24P012-O
Structural and Electrical Properties of BiFeO3 Thin Films Deposited on
Polycrystalline Diamond Substrates
多結晶ダイヤモンド基板上へのBiFeO3薄膜の作製と特性評価
H. Kawasaki1, T. Kawae1, T. Nakajima2, N. Tokuda1, Y. Takano3, S. Okamura2 and A. Morimoto1
川崎寛樹1, 川江 健1，中嶋宇史2，徳田規夫1，高野義彦3，岡村総一郎2，森本章治1
1

Kanazawa University, 2Tokyo University of Science, and 3National Institute for Materials Science1
金沢大学、2東京理科大、3物質・材料研究機構

Pr and Mn co-doped BiFeO3 (BPFM)/B-doped diamond layered film structure was fabricated on apolycrystalline diamond substrate. In the X-ray diffraction analysis, we observed the crystallization ofBPFM and B-doped diamond without impurity phases in the present structure. In the polarization versus
electric field curve, the BPFM/B-doped diamond layered film shows saturated hysteresis behavior at room
temperature. The remnant polarization and coercive field for a maximum electric field of 1000 kV/cm were
135 µC/cm2 and 700 kV/cm, respectively.

1. Introduction
Nonvolatileferroelectric
randomaccessmemories (FeRAM), composed of semiconductor
and ferroelectrics, have attracted attention becauseof low power consumption and high-speed
operation[1]. However, it is not easy to operate theFeRAM devices using Si and Pr(Zr, Ti)O3(PZT) at
high temperature due to the narrow gap ofsemiconductor and low Curie temperature TC offerroelectrics. Hence, the developing of FeRAM
device materials with excellent physical properties
for high temperature operation is required. For thisrequirement, we had proposed the integration ofwide-gap semiconductor diamond and high-TC
ferroelectric material BiFeO3[2], and reported thefabrication and characterization of BFO/B-dopeddiamond layered film capacitor on the single crystal
diamond substrate[3]. In that structure, excellent
ferroelectric properties were observed at room
temperature and the maximum operation
temperature was 150 ˚C [4].
On the other hand, due to the development ofrecent industrial technology for diamond substrate,
large sized polycrystalline diamond wafer
preparation has come to be established. Hence, inthis work, we report on the fabrication of theBFO/B-doped diamond layered film structure on
the polycrystalline diamond substrate and theinvestigation of their structural and electricalproperties.
2. Experimental Methods
Vapor-grown polycrystalline diamonds were usedas substrates of 36 mm2 in areas (Element SixTechnologies). Conductive B-doped diamond layer

was grown on the substrate by microwave
plasma-enhanced chemical vapor deposition
method. The details of deposition conditions weredescribed in the previous works[3-5]. Then, Pr andMn co-doped BFO (BPFM)[5] thin film wasdeposited on the B-doped diamond layer usingchemical solution deposition method. Here, Pr andMn co-doping was used to reduce the leakage
current of BFO film. The BPFM precursor solution
was spin-coated on the B-doped diamond layer at
3000 rpm for 30 sec. After the coating, thespecimen was dried at 240 ℃ for 5 min, andprefired at 350℃ for 10 min in air. This process
was repeated 15 times to obtain the film of desired
thickness. Finally, for crystallization, the film wasannealed at 550 ℃ for 20 min in nitrogen
atmosphere.
For electrical measurement, Au top electrodes of
2.025×10-5 cm2 in areas were deposited on theBPFM film by conventional thermal evaporation
system. The crystal structure of the specimen wasdetermined by X-ray diffraction (XRD; Shimadzu
XD-D1).
Theelectricalproperties
werecharacterized using ferroelectric test system (ToyoFCE-1A).
3. Results & Discussion
Figure 1 shows the XRD θ-2θ scanning pattern of
the BPFM/B-doped diamond layered structure on
the polycrystalline diamond substrate. It isconsidered that the B-doped diamond layer ishomoepitaxially grown on the polycrystalline
diamond substrate since the diffraction peaks ofdiamond, other than (220), have not been detectedin the result. Also, for the BPFM layer, the102030diamond(220)40506070802θ [deg.]
Fig.1 XRD pattern for BPFM/B-doped diamondlayered film deposited on a polycrystalline diamondsubstrate.

2100(a)500-50@10 kHz
R.T.

-1000500 1000

Electric Field [kV/cm]
800

150

2600
1004007550@10 kHz
R.T.

2500200

400600800 1000

2000

Electric Field [kV/cm]
Fig.2 (a) P-E curves and (b) electrical fielddependences of 2Pr and 2Ec for BPFM film onheavily B-doped diamond layer.

2Ec [kV/cm]

(b)

125

2Pr [µC/cm ]References[1] J. F. Scott et al., Science, 246 (1989) 1400.
[2] Y. N. Venestsev et al., Sov. Phys. Dokl., 7(1963) 742.
[3] T. Kawae et al., Electrochem. Solid-State. Lett., 14(2011) G31.
[4] H. Kawasaki et al., Private Communication.
[5] T. Kawae et al., J. Ceram. Soc. Jpn. 118 (2010) 652

BPFM(112)110-1000 -500
SummaryWe have prepared the BPFM/B-doped diamondlayered film structure on the polycrystalline
diamond substrate and investigated the structuraland electrical properties. The BPFM and B-doped
diamond were crystallized on the polycrystalline
diamond substrate. The BPFM/B-doped diamondlayered film showed saturated hysteresis behavior
at room temperature in the P-E curve. 2Pr and 2Ec
for a maximum electric field of 1000 kV/cm were
135 µC/cm2 and 700 kV/cm, respectively.

BPFM(200)

210

BPFM(111)

BPFM(110)

BPFM(100)

Intensity [cps]310

Polarization [µC/cm ]polycrystalline growth of BPFM without any
impurity phases was also observed in the figure.
From the above result, the BPFM/B-doped diamondlayered films are found to be crystallized on thepolycrystalline diamond substrate in our deposition
process.
Figure 2(a) shows the polarization versus electricfield (P-E) curves of the BPFM thin film on theB-doped diamond layer. The curves were measured
at room temperature with a measurement frequencyof 10 kHz. As shown in the figure, saturated
hysteresis loops were observed without influencesof leakage current.
Figure 2(b) shows electric field dependence ofremnant polarization 2Pr and coercive field 2Ec forthe present structure. 2Pr and 2Ec at the maximum
applied electric field of 1000 kV/cm were 135µC/cm2 and 700 kV/cm, respectively. Then, theobserved 2Pr and 2Ec value were roughly
comparable with that of the BPFM thin films on thePt-coated Si substrate (2Pr=125 µC/cm, 2Ec=600kV/cm at maximum electric field of 1000 kV/cm).
This indicates simultaneous achievement ofexcellent ferroelectric properties of the BPFM filmand good conductivity of the B-doped diamondlayer meaning that the dopant activation in the
diamond layer was sufficient at room temperature.
Hence, it is concluded that the present structure andprocessing technique are effective for an integrationof BFO with diamond for high-temperature FeRAM
device applications.