PIEZOELECTRIC DEVICE, ULTRASONIC TRANSDUCER, MICROELECTROMECHANICAL DEVICE AND METHOD FOR FORMING A PIEZOELECTRIC DEVICE.

Abstract

A piezoelectric device is provided. The piezoelectric device includes a piezoelectric layer comprising a first surface and a second surface that oppose each other. The piezoelectric device further includes a first electrode formed on the first surface and a second electrode formed on the second surface. The piezoelectric device includes a dielectric material surrounding the piezoelectric layer. Additionally, the piezoelectric device includes a first interconnection electrically coupled to the first electrode and a second interconnection electrically coupled to the second electrode. The first electrode is disposed between the piezoelectric layer and each of the first interconnection and the second interconnection.The first interconnection and the second interconnection are arranged remote from the first electrode.

Description

Area

[0001] The present disclosure relates to piezoelectric structures. More specifically, examples of the present disclosure relate to a piezoelectric device, an ultrasonic transducer, a microelectromechanical device, and a method for forming a piezoelectric device. background

[0002] Thin-film piezoceramics are used in a wide variety of microelectromechanical systems (MEMS) such as resonators, actuators, ultrasonic transducers, and sensors. Highly doped piezoceramics are gaining ground due to their improved piezoelectric modulus. 33More attention is being paid to the doping of piezoceramics. The doping of piezoceramics causes problems during process integration. Typical dopants, for example, are highly resistant to dry etching and exhibit poor selectivity toward surrounding layers in a layer stack. On the other hand, typical dopants leave residues on the surface during wet etching. Furthermore, creepage paths along the surfaces and sidewalls of the piezoceramic can lead to device failure in conventional architectures.

[0003] Therefore, there may be a need for improved piezoelectric structures. Summary

[0004] This need is met by the subject matter of the independent claims. Advantageous embodiments are addressed by the dependent claims.

[0005] According to a first aspect, the present disclosure provides a piezoelectric device. The piezoelectric device includes a piezoelectric layer comprising a first surface and a second surface that oppose each other. Further, the piezoelectric device includes a first electrode formed on the first surface and a second electrode formed on the second surface. The piezoelectric device includes a dielectric material enclosing the piezoelectric layer. Additionally, the piezoelectric device includes a first interconnection electrically coupled to the first electrode and a second interconnection electrically coupled to the second electrode. The first electrode is disposed between the piezoelectric layer and each of the first interconnection and the second interconnection.The first interconnection and the second interconnection are arranged remote from the first electrode.

[0006] According to a second aspect, the present disclosure provides an ultrasonic transducer comprising the piezoelectric device according to the first aspect. A recess is formed in the dielectric material such that a portion of the dielectric material forms a membrane embedding the piezoelectric layer.

[0007] According to a third aspect, the present disclosure provides a microelectromechanical device comprising a micromirror and a spring structure supporting the micromirror. The spring structure comprises at least one piezoelectric device according to the first aspect.

[0008] According to a fourth aspect, the present disclosure provides a method of forming a piezoelectric device. The method includes forming a piezoelectric layer comprising a first surface and a second surface that oppose each other. The method further includes forming a first electrode on the first surface and forming a second electrode on the second surface. The method includes forming a dielectric material enclosing the piezoelectric layer. Additionally, the method includes forming a first interconnect electrically coupled to the first electrode and forming a second interconnect electrically coupled to the second electrode. The first electrode is disposed between the piezoelectric layer and each of the first interconnect and the second interconnect.The first interconnection and the second interconnection are arranged remote from the first electrode.

[0009] According to the proposed technique, the contacts to the electrodes can be formed without exposing the piezoelectric layer to any etching agents. Furthermore, the sidewalls and surfaces of the piezoelectric layer are insulated by dielectric material to prevent or at least minimize electrical leakage paths. Short description of the characters

[0010] Some examples of devices and / or methods are described below by way of example only and with reference to the accompanying figures, in which Fig. Figure 1 illustrates an example of a piezoelectric device; Fig. Figure 2 illustrates an example of an ultrasonic transducer; Fig. 3 illustrates an example of a microelectromechanical device; Fig. 4 illustrates an example of a method for forming a piezoelectric device; and Fig. 5 illustrates an exemplary piezoelectric device during various steps of its fabrication. Detailed description

[0011] Some examples will now be described in more detail with reference to the accompanying figures. However, other possible examples are not limited to the features of these embodiments described in detail. Other examples may include modifications of the features, as well as equivalents and alternatives to the features. Furthermore, the terminology used herein to describe particular examples should not be limiting of other possible examples.

[0012] Throughout the description of the figures, like or similar reference numerals refer to like or similar elements and / or features, which may be implemented identically or in a modified form while providing the same or a similar function. The thickness of lines, layers, and / or regions in the figures may also be exaggerated for clarity.

[0013] When two elements A and B are combined using "or," this should be understood to disclose all possible combinations, i.e., only A, only B, and both A and B, unless explicitly defined otherwise in the individual case. Alternative wording for the same combinations may be "at least one of A and B" or "A and / or B." This applies equally to combinations of more than two elements.

[0014] When a singular form, such as "a," "an," and "the," is used, and the use of only a single element is neither explicitly nor implicitly defined as mandatory, further examples may also use multiple elements to implement the same functionality. When a functionality is described below as being implemented using multiple elements, further examples may implement the same functionality using a single element or a single processing entity. It is further understood that the terms "include," "including," "comprise," and / or "comprising," when used, describe the presence of the specified features, integers, steps, operations, processes, elements, components, and / or a group thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, processes, elements, components, and / or a group thereof.

[0015] Fig. 1 illustrates a cross-sectional view of an exemplary piezoelectric device 100.

[0016] The piezoelectric device 100 comprises a piezoelectric layer 110. The piezoelectric layer 110 comprises a first surface 111 and a second surface 112 that are opposite to each other. The first surface 111 and the second surface 112 follow each other along a thickness direction of the piezoelectric layer 110 (and the piezoelectric device 100). The first surface 111 and the second surface 112 may be (substantially) parallel to each other, as shown in Fig. 1. The first surface 111 and the second surface 112 may be (substantially) planar (flat) surfaces. The piezoelectric layer 110 further includes sidewalls 113 and 114 that face each other. The sidewalls 113 and 114 laterally bound the piezoelectric layer 110. The sidewalls 113 and 114 connect the first surface 111 and the second surface 112. The first surface 111 and the second surface 112 may have any suitable (target) dimensions. Likewise, the thickness of the piezoelectric layer 110 (i.e., the vertical distance between the first surface 111 and the second surface 112) is generally not limited. For example, the piezoelectric layer 110 may be a thin film. In other words, the thickness of the piezoelectric layer 110 may be at least 0.1 µm, 0.5 µm, or 1 µm. The thickness of the piezoelectric layer 110 may be at most 1 µm, 3 µm, 5 µm, or 10 µm.

[0017] The piezoelectric layer 110 comprises a piezoelectric material, such as one or more of aluminum nitride (AlN), quartz (SiO2), lead zirconate titanate (PZT), polyvinylidene fluoride (PVDF), barium titanate (BaTiO3), lithium niobate (LiNbO3), and gallium orthophosphate (GaPO4). However, it should be noted that the present disclosure is not limited to the aforementioned materials. Other piezoelectric materials may be used instead or in addition. According to examples, the piezoelectric layer 110 may comprise a doped piezoelectric material or may be a doped piezoelectric material. The piezoelectric material may be lightly or heavily doped. For example, an atomic ratio of dopants in the doped piezoelectric material may be at least 1%, 5%, 10%, 15%, 20%, 25%, or 30%.The atomic ratio of dopants in a doped piezoelectric material refers to the ratio of atoms of the dopant element(s) to the atoms of the primary constituent(s) of the piezoelectric material. For a highly doped piezoelectric material, the atomic ratio of dopants in the doped piezoelectric material can be up to 50%, 55%, 60%, 65%, 70%, or 75%. Various dopants (dopant materials), such as one or more of scandium (Sc), chromium (Cr), titanium (Ti), hafnium (Hf), tantalum (Ta), molybdenum (Mo), niobium (Nb), yttrium (Y), and zirconium (Zr), can be used. However, it should be noted that the present disclosure is not limited to the aforementioned materials. Other dopants may be used instead or in addition.In particular, the doped piezoelectric material may be Sc-doped AlN with an atomic ratio of Sc dopants in the doped AlN of at least 20% and at most 60%.

[0018] Further, the piezoelectric device 100 includes a first electrode 120 (direct) formed on the first surface 111 of the piezoelectric layer 110, and a second electrode 130 (direct) formed on the second surface 112 of the piezoelectric layer 110. Each of the first electrode 120 and the second electrode 130 is formed from one or more electrically conductive materials, such as one or more metals. For example, the first electrode 120 and the second electrode 130 may comprise one or more of tungsten (W), copper (Cu), titanium (Ti), titanium nitride (TiN), aluminum (Al), and platinum (Pt). However, it should be noted that the present disclosure is not limited to the aforementioned materials. Other electrically conductive materials may be used instead or in addition.The first electrode 120 and the second electrode 130 may be made of the same material(s) or different materials. The first electrode 120 may partially cover the first surface 111, as shown in FIG. Fig. 1. In alternative examples, the first electrode 120 may completely cover the first surface 111. The second electrode 130 may completely cover the second surface 112, as shown in Fig. 1. In alternative examples, the second electrode 130 may partially cover the second surface 112. The thicknesses of the first electrode 120 and the second electrode 130 are generally not limited. For example, the respective thickness of the first electrode 120 and the second electrode 130 may be at least 1 nm, 10 nm, 20 nm, 50 nm, or 100 nm. On the other hand, the respective thickness of the first electrode 120 and the second electrode 130 may be at most 500 nm, 250 nm, 100 nm, or 50 nm. The first electrode 120 and the second electrode 130 may have the same thickness or different thicknesses. The first electrode 120 and the second electrode 130 are provided for electrically contacting the piezoelectric layer 110. The first electrode 120 and the second electrode 130 make it possible to apply an electrical potential (ieA voltage is applied to the piezoelectric layer 110 for controlled (and reversible) deformation of the piezoelectric layer 110 due to the piezoelectric effect. Similarly, the first electrode 120 and the second electrode 130 enable the measurement of an electrical potential (i.e., a voltage) caused in the piezoelectric layer 110 by a deformation of the piezoelectric layer 110 due to the piezoelectric effect.

[0019] The piezoelectric device 100 includes a dielectric material 140 enclosing the piezoelectric layer 110. The dielectric material 140 further encloses the first electrode 120 and the second electrode 130. In other words, the piezoelectric layer 110, as well as the first electrode 120 and the second electrode 130, are completely embedded in the dielectric material 140. For example, the dielectric material 140 may be one or more of silicon dioxide (SiO2) and silicon nitride (Si3N4). However, it should be noted that the present disclosure is not limited to the aforementioned materials. Other dielectric materials may be used instead or in addition. The dielectric material 140 provides electrical insulation for the piezoelectric layer 110, as well as the first electrode 120 and the second electrode 130.

[0020] In addition, the piezoelectric device 100 comprises a first interconnect 150 electrically coupled to the first electrode 120, and a second interconnect 160 electrically coupled to the second electrode 130. The first interconnect 150 and the second interconnect 160 make it possible to electrically contact the electrodes 120 and 130, and thus the piezoelectric layer 110, from the outside (i.e., from outside the piezoelectric device 100). In the example of Fig. 1, the first interconnect 150 and the second interconnect 160 are both arranged below the stack formed by the piezoelectric layer 110 and the electrodes 120 and 130. More generally, the first interconnect 150 and the second interconnect 160 are both arranged on the same side relative to the stack formed by the piezoelectric layer 110 and the electrodes 120 and 130. In other words, the first electrode 120 is arranged between the piezoelectric layer 110 and each of the first interconnect 150 and the second interconnect 160. The first interconnect 150 and the second interconnect 160 are arranged away (at a distance) from the first electrode 120 (along the thickness direction of the piezoelectric device 100).The vertical distance of the first interconnect 150 to the first electrode 120 is smaller than the vertical distance of the first interconnect 150 to the second electrode 130. Similarly, the vertical distance of the second interconnect 160 to the first electrode 120 is smaller than the vertical distance of the second interconnect 160 to the second electrode 130.

[0021] The thicknesses of the first interconnect 150 and the second interconnect 160 are generally not limited. For example, the respective thickness of the first interconnect 150 and the second interconnect 160 may be at least 10 nm, 20 nm, 50 nm, 100 nm, 250 nm, or 500 nm. On the other hand, the respective thickness of the first electrode 120 and the second electrode 130 may be at most 3 µm, 2 µm, 1.5 µm, 1 µm, 750 nm, 500 nm, 250 nm, 100 nm, or 50 nm. The thickness of the first electrode 120 and the second electrode 130 may be selected to enable or facilitate wire bonding or similar post-assembly processes.

[0022] The first interconnect 150 and the second interconnect 160 are also arranged in the dielectric material 140. The dielectric material 140 partially encloses both the first interconnect 150 and the second interconnect 160. The first interconnect 150 is accessible from the outside via a first opening (recess) 170 formed in the dielectric material 140. The second interconnect 160 is accessible from the outside via a second opening 175 formed in the dielectric material 140. The first opening 170 extends from a surface 141 of the dielectric material 140 to the first interconnect 150. The second opening extends from the surface 141 of the dielectric material 140 to the second interconnect 160. In the example of Fig. 1, the surface 141 of the dielectric material 140 is the top surface of the dielectric material 140, so that the surface 141 of the dielectric material 140 and the interconnects 150 and 160 are arranged on opposite sides of the stack formed by the piezoelectric layer 110 and the electrodes 120 and 130. In other words, the second electrode 130 is arranged between the second surface 112 of the piezoelectric layer 110 and the surface 141 of the dielectric material 140. The first opening 170 and the second opening 175 extend laterally offset from the dielectric layer 140 and along the thickness direction of the piezoelectric device 100.

[0023] In the example of Fig. 1, the first opening 170 and the second opening 175 both taper from the surface 141 of the dielectric material 140 to the respective interconnects 150 and 160. However, it should be noted that the present disclosure is limited thereto. Other geometries may instead be used for the first opening 170 and the second opening 175.

[0024] As described above, the first interconnect 150 is electrically coupled to the first electrode 120. A first electrically conductive path 180 is formed in the dielectric material 140 between the first electrode 120 and the first interconnect 150 for electrically coupling the first interconnect 150 to the first electrode 120. Similarly, a second electrically conductive path 185 is formed in the dielectric material 140 between the second electrode 130 and the second interconnect 160 for electrically coupling the second interconnect 160 to the second electrode 130. The dielectric material 140 separates, ie, electrically insulates, the piezoelectric layer 110 from the electrically conductive paths 180 and 185. Each of the first electrically conductive path 180 and the second electrically conductive path 185 is formed from one or more electrically conductive materials, such as one or more metals.For example, the first electrically conductive path 180 and the second electrically conductive path 185 may comprise one or more of Al, W, Cu, Pt, or doped polysilicon (polycrystalline silicon). However, it should be noted that the present disclosure is not limited to the aforementioned materials. Other electrically conductive materials may be used instead or in addition. The geometries of the first electrically conductive path 180 and the second electrically conductive path 185 shown in FIG. Fig. 1 are for illustrative purposes only. In other examples, the first electrically conductive path 180 and the second electrically conductive path 185 may have different geometries (routes in the dielectric material 140).

[0025] The structures for contacting the electrodes 120 and 130, i.e., the interconnections 150 and 160 and the electrically conductive paths 180 and 185, can be formed without exposing the piezoelectric layer 110 to any etching agents. This is particularly advantageous in the case where the piezoelectric layer 110 comprises a highly doped piezoelectric material, since typical dopants are highly resistant to dry etching and exhibit poor selectivity towards surrounding layers in a layer stack. Furthermore, typical dopants leave residues on the surface in the case of wet etching. Furthermore, the sidewalls 113 and 114 as well as the surfaces 111 and 112 of the piezoelectric layer 110 are electrically insulated by the dielectric material 140 to avoid or at least minimize electrical leakage paths. Accordingly, failure of the piezoelectric device 100 can be avoided.

[0026] The piezoelectric device 100 can be used in various applications due to its advantageous properties. Two exemplary applications are described below with reference to Fig. 2 and Fig. 3. However, it should be noted that the piezoelectric device 100 is not limited to the exemplary applications described below.

[0027] Fig. Figure 2 illustrates a cross-sectional view of an exemplary ultrasonic transducer 200. Ultrasonic transducer 200 may be a microelectromechanical device. In particular, ultrasonic transducer 200 may be a piezoelectric micromachined ultrasonic transducer (PMUT). Ultrasonic transducer 200 includes piezoelectric device 100 as described above. Piezoelectric device 100 is formed on a support substrate 290, such as a silicon substrate.

[0028] A recess (opening) 295 is formed in the dielectric material 140 such that a portion of the dielectric material 140 forms a diaphragm 205 that embeds the piezoelectric layer 110 (together with the electrodes 120 and 130). In particular, the portion of the dielectric material 140 above the recess 295 forms the diaphragm 205. The recess 295 is formed beneath the piezoelectric layer 110 and the first electrode 120. In other words, the recess 295 is formed away from the first electrode 120. The first electrode 120 is disposed between the piezoelectric layer 110 and the recess 295. The recess 295 is formed laterally between the first interconnect 150 and the second interconnect 160. The recess 295 may be filled with air or any other suitable gas. Alternatively, the recess 295 may maintain a vacuum.

[0029] As described above for the piezoelectric device 100, the first interconnect 150 and the second interconnect 160 enable the electrodes 120 and 130, and thus the piezoelectric layer 110, to be electrically contacted from the outside (i.e., from outside the piezoelectric device 100). Accordingly, the piezoelectric layer 110 can be used to generate ultrasonic waves based on an externally provided drive signal and / or used to generate a measurement signal based on received (measured) ultrasonic waves. For example, the piezoelectric device 110 can be configured to deform the diaphragm 205 based on an electrical signal received at the first and second interconnects 150, 160 to emit ultrasonic waves.Alternatively or additionally, the piezoelectric device 110 may be configured to output a respective measurement signal at the first and second interconnections 150, 160 based on a deformation of the membrane 205 by received ultrasonic waves.

[0030] Ultrasonic transducer 200 may be configured to emit and / or detect ultrasonic waves at least between 20 kHz and 1 GHz and / or any subrange thereof. In particular, ultrasonic transducer 200 may be configured to emit and / or detect low-frequency ultrasonic waves (e.g., at approximately 50 kHz) for airborne applications, such as proximity detection (e.g., for vehicle parking sensors) or high-frequency ultrasonic waves (e.g., at approximately 2 to 10 MHz) for diagnostic applications (e.g., medical ultrasound).

[0031] Fig. 3 illustrates a cross-sectional view of an exemplary microelectromechanical device 300.

[0032] The microelectromechanical device 300 includes a micromirror 305. The dimensions of the micromirror 305 may, for example, be on the order of micrometers. A spring structure 310 of the microelectromechanical device 300 supports the micromirror 305. The spring structure 310 includes a freestanding actuator region and a contact region of the lower electrode (first electrode), as shown in Fig. 1. The micromirror 305 is movable relative to the rest of the microelectromechanical device 300 via the spring structure 310. As shown in Fig. 3, the spring structure 310 comprises a piezoelectric device according to the proposed technique.

[0033] Optionally, the spring structure 310 may comprise a plurality of piezoelectric devices according to the proposed technique.

[0034] As described above for the piezoelectric device 100, the first interconnect 150 and the second interconnect 160 enable the electrodes 120 and 130, and thus the piezoelectric layer 110, to be electrically contacted externally (i.e., from outside the piezoelectric device 100). Accordingly, the piezoelectric layer 110 can be used to move the micromirror 305 based on an externally provided drive signal and / or to generate a measurement signal based on a movement and / or position of the micromirror 305 (since the movement / position of the micromirror 305 causes a deformation of the spring structure 310 that is measurable via the piezoelectric layer 110).For example, the piezoelectric device 110 may be configured to deform the spring structure 310 based on an electrical signal received at the first and second interconnects 150, 160 to deflect the micromirror 305. Alternatively or additionally, the piezoelectric device 110 may be configured to output a respective measurement signal at the first and second interconnects 150, 160 based on a deflection of the micromirror 305.

[0035] The microelectromechanical device 300 includes a support substrate 390, such as a silicon substrate, for supporting the remaining elements of the microelectromechanical device 300. One or more layers or elements, such as the buried oxide layer 395, may additionally be formed in the support substrate 390.

[0036] The above description focused on the proposed piezoelectric device and its applications. The following sections of the description focus on the fabrication of the proposed piezoelectric device.

[0037] Fig. 4 illustrates a flow diagram of an exemplary method 400 for forming a piezoelectric device.

[0038] The method 400 includes forming 402 a piezoelectric layer comprising a first surface and a second surface that oppose each other. For example, forming 402 the piezoelectric layer may include depositing a doped piezoelectric material. The atomic ratio of dopants in the doped piezoelectric material may be at least 20% for highly doped piezoelectric materials—as described above for the piezoelectric device 100. Further, the method 400 includes forming 404 a first electrode on the first surface and forming 406 a second electrode on the second surface. The method 400 includes forming 408 a dielectric material enclosing the piezoelectric layer.Additionally, method 400 includes forming 410 a first interconnect electrically coupled to the first electrode and forming 412 a second interconnect electrically coupled to the second electrode. The first electrode is disposed between the piezoelectric layer and each of the first interconnect and the second interconnect. The first interconnect and the second interconnect are disposed remote from the first electrode.

[0039] The method 400 makes it possible to provide a piezoelectric device as described above. Further details and aspects of the method 400 are explained in connection with the proposed technique or one or more examples described above or below. The method 400 may include one or more additional optional features corresponding to one or more aspects of the proposed technique or one or more examples described above or below.

[0040] For example, the method 400 may further include forming 414 a first electrically conductive path in the dielectric material between the first electrode and the first interconnect for electrically coupling the first interconnect to the first electrode. Similarly, the method 400 may further include forming 416 a second electrically conductive path in the dielectric material between the second electrode and the second interconnect for electrically coupling the second interconnect to the second electrode. Forming the first and second electrically conductive paths in the dielectric material enables the first and second interconnects to be coupled to the respective ones of the first electrode and the second electrode.

[0041] Alternatively or additionally, the method 400 may further comprise forming 418 a first opening in the dielectric material. The first opening extends from a surface of the dielectric material to the first interconnect. Similarly, the method 400 may further comprise forming 420 a second opening in the dielectric material. The second opening extends from the surface of the dielectric material to the second interconnect. The second electrode is arranged between the second surface of the piezoelectric layer and the surface of the dielectric material—as described above for the piezoelectric device 100. The first and second openings allow external access to the first and second interconnects to electrically contact the piezoelectric layer.

[0042] Further details of the method 400 will become apparent from the following description of Fig. 5, which illustrates the piezoelectric device 100 during various steps of its manufacture.

[0043] Partial image (a) of Fig. 5 illustrates that first, a layer of the dielectric material 140 (e.g., SiO2 or Si3N4) is deposited on a semiconductor substrate 500 (e.g., a silicon substrate).

[0044] Partial image (b) illustrates that the first interconnect 150 and the second interconnect 160 are subsequently formed on the layer of dielectric material 140. For example, a material for the first interconnect 150 and the second interconnect 160 may be deposited on the layer of dielectric material 140, a photosensitive chemical (such as a photoresist) may be applied to the material, and patterned according to the desired geometry of the first interconnect 150 and the second interconnect 160 using photolithography. Unwanted portions of the material are removed by etching according to the photolithographic patterning to form the first interconnect 150 and the second interconnect 160. Residues of the material and the photosensitive chemical may subsequently be removed in a cleaning process.

[0045] Then, as illustrated in sub-image (c), more of the dielectric material 140 is deposited. The surface of the dielectric material 140 is planarized by chemical mechanical polishing (CMP).

[0046] An opening (recess) 510 is etched into the dielectric material 140 for the first electrically conductive path 180 between the first electrode 120 and the first interconnect 150 (see partial image (d)). The opening 510 is filled with electrically conductive material to form a via as the first electrically conductive path 180 (see partial image (e)). As illustrated in partial image (f), the first electrode 120 is subsequently formed on the planar surface of the dielectric material 140 by depositing and patterning appropriate electrically conductive material, such as metal(s).

[0047] Then, the material for the piezoelectric layer 110 is deposited, as illustrated in sub-image (g). For example, a thin film may be deposited for the piezoelectric layer 110. In particular, the material deposited for the piezoelectric layer 110 may comprise (e.g., highly) doped piezoelectric material, such as Sc-doped AlN. Subsequently, the second electrode 130 is formed on the piezoelectric layer 110 (see sub-image (h)). The second electrode 130 may be formed analogously to the first electrode 120. After forming the second electrode 130, the material for the piezoelectric layer 110 is etched to obtain the desired geometry of the piezoelectric layer 110 (see sub-image (i)). Dry etching and / or wet etching processes may be used to remove the unwanted portions of the deposited material for the piezoelectric layer 110.The unwanted parts of the material for the piezoelectric layer 110 can be removed, for example, by etching according to a photolithographic pattern applied to the material for the piezoelectric layer 110 (and the second electrode 130) to form the piezoelectric layer 110.

[0048] Then, as illustrated in subimage (j), more of the dielectric material 140 is deposited. The surface of the dielectric material 140 is planarized by CMP.

[0049] Openings (recesses) 520 and 530, which extend to the second electrode 130 and the second interconnect 160, are etched into the dielectric material 140 for the second electrically conductive path 185 between the second electrode 130 and the second interconnect 160 (see sub-images (k) and (l)). When forming the openings 520 and 530, the dielectric material 140 is used as an etch stop, preventing the etch from reaching the piezoelectric layer 110 at the cost of some loss of dielectric material. The openings 520 and 530 are filled with electrically conductive material (see sub-image (m)) to form vias. Further electrically conductive material connecting the vias is deposited on the dielectric material 140 to form the second electrically conductive path 185 (see sub-image (n)).The structuring of the electrically conductive material connecting the vias can be carried out analogously to the formation of the first interconnect 150 and the second interconnect 160.

[0050] Then, as illustrated in sub-image (o), more of the dielectric material 140 is deposited. The surface of the dielectric material 140 is planarized by CMP.

[0051] Finally, openings 170 and 175 for accessing the first interconnect 150 and the second interconnect 160 are formed by etching a portion of the dielectric material 140. Accordingly, the first interconnect 150 and the second interconnect 160 can be electrically connected via bond wires, etc.

[0052] It should be noted that the process flow for producing the above-mentioned with reference to Fig.The piezoelectric device 100 described in Figure 5 is merely an example. Other or different process steps may be used to manufacture the piezoelectric device 100 in alternative examples.

[0053] The examples described herein can be summarized as follows: One example (e.g., Example 1) relates to a piezoelectric device comprising a piezoelectric layer comprising a first surface and a second surface opposite each other, a first electrode formed on the first surface, a second electrode formed on the second surface, a dielectric material enclosing the piezoelectric layer, a first interconnect electrically coupled to the first electrode, and a second interconnect electrically coupled to the second electrode, wherein the first electrode is disposed between the piezoelectric layer and each of the first interconnect and the second interconnect, and wherein the first interconnect and the second interconnect are disposed remote from the first electrode.

[0054] Another example (e.g., Example 2) refers to a previous example (e.g., Example 1) or to any other example, further comprising that the piezoelectric layer is a thin film.

[0055] Another example (e.g., Example 3) relates to a previous example (e.g., one of Examples 1 or 2) or to any other example, further comprising that a thickness of the piezoelectric layer is at least 0.5 µm, and / or that the thickness of the piezoelectric layer is at most 3 µm.

[0056] Another example (e.g., Example 4) relates to a previous example (e.g., any of Examples 1 to 3) or to any other example, further comprising that the piezoelectric layer comprises a doped piezoelectric material.

[0057] Another example (e.g., Example 5) relates to a previous example (e.g., Example 4) or to any other example, further comprising that an atomic ratio of dopants in the doped piezoelectric material is at least 20%.

[0058] Another example (e.g., Example 6) relates to a previous example (e.g., one of Examples 4 or 5) or to any other example, further comprising that the doped piezoelectric material is scandium-doped aluminum nitride.

[0059] Another example (e.g., Example 7) relates to a previous example (e.g., any of Examples 1 to 6) or to any other example, further comprising a first electrically conductive path formed in the dielectric material between the first electrode and the first interconnect for electrically coupling the first interconnect to the first electrode, and a second electrically conductive path formed in the dielectric material between the second electrode and the second interconnect for electrically coupling the second interconnect to the second electrode.

[0060] Another example (e.g., Example 8) relates to a previous example (e.g., any of Examples 1 to 7) or to any other example, further comprising a first opening extending from a surface of the dielectric material to the first interconnect, and a second opening extending from the surface of the dielectric material to the second interconnect, wherein the second electrode is disposed between the second surface of the piezoelectric layer and the surface of the dielectric material.

[0061] Another example (e.g., Example 9) relates to a previous example (e.g., Example 8) or to any other example, further comprising the first opening and the second opening extending laterally offset from the dielectric layer.

[0062] Another example (e.g., Example 10) relates to a previous example (e.g., any of Examples 8 or 9) or to any other example, further comprising wherein the first interconnection is accessible via the first opening and wherein the second interconnection is accessible via the second opening.

[0063] Another example (e.g., Example 11) relates to a previous example (e.g., any of Examples 1 to 10) or to any other example, further comprising that a vertical distance of the first interconnection to the first electrode is less than the vertical distance of the first interconnection to the second electrode, and that the vertical distance of the second interconnection to the first electrode is less than the vertical distance of the second interconnection to the second electrode.

[0064] Another example (e.g., Example 12) relates to an ultrasonic transducer comprising the piezoelectric device of any previous example (e.g., any of Examples 1 to 11) or any other example, wherein a recess is formed in the dielectric material such that a portion of the dielectric material forms a membrane embedding the piezoelectric layer.

[0065] Another example (e.g., Example 13) relates to a previous example (e.g., Example 12) or to any other example, further comprising wherein the recess is formed remote from the first electrode, wherein the first electrode is disposed between the piezoelectric layer and the recess, and wherein the recess is formed laterally between the first interconnection and the second interconnection.

[0066] Another example (e.g., Example 14) relates to a previous example (e.g., one of Examples 12 or 13) or to any other example, further comprising that the piezoelectric device is configured to deform the membrane based on an electrical signal received at the first and second interconnections to emit ultrasonic waves and / or output a respective measurement signal at the first and second interconnections based on deformation of the membrane by received ultrasonic waves.

[0067] One example (e.g., Example 15) relates to a microelectromechanical device comprising a micromirror and a spring structure supporting the micromirror, wherein the spring structure comprises at least one piezoelectric device according to a previous example (e.g., any of Examples 1 to 11) or any other example.

[0068] Another example (e.g., Example 16) relates to a previous example (e.g., Example 15) or to any other example, further comprising that the at least one piezoelectric device is configured to deform the spring structure based on an electrical signal received at the first and second interconnects, to deform the spring structure to deflect the micromirror, and / or to output a respective measurement signal at the first and second interconnects based on a deflection of the micromirror.

[0069] One example (e.g., Example 17) relates to a method of forming a piezoelectric device, comprising forming a piezoelectric layer comprising a first surface and a second surface that are opposite each other, forming a first electrode on the first surface, forming a second electrode on the second surface, forming a dielectric material enclosing the piezoelectric layer, forming a first interconnect electrically coupled to the first electrode, and forming a second interconnect electrically coupled to the second electrode, wherein the first electrode is disposed between the piezoelectric layer and each of the first interconnect and the second interconnect, and wherein the first interconnect and the second interconnect are disposed remote from the first electrode.

[0070] Another example (e.g., Example 18) relates to a previous example (e.g., Example 17) or to any other example, further comprising forming a first electrically conductive path in the dielectric material between the first electrode and the first interconnect for electrically coupling the first interconnect to the first electrode, and forming a second electrically conductive path in the dielectric material between the second electrode and the second interconnect for electrically coupling the second interconnect to the second electrode.

[0071] Another example (e.g., Example 19) relates to a previous example (e.g., any of Examples 17 or 18) or to any other example, further comprising forming a first opening in the dielectric material, the first opening extending from a surface of the dielectric material to the first interconnect, and forming a second opening in the dielectric material, the second opening extending from the surface of the dielectric material to the second interconnect, wherein the second electrode is disposed between the second surface of the piezoelectric layer and the surface of the dielectric material.

[0072] Another example (e.g., Example 20) relates to a previous example (e.g., any of Examples 17 to 19) or to any other example, further comprising that forming a piezoelectric layer comprises depositing a doped piezoelectric material, and wherein an atomic ratio of dopants in the doped piezoelectric material is at least 20%.

[0073] The aspects and features described with respect to a particular one of the previous examples may also be combined with one or more of the further examples to replace an identical or similar feature of that further example or to additionally introduce the features into the further example.

[0074] It is further understood that the disclosure of multiple steps, processes, operations, or functions disclosed in the specification or claims should not be construed to imply that these operations necessarily depend on the described order, unless explicitly stated in the particular case or required for technical reasons. Therefore, the foregoing description does not limit the performance of multiple steps or functions to any particular order. Furthermore, in further examples, a single step, function, process, or operation may include and / or be broken down into multiple sub-steps, functions, processes, or operations.

[0075] Where some aspects have been described with respect to a device or system, these aspects should also be understood as a description of the corresponding method. For example, a block, device, or functional aspect of the device or system may correspond to a feature, such as a method step, of the corresponding method. Accordingly, aspects described with respect to a method should also be understood as a description of a corresponding block, element, property, or functional feature of a corresponding device or system.

[0076] The following claims are hereby incorporated into the Detailed Description, and each claim may stand as a separate example. It should also be noted that although in the claims a dependent claim refers to a particular combination with one or more other claims, other examples may also include a combination of the dependent claim with the subject matter of any other dependent or independent claim. Such combinations are hereby explicitly contemplated unless it is stated in a particular case that a particular combination is not intended. Furthermore, features of one claim should also be contemplated for any other independent claim, even if that claim is not directly defined as dependent on that other independent claim.

Claims

[1] Piezoelectric device (100) comprising: a piezoelectric layer (110) comprising a first surface (111) and a second surface (112) opposite each other; a first electrode (120) formed on the first surface (111); a second electrode (130) formed on the second surface (112); a dielectric material (140) surrounding the piezoelectric layer (110); a first interconnection (150) electrically coupled to the first electrode (120); and a second interconnection (160) electrically coupled to the second electrode (130), wherein the first electrode (120) is arranged between the piezoelectric layer (110) and each of the first interconnection (150) and the second interconnection (160), and wherein the first interconnection (150) and the second interconnection (160) are arranged remotely from the first electrode (120). [2] The piezoelectric device (100) of claim 1, wherein the piezoelectric layer (110) is a thin film. [3] Piezoelectric device (100) according to claim 1 or claim 2, wherein a thickness of the piezoelectric layer (110) is at least 0.5 µm, and / or wherein the thickness of the piezoelectric layer (110) is at most 3 µm. [4] Piezoelectric device (100) according to one of claims 1 to 3, wherein the piezoelectric layer (110) comprises a doped piezoelectric material. [5] The piezoelectric device (100) of claim 4, wherein an atomic ratio of dopants in the doped piezoelectric material is at least 20%. [6] A piezoelectric device (100) according to claim 4 or claim 5, wherein the doped piezoelectric material is scandium-doped aluminum nitride. [7] Piezoelectric device (100) according to one of claims 1 to 6, further comprising: a first electrically conductive path (180) formed in the dielectric material (140) between the first electrode (120) and the first interconnect (150) for electrically coupling the first interconnect (150) to the first electrode (120); and a second electrically conductive path (185) formed in the dielectric material (140) between the second electrode (130) and the second interconnect (160) for electrically coupling the second interconnect (160) to the second electrode (130). [8] Piezoelectric device (100) according to one of claims 1 to 7, wherein a first opening (170) extends from a surface of the dielectric material (140) to the first interconnection (150), wherein a second opening (175) extends from the surface of the dielectric material (140) to the second interconnection (160), wherein the second electrode (130) is arranged between the second surface (112) of the piezoelectric layer (110) and the surface of the dielectric material (140). [9] Piezoelectric device (100) according to claim 8, wherein the first opening (170) and the second opening (175) extend laterally offset from the dielectric layer. [10] The piezoelectric device (100) of claim 8 or claim 9, wherein the first interconnection (150) is accessible via the first opening (170) and wherein the second interconnection (160) is accessible via the second opening (175). [11] Piezoelectric device (100) according to one of claims 1 to 10, wherein a vertical distance of the first interconnection (150) to the first electrode (120) is smaller than the vertical distance of the first interconnection (150) to the second electrode (130) and wherein the vertical distance of the second interconnection (160) to the first electrode (120) is smaller than the vertical distance of the second interconnection (160) to the second electrode (130). [12] An ultrasonic transducer (200) comprising the piezoelectric device according to any one of claims 1 to 11, wherein a recess (295) is formed in the dielectric material (140) such that a portion of the dielectric material (140) forms a membrane (205) embedding the piezoelectric layer (110). [13] The ultrasonic transducer of claim 12, wherein the recess (295) is formed remote from the first electrode (120), wherein the first electrode (120) is disposed between the piezoelectric layer (110) and the recess (295), and wherein the recess (295) is formed laterally between the first interconnection (150) and the second interconnection (160). [14] An ultrasonic transducer according to claim 12 or claim 13, wherein the piezoelectric device is configured to: Deforming the membrane (205) based on an electrical signal received at the first and second interconnections (150, 160) to emit ultrasonic waves; and / or Outputting a respective measurement signal at the first and second interconnections (160) based on a deformation of the membrane (205) by received ultrasonic waves. [15] Microelectromechanical device (300) comprising: a micromirror (305); and a spring structure (310) supporting the micromirror (305), the spring structure (310) comprising at least one piezoelectric device according to any one of claims 1 to 11. [16] The microelectromechanical device (300) of claim 15, wherein the at least one piezoelectric device is configured to: Deforming the spring structure (310) based on an electrical signal received at the first and second interconnects (150, 160) to deform the spring structure (310) to deflect the micromirror (305); and / or Outputting a respective measurement signal at the first and second interconnections (160) based on a deflection of the micromirror (305). [17] A method (400) for forming a piezoelectric device, comprising: Forming (402) a piezoelectric layer comprising a first surface and a second surface opposite each other; forming (404) a first electrode on the first surface; forming (406) a second electrode on the second surface; forming (408) a dielectric material surrounding the piezoelectric layer; Forming (410) a first interconnection electrically coupled to the first electrode; and Forming (412) a second interconnection electrically coupled to the second electrode, wherein the first electrode is disposed between the piezoelectric layer and each of the first interconnection and the second interconnection, and wherein the first interconnection and the second interconnection are disposed remote from the first electrode. [18] The method of claim 17, further comprising: Forming (414) a first electrically conductive path in the dielectric material between the first electrode and the first interconnect for electrically coupling the first interconnect to the first electrode; and Forming (416) a second electrically conductive path in the dielectric material between the second electrode and the second interconnect for electrically coupling the second interconnect to the second electrode. [19] A method according to claim 17 or claim 18, further comprising: Forming (418) a first opening in the dielectric material, the first opening extending from a surface of the dielectric material to the first interconnect; and Forming (420) a second opening in the dielectric material, the second opening extending from the surface of the dielectric material to the second interconnect, the second electrode being disposed between the second surface of the piezoelectric layer and the surface of the dielectric material. [20] The method of any one of claims 17 to 19, wherein forming (402) the piezoelectric layer comprises depositing a doped piezoelectric material, and wherein an atomic ratio of dopants in the doped piezoelectric material is at least 20%.

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