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CN-122029740-A - Bulk acoustic wave element and method for manufacturing the same

CN122029740ACN 122029740 ACN122029740 ACN 122029740ACN-122029740-A

Abstract

The invention relates to a bulk acoustic wave element (10) comprising a first electrode (120) and a second electrode (122), a piezoelectric element (100) having at least a first piezoelectric layer element (101) and a second piezoelectric layer element (102), wherein a gap (sp) is provided between at least the first piezoelectric layer element (101) and the second piezoelectric layer element (102), and wherein the acoustic layer thickness of the first piezoelectric layer element (101) and/or the second piezoelectric layer element (102) corresponds to an odd multiple of the acoustic half wavelength of the operating frequency of the bulk acoustic wave element (10), respectively, wherein the first electrode (120) and the second electrode (122) are arranged together with the piezoelectric element (100) in a stacked assembly.

Inventors

  • C. Sherin
  • S. B. Fischer Kennedy

Assignees

  • 罗伯特·博世有限公司

Dates

Publication Date
20260512
Application Date
20240923
Priority Date
20231013

Claims (10)

  1. 1. A bulk acoustic wave element (10) comprising: -a first electrode (120) and a second electrode (122); -a piezoelectric element (100) having at least a first piezoelectric layer element (101) and a second piezoelectric layer element (102), wherein there is a gap (sp) at least between the first piezoelectric layer element (101) and the second piezoelectric layer element (102), and wherein the acoustic layer thickness of the first piezoelectric layer element (101) and/or the second piezoelectric layer element (102) respectively corresponds to an odd multiple of an acoustic half wavelength of an operating frequency of the bulk acoustic wave element (10), wherein the first electrode (120) and the second electrode (122) are arranged together with the piezoelectric element (100) in a stacked assembly.
  2. 2. Bulk acoustic wave element (10) according to claim 1, comprising a Substrate (SB) and at least one acoustically Reflective Element (RE), wherein the acoustically Reflective Element (RE) is arranged in or on the Substrate (SB) and the stack assembly is arranged on the Substrate (SB) and/or on the Reflective Element (RE).
  3. 3. The bulk acoustic wave element (10) according to claim 1 or 2, which is an acoustic resonator.
  4. 4. A bulk acoustic wave element (10) according to any of claims 1 to 3, in which the acoustically Reflective Element (RE) is an air chamber in the Substrate (SB) and/or in a Dielectric (DI) or is arranged as an acoustic bragg reflector on the Substrate (SB) and/or in the stack.
  5. 5. The bulk acoustic wave element (10) according to any of claims 1 to 4, in which a Dielectric (DI) is comprised in the stacked assembly and/or between the first piezoelectric layer element (101) and the second piezoelectric layer element (102), and in which the gap (sp) is shaped as a recess in the Dielectric (DI) in an active Area (AB).
  6. 6. The bulk acoustic wave element (10) according to any one of claims 1 to 5, in which the first piezoelectric layer element (101) and/or the second piezoelectric layer element (102) comprises a single piezoelectric layer or a plurality of piezoelectric layers stacked as layers, wherein each of the single piezoelectric layer or the plurality of piezoelectric layers as a whole has an acoustic layer thickness corresponding to an odd multiple of an acoustic half wavelength of an operating frequency of the bulk acoustic wave element (10).
  7. 7. The bulk acoustic wave element (10) according to any one of claims 1 to 6, comprising a lateral feedthrough contact (FK) leading from an upper side of the bulk acoustic wave element (10) and electrically insulated from the second electrode (122) through an embedded dielectric (DI-E) to the first electrode (120), wherein the embedded dielectric (DI-E) at least partially surrounds the stacked assembly in lateral direction.
  8. 8. The bulk acoustic wave element (10) according to any one of claims 1 to 7, being a MEMS member and being an acoustic filter.
  9. 9. The bulk acoustic wave element (10) according to any one of claims 1 to 8, which is designed to operate as a resonator at an acoustic frequency of 10 GHz or more.
  10. 10. Method for manufacturing a bulk acoustic wave element (10), comprising the steps of: -providing (S1) a substrate (130) and arranging (S2) a first electrode (120) on the Substrate (SB) and arranging a piezoelectric element (100) on the first electrode (120), the piezoelectric element having at least a first piezoelectric layer element (101) and a second piezoelectric layer element (102), wherein there is a gap (sp) between at least the first piezoelectric layer element (101) and the second piezoelectric layer element (102), and wherein the acoustic layer thickness of the first piezoelectric layer element (101) and/or the second piezoelectric layer element (102) respectively corresponds to an odd multiple of the acoustic half wavelength of the operating frequency of the bulk acoustic wave element (10), and arranging a second electrode (122) on the piezoelectric element (100), wherein the first electrode (120) and the second electrode (122) are arranged together with the piezoelectric element (100) in a stacked assembly.

Description

Bulk acoustic wave element and method for manufacturing the same Technical Field The present invention relates to a bulk acoustic wave element and a method for manufacturing a bulk acoustic wave element. Background Bulk acoustic wave elements may be used as resonators in filters and oscillators, where the operating frequency may be determined by the layer thickness of the piezoelectric layer and the speed of sound in the piezoelectric material. In order to be able to achieve higher operating frequencies, the layer thickness thereof can be reduced. In this case, however, the capacitance of the element may increase at small layer thicknesses. Here, if the electromagnetic wave impedance should be maintained, it is therefore necessary to simultaneously reduce the element area, however, acoustic energy may be lost at the edges of the element, so that with shrinking the element the edge loss may increase squarely with the operating frequency. In this case, it is desirable to improve the applicability of the bulk acoustic wave element (BAW) to the range higher than 10 GHz. It is noted that a bimorph effect occurs with temperature changes due to different piezoelectric materials, which can lead to thermal drift. In addition, piezoelectric materials possess different piezoelectric characteristics, which makes it difficult to design low-loss elements. Furthermore, in the case of multilayer piezoelectric layers having alternating polarities, useful oscillations occur not only at that frequency in the case of a single layer having a half-wavelength thickness, but additionally parasitic oscillation modes also occur at those frequencies in the case of multilayer piezoelectric layer stacks corresponding to multiples of the acoustic half-wavelength. In this regard, this results in conventional embodiments in that undesired oscillations may occur throughout the stack. An alternative to reducing the layer thickness may be to excite higher order modes, which are collectively referred to as higher harmonic bulk acoustic wave resonators (Overtoned Bulk Acoustic Resonator, OBAR). However, this concept is susceptible to other modes of vibration initiation and is inefficient in terms of excitation (small piezoelectric coupling). Another alternative is to use a thick chamber with varying polarity of material. The main advantage of these concepts is that the excitation field can directly excite overtones (Oberton) here, since the excitation force also changes direction with changing material polarity. The manufacture of such polarity-changing layers is demanding and the transfer to a mass production process is problematic. In order to be able to use resonance at as high a frequency as possible, the electrode thickness may play a decisive role. If the electrode thickness is not small compared to the acoustic wavelength, the mass of the electrode significantly reduces the resonant frequency. In addition, the electrodes may deteriorate the quality of the resonator. The electrodes may be detached from the piezoelectric material and capacitively coupled to the resonator via the gap, which can be technically challenging. Another possibility is that the electrodes are replaced by two-dimensional electron gases, which can be formed, for example, in the case of AlGaN/GaN heterostructures. With each new generation of mobile communication networks, higher frequencies and greater bandwidths are released for mobile communication. In mobile communication, a passive filter element composed of a bulk acoustic wave (wave) resonator (baw= bulk acoustic wave) is widely accepted due to its small external dimensions, small insertion loss, and steep edge characteristics. Furthermore, BAW resonators are also used in oscillators. In order to achieve higher operating frequencies with resonators as well, it may be necessary to reduce their energy losses. The main source of loss may be the material inherent damping loss. In this case, alN may have a relatively high material inherent damping based on phonon-phonon interactions. The measure of the material's natural damping is the product f of the operating frequency f and the quality factor QQ. The larger the product, the less the corresponding material inherent damping. A bulk acoustic wave element is described in US 2018/085787 A1. Disclosure of Invention The present invention provides a bulk acoustic wave element according to claim 1 and a method for manufacturing a bulk acoustic wave element according to claim 10. Preferred further developments are the subject matter of the dependent claims. Advantages of the invention The invention is based on the idea of providing a bulk acoustic wave element and a method for producing a bulk acoustic wave element, wherein the suitability of the bulk acoustic wave element for operation in a high frequency range, in particular above 10 GHz, can be improved. The parasitic oscillation mode whose frequency is determined by the entire layer stack can be better suppressed and