Method and setup for growing bulk single crystals

Abstract

The invention relates to a method for growing a bulk single crystal, wherein the method comprises the steps of inserting a starting material into a crucible, melting the starting material in the crucible by heating the starting material, arranging a thermal insulation lid at a distance above a melt surface of said melt such that at least a central part of the melt surface is covered by the lid, and growing the bulk single crystal from the melt by controllably cooling the melt with the thermal insulation lid arranged above the melt surface.

Claims

1. A single crystalline Ba.sub.2ScNbO.sub.6 substrate having a diameter in lateral extent that is equal to or larger than 6 mm.

2. A (multi)layer structure comprising the single crystalline Ba.sub.2ScNbO.sub.6 substrate of claim 1 and one or more crystal layers grown on said Ba.sub.2ScNbO.sub.6 substrate.

3. The (multi)layer structure of claim 2, wherein the one or more crystal layers comprise a perovskite, preferably at least one of the perovskites BaSnO.sub.3, LaInO.sub.3, BiScO.sub.3, PbZrO.sub.3, SrZrO.sub.3, SrHfO.sub.3, PrInO.sub.3, LaScO.sub.3, SrSnO.sub.3, BaHfO.sub.3, LaLuO.sub.3, CeLuO.sub.3, PrLuO.sub.3, NdLuO.sub.3, CeYbO.sub.3, PrYbO.sub.3, or BaZrO.sub.3, and/or the one or more crystal layers comprise at least one of the perovskite solid solutions PbZr.sub.1-xTi.sub.xO.sub.3 (PZT), PbCa.sub.1-xTi.sub.xO.sub.3 (PCT), or Ba.sub.1-xSr.sub.xSnO.sub.3, wherein x is a number between 0 and 1, and/or the one or more crystal layers comprise at least one of the relaxor-ferroelectric solid solutions PbMg.sub.1/3Nb.sub.1/2O.sub.3—PbTiO.sub.3 (PMN-PT), PbZn.sub.1/3Nb.sub.2/3O.sub.3—PbTiO.sub.3 (PZN-PT), and PbIn.sub.1/2Nb.sub.1/2O.sub.3—PbMg.sub.1/3Nb.sub.2/3O.sub.3—PbTiO.sub.3 (PIN-PMN-PT).

4. The (multi)layer structure of claim 2, wherein one of the one or more crystal layers is a BaSnO.sub.3 crystal layer that is grown directly on the Ba.sub.2ScNbO.sub.6 substrate, the BaSnO.sub.3 crystal layer having an average threading dislocation density of less than 10.sup.8 dislocations per cm.sup.2 and/or an electron mobility larger than 190 cm.sup.2V.sup.−1s.sup.−1 and/or a full width at half maximum (FWHM) of its rocking curve that is less than or equal to 23 arcsec (0.006°).

5. An electronic device comprising a (multi)layer structure according to claim 2.

6. A method for fabricating a Ba.sub.2ScNbO.sub.6 substrate according to claim 1 from a bulk Ba.sub.2ScNbO.sub.6 single crystal having a cross-sectional area that is equal to or larger than 6 mm×6 mm, wherein the method comprises the steps of inserting a starting material comprising at least Ba, Sc, Nb and O into a crucible, melting the starting material in the crucible by heating the starting material, arranging a thermal insulation lid at a distance above a melt surface of said melt such that at least a central part of the melt surface is covered by the lid, and growing the bulk Ba.sub.2ScNbO.sub.6 single crystal from the melt by controllably cooling the melt with the thermal insulation lid arranged above the melt surface such that the bulk Ba.sub.2ScNbO.sub.6 single crystal has a cross-sectional area that is equal to or larger than 6 mm×6 mm.

7. The method according to claim 6, wherein the cooling of the melt is passively controlled by reducing heat provided by a heating element over a predefined period of time and/or actively controlled.

8. The method according to claim 6, wherein the distance at which the thermal insulation lid is arranged above the melt surface of said melt is between 1 mm and 100 mm.

9. The method according to claim 8, wherein the distance at which the thermal insulation lid is arranged above the melt surface of said melt is between 5 mm and 20 mm.

10. The method according to claim 8, wherein the thermal insulation lid is arranged at a distance of 10 mm above the melt surface.

11. The method according to claim 6, wherein the starting material is compacted before melting and preferably before inserting the starting material in the crucible.

12. The method according to claim 6, wherein the crucible is arranged in an inert gas atmosphere.

13. The method according to claim 12, wherein the crucible is arranged in an inert gas atmosphere of argon or nitrogen.

14. The method according to claim 6, wherein the starting material additionally comprises MgO and/or CaO at a content of less than 5 mol % and the resulting bulk Ba.sub.2ScNbO.sub.6 single crystal is doped with Mg and/or Ca.

15. The method according to claim 6, additionally comprising separating the bulk Ba.sub.2ScNbO.sub.6 single crystal from a multicrystalline or polycrystalline matrix that at least partly surrounds the Ba.sub.2ScNbO.sub.6 single crystal.

16. The method according to claim 6, additionally comprising cutting a slice of the bulk Ba.sub.2ScNbO.sub.6 single crystal.

17. The method according to claim 16, additionally comprising fabricating a Ba.sub.2ScNbO.sub.6 substrate from the slice having a diameter in lateral extent that is equal to or larger than 6 mm.

18. A bulk Ba.sub.2ScNbO.sub.6 single crystal having a cross-sectional area that is equal to or larger than 6 mm×6 mm.

19. The bulk Ba.sub.2ScNbO.sub.6 single crystal of claim 18, having cubic symmetry and a lattice parameter of 412 pm.

20. The bulk Ba.sub.2ScNbO.sub.6 single crystal of claim 18, having a melting point at 2165 +/−30° C. in inert gas atmosphere at ambient pressure.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the following, preferred embodiments of the invention will be described with reference to the figure. In the figures:

(2) FIG. 1: shows a flow diagram representing a method for growing a bulk single crystal;

(3) FIG. 2: shows a flow diagram representing a method for growing a bulk Ba.sub.2ScNbO.sub.6 single crystal;

(4) FIG. 3: schematically shows an embodiment of a growth setup for growing a bulk single crystal;

(5) FIG. 4: schematically shows an embodiment of a thermal insulation lid with a shutter function being in its open state a) and in its closed state b);

(6) FIG. 5: schematically shows a further embodiment of a thermal insulation lid with a shutter function being in its open state a) and in its closed state b);

(7) FIG. 6: shows in a) a grey scale intensity plot of a selected Bragg reflection produced from the bulk Ba.sub.2ScNbO.sub.6 single crystal shown in a photograph in b) and in c) the sum spectra collected within the bulk Ba.sub.2ScNbO.sub.6 single crystal area;

(8) FIG. 7: shows a chemo-mechanically polished (001)-oriented Ba.sub.2ScNbO.sub.6 single crystal substrate with a lateral extent of 10 mm;

(9) FIG. 8: shows a transmission electron microscope (TEM) micrograph of a structure comprising a Ba.sub.2ScNbO.sub.6 single crystal substrate and a BaSnO.sub.3 crystal layer epitaxially grown on top;

(10) FIG. 9: schematically shows a disk of a further embodiment of a thermal insulation lid with a shutter function;

(11) FIG. 10: schematically shows a disk of a further embodiment of a thermal insulation lid with a shutter function;

(12) FIG. 11: schematically shows a disk of a further embodiment of a thermal insulation lid with a shutter function.

DETAILED DESCRIPTION

(13) FIG. 1 shows a flow diagram representing a method for growing a bulk single crystal. The growth method can be conducted using, e.g., a growth setup as described with respect to FIG. 3.

(14) In a first step S1, a starting material is inserted into a crucible. The starting material is provided in dried powder form with a purity of 99.99%. In various other embodiments of the method the starting material comprises impurities in the 1% range and dopants in the 5% range. It is advantageous if before inserting the starting material into the crucible a powder mixture is produced from the starting material, e.g., including weighing, mixing and calcining the powders of the different chemical species.

(15) Here, the starting material is inserted into the crucible as a loose powder. Before melting the loose powder can be compacted inside the crucible. However, in various other embodiments it is preferred that the starting material is compacted before inserting into the crucible. Compacting the starting material before inserting the starting material into the crucible is often preferred because it allows the crucible to be filled more efficiently with starting material and also enables the starting material in the crucible to be more efficiently melted.

(16) The starting material can comprise, e.g., oxygen in combination with a cation species that can assume multiple oxidation states. In particular, it is preferred if the starting material comprises at least Ba, Sc, Nb and O.

(17) After inserting, the starting material is melted in step S2 in the crucible by heating the starting material, e.g., with a heating element. If the starting material is inserted into the crucible in compacted form, e.g., in the form of a cylindrical bar, the bar sinks to the lower part of the crucible while melting.

(18) After melting the starting material to a melt, a thermal insulation lid is arranged in step S3 at a distance above a melt surface of said melt to block radiation emitted from the melt surface. In particular, the thermal insulation lid is arranged above the melt surface such that at least a central part of the melt surface is covered by the lid. Preferably, the lid is arranged close to the melt surface, e.g. within the range of 1 mm and 10 mm. However, in various embodiments it is beneficial if the thermal insulation lid is arranged above the melt surface at a distance between 1 mm and 100 mm. The thermal insulation lid can also be arranged above the melt or unmolten starting material before melting the starting material or while melting the starting material in further embodiments.

(19) With the thermal insulation lid arranged at a distance above the melt surface a bulk single crystal is grown from the melt in step S4. Hereby, crystals nucleate at the crucible wall and grain-selection and continuous grain enlargement towards the central part of the crucible occur such that the bulk single crystal grows from the crucible wall towards the central region of the crucible.

(20) Crystal growth is achieved by controllably cooling the melt with the thermal insulation lid arranged above the melt surface. Controllably cooling the melt can be performed passively, e.g., by reducing the heat provided by a heating element over a predefined period of time and/or can be performed actively, e.g., by directing an inert gas flux onto the melt surface.

(21) While conducting the steps of the method for growing a bulk single crystal as described above, preferably, the crucible is arranged in an inert gas atmosphere, e.g., argon or a nitrogen atmosphere, preferably, under ambient pressure.

(22) FIG. 2 shows a flow diagram representing a method for growing a bulk Ba.sub.2ScNbO.sub.6 single crystal. The method of growing a bulk Ba.sub.2ScNbO.sub.6 single crystal can be conducted using, e.g., a growth setup as described with respect to FIG. 3. The growth method described with respect to FIG. 2 constitutes a variant of the growth method described with respect to FIG. 1.

(23) In the growth method represented by the flow diagram of FIG. 2, a starting material comprising at least Ba, Sc, Nb and O is provided in dried powder form with a purity of 99.99%. The starting material can also comprise dopants, e.g., MgO and/or CaO at a content of less than 5 mol %. The starting material is then inserted in step B1 into the crucible. In various embodiments before inserting the starting material into the crucible, a powder mixture is produced from the starting material comprising at least Ba, Sc, Nb and O. One possible way of producing the powder mixture from the starting material is to weigh, mix and calcine the dried powders. Calcining the starting material can be performed, e.g., in air at 1300° C. for 12 hours. The powder mixture produced from the starting material is then inserted into the crucible. Often it is beneficial, in particular, for the filling process and the subsequent melting, that the starting material or a powder mixture produced therefrom is compacted. For example, the starting material can be compacted to a cylindrically shaped bar that is then inserted into the crucible. One possible way of compacting the starting material is to use cold isostatic pressing at 0.2 GaP.

(24) The starting material held in the crucible is then melted in step B2 by heating the starting material. For melting the starting material to a melt, the crucible is heated at least to the melting temperature of a bulk Ba.sub.2ScNbO.sub.6 single crystal. To be well above the melting temperature of a bulk Ba.sub.2ScNbO.sub.6 single crystal the crucible can be heated, e.g., to a temperature of 2200° C.

(25) After melting the starting material, a thermal insulation lid is arranged in step B3 at a distance above a melt surface of said melt to block radiation emitted from the melt surface. In particular, the thermal insulation lid is arranged above the melt surface such that at least a central part of the melt surface is covered by the lid. Preferably, the lid is arranged close to the melt surface, e.g., within the range of 1 mm and 10 mm. However, in various embodiments it is beneficial if the thermal insulation lid is arranged above the melt surface at a distance between 1 mm and 100 mm. The thermal insulation lid can also be arranged above the melt or unmolten starting material before melting the starting material or while melting the starting material in further embodiments.

(26) The melt held in the crucible is then controllably cooled—passively and/or actively—for growing B4 a bulk Ba.sub.2ScNbO.sub.6 single crystal from the melt. During growth of the bulk Ba.sub.2ScNbO.sub.6 single crystal the thermal insulation lid is arranged above the melt surface to block thermal radiation emitted from the melt surface and to produce a specific temperature distribution favouring crystal growth. Such a temperature distribution beneficial for crystal growth can include a temperature gradient with lower (colder) temperatures close to the crucible wall and higher (hotter) temperatures in the central part of the crucible.

(27) With the growth methods as described with respect to FIG. 1 and, in particular, with the variant of this growth method that is described with respect to FIG. 2, a bulk Ba.sub.2ScNbO.sub.6 single crystal can be grown having a volume larger than 5 mm×5 mm×5 mm (length×width×height). Consequently, from bulk Ba.sub.2ScNbO.sub.6 single crystals grown with the methods described with respect to FIGS. 1 and 2, Ba.sub.2ScNbO.sub.6 single crystal substrates can be fabricated and used in the electronics industry for fabricating electronic devices.

(28) FIG. 3 schematically shows a growth setup 300 in a longitudinal sectional view for growing a bulk single crystal. The growth setup 300 can be used for implementing the growth methods as described with respect to FIGS. 1 and 2.

(29) The growth setup comprises a crucible 302 that is embedded in a thermal insulation 304. The thermal insulation 304 can comprise, e.g., ZrO.sub.2 and Al.sub.2O.sub.3. The crucible itself can be made of, e.g., iridium or platinum. Preferably, the crucible 302 has a cylindrical shape. However, the crucible 302 can also be realised in different shapes, e.g., the crucible 302 can have a hemispherical shape or the crucible 302 can be cube-shaped. With larger crucibles larger bulk single crystals can be grown. Thus, preferably for growing a bulk single crystal having a specific size a respective crucible is selected that also is not too large as too save energy needed for melting the starting material. For growing a bulk single crystal having a volume of about 15 mm×15 mm×15 mm (length×width×height), e.g., a crucible can be used having an inner diameter of 30 mm and a height of 50 mm.

(30) The crucible 302 is covered with a punched disc 303 that, preferably, is made of the same material as the crucible 302, e.g., iridium or platinum. The punched disc 303 serves for blocking thermal radiation emitted from the melt surface. The punched disc 303 is optional and is not mandatory for growing a bulk single crystal, e.g., by implementing one of the growth methods as described with respect to FIG. 1 or 2.

(31) The growth setup 300 further comprises a heating element 306 that is arranged and configured for melting a starting material that is held in the crucible 302 and melted. In particular, the heating element 306 comprises an induction heating coil that is wrapped around the crucible 302. Thus, heating the starting material to a melt is accomplished by radio frequency (RF) induction mainly into the crucible and crucible lid.

(32) In the growth setup 300 a melt 308 is shown. At a distance above the melt 308 held inside the crucible 302 a thermal insulation lid 310 is arranged that at least partly covers part the surface of the melt 308. In particular, the thermal insulation lid 310 is arranged and configured for influencing and controlling the temperature distribution in the melt 308 held inside the crucible 302 to favor crystal growth from the crucible wall towards the crucible center. The thermal insulation lid 310 can comprise a shutter as described with respect to FIGS. 4a and 4b and FIGS. 5a and 5b and FIGS. 9, 10 and 11. With a thermal insulation lid comprising a shutter, the amount of the melt surface that is covered by the thermal insulation lid while growing a bulk single crystal can be adjusted. The thermal insulation lid 310 can be made of, e.g., iridium. In particular, if the starting material comprises Ba, Sc, Nb and O and the growth setup 300 is used for growing a bulk Ba.sub.2ScNbO.sub.6 single crystal, the thermal insulation lid 310 can be made of a disc-shaped piece of Ba.sub.2ScNbO.sub.6.

(33) The thermal insulation lid 310 is attached to an arm 312 as a mounting with which the thermal insulation lid 310 can be lifted up or brought closer to the surface of the melt 308.

(34) The arm extends vertically though the hole of the punched disc 303 such that the thermal insulation lid attached to the arm can be lifted. For example, the arm can have a screw thread at its end outside the crucible and can moved manually. It is also possible that the arm can be lifted automatically, e.g., with an electrically driven motor that is connected to the arm.

(35) This growth setup is in particular useful for growing a bulk Ba.sub.2ScNbO.sub.6 single crystal, especially with the method described with respect to FIG. 2.

(36) FIGS. 4a, 4b and 5a, 5b schematically show two different embodiments of a thermal insulation lid having a shutter function. The thermal insulation lids having a shutter function as described with respect to FIGS. 4a, 4b and 5a, 5b can be used as a thermal insulation lid in a growth setup as described with respect to FIG. 3. By opening and closing the shutter the amount of the melt surface that is covered by the thermal insulation can be adjusted. Correspondingly, the amount of thermal radiation that is allowed to escape from the crucible can be adjusted with the shutter. The shutter can be implemented in different ways of which FIGS. 4a, 4b and 5a, 5b only show simplified selected examples. In particular, the shutter geometry of the thermal insulation lid can be adapted to specific growth scenarios.

(37) The thermal insulation lid 400 having a shutter function as shown in FIGS. 4a and 4b comprises two disks 402, 404 arranged one above the other to have the same midpoint. Both disks can have the same diameter but also different diameters as depicted in FIGS. 4a and 4b work. Both disks comprise a plurality of circularly shaped perforations 406, 408, the perforations 406, 408 of both disks 402, 404 being distributed along the circumference of circles having the same diameter. Further, the two disks 402, 404 are arranged one above the other such that they can be rotated relative to each other. As shown in FIG. 4a the two disks 402, 404 can then be arranged such that the perforations of the one disk 402 are congruent with the perforations of the other disk 404. Then the shutter is open and the amount of the melt surface that is covered by the thermal insulation is minimum. In FIG. 4b the opposite is the case, namely, the two disks 402, 404 are arranged one above the other such that the perforations 406, 408 of the two disks 402, 404 do not overlap such that the amount of the melt surface that is covered by the thermal insulation is maximum. Of course the two disks 402, 404 can be arranged one above the other to have an overlapping state in between completely open and completely closed.

(38) Also a thermal insulation lid having a shutter function can have more perforations, perforations of different sizes and shapes and a plurality of perforations arranged in a different pattern. For example, in a pattern as shown in FIGS. 5a and 5b. Comparable to the thermal insulation lid 400 as described with respect to FIGS. 4a and 4b, the thermal insulation shutter 500 of FIGS. 5a and 5b comprises two disks 502, 504 each having a plurality of perforations 506, 508. As described with respect to FIGS. 4a and 4b, the two disks 502, 504 can be rotated relative to each other to close or open the shutter. Hereby, FIG. 5a depicts the thermal insulation lid 500 having a shutter in its open state and FIG. 5b depicts the thermal insulation lid 500 having a shutter in its closed state.

(39) Here, the perforations 506, 508 are triangularly shaped with one of the vertices being the closest to the rim of the disks 502, 504. For a particular design of a temperature distribution of the melt it can be of advantage if each of the triangles are rotated by 180° such that the shortest edge is the closest to the rim of the disks 502, 504.

(40) In various other embodiments of a thermal insulation lid comprising a shutter, the shutter is implemented by one or more windows that can be opened or closed. By choosing an opening angle of the one or more windows the amount of thermal radiation emitted from the melt surface per time period can be controlled.

(41) It is also possible to implement a thermal insulation lid comprising a shutter by means of a thermal insulation lid having a plurality of perforations such that each can be closed by a corresponding lid. Such a lid for closing a plurality of perforations can also be made of one piece such that the plurality of perforations can be closed and opened in one step.

(42) FIG. 6 shows in a) a grey scale intensity plot of a selected Bragg reflection produced from the bulk Ba.sub.2ScNbO.sub.6 single crystal photographed in b). The measurement shown in a) was performed on the bulk Ba.sub.2ScNbO.sub.6 single crystal within the area indicated by the white box in b). The bulk Ba.sub.2ScNbO.sub.6 single crystal was grown from the melt using an iridium crucible with the method as described with respect to FIG. 2 and has a volume of 17 mm×17 mm×15 mm (length×width×height).

(43) The region in a) surrounded by the white dashed lines represents the single crystal region of the bulk Ba.sub.2ScNbO.sub.6 single crystal. This bulk Ba.sub.2ScNbO.sub.6 single crystal shown in FIG. 6b) is thus part of a larger multicrystalline volume. Slight differences in Bragg peak intensity are related to topographic effects, since the bulk Ba.sub.2ScNbO.sub.6 single crystal was measured in the as-grown state. In c) the sum spectra collected within the single-crystal area are shown.

(44) FIG. 7 shows a differential interference contrast (DIG) micrograph of a chemo-mechanically polished (001)-oriented Ba.sub.2ScNbO.sub.6 single crystal substrate with a surface area of 10×10 mm.sup.2. The Ba.sub.2ScNbO.sub.6 single crystal substrate was prepared from the bulk Ba.sub.2ScNbO.sub.6 single crystal shown in FIG. 6b).

(45) FIG. 8 shows transmission electron microscope (TEM) micrographs at different magnifications in a), b) and c) of a multilayer structure comprising a Ba.sub.2ScNbO.sub.6 single crystal substrate and a 250 nm thick undoped BaSnO.sub.3 crystal layer epitaxially grown on top of it followed by a 130 nm thick La-doped BaSnO.sub.3 layer, doped to yield a free electron concentration of 3×10.sup.19 cm.sup.−3. In particular, in c) it can be clearly seen that at the interface (indicated by the dashed line) between the Ba.sub.2ScNbO.sub.6 single crystal substrate and the BaSnO.sub.3 crystal layer of the multilayer structure has high structural perfection. This due to the high structural quality of the Ba.sub.2ScNbO.sub.6 single crystal substrate itself. From the multilayer structure shown comprising the single crystalline Ba.sub.2ScNbO.sub.6 substrate and a 250 nm thick undoped BaSnO.sub.3 crystal layer followed by a 130 nm thick La-doped BaSnO.sub.3 layer having an average threading dislocation density of less than 10.sup.8 dislocations per cm.sup.2 and a full width at half maximum (FWHM) of its rocking curve that is equal to 23 arcsec (0.006°). Electrical transport measurements on this film made using the Hall effect method indicate that the layer contains a concentration of 3×10.sup.19 electrons cm.sup.−3 and that the mobility of these electrons at room temperature exceeds 190 cm.sup.2V.sup.−1s.sup.−1. This mobility is higher than any report in the literature and is indicative of the electron mobility that can be achieved in electronic devices utilizing these films, e.g., a field-effect transistor.

(46) FIGS. 9, 10 and 11 show embodiments of disks, which are used as disks of an embodiment of a thermal insulation lid having a shutter function. As in FIGS. 4a, 4b, 5a and 5b each thermal insulation lid comprises two disks with identical shape, which can be rotated with respect to each other to open and close the shutter. By appropriate design of the holes and openings in such lids as well as the mutual rotation between them, the temperature profile of the melt can be controlled, which in turn effects the nucleation and growth of the crystal in the crucible.

(47) FIG. 9 shows schematically one of two disks 900 of identical shape, which function as a thermal insulation lid having a shutter function. The disk 900 extends over three quadrants of a circle. The fourth quadrant 904 is left open except for a small inner circle for mounting the disk forming an opening such that when arranged at a distance above a melt surface, thermal radiation emitted from the melt surface can escape through the opening, when the fourth quadrants 904 of both disks are arranged at least partly overlapping each other. In one example, the disk nearer to the melt stays fixed on top of the crucible while the disk arranged above can be rotated with respect to the other disk. In other examples both disks can be rotated. When the two disks 900 implementing a thermal insulation lid are arranged congruently, the opening is maximum. By further rotating the disks with respect to each other the area of the opening decreases such that the amount of thermal radiation that can escape is reduced. The shutter can be closed by arranging the two disks with respect to each other such that the opening in the fourth quadrant 904 of each of the respective disks 900 is completely covered by the respective other disk. If the crucible that shall be covered by the thermal insulation lid comprising the two disks 900 has an inner diameter of 42 cm, the disks of the thermal insulation lid, too, can have a diameter of 42 cm. Preferably, each of the disks 900 has a thickness of 1.5 cm.

(48) FIG. 10 shows schematically one of two disks 910 of identical shape, which function as a thermal insulation lid having a shutter function. The disk 910 is merely constructed and functions like the disk shown in FIG. 9. Thus only differences to the disk 900 of FIG. 9 are described. Additionally to the opening in the fourth quadrant 914 disk 910 comprises in the second quadrant 912 which is opposite to the opening in the fourth quadrant, a plurality of elongated curved perforations 915 that are arranged evenly spaced in radial direction of the disk 910. A thermal insulation lid comprising two of the disks 910 shown, can have a plurality of opening states depending on the arrangement of the disks with respect to each other. For example, the opening and the perforations 915 can be fully covered or left uncovered by the respective other disk. It is also possible that only the perforations 915 of each disk are open, when the opening of fourth quadrant 914 of the respective other disk overlaps the second quadrant 912 with the perforations 915. Furthermore, the disk 910 has a central opening 916 for receiving a mounting for the thermal insulation lid.

(49) FIG. 11 shows schematically a further embodiment of one of two disks 920 of identical shape, which function as a thermal insulation lid having a shutter function. The disk 920 is merely constructed and functions like the disk shown in FIG. 9. Thus only differences to the disk 900 of FIG. 9 are described. The fourth quadrant 924 and the second quadrant 922 in this embodiment do not have openings or perforations. Instead in the first quadrant 921 and the third quadrant 923 a plurality of elongated curved perforations 925 that are arranged evenly spaced in radial direction of the disk 920 is arranged, wherein the perforations 925 nearer to the centre of the disk 920 are smaller in thickness than the perforations 925 farer to the centre. As the disk 910 of FIG. 10 the disk 920 has a central opening 926 for receiving a mounting for the thermal insulation lid.