ISSN 0020-1685, Inorganic Materials, 2008, Vol. 44, No. 5, pp. 527–529. © Pleiades Publishing, Ltd., 2008.Original Russian Text © V.V. Klimov, I.K. Skirdina, N.I. Selikova, A.N. Bronnikov, S.N. Loboda, A.S. Shtonda, 2008, published in Neorganicheskie Materialy, 2008, Vol. 44, No. 5,pp. 608–610.

527

INTRODUCTION

Films of functional materials find wide practicalapplication and play an ever more important role in theminiaturization of electronic components [1]. Lead zir-conate titanate (PZT) based films are used in the fabri-cation of sensors and micromechanical systems (micro-activators, micropumps, piezotransformers, andpiezoengines) [2, 3].

In some instances, thick films can be produced bythe same techniques as thin films, but the depositioncycle is repeated many times.

In recent years, thick films were also produced usingpowders prepared by long-term (80–100 h) grinding invarious high-energy mills.

Powders prepared in such mills consist of micron-sized particles. After the addition of various binders,the resultant paste is applied to a substrate by screenprinting or another process and then heat-treated [4].Lebedev and Akedo [5] produced thick films by aerosoldeposition using fine powder. The drawbacks to thesemethods are the high sintering temperature (above

1000°

C) and the need for expensive (Pt–Pd–Ag) elec-trodes. At high sintering temperatures, lead oxidevaporization is difficult to control.

In recent years, a combined method has been pro-posed for the preparation of thick PZT films: PZT mate-rials are produced by sol–gel processing and are thenmixed with fine powder of the same composition; theresultant paste is applied to a substrate and heat-treatedat temperatures from 800 to 1000

°

C. The sintering tem-perature can be reduced by adding PbO or Cu

2

O [6].In this paper, we describe a simple process for the

preparation of thick PZT-based films using the samestarting mixture composition as in the preparation ofPZTSr-3 [7], but with bismuth oxide additions. Aftergrinding the mixture in a vibratory mill for 0.5 h, apaste is prepared and applied to a substrate by screen

printing or another method. The firing temperature is

820–850°

C.

EXPERIMENTAL

PZT-based piezoceramics were prepared usinggrinding in a vibratory mill.

As a ferroelectric filler, we used PZTSr-3 [7] pre-pared by a conventional ceramic processing technique.After synthesis (at

800–850°

C), the PZTSr-3 powder wasground in a high-energy vibratory mill for 15–60 min withbismuth oxide additions (2 wt %). The resultant finepowder (0.5- to 1-

µ

m particles) was mixed with anorganic binder (powder : binder weight ratio of 3 : 1) for0.5 h using a variety of grinding devices to give a pastewith a Redwood viscosity on the order of 25–30 mm.

The organic binder had the form of a viscous trans-parent substance of complex composition, soluble inethanol and acetone and insoluble in water. It consistedof ethyl cellulose, terpineol, benzyl alcohol, and oxys-tearic acid.

The substrates we used were of sintered PZTSr-3,metallic nickel, or alumina (94% Al

2

O

3

). The substratesurface was degreased before use. Electrodes weremade of silver paste by screen printing, as was thepiezoelectric layer.

The accuracy of the electrode pattern (sharp bound-aries) was checked under a microscope, by comparingit with a test pattern.

The ferroelectric layer, as well as the electrodesbefore sintering, was dried in a dry box at

80–100°

C.Next, the binder was burnt out at

200–250°

C. The finalheat treatment of the ferroelectric layer was performedin a tube furnace at

820–850°

C for various lengths oftime. The thickness of the resultant film was 30–80

µ

m.Silver paste electrodes were made by firing at 750–800

°

Cfor 10–15 min.

Electrical Properties of Thick PZT-Based Films

V. V. Klimov, I. K. Skirdina, N. I. Selikova, A. N. Bronnikov, S. N. Loboda, and A. S. Shtonda

Donetsk National University, Universitetskaya ul. 24, Donetsk, 83055 Ukrainee-mail: klimov@dongu.donetsk.ua

Received January 11, 2007; in final form, August 29, 2007

Abstract

—We have studied the effect of bismuth oxide additions (2 wt %) on the electrical properties of thicklead zirconate titanate films. The results demonstrate that the addition of bismuth oxide to the starting mixture,followed by grinding in a high-energy vibratory mill, enables the sintering temperature to be lowered to820

−

850

°

C.

DOI:

10.1134/S0020168508050178

528

INORGANIC MATERIALS

Vol. 44

No. 5

2008

KLIMOV et al.

The appearance of the electrodes and ferroelectriclayer was checked under a microscope.

X-ray diffraction studies were carried out by stan-dard techniques on a URS-50I diffractometer with

ë

u

K

α

radiation.

Film thickness was measured by a micrometer (

h

=20–100

µ

m). The parameters of thick ferroelectric films(relative dielectric permittivity

ε

r

, dielectric loss tangent, Curie temperature, coercive force

Ö

c

, and rema-nent polarization

P

0

) are commonly determined by thesame techniques as those of bulk samples. The loss tan-gent of the ferroelectric films was determinedusing an MLE-1 high-sensitivity measuring bridge atapplied voltages in the range 0.2–1.0 V.

P

0

and

Ö

c

wereextracted from hysteresis loop measurements at 50 Hzin fields

E

= 2–8 kV/mm.

RESULTS AND DISCUSSION

The films produced on PZTSr-3 substrates werehighly homogeneous and had no surface flaws. Thesame refers to the films prepared on the other substrates(94% Al

2

O

3

and Ni).

Figure 1 shows the XRD patterns of a film, startingmixture, and ceramic based on PZTSr-3 with bismuthoxide additions (2 wt %). The XRD patterns are seen todiffer little, except for that of the starting mixture. Thethree diffraction patterns can be indexed in a tetrago-nally distorted perovskite cell. The XRD pattern of thestarting mixture shows weak peaks arising from unre-acted bismuth oxide.

Figure 2 shows the dielectric hysteresis loop of thefilm produced on a PZTSr-3 substrate. Its characteris-tics are

Ö

max

= 2200 V/mm (50 Hz), coercive field

Ö

c

=

δtan

δtan

730 V/mm, and remanent polarization

P

0

= 4.03

µ

C/cm

2

.These characteristics differ somewhat from thoseobtained on other substrates.

Figure 3 presents the temperature dependences of

ε

r

and which are seen to be typical of ceramics.The table summarizes the properties of films pre-

pared under different conditions. It can be seen that thebest results were achieved by sintering at

820–850°

Cfor 0.5–1 h.

CONCLUSIONS

We developed a process for the preparation of thickPZT-based films. The method is simple to implement

δtan ,

1

2

3

Inte

nsity

, arb

. uni

ts

2

θ

,

deg

24 30 36 42 48 54 60 66 72 7818

−

300

200

700

1200

1700

2200

2700

3200

3700

4200

Fig. 1.

XRD patterns of a (

1

) film, (

2

) starting mixture, and(

3

) ceramic.

–8

–6

–2

2

6

500 1000 1500

−

500

−

1500

−

2000

P

,

µ

C/cm

2

E

, V/mm

E

c

−

P

0

P

0

E

c

−

1000

–4

4

Fig. 2.

Dielectric hysteresis loop of a film produced on aPZTSr-3 substrate.

50 100 150 200 250 300 350

0

50

1000

1500

2000

2500

30000.24

0.20

0.16

0.12

0.08

0.04

0

tan

δ ε

r

t

, °C

tan

δ

ε

r

Fig. 3.

Temperature dependences of

ε

r

and for a filmproduced on a PZTSr-3 substrate.

δtan

INORGANIC MATERIALS

Vol. 44

No. 5

2008

ELECTRICAL PROPERTIES OF THICK PZT-BASED FILMS 529

and uses a bismuth-oxide-containing starting mixtureground in a high-energy vibratory mill, which isapplied to degreased substrates by screen printing or

another process and fired at

800–850°

C. The filmretains the stoichiometric composition because thevapor pressure of lead oxide in the range

820–850°

C isvery low and, accordingly, it vaporizes insignificantly.

REFERENCES

1. Sayer, M. and Screenivas, K., Ceramic Thin Films: Fab-rication and Application,

Science

, 1990, vol. 247,pp. 1056–1060.

2. Barrow, D.A., Petroff, T.E., and Sayer, M., ThickCeramic Coatings Using a Sol Gel Based Ceramic–Ceramic 0–3 Composite,

Surf. Coat. Technol.

, 1995,vols. 76–77, pp. 113–118.

3. Le Dren, S., Megriche, A., Gonnard, P., and Troccaz, M.,Thick Films on Alumina Substrates for PiezoelectricDevices Applications,

Ferroelectrics

, 2000, vol. 238,pp. 227–234.

4. Vechembre, J., Fox, G., and Setter, N., Parameters Influ-encing PZT Thick Films Densification,

Ferroelectrics

,1999, vol. 224, pp. 347–354.

5. Lebedev, M. and Akedo, J., Patterning Properties of PZTThick Films Made by Aerosol Deposition,

Ferroelec-trics

, 2002, vol. 270, pp. 117–122.

6. Dorey, R.A., Duval, F.F.C., Haigh, R.D., and What-more, R.W., The Effect of Repeated Sol Infiltrations onthe Microstructure and Electrical Properties of PZTComposite Sol–Gel Films,

Ferroelectrics

, 2002, vol.267, pp. 373–378.

7.

TU

(Technical Specifications)

6-09-5137-84

, 1984.

Electrical properties of films prepared under different condi-tions

t

sint,

°

C

Sintering time, h Substrate

h

,

µ

m

ε

r

800 0.5 PZTSr-3 46 756 0.01

Al

2

O

3

35 354 0.01

Ni 60 337 0.01

800 1 PZTSr-3 46 509 0.01

Al

2

O

3

45 393 0.01

Ni 80 491 0.01

820 0.5 PZTSr-3 65 706 0.01

Al

2

O

3

65 404 0.01

Ni 80 350 0.01

820 1 PZTSr-3 70 650 0.01

Al

2

O

3

55 708 0.07

Ni 40 442 0.01

850 1 PZTSr-3 60 447 0.01

Al

2

O

3

70 510 0.01

Ni 90 649 0.01

δtan