Electro-acoustic resonator

• US 20060131990A1
• Filed: 12/04/2003
• Published: 06/22/2006
• Est. Priority Date: 12/13/2002
• Status: Active Grant

• Current Assignee: Qorvo US, Inc. (Qorvo, Inc.)
• Original Assignee: NXP B.V. (NXP Semiconductors NV)
• Inventors: Lobl, Hans-Peter, Milsom, Robert Frederick
• Granted Patent: US 7,522,018 B2
• Time in Patent Office: Days
• US Class Current: 310/311
• CPC Class Codes: H03H 2003/0428 of an electrode
• CPC Class Codes: H03H 9/02149 of ageing changes of characteristics, e.g. electro-acousto-migration
• CPC Class Codes: H03H 9/131 consisting of a multilayered structure
• CPC Class Codes: H03H 9/174 Membranes
• CPC Class Codes: H03H 9/175 Acoustic mirrors
• CPC Class Codes: H04N 19/13 Adaptive entropy coding, e.g. adaptive variable length coding [AVLC] or context adaptive binary arithmetic coding [CABAC]
• CPC Class Codes: H04N 19/61 in combination with predictive coding
• CPC Class Codes: H04N 19/615 using motion compensated temporal filtering [MCTF]
• CPC Class Codes: H04N 19/63 using sub-band based transform, e.g. wavelets

Abstract

An electro-acoustic resonator (1, 8, 17) of the membrane or FBAR type (1) or the solidly-mounted or SBAR type (8), with electrodes comprising a single conducting layer or multiple conducting layers, i.e. sandwich construction (17) with an optimum coupling factor kr and thus an improved filter bandwidth. The optimum coupling factor kr is achieved by the arrangement that the top electrode (6, 15, 25) is thinner than the bottom electrode (4, 13, 23). The coupling factor is independent of the resonator'"'"'s layout defined by the mask.

Claims

1. Electro-acoustic resonator (1, 8, 17) with a layer structure comprising a piezoelectric layer (5, 14, 24) and a top (6, 15, 25) and a bottom (4, 13, 23) electrode layer, with the thickness (T1, T2, . . . T6) of the two electrode layers being unequal, characterised in that the top electrode layer (T1, T3, T5) is thinner than the bottom (T2, T4, T6) electrode layer.

2. Electro-acoustic resonator (1, 8, 17) as claimed in claim 1, characterised in that the electro-acoustic resonator (1, 8, 17) is a solidly-mounted resonator or SBAR (8,17) or that it has a membrane structure FBAR (1).

3. Electro-acoustic resonator (1, 8, 17) as claimed in claim 1, characterised in that at least one of the electrode layers (25, 26 or 22, 23) is formed by a stack of conductive materials.

4. Electro-acoustic resonator (1, 8, 17) as claimed in claim 1, characterised in that between the electrode layers 22 and 23 and/or 25 and 26 a conductive thin diffusion barrier is formed.

5. Electro-acoustic resonator (1, 8, 17) as claimed in claim 3, characterised in that in the stack the conductive material (23, 25) that is in contact with the piezoelectric layer (24) has a higher acoustic impedance than the conductive material (22, 26) that is not in contact with the piezoelectric layer (24).

6. Electro-acoustic resonator (1, 8, 17) as claimed in claim 3, characterised in that in the stack the conductive material (23, 25) in contact with the piezoelectric layer (24) has a lower acoustic impedance than the conductive material (22, 26) that is not in contact with the piezoelectric layer (24).

7. Electro-acoustic (1, 8, 17) resonator as claimed in claim 5, characterised in that the conductive material with the lower acoustic impedance comprises Aluminium (Al).

8. Electro-acoustic resonator (1, 8, 17) as claimed in claim 5, characterised in that the conductive material with the higher acoustic impedance comprises platinum (Pt), wolfram (W), molybdenum (Mo), titan-wolfram (Ti_xW_1-x, 0<

x<

1), Gold (Au).

9. Electro-acoustic resonator (1, 8, 17) as claimed in claim 5, characterised in that the diffusion barrier between the electrode layers 22 and 23 and/or between the electrodes 25 and 26 consists of titanium nitride (TiN), or titanium (Ti), or consists of comminations of titanium nitride (TiN) and titanium (Ti).

10. Electro-acoustic resonator (1, 8, 17) as claimed in claim 1, characterised in that the electrode layers (4, 6, 13, 15, 23, 25) comprise Molybdenum (Mo) and that, for a resonant frequency in the region of 2 GHz, the thickness (T1, T3, T5) of the top Molybdenum layer (6, 15,25) is in the region of 200 nm and the thickness (T2, T4, T6) of the bottom Molybdenum layer (4, 13, 23) is in the region of 300 nm, these thicknesses scaling approximately inversely with resonant frequency.

11. Electro-acoustic resonator (1, 8, 17) as claimed in claim 1, characterised in that the electrode layers (4, 6, 13, 15, 23, 25) comprise platinum (Pt) and that, for a resonant frequency in the region of 2 GHz, the thickness (T1, T3, T5) of the top platinum layer (6, 15,25) is in the region of 50 nm and the thickness (T2, T4, T6) of the bottom platinum layer (4, 13, 23) is in the region of 150 nm, these thicknesses scaling approximately inversely with resonant frequency.

12. Use of an electro-acoustic resonator (1, 8, 17), especially an electro-acoustic resonator as claimed in claim 1, as a component of a radio frequency (RF) filter, or as a component used in a sensor, or used in an ultrasonic transducer, or used in an array of ultrasonic transducers.