RSM2013 Proc. 2013, Langkawi, Malaysia

Ba0.7 Sr0.3 TiO3Thin Film Dielectric Properties with Different Deposition Layer

1Chin, T.Y., 1Sauli, Z.,1Retnasamy, V.*&1Ramli, N. 1School of Microelectronic Engineering, Universiti Malaysia Perlis (UniMAP),

Kampus Alam,Pauh Putra Perlis, Malaysia. *Corresponding email: vc.sundres@gmail.com

Abstract– Barium strontium titanate(BaxSr1-xTiO3), BST thin

film was a ferroelectric material used commercially in worldwide since decades ago. Many researches were done on this BST thin film. In this work, the experiment is focus on the dielectric properties of Ba0.7Sr0.3TiO3 thin film with different deposition layer. As the deposition layer of Ba0.7Sr0.3TiO3 increase, the dielectric properties of the thin film increase.

Keywords- BST; Thin Flim

I INTRODUCTION

Barium strontium titanate BaxSr1-xTiO3, BST has captured many attentions to apply it as a dielectric material for dynamic random access memories (DRAM), uncooled focal plane array (UFPA), and electricaltunable microwave devices for example voltage phase shifters, oscillators, delay lines, and parametric amplifiers[1-6].

Ba0.7Sr0.3TiO3 thin film is a composition with Curie point almost near to the room temperature where observation on the giant room-temperature dielectric tunability can be done[7]. In the year 1992, the use of BST capacitor in GaAs MMICs for 2.3GHz operation had been accomplished by Symetrix-Matsushita collaboration and resulted in commercial production where at ambient temperature the maximum dielectric constant is when x~0.7[8].

Recent years, attentions on substrate effect on thin-film properties keep increasing because the ferroelectric properties can be improve by the modification via the film-substrate interface[7].

In this present work, Ba0.7Sr0.3TiO3 thin films with 4 different layers were prepared on Pt/SiO2/Si substrates to investigate the difference in dielectric constant, tunability and dielectric loss on the microstructure of 25°C.

II METHODOLOGY

A. BaxSr1-xTiO3 Solution Preparation

The starting material used as the precursor solution on BaxSr1-xTiO3 was synthesized using barium acetate (Ba(CH3CO2)2), strontium acetate (Sr(CH3CO2)2), and titanium (IV) isopropoxide (Ti((CH3)2CHO)4) . The solvent used were 2-methoxyethanol (C3H8O2) and glacial acetic acid (CH3COOH). To obtain clear and transparent solution, appropriate amount based on x=0.7 of barium acetate and strontium acetate is mixed and stirred in heated acetic acid at

80°C for 1 hour. Reflux condenser was used to flux the Ba-Sr solution. Titanium (IV) isopropoxide was dissolved in 2-methoxy ethanol at room temperature and stirred after reflux. Ba-Sr solution was dropped into Ti solution at room temperature and refluxed for 30 minutes at 120°C so that the solution becomes thicker. The solution was filtered to obtain clear yellowish solution.

B. BaxSr1-xTiO3 solutions Deposition Process

The first step involved in deposition process of BaxSr1-xTiO3 solution is substrate cleaning. After that, dry oxidation taking place for 25 minutes to grow thin layer of silicon oxide on substrate. Next step was the platinum deposition process on SiO2/Si substrate using Auto Fine Coater. Then the sample was annealed at 900°C for 30 seconds to get uniform surface layer. After platinum deposition process, Ba0.7Sr0.3TiO3 solution was deposited to the Pt/SiO2/Si substrates. The thin films are baked on hot plate at 200°C for 20 minutes to vaporize the organic solvents. The thin films are then heated in furnace at 500°C for 30 minutes. The thin films are annealed in O2 atmosphere at 800°C for 2 hours to obtain crystalline phase of the thin films. The deposition process is repeated 4 times to produce multiple layer of Ba0.7Sr0.3TiO3 which noted as layer 1, layer 2, layer 3 and layer 4.

III RESULTS AND DISCUSSION

Fig. 1 (a), (b), (c) and (d) shows the variation of dielectric

constant (r) of Ba0.7Sr0.3TiO3 thin films for 1 layer, 2 layer and 4 layer film thickness respectively. The non-linear εr -V curves of Ba0.7Sr0.3TiO3 thin films exhibit hysteresis with two peaks of spontaneous polarization switching obviously shown in the Fig. 1. All the εr -V curves of Ba0.7Sr0.3TiO3 thin films with butterfly-shaped curves indicate that the films have ferroelectric nature[9, 10]. The asymmetry of the εr -V curves may be due to the different materials used as top and bottom electrodes.

Table 1 listed the film thickness, grain size, dielectric constant, dielectric loss and dielectric tunability of Ba0.7Sr0.3TiO3 thin films. The results indicate that the higher dielectric constant and tunability at higher film thickness. The dielectric loss of the Ba0.7Sr0.3TiO3 thin films increases from 0.0583 to 0.0726 with the increasing of film thickness. As the

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RSM2013 Proc. 2013, Langkawi, Malaysia

(a)

(b)

(c)

(d)

Fig. 1. εr-V characteristics of Ba0.7Sr0.3TiO3 thin films with 4 different thickness

TABLE 1

FILM THICKNESS, GRAIN SIZE, DIELECTRIC CONSTANT, DIELECTRIC LOSS AND DIELECTRIC TUNABILITY OF Ba0.7Sr0.3TiO3 THIN FILMS

Thickness Thickness (nm)

Grain Size (nm)

Dielectric constant

Dielectric loss

Tunability (%)

1 Layer 163.84 67.696 161.03 0.0583 6.63 2 Layer 241.02 70.982 249.73 0.0651 12.18 3 Layer 368.68 84.796 388.43 0.0696 12.90 4 Layer 447.6 112.42 485.02 0.0726 34.75

film thickness increase, the surface roughnesses also increase. Therefore, the increase in dielectric loss is due to the increase of surface roughness which can be explained by Cole and Geyer that state that a rough film surface contributes to the conductor loss thus resulted in higher device insertion loss[11]. It is also clearly seen that the tunability increases as dielectric constant increase.

IV CONCLUSION

As a conclusion, the electrical propertiesare directly proportional to the layer of Ba0.7Sr0.3TiO3. As the number of layer increase, the electrical properties in term of dielectric constant, tunability and dielectric loss increase. Therefore, Ba0.7Sr0.3TiO3 thin film with 4 layer deposition possess highest value of dielectric constant, tunability and dielectric loss due to the higher grain size and thickness. There is of course disadvantage this finding also where the dielectric loss is quite high. In future works, experiment can be done to reduce the dielectric loss while increasing the dielectric constant and tunability.

ACKNOWLEDGEMENT

The authors would like to thank and acknowledge the School

of Microelectronic Engineering,Universiti Malaysia Perlis for their support and facility. The authors appreciation are extended to the Ministry of Higher Education for the support given.

REFERENCES

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