Piezoelectric device, ultrasonic transducer, microelectromechanical device and method for forming a piezoelectric device

Abstract

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) that surrounds the piezoelectric layer (110); a first intermediate connection (150) which is electrically coupled to the first electrode (120); and a second intermediate connection (160) which is electrically coupled to the second electrode (130), wherein the first electrode (120) is arranged between the piezoelectric layer (110) and each of the first intermediate connection (150) and the second intermediate connection (160), and wherein the first intermediate connection (150) and the second intermediate connection (160) are arranged remotely from the first electrode (120), and wherein a first opening (170) extends from a surface of the dielectric material (140) to the first intermediate connection (150), wherein a second opening (175) extends from the surface of the dielectric material (140) to the second intermediate connection (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).

Description

Area

[0001] The present disclosure relates to piezoelectric structures. In particular, 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 variety of microelectromechanical systems (MEMS) such as resonators, actuators, ultrasonic transducers, and sensors. Highly doped piezoceramics are gaining popularity due to their improved piezoelectric modulus. 33More attention is needed. The doping of piezoceramics causes problems during process integration. Typical dopants, for example, are highly resistant to dry etching and exhibit poor selectivity towards surrounding layers in a layer stack. On the other hand, typical dopants leave residues on the surface in the case of wet etching. Furthermore, creep paths along the surfaces and sidewalls of the piezoceramic can lead to device failure in conventional designs.

[0003] WO 2007 / 022633 A2 discloses an RF device comprising first and second electrodes and a polar dielectric. The RF device further comprises one or more layers that influence the acoustic properties of the RF device.

[0004] DE 10 2022 203 971 A1 discloses a volume acoustic device comprising a first electrode, a second electrode, and a piezoelectric element arranged between the first and second electrodes. The piezoelectric element comprises at least two piezoelectric layers with the same polarity and at least one intermediate layer located between the at least two piezoelectric layers.

[0005] Therefore, there may be a need for improved piezoelectric structures. Summary

[0006] This need is met by the subject matter of the independent claims. Advantageous embodiments are addressed by the dependent claims.

[0007] According to a first aspect, the present disclosure provides a piezoelectric device. The piezoelectric device comprises a piezoelectric layer, including a first surface and a second surface facing each other. Furthermore, the piezoelectric device comprises 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 intermediate connection electrically coupled to the first electrode and a second intermediate connection electrically coupled to the second electrode. The first electrode is arranged between the piezoelectric layer and each of the first and second intermediate connections.The first intermediate connection and the second intermediate connection are located away from the first electrode.

[0008] 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.

[0009] 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.

[0010] According to a fourth aspect, the present disclosure provides a method for forming a piezoelectric device. The method comprises forming a piezoelectric layer, comprising a first surface and a second surface facing each other. Furthermore, the method comprises 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 comprises forming a first intermediate electrically coupled to the first electrode and forming a second intermediate electrically coupled to the second electrode. The first electrode is arranged between the piezoelectric layer and each of the first and second intermediates.The first intermediate connection and the second intermediate connection are located away from the first electrode.

[0011] According to the proposed technique, 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 creepage paths. Brief description of the characters

[0012] Some examples of devices and / or methods are described below only by way of example and with reference to the accompanying figures, whereby Fig. 1. An example of a piezoelectric device is illustrated; Fig. 2. An example of an ultrasound transducer is illustrated; Fig. 3 illustrates an example of a microelectromechanical device; Fig. 4 illustrates an example of a method for forming a piezoelectric device; and Fig. Figure 5 illustrates an exemplary piezoelectric device during various stages of its manufacture. Detailed description

[0013] Some examples are now 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 certain examples should not be considered restrictive for other possible examples.

[0014] Throughout the description of the figures, identical or similar reference symbols refer to identical 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 areas in the figures may also be exaggerated for clarity.

[0015] When two elements A and B are combined using "or," this is to be understood as revealing all possible combinations, i.e., only A, only B, and A and B, unless explicitly defined otherwise in a specific case. As an alternative formulation for the same combinations, "at least one of A and B" or "A and / or B" can be used. This applies equivalently to combinations of more than two elements.

[0016] 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, subsequent examples may also use multiple elements to implement the same function. Similarly, when a function is described below as being implemented using multiple elements, subsequent examples may implement the same function using a single element or a single processing entity. Furthermore, it is understood that the terms "include," "containing," "comprise," and / or "comprehensive," when used, describe the presence of the specified features, integers, steps, operations, processes, elements, components, and / or a group thereof, but do not exclude the presence or addition of one or more other features, integers, steps, operations, processes, elements, components, and / or a group thereof.

[0017] Fig. Figure 1 illustrates a sectional view of an exemplary piezoelectric device 100.

[0018] The piezoelectric device 100 comprises a piezoelectric layer 110. The piezoelectric layer 110 comprises a first surface 111 and a second surface 112, which are opposite 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 can be (essentially) parallel to each other, as shown in Fig. Figure 1 shows that the first surface 111 and the second surface 112 can be (essentially) planar (flat) surfaces. The piezoelectric layer 110 further comprises side walls 113 and 114, which face each other. The side walls 113 and 114 laterally delimit the piezoelectric layer 110. The side walls 113 and 114 connect the first surface 111 and the second surface 112. The first surface 111 and the second surface 112 can 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 can be a thin film. In other words, the thickness of the piezoelectric layer 110 can be at least 0.1 µm, 0.5 µm, or 1 µm. The thickness of the piezoelectric layer 110 can be at most 1 µm, 3 µm, 5 µm, or 10 µm.

[0019] 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). It should be noted, however, that the present disclosure is not limited to the aforementioned materials. Other piezoelectric materials may be used instead or in addition. By way of example, the piezoelectric layer 110 may comprise or be a doped piezoelectric material. The piezoelectric material may be lightly or heavily doped. For example, the 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 as high as 50%, 55%, 60%, 65%, 70%, or 75%. Various dopants (doping 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 can be used instead or in addition.In particular, the doped piezoelectric material can be Sc-doped AlN with an atomic ratio of Sc dopants in the doped AlN of at least 20% and at most 60%.

[0020] Furthermore, the piezoelectric device 100 comprises 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 can be made of the same material(s) or of different materials. The first electrode 120 can partially cover the first surface 111, as shown in . Fig. Figure 1 illustrates this. In alternative examples, the first electrode 120 can completely cover the first surface 111. The second electrode 130 can completely cover the second surface 112, as shown in Figure 1. Fig. Figure 1 illustrates this. In alternative examples, the second electrode 130 can 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 can 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 can be at most 500 nm, 250 nm, 100 nm, or 50 nm. The first electrode 120 and the second electrode 130 can have the same thickness or different thicknesses. The first electrode 120 and the second electrode 130 are provided for electrical contacting the piezoelectric layer 110. The first electrode 120 and the second electrode 130 make it possible to establish an electrical potential (i.e.,a voltage) for the piezoelectric layer 110 to provide controlled (and reversible) deformation of the piezoelectric layer 110 due to the piezoelectric effect. Analogously, the first electrode 120 and the second electrode 130 make it possible to measure an electrical potential (i.e., a voltage) that is caused in the piezoelectric layer 110 by deformation of the piezoelectric layer 110 due to the piezoelectric effect.

[0021] The piezoelectric device 100 comprises a dielectric material 140 that surrounds the piezoelectric layer 110. The dielectric material 140 further surrounds 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 can be one or more 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 can 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.

[0022] Additionally, the piezoelectric device 100 comprises a first intermediate connection 150, which is electrically coupled to the first electrode 120, and a second intermediate connection 160, which is electrically coupled to the second electrode 130. The first intermediate connection 150 and the second intermediate connection 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. The first intermediate connection 150 and the second intermediate connection 160 are both arranged below the stack formed by the piezoelectric layer 110 and the electrodes 120 and 130. More generally, the first intermediate connection 150 and the second intermediate connection 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 intermediate connection 150 and the second intermediate connection 160. The first intermediate connection 150 and the second intermediate connection 160 are arranged at a distance from the first electrode 120 (along the thickness direction of the piezoelectric device 100).The vertical distance between the first intermediate connection 150 and the first electrode 120 is smaller than the vertical distance between the first intermediate connection 150 and the second electrode 130. Similarly, the vertical distance between the second intermediate connection 160 and the first electrode 120 is smaller than the vertical distance between the second intermediate connection 160 and the second electrode 130.

[0023] The thicknesses of the first intermediate connection 150 and the second intermediate connection 160 are generally not limited. For example, the respective thicknesses of the first intermediate connection 150 and the second intermediate connection 160 can be at least 10 nm, 20 nm, 50 nm, 100 nm, 250 nm, or 500 nm. On the other hand, the respective thicknesses of the first electrode 120 and the second electrode 130 can 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 can be selected to allow or facilitate wire bonding or similar post-assembly processes.

[0024] The first intermediate connection 150 and the second intermediate connection 160 are also arranged in the dielectric material 140. The dielectric material 140 partially encloses both the first intermediate connection 150 and the second intermediate connection 160. The first intermediate connection 150 is accessible from the outside via a first opening (recess) 170 formed in the dielectric material 140. The second intermediate connection 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 intermediate connection 150. The second opening extends from the surface 141 of the dielectric material 140 to the second intermediate connection 160. In the example of Fig. 1. Surface 141 of the dielectric material 140 is the upper surface of the dielectric material 140, such that surface 141 of the dielectric material 140 and the intermediate connections 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 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.

[0025] 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 intermediate connections 150 and 160. However, it should be noted that the present disclosure is limited to this. Other geometries can be used instead for the first opening 170 and the second opening 175.

[0026] As described above, the first intermediate connection 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 intermediate connection 150 for electrically coupling the first intermediate connection 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 intermediate connection 160 for electrically coupling the second intermediate connection 160 to the second electrode 130. The dielectric material 140 separates, i.e., 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). It should be noted, however, that the present disclosure is not limited to the aforementioned materials. Other electrically conductive materials may be used instead or additionally. The geometries of the first electrically conductive path 180 and the second electrically conductive path 185, which are described in [reference], are not limited to the aforementioned materials. Fig. The figures shown in point 1 are for illustrative purposes only.

[0027] In other examples, the first electrically conductive path 180 and the second electrically conductive path 185 can have different geometries (routes in the dielectric material 140).

[0028] The structures for contacting the electrodes 120 and 130, i.e., the intermediate connections 150 and 160, as well as the electrically conductive paths 180 and 185, can be formed without exposing the piezoelectric layer 110 to any etching agents. This is particularly advantageous when the piezoelectric layer 110 comprises a highly doped piezoelectric material, since typical dopants are highly resistant to dry etching and exhibit poor selectivity with respect to surrounding layers in a layer stack. Furthermore, typical dopants leave residues on the surface in the case of wet etching. Additionally, 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 prevent or at least minimize electrical creepage paths. Accordingly, failure of the piezoelectric device 100 can be avoided.

[0029] 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 described. However, it should be noted that the piezoelectric device 100 is not limited to the exemplary applications described below.

[0030] Fig. Figure 2 illustrates a sectional view of an exemplary ultrasonic transducer 200. The ultrasonic transducer 200 can be a microelectromechanical device. In particular, the ultrasonic transducer 200 can be a piezoelectric micromachined ultrasonic transducer (PMUT). The ultrasonic transducer 200 comprises the piezoelectric device 100 as described above. The piezoelectric device 100 is formed on a support substrate 290, such as a silicon substrate.

[0031] A recess (opening) 295 is formed in the dielectric material 140 such that part of the dielectric material 140 forms a membrane 205 which embeds the piezoelectric layer 110 (together with the electrodes 120 and 130).

[0032] In particular, the portion of the dielectric material 140 above the recess 295 forms the membrane 205. The recess 295 is formed below the piezoelectric layer 110 and the first electrode 120. In other words, the recess 295 is formed at a distance from the first electrode 120. The first electrode 120 is located between the piezoelectric layer 110 and the recess 295. The recess 295 is formed laterally between the first intermediate connection 150 and the second intermediate connection 160. The recess 295 can be filled with air or any other suitable gas. Alternatively, the recess 295 can maintain a vacuum.

[0033] As described above for the piezoelectric device 100, the first intermediate connection 150 and the second intermediate connection 160 allow 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 supplied drive signal and / or to generate a measurement signal based on received (measured) ultrasonic waves. For example, the piezoelectric device 110 can be configured to deform the membrane 205 based on an electrical signal received at the first and second intermediate connections 150, 160, in order to emit ultrasonic waves.Alternatively or additionally, the piezoelectric device 110 can be configured to output a respective measurement signal at the first and second intermediate connections 150, 160 based on a deformation of the membrane 205 by received ultrasonic waves.

[0034] The Ultrasonic Transducer 200 can be configured to emit and / or detect ultrasonic waves at least between 20 kHz and 1 GHz and / or any subrange thereof. In particular, the Ultrasonic Transducer 200 can 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).

[0035] Fig. Figure 3 illustrates a sectional view of an exemplary microelectromechanical device 300.

[0036] The microelectromechanical device 300 comprises a micromirror 305. The dimensions of the micromirror 305 can be, for example, on the order of micrometers. A spring structure 310 of the microelectromechanical device 300 supports the micromirror 305. The spring structure 310 comprises a free-standing actuator area and a contact area of ​​the lower electrode (first electrode), as shown in Fig. Figure 1 illustrates that the micromirror 305 is movable relative to the rest of the microelectromechanical device 300 via the spring structure 310. As shown in Fig. As specified in Figure 3, the spring structure 310 comprises a piezoelectric device according to the proposed technique. Optionally, the spring structure 310 can comprise several piezoelectric devices according to the proposed technique.

[0037] As described above for the piezoelectric device 100, the first intermediate connection 150 and the second intermediate connection 160 allow 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 move the micromirror 305 based on an externally supplied 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, which is measurable via the piezoelectric layer 110).For example, the piezoelectric device 110 can be configured to deform the spring structure 310 based on an electrical signal received at the first and second intermediate connections 150, 160, in order to deform the spring structure 310 to deflect the micromirror 305. Alternatively or additionally, the piezoelectric device 110 can be configured to output a respective measurement signal at the first and second intermediate connections 150, 160 based on a deflection of the micromirror 305.

[0038] The microelectromechanical device 300 comprises a support substrate 390, such as a silicon substrate, for holding 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.

[0039] 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.

[0040] Fig. Figure 4 illustrates a flowchart of an exemplary method 400 for forming a piezoelectric device.

[0041] Method 400 comprises forming a piezoelectric layer comprising a first surface and a second surface facing each other. For example, forming 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. Method 400 further comprises forming a first electrode on the first surface and forming a second electrode on the second surface. Method 400 also comprises forming a dielectric material surrounding the piezoelectric layer.In addition, the method 400 comprises forming 410 a first intermediate connection electrically coupled to the first electrode, and forming 412 a second intermediate connection electrically coupled to the second electrode. The first electrode is positioned between the piezoelectric layer and each of the first and second intermediate connections. The first and second intermediate connections are positioned remotely from the first electrode.

[0042] Method 400 enables the provision of a piezoelectric device as described above. Further details and aspects of Method 400 are explained in connection with the proposed technology or one or more examples described above or below. Method 400 may include one or more additional optional features corresponding to one or more aspects of the proposed technology or one or more examples described above or below.

[0043] For example, method 400 can further comprise forming 414 a first electrically conductive path in the dielectric material between the first electrode and the first intermediate connection for electrically coupling the first intermediate connection to the first electrode. Similarly, method 400 can further comprise forming 416 a second electrically conductive path in the dielectric material between the second electrode and the second intermediate connection for electrically coupling the second intermediate connection to the second electrode. Forming the first and second electrically conductive paths in the dielectric material makes it possible to couple the first and second intermediate connections to the respective first and second electrodes.

[0044] Alternatively or additionally, the method 400 can 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 intermediate connection. Analogously, the method 400 can 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 intermediate connection. 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 intermediate connections for electrical contact with the piezoelectric layer.

[0045] Further details of Procedure 400 can be found in the following description of Fig. Figure 5 illustrates the piezoelectric device 100 during various stages of its manufacture.

[0046] Partial image (a) of Fig. Figure 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).

[0047] Figure (b) illustrates that the first intermediate 150 and the second intermediate 160 are subsequently formed on the layer of dielectric material 140. For example, a material for the first intermediate 150 and the second intermediate 160 can be deposited on the layer of dielectric material 140, a photosensitive chemical (such as a photoresist) can be applied to the material, and it can be patterned according to the desired geometry of the first intermediate 150 and the second intermediate 160 by photolithography. Unwanted parts of the material are removed by etching according to the photolithographic pattern to form the first intermediate 150 and the second intermediate 160. Residues of the material and the photosensitive chemical can then be removed in a cleaning process.

[0048] Then, as illustrated in partial image (c), more of the dielectric material 140 is deposited. The surface of the dielectric material 140 is planarized by chemical-mechanical polishing (CMP).

[0049] 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 intermediate connection 150 (see partial figure (d)). The opening 510 is filled with electrically conductive material to form a via as the first electrically conductive path 180 (see partial figure (e)). As illustrated in partial figure (f), the first electrode 120 is subsequently formed on the planar surface of the dielectric material 140 by depositing and structuring appropriate electrically conductive material, such as metal(s).

[0050] The material for the piezoelectric layer 110 is then deposited, as illustrated in sub-figure (g). For example, a thin film can be deposited for the piezoelectric layer 110. In particular, the material deposited for the piezoelectric layer 110 can include (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-figure (h)). The second electrode 130 can be formed analogously to the first electrode 120. After the formation of 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-figure (i)). Dry etching and / or wet etching processes can be used to remove the unwanted parts 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 structure applied to the material for the piezoelectric layer 110 (and the second electrode 130) to form the piezoelectric layer 110.

[0051] Then, as illustrated in partial image (j), more of the dielectric material 140 is deposited. The surface of the dielectric material 140 is planarized by CMP.

[0052] Openings (recesses) 520 and 530, extending to the second electrode 130 and the second intermediate connection 160, are etched into the dielectric material 140 for the second electrically conductive path 185 between the second electrode 130 and the second intermediate connection 160 (see inset figures (k) and (1)). During the formation of the openings 520 and 530, the dielectric material 140 acts as an etch stop, preventing the etch from reaching the piezoelectric layer 110 at the cost of some dielectric material loss. The openings 520 and 530 are filled with electrically conductive material (see inset figure (m)) to form vias. Additional electrically conductive material, connecting the vias, is deposited on the dielectric material 140 to form the second electrically conductive path 185 (see inset figure (n)).The structuring of the electrically conductive material that connects the vias can be carried out analogously to the formation of the first intermediate connection 150 and the second intermediate connection 160.

[0053] Then, as illustrated in partial image (o), more of the dielectric material 140 is deposited. The surface of the dielectric material 140 is planarized by CMP.

[0054] Finally, the openings 170 and 175 for accessing the first intermediate connection 150 and the second intermediate connection 160 are formed by etching a portion of the dielectric material 140. Accordingly, the first intermediate connection 150 and the second intermediate connection 160 can be electrically contacted via bond wires, etc.

[0055] It should be noted that the process flow for producing the above with reference to Fig.The piezoelectric device 100 described in Section 5 is merely an example. Other or different process steps can be used to manufacture the piezoelectric device 100 in alternative examples.

[0056] The examples described herein can be summarized as follows: An example (e.g., Example 1) relates to a piezoelectric device comprising a piezoelectric layer, comprising a first surface and a second surface facing 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 intermediate electrically coupled to the first electrode, and a second intermediate electrically coupled to the second electrode, wherein the first electrode is positioned between the piezoelectric layer and each of the first intermediate and the second intermediate, and wherein the first intermediate and the second intermediate are positioned remotely from the first electrode.

[0057] 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.

[0058] Another example (e.g., example 3) refers to a previous example (e.g., one of examples 1 or 2) or to any other example, further comprising that the 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.

[0059] Another example (e.g., Example 4) refers to a previous example (e.g., one of Examples 1 to 3) or to any other example, further comprising that the piezoelectric layer comprises a doped piezoelectric material.

[0060] Another example (e.g., Example 5) refers 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%.

[0061] Another example (e.g., example 6) refers 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.

[0062] Another example (e.g., Example 7) refers to a previous example (e.g., one 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 intermediate for electrically coupling the first intermediate to the first electrode, and a second electrically conductive path formed in the dielectric material between the second electrode and the second intermediate for electrically coupling the second intermediate to the second electrode.

[0063] Another example (e.g., Example 8) refers to a previous example (e.g., one of Examples 1 to 7) or to any other example, further comprising that a first opening extends from a surface of the dielectric material to the first intermediate connection, and that a second opening extends from the surface of the dielectric material to the second intermediate connection, the second electrode being arranged between the second surface of the piezoelectric layer and the surface of the dielectric material.

[0064] Another example (e.g., Example 9) refers to a previous example (e.g., Example 8) or to any other example, further comprising that the first opening and the second opening extend laterally offset from the dielectric layer.

[0065] Another example (e.g., Example 10) refers to a previous example (e.g., one of Examples 8 or 9) or to any other example, further comprising that the first intermediate connection is accessible via the first opening and wherein the second intermediate connection is accessible via the second opening.

[0066] Another example (e.g., Example 11) refers to a previous example (e.g., one of Examples 1 to 10) or to any other example, further comprising that a vertical distance of the first intermediate connection to the first electrode is less than the vertical distance of the first intermediate connection to the second electrode, and that the vertical distance of the second intermediate connection to the first electrode is less than the vertical distance of the second intermediate connection to the second electrode.

[0067] Another example (e.g., Example 12) relates to an ultrasonic transducer comprising the piezoelectric device according to a previous example (e.g., one of Examples 1 to 11) or according to any other example, wherein a recess in the dielectric material is formed such that part of the dielectric material forms a membrane embedding the piezoelectric layer.

[0068] Another example (e.g., Example 13) refers to a previous example (e.g., Example 12) or to any other example, further comprising that the recess is formed remotely from the first electrode, wherein the first electrode is arranged between the piezoelectric layer and the recess, and wherein the recess is formed laterally between the first intermediate connection and the second intermediate connection.

[0069] Another example (e.g., Example 14) refers 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 junctions in order to emit ultrasonic waves and / or output a respective measurement signal at the first and second junctions based on a deformation of the membrane by received ultrasonic waves.

[0070] An 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., one of Examples 1 to 11) or according to any other example.

[0071] Another example (e.g., Example 16) refers 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 intermediate junctions, in order to deform the spring structure to deflect the micromirror and / or output a respective measurement signal at the first and second intermediate junctions based on a deflection of the micromirror.

[0072] An example (e.g., Example 17) relates to a method for forming a piezoelectric device, comprising forming a piezoelectric layer, comprising a first surface and a second surface facing 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 intermediate electrically coupled to the first electrode, and forming a second intermediate electrically coupled to the second electrode, wherein the first electrode is positioned between the piezoelectric layer and each of the first intermediate and the second intermediate, and wherein the first intermediate and the second intermediate are positioned remotely from the first electrode.

[0073] Another example (e.g., Example 18) refers 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 intermediate for electrically coupling the first intermediate to the first electrode, and forming a second electrically conductive path in the dielectric material between the second electrode and the second intermediate for electrically coupling the second intermediate to the second electrode.

[0074] Another example (e.g., Example 19) refers to a previous example (e.g., one of Examples 17 or 18) or to any other example, further comprising forming a first opening in the dielectric material, wherein the first opening extends from a surface of the dielectric material to the first intermediate connection, and forming a second opening in the dielectric material, wherein the second opening extends from the surface of the dielectric material to the second intermediate connection, the second electrode being arranged between the second surface of the piezoelectric layer and the surface of the dielectric material.

[0075] Another example (e.g., Example 20) refers to a previous example (e.g., one of Examples 17 to 19) or to any other example, further comprising that the formation of a piezoelectric layer includes the deposition of a doped piezoelectric material, and wherein an atomic ratio of dopants in the doped piezoelectric material is at least 20%.

[0076] The aspects and features described in relation to a particular of the previous examples can 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.

[0077] It is further understood that the disclosure of multiple steps, processes, operations, or functions in the description or claims is not to be interpreted as implying that these operations are necessarily dependent on the described sequence, unless explicitly stated in a specific case or required for technical reasons. Therefore, the preceding description does not restrict the execution of multiple steps or functions to a specific sequence. Furthermore, in other examples, a single step, function, process, or operation may include and / or be broken down into multiple sub-steps, functions, processes, or operations.

[0078] When certain aspects relating to a device or system are described, these aspects should also be understood as a description of the corresponding procedure. For example, a block, device, or functional aspect of the device or system may correspond to a feature, such as a process step, of the corresponding procedure. Accordingly, aspects described in relation to a procedure should also be understood as a description of a corresponding block, element, property, or functional feature of that device or system.

[0079] The following claims are hereby included in the detailed description, each claim being a separate example. It should also be noted that, although in the claims a dependent claim refers to a specific 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 suggested unless it is stated in a particular case that a specific combination is not intended. Furthermore, features of a claim should also be included 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) that surrounds the piezoelectric layer (110); a first intermediate connection (150) which is electrically coupled to the first electrode (120); and a second intermediate connection (160) which is electrically coupled to the second electrode (130), wherein the first electrode (120) is arranged between the piezoelectric layer (110) and each of the first intermediate connection (150) and the second intermediate connection (160), and wherein the first intermediate connection (150) and the second intermediate connection (160) are arranged remotely from the first electrode (120), and wherein a first opening (170) extends from a surface of the dielectric material (140) to the first intermediate connection (150), wherein a second opening (175) extends from the surface of the dielectric material (140) to the second intermediate connection (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). [2] Piezoelectric device (100) according to claim 1, wherein the piezoelectric layer (110) is a thin film. [3] Piezoelectric device (100) according to claim 1 or claim 2, wherein the 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 any one of claims 1 to 3, wherein the piezoelectric layer (110) comprises a doped piezoelectric material. [5] Piezoelectric device (100) according to claim 4, wherein the atom ratio of dopants in the doped piezoelectric material is at least 20%. [6] 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 any 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 intermediate connection (150) for electrically coupling the first intermediate connection (150) with 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 intermediate connection (160) for electrically coupling the second intermediate connection (160) with the second electrode (130). [8] Piezoelectric device (100) according to any one of claims 1 to 7, wherein the first opening (170) and the second opening (175) extend laterally offset to the dielectric layer. [9] Piezoelectric device (100) according to any one of claims 1 to 8, wherein the first intermediate connection (150) is accessible via the first opening (170) and wherein the second intermediate connection (160) is accessible via the second opening (175). [10] Piezoelectric device (100) according to any one of claims 1 to 9, wherein the vertical distance of the first intermediate connection (150) to the first electrode (120) is smaller than the vertical distance of the first intermediate connection (150) to the second electrode (130) and wherein the vertical distance of the second intermediate connection (160) to the first electrode (120) is smaller than the vertical distance of the second intermediate connection (160) to the second electrode (130). [11] Ultrasound transducer (200) comprising the piezoelectric device according to any one of claims 1 to 10, wherein a recess (295) in the dielectric material (140) is formed such that part of the dielectric material (140) forms a membrane (205) which embeds the piezoelectric layer (110). [12] Ultrasound transducer according to claim 11, wherein the recess (295) is formed remotely from the first electrode (120), wherein the first electrode (120) is arranged between the piezoelectric layer (110) and the recess (295), and wherein the recess (295) is formed laterally between the first intermediate connection (150) and the second intermediate connection (160). [13] Ultrasonic transducer according to claim 11 or claim 12, wherein the piezoelectric device is configured to: Deformation of the membrane (205) based on an electrical signal received at the first and second junctions (150, 160) to emit ultrasonic waves; and / or Output of a respective measurement signal at the first and second intermediate connection (160) based on a deformation of the membrane (205) by received ultrasound waves. [14] Microelectromechanical device (300), comprising: a micromirror (305); and a spring structure (310) supporting the micromirror (305), wherein the spring structure (310) comprises at least one piezoelectric device according to any one of claims 1 to 10. [15] Microelectromechanical device (300) according to claim 14, wherein the at least one piezoelectric device is configured to: Deformation of the spring structure (310) based on an electrical signal received at the first and second intermediate connections (150, 160) to deform the spring structure (310) to deflect the micromirror (305); and / or Output of a respective measurement signal at the first and second intermediate connection (160) based on a deflection of the micromirror (305). [16] 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 that surrounds the piezoelectric layer; Forming (410) a first intermediate connection which is electrically coupled to the first electrode; Forming (412) a second intermediate connection which is electrically coupled to the second electrode; Forming (418) a first opening in the dielectric material, wherein the first opening extends from a surface of the dielectric material to the first intermediate connection; and Forming (420) a second opening in the dielectric material, wherein the second opening extends from the surface of the dielectric material to the second intermediate connection, wherein the first electrode is arranged between the piezoelectric layer and each of the first and second intermediate connections, wherein the first and second intermediate connections are arranged remotely from the first electrode, and wherein the second electrode is arranged between the second surface of the piezoelectric layer and the surface of the dielectric material. [17] The method of claim 16, further comprising: Forming (414) a first electrically conductive path in the dielectric material between the first electrode and the first intermediate connection for electrically coupling the first intermediate connection to the first electrode; and Forming (416) a second electrically conductive path in the dielectric material between the second electrode and the second intermediate connection for electrical coupling of the second intermediate connection with the second electrode. [18] Method according to claim 16 or 17, wherein forming (402) the piezoelectric layer comprises depositing a doped piezoelectric material, and wherein an atom ratio of dopants in the doped piezoelectric material is at least 20%.

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