AC conductivity and dielectric properties of sol-gel PZT thin films for ferroelectric memory applications (original) (raw)
Related papers
1999
Ferroelectric SBT (Sr/Bi/Ta = 0.8/2.3/2) thin films on Pt/ZrO 2 /SiO 2 /Si were successfully prepared by using an alkanolamine modified chemical solution deposition method. Acetic acid as a solvent led to the formation of water in the solution, which might continuously induce the hydrolysis and condensation of the precursors, leading to reducing the stability of the solution with aging time. It was observed that alkanolamine provided the stability to the SBT solution by retarding the hydrolysis and condensation rates. This solution could be used as long as up to 30 days without any appreciable change of the solution properties. The typical hysteresis loop of SBT thin films was obtained at 2 V, and it was fully saturated even below an applied voltage of 3 V (2P r ≈ 16 µC/cm 2). The measured 2P r value of the SBT thin film at 5 V was almost 20 µC/cm 2. Fatigue and breakdown characteristics of the films, measured at 5 V, showed a stable behavior, and negligible degradation was observed up to 10 10 cycles.
1999
The paper presents short review of the works performed during the last few years in the field of the alkoxy-derived ferroelectric films. PZT films were prepared using titanium and zirconium alkoxides and Pb(CH 3 COO) 2 •2H 2 O as precursors. Different way of lead acetate dehydration and the impact of lead excess in the precursor solutions on the properties of the PZT films are discussed. Trimetallic alkoxide systems Bi(OR) 3-Ta(OR) 5-ROH (R = Me, Et or i Pr) were studied as precursors for preparation of SrBi 2 Ta 2 O 9 films. Films prepared from these solutions and annealed at the temperature between 700 and 750 • C demonstrated the remanent polarization P * r − Pr = 7-9 µC/cm 2. Ba 1−x Sr x TiO 3 films we applied from modified alkoxide solutions. Decomposition of the organic phase in the course of thermal treatment of the films is studied by IR-spectroscopy. The dependence of the dielectric permittivity of the films via the annealing temperature is reported. Preparation of LiNbO 3 , SrZr 0.2 Ti 0.8 O 3 , Zr 0.8 Sn 0.2 TiO 4 is briefly discussed.
Low-temperature PZT thin-film ferroelectric memories fabricated on SiO 2 /Si and glass substrates
Journal of Science: Advanced Materials and Devices, 2016
In a ferroelectric-gate thin film transistor memory (FGT) type structure, the gate-insulator layer is extremely important for inducing the charge when accumulating or depleting. We concentrated on the application of low-temperature PZT films crystallized at 450, 500 and 550 C, instead of at conventional high temperatures (!600 C). Investigation of the crystalline structure and electrical properties indicated that the PZT film, crystallized at 500 C, was suitable for FGT fabrication because of a high (111) orientation, large remnant polarization of 38 mC/cm 2 on SiO 2 /Si substrate and 17.8 mC/cm 2 on glass, and low leakage current of 10 À6 A/cm 2. In sequence, we successfully fabricated FGT with all processes below 500 C on a glass substrate, whose operation exhibits a memory window of 4 V, ON/OFF current ratio of 10 5 , field-effect mobility of 0.092 cm 2 V À1 s À1 , and retention time of 1 h.
Effect of Zr/Ti stoichiometry ratio on the ferroelectric properties of sol-gel derived PZT films
1992
A series of sol-gel derived PZT films with Zr:Ti ratios including 100:0, 94:6. 80:20, 65:35, 53:47. 35:65, 20:80 and 0: 100 was prepared on platinized Si wafers. The precursor chemistries were based on lead acetate and Zr/Ti alkoxides containing the appropriate amounts of cations in the required stoichiometries. Excess PbO was incorporated to compensate for PbO loss during processing. Films were fired to 700C where they were all single-phase perovskite as determined by XRD. Microlithography was performed to obtain Pt-PZT-Pt monolithic capacitors with 130 pm square electrode pads. Ferroelectric properties were obtained on these pads using a Radiant Technologies RT-66A Tester while the leakage characteristics were measured using a Keithley 617 Electrometer. The dielectric and ferroelectric properties of the PZT films were highly dependent on composition and processing conditions.
Dielectric and ferroelectric properties and electric conductivity of sol–gel derived PBZT ceramics
Journal of Alloys and …, 2011
a b s t r a c t (Pb 1−x Ba x )(Zr 1−y Ti y )O 3 (PBZT) is a solid solution in which ferroelectric, relaxor or antiferroelectric properties are observed depending on composition. The substitution of Ba 2+ into A position of the perovskite structure leads to the decrease in phase transition temperature and it gradually leads to relaxor properties. The majority of papers describe PBZT obtained from oxides. We report the results of the investigation of the properties and phase transitions of (Pb 1−x Ba x )(Zr 0.65 Ti 0.35 )O 3 ceramics with x = 0.09, 0.25 and 0.35 obtained by the sol-gel method with final free sintering (FS) at 1573 K/4 h and by the hot pressing (HP) method at 1473 K/2 h/20 MPa. Unlike pure PZT, the properties of HP-PBZT samples obtained at lower (1473 K) temperature are a little inferior than FS samples. It is probably related to the fact that barium requires higher final sintering temperatures.
Asymmetric metal-ferroelectric-metal ͑MFM͒ structures were manufactured by sol-gel deposition of a lead zirconate-titanate ͑PZT with Zr/Ti ratio 65/35͒ film on Pt-coated Si, with a Au top electrode. The average remnant polarization of 9 C/cm 2 and the coercive field of 39 kV/cm were obtained from the hysteresis loop measurements. A detailed analysis of the polarization-electric field (P-E), capacitance-voltage (C-V), and current-voltage (I-V) measurement results allowed us to estimate the near-electrode space-charge region thickness ͑roughly half of the film thickness at zero voltage͒, net doping concentration ͑around 10 18 cm Ϫ3), built-in potential ͑in the 0.4-0.8 V range, depending on the injecting electrode͒, and dynamic dielectric constant ͑5.2͒. The current logarithm-voltage dependence for the field-enhanced Schottky emission obeys a ''1/4'' law. The spectral distribution of the short circuit current measured under continuous light illumination in the 290-800 nm range exhibits a cutoff wavelength at 370 nm and a maximum sensitivity at about 340 nm. The estimated band-gap energy of the PZT material is 3.35 eV. The MFM structure is discussed in terms of two back-to-back Schottky diodes with a ferroelectric material in between. It is concluded that the semiconductor properties of the films are not negligible and, in certain conditions, are dominating over the ferroelectric ones.
Journal of Applied Physics, 2001
Ferroelectric thin films of barium titanate were fabricated by sol-gel technique on platinum substrates. The processing temperature was 700°C. The films obtained with a thickness of 1.5 m were dense, transparent, and showed ferroelectricity. Scanning electron microscopy and x-ray diffraction were used for studying the surface morphology and crystallographic structure of the film. Films in the metal-ferroelectric-metal configuration ͑MFM͒ were used for the electrical measurements. Dielectric constant and loss tangent were found to be 430 and 0.015, respectively, at 10 kHz under ambient conditions. The ⑀Ј(T) curve shows broad peak centered around 120°C as in the case of diffuse phase transition. The ac conductivity is proportional to 0.9 in the low frequency region and 1.8 in the high frequency region. The dc conductivity versus temperature curve showed a change in the slope around 125°C, corresponding to the phase transition. To study the low temperature phase transitions, dielectric parameters on the films were measured to a temperature down to about 10 K. Remanent polarization ( P r ) and coercive field (E c ) obtained from the hysteresis loop at room temperature are ϳ2.0 C/cm 2 and ϳ27 kV/cm, respectively. Capacitancevoltage studies performed on the MFM structures showed butterfly loop at 135°C.
Electrical characteristics of ferroelectric PZT thin films for DRAM applications
Electron Devices, IEEE …, 1992
Ferroelectric lead zirconate titanate (PZT) films with as much as 2.5 times the storage capacity of the best reported silicon oxidelnitrideloxiPe (ONO) stacked dielectrics have been fabricated. A 2OOO-fi PbZr0.STi0.S03 film with an effective SiOz thickness of 10 A is demonstrated. Because of the extremely high dielectric constant (er L lOOO), even larger storage capacities can be obtained by scaling the ferroelectric film thickness whereas the thickness of ONO films is limited by direct tunneling through the film. Electrical conduction in the PZT films studied here is ohmic at electric fields below 250 kV/cm and follows an exponential field dependence at higher fields. This type of behavior is shown to be consistent with a simple model for electronic hopping through the film. Leakage current as low as 9 x lo-* A/cmZ at 2.5 V for a 4000 A film is obtained with the addition of lanthanum and iron to compensate for lead and oxygen vacancies in the film. Further improvement in both leakage current and time-dependent dielectric breakdown characteristics are necessary to ensure reliable DRAM operation.
Lead free ferroelectric films deposited by sol-gel for electronic applications
2010
Lead in electronic components is prohibited by the RoHS directive since july 2006. Nevertheless, there are some exceptions for example PbZr X Ti 1-X O 3 (PZT) materials because they present exceptional piezoelectric properties. PZT is used as sensors and actuators in numerous applications such in sonar, echography, alarm, etc…Up to now, neither in ceramic form nor in film form, it have been surpassed by lead free materials. At present, many studies are devoted to find a substitute to PZT as it will be probably banned in five years or so. Our work is in this objective and concerns the study of the electrical properties at low frequency, from DC to 1MHz, of ferroelectric films with thickness inferior or equal to 1µm. The starting material is BaTiO 3 in which Ba is exchanged by Sr at different levels and also doped with various cations (monovalent, divalent, trivalent…). This permits us to improve the dielectric and ferroelectric properties: for example to decrease the losses and to increase the tunability. Another method to optimize the electrical properties is to study the annealing conditions: very high temperature applied a short time (950°C@15mn) should be favoured. This leads to both higher dielectric constant and polarization. The pyroelectric and piezoelectric coefficients have also been improved but as concerns the *
VNU Journal of Science: Mathematics - Physics, 2019
Ba0.85Sr0.15)(Ti0.9Zr0.1)O3 (BSZT) lead-free ferroelectric thin films at the vicinity of the morphotropic phase boundary (MPB) were successfully deposited on Pt/Ti/SiO2/Si using a modified spin-coated sol-gel method. Microstructure and electrical properties of the thin film were studied. High resolution synchrotron X-ray powder diffraction (SXRD) combined with Rietveld refinement revealed that the samples were crystalized in tetragonal perovskite structure with in-plane symmetry (c < a). Raman spectra also confirmed a tetragonal perovskite crystalline lattice structure. Polarisation studies demonstrate that BSZT films exhibit a rather high saturation polarisation of 22.25 µC.cm −2. Leakage current behaviour was obtained and possible conduction mechanism is discussed.