METHOD OF FABRICATING THIN DIELECTRIC FILM AND THIN FILM CAPACITOR INCLUDING THE DIELECTRIC FILM
A method of fabricating a thin dielectric film, a thin dielectric film formed according to the method, and a system including the thin dielectric film. The method includes: depositing a ceramic precursor material on a metal sheet, the ceramic precursor material including a mixture comprising ceramic particles and an organic carrier medium; heat treating the ceramic precursor material such that the organic carrier medium is substantially burnt off, and further such that a dielectric layer is formed including ceramic grains formed from the ceramic particles, and having grain sizes between about 100 nm and about 500 nm; depositing a CSD precursor material onto the dielectric layer; and heat treating the CSD precursor material such that organics in the CSD precursor material are substantially burnt off, and further such that a CSD medium is formed from the CSD precursor material including CSD grains substantially filling the voids between the ceramic grains
Embodiments of the present invention relate to thin film capacitors and to methods of fabricating same.
BACKGROUNDCreating thin films having a large capacitance density, that is, a capacitance density above about 1 μF/cm2 on metal sheets presents a number of challenges. One way to achieve large capacitance density would be to achieve a large dielectric constant, given that capacitance density and dielectric constant are directly proportional to one another. It is well known that the dielectric constant of a material is among other things a function of the grain size of that material. In particular, as the grain size of a material increases, generally, so will its dielectric constant. However, growing thin films having large grain sizes, that is, thin films having grain sizes above about 50 nm to about 100 nm is a challenge. For example, growing a large grain microstructure requires an optimum combination of nucleation and grain growth. This is hard to achieve on a polycrystalline metal sheet. Typically, the multitude of random sites on the rough polycrystalline metal sheet acts as nucleation sites, resulting in a microstructure with very small grain size (about 10 nm to about 50 nm). Once the film microstructure is composed of a large number of small grains, further heating will not result in a large grain microstructure, because larger grains would grow at the expense of the smaller grains. However, a large number of similar-sized grains cannot grow into each other to form larger grains.
As a result of the above, attempts at creating thin films having a large capacitance density has shifted toward reducing a thickness of the deposited thin film dielectric, while avoiding the problems noted above with respect to creating dielectrics of large grain size. Thus, the prior art typically focuses on small grain sized thin film technology (that is dielectric thin films having grain sizes in the range from about 10 nm to about 50 nm, with dielectric constants ranging from about 100 to about 450. To the extent that the capacitance density of a material is known to be inversely proportional to its thickness, the prior art has aimed at keeping the thickness of such dielectric films in the order of about 0.1 microns. However, disadvantageously, such films have tended to present serious shorting issues. First, a surface roughness of the metal sheet onto which the dielectric film has been deposited, to the extent that it is usually significant with respect to a thickness of the dielectric film, tends to present metal peak and valleys into the dielectric film which in turn can lead to a direct shorting between the electrodes of a capacitor that includes the dielectric film. In addition, again, since a thickness of the dielectric film is small, voids typically present in the film will allow metal from at least one of the capacitor electrodes to seep into the voids, leading to shorting and leakage between the electrodes.
Voids in dielectric layers are disadvantageous for a number of other reasons. First, because of the presence of air pockets brought about as a result of the presence of voids, stress concentration points are typically created in the dielectric film, thus increasing the risk of crack propagation therein. In addition, to the extent that the dielectric constant of air is very small, the presence of air pockets results in an overall decrease in the dielectric constant of the dielectric layer. Thus, voids present disadvantages with respect to both the mechanical integrity and the electrical performance of a dielectric layer. The prior art proposes solving the problem of voids by exposing the dielectric layer to relatively long periods of sintering in order to densify the layer. However, such a solution disadvantageously increases the thermal budget required for the fabrication of a dielectric film, increasing cost while not necessarily guaranteeing a satisfactory reduction in the number of voids.
With respect to fabricating thin film capacitors, as noted above, a predominant prior art method involves chemical solution deposition (CSD). Referring to
Conventional thin film dielectric fabrication methods thus do not allow the formation of a dielectric film that both exhibits a high capacitance density and substantially avoids shorting and/or leakage issues between electrodes in a capacitor including the film.
BRIEF DESCRIPTION OF THE DRAWINGSEmbodiments of the present invention are illustrated by way of example and not by way of limitation in the figures of the accompanying drawings, in which the like references indicate similar elements and in which:
Embodiments of the present invention pertain to methods of creating a high dielectric constant thin film on a metal sheet, to a thin film capacitor fabricated from a combination of the thin film, the metal sheet, and to a system including the thin film capacitor.
Various aspects of the illustrative embodiments will be described using terms commonly employed by those skilled in the art to convey the substance of their work to others skilled in the art. However, it will be apparent to those skilled in the art that the present invention may be practiced with only some of the described aspects. For purposes of explanation, specific numbers, materials and configurations are set forth in order to provide a thorough understanding of the illustrative embodiments. However, it will be apparent to one skilled in the art that the present invention may be practiced without the specific details. In other instances, well-known features are omitted or simplified in order not to obscure the illustrative embodiments.
Various operations will be described as multiple discrete operations, in turn, in a manner that is most helpful in understanding the present invention; however, the order of description should not be construed as to imply that these operations are necessarily order dependent. In particular, these operations need not be performed in the order of presentation.
The word “embodiment” is used repeatedly. The word generally does not refer to the same embodiment, however, it may. The terms “comprising”, “having” and “including” are synonymous, unless the context dictates otherwise.
The phrases “thin film” and “dielectric film” are used interchangeably in the instant description, and refer to a dielectric film adapted to be used in a thin film capacitor. In addition, “metal sheet” as used herein refers to a sheet of metal adapted to be used as an electrode in a thin film capacitor.
Referring now to
As seen in
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Referring next to
Thereafter, at
An alternate embodiment of the present invention would involve the deposition of the CSD precursor material 160 directly onto the ceramic precursor material 100 before heat treatment of the ceramic precursor material. Heat treatment of both CSD precursor material and of the ceramic precursor material would then take place simultaneously, yielding the structure shown in
Referring next to
Advantageously, embodiments of the present invention yield thicker and hence more mechanically and electrically reliable dielectric films for thin film capacitors. Dielectric films according to embodiments of the present invention have higher dielectric constants (typically in the range between 700 and 4000) than dielectric films of the prior art (typically in the range between 100 and 450). The higher dielectric constants are a result of the dominant presence of large grain high k material, in this way potentially yielding large capacitance densities, despite a greater thickness of the dielectric films. The greater thickness of the dielectric films according to embodiments of the present invention further contributes to a minimization in shorting and/or leakage issues of the prior art. In addition, embodiments of the present invention advantageously avoid the need to grow large grains starting from CSD precursor materials, and the problems associated therewith, since large grains would already be present in the ceramic precursor material for the dielectric film. Moreover, embodiments of the present invention would advantageously reduce manufacturing costs for thin films to the extent that they make possible the use of high volume manufacturing powder green sheets as opposed to the use of CSD precursor chemicals.
Referring to
For the embodiment depicted by
Although specific embodiments have been illustrated and described herein for purposes of description of the preferred embodiment, it will be appreciated by those of ordinary skill in the art that a wide variety of alternate and/or equivalent implementations calculated to achieve the same purposes may be substituted for the specific embodiment shown and described without departing from the scope of the present invention. Those with skill in the art will readily appreciate that the present invention may be implemented in a very wide variety of embodiments. This application is intended to cover any adaptations or variations of the embodiments discussed herein. Therefore, it is manifestly intended that this invention be limited only by the claims and the equivalents thereof.
Claims
1. A method of fabricating a thin dielectric film comprising:
- depositing a ceramic precursor material on a metal sheet, the ceramic precursor material including a mixture comprising ceramic particles and an organic carrier medium;
- heat treating the ceramic precursor material such that the organic carrier medium is substantially burnt off, and further such that a dielectric layer is formed including ceramic grains formed from the ceramic particles, and having grain sizes between about 100 nm and about 500 nm;
- depositing a CSD precursor material onto one of the ceramic precursor material and the dielectric layer;
- heat treating the CSD precursor material after depositing the CSD precursor material such that organics in the CSD precursor material are substantially burnt off, and further such that a CSD medium is formed from the CSD precursor material including CSD grains substantially filling the voids between the ceramic grains
2. The method of claim 1, wherein the CSD grains have grain sizes between about 0.02 and about 0.04 microns.
3. The method of claim 1, wherein the ceramic particles have particle sizes between about 0.05 micron and about 0.50 micron.
4. The method of claim 1, wherein the ceramic precursor material includes a ceramic green sheet.
5. The method of claim 4, wherein the ceramic green sheet includes one of Z5U, X6S, X7R, and X7S.
6. The method of claim 4, wherein depositing the ceramic precursor material includes one of roller pressing the ceramic green sheet onto the metal sheet, and adhering the green sheet onto the metal sheet via an adhesive provided on one side of the green sheet, and laminating the green sheet onto the metal sheet,
7. The method of claim 1, wherein heat treating the ceramic precursor material comprises:
- drying the ceramic precursor material to yield a dried deposit;
- burning-out the organic carrier medium from the organic carrier medium from the dried deposit to yield an intermediate deposit; and
- annealing the intermediate deposit.
8. The method of claim 7, wherein:
- drying the ceramic precursor material comprises exposing the ceramic precursor material to temperatures between about 200 degrees Centigrade and about 300 degrees Centigrade for about 2 hours to about 5 hours to yield the dried deposit;
- burning out the organic carrier medium comprises exposing the dried deposit to temperatures between about 400 degrees Centigrade and about 600 degrees Centigrade for about 3 hours to about 7 hours to yield the intermediate deposit; and
- annealing comprises exposing the intermediate deposit to temperatures between about 1000 degrees Centigrade and about 1400 degrees Centigrade for about 6 hours to about 24 hours.
9. The method of claim 1, wherein heat treating the ceramic precursor material comprises heat treating in a reducing atmosphere.
10. The method of claim 1, wherein the CSD precursor material comprises an organic liquid solution of organic molecules with embedded metal atoms.
11. The method of claim 10, wherein the CSD precursor material comprises one of:
- barium and strontium acetates, dissolved in acetic acid, mixed with titanium tetra-isopropoxide in isopropanol;
- barium and strontium acetate dissolved in acetic acid mixed with titanium tetra n-butoxide stabilized with acetylacetone and diluted with 2-methoxyethanol; and
- barium and strontium propionates and titanium tetra n-butoxide stabilized with acetylacetone dissolved in a mixture of propionic acid and 1-butanol.
12. The method of claim 1, wherein the CSD medium comprises barium strontium titanate.
13. The method of claim 1, wherein depositing the CSD precursor material comprises one of spinning the CSD precursor material onto the dielectric layer, spraying the CSD precursor material onto the dielectric layer, and dipping the dielectric layer into a CSD precursor material bath.
14. The method of claim 1, wherein heat treating the CSD precursor material comprises:
- drying the CSD precursor material to yield a dried CSD deposit;
- burning out organics from the CSD precursor material to yield an intermediate CSD deposit; and
- annealing the intermediate CSD deposit.
15. The method of claim 14, wherein:
- drying the CSD precursor material comprises exposing the CSD precursor material to temperatures between about 100 degrees Centigrade and about 200 degrees Centigrade for about 15 minutes to about 30 minutes to yield the dried CSD deposit;
- burning out organics comprises exposing the dried CSD deposit to temperatures between about 300 degrees Centigrade and about 500 degrees Centigrade for about 1 hour to about 3 hours to yield the intermediate CSD deposit; and
- annealing comprises exposing the intermediate CSD deposit to temperatures between about 500 degrees Centigrade and about 1000 degrees Centigrade for about 0.5 hour and about 3 hours.
16. The method of claim 1, wherein the metal sheet comprises one of Cu and Ni.
17. A thin film capacitor comprising:
- a first electrode and a second electrode;
- a thin dielectric film disposed between the first electrode and the second electrode, the dielectric film comprising a first set of ceramic grains having grain sizes between about 0.1 micron and about 0.5 micron, the first set of ceramic grains being embedded in a second set of ceramic grains having grain sizes between about 0.02 and about 0.04 micron.
18. The thin film capacitor of claim 17, wherein the thin dielectric film has a thickness between about 0.3 micron to about 1 micron.
19. The thin film capacitor of claim 18, wherein the thin film dielectric film has a thickness of about 0.5 micron.
20. The thin film capacitor of claim 17, wherein the thin dielectric film has a capacitance density between about 1 μF/cm2 and about 6 μF/cm2.
21. The thin film capacitor of claim 17, wherein the first electrode and the second electrode are both made of one of Cu and Ni.
22. A system comprising:
- an electronic assembly comprising a thin film capacitor, the capacitor including: a first electrode and a second electrode; and a thin dielectric film disposed between the first electrode and the second electrode, the dielectric film comprising a first set of ceramic grains having grain sizes between about 0.1 micron and about 0.5 micron, the first set of ceramic grains being embedded in a second set of ceramic grains having grain sizes between about 0.02 and about 0.04 microns; and
- a graphics processor coupled to the electronic assembly.
23. The thin film capacitor of claim 22, wherein the thin dielectric film has a thickness between about 0.3 micron to about 1 micron.
24. The thin film capacitor of claim 23, wherein the thin film dielectric film has a thickness of about 0.5 micron.
25. The thin film capacitor of claim 22, wherein the thin dielectric film has a capacitance density between about 1 μF/cm2 and about 6 μF/cm2.
26. The thin film capacitor of claim 22, wherein the first electrode and the second electrode are both made of one of Cu and Ni.
Type: Application
Filed: Sep 27, 2004
Publication Date: Mar 30, 2006
Inventor: Cengiz Palanduz (Chandler, AZ)
Application Number: 10/951,054
International Classification: C03B 29/00 (20060101); H01G 4/06 (20060101);