lead-zirconate-titanate ferroelectric thin films using radio frequency planar magnetron sputtering

Preparation and properties of lead-zirconate-titanate ferroelectric thin films using radio frequency planar magnetron sputteringC. C. Chang and C. S. TangCitation: J. Appl. Phys. 87, 3931 (2000); doi: 10.1063/1.372437View online: /10.1063/1.372437View Table of Contents: /resource/1/JAPIAU/v87/i8Published by the American Institute of Physics.Related ArticlesEnergetic igniters realized by integrating Al/CuO reactive multilayer films with Cr filmsJ. Appl. Phys. 110, 074513 (2011)C/CrC nanocomposite coating deposited by magnetron sputtering at high ion irradiation conditionsJ. Appl. Phys. 110, 073301 (2011)Vertically aligned biaxially textured molybdenum thin filmsJ. Appl. Phys. 110, 064311 (2011)Low emissivity Ag/Ta/glass multilayer thin films deposited by sputteringJ. Appl. Phys. 110, 063508 (2011)Polycrystalline iron nitride films fabricated by reactive facing-target sputtering: Structure, magnetic and electrical transport propertiesJ. Appl. Phys. 110, 053911 (2011)Additional information on J. Appl. Phys.Journal Homepage: /Journal Information: /about/about_the_journalTop downloads: /features/most_downloadedInformation for Authors: /authorsPreparation and properties of lead-zirconate-titanate ferroelectric thinfilms using radio frequency planar magnetron sputteringC.C.Chang a)and C.S.TangDepartment of Electrical Engineering,National Taiwan Ocean University,Keelung,Taiwan͑Received7April1999;accepted for publication14January2000͒Lead-zirconate-titanate͓Pb͑Zr52Ti48͒O3,PZT͔thinfilms,0.5␮m thick,were deposited onto Pt/Sisubstrate at room temperature using the radio frequency planar magnetron sputtering technique.Aperovskite structure in the PZT thinfilm was obtained after the annealing processes.The annealingtemperature varied from650to750°C in this experiment tofind the optimized annealinging x-ray diffraction analysis,the lowest full width of the half maximum͑110͒planewas0.23°for the sample at650°C annealing temperature.The values of the remanent polarizationPr and coercivefield E c of the PZT thinfilm were100nC cmϪ2and0.6kV cmϪ1,respectively,at60Hz.The measured pyroelectric coefficient in0.5␮m thinfilms was3.12ϫ10Ϫ4C/m2K at50°C.Their dielectric constant and loss tangent were494and0.072,respectively,at1kHz.The surfacestructure of the PZT thinfilm was examined using scanning electron microscopy and the grain sizewas in the range of0.08–0.14␮m.©2000American Institute of Physics.͓S0021-8979͑00͒02508-1͔I.INTRODUCTIONABO3perovskite structure materials have been studiedextensively since1945.The ferroelectricity concept was pro-posed by Von Hippel.The standard ferroelectric materialsproduced are lead-zirconate-titanate͑PZT͒,1,2LiTaO3,3PbTiO3,4TGS,5PVDF,6etc.In the past year,one of theperovskite ferroelectric materials,PZT has been widely dis-cussed for use in preparing dynamic random access memorychips,nonvolatile memory chips,thinfilm capacitance chips,pyroelectric infrared sensors,and surface acoustic wave de-vices,etc.7–11The perovskite PZT ceramic soluble solid inthe composition(PbZrO3:PbTiO3ϭ0.52:0.48)around the morphotropic phase boundary has a very good electrome-chanical coupling coefficient,pyroelectric coefficient,dielec-tric constant,etc.Strong ferroelectrical properties make PZTan excellent ferroelectric material.In this experiment,PZT thinfilm was deposited ontoPt/Si substrates using radio frequency͑rf͒planar magnetronsputtering at room temperature.RF planar magnetron sput-tering method is an effective method for depositing thesefilms.12–14This process has the advantages of low tempera-ture,low damage,and a simple process procedure.The char-acteristics of the deposited PZT thinfilms were analyzedusing x-ray diffraction͑XRD͒,scanning electron microscope ͑SEM͒,and P–E hysteresis loop.An optimized thinfilm deposition process was obtained as a result of these experi-ments.II.EXPERIMENTIn this study,a rf planar magnetron sputtering method was used to grow PZT thinfilm.First,a clean Si͑100͒n/pϩsubstrate wafer was placed into a rf planar magnetron sputter system chamber with pressure set at2ϫ10Ϫ5Torr.The sput-tering medium,Ar͑100sccm͒was then added into the cham-ber and the Pt was deposited at an air pressure of40mTorr and rf power of80W.The rf power was reset at100W and the PZT thinfilm was deposited onto the Pt/Si substrate at room temperature.At room temperature,PZT is deposited in a near amor-phous state.In order to transfer the PZT from the near amor-phous state into a polycrystalline state,it is annealed in N2 under suitable parameters.In this experiment,the range of annealing temperatures was from650to750°C,at a time range of3–15min.The effects of annealing times and tem-peratures upon the PZT thinfilm properties were analyzed using XRD͑Siemens B5000͒,SEM͑Hitachi S-4100͒,and P–E hysteresis loop.III.RESULTS AND DISCUSSIONA.Crystallographic propertiesFrom the x-ray diffraction pattern,a perovskite structure can be obtained under various annealing temperatures if the annealing time is long enough.If the annealing time is not long enough,the pyrochlore phase will continue to exit,as shown in Fig.1.At lower annealing temperatures,a longer annealing time is required to form the perovskite structure. At an annealing temperature of750°C,3min are required.A 700°C temperature requires5and15min is needed at 650°C.The x-ray diffraction results for samples produced under these parameters are shown in Fig.1.A longer anneal-ing time can produce a perovskite structure but the extended time will also introduce the crack problem.The crack prob-lem is especially serious at higher annealing temperatures. Furthermore,a phase change will also be observed.At 650°C for15min,the greatest diffraction intensity,͑110͒, can be obtained.a͒Electronic mail:ccchang@.twJOURNAL OF APPLIED PHYSICS VOLUME87,NUMBER815APRIL200039310021-8979/2000/87(8)/3931/6/$17.00©2000American Institute of PhysicsB.Full width at half maximum …FWHM …analysisThe FWHM values have obvious differences for differ-ent annealing temperatures and annealing times.As Fig.2shows ͑the FWHM values are the average of three samples for each data point ͒,at 650°C and 15min annealing time,the FWHM value for the deposited PZT thin film is the smallest.This indicates a perfect perovskite structure phase quality.The best FWHM is 0.23°.C.…110…-oriented analysisThe following perovskite structure peaks ͑100͒,͑110͒,͑111͒,͑201͒,and ͑211͒were observed from the XRD pat-terns with Cu K ␣radiation ͑1.5418Å͒as Fig.1shows.The ␣value is defined as follows:␣ϭI ͑110͒Is ͑110͒I ͑100͒Is ͑100͒ϩI ͑110͒Is ͑110͒ϩI ͑111͒Is ͑111͒ϩI ͑210͒Is ͑210͒ϩI ͑211͒Is ͑211͒.I (100),I (110),I (111),I (201),and I (211)represent the x-ray diffraction intensities of ͑100͒,͑110͒,͑111͒,͑201͒,and ͑211͒from Fig.1.Is (100),Is (110),Is (111),Is (201),and Is (211)are the standard intensity from the Joint Com-mittee on Powder Diffraction Standards ͑JCPDS ͒.A larger ␣value indicates a larger piezoelectric coefficient.Therefore,as shown in Fig.3͑the ␣values are the average of three samples for each data point ͒,650°C at 15min will produce the maximum ␣value,which is approximate to a value of0.12.FIG.1.XRD comparison pattern of PZT thin film on Pt/Si substrate with various annealedtemperature.FIG.2.FWHM on the PZT/Pt/Si substrate as a function of annealed tem-perature.FIG.3.Preferred ϩof ͑110͒orientation ␣on the PZT/Pt/Si substrate as a function of annealedtemperature.FIG.4.SEM photograph of the surface morphology of PZT thin film on Pt/Si substrate nonannealed.D.SEM analysisThe surface morphology of the nonannealed PZT thin film shown in Fig.4is a little rough and its uniformity is not very good.The surface morphology of the annealed PZT thin film,at 700°C and 5min,exhibits serious cracking,as shown in the photograph in Fig.5.When the annealing tem-perature and time were 750°C and 3min,respectively,cracking and blistering were also observed,as shown in Fig.6.The surface morphology of Pb ͑Zr 0.52Ti 0.48͒O 3thin film on Pt/Si substrate annealed at 650°C for 15min was very smooth and uniform without interference patterns.No crack-ing or blistering is observed.The grain size is in the range of 0.08–0.14␮m,estimated from a SEM photomicrograph,as shown in Fig.7.From A to D it can be seen that 650°C for 15min are the optimal annealing parameters for perovskite PZT thin film.The thin film deposited and annealed using above parameters was used for other characteristic measure-ments as follows.E.Remanent polarization-coercive field …P –E …analysisThe ferroelectric properties of the deposited PZT thin film were investigated by P –E hysteresis loop measure-ments using a Sawyer–Tower circuit.The reference capaci-tor was 100nF and the area of the top Pt contact electrode was about 4ϫ10Ϫ2cm 2.From Fig.8,the remanent polariza-tion P r and the coercive field E c of Pb ͑Zr 0.52Ti 0.48͒O 3thin film,which was nonannealed,were 42.5nC cm Ϫ2and 0.78kV cm Ϫ1,respectively.From these results,it appears that the nonannealed PZT thin film did not completely achieve the amorphous state.It may be formed some microdomain crys-tallized regions.Figure 9shows the P –E hysteresis loop of the Pb ͑Zr 52Ti 48͒O 3thin film,annealed at 650°C for 15min at 60Hz.The measured remanent polarization P r and coer-cive field E c were 100nC cm Ϫ2and 0.6kV cm Ϫ1,respec-tively.Annealing PZT thin films leads to some improvement in the P –E hysteresis properties,i.e.,the loops become more squared with a higher remanent polarization P r and the co-ercive field E c is slightly reduced.From the above,the an-nealed PZT thin film at 650°C for 15min has the better piezoelectricity.F.Dielectric propertiesIn this experiment,the bottom electrode Pt film was de-posited onto Si substrate using rf planar magnetron sputter-ing at room temperature.The thickness of the Pt filmwasFIG.5.SEM photograph of the surface morphology of PZT thin film on Pt/Si substrate with various annealed temperature 700°C.FIG.6.SEM photograph of the surface morphology of PZT thin film on Pt/Si substrate with various annealed temperature 750°C.FIG.7.SEM photograph of the surface morphology of PZT thin film on Pt/Si substrate with various annealed temperature 650°C.FIG.8.P –E hysteresis loop of the Pb ͑Zr 52Ti 48͒O 3thin film on Pt/Si sub-strate non-annealed.0.168␮m.The PZT thin film was deposited onto a Pt/Si substrate at room temperature.The thickness was 0.474␮m thick,as shown in Fig.10.The surface and cross section view of that PZT thin film on Pt/Si substrate is shown in Fig.11.The loss tangent and dielectric constant versus frequency were measured using a HP4192A impedance analyzer,as shown in Figs.12and 13,respectively.We observed that when the frequency increases the loss tangent also increases.The loss tangent of the Pb ͑Zr 52Ti 48͒O 3thin film at room temperature and 1kHz was about 0.072.The loss tangent had the maximum values when the resonant frequency was 1.05MHz.As the frequency increases,the dielectric constant of the materials will decrease.Because some kind of polar-ization will disappear to accompany the increase of fre-quency.The charge,dipole,ionic,etc.each polarization dis-appears in order.15Only electronic polarization exits at the photofrequency.The dielectric constant ⑀r of Pb ͑Zr 52Ti 48͒O 3thin film at room temperature,1kHz is about 494in this experiment.G.Pyroelectric propertiesIn this experiment,bottom electrode Pt thin film was deposited onto Si substrates using rf planar magnetron sput-tering at room temperature.The PZT thin film was then de-posited under the best deposition parameters.After annealing at 650°C for 15min,the top electrode Pt ͑area is 4␮m 2͒was deposited using rf planar magnetron sputtering at room tem-perature.The pyroelectric coefficient of the PZT thin films on Pt/Si substrate was then measured.In this measurement,the measurement temperature was ramped from 50to 250°C three times in the same sample.The ambient temperature of the sample was controlled with a PID controlled furnace ͑tol-erance Ϯ1°C ͒.A thermocouple was used to check the tem-perature of the sample.The electrodes of the sample were bonded with two fine copper wires to take the electrical sig-nal.In addition,these fine Cu wires are connected to a large diameter Cu wire.The sample was floated in the furnace by two fine Cu wires to approach a thermal isolated environ-ment.The electrical signal through Cu wire was then con-nected to current amplifier circuit and digital meter to take the measured signal.Figure 14shows the results.It shows that the pyroelectric coefficients were determined at different ambient temperatures.The pyroelectric coefficient was mea-sured as a function of temperature which was3.12FIG.9.P –E hysteresis loop of the Pb ͑Zr 52Ti 48͒O 3thin film on Pt/Si sub-strate annealed at 650°C for 15min.FIG.10.SEM cross section view of PZT thin film on Pt/Si substrate.The deposition time was set at 1h.FIG.11.SEM cross section view of PZT thin film on Pt/Si substrate.The deposition time was set at 1h.ϫ10Ϫ4C/m 2K at 50°C.There was a rapid change at 250°C.This may have occurred because the measurement tempera-ture was close to the curie temperature (T c ϭ250°C)of PZT thin film which would cause the pyroelectric coefficient to rise rapidly.16H.Results of pyroelectric figures of meritIn this experiment,the pyroelectric coefficient was mea-sured as a function of temperature which was 3.12ϫ10Ϫ4C/m 2K at 50°C.The value of the loss tangent of the Pb ͑Zr 52Ti 48͒O 3thin film at room temperature,1kHz,was about 0.072.The value of the dielectric constant ⑀r of the Pb ͑Zr 52Ti 48͒O 3thin film at room temperature,1kHz,was about 494.The specific heat volume was 2.5ϫ106J m Ϫ3K Ϫ1.17Therefore,the current (F i ),voltage (F v ),and detectivity (F D )figures of merit are calculated.18The results for F v ,F i ,and F D were 1.25ϫ10Ϫ10m V Ϫ1,0.03m 2C Ϫ1,and 0.7ϫ10Ϫ5ͱm 3J Ϫ1.For convenience,the Pb ͑Zr 52Ti 48͒O 3thin film pyroelectric properties are summa-rized in Table I.IV.CONCLUSIONSIn this experiment,we successfully used an rf planar magnetron sputtering method to deposit PZT thin films onto Pt/Si substrates at room temperature using an rf power of 100W and Ar gas sputtering of 40nTorr.The thickness of the PZT thin film was 0.5␮m.At an annealing temperature 650°C for 15min,a good perovskite structure was obtained.The Pb ͑Zr 52Ti 48͒O 3thin film was measured with a pyroelec-tric coefficient of 3.12ϫ10Ϫ4C/m 2K at 50°C,dielectric constant ⑀r of 494at 1kHz,tan ␦of 0.072at 1kHz,FWHM of 0.23°and ͑110͒orientation ␣of 0.12.The current,volt-age,and detectivity figures of merit were 1.25ϫ10Ϫ10m V Ϫ1,0.03m 2C Ϫ1,and 0.7ϫ10Ϫ5ͱm 2Ϫ1.TheFIG.12.Frequency dependence of loss tangent tan ␦of Pb ͑Zr 52Ti 48͒O 3thin film on Pt/Si substrate annealed at 650°C for 15min.FIG.13.Frequency dependence of dielectric constant ␧r of Pb ͑Zr 52Ti 48͒O 3thin film on Pt/Si substrate annealed at 650°C for 15min.FIG.14.Pyroelectric coefficient of PZT thin film annealed at 650°C,15min versus temperature.TABLE I.Pyroelectric properties of Pb ͑Zr 52Ti 48͒O 3thin film.TitleValues Units Pyroelectric coefficient P ͑50°C ͒3.1210Ϫ4C m Ϫ2K Ϫ1Dielectric constant ␧r ͑1kHz ͒494¯Loss tangent tan ␦͑1kHz ͒0.072¯Volume specific heat S 2.5J m Ϫ3K Ϫ1Current figure of merit F i 1.2510Ϫ10m V Ϫ1Voltage figure of merit F V 0.03m Ϫ2C Ϫ1Detectivity figure of merit F D0.710Ϫ5ͱm 3J Ϫ1remanent polarization P r and the coercivefield E c of the Pb͑Zr52Ti48͒O3thinfilm were100nC cmϪ2and0.6kV cmϪ1 at60Hz.1L.E.Sanchez,S.-Y.Wu,and I.K.Naik,Appl.Phys.Lett.56,2399͑1990͒.2R.Takayama,Y.Tomita,K.Iijima,and 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