical resonator.

[0030] Fig. 2a-g depicts schematically the steps in producing a micro- or nanomechanical resonator.

[0031] Fig. 3 shows a method for producing high-Q mechanical resonators.

[0032] Fig. 4a-c depicts designs for high-Q micro- and nanomechanical resonators.

[0033] Fig. 5a-b shows line drawings of images of produced example AIN micro- and nanomechanical resonators.

[0034] DETAILED DESCRIPTION

[0035] Throughout the figures, the same reference numerals refer to the same parts, concepts, and / or structures. Consequently, what will be said regarding a reference numeral in one figure applies equally to the same reference numeral in other figures unless explicitly stated otherwise.

[0036] Terms and expressions

[0037] The term resonator relates to a device that exhibits resonator behaviour, i.e. , only close to the resonance frequency the device absorbs and stores energy. A mechanical resonator absorbs mechanical waves (phonons) close to the resonance frequency and stores mechanical energy.

[0038] The term resonating part relates to the part of the resonator arranged to maintain a vibration. Typically, the resonating part is the vibrating part of the resonator that oscillates at a specific frequency and is responsible for generating the resonant frequency of the resonator. The resonating part can take many forms, such as a beam, membrane, or interconnected combinations thereof, depending on the design of the resonator. The term membrane relates to a thin and wide structure. Herein, the term does not relate to a resonating part that covers the area between anchor parts.

[0039] The term anchor part relates to the only part of the resonator that rigidly connects the resonator to the substrate and thereby to the environment.

[0040] The term substrate relates to the base material upon which a device or structure is built. The surface of the silicon substrate is oriented along {111} and enables the epitaxial growth of wurtzite AIN or InGaAIN.

[0041] The term epitaxy relates to the deposition of material in which the deposited layers form one or more crystallographic domains with well-defined crystal lattice orientation with respect to the crystalline substrate.

[0042] The term crystalline substrate relates to a material that is used as a base for the epitaxy of a crystalline film that has a well-defined crystallographic orientation.

[0043] The term stress relates to the force that the deposited film is under. In case of tensile stress, the deposited film is stretched. The stress pulls the film out of the equilibrium, for example, the length of a beam increases in comparison to an unstressed beam. For compressive stress on the other hand the film compresses, for example, the length of a beam decreases in comparison with an unstressed beam. The term tensile-stressed and tensile-strained film relates to the film that has a tensile stress after the growth due to a lattice mismatch and a thermal mismatch between the substrate and film.

[0044] The expression “release from silicon substrate” relates to the removal of parts of the silicon substrate directly underneath the structure and subsequently the suspension of said structure.

[0045] The expression “arranged to maintain a vibration” relates to the fact that a mechanical resonator is formed, which can absorb mechanical excitations close to a specific frequency and store this mechanical energy over a long time, for example, maintain the vibration for a long duration.

[0046] The term quality factor, Q, relates to the dimensionless parameter that quantifies the resonance behaviour, which is defined as the ratio of the total energy in the resonator to the energy lost within a single cycle of its oscillation.

[0047] The expression “hierarchically clamped nanomechanical resonator” relates to a resonator, where the beams that clamp the resonator to the substrate branch of at successive junctions in a hierarchical fashion. For example, a resonator with six beams attached to the substrate at one end of the beams, wherein each pair of said beams are attached at the other end at a junction, and wherein from each of said three junctions a beam is attached at one end and the other end of said three beams meet at one central junction.

[0048] The expression “hierarchically clamped triangline” relates to a resonator that comprises a central pad in the centre of the resonating part structure that has a triangular shape and, that the three beams that clamp this pad to the substrate branch in a hierarchical fashion.

[0049] Fig. 1a-b shows schematically an example mechanical resonator 100. Fig. 1a shows a top view of the resonator 100. Fig. 1b shows a cross-sectional side view of the resonator 100, with the cross-section corresponding to the A-A line and the side-view corresponding to the eye symbol in Fig. 1a. The example resonator 100 is formed from a stack 150 comprising a substrate 151 and a strained lll-N film 152 grown on the substrate 151. The resonator 100 comprises a suspended resonating part 110 and two anchor parts 120. The resonating part 110 is separated from the substrate 151 by a gap 157, and is held in place by the anchor parts 120 which are in contact with the substrate 151. The example in Fig. 1a-b is an aluminium nitride beams resonator 100 grown on silicon {111} substrate 151. The resonating part 110 is shaped to maintain a vibration at the kHz to MHz range of frequencies, as indicated by arrows in Fig. 1b. It is to be understood that the design of the example resonator 100 is selected for readability. Typically, a micro- or nanomechanical resonator 100 may comprise various shapes of resonating parts 110 and multiple anchor parts 120 with varying degrees of interconnectedness within the resonating part 110. For example, a resonator 100 may comprise a resonating part 110 comprising of a central pad that is hierarchically clamped to the anchor parts 120 as shown in Fig. 4a-b, or comprise a resonating part 110 of variable width that is attached to two-anchor part 120 as shown in Fig. 4c.

[0050] Fig. 1a-b shows the example anchor parts 120 at a vertically protruding rectangular pillar of silicon 151. The example resonating part 110 is shaped like a beam connected to the square anchor parts 120. In Fig. 1b depicts the gap 157 between the suspended resonating part 110 and the substrate 151.

[0051] Typically, the anchor parts 120 comprises the lll-N film 152. In some examples, the anchor parts 120 comprise AIN, GaN, and / or InAIGaN film, on a Si substrate 151. In some examples, the resonating part 110 comprises AIN, GaN, and / or InAIGaN film. In some examples, the substrate 151 is a crystalline substrate. In some of these examples, the substrate 151 is a Si substrate.

[0052] It should be understood that the depicted width of the resonating part 110 compared to the anchor parts 120 was selected for readability. Typically, the footprint area or diameter of the resonating part 110 is significantly smaller than each anchor part 120. A difference in area of the resonating parts 110 and anchor parts 120 allows for the resonating part 110 to be released in a single isotropic etching step, by removing the underlying silicon below the resonating part 110 while the anchor parts 120 remain in direct contact with the substrate 151.

[0053] It is to be understood that the term footprint relates to the area of a future part 110,120 in direct contact with the substrate 151 prior to etching away the substrate 151. The footprint of a part 110,120 corresponds to said part’s projected area on to the substrate 151 from above, such as the shape of the parts 110,120 depicted in Fig. 1a.

[0054] In some examples, the resonator 100 is a micro- and / or nanomechanical resonator.

[0055] In some examples, the thickness of the resonating part 110 is in the range of 10 nm to 2000 nm. In some of these examples, the thickness of the resonating part 110 is in the range of 20- 1000 nm, 40-700 nm, 60-500 nm, or 100-300 nm.

[0056] In a preferred example, the resonating part 110 consists of aluminium nitride and is 290 nm thick. In some examples, the width of the resonating part 110 is between 200 nm and 60 microns, while the length is between 75 microns and 5 mm or longer. High-aspect ratio resonators 100 with high quality factor can be realized in various geometries. In some examples, the resonator 100 is configured for the frequency range 50 kHz to 5 MHz.

[0057] Typically, the thickness of the resonating part 110 corresponds to the thickness of the lll-N film 152 grown on the substrate 151. In some examples, the lll-N film 152 is grown on Si {111} 151. In some examples, the lll-N film 152 is grown on sapphire 151. In some examples, the high-quality single-crystal lll-N film 152 is grown utilizing metal organic chemical vapor deposition, MOCVD, epitaxial sputtering or molecular beam epitaxy, MBE.

[0058] In some examples, the resonator 100 is formed from a substrate 151 with an epitaxially grown lll-N film 152, whereby a strain is formed in the lll-N film 152. In some examples, the tensile stress of an epitaxially grown AIN film 152 on Si {111} 151 is reaching 1.5 GPa and the released AIN resonating part 110 has a tensile stress of 1 GPa.

[0059] The performance of a resonator 100 may be described by its mechanical quality factor, Q- factor. The value for Q may be defined as the ratio of the energy stored in the oscillating resonating part 110 to the energy dissipated per cycle. In some examples, the mechanical resonating part 110 is formed in 290 nm-thick AIN. In some examples, the resonator 100 has a Q-factor larger than 107at room temperature at a pressure below 10'5mbar. Another metric is the multiplication of the Q-factor with the mechanical frequency, the so-called Q*f-product. In some examples, the resonator 100 has a Q*f-product of larger than 1012Hz. In some examples, the resonating part 110 is a beam-type resonator attached to an anchor part 120 at each end. In some of these examples, the resonating part 110 is shaped as a onedimensional phononic crystal with a defect in the centre, as shown in Fig. 4c.

[0060] In some examples, the resonating part 110 comprises a junction branching to three or more attached anchor parts 120. In some of these examples the junction branches out to three attached anchor parts 120, and the angle between branches is 120°.

[0061] In some examples, the resonating part 110 is a hierarchically clamped nanomechanical resonator, wherein the resonating part 110 is held in place by at least three anchor parts 120. In some of these examples, the resonating part 110 is attached to at least four, at least five, at least six, at least eight, at least ten, at least twenty, at least fifty, and / or at least one hundred anchor parts 120.

[0062] In some examples, the resonating part 110 comprises triangline-shaped structures, wherein the resonating part 110 is held in place by three anchor parts 120. In some of these examples, hierarchically clamped triangline resonating part 110 comprises branching angles of 10° to 180°. In some of these examples, resonating part 110 comprises branching angles of 20° to 170°, 30° to 160°, 40° to 150°, 50° to 140°, 60° to 130°, 70° to 120°, and / or 120°. A triangline resonator provides a functional central pad area, typically at a central junction. In some of these examples, the resonating part 110 comprises a photonic crystal pattern on the central pad. This photonic crystal pattern facilitates the release of the central pad. And the photonic crystal pattern may be designed to modify the optical reflectivity of the AIN in the resonating part 110.

[0063] In some examples, the resonator comprises a resonating part 110 with a quality factor of at least 10 000 at room temperature at a pressure below 10'5mbar.

[0064] Fig. 2a-g depict schematically example steps in producing a micro- or nanomechanical resonator 100. The example production steps include an optional step of applying a hard mask 154, applying and exposing resist 155, performing reactive ion etching, removing hard mask 154 and resist 155, and chemically etching silicon 151 to release the resonating parts 110 from the silicon substrate 151 . The example steps in producing a micro- or nanomechanical resonator 100 in Fig. 2a-g may correspond to producing the example resonator 100 in Fig. 1a-b.

[0065] The example production of a resonator 100 starts with creating a stack comprising aluminium nitride 152, AIN, epitaxially grown on crystalline substrate 151 of Si {111}, as shown in Fig. 2a. The lattice and thermal mismatch between Si {111} 151 and AIN 152 at their interface 153 results in tensile strain in the grown AIN film 152. Fig. 2b shows the stack 150 with a hard mask 154 on the AIN layer 152. In some examples the hard mask 154 could be SiC>2, SisN^ SiC.

[0066] A layer of resist 155 has been coated on top of the hard mask 154. In some examples, the resist 155 is exposed to electron radiation in a pattern (not shown in Fig. 2b) corresponding to the region of silicon substrate 151 exposed in Fig. 1a. In some examples, the resist 155 comprises a photoresist.

[0067] In some examples, an adhesion promoter (not shown) is applied on top of the hard mask 154 prior to coating a layer of resist 155. The choice of adhesion promoter depends on the type of lithography. In some examples, the adhesion promoter comprises Ti-prime, MicroChemicals GmbH, for electron-beam lithography, diphenylsilanediol-derivatives and / or hexamethyldisilazane, HMDS, for optical lithography.

[0068] The exposed and developed pattern is first transferred into the hard mask 154. In some examples the SiC>2 hard mask 154 is etched by inductively coupled plasma - reactive ion etching, ICP-RIE, in CF4 / CHF3 mixture. Then the pattern is transferred into AIN film 152 by ICP-RIE etching with a Ch / Ar mixture, resulting in Fig. 2c. A cross-section view after ICP-RIE resembles the cross-section of Fig. 1b, however, the silicon material under the future resonating part 110 is still present. A top-down view of Fig. 2c has a pattern of removed AIN layer 152 material corresponding to the exposed substrate 151 in Fig. 1a.

[0069] Fig. 2d shows the resist 155 and hard mask 154 removed from the AIN surface 152.

[0070] Fig. 2e shows a cross-section corresponding to the line B-B in Fig. 2d, with the small crosssection of AIN 152’ is part of the future resonating part 110 before release.

[0071] Due to the smaller footprint of the resonating part 110 compared to the anchor part 120 isotropic silicon etch by XeF2 can be applied to remove the silicon material under the future resonating part 110 without releasing the anchor part 120 from the silicon substrate 151.

[0072] Fig. 2f shows the resonator 100 after removing silicon 151 to form a gap 157 between the resonating part 110 and the silicon substrate 151 , thus releasing the resonating part 110 from the silicon substrate 151 . The footprint area and / or diameter of the anchor parts 120 being significantly larger than the footprint of the resonating part 110 allows the resonating part 110 to be released while the anchor parts 120 stay in direct contact with the substrate 151.

[0073] Fig. 2g shows a cross section corresponding to the line B-B in Fig. 2f. Silicon 151 has been etched away to form a gap 157 between the resonating part 110 and the silicon substrate 151. The resulting resonator geometry in Fig. 2f-g corresponds to the geometry of the example resonator 100 in Fig. 1a-b. Fig. 3 shows an example method for producing high-Q mechanical resonators. The method 300 comprises

[0074] - providing 310 a crystalline substrate;

[0075] - growing 320 a lll-N film on the substrate, wherein the grown lll-N film is strained;

[0076] - forming 330 a resonator of said Ill-nitride film grown on the substrate, wherein forming the resonator comprises applying a resist 332, performing lithography 333, and an etching step 335 to release at least part of the resonator from the substrate, and wherein the formed resonator comprises a resonating part and at least two anchor parts; wherein the resonating part is released from the substrate by said etching 335 and the geometry of the released resonating part is arranged to maintain a vibration, wherein the anchor parts are in contact with the substrate, and wherein the resonating part is attached to two or more of said anchor parts.

[0077] In some examples, forming 330 the resonator comprises inductively coupled plasma etching, and / or cleaning (not shown).

[0078] In some examples, the provided substrate is a Si substrate.

[0079] In some examples, providing 310 a substrate comprises providing a Si {111} substrate, and growing 320 said lll-N film on the {111}-oriented Si substrate.

[0080] In some examples, growing 320 Ill-nitride film on the Si substrate is performed utilizing epitaxy.

[0081] In some examples, the grown lll-N film is an aluminium nitride film, AIN. In some examples, the lll-N film and / or the resonating part comprises of InAIGaN. In some examples, the lll-N film and / or the resonating part consist of InAIGaN.

[0082] In some examples, exposing resist 333 comprises exposing the resist to electromagnetic radiation and / or electron radiation.

[0083] In some examples, forming the resonator comprises applying 331 a hard mask. In some of these examples, said hard mask comprises SiO2, SisN^ and / or SiC. In some examples, applying 331 a hard mask comprises applying an adhesion promoter to hard mask, such as to improve adhesion between the hard mask and a resist.

[0084] In some examples, forming the resonator comprises removing the resist and / or the hard mask prior the release of the resonator.

[0085] In some examples, the release of the resonator is performed by XeF2 etching of Si substrate and / or by HF:H2O2 based mixtures for wet chemical etching of Si. In some examples, forming 330 the resonator comprises performing lift-off 334. In some of these examples, performing lift-off 334 results in applying one or more electrodes on and / or at the resonator. Typically, lift-off 334 is performed in a release step of forming 330 the resonator.

[0086] In some examples, said formed resonator is a nano- or micromechanical resonator.

[0087] In some examples, the formed resonator comprises a plurality of anchor parts that are attached to one resonating part.

[0088] Fig. 4a-c schematically shows different designs for high-quality factor micro- and nanomechanical resonators with varying geometries and positions for the resonating part 110 and the anchor parts 120. Fig. 4a shows a resonating part 110 attached to three anchor parts 120. Fig. 4b shows a resonating part 110 comprising a central pad attached to six anchor parts 120. Fig. 4c shows a resonating part 120 with varying width along its length that is attached to an anchor part 120 at each end.

[0089] Fig. 4a depicts an example resonator comprising one resonating part 110 attached to three anchor parts 120. The resonating part 110 comprises a junction 115 leading to each region of the resonating part 110 that attaches to an anchor part 120. The example resonating part 110 corresponds to three beams joining at the junction 115, wherein the angle between the beams is 120°. Typically, the regions of the resonating part 110 further away from the anchor parts 120 will be able to move more readily than the regions of the resonating part 110 closer to the anchor part attachments points.

[0090] In some examples, the angle between the beams is in the range of 60° to 180°. In some of these examples, the angle between the beams is in the range of 90° to 150°. Fig. 4b depicts an example resonator 100 comprising one resonating part 110 attached to six anchor parts 120. The resonating part 110 comprises three junction 115 and a central pad 112, wherein the central pad 112 is a central junction. Each junction 115 connects to two anchor parts 120 and the central pad 112. Compared to the junction 115 in Fig. 4a, the central pad 112 in Fig. 4b has a junction brunching junction 115 on each beam that attach the resonator to the anchor parts 120. Beams or beam-like structures form the connections between anchor parts 120, junctions 115 and any central pads 112. This has the advantage of allowing for a resonating part with a junction connected via beams to at least three anchor parts and / or other junctions, wherein the junction and beams functions as high quality factor nano- and micromechanical resonator.

[0091] In some examples, the resonating part 110 comprises a junction connected via beams to at least three anchor parts and / or other junctions. In some of these examples, the resonating part 110 comprises at least four junctions each connected to at least three anchor parts and / or other junctions.

[0092] In some examples, the resonating part 110 comprising a membrane shaped a central pad 112 and a plurality of interconnected beams, wherein the beams extend from the central pad 112 and branch into two beams to form junctions 115. Typically, the beams extending from the junctions furthest from the central pad 112 attach to the anchor parts 120.

[0093] The example resonator 100 in Fig. 4b is a hierarchically-clamped triangline. This example shows a high-aspect ratio resonator 100, which can be produced in a highly strained lll-N film. The hierarchically clamped triangline achieves lower bending and less energy loss at the clamping points. As a result, a quality factor above 107can be achieved at room temperature and at a pressure of lower than 10'5mbar. Additionally, the hierarchical clamping of the resonator allows reducing the footprint of the 4.7 mm-long beam on the chip.

[0094] In some examples, the resonating part 110 comprises a junction 115 leading to at least three anchor part(s) 120 and / or other junctions 115. In some of these examples the resonator comprises at least six anchor parts 120, and the resonating part 110 comprises at least three junctions 115, wherein each junction 115 leads to at least three anchor part(s) 120 and / or other junctions 115. It is to be understood that the central pad is considered a junction for the expression “each junction 115 leading to at least three anchor part(s) 120 and / or other junctions 115”.

[0095] In some example, the junction 115 is the intersection of connected beams or beam-like structures. In some examples, the junction 115 comprises a pad 112 arranged to, upon resonating, be detected or to be interact with, such as reflecting electromagnetic radiation. The pad 112 shown in fig. 4b is considered a type of junction 115 or being part of a junction 115, as it connects beams.

[0096] Fig. 4c depicts a top-down view of an example of a phononic crystal on a strained beam, which allows to localize a defect mode in the centre of the beam. Such a phononic crystal nanobeam achieves simultaneously high quality factor and high mechanical frequency of defect modes. The utilization of shaping the phononic crystal pattern as ellipses prevents the highly strained crystalline material from breaking upon release. Fig 5b is an image of a resonator with a resonating part with a design corresponding to the depiction in Fig. 4c.

[0097] Fig. 5a-b shows line drawings of examples of produced AIN micro- and nanomechanical resonators. Fig. 5a is a line drawing of an optical image of a hierarchically clamped triangline resonator 100. Fig. 5a depicts a hierarchically clamped triangline resonator part 110 corresponding to a concept of Fig. 4b, but with six junctions 115 separating the central pad 112 and the anchor points 120 instead of one junction 115, such that the resonator has 192 anchor parts 120 instead of six anchor parts 120.

[0098] Fig. 5b is a line drawing of a scanning electron microscope image of a phononic crystal nanobeam array. The beam in Fig. 5b corresponds to the resonating part 110 in Fig. 1a-b, however, the width of the beam varies in Fig. 5b, as shown in Fig 4c, while the beam width is depicted as substantially constant in Fig. 1a.

[0099] The fabricated resonators (devices under test, DUT) are characterized for the mechanical resonance frequency and mechanical quality factor. To this end, the DUT is placed inside a vacuum chamber, where the pressure can be regulated between atmospheric pressure and a pressure of 10'6mbar. The mechanical displacement of the DUT is measured using optical interferometry.

Claims

CLAIMS1 . A method for producing a mechanical resonator (100), the method (300) comprises- providing (310) a crystalline substrate (151 );- growing (320) a lll-N film (152) on the substrate (151 ), wherein the grown lll-N film (152) is tensile-strained;- forming (330) the resonator (100) of said lll-N film (152) grown on the substrate (151 ), wherein forming the resonator (100) comprises applying (332) a resist (155), performing lithography (333), and etching (335) steps, and wherein the formed resonator (100) comprises a resonating part (110) arranged to maintain a vibration and at least two anchor parts (120); wherein the resonating part (110) is released from the substrate (151 ) by said etching (335), wherein the anchor parts (120) are in contact with the substrate (151 ), and wherein the resonating part (110) is attached to two or more of said anchor parts (120).

2. The method according to claim 1 , wherein forming the resonator (100) comprises applying (331 ) a hard mask (154) to the lll-N film (152).

3. The method according to claim 1 or 2, wherein the grown lll-N film (152) and the resonating part (110) comprises aluminium nitride and / or InAIGaN.

4. The method according to any preceding claim, wherein said resonator (100) is a nanomechanical resonator or micromechanical resonator that operates at pressures below 10’5mbar at room temperature and / or temperatures below.

5. The method according to any preceding claim, wherein the crystalline substrate (151 ) is a {111 }-oriented Si substrate (151 ) and / or a {110}-oriented Si substrate (151 ), and the crystalline lll-N film (152) is grown on said Si substrate (151 ).

6. The method according to any preceding claim, wherein the resonating part (110) is attached to three or more anchor parts (120), and the resonating part (110) comprises at least one junction (115), wherein each junction (115) leads to at least three anchor part(s) (120) and / or other junctions (115).

7. The method according to claim 6, wherein the resonator part (110) comprises a central pad (112) that is attached to three or more junctions (115), wherein, from thecentral pad (112) to the anchor parts (120), each junction is branched off into two at successive junctions (115) in a hierarchical structure.

8. A mechanical resonator (100) comprising- a resonating part (110) comprising a strained lll-N film (152), and- at least two anchor parts (120) attached to the resonating part (110); wherein the resonating part (110) is arranged to maintain a vibration, and wherein the anchor parts (120) are in contact with a substrate (151 ).

9. The resonator according to claim 8, wherein the resonating part (110) comprises tensile-strained aluminium nitride, and / or InAIGaN.

10. The resonator according to claim 8 or 9, wherein the substrate (151 ) is a Si substrate(151 ).

11. The resonator according to claim 8 to 10, wherein said resonators (100) is a nanomechanical resonator and / or a micromechanical resonator.

12. The resonator according to claim 8 to 11 , wherein the resonating part (110) is attached to at least three anchor parts (120); and- wherein the resonating part (110) comprises a junction (115) leading to at least three anchor part(s) (120) and / or other junctions (115).

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