Dielectric properties of low-firing Bi2Mo2O 9 thick films screen printed on Al foils and alumina substrates

Article abstract of DOI:10.1111/j.1551-2916.2010.03719.x

Low-firing Bi₂Mo₂O₉ thick films with a thickness of 15-20 μm were screen printed on Al foils and alumina substrates by screen-printing technology. The phase evolution, morphologies, and dielectric properties of the thick films were investigated. The thick films showed a pure Bi₂Mo₂O₉ phase at temperatures below 610°C. A mixture of Bi₂MoO₆, Bi₂Mo₃O ₁₂, and Bi₂Mo₂O₉ phases was found in the thick films sintered at 610°C and higher temperatures. The Bi ₂Mo₂O₉ thick films on Al foils sintered at 645°C showed excellent dielectric properties with a relative permittivity of 38 and a dielectric loss of 0.7% at 5 MHz. At the microwave frequency range from 5 to 19 GHz, the Bi₂Mo₂O₉ thick films on alumina substrates sintered at 645°C had a relative permittivity of ～35 and Q × f of ～12 500 GHz. It indicates that the Bi₂Mo ₂O₉ composition as potentially useful for low-temperature cofired ceramic using Al electrode.

Full text of DOI:10.1111/j.1551-2916.2010.03719.x

J. Am. Ceram. Soc., 93 [8] 2202–2206 (2010)
DOI: 10.1111/j.1551-2916.2010.03719.x
r 2010 The American Ceramic Society
ournal
J
Dielectric Properties of Low-Firing Bi Mo O Thick Films Screen
2
2
9
Printed on Al Foils and Alumina Substrates
w
Weihong Liu, Hong Wang, Di Zhou, and Kecheng Li
Electronic Materials Research Laboratory, Key Laboratory of the Ministry of Education, Xi’an Jiaotong University,
Xi’an 710049, China
Low-firing Bi Mo O thick films with a thickness of 15–20 lm
systems, BaO–TiO –TeO ternary system, and Bi W O
2 2 2 2 9
2
2
9
6
–11
were screen printed on Al foils and alumina substrates by screen-
printing technology. The phase evolution, morphologies, and di-
electric properties of the thick films were investigated. The thick
films showed a pure Bi Mo O phase at temperatures below
systems.
12
Recently Zhou et al. demonstrated that a single-phase
Bi Mo O could be sintered at a temperature of B6201C and
2
2
9
possessed excellent microwave dielectric properties. It has a rel-
ative permittivity B38, Q ꢀ f B12 500 GHz, and a TCF about
131 ppm/1C. In spite of their low sintering temperature and
excellent dielectric properties, the application of the Bi Mo O
2
2
9
6
101C. A mixture of Bi MoO , Bi Mo O , and Bi Mo O
2 6 2 3 12 2 2 9
phases was found in the thick films sintered at 6101C and higher
temperatures. The Bi Mo O thick films on Al foils sintered at
2
2
9
2
2
9
6
451C showed excellent dielectric properties with a relative per-
to LTCC technology has been limited because of its poor chem-
ical compatibility with silver. This problem was also observed in
mittivity of 38 and a dielectric loss of 0.7% at 5 MHz. At the
microwave frequency range from 5 to 19 GHz, the Bi Mo O
9
thick films on alumina substrates sintered at 6451C had a rel-
ative permittivity of B35 and Q ꢀ f of B12500 GHz. It indi-
cates that the Bi Mo O composition as potentially useful for
BaTe
through the use of Al or gold electrodes.
investigations have been carried out on Bi
its compatibility with Al. The results of prototype MLCC by
Bi Mo O ceramic with Al paste as an internal electrode proved
that Al can be used as an internal electrode for Bi Mo O ce-
4 9 2 3 8
O and Zn Te O -based ceramics, and has been overcome
2
2
1
0,13,14
More extensive
2 9
Mo O ceramic and
2
1
5
2
2
9
low-temperature cofired ceramic using Al electrode.
2
2
9
2
2
9
ramic’s application to multilayer devices.
In this work, the Bi Mo O thick films were fabricated on Al
I. Introduction
2
2
9
foils and alumina substrates using screen-printing technology.
The structure and dielectric properties of the thick films were
HE rapidly growing wireless industry requires high-perfor-
mance dielectric materials for microwave device applica-
T
2 2 9
investigated. The interaction between Al and Bi Mo O was
tions such as filters, duplexers, voltage-controlled oscillators,
and antennas. The low-temperature cofired ceramic (LTCC)
technology offers significant benefits over other established
packaging technologies for high density, reliable RF, and fast
digital applications requiring hermetical packaging and good
studied. The dielectric properties of the Bi Mo thick films on
2
2 9
O
Al foils and alumina substrates were evaluated for the applica-
tions in LTCC microwave circuits.
1
–4
thermal management. Microwave LTCC dielectric materials
II. Experimental Procedures
with low sintering temperature, high relative permittivity e , low
r
dielectric loss, and near-zero temperature coefficient of resonant
frequency temperature coefficient (TCF) are needed to be co-
fired with low-loss, low-melting-point conductors such as Ag,
Cu, Au, or Al.
Although there are many microwave dielectric compositions
r
with high quality factor Q and high relative permittivity e , their
To synthesize the Bi
Shu-Du Powders Co. Ltd., Chengdu, China) and MoO3
499%, Fuchen Chemical Reagents, Tianjin, China) were
used as the starting materials. A mixture of Bi and MoO
in a stoichiometric molar ratio of Bi Mo was ball milled for
h in a planetary mill (Nanjing Machine Factory, Nanjing,
2 2 9 2 3
Mo O ceramic powder, Bi O (499%,
(
O
2 3
3
2
2 9
O
4
densification temperatures are typically 410001C, such as ZnO–
China) and calcined at 6001C. Experimental details, together
with the properties of the synthesized material, are given in our
Nb O , Bi(Nb,Ta,Sb)O , BaO–TiO –Nb O system, Li O–
com-
2
5
4
2
2
5
2
Nb
2
O
5
–TiO
2
system, (Zr,Sn)TiO , and (A
4
A )(B B )O
1 2 1 2 3
12
previous work. The calcined powders were ball milled again to
5
plex perovskite system. To utilize these dielectric compositions
in LTCC technology, it is required to lower their densification
temperatures to o9611C (melting point of Ag) because Ag is a
typically used internal electrode in LTCC technology. To lower
the sintering temperature, the addition of some sintering aids,
such as V O , CuO, and B O , are normally used, which could
obtain submicrometer-size powder appropriate for screen-print-
ing technology.
The dried submicrometer-sized powder was mixed with an
organic vehicle (ceramic powder: organic vehicle5 66.7:33.3
wt%) by stirring for about 1 h to form a paste for screen-print-
ing technology. To test the dielectric properties of thick films
2
5
2
3
lower the sintering temperature but also increase the dielectric
loss (B1/Q). Hence, more attention has been paid for seeking
new dielectric compounds with intrinsically low sintering tem-
peratures, which include materials in the following systems:
2 2 9
and the interaction between Bi Mo O and Al, Al (99%) foils
are used as substrates. For testing the microwave dielectric
properties of thick films, alumina (99%) substrates were used.
The screen-printing process was repeated until the desired thick-
ness was attained. Each layer of the thick films was preheated at
Bi
2
3 2
O –TeO ,
TiO –TeO
2
2
,
CaO–TeO
2
,
BaO–TeO
2
binary
1
001C for 10 min subsequently. Then, the thick films were sin-
D. Lupascu—contributing editor
tered at temperatures ranging from 5501 to 6501C for different
dwell time in the furnace.
The phases of the deposited thick films were identified by X-
ray diffraction with CuKa radiation (X-ray diffractometry, Rig-
aku D/MAX-2400, Tokyo, Japan). A scanning electron micro-
scope (SEM, JSM-6460, JEOL, Tokyo, Japan), equipped with a
Tracor-Northern energy-dispersive system (EDS) (Tokyo,
Japan), was used for the microstructure analysis. For the
Manuscript No. 26699. Received September 15, 2009; approved February 4, 2010.
This work was supported by the National 973-project of China (2009CB623302), NSFC
projects of China (10979035, 60871044, 50835007), and International S&T Cooperation
Program of China (2009DFA51820).
wAuthor to whom correspondence should be addressed. e-mail: hwang@mail.xjtu.
edu.cn
2
202

August 2010
Dielectric Properties of Bi Mo O thick films
2
2203
2
9
Fig. 1. X-ray diffraction patterns of Bi Mo
2
2
O
9
thick films on Al foils
Mo
MoO ).
under different sintering temperatures for 3 h (o—phase of Bi
2
3 12
O ,
Ã
D—phase of Al, —phase of Bi
2 2 9
Mo O , m—phase of Bi
2
6
low-frequency measurements of the thick films on Al foils, top
electrodes with dimensions of 3.14 mm were deposited by gold
2
sputtering. The relative permittivity and dielectric losses were
measured using a high-precision LCR meter (Agilent 4294A
LCR meter, Agilent, Palo Alto, CA). The microwave dielectric
properties of thick films on alumina substrates were measured
1
6
by the split postresonator method with a vector network an-
alyzer (8720ES, Agilent) and a temperature chamber (Delta
9
023, Delta Design, Poway, CA). The TCe (t ) was calculated
e
by the following formula:
e85 ꢁ e25
te ¼
Fig. 3. Scanning electron microscope photos of surface morphologies
of Bi Mo thick films on Al foils sintered at (a) 5501C, (b) 5801C, (c)
101C, (d) 6201C, (e) 6301C, (f) 6351C, (g) 6451C, and (h) 6501C for 3 h.
(1)
e25 ꢀ ð85 ꢁ 25Þ
2
2 9
O
6
where e85 and e25 were the relative permittivity at 851 and 251C,
respectively.
III. Results and Discussion
The X-ray diffraction patterns of Bi
foils and alumina substrates sintered at temperatures of 5501–
501C for 3 h are shown in Figs. 1 and 2, respectively. The
2 2 9
Mo O thick films on Al
6
Fig. 2. X-ray diffraction patterns of Bi
2
Mo
2
O
9
thick films on alumina
substrates sintered at different temperatures for 3 h (o—phase of
Fig. 4. Scanning electron microscope photos of surface morphologies
of Bi Mo thick films on alumina substrates sintered at (a) 5501C, (b)
5801C, (c) 6101C, (d) 6301C, (e) 6351C, and (f) 6451C for 3 h.
2
2 9
O
Ã
2 3 12 2 2 9 2 6
Bi Mo O , —phase of Bi Mo O , m—phase of Bi MoO ).

2
204
Journal of the American Ceramic Society—Liu et al.
Vol. 93, No. 8
Fig. 8. Dielectric properties of Bi Mo
2
O
2 9
thick films on Al foils sin-
tered at different temperatures.
Fig. 5. Cross-sectional scanning electron microscope photo of the co-
fired Bi Mo /Al sample sintered at 6451C for 3 h in air.
2
2 9
O
Fig. 9. Dielectric properties of Bi Mo
2
O
2 9
thick films on Al foils sin-
tered at 6451C for different dwell time.
secondary phases in the thick films is ascribed to the interaction
between the substrates (Al and alumina) and Bi Mo O during
2
2
9
the sintering process. With the emergence of a small amount of
the Bi MoO and Bi Mo 12 phase in the thick films on Al foils
2
6
2
3
O
sintered at 6101C, the Al diffraction peak became weak and then
disappeared at higher temperatures. This means that the surface
2 3
of the Al foil is probably oxidized to a layer of Al O at 6101C
3
1
and higher temperatures. Then, the Al ions from the Al
O
2 3
Fig. 6. Energy-dispersive system result of Bi
foils sintered at 6451, 6301, and 5801C for 3 h.
2 2 9
Mo O thick film on Al
layer on the Al foils or Al O substrates entered the Bi Mo O
2
3
2
2
9
lattice and partly occupied the sites of molybdenum to form the
Bi
9ꢁ3x solid solution, while at the same time
Bi Mo 12 emerged to maintain the stoichiomet-
2
Mo2ꢁ2xAl2x
O
diffraction peaks of the thick films sintered below 6101C can be
2
MoO
6
and Bi
2
3
O
indexed as single phase Bi Mo O . A small amount of the
Bi MoO and Bi Mo O phase is found to be formed in the
rics. This is supported by the EDS analysis as shown in Fig. 6. A
small amount of Al element of about 2 mol% is observed in the
thick films on Al foils sintered at 6301C (Fig. 6(b)), but is not
detected in the compound sintered at 5801C (Fig. 6(c)).
Figure 3 is the SEM images of the thick films on Al foils
with different sintering temperatures for 3 h. For the thick films
sintered below 6451C, it shows the presence of pores and
the number of pores decreases with increasing the sintering
2
2
9
2
6
2
3
12
thick films sintered at 6101C and higher temperatures. These
results are different from that of the bulk Bi Mo ceramics.
According to our previous work, when the sintering temper-
2
2 9
O
1
2
ature is below 6451C, all peaks are indexed as a single phase
2 2 9 2 6 2 3 12
Bi Mo O , and no secondary phase of Bi MoO or Bi Mo O
is observed in the bulk ceramics. Hence, the emergence of the
2 2 9
Fig. 7. Scanning electron microscope photos of Bi Mo O thick films on Al foils sintered at 6451C for different dwell times: (a) 3 h, (b) 4 h, and (c) 5 h.

August 2010
Dielectric Properties of Bi Mo O thick films
2
2205
2
9
Table 1. The Value TCe of the Thick Films on Alumina
Substrate Sintered at Temperatures Ranging from 5501 to
6
451C for 3 h
Sintering temperature (1C)
550
580
610
645
te (ppm/1C)
17.8
15.2
34
124
ties on dwell time is shown in Fig. 9. The low frequency depen-
dence of the relative permittivity and dielectric loss of the
samples sintered at 6451C for different dwell times are observed.
The relative permittivity shows a slight decrease from about 36
to 34.5 as the dwell time increases from 3 to 5 h. This could be
ascribed to the phase assemblage change. As shown in Fig. 7, the
secondary phases increase with the increasing dwell time. The
secondary phases Bi
relative permittivities but the same dielectric losses when com-
paring with that of the Bi Mo phase.
2 6 2 3
MoO and Bi Mo O12 have slightly lower
2 2 9
Fig. 10. Microwave dielectric properties of Bi Mo O thick films on
alumina substrates as a function of sintering temperature.
2
2 9
O
The influence of sintering temperatures on microwave dielec-
tric properties was measured at 5.011 GHz for the thick films on
alumina substrates as shown in Fig. 10. It can be seen that the
microwave relative permittivity and Q ꢀ f are strongly depen-
dent on the sintering temperatures. When the sintering temper-
ature increased from 5501 to 6451C, the microwave relative
permittivity increased from 15 to 35, and Q ꢀ f increased from
temperatures. The thick films sintered at 6451C for 3 h show a
dense structure, which does improve the dielectric properties of
the thick films. A plate-like secondary phase that appears at
2 6 2 3 12
6201C was approximately identified as Bi MoO and Bi Mo O
by XRD (Fig. 1) and EDS analysis (Fig. 6(a)) with the atom
ratio of Bi:Mo being about 1.8 (point 1). Figure 4 shows the
similar morphologies of the thick films deposited on alumina
substrates. Figure 5 presents the cross-section SEM image of
Bi Mo O /Al sample cofired at 6451C for 3 h in air. As observed
208 to 12 700 GHz. This is ascribed to a significant change in the
microstructure of the thick films. As seen in Fig. 4, the micro-
structure of thick films on alumina substrates sintered at 6451C
is denser than other samples. The frequency effects on the mi-
crowave relative permittivity and Q ꢀ f of the thick films sin-
tered at 6451C for 3 h on alumina substrates are shown in
Fig. 11. It is clear that the microwave dielectric properties are
nearly frequency independent. The microwave relative permit-
tivity is about 35, and the Q ꢀ f is about 12 500 GHz. The TCe
2
2
9
2 2 9
in the micrograph, the Bi Mo O thick film shows a dense mi-
crostructure and has a good contact with the Al electrode.
Figure 6(a) shows the EDS analysis of thick film on Al foils
sintered at 6451C for 3 h, the sphere-like phase is the Bi Mo O
9
2
2
phase (point 3), and the plate-like phase is secondary phases
(
points 1 and 2). The SEM photos of Bi Mo thick films on
2
2 9
O
e
(t ) value of the thick films as a function of sintering temperature
Al foils sintered at 6451C for different dwell time are shown in
Fig. 7. The secondary phases increase with the dwell time in-
creasing from 3 to 5 h.
is shown in Table I. The TCe value increases from 17.8 to 124
ppm/1C with the increasing sintering temperatures from 5501 to
2 2 9
6451C for 3 h. In summary, the Bi Mo O thick films show good
The frequency dependence of relative permittivity and dielec-
tric loss of the thick films on Al foils are shown in Fig. 8. The
relative permittivity and dielectric loss of the samples are
strongly dependent on the sintering temperature. For the sam-
ples sintered at 5501–6451C, the relative permittivity increases
remarkably from 15 to 38 with the sintering temperature in-
creasing, while the dielectric loss decreases slightly. In addition,
the frequency dependence of dielectric loss is lowered by in-
creasing sintering temperatures. These results indicate that the
dense and pore-free thick films possess better dielectric proper-
microwave dielectric properties.
IV. Conclusions
Dense and pore-free Bi Mo thick films on Al foils and al-
2
2 9
O
umina substrates were prepared by screen-printing technology.
The XRD analysis indicates that no second phase was detected
in both the thick films on Al foils and alumina substrates when
they were sintered at temperatures below 6101C. A small
2 6 2 3
amount of secondary phases Bi MoO and Bi Mo O12 were
2 6 2 3
ties. The effect of secondary phase Bi MoO and Bi Mo O12 on
observed in the thick films sintered at 6101C and higher tem-
peratures. The effects of sintering temperature and dwell time on
the relative permittivity and dielectric loss of the thick films have
been studied. The sample sintered at 6451C for 3 h showed ex-
cellent dielectric properties. The relative permittivity is about 38
and the dielectric loss is about 0.7% in the frequency range from
dielectric properties could be neglected because these two com-
positions have the same dielectric properties and their content in
the composite is too little. The dependence of dielectric proper-
1 kHz to 5 MHz. In the microwave frequency range from 5 GHz
to 19 GHz, the relative permittivity of the thick films deposited
on alumina substrates is 35, and the Q ꢀ f is about 12 500 GHz.
2 2 9
The Bi Mo O thick films obtained show potential application
for LTCC device applications using Al electrode.
References
1
Y.-J. Choi, J.-H. Park, and W.-J. Ko, ‘‘Low Temperature Sintering of
4 9
BaTi O -Based Middle-k Dielectric Composition for LTCC Applications,’’
J. Electrocera., 14, 157–62 (2005).
J.-H. Park, Y.-J. Choi, J.-H. Park, and J.-G. Park, ‘‘Low-Fire Dielectric Com-
2
positions with Permittivity,’’ Mater. Chem. Phys., 88, 308–12 (2004).
E. S. Kim, S. H. Kim, and B. I. Lee, ‘‘Low-Temperature Sintering and Mi-
3
4
crowave Dielectric Properties of CaWO Ceramics for LTCC Applications,’’
J. Eur. Ceram. Soc., 26, 2101–4 (2006).
4
M. T. Sebastian and K. P. Surendran, ‘‘Tailoring the Microwave Dielectric
Ceramics 20–60 for LTCC Applications,’’ J. Eur.
Fig. 11. Frequency dependence of microwave dielectric properties of
Bi Mo O thick films sintered at 6451C for 3 h on alumina substrates.
2 2 9
Properties of Ba(Mg1/3Ta2/3)O
Ceram. Soc., 26, 1791–9 (2006).
3

2
206
Journal of the American Ceramic Society—Liu et al.
Vol. 93, No. 8
5
11
M. T. Sebastian and H. Jantunen, ‘‘Low Loss Dielectric Materials for LTCC
Applications: A Review,’’ Int. Mater. Rev., 53, 57–90 (2008).
A. Feteira and D. C. Sinclair, ‘‘Microwave Dielectric Properties of Low Firing
Ceramics,’’ J. Am. Ceram. Soc., 91, 1338–41 (2008).
D. Zhou, H. Wang, and X. Yao, ‘‘Microwave Dielectric Properties of Low
Temperature Firing Bi Mo Ceramic,’’ J. Am. Ceram. Soc., 91, 3419–22 (2008).
J. Honkamo, H. Jantunen, G. Subodh, M. T. Sebastian, and P. Mohanan,
‘‘Tape Casting and Dielectric Properties of Zn Te -Based Ceramics with an
Ultra-Low Sintering Temperature,’’ Int. J. Appl. Ceram. Technol., 6, 531–6 (2009).
2 2 9
Temperature Bi W O
12
6
M. Udovic, M. Valant, and D. Suvorov, ‘‘Phase Formation and Dielectric
System Prepared in an Oxygen Atmosphere,’’
J. Am. Ceram. Soc., 87, 591–7 (2004).
Characterization of the Bi
2 3
O
–TeO
2
2
2 9
O
13
7
M. Udovic, M. Valant, and D. Suvorov, ‘‘Dielectric Characterisation of Ce-
ramics from the TiO –TeO System,’’ J. Eur. Ceram. Soc., 21, 1735–8 (2001).
M. Valant and D. Suvorov, ‘‘Glass-Free Low-Temperature Co-Fired Ceram-
2
3 8
O
2
2
8
14
G. Subodh and M. T. Sebastian, ‘‘Glass-Free Zn
2 3 8
Te O Microwave Ceramic
ics: Calcium Germanates, Silicates and Tellurates,’’ J. Eur. Ceram. Soc., 24, 1715–9
(
for LTCC Applications,’’ J. Am. Ceram. Soc., 90, 2266–8 (2007).
15
2004).
D. Zhou, C. A. Randall, H. Wang, L.-X. Pang, and X. Yao, ‘‘Dielectric
Properties of a Ultra-Low Temperature Firing Bi Mo MLCCs Prepared by
Tape-Casting,’’ J. Am. Ceram. Soc., (2010). doi: 10.1111/j.1551-2916.2010.03602.x.
9
D. K. Kwon, M. T. Lanagan, and T. R. Shrout, ‘‘Microwave Dielectric Prop-
erties of BaO–TeO Binary Compounds,’’ Mater. Lett., 61, 1827–31 (2007).
D. K. Kwon, M. T. Lanagan, and T. R. Shrout, ‘‘Microwave Dielectric Prop-
erties and Low-Temperature Cofiring of BaTe with Aluminum Metal Elec-
trode,’’ J. Am. Ceram. Soc., 88, 3419–22 (2005).
2
2 9
O
2
10
16
J. Krupka and W. Gwarrek, ‘‘Measurements and Modeling of Planar Metal
Film Patterns Dielectric Substrates,’’ IEEE Microwave Wireless Comp. Lett., 19,
O
4 9
134–6 (2009).
&