Showing papers on "Lead zirconate titanate published in 1992"

Fatigue and retention in ferroelectric Y‐Ba‐Cu‐O/Pb‐Zr‐Ti‐O/Y‐Ba‐Cu‐O heterostructures

Abstract: Fatigue and retention characteristics of ferroelectric lead zirconate titanate thin films grown with Y‐Ba‐Cu‐O(YBCO) thin‐film top and bottom electrodes are found to be far superior to those obtained with conventional Pt top electrodes. The heterostructures reported here have been grown in situ by pulsed laser deposition on yttria‐stabilized ZrO2 buffer [100] Si and on [001] LaAlO3. Both the a‐ and c‐axis orientations of the YBCO lattice have been used as electrodes. They were prepared using suitable changes in growth conditions.

Piezoelectric micromotors for microrobots

Abstract: The authors have begun research into piezoelectric ultrasonic motors using ferroelectric thin films. The authors have fabricated the stator components of these millimeter diameter motors on silicon wafers. Ultrasonic motors consist of two pieces: a stator and a rotor. The stator includes a piezoelectric film in which bending is induced in the form of a traveling wave. A small glass lens placed upon the stator becomes the spinning rotor. Piezoelectric micromotors overcome the problems currently associated with electrostatic micromotors such as low torque, friction, and the need for high voltage excitation. More importantly, they may offer a much simpler mechanism for coupling power out. Using thin films of lead zirconate titanate on silicon nitride membranes, various types of actuator structures can be fabricated. By combined new robot control systems with piezoelectric motors and micromechanics, the authors propose creating micromechanical systems that are small, cheap and completely autonomous. >

Electrical characteristics of ferroelectric PZT thin films for DRAM applications

Abstract: Ferroelectric lead zirconate titanate (PZT) films with as much as 2.5 times the storage capacity of the best reported silicon oxide/nitride/oxide (ONO) stacked dielectrics have been fabricated. A 2000-AA film with an effective SiO/sub 2/ thickness of 10 AA is demonstrated. Because of the extremely high dielectric constant ( epsilon /sub r/>or approximately=>1000), 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 is ohmic at electric fields below 250 kV/cm and follows an exponential field dependence at higher fields, which is shown to be consistent with a simple model for electronic hopping through the film. Leakage current as low as 9*10/sup -8/ A/cm/sup 2/ at 2.5 V for a 4000-AA film is obtained with the addition of La and Fe to compensate for Pb and O vacancies in the film. Further improvement in both leakage current and time-dependent dielectric breakdown characteristics are necessary to ensure reliable DRAM operation. >

Metal–Ceramic Composite Actuators

Abstract: A new type of actuator composed of metal (brass) end caps and piezoelectric ceramics has been developed as a displacement transducer. Shallow cavities positioned between the metal caps and the central ceramic disk convert and amplify the radial displacement of the piezoelectric ceramic into a large axial motion of the metal end caps. Large d33 coefficients exceeding 2500 pC/N are obtained with the composite actuators. The behavior of the electrically induced strain with geometric variables, such as the thickness of the metal end caps, and with pressing force and driving frequency has been evaluated. Sizeable strains are obtained with both PZT (piezoelectric lead zirconate titanate) and PMN (electrostrictive lead magnesium niobate) ceramics.

Crystallization of sputtered lead zirconate titanate films by rapid thermal processing

Abstract: A rapid thermal annealing (RTA) technique has been employed to process lead zirconate titanate (PZT) films prepared by reactive magnetron sputtering. The films were fabricated by dc sputtering a multielement metal target in an oxygen ambient at a substrate temperature of 200 °C. A subsequent postdeposition RTA at 600 °C for 5 s crystallizes the films into a perovskite‐type structure through various intermediate phases. Due to the short postdeposition processing times inherent in the RTA method, the initial nature of the as‐grown films has a critical influence on the crystallization kinetics. The reaction sequence in the formation of perovskite PZT from the films deposited at low substrate temperatures by the sputtering technique has been evaluated, and various key factors influencing the crystallization of PZT have been identified. As‐grown films are constituted of polycrystalline orthorhombic lead oxide in an amorphous matrix of titania and zirconia. During annealing lead oxide transforms into a cubic ph...

Pyrochlore to Perovskite phase-transformation in sol-gel derived lead-zirconate-titanate thin-films

Abstract: Pyrochlore to perovskite phase transformation in sol‐gel derived lead‐zirconate‐titanate (PZT) films was studied by x‐ray diffraction and transmission‐electron microscopy (TEM). X‐ray diffraction studies of PZT films on sapphire substrates indicated that the pyrochlore to perovskite phase transformation was completed at 650 °C. In contrast, TEM investigations of free‐standing PZT films showed that the phase transformation was completed at much higher temperatures. This discrepancy in the behavior of free‐standing films versus films on substrate can be related to the size effect.

Multi‐ion‐beam reactive sputter deposition of ferroelectric Pb(Zr,Ti)O3 thin films

Abstract: A multi‐ion‐beam reactive sputter (MIBERS) deposition technique was devised to grow ferroelectric lead zirconate titanate (PZT) thin films of different compositions (Zr/Ti ratios of 50/50 and 56/44) from individual metal targets of Pb, Zr, and Ti. This technique offers a highly controllable deposition process allowing excellent uniformity in composition and thickness over a large area (7.5 cm diameter) on a reproducible basis. The PZT films were deposited on a variety of unheated substrates and annealed by two different techniques, rapid thermal annealing and conventional furnace annealing. Both techniques induced a perovskite phase with good morphology. The effect of the excess Pb content was observed in terms of the crystallization and morphology. It was seen that the presence of excess Pb tends to enhance perovskite phase formation but degrades the morphology. The effect of the substrates was observed in terms of crystallization and orientation. A low‐energy oxygen ion beam was employed to modify the f...

Crystallographically Aligned Ferroelectric Films Usable in Memories and Method of Crystallographically Aligning Perovskite Films

Abstract: A ferroelectric memory and its method of making in which a highly c-axis oriented layer (56) of ferroelectric lead zirconate titanate (PZT) is epitaxially deposited at between 640° and 710° C. upon a crystalline film (54) of yttrium barium copper oxide (YBCO), acting both as growth template and bottom electrode. A top electrode (58) is formed over the ferroelectric layer to complete the memory element. The two electrodes are preferably composed of the same perovskite conductor of the same cyrstalline orientation, most preferably, a-axis oriented YBCO. The structure can be grown on a silicon substrate (50) with an intermediate buffer layer (52) of yttria-stabilized zirconia. The ferroelectric behavior is optimized if the structure is cooled from its growth temperature at about 20° C./min. Such a-axis oriented perovskite thin films can be grown by continuously depositing the same or different perovskite material, but dividing the deposition into three temperature stages, a first at a temperature favoring a-axis oriented growth, a second gradually increasing the temperature to a temperature favoring c-axis growth, and a third at the c-axis growth temperature. Nonetheless, a high-quality a-axis oriented film is grown. The memory can be rejuvenated after it has become fatigued by applying a pulse of magnitude equal to that of the writing pulse but of considerably longer duration.

Rapid thermal annealing of sol‐gel derived lead zirconate titanate thin films

Abstract: Sol‐gel derived ferroelectric thin films of lead zirconate titanate have been annealed through the rapid thermal annealing (RTA) technique to investigate the effect of various annealing temperature‐time combinations. Crystallization of the film into the perovskite phase required 10 s at 600 °C and a mere 1 s at 700 °C. Rapid thermally annealed films recorded weak‐field permittivities greater than 1000, dissipation losses of 0.02–0.05, maximum remanent polarization of 29 μC/cm2, and coercive field around 40 kV/cm. RTA films are distinguished by superior breakdown strengths, and morphologically smoother surfaces. The frequency dependent dielectric constants have been discussed in terms of a lumped circuit model.

Thermal stability of field-forced and field-assisted antiferroelectric-ferroelectric phase transformations in Pb(Zr,Sn,Ti)O3

Abstract: Antiferroelectric (AFE)‐ferroelectric phase transformations in tin‐modified lead zirconate titanate, i.e., Pb(Zr,Sn,Ti)O3 are reported. A martensitic‐type approach is developed to explain the observed thermal hysteresis and field‐induced transformation behavior. A model is proposed with transformation fields where the forward EF and reverse EA field strengths are related to the transformation barrier to the ferroelectric state, and to the AFE sublattice coupling, respectively. The thermal stability of the AFE state can therefore be determined with respect to the field‐induced transformation behavior. A distinction is made between field‐forced and field‐assisted transformations, which depend on temperature and thermal hysteresis, and which are related to reversible and irreversible field‐induced characteristics. Data are reported for polarizations and strains, and discussed with respect to the proposed thermodynamic model and device applications.

Fabrication and characterization of transducer elements in two-dimensional arrays for medical ultrasound imaging

Abstract: Some of the problems of developing a two-dimensional (2-D) transducer array for medical imaging are examined. The fabrication of a 2-D array material consisting of lead zirconate titanate (PZT) elements separated by epoxy is discussed. Ultrasound pulses and transmitted radiation patterns from individual elements in the arrays are measured. A diffraction theory for the continuous wave pressure field of a 2-D array element is generalized to include both electrical and acoustical cross-coupling between elements. This theory can be fit to model the measured radiation patterns of 2-D array elements, giving an indication of the level of cross-coupling in the array, and the velocity of the acoustic cross-coupling wave. Improvements in bandwidth and cross-coupling resulting from the inclusion of a front acoustic matching layer are demonstrated, and the effects of including a lossy backing material on the array are discussed. A broadband electrical matching network is described, and pulse-echo waveforms and insertion loss from a 2-D array element are measured. >

Vibration-Level Characteristics of Lead-Zirconate-Titanate Ceramics

Abstract: Vibration-level characteristics of lead-zirconate-titanate ceramics were studied using the constant current driving method. It was found that resonant frequency and mechanical Q markedly decreased with increasing vibration level, accompanying heat generation. The heat generation was assumed to be caused by vibration loss. The vibration loss was reduced by doping Fe atoms to the ceramics. On the contrary, the vibration loss was increased by doping Nb atoms.

Fatigue modeling of lead zirconate titanate thin films

Abstract: Polarization of ferroelectrics decreases as the number of polarization reversals increase. This phenomenon is known as fatigue. Understanding fatigue mechanisms is important for improving the reliability of ferroelectric thin films. A quantitative fatigue model is proposed for lead zirconate titanate (PZT) thin film capacitors on the basis of effective one-directional movement of defects, defect intrapment at electrode-PZT interfaces (and/or at grain and domain boundaries) and the resultant polarization loss at those surfaces under an alternating pulse. An asymmetric polarization may occur on alternating polarity because of asymmetry in electrode-ferroelectric interfaces, and/or non-uniform defect distribution in the bulk. The internal field difference owing to the asymmetric polarization causes an effective one-directional movement of defects such as oxygen vacancies, lead vacancies, mobile impurity ions, etc. These defects can be trapped at electrode-PZT interfaces, grain boundaries, and/or domain boundaries because of their lower potential energies at those sites than those in PZT bulk. This entrapment in turn results in the loss of polarization. In accordance with this fatigue source, a fatigue equation is derived which consists of three constants: initial saturation polarization, piling constant, and decay constant. The predicted values from the model agree very well with the experimental data.

Comparison of electro‐optic lead‐lanthanum zirconate titanate films on crystalline and glass substrates

Abstract: It has been demonstrated that electro‐optically active lead zirconate titanate (PZT) and lanthanum‐modified lead zirconate titanate (PLZT) films derived from a water‐soluble acetate precursor system can be produced on glass substrates at a processing temperature of 600 °C through the initial application of a lanthanum‐modified lead titanate (PLT) buffer layer. A comparison of the electro‐optic behavior is made between films deposited onto glass and single‐crystal sapphire substrates when processed under the same conditions. Memory effects were observed in PZT 0/65/35 films, while quadratic behavior was exhibited by the PLZT 9/65/35 films consistent with expected bulk behavior. However, the measured birefringent shift in the films on glass substrates was lower than that on sapphire.

New opportunities in ultrasonic transducers emerging from innovations in piezoelectric materials (Invited Paper)

Abstract: Piezoelectric materials lie at the heart of ultrasonic transducers. These materials convert electrical energy into mechanical form when generating an interrogating acoustic pulse and convert mechanical energy into an electric signal when detecting its echoes. This paper first surveys the piezoelectric materials in current use: piezoceramics, such as barium titanate, lead zirconate titanate, and modified lead titanate; piezopolymers, such as polyvinylidene difluoride and its copolymer with trifluroethylene; and piezocomposites, consisting of piezoceramic rods in a passive polymer matrix. Each material system has properties which commend them for use in the present single element transducers, annular arrays, sequenced linear arrays, and steered phased arrays. Looking to the future, new transducer possibilities are opening up due to recent piezoelectric material developments, such as, for example, synthesis techniques for fine-grained high-density piezoceramics, electrostrictive relaxor ferroelectric ceramics, novel piezoceramic forming methods, piezoceramic fiber synthesis, piezoceramic/metal multilayer structures, composite acoustoelectric materials, ferroelectric thin film growth and processing, and new piezopolymers. These innovations lead to fabrication of conventional transducers at high frequencies, fine-scale piezocomposites, 11/2-D and 2-D arrays, small intravascular transducers, as well as provide opportunities for new ultrasonic imaging techniques, using pitch-catch and non-resonant traveling wave transducers.

Growth of epitaxial Pb(Zr,Ti)O3 films by pulsed laser deposition

Abstract: Lead zirconate titanate (PZT) thin films with a composition near the morphotropic phase boundary have been grown on MgO (100) and Y1Ba2Cu3Ox (YBCO) coated MgO substrates. Substrate temperature and oxygen pressure were varied to achieve ferroelectric films with a perovskite structure. Films grown on MgO had the perovskite structure with an epitaxial relationship with the MgO substrate. On the other hand, films grown on the YBCO/MgO substrate had an oriented structure to the surface normal with a misorientation in the plane parallel to the surface. The measured dielectric constant and loss tangent at 1 kHz were 670 and 0.05, respectively. The remnant polarization and coercive field were 42 μC/cm2 and 53 kV/cm. A large internal bias field (12 kV/cm) was observed in the as‐deposited state of the undoped PZT films.

Enhanced fatigue and retention in ferroelectric thin film memory capacitors by post-top electrode anneal treatment

Abstract: Thin film ferroelectric capacitors (10) comprising a ferroelectric film (18) sandwiched between electrodes (16 and 20) for nonvolatile memory operations are rendered more stable by subjecting the capacitors to an anneal following deposition of the top electrode (20). The anneal is done so as to form the interface (22) between the ferroelectric film and the top electrode. Heating in an air oven, laser annealing, or electron bombardment may be used to form the interface. Heating in an air oven is done at a temperature at least equal to the crystallization temperature of the ferroelectric film. Where the ferroelectric film comprises lead zirconate titanate, annealing is done at about 550° to 600° C. for about 10 to 15 minutes. The formation treatment reduces the magnitude of charge associated with the non-switching pulse in the thin film ferroelectric capacitors. Reduction of this charge leads to significantly more stable nonvolatile memory operations in both digital and analog memory devices. The formation treatment also reduces the ratio of change of the charge associated with the non-switching pulse as a function of retention time. These improved memory devices exhibit greater performance in retention and reduced fatigue in memory arrays.

Preparation and properties of (Pb,La)(Zr,Ti)O3 thin films by metalorganic chemical vapor deposition

Abstract: Lanthanum‐modified lead zirconate titanate (PLZT) thin films have been grown on Pt/MgO(100) and Pt/SiO2/Si substrates at 650 °C by metalorganic chemical vapor deposition using Pb(C2H5)4, La(DPM)3, Zr(DPM)4 and Ti(i − OC3H7)4 as the source materials. The properties of PLZT films were investigated as a function of the La content in a range of 0–15 at.% with a composition ratio of Zr/(Zr+Ti)<0.5. The films were of a single perovskite structure, and highly oriented to the c axis of the tetragonal phase on a Pt/MgO(100) substrate. The films were transformed from tetragonal to nearly cubic as the La content was increased. The films were colorless and transparent, and the surface morphology became smoother through an La addition. The relative dielectric constants increased as the La content was increased up to about 5 at.%. The remanent polarizations were 25–30 μC/cm2, and the coercive field decreased from 53 to 30 kV/cm as the La content was increased in the films having Zr/Ti=40/60.

Phase Homogeneity and Segregation in PZT Powders Prepared by Thermal Decomposition of Metal–EDTA Complexes Derived from Nitrate and Chloride Solutions

Abstract: Fine, homogeneous lead zirconate titanate (PZT) powders have been prepared by the thermal decompostion of metalorganic complexes derived from nitrate solutions using ethylenediaminetetraacetic acid (EDTA) as a complexing agent. It has been shown that nitrate ions accelerate the decomposition of the precursor and the crystallization of the PZT phase initiates at temperatures as low as 250°C. No intermediate phases, other than PbO, were found. The coexistence region of the rhombohedral and tetragonal phases in the sintered ceramic was found to be a little over 1 at.%. The chloride-EDTA precursor did not form the desired PZT phase, even after calcination at 1000°C. The segregation and loss of lead was observed for this material, due to the formation and evaporation of PbCl2. DTA/TGA, SEM, and XRD were employed to characterize the powders. The use of TEM with nanoprobe energy dispersive X-ray analysis (EDX), allowed the identification of the phase segregation in the chloride-EDTA derived powder. A possible reaction mechanism for this phase segregation is suggested.

Fabrication of piezoelectric ceramic/polymer composites by injection molding

Abstract: Ceramic injection molding has been shown to be a viable process for fabricating both PZT (lead zirconate titanate) ceramics and piezoelectric ceramic/polymer transducers. The electrical properties of injection-molded PZT ceramics are comparable with those of ceramics prepared by conventional powder pressing, with no evidence of deleterious effects from metallic contamination and molding equipment. By using ceramic injection molding to fabricate composite preforms and then laying up the preforms to form larger composite arrays, an approach has been demonstrated for net-shape manufacturing of piezoelectric composite transducers in large quantities. The authors review key features of the ceramic injection molding process, and describe the approach and methodology being used to fabricate the PZT ceramic/polymer composites. >

Metalorganic chemical vapor deposition of ferroelectric thin films

Abstract: A method to produce high quality doped and undoped lead zirconate titanate (PZT) thin films by metalorganic chemical vapor deposition is disclosed. The PZT thin films with the perovskite structure were deposited on sapphire disks, Pt/Ti/SiO2 /Si wafers, and RuOx /SiO2 /Si wafers by both hot-wall and cold-wall CVD reactors at deposition temperature as low as 550° C. and a reduced pressure 6 torr. The source materials include metalorganic precursors and oxidizing agent. The metalorganic precursors can be metal alkoxides, metal acetylacetonates, or metal β-diketonates. Preferably, the precursors are lead tetramethylheptadione for Pb component, zirconium tetramethylheptadione for Zr component, and titanium ethoxide for Ti component and the oxidizing agent is oxygen. The stoichiometry of the films can be easily controlled by varying the individual precursor temperature and/or the flow rate of the carrier gas. The Pb(Zr0.82 Ti0.18)O3 film produced by the present invention shows a spontaneous polarization of 23.3 μC/cm2, a remanent polarization of 12.3 μC/cm2, and coercive field of 64.5 kV/cm.

Thickness dependence of D.C. leakage current in lead zirconate-titanate (PZT) memories

Abstract: We have measured the voltage (field) dependence, the thickness dependence, and the temperature dependence of d.c. leakage currents in PbZr0.40Ti0.60O3. In agreement with our earlier results [Scott et al., J. Appl. Phys. 70, 382 (1991)], the voltage dependence is given by I(V) = AV + B(V - V 0)2, implying space-charge limited currents. In addition, in the present work we find that I(d) = C/d 3 at constant voltage, where d is the thickness and C is a constant dependent upon voltage and cross-sectional area. This inverse-cubic dependence of current confirms that the leakage is dominated by space charge effects.

Deposition of ferroelectric PZT thin films by planar multi-target sputtering

Abstract: A planar multi-target sputtering system was used to deposit ferroelectric lead zirconate titanate (PZT) films. At substrate temperatures of about 450°C “in-situ” deposition of single phase perovskite PZT was obtained. By investigation with SEM and TEM films exhibited a columnar structure with crystallites of about 200 nm in size. The permittivity of the films varied from 450-600. The films exhibited hysteresis loops, remanent polarization of 15-20 μC/cm2 and coercive field strength of 70-85 kV/cm.

Ferroelectric thin films in integrated microelectronic devices

Abstract: We present results on four integrated ferroelectric projects: 1) An integrated barium strontium titanate thin-film on GaAs MMIC (monolithic microwave integrated circuit) with dielectric constant of 450 and loss tangent of 10−3 at 2.2 GHz operation, done as a Symetrix/Matsushita Electronics Corp. joint development; 2) A low-density (1 Kb) ferroelectric RAM (random access memory) done with PZT (lead zirconate titanate) and other ferroelectrics on CMOS (complementary metal oxide semiconductor) Si, carried out as a joint development with Olympus Optical Co.; 3) A liquid-source CVD (chemical vapor deposition) machine and its deposition of strontium titanate and barium strontium titanate films of exceptionally low d.c. leakage current (1 nA/cm2 at 120 nm thickness and 3V operation) for DRAM (dynamic RAM) applications; and 4) performance parameters of a properietary material for RAM application which is totally fatigue-free up to at least 5 × 1011 cycles.

The Ratio of Rhombohedral and Tetragonal Phases on the Morphotropic Phase Boundary in Lead Zirconate Titanate

Abstract: A method is introduced to determine the statistical distribution of energetically degenerate but geometrically inequivalent states in a temperature induced phase transition in solids. The method has been employed to calculate the ratio of the rhombohedral and tetragonal phases in the Pb(ZrxTi1-x)O3 solid solution of the morphotropic phase boundary (MPB) composition. Our results indicate that the MPB determined by Jaffe, Cook and Jaffe [Piezoelectric Ceramics (Academic Press, London, 1971) p. 136] from structural measurements should be shifted to the rhombohedral side, which is more consistent with the MPB determined from dielectric measurements.

Anion‐assisted pulsed laser deposition of lead zirconate titanate films

Abstract: A modification of the conventional pulsed laser deposition technique is presented whereby a low energy (≤0.5 eV) electron emitting filament was placed over the substrate during deposition. Using this experimental arrangement, it was possible to deposit oriented films of the ferroelectric perovskite PbZr0.52Ti0.48O3 on 〈100〉 MgO substrates at 550 °C. When optimized in terms of emission current, the use of the filament caused a decrease by six orders of magnitude in the ratio of a nonferroelectric pyrochlore phase relative to the ferroelectric perovskite phase. The surface morphology concomitantly changed from porous to essentially smooth as the electron emission current was increased. The surface reaction of oxygen anions generated by electron attachment to oxygen molecules is believed to be responsible for these crystallographic and morphological changes.

High speed, nondestructive readout from thin‐film ferroelectric memory

Abstract: High-speed polarization-direction-dependent photoresponse from ferroelectric lead zirconate titanate (PbZr(0.53)Ti(0.47)O3) thin films sandwiched between conducting electrodes to form a memory capacitor is reported. Laser pulses with a full width at half maximum of around 10 ns at 532-nm wavelength are utilized to readout the photoresponse signal from individual polarized elements. Such readout is repeated over a million times, with no detectable degradation in the photoresponse or the remanent polarization suggesting its potential as a nondestructive readout (NDRO) of nonvolatile polarization state in thin-film ferroelectric memories. In principle both electronic as well as thermal mechanisms could be triggered by such photon exposure of ferroelectric thin films. A comparison of the photoresponse from capacitors with semitransparent and opaque top electrodes suggests that the observed NDRO signal is primarily due to thermally triggered mechanisms.

Bending Actuator Using Lead Zirconate Titanate Thin Film Fabricated by Hydrothermal Method

Abstract: Thin films of lead zirconate titanate (PZT) were fabricated by the hydrothermal method which consisted of two steps in the hydrothermal process: "nucleation" and "crystal growth" processes. The PZ nuclei were formed by the reaction at 140°C in a solution containing 4N potassium hydroxide. The growth rate of PZT crystals decreased at temperatures below and above 120°C. Bimorph-type bending actuators were made using as-deposited PZT films. The actuators showed large and visible electric-field-induced displacement even at driving voltage less than 10 V. From the displacement-voltage curve of an unimorph actuator and that of a heat-treated specimen, it may be concluded that the polar axes of PZT crystals had an orientation toward the substrate, giving rise to the piezoelectric effect without poling procedure.

Anisotropic titanate etch

Abstract: A titanate substrate (e.g. lead zirconate titanate 34) is immersed in a liquid ambient (e.g. 12 molar concentration hydrochloric acid 30) and illuminated with radiation (e.g. collimated visible/ultraviolet radiation 24) produced by a radiation source (e.g. a 200 Watt mercury xenon arc lamp 20). A window 26 which is substantially transparent to the collimated radiation 24 allows the radiated energy to reach the titanate substrate 34. An etch mask 32 may be positioned between the radiation source 20 and the substrate 34. The titanate substrate 34 and liquid ambient 30 are maintained at a nominal temperature (e.g. 25° C.). Without illumination, the titanate is not appreciably etched by the liquid ambient. Upon illumination the etch rate is substantially increased.

D.C. leakage currents in ferroelectric memories

Abstract: Experimental data on d.c. leakage currents in lead zirconate titanate thin films (210 nm) are presented. The data show a flat, ohmic response up to a thresh-hold of approximately 2.0 V, above which they satisfy a modified Childl's Law, with a perfectly quadratic dependence: I = aV2. This suggests that at 5 V operation the film behaves as a fully depleted device. The difficulty in distinguishing between Frenkel-Poole, Schottky emission, and true space-charge limited currents is briefly discussed.