US-12628563-B2 - Piezoelectric element and method for producing a piezoelectric element

US12628563B2US 12628563 B2US12628563 B2US 12628563B2US-12628563-B2

Abstract

A piezoelectric element and a method of manufacturing the piezoelectric element are provided. The piezoelectric element is provided with a substrate having an intermediate layer disposed between a first substrate layer and a second substrate layer, a first electrode layer of an electrically conductive non-ferroelectric material disposed on the second substrate layer, a ferroelectric, piezoelectric and/or flexoelectric layer disposed on the first electrode layer, and a second electrode layer of an electrically conductive non-ferroelectric material disposed on the ferroelectric, piezoelectric and/or flexoelectric layer. The intermediate layer and/or the first substrate layer is removed below a layer stack formed by the first electrode layer, the ferroelectric, piezoelectric and/or flexoelectric layer, and the second electrode layer so that the layer stack can be moved in a translatory manner along its normal directed along the layer sequence.

Inventors

Thomas Kämpfe

Assignees

Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.

Dates

Publication Date: 20260512
Application Date: 20201218
Priority Date: 20191219

Claims (10)

1 . A piezoelectric element, comprising: a substrate in which an intermediate layer is arranged between a first substrate layer and a second substrate layer, a first electrode layer of an electrically conductive, non-ferroelectric material disposed on the second substrate layer of the substrate, a ferroelectric, piezoelectric and/or flexoelectric layer arranged on the first electrode layer, and a second electrode layer of an electrically conductive, non-ferroelectric material arranged on the ferroelectric, piezoelectric and/or flexoelectric layer, wherein the intermediate layer and/or the first substrate layer of the substrate is removed below a layer stack formed by the first electrode layer, the ferroelectric, piezoelectric and/or flexoelectric layer and the second electrode layer, so that the layer stack can be moved in a translatory manner along its normal directed along the layer stack, and wherein the ferroelectric, piezoelectric and/or flexoelectric layer comprises undoped or doped hafnium oxide.
2 . The piezoelectric element according to claim 1 , wherein the intermediate layer is formed of an electrically insulating material or as a dielectric.
3 . The piezoelectric element according to claim 1 , wherein the second substrate layer has a smaller layer thickness than the first substrate layer.
4 . The piezoelectric element according to claim 1 , wherein the ferroelectric, piezoelectric and/or flexoelectric layer has a layer thickness of at most 500 nm.
5 . The piezoelectric element according to claim 1 , wherein the intermediate layer is removed below a ridge formed from the second substrate layer such that the ridge can be moved in a translatory manner parallel to the layer stack.
6 . The piezoelectric element according to claim 1 , wherein the doped hafnium oxide is preferably doped with silicon, aluminum, germanium, magnesium, calcium, strontium, barium, titanium, zirconium and/or a rare earth element.
7 . The piezoelectric element according to claim 1 , wherein the ferroelectric, piezoelectric and/or flexoelectric layer comprises at least one ultra-laminate of a layer of hafnium oxide and a layer of another oxide.
8 . An ultrasonic transducer, spectrometer, radio frequency switch, or fingerprint sensor comprising a piezoelectric element according to claim 1 .
9 . A method of manufacturing a piezoelectric element in which, on a substrate in which an intermediate layer is disposed between a first substrate layer and a second substrate layer, on the second substrate layer of the substrate, a first electrode layer made of an electrically conductive, non-ferroelectric material, on the first electrode layer a ferroelectric, piezoelectric and/or flexoelectric layer and on the ferroelectric, piezoelectric or flexoelectric layer, a second electrode layer of an electrically conductive non-ferroelectric material is applied, wherein the intermediate layer and/or the first substrate layer is removed below a layer stack formed by the first electrode layer, the ferroelectric, piezoelectric or flexoelectric layer and the second electrode layer so that the layer stack can be moved in a translatory manner along its normal directed along the layer stack, and wherein the ferroelectric, piezoelectric and/or flexoelectric layer comprises undoped or doped hafnium oxide.
10 . The method according to claim 9 , wherein the second substrate layer is perforated before removing the intermediate layer and/or the first substrate layer.

Description

FIELD The present invention relates to a piezoelectric element and a method of manufacturing a piezoelectric element. BACKGROUND So far, piezoelectric components such as ultrasonic transducers as well as RF (radio frequency) switches or Fabry-Pérot interferometers cannot be easily integrated into a CMOS (complementary metal-oxide-semiconductor) process and therefore require complex and expensive integrated circuit packaging. In particular, the piezoelectric materials commonly used for this purpose such as lead zirconate titanate (PZT) are not CMOS compatible (complementary metal-oxide-semiconductor) and furthermore not RHoS compatible (Restriction of Hazardous Substances, EU Directive 2011/65/EU). Therefore, aluminum nitride (AlN) or scandium-doped AlN has often been used for such components up to now. This material has, on the one hand, a low piezoelectric coefficient and, on the other hand, strong polymorphism, which causes the material to be frequently grown in the non-piezoelectric crystal phase. Typical applications of piezoelectric ultrasonic transducers are in the field of ultrasonic sensor technology and fingerprint sensors, but several problems arise here, such as a limited area filling as well as limitations with regard to a diaphragm thickness and diaphragm size, which also limit the usable frequencies and measurement resolution. This is in particular a hindrance for high-frequency switch systems. In addition, the electrical control voltages used are often comparatively high, so that applications in the field of “Internet of Things (IoT)” or in applications with direct physical contact are problematic. SUMMARY The present invention is therefore based on the object of proposing a piezoelectric element and a method for its manufacture which avoids the abovementioned disadvantages, i.e. which enable the simple manufacture of a piezoelectric element which operates reliably and can be used in a wide range of applications. According to the invention, this object is achieved by a piezoelectric element and by a method according to the claims. Advantageous embodiments and further developments are described in the dependent claims. A piezoelectric element has a substrate with an intermediate layer disposed between a first substrate layer and a second substrate layer. A first electrode layer of an electrically conductive, non-ferroelectric material is applied to the second substrate layer. A second electrode layer is disposed on the ferroelectric, piezoelectric and/or flexoelectric layer, which is formed from an electrically conductive, non-ferroelectric material. The intermediate layer and/or the first substrate layer is or are removed below a layer stack. The layer stack is formed by the first electrode layer, the ferroelectric, piezoelectric and/or flexoelectric layer and the second electrode layer. The layer stack can be moved in a translatory manner along its normal directed along the layer sequence. By structuring the substrate in such a way that the layer stack together with the region of the second substrate layer connected thereto can be moved in a translatory manner, i.e. in particular can oscillate, a system capable of oscillating is realized which, in addition, can be controlled or regulated in its movement via the electrode layers and the ferroelectric, piezoelectric and/or flexoelectric layer by applying and changing an electrical voltage. The layer stack is typically only connected at one end to the other regions of the respective layers. Moreover, since the intermediate layer or the first substrate layer is removed, i.e. the second substrate layer is physically spaced from the first substrate layer by a free space in the region of the layer stack, a diverse vibration behavior can be realized at comparatively low electrical control voltages. The first electrode layer and the second electrode layer can here be formed from a material that is the same or identical, but different materials can also be used for these layers. Typically, the first electrode layer or the second electrode layer is formed of titanium nitride (TiN), tantalum nitride (TaN), ruthenium (Ru), ruthenium oxide (RuO) or platinum. Atomic layer deposition and/or physical vapor deposition can be used. The substrate can be designed as a so-called “silicon-on-insulator” (SOI) wafer, i.e. the first substrate layer and the second substrate layer are separated from each other by an electrically insulating layer. The electrically insulating layer is thus arranged between the two substrate layers and is in direct contact, that is in proximate touching contact, with each of the layers. Any material with an electrical conductivity of less than 10−8 S/m is to be considered electrically insulating. The intermediate layer can, however, also be formed from a dielectric material. Heavily doped silicon that has a sufficiently high electric conductivity and can simultaneously have a good structure can be used as the substrate. Provision can be m