Method for fabrication of crack-free ceramic dielectric films
The invention provides a process for forming crack-free dielectric films on a substrate. The process comprises the application of a dielectric precursor layer of a thickness from about 0.3 μm to about 1.0 μm to a substrate. The deposition is followed by low temperature heat pretreatment, prepyrolysis, pyrolysis and crystallization step for each layer. The deposition, heat pretreatment, prepyrolysis, pyrolysis and crystallization are repeated until the dielectric film forms an overall thickness of from about 1.5 μm to about 20.0 μm and providing a final crystallization treatment to form a thick dielectric film. The process provides a thick crack-free dielectric film on a substrate, the dielectric forming a dense thick crack-free dielectric having an overall dielectric thickness of from about 1.5 μm to about 20.0 μm.
1. A process for forming a crack-free barium strontium titanate (BST) dielectric comprising:
providing a substrate;
depositing a first dielectric precursor BST sol-gel layer having a thickness from about 0.3 μm to about 1.0 μm on a substrate;
heating the first dielectric precursor BST sol-gel layer at a preheat temperature from about 100° C. to about 200° C. for a preheat temperature heating time from about 1 minute to about 30 minutes;
initiating a step-wise preheat treatment using three distinct temperatures comprising increasing the temperature from about 275° C. to about 325° C. in a pre-pyrolysis step and maintaining the temperature at the pre-pyrolysis temperature for a pre-pyrolysis period of time;
increasing the temperature from about 375° C. to about 425° C. in a first pyrolysis step and maintaining the temperature at the first pyrolysis temperature for a first pyrolysis period of time;
increasing the temperature from about 425° C. to about 475° C. in a second pyrolysis step and maintaining the temperature at the second pyrolysis temperature for a second pyrolysis period of time;
initiating a crystallization treatment comprising increasing the temperature from about 600° C. to about 800° C. for a period of time to crystallize at least one layer; wherein all heat treatments were performed in an ambient atmosphere and wherein temperature changes are achieved by moving the film into different zones; and
repeating the deposition step, initial heating step, pyrolyzing and crystallization steps to form a BST layer having a total thickness from about 1.5 μm to about 20.0 μm on a substrate to form a crystallized dielectric.
2. The process of claim 1 , further comprising heating the substrate and BST layer to crystallize the BST at a temperature from about 600° C. to about 800° C. for a final crystallization time to form crystallized BST.
3. The process of claim 1 wherein the pre-heating time is from about 2 minutes to about 10 minutes.
4. The process of claim 1 , wherein the first dielectric precursor is a barium strontium titanate (BST) soluble gel solution containing polyvinylpyrrolidone.
5. The process of claim 1 wherein the deposition step, initial heating step, pyrolyzing and crystallization steps are repeated to form a dielectric precursor layer having a thickness from about 2.0 μm to about 5.0 μm on the substrate.
6. The process of claim 1 wherein the final crystallization time is from about 10 to about 40 minutes.
7. The process of claim 1 wherein said substrate comprises a base metal.