Low temperature CVD of Pb(Zr,Ti)O3 using Pb(tmhd)2, Zr(dmae)4, and Ti(dmae)4

Article abstract of DOI:10.1149/1.1584441

Pb(Zr,Ti)O₃ (PZT) thin films were deposited at low temperatures by direct liquid injection metallorganic chemical vapor deposition (MOCVD) process using Pb 2,2,6,6-tetramethyl 3,5-heptanedionate (tmhd)₂, Zr dimethyl aminoethoxide (dmae)₄, and Ti(dmae)₄. Zr(dmae)₄, and Ti(dmae)₄ were found to be less sensitive to moisture and air but their dissociation temperature was about the same as alkoxides. Two separate solution of Pb(tmhd)₂ and of Zr(dmae)₄ and Ti(dmae)₄ were used and the growth rate of PZT films was around 11 nm/min at substrate temperatures of 380-440°C. Because decomposition temperatures of Pb(tmhd)₂, Ti(dmae)₄, and Zr(dmae)₄ are in the same range, control of the film composition was comparatively easy. PZT films deposited below 450°C had negligible carbon and nitrogen content. Pure perovskite PZT films were obtained at temperatures as low as 440°C on Pt/Ti/SiO₂/Si substrate and 425°C on Ir/Ti/SiO₂/Si substrate, respectively. The remnant polarization of PZT films prepared at 425°C on Ir/Ti/SiO₂/Si substrate was 21μC/cm² and the leakage current density at 100 kV/cm was less than 10^-6 A/cm².

Full text of DOI:10.1149/1.1584441

C516
Journal of The Electrochemical Society, 150 ͑8͒ C516-C522 ͑2003͒
0
013-4651/2003/150͑8͒/C516/7/$7.00 © The Electrochemical Society, Inc.
Low Temperature CVD of Pb„Zr,Ti…O Using Pb„tmhd… ,
3
2
Zr„dmae… , and Ti„dmae…
4
4
Dae-Hwan Kim, Woo-Young Yang, and Shi-Woo Rhee*,
z
Laboratory for Advanced Materials Processing, Department of Chemical Engineering, Pohang University
of Science and Technology, Pohang 790-784, Korea
Pb͑Zr,Ti͒O ͑PZT͒ thin films were deposited at low temperatures by direct liquid injection metallorganic chemical vapor deposi-
3
tion ͑MOCVD͒ process using Pb 2,2,6,6,-tetramethyl 3,5-heptanedionate (tmhd) , Zr dimethyl aminoethoxide (dmae) , and
2
4
Ti͑dmae͒ . Zr͑dmae͒ , and Ti͑dmae͒ were found to be less sensitive to moisture and air but their dissociation temperature was
4
4
4
about the same as alkoxides. Two separate solution of Pb͑tmhd͒ and of Zr͑dmae͒ and Ti͑dmae͒ were used and the growth rate
2
4
4
of PZT films was around 11 nm/min at substrate temperatures of 380-440°C. Because decomposition temperatures of Pb͑tmhd͒2 ,
Ti͑dmae͒ , and Zr͑dmae͒ are in the same range, control of the film composition was comparatively easy. PZT films deposited
4
4
below 450°C had negligible carbon and nitrogen content. Pure perovskite PZT films were obtained at temperatures as low as
4
40°C on Pt/Ti/SiO /Si substrate and 425°C on Ir/Ti/SiO /Si substrate, respectively. The remanant polarization of PZT films
2
2
2
prepared at 425°C on Ir/Ti/SiO /Si substrate was 21 ␮C/cm and the leakage current density at 100 kV/cm was less than
1
©
2
Ϫ6
2
0
A/cm .
2003 The Electrochemical Society. ͓DOI: 10.1149/1.1584441͔ All rights reserved.
Manuscript received September 12, 2002. Available electronically June 16, 2003.
i
6,7
Lead zirconate titanate, Pb͑Zr,Ti͒O ͑PZT͒ thin films were de-
posited by metallorganic chemical vapor deposition ͑MOCVD͒ us-
zirconium ␤-diketonate, or ͓Zr͑tmhd͒(O Pr) ͔ has high thermal
3
3
stability and allows the optimized growth of ZrO but is not suitable
2
ing
Pb(2,2,6,6,-tetramethyl 3,5-heptanedionate)2
(tmhd)2 ,
for the low temperature CVD processing.
Zr͑dimethyl aminoethoxide͒4 (dmae) , and Ti͑dmae͒ . PZT film
In order to lower the growth temperature of PZT thin films in
DLI-MOCVD processes, a new approach was pursued by using new
precursors having donor-functionalized alkoxy ligand such as dim-
ethylaminoethoxide ͑dmae͒. In the previous study, titanium tetrakis
4
4
has been investigated for the application in nonvolatile ferroelectric
random access memory ͑NVFeRAM͒, dynamic random access
memory ͑DRAM͒, electro-optic devices, and microactuators be-
1
8
9
cause of its superior ferroelectricity and piezoelectricity. In high-
dmae ͓Ti͑dmae͒ ͔ and Zr͑dmae͒ ͑zirconium tetrakis dmae͒ were
4 4
density NVFeRAM, three-dimensional ͑3-D͒ capacitor cells will be
required and continued downscaling dictates the needs to shift to a
deposition method such as MOCVD ͑metallorganic chemical depo-
sition͒ with better step coverage. MOCVD is one of the most im-
portant techniques for practical applications because of its confor-
mal coverage, high deposition rate, large area uniformity and high
throughput. Also, with the introduction of a direct liquid injection
used to deposit metal oxides such as ͑Ba,Sr͒TiO and ZrO using
3 2
DLI-MOCVD. Since the dmae ligand has an additional Lewis base
site that is able to form chelate rings, M͑dmae͒ (M ϭ Zr, Ti͒ is
4
i
t
more stable to air and moisture than Ti(O Pr) and Zr(O Bu) . due
4
4
to their more saturated metal center, and are more favorable to
solution-based processes.
In this study, low temperature MOCVD process for PZT films
͑
DLI͒ system, there is a great improvement in the delivery of pre-
cursors.
In the DLI-MOCVD process used in this study, precursors are
with lead bis͑tmhd͒ ͓Pb͑tmhd͒ ͔, Ti͑dmae͒ , and Zr͑dmae͒ , was
2
4
4
studied. It was shown that the newly adopted PZT precursors were
effective in lowering the fabrication temperature of PZT films in the
solution-based DLI system.
dissolved in a solvent and a controlled amount of the solution is
injected into the flash evaporator. Evaporated gas mixture is intro-
duced into the deposition chamber and film is deposited on the sub-
strate as in an ordinary CVD process. It is an attractive method to
Experimental
Preparation and characterization of Ti(dmae)4 and
Zr(dmae) .—Zr͑dmae͒ was synthesized with zirconium tetradi-
inject exact amount of solid precursors and schematic diagram of the
DLI-MOCVD apparatus was shown elsewhere.2,3 Vaporization char-
4
4
ethylamine ͓Zr(NEt ) ͔ and dimethyl-aminoethanol. Zr(NEt )
acteristics of the precursor is important in DLI-MOCVD as in other
CVD process and also the solubility of the precursor in a solvent and
the stability of the solution is important.
2
4
2 4
͑24.68 g, 65 mmol͒ was added to 150 mL of dry toluene and N,N-
dimethylaminoethanol ͑26 mL, 260 mmol͒ was then added slowly to
that solution. The mixture was refluxed for 20 h and then cooled.
There is much interest in low temperature MOCVD process to
realize good surface roughness, good step coverage, and a low
chemical interaction with a substrate. Low temperature fabrications
The solvent was removed under a reduced pressure to obtain
1
Zr͑dmae͒ as a viscous liquid (yield Ͼ 90%). H nuclear magnetic
4
4
5
resonance ͑NMR, C D , 300 MHz͒: ␦ 4.35 ͑s, OCH , 8H͒, 2.61 ͑s,
of PZT films using a PbTiO seed and a pulse-CVD have already
6
6
2
3
1
3
NCH , 8H͒, 2.30 ͑s, CH , 24H͒, C NMR (C D , 300 MHz͒: ␦
been reported.
2
3
6
6
Various precursors such as metal alkoxide, ␤-diketonates, fluori-
nated ␤-diketonates, and anhydrous nitrates have been used for the
MOCVD of TiO and ZrO . But there are few precursors that sat-
68.11 ͑s, OCH2), 64.95 ͑s, NCH2), 47.34 ͑s, CH3).
Ti͑dmae͒4 was synthesized with titanium (NEt2)4 ͓Ti(NEt2)4͔
and dimethyl-aminoethanol. Ti(NEt2)4 ͑21.87 g, 65 mmol͒ was
added to 150 ml of dry hexane and N,N-dimethylaminoethanol ͑26
ml, 260 mmol͒ was then added slowly to that solution. The mixture
was refluxed for 20 h and then cooled. The solvent was removed
under a reduced pressure to obtain Ti͑dmae͒4 as a viscous liquid
2
2
isfy both high reactivity at low temperature and long-term stability
in the solution-based process. Though zirconium tetrakis͑t-butoxide͒
t
i
͓
Zr(O Bu) ͔ and titanium tetrakis͑i-propoxide͒ ͓Ti(O Pr) ͔ are ef-
4
4
fective in low temperature growth, they are inadequate at solution-
based DLI process due to their high sensitivity to air and moisture.
1
(yield Ͼ 90%). H NMR (C D , 300 MHz͒: ␦ 4.55 ͑s, CH , 8H͒,
6
6
2
On the other hand, zirconium tetrakis ͓Zr͑tmhd͒ ͔, a homoleptic
2.58 ͑s, CH2 , 8H͒, 2.23 ͑s, CH3 , 24H͒.
4
To investigate the stability of the precursor solution with respect
1
to shelf time, H NMR ͑300 MHz Varian, Unity Plus͒ studies were
*
Electrochemical Society Active Member.
E-mail: srhee@postech.ac.kr
6
performed. Precursor solutions were made in a glove box with C D6
z
solvent. NMR tubes, filled with solution sample, were sealed to
Downloaded on 2015-04-20 to IP 138.251.14.35 address. Redistribution subject to ECS terms of use (see ecsdl.org/site/terms_use) unless CC License in place (see abstract).

Journal of The Electrochemical Society, 150 ͑8͒ C516-C522 ͑2003͒
C517
1
Table I. Parameters for the deposition of PZT films by DLI-
MOCVD.
storage time was studied using H NMR. The solution of Ti͑dmae͒4
and C D and that of Zr͑dmae͒ and C D showed no significant
6
6
4
6
6
change in chemical shift (␦ ϭ 4.56, 2.58, and 2.24 ppm͒ for
Ti͑dmae͒ and ␦ ϭ 4.37, 2.62, and 2.31 ppm for Zr͑dmae͒ and no
precipitation even after ten days. These results indicate that
Bottom electrode
Pt(150 nm)/TiO (20 nm)/SiO (300 nm)/Si
2 2
4
4
Ir(150 nm)/Ti(5 nm)/SiO (200 nm)/Si
2
Precursors
Pb(tmhd) , Ti(dmae) , Zr(dmae)
2
4
4
M͑dmae͒ are stable enough in the solution state.
4
Substrate temperature
Deposition pressure
Deposition time
Gas flow rate
300-480°C
1.4 Torr
Further investigation was performed with the single mixture so-
5-30 min
lution of Pb͑tmhd͒ , Ti͑dmae͒ , and Zr͑dmae͒ to find out the pre-
2
4
4
a
Ar 50 sccm ͑vaporizer͒
cursor interaction in the mixed solution. From NMR analysis, it was
found out that there was a serious cross interactions such as ligand
Ar 200 sccm, O 300 sccm ͑under vaporizer͒
2
Solvent
Vaporizer pressure
Vaporizer temperature
n-octane
7 Torr
240°C
exchange reactions between Pb precursors and M͑dmae͒ . Thus one
4
should use a solution of Pb precursor and a solution of M͑dmae͒4
mixture injected separately into the evaporator.
a
To investigate the oxidation temperature of the precursors, dif-
ferential scanning calorimetry ͑DSC͒ measurements were performed
at a heating rate of 10°C/min. Initial decomposition temperatures are
Sccm is standard cubic centimeters per minute.
2
70°C for Pb͑tmhd͒ and Ti͑dmae͒ and 310°C for Zr͑dmae͒ . Note
2 4 4
prevent oxygen and moisture penetration and were stored at room
temperature. There was no precipitant in all precursor solutions for
up to 10 days.
that the major exothermic peak of Zr͑tmhd͒4 appears at 410°C.
These results suggest that precursors in this study are oxidized at
lower temperature. The decomposition temperature of Pb͑tmhd͒ on
2
MOCVD of PZT thin films.—A cold wall, low pressure DLI CVD
reactor with solution delivery system was fabricated. A schematic
diagram of the MOCVD apparatus used in this study was shown
a heated surface is known to be 350°C at vacuum and 260°C at the
11
presence of oxygen. It seems that the increased saturation of the
metal center with the introduction of the dmae ligand is not related
closely to the oxidation temperature of Ti and Zr precursor.
Ti͑dmae͒4 and Zr͑dmae͒4 have low oxidation temperatures like
2
,3
elsewhere.
PZT thin films were prepared using Pb͑tmhd͒2 ,
Ti͑dmae͒ , Zr͑dmae͒ , and O as source materials. The total pres-
4
4
2
i
t
sure in the reactor was adjusted to 1.4 Torr. PZT films were depos-
ited on a Pt/TiO /SiO /Si and Ir/Ti/SiO /Si layered substrate. The
simple metal alkoxides such as Ti(O Pr) and Zr(O Bu) .
4
4
2
2
2
MOCVD of PbO, TiO , ZrO and PZT films.—The PbO, TiO ,
vaporizer temperature and the feed line temperature after the vapor-
izer were held at 240°C. The experimental conditions of PZT prepa-
ration are summarized in Table I.
2
2
2
ZrO , and PZT thin films were deposited on Pt/TiO /SiO /Si sub-
2
2
2
strate using flash-vaporized metalorganic precursor solutions with
Pb͑tmhd͒2 , Ti͑dmae͒4 , and Zr͑dmae͒4 dissolved in an n-octane sol-
vent (bp ϭ 126°C). Prior to PZT deposition, the growth
rate of single oxide with each precursor was studied as a
function of the substrate temperature. For compari-
The composition of the film was analyzed using inductively
coupled plasma-atomic emission spectrometry ͑ICP-AES, Jobin-
Yvon, JY 38 plus͒ and the deposition rate was measured by scanning
electron microscopy ͑SEM, Hitachi S-4200͒. The surface morphol-
ogy and roughness were investigated using SEM, ͑Hitachi S-4200͒
and atomic force microscopy ͑AFM, PSIA XE-100͒. The crystal
structure was analyzed by X-ray diffractometer ͑XRD, MAC Sci-
ence M18XHF͒ with Cu K␣ radiation operating at 30 kV and 40 mA
and the depth profile and film composition were investigated by
X-ray photoelectron spectroscopy ͑XPS, PHI 5400 ESCA͒ with Al
K␣ radiation. For electrical characterizations, the metal-insulator-
metal ͑MIM͒ capacitors were fabricated and platinum dot electrode
was deposited by the thermal evaporation through a metallic mask.
Polarization-electric field ͑P-E͒ and leakage current-voltage ͑I-V͒
characteristics of MIM structure were measured using an RT6000
ferroelectric tester ͑Radiant Technologies͒ and HP4140B semicon-
ductor parameter analyzer, respectively.
son, Pb͑methoxyethoxytetramethylheptanedionate͒ Pb͑methd͒ ,
͓
͔
2
2
Ti͑methylpentanedioxy͒͑methd͒ ͓Ti͑mpd͒(methd )͔ and Zr͑methd͒
2
2
4
were also used to deposit each single oxide. Methd compound of
barium and strontium were used to deposited barium strontium ti-
2
tanate films. Figure 1 shows deposition rate of PbO, ZrO , and
2
TiO2 films as a function of the substrate temperature at a fixed
vaporizer temperature of 240°C. As shown in Fig. 1a, the deposition
rate of PbO shows a sharp increase reaching a maximum value at
around 400°C and decrease at higher temperature. It was pointed out
that the decrease of the growth rate at high temperature was due to
the short residence time of Pb oxide molecules especially on Pt
11
substrate. The deposition characteristic of Pb͑tmhd͒ is similar to
2
that of Pb͑methd͒ . It seems that the modification of the tmhd
2
ligand to the ‘‘lariat’’ method ligand does not influence significantly
the decomposition temperature range of precursor molecules.
The deposition rate of ZrO using Zr͑dmae͒ shows a high value
Results and Discussion
Characterization of PZT precursors.—Dmae group precursors
are slightly viscous liquid at room temperature. The H NMR and
2
4
1
of above 10 nm/min even at 375°C. The decrease of the growth rate
at high temperatures above 450°C is probably due to the pre-
decomposition of precursor molecules in the gas phase with
13
C NMR spectra of M͑dmae͒ show three distinct proton and car-
4
1
13
bon environments. There is no evidence in the H and C NMR
spectra to suggests a presence of dimeric species of M͑dmae͒4 .
Similar results supporting that M͑dmae͒4 exists as a monomeric
state were obtained in the previous studies on the mass spectra of
M͑dmae͒4 . Only mass peaks lower than the parent molecular
mass of Ti͑dmae͒4 and Zr͑dmae͒4 were observed. Consequently,
1
2
oxygen. The deposition rate with Zr͑methd͒ shows a lower value
4
of 5 nm/min at 425°C and the maximum deposition rate was ob-
served at 500°C. The deposition rate of TiO using Ti͑dmae͒ is 12
2
4
8
,9
nm/min even at 330°C and reaches a maximum value of 16 nm/min
at 410°C while the deposition rate with Ti͑mpd͒͑methd͒ reaches a
2
M͑dmae͒ seems to exist as a monomer in solution and in gas phase
maximum value of 12 nm/min at 440°C. It is apparent that two
dmae group precursors have high deposition rate at lower tempera-
tures, which is consistent with DSC measurement. Also, Pb͑tmhd͒2
4
without forming aggregated species such as dimer and trimer which
may deteriorate vaporization efficiency of precursor solutions.
In the liquid delivery system, one of the key problems is the
shows adequate reactivity at low temperature. Thus M͑dmae͒ and
4
i
solution stability. For example, Zr(O Pr) (tmhd) , which has two
Pb͑tmhd͒2 are possible candidates for the low temperature
( Ͻ 450°C) deposition of PZT.
2
2
i
different
ligands,
disproportionates
Zr (O Pr) (tmhd) and Zr͑tmhd͒ on dissolution. Also, Ti(O Pr)
and Zr(O Bu)4 are not suitable for DLI process due to their low
to
Zr(O Pr) ,
4
i
10
i
2
6
2
4
4
To investigate optimum vaporizer temperature, the growth rate of
t
PbO, TiO , and ZrO as a function of the vaporizer temperature was
2
2
solution stability. Stability of M͑dmae͒4 solutions with respect to
investigated at a fixed substrate temperature of 410°C. 0.05 M so-
Downloaded on 2015-04-20 to IP 138.251.14.35 address. Redistribution subject to ECS terms of use (see ecsdl.org/site/terms_use) unless CC License in place (see abstract).

C518
Journal of The Electrochemical Society, 150 ͑8͒ C516-C522 ͑2003͒
Figure 2. Pb/(Zr ϩ Ti) and Zr/(Zr ϩ Ti) concentration ratio in the PZT
film as a function of (A/B)solution . (A/B)solution values are ͑a͒ 0.6, ͑b͒ 0.8, and
c͒ 1. Deposition temperature was 410°C.
͑
200-260°C. We have selected a vaporizer temperature of 240°C for
PZT depositions in this study.
PZT films were deposited using Pb͑tmhd͒ , Ti͑dmae͒ , and
2
4
Zr͑dmae͒ . To avoid chemical interaction in the mixed solution, we
4
used two individual solutions, i.e., A site (ϭPb) solution and B site
(
ϭZr ϩ Ti) solution. Three precursor solutions of 0.07 M ͑cation
mole/liter͒ were prepared with n-octane solvent. Then, Ti͑dmae͒4
and Zr͑dmae͒ precursor solutions were mixed to make B site solu-
4
tion having a particular molar ratio of Zr:Ti ϭ 3:7 or 4:6.
Figure 2 shows A site to B site ratio in the films, (A/B)film , and
Zr to B site ratio in the films, ͓Zr/(Zr ϩ Ti)͔film , as a function of
the A site to B site ratio in solutions, (A/B)solution . PZT films were
deposited at 410°C. Because the total solution injection rate was
fixed at 0.1 mL/min, an increase in the amount of A site solution was
accompanied by a decrease in amount of B site solution. With in-
creasing (A/B)solution , (A/B)film increased linearly and ͓Zr/(Zr
ϩ Ti)͔film slightly increased. We found there exists a linear re-
sponse of (A/B)film to (A/B)solution at 410°C. Generally the ‘‘self-
regulating phenomenon’’ that (A/B)film stays unchanged with the
different (A/B)
, frequently appears at high temperatures
solution
1
2
above 550°C. There is no self-regulating phenomenon in this
study, because the volatilization of PbO is not significant at low
Figure 1. Deposition rate of ͑a͒ PbO, ͑b͒ ZrO , and ͑c͒ TiO2 films as a
2
function of the substrate temperature at a fixed vaporizer temperature of
240°C. 0.05 M solution was injected with a rate of 0.15 mL/min.
lution was injected at a rate of 0.15 mL/min. For the Ti precursor,
the growth rate increased with increasing vaporizer temperature and
the highest growth rate appeared at 240°C. For the Zr precursor, the
highest growth rate appeared at 230°C. For Pb precursor, the growth
rate remained constant apparently with vaporizer temperatures of
Figure 3. Pb/(Zr ϩ Ti) and Zr/(Zr ϩ Ti) concentration ratio in the PZT
film as a function of the substrate temperature when (A/B)solution values are
0.6, 0.8, and 1.
Downloaded on 2015-04-20 to IP 138.251.14.35 address. Redistribution subject to ECS terms of use (see ecsdl.org/site/terms_use) unless CC License in place (see abstract).

Journal of The Electrochemical Society, 150 ͑8͒ C516-C522 ͑2003͒
C519
Figure 6. XRD patterns of as-deposited and furnace annealed ͑700°C, 30
min, O ambient͒ PZT/Pt films as a function of (A/B)
Figure 4. XRD patterns of as-deposited PZT films as a function of the
substrate temperature when (A/B)solution ϭ 1.
.
solution
2
sufficient reactivity of three precursors at low temperatures. Based
on Fig. 3, the required (A/B)solution is 0.8 to obtain 1.0 of (A/B)film
at around 410°C. The growth rate of PZT films near stoichiometry is
temperatures. Thus, various PZT films having different (A/B)film
values can be prepared easily by adjusting the solution composition
precisely at low temperature.
Further experiments were performed under different substrate
temperatures when (A/B)solution are 0.6, 0.8, and 1 ͑Fig. 3͒. At tem-
peratures between 340°C and 465°C, the (A/B)film shows a gradual
increase reaching a maximum value at around 410°C and a gradual
decrease at higher temperature in case of (A/B)solution ϭ 0.8-1.
Practically, (A/B)film and ͓Zr/(Zr ϩ Ti)͔film are not varied much at
temperatures between 375 and 440°C, which is probably due to the
1
1 nm/min. In the case of the Pb͑tmhd͒ , Zr͑tmhd͒4 , and
2
i
12
Ti(O Pr) (tmhd) precursor set,
the difference between the
2
2
(
A/B)film and the (A/B)solution is large and the required (A/B)solution
is below 0.5 to obtain stoichiometric PZT films at temperatures be-
low 475°C. This means that more B site solution should be injected
to compensate the high reactivity of Pb precursor due to the mis-
match of thermal decomposition temperature of different precursors.
With M(dmae) , we found that the difference between the (A/B)
4
film
Figure 5. XRD pattern of PZT film as a function of the annealing tempera-
ture. Films were deposited at 410°C with (A/B)solution ϭ 1.
Figure 7. XRD patterns of as-deposited and furnace annealed ͑700°C, 30
min, O ambient͒ PZT/Ir films as a function of (A/B)
.
solution
2
Downloaded on 2015-04-20 to IP 138.251.14.35 address. Redistribution subject to ECS terms of use (see ecsdl.org/site/terms_use) unless CC License in place (see abstract).

C520
Journal of The Electrochemical Society, 150 ͑8͒ C516-C522 ͑2003͒
Figure 9. I-V characteristics of PZT films deposited on ͑a͒ Pt substrate and
b͒ Ir substrate with various (A/B)solution values. Thickness of PZT samples
͑
ranges from 320 to 330 nm.
substrate temperature and concentration of Pb species. In this study,
the Pt5-7Pb phase appeared at temperatures of 375-430°C when
(
A/B)film exceeded 0.8. The Pt5-7Pb intermetallic phase disappeared
after 500°C annealing. Chen et al. reported that Pt5-7Pb can provide
template for the growth of ͑111͒-oriented PZT.13 However, the
Pt5-7Pb phase, in this study, has no relation with ͑111͒ PZT probably
due to the low substrate temperature. More studies on the phase
evolutions of PZT films deposited at low temperature are required.
Further experiments were performed under narrower (A/B)solution
range of 0.7-0.9 on different substrates (Pt/TiO /SiO /Si and
Figure 8. SEM images of PZT films deposited on Ir substrate with various
(
A/B)solution . (A/B)solution values are ͑a͒ 0.7, ͑b͒ 0.8, and ͑c͒ 0.9.
2
2
Ir/Ti/SiO /Si) at a fixed substrate temperature of 425°C. The com-
position and the growth rate of PZT/Pt were similar to those of
PZT/Ir. Also, the composition ratios in the PZT films ͓(A/B)film͔ are
2
and the (A/B)solution is 0.2 for 410°C and there exists a linear re-
sponse of (A/B)film to (A/B)solution . These results imply that chemi-
cal reactivity of three precursors matches well and the composition
0.83 for (A/B)solution ϭ 0.7, 1.0 for (A/B)solution ϭ 0.8 and 1.12 for
control can be achieved easily with changing (A/B)solution
.
(A/B)solution ϭ 0.9, respectively.
Figure 4 shows XRD patterns of as-deposited PZT films as a
function of the substrate temperature when (A/B)solution ϭ 1. Figure
Figure 6 shows XRD patterns of as-deposited and furnace an-
nealed ͑700°C, O ) PZT/Pt films as a function of (A/B)
. The
2
solution
5
shows XRD patterns of PZT films, deposited at 410°C with
Pb-deficient PZT film ͓(A/B)solution ϭ 0.7͔ shows a perovskite
phase with traces of pyrochlore and Pt5-7Pb. The pyrochlore phase
was not removed after furnace annealing due to the lead deficiency.
The stoichiometric PZT film shows mixed phases of perovskite, py-
rochlore, and Pt5-7Pb. Even though the film stoichiometry is satis-
fied to unity, the film shows mixed perovskite and second phase due
to the low processing temperature. A pure perovskite PZT phase was
obtained after annealing. The Pb-rich PZT film ͓(A/B)solution
(
(
A/B)solution ϭ 1, as a function of annealing temperature. For
A/B)solution ϭ 0.6, films show an amorphous phase below 410°C
and only show a Pb-deficient pyrochlore phase at 440°C. For
(
A/B)solution ϭ 1.0, films show a perovskite phase with a strong
Pt5-7Pb intermetallic phase at 410°C ͓(A/B)film ϭ 1.2͔ and a pure
perovskite phase at 440°C ͓(A/B)film ϭ 1.1͔. We believe that the
evolution of a Pt5-7Pb intermetallic phase is closely related with
Downloaded on 2015-04-20 to IP 138.251.14.35 address. Redistribution subject to ECS terms of use (see ecsdl.org/site/terms_use) unless CC License in place (see abstract).

Journal of The Electrochemical Society, 150 ͑8͒ C516-C522 ͑2003͒
C521
Figure 10. I-V characteristics of stoichiometric PZT thin films deposited on
a͒ Pt substrate and ͑b͒ Ir substrate with various annealing temperatures.
Thickness of PZT samples ranges from 210 to 220 nm.
͑
Figure 11. P-E hysteresis loops of ͑a͒ Pt͑top͒/PZT/Pt and ͑b͒ Pt͑top͒/PZT/Ir
capacitors formed at various annealing temperatures.
current densities were below 7 ϫ 10Ϫ7 A/cm2 up to 100 kV/cm,
irrespective of the bottom electrode. However, the 12% lead-rich
Pt͑top͒/PZT/Ir capacitor shows high leakage current density. High
leakage current density in Pb-rich PZT films on Ir substrate may be
caused by unknown electrically leaky phases such as amorphous
Pb-Ir-O phase. It seems that excess Pb ͑or PbO͒ promotes the
reaction between Pb ͑or PbO͒ and Ir during furnace annealing. Con-
sequently, more precise composition control may be needed for the
PZT/Ir system to avoid high leakage current after annealing.
Leakage current characteristics of the stoichiometric PZT capaci-
tors with different annealing temperatures are shown in Fig 10.
Thickness of PZT samples ranges from 210 to 220 nm. Above an-
nealing temperatures of 650°C, Pt͑top͒/PZT/Ir capacitors show high
leakage current density. From the XRD patterns of these samples,
not shown in this paper, we find that IrO2 phase appears above
ϭ 0.9͔ shows a perovskite phase and Pt5-7Pb with the trace of
pyrochlore and shows single perovskite in annealed film.
XRD patterns of as-deposited and furnace-annealed PZT films on
Ir electrode are also shown in Fig. 7. The surface microstructures of
PZT/Ir thin films are also shown in Fig. 8. PZT films show well-
developed grains with a dense and smooth morphology. With the
increase of the (A/B)solution from 0.7 to 0.8, the grain size gradually
increased. However, the Pb-rich PZT film shows unknown irregular
PbO-like second phase. In XRD spectrums, the Pb-deficient PZT/Ir
film shows only the perovskite phase without nonferroelectric
phases in appearance. However, lead-deficient pyrochlore and IrO2
1
4
phases appear in annealed film. In this study, IrO phase appears at
2
annealing temperatures above 650°C. Unlike the PZT/Pt film, the
stoichiometric PZT/Ir film deposited at 425°C shows a single per-
ovskite phase. The Pb-rich PZT film shows a perovskite phase with
the trace of PbO. The pyrochlore phase, which may be attributed to
the excess lead, appears after annealing.
We investigated the fundamental electrical properties, such as
P-E hysteresis loop and the I-V characteristics of PZT thin film
capacitors. Leakage current characteristics of the PZT capacitors
with different (A/B)solution are shown in Fig. 9. Before constructing
the PZT capacitor, furnace annealing was carried out at 700°C for 30
min in oxygen ambient. Thickness of PZT samples ranged from 320
to 330 nm and root-mean-square roughness ranged from 26 to 28
nm. For lead deficient and stoichiometric PZT films, the leakage
650°C.
Figure 11 shows P-E hysteresis loops of Pt/PZT/Pt and Pt/PZT/Ir
capacitors formed at various annealing temperatures. PZT samples
are identical with samples in Fig. 10. Well-saturated P-E hysteresis
loops were obtained when PZT films were prepared on Ir electrode.
The remanant polarization (P ) values of Pt/PZT/Pt capacitors are
r
2
2
5
8
.2 ␮C/cm ͑as-deposited͒, 7 ␮C/cm ͑annealed at 550°C͒,
.3 ␮C/cm ͑650°C͒, and 21 ␮C/cm ͑750°C͒, respectively. Also P
values of Pt/PZT/Ir capacitors are 21 ␮C/cm ͑as-deposited͒,
23 ␮C/cm ͑550°C͒, 34 ␮C/cm ͑650°C͒, and 37 ␮C/cm ͑750°C͒,
2
2
r
2
2
2
2
Downloaded on 2015-04-20 to IP 138.251.14.35 address. Redistribution subject to ECS terms of use (see ecsdl.org/site/terms_use) unless CC License in place (see abstract).

C522
Journal of The Electrochemical Society, 150 ͑8͒ C516-C522 ͑2003͒
sity at 100 kV/cm was less than 10Ϫ6 A/cm . It is believed that this
precursor set is a useful candidate for DLI-MOCVD of PZT thin
films at the temperature range between 350 and 460°C.
2
respectively. The increase of P with the annealing temperature on
r
Pt/PZT/Ir capacitor is partially ascribed to the increase of leakage
current density. The Pt/PZT/Pt capacitor prepared at 425°C shows
poor ferroelectric property due to the imperfect crystallinity, as
shown in Fig. 10. On the contrary, since PZT films prepared on Ir
substrate at 425°C shows a single perovskite phase, Pt/PZT/Ir ca-
Acknowledgment
2
pacitor prepared at 425°C shows P of 21 ␮C/cm and coercive
r
This work is partly financed by the Consortium of Semiconduc-
tor Advanced Research ͑project no. 00-B6-C0-00-09-00-01͒.
electric field (E ) of 62 kV/cm. From these results on the electrical
c
properties, it was found that PZT films on Ir electrode prepared by
low temperature DLI-MOCVD, even below 425°C, showed good
ferroelectric properties. This is one of the lowest deposition tem-
Pohang University of Science and Technology assisted in meeting the
publication costs of this article.
peratures reported at which a PZT film with large P value was
obtained. We also found from XPS depth profiles of PZT films that
percentage order nitrogen and carbon are not incorporated even at
r
References
1. J. F. Scott and C. A. Paz Araujo, Science (Washington, DC, U.S.), 246, 1400
͑
1989͒.
375°C.
2
3
. J.-H. Lee and S.-W. Rhee, J. Mater. Res., 14, 3988 ͑1999͒.
. S.-W. Kang, K.-J. Yang, K. Yong, and S.-W. Rhee, J. Electrochem. Soc., 149, C44
Conclusions
Dmae group precursors are moderately stable with air and mois-
ture and have low oxidation temperature, indicating that they are
favorable to low temperature process. It was found that separate
solution should be prepared for direct injection CVD of PZT be-
͑
2002͒.
4. H. Fujisawa, K. Kita, M. Shimizu, and H. Hiu, Jpn. J. Appl. Phys., 40, 5551 ͑2001͒.
5
6
. M. Aratani, T. Ozeki, and H. Funakubo, Jpn. J. Appl. Phys., 40, L343 ͑2001͒.
. A. C. Jones, T. J. Leedham, P. J. Wright, M. J. Crosbie, P. A. Lane, D. J. Williams,
K. A. Fleeting, D. J. Otway, and P. O’Brien, Chem. Vap. Deposition, 4, 46 ͑1998͒.
. D.-H. Kim, J. S. Na, and S.-W. Rhee, J. Electrochem. Soc., 148, C668 ͑2001͒.
7
cause there is a serious cross interaction between Pb(tmhd) precur-
8. J.-H. Lee, J.-Y. Kim, J.-Y. Shim, and S.-W. Rhee, J. Vac. Sci. Technol. A, 17, 3033
1999͒.
. J. S. Na, D.-H. Kim, K. Yong, and S.-W. Rhee, J. Electrochem. Soc., 149, C23
2002͒.
2
͑
sor and M(dmae) . With Zr and Ti dmae group precursors we have
4
9
developed a low temperature MOCVD process for the deposition of
͑
PZT with Pb(tmhd) . The growth rate was around 11 nm/min at
10. K. A. Fleeting, P. O’Brien, D. J. Otway, A. J. P. White, D. J. Williams, and A. C.
2
Jones, Inorg. Chem., 38, 1432 ͑1999͒.
410°C. Because there exists a linear response of (A/B)film to
11. S.-O. Chung, J. W. Kim, G. H. Kim, C. O. Park, and W. J. Lee, J. Appl. Phys., 36,
(
A/B)solution at low temperatures, we could easily prepare PZT films
4386 ͑1997͒.
with various (A/B)film values by adjusting the solution composition.
We obtained single perovskite PZT film at substrate temperatures as
12. A. C. Jones, T. J. Leedham, P. J. Wright, M. J. Crosbie, K. A. Fleeting, D. J. Otway,
P. O’Brien, and M. E. Pemble, J. Mater. Chem., 8, 1773 ͑1998͒.
1
3. I.-S. Chen and J. F. Roeder, in the Proceedings of the Synposium on Ferroelectric
Thin Films VII, Materials Research Society, Vol. 541, p. 375 ͑1999͒.
low as 425°C. The remanant polarization of PZT films prepared at
2
4
25°C on Ir substrate was 21 ␮C/cm and the leakage current den-
14. S. Y. Chen and I. W. Chen, J. Am. Ceram. Soc., 77, 2332 ͑1994͒.
Downloaded on 2015-04-20 to IP 138.251.14.35 address. Redistribution subject to ECS terms of use (see ecsdl.org/site/terms_use) unless CC License in place (see abstract).