[TechNOLOGY OPPORTUNITY 2003-043 ]

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Barium Strontium Titanate (BST) Sol-Gel Process and Applications
 
The development of a novel low-temperature BST sol-gel composite incorporating hydrothermal treatment has been developed by researchers at Queen’s University.

Description:
Conventionally processed sol-gel composite films have poor electrical characteristics due to the large number of boundaries inherent in the film. At high frequencies, the effect of these boundaries becomes more significant. It has been shown at Queen’s University for the first time that the replacement of conventional thermal sintering of sol-gel composite films with a chemical hydrothermal treatment gives rise to a unique microstructure with few barriers. This yields films with excellent electrical characteristics, even at GHz frequencies.

Applications:
1. Certain substrates, used in high speed integrated circuits for operation at tens of GHz frequencies, cannot be subjected to temperatures over 200° C while retaining optimal material characteristics. Hydrothermal processing of sol-gel composites is both compatible with the temperature limitations of these substrates and produces BST films with excellent electrical characteristics at GHz frequencies. The hydrothermal processing of sol-gel composite BST films is also able to produce films with permittivity as high as or higher than conventionally deposited films This is the first technique which is able to do so at temperatures below 200° C for sol-gel composite films.

2. The application of hydrothermally processed sol-gel to bulk materials was also demonstrated here. Previously, sol-gels were used only to precipitate powders or to fabricate films. In this work bulk BST pellets are impregnated with BST so!- gel and then hydrothermally processed. The permittivity of the pellets increases far beyond what is predicted by the minimal increase in density of the pellets.

3. The application of hydrothermally processed sol-gel composites may be extended to include an adhesion layer between circuits and structures such as dielectric resonators. Conventionally, air gaps between the substrate and the resonator contribute significantly to the losses of the structure and repeatability of electrical circuit performance. As in the bulk BST pellets, hydrothermally processed sol-gel composites could be used to grow an adhesion layer without such gaps.

4. This invention also suggests for the first time that hydrothermal processing of sol-gel composites may be applicable to a wide range of ceramic materials. This would allow for low- temperature deposition of various materials on substrates whose temperature limitations previously made them poor candidates for substrates for ceramic films. These substrates include such materials as GaAs, Si, polymers, and substrates with pre-patterned elements which are temperature sensitive. The technique may be useful in such applications as flexible circuits and flat-panel displays.

5. Some of the applications of the process could be in the area of passive microwave circuit size reduction and the integration of bulk BST materials with ICs that could include high Q resonators, filters and antennae. This would save cost in the manufacturing of smaller ICs and a higher level of integration of of chip components. These applications could also include capacitors, tunable microwave devices, electronically tunable mixers, delay lines, filters, oscillators, resonators, phase shifters, thermistors, capacitative sensors, reduction of voltage fluctuations on bypass capacitors, DRAMS, and reduction of lead inductance by placing structures on chip.

Status of Development:
The researchers intend to explore further refinements of the process.

Status of Commercialization:
PARTEQ Innovations, the technology transfer arm of Queen’s University, is seeking industrial partners willing to support on-going development of the product and/or are interested in licensing the intellectual property

Contact:
Randall North Associate Director, Commercial Development
P: (613) 533-2342
F: (613) 533-6853
E: rnorth@parteqinnovations.com
 

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