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WO1982003876A1 - Materiaux ceramiques de bioxyde de zirconium et d'hafnium partiellement stabilises a monocristaux - Google Patents

Materiaux ceramiques de bioxyde de zirconium et d'hafnium partiellement stabilises a monocristaux Download PDF

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Publication number
WO1982003876A1
WO1982003876A1 PCT/US1982/000557 US8200557W WO8203876A1 WO 1982003876 A1 WO1982003876 A1 WO 1982003876A1 US 8200557 W US8200557 W US 8200557W WO 8203876 A1 WO8203876 A1 WO 8203876A1
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WIPO (PCT)
Prior art keywords
dioxide
ceramic material
stabilizing agent
partially stabilized
zirconium dioxide
Prior art date
Application number
PCT/US1982/000557
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English (en)
Inventor
Roy W Rice
Joseph F Wenckus
Wilson P Menashi
Original Assignee
Roy W Rice
Joseph F Wenckus
Wilson P Menashi
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Roy W Rice, Joseph F Wenckus, Wilson P Menashi filed Critical Roy W Rice
Publication of WO1982003876A1 publication Critical patent/WO1982003876A1/fr

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    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B11/00—Single-crystal growth by normal freezing or freezing under temperature gradient, e.g. Bridgman-Stockbarger method
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
    • C30B29/10—Inorganic compounds or compositions
    • C30B29/16—Oxides

Definitions

  • This invention is in the field of ceramics, crystallography and chemistry.
  • Zirconium is an element with an atomic number of 40, an atomic weight of 91.22, and a valence 10 of 4.
  • Hafnium (Hf) has an atomic number of 72, an atomic weight of 178.49, and a valence of 4.
  • the pre ⁇ dominant oxidized forms are commonly ' referred to as zirconia (ZrO ⁇ ) and hafnia (HfO_) .
  • Zirconia and hafnia ea h have three principle 15 crystal structures: cubic, tetragonal, and monoclinic. As zirconia is cooled after being heated to its molten state in the absence of stabilizing agents, it progresses through all three crystal structures. In the absence of stabilizing agents, the cubic 20 structure is the most stable, and the monoclinic structure is the least stable. At low temperatures, these relative stabilities are reversed. Therefore, during cooling, zirconia normally progresses from the cubic structure, to the tetragonal structure, 25 to the monoclinic structure.
  • Cubic zirconia can be stabilized by the addi ⁇ tion of sufficient quantities of one or more sta ⁇ bilizing agents.
  • U. S. patent 4,153,469 discloses that 10 to 30. 30 mole percent of yttrium oxide (Y clove0-,, commonly called yttria) stabilizes zirconia in the cubic crystal configuration. Such crystals are transparent and have a high optical quality, and are used as
  • PSZ Partially stabilized zirconia
  • Partially stabilized is a functional term. if less than an ascertainable amount of stabilizing agent is added to molten zirconia, then not all of the zirconia will retain the cubic crystal configu ⁇ ration when it is cooled to room temperature. If this is the case, several things can happen. It is possible for localized areas of cubic, tetragonal and monoclinic crystals to be interspersed in a PSZ crystal. One possible way this can occur is for tetragonal particles to exist in a matrix of cubic zirconia. See D. L. Porter et al., "Mechan- isms of Toughening Partially Stabilized Zirconia
  • OMP terms of pounds per square inch (psi) or pascals (Pa) OMP terms of pounds per square inch (psi) or pascals (Pa) .
  • a pascal is equal to 1 newton of force applied to 1 square meter;
  • a megapascal (MPa) is equal to 1 million pascals.
  • MPa is equal to approximately 145 psi.
  • Tensile strength is often approxi ⁇ mated by measuring flexure strength. In ⁇ stead of pulling a specimen apart along one axis (which would determine tensile strength) , a specimen is bent until it breaks, and the maximum tensile force (which occurs along one edge of the specimen) is calculated. Flexure strength is measured in psi or MPa. It tends to be somewhat higher than tensile strength, since a flaw in the interior of a speci ⁇ men that might cause a tensile break might not cause a flexure break.
  • Fracture toughness usually ex ⁇ pressed as K-_
  • Fracture toughness is usually measured by creating a flaw of a known size in the specimen being studied, then breaking the specimen under controlled loading conditions using, for example, a double cantilever beam (DCB) technique. The force required to break the specimen is then divided by the cross-sectional area of the break times the square root of the length of the flaw.
  • DCB double cantilever beam
  • the Applicants have invented a method of cre ⁇ ating such single crystals that are large enough 30 for ceramic uses.
  • Zirconia and hafnia are partially stabilized by adding a predetermined quantity of stabilizing agent to a predetermined quantity of zir ⁇ conia or hafnia. This normally is accomplished by mixing the stabilizing agent with the zirconia or haf ⁇ nia while both substances comprise fine powders at room temperature.
  • the mixture is then heated to a melting temperature (normally in excess of 2500°C) .
  • This can be accomplished by inductive high-frequency radio waves.
  • the powder is placed in a water-cooled vessel prior to heating.
  • the cooling surfaces of the vessel prevent the powder that touches the cooling surfaces from becoming molten. This forms a shell (often called a skull) of sintered material between the cooling surfaces and the molten zirconia or hafnia; this avoids problems that can arise when extremely hot molten substances " come in contact with solid surfaces.
  • the molten mixture is allowed to cool slowly, to promote the formation of a regular crystalline. structure. This can be accomplished by slowly lower ⁇ ing the vessel out of the heating field, and reduc ⁇ ing or eliminating the radio frequency power at an appropriate time.
  • the resulting material comprises a large (from approximately 3 inches to over 1 foot in diameter) block of crystalline material surrounded by a sintered shell. The shell is removed by mechani ⁇ cal means.
  • the resultant crystalline body typically comprises several relatively small (largest dimension approximately 1/4 inch to 1 inch) crystals near the bottom of the block of material, interspersed with larger crystals that may exceed 1 inch in diameter and several inches in length. Although these crystals do not adhere tightly to each other, each crystal has a single consistent composition of tetragonal and possibly monoclinic crystallites within a matrix of cubic crystalline structure. Each such crystal 5 can be referred to as a single grain.
  • crystals may be machine d into desirable configurations using diamond-edged cutting instru ⁇ ments and other conventional techniques.
  • numerous crystals may be plastic-deformed into 10 desirable configurations by press-forging at elevated temperatures, although problems involving oxygen loss may require special techniques.
  • Single-crystal PSZ has -ionic conductivity and electromagnetic transmissibility properties that are 15 superior to polycrystalline PSZ. These properties al ⁇ low for improvements in the use of PSZ for purposes that involve ionic conductivity or electromagnetic transmissibility.
  • Figure 1 is a cross section of an apparatus used to heat zirconia or hafnia mixed with a stabilizing agent to the molten state.
  • Figure 2 is a cross section of zirconia or hafnia mixture being withdrawn from the heating zone.
  • Figure 3 is a cross section of zirconia or hafnia mixture after it has cooled into a crystalline structure.
  • Figure 4 is a graph that indicates the flexure strength and fracture toughness of several partially stabilized zirconia crystals.
  • Figure 5 is a graph that indicates the flexure strength of various ceramic materials as a function of temperature.
  • 450 grams of Y 2 °3 (yttria) powder were dry-mixed with 8,550 grams of ZrO (zirconia) powder, to give 5 , a mixture containing 5 % yttria by weight.
  • the powders were mixed by placing both in a polyethylene jar, and roll-milling for several hours. Alterna ⁇ tively, V-blending or other conventional mixing means may be used.
  • the mixture was then loaded into a 10 6 inch diameter skull-melting furnace, which has a standard melt capacity of 9 kilograms of zirconia.
  • the powder rests upon a water-cooled plate, and is surrounded by vertical copper tubes which contain circulating cooled water. There is no lid on this 15 furnace, so the top of the powder is exposed to the air.
  • the loaded furnace was then placed in the middle of. a radio frequency generating coil, operating at up to 50 kilowatts of output at 2.5 to 3.5 megahertz.
  • the skull container is first charged with 3,000 20 grams of mixed powder, and a 30 gram cluster of zir ⁇ conium metal. Since the mixed powder at room tempera ⁇ ture does not absorb the energy of the high-frequency radio waves, the zirconium metal is added to begin the heating process. The metal chips heat rapidly 25 and cause the surrounding powder to be heated to a temperature at which they begin to absorb the high- frequency waves directly. After approximately 10 minutes, the interior of the 3030 gram initial charge is molten. It is contained within a sintered shell 30 of unmelted powder, which is being cooled by the ⁇ water in the copper tubes. This sintered shell (often called a skull) prevents the molten zirconia from coming into direct contact with the copper tubes.
  • the remaining 6 kilograms of powder mixture are 35 added to the skull container over a period of ap ⁇ proximately one hour.
  • the radio frequency input power is slowly increased to approximately 35 kilowatts.
  • the molten charge is allowed to remain stationary for a period, while convection currents mix the zirconia and yttria thoroughly.
  • the skull container is then mechanically lowered at a fixed rate of about 1.1 centimeter per hour. This allows for the bottom portion of the skull container to leave the heating zone and begin the cooling process, allowing crystals to begin forming near the bottom of the skull.
  • the skull is rotated with a bi- direction oscillatory motion through an angle of about 45 degrees at a frequency of about 10 times per minute.
  • the radio frequency power is shut off, and the crystals are allowed to cool to room tempera ⁇ ture before removal.
  • the cooled crystals are sub ⁇ sequently removed from the skull container.
  • the sintered shell surrounding the crystals is removed, and the crystal grains are separated carefully.
  • Several grains were subsequently analyzed to deter ⁇ mine their flexure strength, fracture toughness, and other properties, as described in Example 5-7. This process is further described by reference to Figures 1 through 3.
  • powder mixture 2 is placed in skull container 4.
  • the loaded skull container is then placed within circular high frequency induction heating coil 6. Cooling water enters water inlet 8 r and circulates within vertical tubes 10 and container base 12, before exiting through water outlet 14.
  • the interior 16 of the powder mixture becomes molten. This molten region is surrounded by sintered shell 18, which is prevented from melting because it is in contact with water-cooled tubes 10 and base 12.
  • An un- 5 melted porous crust 20 typically forms above the surface of the melt.
  • Figure 1 indicates the positioning of the skull container 4 and the mixed powder charge 2 within the region that is heated by induction coils 6. In 10 this position, all of the powder will become molten except for sintered shell 18 and crust 20.
  • Figure 2 indicates that the skull container 4 is being slowly lowered by mechanical means. The bottom of molten region 16 leaves the heated region and begins to 15 form crystals 24 upon the base of the centered skull 18. These crystals initially comprise the cubic crystalline structure, which is the most stable crys ⁇ talline form at temperatures near the melting point. However, as these crystals cool further, a dispersion 20 of numerous minute crystallites, in the form of tetragonal and possibly monoclinic crystallites, forms within the matrix of the partially stabilized cubic zirconia.
  • FIG. 3 indicates that skull container 4 has 25 been mechanically lowered by mechanical means 26 until crystals 24 have left the region heated by induction coils 6.
  • the crystal region 24 is comprised of numerous individual grains, including grains 28, 30, 32, 34, and 36. Within each of these grains, 30 the tetragonal crystallites are arranged on a regular
  • Each of these grains exhibits extremely high flexure strength and fracture toughness. However, the boundary or interface between any two grains is relatively weak, and each grain may be separated easily from the other grains.
  • Table 1 and Figures 4 and 5 contain data com ⁇ paring the flexure strength and fracture toughness of the single-crystal PSZ with several other ceramic materials.
  • PSZ 1027 is a commercially available form of zirconia, partially stabilized with about 3.5 weight percent MgO, with a relatively large grain structure.
  • Zyttrite is a form of zirconia, fully stabilized with from 12 to 20 weight percent of yttria, with an intermediate grain size, that is used as a reference standard. Both are polycrystal- line substances, formed by conventional pressing and sintering techniques.
  • Zirconia (ZrOfact) powder was obtained from Magnesium Elektron, with a purity of 99%. It has an average particle size of approximately 10-16 microns, and contained approximately 2% Hf0 2 . Yttria ( ⁇ 2 °3 ⁇ powder was obtained from Megon (purity 99.99%). It had an average particle size of approximately 10- 16 microns. Carefully weighed quantities of each powder were mixed by placing both in a polyethylene jar, and rolling the jar on mixing rollers for approximately 12 hours. Approximately 3,000 grams of the mixed powder was placed in a skull container. The skull container comprised a 6 inch diameter water-cooled copper base plate, surrounded by vertical copper tubes at the perimeter of the base plate. Each copper tube contained an inner tube. Cooling water was circulated up through the annulus of each tube, and down through the interior tube.
  • the loaded skull container was then placed within a C-rcular induction heating coil.
  • the heating coil was powered by a 50 kilowatt radio frequency gener ⁇ ator, v/hich operated at 2.5 to 3.5 megahertz.
  • Example 2 ' Heating the Zirconia Mixture
  • the generator power When the generator power is turned on, the radio waves which are concentrated within the coil excite the zirconia and yttria molecules causing them to become heated.
  • about 30 grams of zirconium metal (Ventron sponge, purity 99.5%) was placed in a cluster on the surface of the powder.
  • the metal chips heat rapidly and cause the surrounding powder to be preheated to a temperature high enough for direct induction heating.
  • An expanding zone of powder becomes molten, until the entire powder charge becomes molten except for a sintered skull surrounding the molten region. This skull is pre ⁇
  • the remainder of the mixed powder is then added to the skull container in small increments over a period of approximately one hour.
  • the 20 heating input power is also increased.
  • the applied heating power is approximately 35 kilowatts.
  • the heating continues for a period of approximately 25 ⁇ o to 20 minutes to allow the molten substance to become thoroughly mixed by convection currents.
  • Example 3 Controlled Cooling and Crystal Formation After the molten mixture described in Example 2 is allowed to stand for an appropriate time, the 30 skull container is mechanically lowered at a fixed rate of 1.1 centimeter per hour. Since the induction heating occurs only within a certain region, this removes the bottom of the skull out of the heated area, allowing the molten mixture on the bottom to
  • the skull is also rotated about its axis with a bi-directional oscil ⁇ latory motion through an angle of 45° at a fre- quency of 10 times per minute.
  • the partially stabilized zir ⁇ conia adopts a cubic crystalline configuration, which is the most stable crystalline configuration at temperatures near the melting point.
  • numerous crystallites comprising ⁇ tetragonal and possibly monoclinic crystallites, form within the matrix of cubic zirconia.
  • the heating power input level, frequency and coupling efficiency are constantly monitored. When the skull container is lowered until the molten/crystalline region is no longer in the region of heating, the heating input power is shut off and the charge is allowed to cool to room temperature before removal.
  • Example 3 The crystals that were formed as ⁇ escribed in Example 3 were allowed to cool to re temperature. The entire charge was then removed from the skull container by raising the base plate in relation to the vertical cooling tubes. The sintered shell was removed from the crystals. The remaining crystal ⁇ line material was in a configuration indicated- y grains 28 through 36 in Figure 3. Each grain com ⁇ prised a matrix of cubic zirconia interspersed with minute tetragonal and possibly monoclinic crystallites that were in a consistent pattern throughout that grain.
  • Example 5 Crystallographic Analysis Crystals with 12 to 20 per cent by weight of yttria were clear or transparent. This indicated that such crystals were fully stabilized in the c ⁇ bic crystalline configuration. Crystals with 8% by weight of yttria were cloudy, and crystals with 4% by weight yttria were opaque white. This indicated that the number of minute tetragonal and possibly monoclinic crystallites increases with decreasing yttria content. Examination under light microscope, and x-ray diffrac ⁇ tion analysis confirmed this correlation. Laue back reflection analysis typically showed a [110] orienta ⁇ tion along the length of the columnar crystals for all crystal compositions. Crystals with less than 8% by weight yttria contains an additional and distinct stereographic projection with a [100] orientation, indicating a greater percentage of tetragonal crystal ⁇ lites with a regular orientation within the cubic matrix.
  • Example 6 Determination of Fracture Toughness Fracture toughness, commonly expressed as K-. , was determined by two techniques: indentation using a pyramidal diamond (described by A. G. Evans et al, "Fracture Toughness Determinations by Indenta ⁇ tion,” J. Amer. Ceramics Soc. 59, Nos.7-8, pp 371-372 (1976) ) ; and double cantilevered beam analysis (S. W. Freiman et al, "Crack Propagation Studies in Brittle Materials," J. Mat. Sci. _8_, No. 11, pp. 1527-1533 (1973) .
  • Typical specimen dimensions for the DCB analysis were 1x5x12 mm with a center groove 0.3
  • 3-point flexure tests (0.9 centimeter span; 1 mm/min crosshead speed) were conducted on bars that were 0.22 by 0.23 cm in crossection, cut parallel with the crystal length and ground lengthwise.
  • the -tensile strength of the cubic zirconia was approx ⁇ imately 210 MPa for the 20 and 12 per cent by weight yttria crystals.
  • the tensile strength of 8% by weight crystals increased to approximately 520 MPa, and the tensile strength of 6 and 4 percent by weight yttria crystals increased to approximately 1,000 MPa.
  • the coefficients of variation for all measurements were about 10%. Additional data are contained in . Table 1 and Figures 4 and 5.
  • the invention described herein has industrial applicability in the manufacture and use of ceramic materials with superior tensile strength and fracture 5 toughness.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Inorganic Chemistry (AREA)
  • Compositions Of Oxide Ceramics (AREA)
  • Inorganic Compounds Of Heavy Metals (AREA)

Abstract

Procede de fabrication d'un monocristal de bioxyde de zirconium ou de bioxyde d'hafnium partiellement stabilise en melangeant du bioxyde de zirconium ou du bioxyde d'hafnium en poudre avec 2 a 7 moles% d'un agent de stabilisation, tel qu'un oxyde soit d'un metal de transition soit d'un element de terre rare, en chauffant ce melange jusqu'a son etat de fusion et en refroidissant le melange en le retirant de la zone de chauffage a une vitesse de 2-30mm/heure. Les cristaux obtenus comprennent une matrice de materiau cubique cristallin et de nombreux materiaux cristallins minuscules tetragones et eventuellement monocliniques. De tels cristaux peuvent etre produits avec une resistance a la flexion d'environ 200.000 psi et une resistance a la cassure d'environ 7,85 Ksc.
PCT/US1982/000557 1981-04-29 1982-04-29 Materiaux ceramiques de bioxyde de zirconium et d'hafnium partiellement stabilises a monocristaux WO1982003876A1 (fr)

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US25879181A 1981-04-29 1981-04-29
US258791810429 1981-04-29

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Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4851293A (en) * 1987-04-22 1989-07-25 Tioxide Group Plc Stabilized metallic oxides
US4985379A (en) * 1985-10-01 1991-01-15 Egerton Terence A Stabilized metallic oxides
US5460770A (en) * 1989-06-15 1995-10-24 Tioxide Group Plc Method for protecting shaped articles from attack by water
WO2002081073A1 (fr) * 2001-04-03 2002-10-17 Paul Scherrer Institut Oxyde de zirconium stabilise pour fenetres d'observation
US6783855B1 (en) 1998-12-17 2004-08-31 Isis Innovation Limited Rare-earth-activated phosphors
US6924040B2 (en) * 1996-12-12 2005-08-02 United Technologies Corporation Thermal barrier coating systems and materials
EP1372160B1 (fr) * 2002-06-10 2008-05-28 Interuniversitair Microelektronica Centrum (IMEC) Transistors et condensateurs mémoires comprenant une composition de HfO2 avec constante diélectrique augmentée
EP2316805A1 (fr) * 2009-10-29 2011-05-04 Golsen Limited Un matériau basé sur l'oxyde de zirconium

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1373888A (en) * 1972-12-15 1974-11-13 Fizichesky I Im P N Lebedeva A Monocrystals based on stabilized zirconium or hafnium dioxide and method of production thereof
US4049384A (en) * 1975-04-14 1977-09-20 Arthur D. Little, Inc. Cold crucible system
GB1491362A (en) * 1975-06-11 1977-11-09 Fiz I Im P N Lebedeva An Sssr Single crystals based on stabilised zirconia or hafnia
US4153469A (en) * 1977-03-29 1979-05-08 Alexandrov Vladimir I Monocrystals based on stabilized zirconium or hafnium dioxide and method of production thereof

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1373888A (en) * 1972-12-15 1974-11-13 Fizichesky I Im P N Lebedeva A Monocrystals based on stabilized zirconium or hafnium dioxide and method of production thereof
US4049384A (en) * 1975-04-14 1977-09-20 Arthur D. Little, Inc. Cold crucible system
GB1491362A (en) * 1975-06-11 1977-11-09 Fiz I Im P N Lebedeva An Sssr Single crystals based on stabilised zirconia or hafnia
US4153469A (en) * 1977-03-29 1979-05-08 Alexandrov Vladimir I Monocrystals based on stabilized zirconium or hafnium dioxide and method of production thereof
US4153469B1 (fr) * 1977-03-29 1984-06-05

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
"Cubic Zirconia", The Lapidary Journal, volume 35, pages 1194-1200, 1210-1214, September 1981, NASSAU. *
"Mechanisms of Toughening Partially Stabilized Zirconia", Journal of the American Ceramic Society, published March 1977, volume 60, PORTER et al. *

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4985379A (en) * 1985-10-01 1991-01-15 Egerton Terence A Stabilized metallic oxides
US4851293A (en) * 1987-04-22 1989-07-25 Tioxide Group Plc Stabilized metallic oxides
US5460770A (en) * 1989-06-15 1995-10-24 Tioxide Group Plc Method for protecting shaped articles from attack by water
US6924040B2 (en) * 1996-12-12 2005-08-02 United Technologies Corporation Thermal barrier coating systems and materials
US6783855B1 (en) 1998-12-17 2004-08-31 Isis Innovation Limited Rare-earth-activated phosphors
WO2002081073A1 (fr) * 2001-04-03 2002-10-17 Paul Scherrer Institut Oxyde de zirconium stabilise pour fenetres d'observation
EP1372160B1 (fr) * 2002-06-10 2008-05-28 Interuniversitair Microelektronica Centrum (IMEC) Transistors et condensateurs mémoires comprenant une composition de HfO2 avec constante diélectrique augmentée
EP2316805A1 (fr) * 2009-10-29 2011-05-04 Golsen Limited Un matériau basé sur l'oxyde de zirconium

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