US-12627277-B2 - Thin-film surface-acoustic-wave resonator with aluminum nitride layer

Abstract

An apparatus is disclosed for a surface-acoustic-wave device having an Aluminum Nitride substrate layer. In one aspect, a surface acoustic wave (SAW) includes a substrate layer comprising an Aluminum Nitride (AlN) substrate layer, an electrode structure comprising an interdigital transducer, and a piezoelectric layer disposed between the electrode structure and the substrate layer. In some aspects, the piezoelectric layer is Lithium Niobate or Lithium Tantalate.

Inventors

• Ulrike Monika Roesler

Assignees

• RF360 SINGAPORE PTE. LTD.

Dates

Publication Date

20260512

Application Date

20231107

Claims (20)

1. 1 . A surface acoustic wave (SAW) resonator comprising: a substrate layer comprising an Aluminum Nitride (AlN) substrate layer, an electrode structure comprising an interdigital transducer, and a piezoelectric layer disposed between the electrode structure and the substrate layer, wherein the AlN substrate layer is a deposited thin film layer and comprises a Scandium doped thin film layer.
2. 2 . The SAW resonator of claim 1 , wherein the piezoelectric layer comprises lithium tantalate (LT), wherein a crystalline structure of the piezoelectric layer is defined by Euler angles lambda (λ), mu (μ), and theta (θ).
3. 3 . The SAW resonator of claim 2 , wherein a thickness of the piezoelectric layer is approximately 0.4 times a pitch value for fingers of the interdigital transducer.
4. 4 . The SAW resonator of claim 3 , wherein a thickness of the AlN substrate layer is less than four times the pitch value.
5. 5 . The SAW resonator of claim 2 , wherein μ is a value in a range from −80 degrees to −30 degrees.
6. 6 . The SAW resonator of claim 2 , wherein the piezoelectric layer is in a configuration selected from LT0 through LT 60.
7. 7 . The SAW resonator of claim 2 , wherein the piezoelectric layer is in a configuration selected from LT25 through LT 50.
8. 8 . The SAW resonator of claim 2 , wherein a thickness of the piezoelectric layer is between 0.2 and 0.8 times a pitch value for fingers of the interdigital transducer.
9. 9 . The SAW resonator of claim 1 , wherein the Scandium doped thin film layer is configured to adjust a velocity (v sh ) value.
10. 10 . The SAW resonator of claim 9 , wherein the substrate layer further comprises a glass support layer wherein the AlN substrate layer is disposed between the piezoelectric layer and the glass support layer.
11. 11 . The SAW resonator of claim 10 , wherein the glass support layer is doped to match a thermal expansion coefficient of the glass support layer to a thermal expansion coefficient of the piezoelectric layer.
12. 12 . The SAW resonator of claim 1 , wherein the substrate layer further comprises a glass support layer, wherein the AlN substrate layer is disposed between the glass support layer and the piezoelectric layer.
13. 13 . The SAW resonator of claim 12 , wherein the glass support layer is formed of amorphous SiO2.
14. 14 . The SAW resonator of claim 12 , wherein the glass support layer is formed of crystalline SiO2.
15. 15 . The SAW resonator of claim 1 , wherein the AlN substrate layer comprises a ceramic AlN layer.
16. 16 . The SAW resonator of claim 15 , wherein the AlN substrate layer is fabricated comprising a non-piezoelectric layer using ceramic material and unordered polycrystalline AlN or amorphous AlN.
17. 17 . The SAW resonator of claim 1 , further comprising an SiO2 compensation layer between the piezoelectric layer and the AlN substrate layer.
18. 18 . The SAW resonator of claim 17 , wherein the SiO2 compensation layer is approximately between 0.2 and 0.8 a pitch value for fingers of the interdigital transducer.
19. 19 . The SAW resonator of claim 1 , wherein the substrate layer and the piezoelectric layer are configured for excitation of surface waves, and wherein the AlN substrate layer is configured as a fast layer to confine wave energy to a top surface of the SAW resonator.
20. 20 . The SAW resonator of claim 1 , wherein the piezoelectric layer comprises lithium tantalate (LT) or lithium niobate (LN).

Description

TECHNICAL FIELD This disclosure relates generally to filters and, more specifically, to surface-acoustic-wave (SAW) filters with an Aluminum Nitride layer (AlN) layer. BACKGROUND Electronic devices include traditional computing devices such as desktop computers, notebook computers, tablet computers, smartphones, wearable devices like a smartwatch, internet servers, and so forth. These various electronic devices provide information, entertainment, social interaction, security, safety, productivity, transportation, manufacturing, and other services to human users. These various electronic devices depend on wireless communications for many of their functions. Wireless communication systems and devices are widely deployed to provide various types of communication content such as voice, video, packet data, messaging, broadcast and so on. These systems may be capable of supporting communication with multiple users by sharing the available system resources (e.g., time, frequency, and power). Examples of such systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, and orthogonal frequency division multiple access (OFDMA) systems, (e.g., a Long Term Evolution (LTE) system, or a New Radio (NR) system). Wireless communication transceivers used in these electronic devices generally include multiple radio frequency (RF) filters for filtering a signal for a particular frequency or range of frequencies. Electroacoustic devices (e.g., “acoustic filters”) are used for filtering high-frequency (e.g., generally greater than 100 MHz) signals in many applications. Using a piezoelectric material as a vibrating medium, acoustic resonators operate by transforming an electrical signal wave that is propagating along an electrical conductor into an acoustic wave that is propagating via the piezoelectric material. The acoustic wave propagates at a velocity having a magnitude that is significantly less than that of the propagation velocity of the electromagnetic wave. Generally, the magnitude of the propagation velocity of a wave is proportional to a size of a wavelength of the wave. Consequently, after conversion of an electrical signal into an acoustic signal, the wavelength of the acoustic signal wave is significantly smaller than the wavelength of the electrical signal wave. The resulting smaller wavelength of the acoustic signal enables filtering to be performed using a smaller filter device. This permits acoustic resonators to be used in electronic devices having size constraints, such as the electronic devices enumerated above (e.g., particularly including portable electronic devices such as cellular phones). SUMMARY An apparatus is disclosed that implements a surface-acoustic-wave (SAW) filter using an Aluminum Nitride layer (AlN) substrate layer. In one aspect, an apparatus is provided. The apparatus is surface acoustic wave (SAW) filter apparatus comprising: a substrate layer comprising an Aluminum Nitride (AlN) substrate layer, an electrode structure comprising an interdigital transducer, the interdigital transducer having an input, an output, and a central track, and a piezoelectric layer disposed between the electrode structure and the substrate layer, where a crystalline structure of the piezoelectric layer is defined by Euler angles lambda (λ), mu (μ), and theta (θ), where the substrate layer and the piezoelectric layer are configured for excitation of selected electroacoustic wave modes confined by the AlN substrate layer to limit excitation spurious wave modes in a stack structure of the SAW filter apparatus. Some such aspects are configured where the piezoelectric layer comprises Lithium Tantalate, and where the Euler angles for the piezoelectric layer are selected in a range from LT0 through LT60. Another aspect is a resonator device. The resonator device comprises a SAW resonator that includes a glass support layer and a fast AlN layer disposed on the glass support layer. Aspects may also additionally comprise a slow layer disposed on the AlN layer. Aspects can further include an electrode structure comprising an interdigital transducer, and a piezoelectric layer disposed between the electrode structure and the fast layer. Some such aspects are configured where the substrate layer and the piezoelectric layer are configured for excitation of surface waves. Some such aspects are configured where a slow layer is an SiO2 layer configured to limit excitation of spurious surface waves. Another aspect is a method. The method comprises forming a substrate layer comprising an Aluminum Nitride (AlN) substrate layer, forming a piezoelectric layer on a top surface of substrate layer, where a crystalline structure of the piezoelectric layer is defined by Euler angles lambda (λ), mu (μ), and theta (θ), and forming an electrode layer on a top surface of the piezoelectric layer, where the substrate layer and the piezoelectric laye