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KR-20260066739-A - Multilayer structure and filter including the same

KR20260066739AKR 20260066739 AKR20260066739 AKR 20260066739AKR-20260066739-A

Abstract

A multilayer structure for a bulk acoustic wave resonator is provided, and the multilayer structure comprises a piezoelectric layer (702), a first upper electrode layer (704) above the piezoelectric layer, a first lower electrode layer (714) below the piezoelectric layer (702), a second upper electrode layer (706) above the first upper electrode layer (704), a second lower electrode layer (716) below the first lower electrode layer (714), a third upper electrode layer (708) above the second upper electrode layer (706), and a third lower electrode layer (718) below the second lower electrode layer (716). The first upper electrode layer (704) and the first lower electrode layer (714) are configured to form an acoustic confinement layer, the second upper electrode layer (706) and the third upper electrode layer (708) are configured to form a first acoustic free surface toward the first upper electrode layer (704), and the second lower electrode layer (716) and the third lower electrode layer (718) are configured to form a second acoustic free surface toward the first lower electrode layer (714).

Inventors

  • 모리츠 드미트리
  • 칸데미르 하칸
  • 펜살라 투오마스
  • 막코넨 타파니

Assignees

  • 테크놀로지안 투트키무스케스쿠스 브이티티 오와이

Dates

Publication Date
20260512
Application Date
20240909
Priority Date
20230907

Claims (20)

  1. As a multilayer structure for a bulk acoustic wave resonator, - Single piezoelectric layer (702); - First upper electrode layer (704) on the single piezoelectric layer (702); - First lower electrode layer (714) below the single piezoelectric layer above; - Second upper electrode layer (706) above the first upper electrode layer; - Second lower electrode layer (716) below the first lower electrode layer; - A third upper electrode layer (708) above the second upper electrode layer, or a passivation layer (1008) above the second upper electrode layer; and - Includes a third lower electrode layer (718) below the second lower electrode layer; A multilayer structure characterized in that the first upper electrode layer (704) and the first lower electrode layer (714) are configured to form an acoustic confinement layer, the second upper electrode layer (706) and the third upper electrode layer (708) or the passivation layer are configured to form a first acoustic free surface toward the first upper electrode layer (704), and the second lower electrode layer (716) and the third lower electrode layer (718) are configured to form a second acoustic free surface toward the first lower electrode layer (714).
  2. In claim 1, the first upper electrode layer (704) and the third upper electrode layer (708) have a multilayer structure having an acoustic impedance higher than the acoustic impedance of the second upper electrode layer (706).
  3. A multilayer structure according to claim 1 or 2, wherein each of the first lower electrode layer (714) and the third lower electrode layer (718) has an acoustic impedance higher than the acoustic impedance of the second lower electrode layer (716).
  4. A multilayer structure according to any one of claims 1 to 3, wherein each of the first upper electrode layer (704) and the first lower electrode layer (714) has an acoustic impedance higher than the acoustic impedance of the piezoelectric layer (702).
  5. A multilayer structure according to any one of claims 1 to 4, wherein each of the first upper electrode layer (704), the third upper electrode layer (708), the first lower electrode layer (714), and the third lower electrode layer (718) has a longitudinal acoustic impedance of 60 x 10⁶ kg/ m² s or more.
  6. In any one of claims 1 to 5, the first upper electrode layer (704) and the first lower electrode layer (714) each have a thickness thinner than 1/4 of the acoustic wavelength at the resonant frequency of the resonator, in a multilayer structure.
  7. In any one of claims 1 to 6, the first upper electrode layer (704) and the first lower electrode layer (714) each have a thickness of 0.07 to 0.13 of the acoustic wavelength at the resonant frequency of the resonator, a multilayer structure.
  8. In any one of claims 1 to 7, the second upper electrode layer (706), the second lower electrode layer (716), the third upper electrode layer (708) and the third lower electrode layer (718) each have a thickness close to 1/4 of the acoustic wavelength at the resonant frequency of the resonator, in a multilayer structure.
  9. A multilayer structure according to any one of claims 1 to 8, comprising an acoustic Bragg reflector in at least one of the third upper electrode layer (708) and the third lower electrode layer (718).
  10. In claim 9, the acoustic Bragg reflector is a multilayer structure in which the acoustic Bragg reflector is an insulator-metal Bragg reflector, a full metal Bragg reflector, or a full insulator Bragg reflector.
  11. A multilayer structure according to any one of claims 1 to 10, wherein at least one of the first upper electrode layer (704) and the first lower electrode layer (714) is made of a high acoustic impedance material such as, for example, tungsten (W) or tungsten-titanium (TiW).
  12. A multilayer structure in which, in any one of claims 1 to 11, at least one of the second upper electrode layer (706) and the second lower electrode layer (716) is aluminum.
  13. A multilayer structure according to any one of claims 1 to 12, wherein at least one of the third upper electrode layer (708) and the third lower electrode layer (718) is made of a high acoustic impedance material such as, for example, tungsten (W) or tungsten-titanium (TiW).
  14. A multilayer structure according to any one of claims 1 to 13, wherein the first acoustic free surface is between the first upper electrode layer (704) and the second upper electrode layer (706), the second acoustic free surface is between the first lower electrode layer (714) and the second lower electrode layer (716), and each of the first acoustic free surface and the second acoustic free surface has a substantially minimum impedance at or near the operating frequency of the resonator.
  15. In any one of claims 1 to 14, the passivation layer (1008) has a multilayer structure having a thickness close to 1/4 of the acoustic wavelength at the resonant frequency of the resonator.
  16. In any one of claims 1 to 15, the passivation layer (1008) is a multilayer structure trimmed to a thickness of 0.1 to a maximum of 0.5 of the wavelength.
  17. In any one of claims 1 to 16, the passivation layer (1008) is a multilayer structure trimmed to a thickness of 0.1 to a maximum of 0.4 of the wavelength.
  18. A bulk acoustic resonator comprising a multilayer structure according to any one of claims 1 to 17.
  19. In paragraph 18, a bulk acoustic resonator comprising a membrane bulk acoustic wave resonator or a solidly mounted resonator.
  20. A multilayer structure according to any one of claims 1 to 17; or a filter for a radio frequency band of 6 GHz to 30 GHz comprising the bulk acoustic resonator of claim 18 or the bulk acoustic resonator of claim 19.

Description

Multilayer structure and filter including the same The present invention relates to a structure for a bulk acoustic wave resonator, and more specifically, to an electrode structure for a bulk acoustic wave resonator that can be extended to form a filter over a wide frequency range. Mobile communication radios must be able to strictly transmit and receive only within their allocated frequency bands and block transmissions and noise from other frequencies. This can be implemented using bandpass or passband filters, and in small mobile devices, it is based on microacoustic technology—specifically, a technique that utilizes the piezoelectric effect to convert radio signals into surface acoustic waves (SAW) or bulk acoustic waves (BAW) within an acoustic resonance structure. A BAW can be a film bulk acoustic wave resonator (FBAR) or a solidly mounted resonator (SMR) containing a thin film piezoelectric layer sandwiched between an upper and lower electrode. While FBARs can be based on floating films or cavity structures, SMRs are fabricated directly on a substrate. Film bulk acoustic wave resonators (FBARs) operate in dedicated frequency bands within a broad spectrum ranging from less than 1 GHz to 6 GHz and are used to construct bandpass filters for mobile communication systems that extend to higher frequencies. BAW-based technology is more suitable for frequencies above 2 GHz than SAW-based technology. While 4G mobile communication bands were mostly allocated below 2.5GHz, 5G introduced bands between 3GHz and 6GHz and 30GHz. Frequency bands above 6GHz are also gradually expanding. This poses a significant challenge for filters, as extending acoustic filters beyond 5GHz is burdensome, and extending them to 30GHz with low loss and high bandwidth currently appears impossible. Currently, there are no filters in the 30GHz range that are capable of miniaturization, high performance, and mass production. FIG. 1 illustrates an example of a bulk acoustic wave resonator. The BAW resonator (100) may be an FBAR comprising a stack or stack of layers. The stack comprises a thin piezoelectric film or piezo layer (102) sandwiched between metal electrodes (104). An RF signal applied to the electrodes is converted into an acoustic wave having a resonator volume defined by the thickness ( t ) of the piezoelectric layer and the electrodes. The dashed line illustrates the stress distribution of the fundamental half-wavelength thickness resonance. Fundamental acoustic resonance occurs when the acoustic wavelength at the RF signal frequency substantially corresponds to half the acoustic wavelength within the thickness of the piezoelectric layer and the electrodes. In a simplified example of a BAW resonator (100), since the electrode (104) has the same acoustic velocity as the piezo layer (102), resonance occurs at the following frequency. Here ε is the acoustic velocity and t is the total thickness of the stack of electrodes and piezo layers. Resonance forms a frequency-selective function, enabling a constructed filter, or BAW filter. A BAW filter is a passband filter constructed by connecting at least two BAW resonators of different frequencies ( f ) in a network commonly referred to as a ladder configuration. It should be noted that the BAW/FBAR resonator behaves like a capacitance ( Co ) having a local low-impedance point corresponding to local resonance and a local high-impedance point corresponding to local anti-resonance. This behavior can be described by a Butterworth-van Dyke equivalent circuit. FIG. 2 illustrates an example of the electrical impedance of a BAW resonator. The magnitude of the electrical impedance (202) is shown in ohms over a frequency range from just above 0 GHz to 3 GHz. The BAW resonator has a resonant frequency ( fr ) (204) at 2 GHz and an anti-resonant frequency ( f a ) (206) just above 2 GHz. The resonant frequency ( f r ) is the point where the electrical impedance is lowest over the corresponding frequency range, and the anti-resonant frequency ( f a ) is the point where the electrical impedance is highest over the corresponding frequency range. The difference between the resonant frequency ( f r ) and the anti-resonant frequency ( f a ) determines the electromechanical coupling coefficient ( K 2 ) of the BAW resonator and how wide a bandwidth filter can be formed from the BAW resonator. The specifications for K2 according to the IEEE standard regarding piezoelectricity are as follows, and Here, f s is the resonant frequency (f r ) and f p is the anti-resonant frequency (f a ). However, a simpler indicator of electromechanical coupling strength directly related to bandwidth is expressed as a % It is. Based on simple experience, a ladder filter with a bandwidth of 1.2Δf can be constructed without additional external components. FIG. 3 illustrates an example of a Butterworth van Dyke equivalent circuit of a bulk acoustic wave resonator. The Butterworth van Dyke equivalent circuit describes the electrica