# US 8,569,864 B2 · Piezo-acoustic thin film resonator having a crystalline zinc oxide layer

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- Number: US 8,569,864 B2
- Document ID: US8569864B2
- Status: Granted
- Kind: B2
- Application number: 11/663,831
- Filed: 2005-08-02
- Published: 2009-03-26
- Granted: 2013-10-29
- Earliest claimed: 2004-09-28
- Assignees: Siemens Aktiengesellschaft
- Applicants: Reinhard Gabl; Mathias Link
- Inventors: Reinhard Gabl; Mathias Link
- Web page: https://patentgrep.com/patent/US8569864B2

## CPC

- G01N 29/022: {Fluid sensors based on microsensors, e.g. quartz crystal-microbalance [QCM], surface acoustic wave [SAW] devices, tuning forks, cantilevers, flexural plate wave [FPW] devices (microdevices per se B81B)}
- G01N 29/2437: {Piezoelectric probes}
- G01N 2291/0256: Adsorption, desorption, surface mass change, e.g. on biosensors
- G01N 2291/0426: Bulk waves, e.g. quartz crystal microbalance, torsional waves
- Y10T 29/435: Solid dielectric type
- G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q)
- Y10T: TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION

## Abstract

A capacitor structure includes a lower electrode layer disposed on a substrate, an upper electrode layer and a crystalline zinc oxide-containing dielectric layer interposed between the electrode layers. The amorphous dielectric intermediate layer is interposed between the lower electrode layer and the crystalline zinc oxide-containing dielectric layer. A method for producing the aforementioned capacitor structure is also disclosed. The amorphous dielectric layer is adapted to produce during deposition of the zinc oxide an electrical field which is tipped in relation to the normal to the surface of the substrate surface or the lower electrode layer. The zinc oxide monocrystals grow at an angle, thereby providing a crystalline dielectric layer that can be induced to shear vibrations.

## Claims

### Claim 1

A capacitor structure (1) for forming a piezo-acoustic resonator, comprising:
a lower electrode layer (5) arranged on a substrate surface (31) of a substrate (3);
an upper electrode layer (6);
a crystalline zinc oxide-containing dielectric layer (2) arranged between the electrode layer (5, 6), which has a plurality of zinc oxide single crystals each with a polar crystal axis, the polar crystal axes of the zinc oxide single crystals of the dielectric layer being tipped relative to the substrate surface (31); and
an amorphous dielectric intermediate layer (4) interposed between the lower electrode (5) and the crystalline zinc oxide-containing dielectric layer (2), the intermediate layer (4) having an intermediate layer thickness (41) of 20 nm to 500 nm.

### Claim 2 (depends on 1)

The capacitor structure as claimed in claim 1, with the intermediate layer (4) at least comprising at least one ceramic material selected from the group consisting of aluminum oxide, silicon dioxide, titanium dioxide and zirconium dioxide.

### Claim 3 (depends on 1)

The capacitor structure as claimed in claim 1, with the crystalline zinc oxide-containing dielectric layer (2) having a layer thickness (21) of 0.1 μm to 20 μm.

### Claim 4 (depends on 1)

The capacitor structure as claimed in claim 1, with the lower electrode layer (5) comprising an electrode material selected from the group consisting of tungsten and platinum.

### Claim 5 (depends on 1)

The capacitor structure as claimed in claim 1, with the upper electrode layer (6) comprising an electrode material selected from the group consisting of aluminum and gold.

### Claim 6 (depends on 1)

The capacitor structure as claimed in claim 1, with the substrate (3) being a semiconductor substrate with a semiconductor material.

### Claim 7 (depends on 1)

A method for producing the capacitor structure as claimed in claim 1 having the method steps:
a) providing the substrate (3)
b) producing the lower electrode layer (5) on a substrate surface (31) of the substrate (3)
c) producing the amorphous intermediate layer (4) on the lower electrode layer (5)
d) producing the crystalline zinc oxide-containing dielectric layer (2) on the intermediate layer (4), and
e) producing the upper electrode layer (6) on the crystalline zinc oxide-containing dielectric layer (4).

### Claim 8 (depends on 7)

The method as claimed in claim 7, with a deposition being carried out from a vapor phase in order to produce the lower electrode layer (5), the amorphous intermediate layer (4), the crystalline zinc oxide-containing dielectric layer and/or the upper electrode layer (6).

### Claim 9 (depends on 8)

The method as claimed in claim 8, with a deposition of zinc oxide from the vapor phase being carried out in order to produce the crystalline dielectric layer (2) and an electrical field being generated during the deposition of the zinc oxide, said electrical field being tipped in respect of a normal of the surface of the lower electrode layer (5).

### Claim 10 (depends on 1)

Method of using the capacitor structure as claimed in claim 1 as a piezo-acoustic resonator, with the crystalline zinc oxide-containing dielectric layer forming a piezo-electric layer of the resonator (10) and the piezo-electric layer (2) and the electrode layers (5, 6) being arranged next to one another such that an electrical control of the electrode layers (5, 6) results in the resonator (10) vibrating at a specific resonance frequency.

### Claim 11 (depends on 10)

The method as claimed in claim 10, with the resonance frequency of the vibration being selected from the range of exclusively 500 MHz to exclusively 10 GHz.

### Claim 12 (depends on 10)

The method as claimed in claim 10 for detecting at least one substance of a fluid (13), with the following method steps being carried out:
a) combining the fluid (13) and the piezo-acoustic resonator (10) such that the substance is able to be sorbed on the surface segment (12) of the resonator (10) and
b) determining a resonance frequency of the resonator (10), with the substance being concluded from the resonance frequency on the quantity sorbed by the surface segment (12).

### Claim 13 (depends on 12)

The method as claimed in claim 12, with a surface segment (12) for sorbing a substance of a fluid (13) being arranged at the resonator (10) such that the resonance frequency of the resonator (10) is dependent on a quantity of the substance sorbed at the surface segment (12).

### Claim 14 (depends on 12)

The method as claimed in claim 12, with the surface segment (12) being formed to sorb the substance of the fluid (13) from a chemically sensitive coating (14) of the resonator (10).

### Claim 15 (depends on 12)

The method as claimed in claim 12, with the resonance frequency being determined in the presence of the fluid (13).

### Claim 16 (depends on 1)

The capacitor structure as claimed in claim 1, with the intermediate layer thickness being from 50 nm to 200 nm.

### Claim 17 (depends on 1)

The capacitor structure as claimed in claim 1, with the intermediate layer thickness being sufficient to achieve a tipping of zinc oxide monocrystals.

### Claim 18

A capacitor structure (1) for forming a piezo-acoustic resonator, comprising:
a lower electrode layer (5) arranged on a substrate surface (31) of a substrate (3);
an upper electrode layer (6);
a crystalline zinc oxide-containing dielectric layer (2) arranged between the electrode layer (5, 6), the zinc oxide-containing dielectric layer (2) having a plurality of zinc oxide monocrystals each with a polar crystal axis, the polar crystal axes of the zinc oxide monocrystals of the dielectric layer being tipped relative to the substrate surface (31); and
an amorphous dielectric intermediate layer (4) interposed between the lower electrode (5) and the crystalline zinc oxide-containing dielectric layer (2), the intermediate layer (4) having an intermediate layer thickness (41) of 20 nm to 500 nm, the with the intermediate layer thickness being sufficient to achieve a tipping of the zinc oxide monocrystals.

### Claim 19 (depends on 18)

The capacitor structure as claimed in claim 18, with the zinc oxide monocrystals having a tipping of a c-axis of the monocrystals at approximately 16° toward a normal of the substrate's surface.