Chemistry: electrical and wave energy – Processes and products – Coating – forming or etching by sputtering
Patent
1990-01-18
1991-12-31
Langel, Wayne A.
Chemistry: electrical and wave energy
Processes and products
Coating, forming or etching by sputtering
20419218, 20419222, 423593, 501134, C23C 1434, C01F 1700
Patent
active
050769014
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method of manufacturing perovskite lead scandium tantalate (PST) and more particularly, but not exclusively, to a method of manufacturing PST thin films.
The fabrication of ceramic derived thermal detectors often requires the production of very thin slices of material. This is traditionally achieved by difficult and time consuming lappina dn polishing techniques. In order to develop alternate routes to thin film ceramic, methods exploiting the recently developed emtal organic precursors of these ceramics have been extensively utilised. These techniques include the deposition of thin films from metal organic solutions and by metal organic chemical vapour deposition (MOCVD). Both these methods allow the controlled deposition of ceramic films with thicknesses less than 0.1 .mu.m and upwards.
These techniques have been successfully developed for material such as lead titanate but extension to lead scandium tantalate (PST) has been prevented by the inability to deposit the PST films with the desired 100% perovskite rystal structure. By depositing the lead, scandium and tantalum from a single metal organic solution only small amounts of the perovskite phase were obtained after firing.
An objective of the present invention is to provide an improved method of manufacturing perovskite lead scandium tantalate.
According to the present invention there is provided a method of manufacturing perovskite lead scandium tantalate comprising heating scandium oxide and tantalum oxide to form scandium tantalate and heating the scandium tantalate in the presence of lead.
In one embodiment a film of perovskite lead scandium tantalate is formed by first depositing layers of scandium oxide and tantalum oxide or a mixed oxide layer of scandium oxide and tantalum oxide, heating the layers or the mixed layer to form a layer of scandium tantalate and heating the scandium tantalate layer in the presence of lead.
Preferably the scandium tantalate is heated in the presence of lead oxide.
In one embodiment, perovskite PbSc.sub.1/2 Ta.sub.1/2 O.sub.3 (PST) films are manufactured by first depositing layers of Sc.sub.2 O.sub.3. Ta.sub.2 O.sub.5 or a mixed oxide layer of Sc.sub.2 O.sub.3 and Ta.sub.2 O.sub.5, heating to form ScTaO.sub.4 and then heating the ScTaO.sub.4 layer in the presence of lead. In one embodiment the layers of scandium and tantalum oxides or the mixed oxide layer of scandium and tantalum oxides are heated to temperatures above 1000.degree. C., and preferably to temperaturse between 1000.degree. C. and 1400.degree. C.
A mixed layer of Sc.sub.2 O.sub.3 and Ta.sub.2 O.sub.5 may be deposited from solution, starting with scandium (III) acetylacetonate (Scacac).sub.3 and tantalum ethoxide Ta(OEt).sub.5 as precursors in methoxyethanol solution, consisting of taking the Sc(acac).sub.3 into solution at for example 120.degree. C. cooling to 90.degree. C. adding Ta(OEt).sub.5, complexing at 120.degree. C., cooling and spinning the resulting solution onto the selected substrate and drying the film at 150.degree. C. Thick layers of mxied scandium and tantalum oxides are formed by repeating the process.
Alternatively mixed layers of scandium and tantalum oxides are formed by using metal organic chemical vapour deposition (MOCVD), consisting of passing volatile metal organic compounds of scandium and tantalum over a heated substrate at reduced pressure where they decompose to give the oxides. The metal organic compounds are advantageously scandium (FOD).sub.3 as described later and tantalum ethoxide respectively.
Typically the perovskite PST layers may be formed by reacting ScTaO.sub.4 layers in the presence of lead oxide at temperature for example of between 850.degree. C. and 1300.degree. C. The lead oxide may in one embodiment be in the form of a vapour produced by lead zirconate or a mixture of lead zirconate and lead oxide.
Alternatively the lead oxide is first deposited as a layer onto the surface of the ScTaO.sub.4 layer; for example by spinning onto the ScTaO.sub.4 a dehydrated solution of lead
REFERENCES:
patent: 4853199 (1989-08-01), Inoue et al.
Considine Laurence
Goosey Martin T.
Patel Anil
Whatmore Roger W.
GEC--Marconi Limited
Langel Wayne A.
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