A. Patel

Ferroelectric materials for thermal ir sensors state-of-the-art and perspectives

Abstract The current state of the art with respect to the development of materials for use in pyroelectric infra-red detectors is reviewed and their relevant properties are compared using the appropriate materials figures-of-merit with reference to the physics of their operation. The specific application of these materials to uncooled thermal imaging arrays is discussed and it is shown that the best materials for use in this application are those with high permittivities and high pyroelectric coefficients. The concept of using ferroelectrics in the region of Tc as dielectric bolometers is introduced and it is shown that lead scandium tantalate (PST) is one of the most promising materials for use in this mode. Finally, the technologies for direct deposition of the materials as thin films are introduced and compared and the results of using sol-gel technology for depositing PST thin films are presented.

Microstructural characterization of sol–gel lead–zirconate–titanate thin films

The techniques of x-ray diffraction, x-ray photoelectron spectroscopy (XPS), Auger analysis, and transmission and scanning transmission electron microscopy (TEM) have been applied to the analysis of thin films of Pb(Zr0.30Ti0.70)O3 (PZT30/70) deposited at low temperatures (510u2009°C) by a sol–gel process onto Pt/Ti electrodes on SiO2/Si 100 substrates. It is found that the platinum film is highly oriented with the [111] axis perpendicular to the substrate plane. The ferroelectric film tends to crystallize epitaxially upon this as columnar crystals. There are indications from the TEM of the existence of a second metallic phase at the interface between the platinum and the PZT30/70 film, which may be associated with its nucleation. The TEM shows the boundaries between the individual sol–gel layers, although the growing crystallites of the PZT30/70 propagate through these boundaries unhindered. The XPS and Auger analyses have shown that Pb penetrates through the Pt layer to the underlying Ti layer, even at the ...

TfP258. Physicochemical properties of SOL-GEL derived lead scandium tantalate Pb(Sc0.5Ta0.5)O3 thin films

Abstract Thin films of lead scandium tantalate Pb(Sc0.5Ta0.5)03 (PST) have been prepared by a novel sol-gel process. The process involves two deposition steps. In the first, layers of ScTaO4 are deposited by spin coating a solution of metallorganic compounds of scandium and tantalum. A film of lead oxide is deposited intermittently onto the surface using a solution of lead acetate, and the process repeated to obtain thicker films. After firing, the composite film, a transparent film of PST is obtained. The crystallographic and morphological properties of the films have been analysed by X-ray diffraction and SEM and elemental analyses determined using EPMA. The films’ electrical properties have been measured against field and temperature, showing a strong induced pyroelectric response (3. 8 × 10−3Cm−2K−1), peak permittivities of 4500 and low loss. A high material figure-of-merit (11 × 10−5Pa−1/2) was obtained. Results are presented which illustrate the relationships between the properties and the observed ...

Determination of Particle Size and Shape during the Hydrolysis of Pb(Zr0.3Ti0.7)O3 Precursor Solutions

The formation and growth of polymeric particles during the hydrolysis and condensation of PbZr0.3Ti0.7 O3 (PZT 30/70) sol-gel precursor solutions have been investigated by using photon correlation spectroscopy (PCS), small angle X-ray scattering (SAXS) and by measuring their rheological properties. The measurements showed that the growth of the particles in the transition of PZT sol to gel followed a simple polymerisation process. Solution A (containing ‘by-products’) and Solution B (‘by-products’ removed) displayed a similar plot of logarithmic viscosity against logarithmic time, indicating that the particles in both solutions have similar structures after hydrolysis. The changes in viscosity and particle size with time were described by single logarithmic growth models. However, the increasing rate of logarithmic particle size in Solution B is higher than that in Solution A. A model for the form of the aggregates is discussed which is applicable to PZT organometal-particle aggregation process in systems with acetic acid as a modifier.

PyI11: Pyroelectric properties of thin film lead scandium tantalate

Abstract Electrical measurements on thin film ferroelectric lead scandium tantalate, deposited from solution, are described. It has good pyroelectric properties, approaching those of the bulk ceramic material. Its potential for thermal imaging applications is discussed. A theoretical specific detectivity of 4 × 108cmHz1/2W−1 has been calculated using measured film properties in a simple detector array structure.

Preparation and properties of PbTiO/sub 3/ and Pb(Sc/sub 0.5/Ta/sub 0.5/)O/sub 3/ thin films by sol-gel processing

Crack-free and dense PbTiO/sub 3/ films 1-2 mu m thick were prepared by spinning a sol-gel derived solution onto an appropriate substrate, and firing and annealing the film at temperatures of 750-800 degrees C. The electrical properties of the films were studied as a function of temperature, frequency, and DC bias. Also, crack-free films of Pb(Sc/sub 0.5/Ta/sub 0.5/)O/sub 3/ with an average grain size of 0.4 mu m were prepared using a novel two-stage process. Films 4 mu m thick had moderately high relative permittivities, low dissipation factors, and high resistivity.<<ETX>>

Thin Ferroelectric Films for Thermal Detector Applications

Abstract The deposition of thin films of lead scandium tantalate (Pb(Sc1/2Ta1/2O3) have been investigated by two processing routes. In the first, progress is reviewed for chemical vapour deposition in a purpose built low pressure reactor, utilising suitable modified proprietary precursors. Deposition has been studied over the temperature range 400–800°C and, in general, amorphous films result which convert to crystalline perovskites on subsequent annealing. However, inclusion of hydroxy compounds in the vapour train catalyses the crystallisation process and enhances the growth rate at above 600°C. It was found that the best thin films, in terms of density and morphology, are formed at low deposition rates 1–2μm/hr. The perovskite phase is obtained if the gas phase composition is controlled throughout growth. The choice of precursors, gas compositions and growth conditions will be described. In the second process, lead scandium tantalate thin films (ue4211μm) were deposited using a modified sol-gel solution ro...

Ferroelectric ceramics and thin films for uncooled thermal imaging arrays

The pyroelectric effect in ferroelectric materials has long been used for the detection and imaging of long wavelength infra-red radiation. Lead scandium tantalate (PST) has been shown to have exceptionally good pyroelectric figures of merit, especially for small detectors of the type involved in the large arrays needed for uncooled solid state thermal imaging. This paper will review the properties of PST in relation to those of other materials which have been considered for use in this role and discuss how the inclusion of dopants can be used to modify the properties of the material in a way which would be beneficial to certain modes of detector operation, particularly with respect to the elimination of the requirement of cooling. Single element detectors and linear and two dimensional arrays have been made using PST. Their properties are compared with those of similar devices made using conventional pyroelectric ceramics. Ferroelectric thin films can now be made using sol-gel techniques whose figure-of-merit are comparable with those of bulk ceramic materials and the properties of these will be reviewed in relation to those of the ceramics discussed above and their potential for device applications discussed.

Pyroelectric and electro-optic properties of sol-gel and dual ion beam sputtered PLZT thin films

The deposition of ferroelectric films using sol-gel and dual ion beam sputtering (DIBS) has been demonstrated. In the DIBS process, the presence of active oxygen has been found to be essential to the formation of perovskite PLZT (La-doped lead zirconate titanate) films. Electrooptic (EO) and pyroelectric effects have been observed in these films. A large quadratic EO efficient of 2.1*10/sup -16/ m/sup 2//V/sup 2/ was observed in reflection mode for PLZT (28/0/100), but this could not be repeated in a transmission mode, presumably because birefringence and thickness changes work in opposite senses. Peak pyroelectric coefficients of 400 mu mC/m/sup 2/K have been observed for PLZT (0/0/100) and (7/0/100) films. Sol-gel has produced PLZT (0/50/50) and (0/30/70) films with similar properties and has shown potential for film formation at temperatures as low as 450 degrees C. The results reported here are encouraging with respect to the goal of fully integrating uncooled infrared-detector elements on silicon readout circuitry.<<ETX>>

Preparation of electroceramics from metal organic precursors

Abstract This paper details the use of metal-organic compounds to prepare piezoelectric and pyroelectric ceramics. Formulations investigated include lead titanate, lead zirconate titanate and a proprietary uranium doped lead zirconate titanate, lead iron niobate pyroelectric ceramic. The principal ceramics with improved properties are described. Results of microstructural and X-ray analysis together with dielectric characterisation of the materials are presented and comparisons made with conventionally prepared material.