Thin-film bulk acoustic resonator with enhanced power handling capacity

• US 6,515,558 B1
• Filed: 11/06/2000
• Issued: 02/04/2003
• Est. Priority Date: 11/06/2000
• Status: Expired due to Fees

• Current Assignee: Avago Technologies General IP PTE Limited (Broadcom, Inc.)
• Original Assignee: Nokia Mobile Phones UK Limited (Nokia Corporation)
• Inventors: Ylilammi, Markku Antero
• Primary Examiner(s): Pascal, Robert
• Assistant Examiner(s): TAKAOKA, DEAN O
• Application Number:
  US09/707,092
• Time in Patent Office: 820 Days
• Field of Search: 333/187, 333/189, 333/190, 333/191, 310/324, 310/364
• US Class Current: 333/189
• CPC Class Codes: H03H 3/02 for the manufacture of piezoelectric or electrostrictive resonators or networks H03H3/08 takes precedence
• CPC Class Codes: H03H 9/02094 of adherence
• CPC Class Codes: H03H 9/02133 of stress
• CPC Class Codes: H03H 9/175 Acoustic mirrors

Abstract

A filter and a method for fabricating a filter comprising a thin film bulk acoustic wave resonator (FBAR), the FBAR including a plurality of layers of different materials deposited on top of each other and oh top of a substrate, the FBAR including a piezolayer sandwiched between a top electrode on the side of the piezolayer facing away from the substrate, and a bottom electrode on the side of the piezolayer facing the substrate, the FBAR further including an acoustic mirror made from a number of layers of different materials selected to provide in combination high reflectivity of sound energy, the method comprising the step of forming the bottom electrode from a material having a small acoustic impedance. A filter fabricated according to the method is advantageously used as part of a mobile phone, in the transmitter/receiver section of the mobile phone, the transmitter section including a power amplifier used to amplify signals before transmitting the signals via an antenna, and in particular as a component of a transmitter filter, coupling the power amplifier of the transmitter section to the antenna.

Claims

1. A method for fabricating a filter including a thin film bulk acoustic wave resonator (FBAR), the FBAR having a plurality of layers of different materials deposited on top of each other and on top of a substrate, the FBAR including a piezolayer sandwiched between a top electrode on the side of the piezolayer facing away from the substrate, and a bottom electrode on the side of the piezolayer facing the substrate, the FBAR also including an acoustic mirror situated closer to the substrate with a lowest layer in contact with the substrate over the entire surface of the lowest layer facing the substrate, the method characterized by a step of selecting from only among low acoustic impedance materials one or more materials from which to form the bottom electrode, and a step of forming the bottom electrode only from the one or more materials so selected, thereby increasing the power handling capacity of the filter.

2. The method of claim 1, wherein the bottom electrode is made from a material having a specific acoustic impedance of at most approximately 50 Gg/m²s.

3. The method of claim 1, wherein the substrate is made from material selected from the group consisting of glass, silicon dioxide, and gallium arsenide.

4. The method of claim 1, wherein the filter is fabricated to be a band-pass type filter.

5. The method of claim 4, wherein the filter is fabricated so as to comprise at least four FBARs.

6. A filter, including a thin film bulk acoustic wave resonator (FBAR) made according to the method of claim 1.

7. The filter of claim 6, wherein the bottom electrode is made from a material having a specific acoustic impedance of at most approximately 50 Gg/m²s.

8. The filter of claim 6, wherein the substrate is made from material selected from the group consisting of glass, silicon dioxide, and gallium arsenide.

9. The filter of claim 6, wherein the filter is a band-pass type filter.

10. The filter of claim 9, wherein the filter comprises at least four FBARs.

11. The filter of claim 10, wherein the filter is used as part of a transmitter in a mobile phone, the mobile phone including an antenna and including a power amplifier, the filter coupling the power amplifier to the antenna.

12. The filter of claim 11, wherein the-filter is a band-pass type filter.

13. The filter of claim 12, wherein the filter comprises at least four FBARs.