| EPSRC Reference: |
GR/J16428/01 |
| Title: |
PROCESSING OF NOVEL DIELECTRIC STRUCTURES FOR MICROWAVE AND MILLIMETRE-WAVE INTEGRATED CIRCUITS |
| Principal Investigator: |
Robertson, Professor I |
| Other Investigators: |
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| Department: |
Electronic Engineering |
| Organisation: |
Kings College London |
| Scheme: |
Standard Research (Pre-FEC) |
| Starts: |
01 February 1994 |
Ends: |
30 October 1995 |
Value (£): |
85,193
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| EPSRC Research Topic Classifications: |
| RF & Microwave Technology |
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| Panel History: |
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Summary on Grant Application Form |
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MMICs still use large numbers of passive components, both lumped elements (spiral inductors and overlay capacitors) and transmission lines and couplers. The area consumed by these can be drastically reduced by the use of multilayer techniques. However, producing MMICs with 3 or more metal layers requires research into the optimum processing of the dielectric spacer layers. This project on the fabrication of novel dielectric structures is therefore aimed at researching into fabrication procedures for these multilayer circuits in order to facilitate an increase in the packing density of commercially fabricated MMICs in the future. Progress:Mask design:The initial work involved multilayer passive components design. Structures included capacitors for dielectric property study; spiral inductors; spiral transformers; couplers; coplanar waveguide; antennas; resonators and structures for the process validation checking. The test mask was fabricated by Rutherford Appleton Laboratory.Polyimide processing:We have investigated polyimide film formation and curing, dielectric constant, electric strength, interconnection of different layers through dielectric windows, contact resistance, dielectric edge profile, plasma etching of polyimide.We firstly tried the DuPont PI2610 polyimide which was available at that time. It was found that it is not good enough for our multilayer application due to the viscosity change of the products with time. After further study, we bought PIQ-1 3 from Hitachi Chemicals Europe. This polyimide product could provide a cured film thickness of around 2,um. In addition no adhesion promoter is required for this material when used on GaAs substrates. The water contents of the polyimides were studied while the material was cured at different temperatures. The polyimide was initially soft cured at around 200C due to the equipment limitations. This proved to be not good enough for our MMIC application. By modifying the existing equipment we now have achieved a curing temperature at 315C with a ramp time of about one hour. A better cured film could thus be obtained. For better interconnection, a positive edge of the polyimide is required: The edge profile of the polyimide was studied using scanning electron microscopy (SEM), we found that the polyimide edge was exactly a replica of the resist edge profile. Thus a different edge profile of polyimide could be achieved by changing the resist processing method. We have studied the edge profile of the photoresist and polyimide obtained by reactive ion etching. Different etching conditions have been studied. Metal layer formation:Due to various difficulties and the expense of using gold evaporation, we have been temporarily using A1 as the metal layer in order to investigate the dielectric behaviour. We are liaising with RAL for gold sputtering and milling services. We hope the final circuits will be realised using gold in the near future. Circuits fabrication:So far, several batches of samples have been fabricated. Because of the novel nature of the project, we initially encountered various problems during circuit fabrication. We can now achieve a nearly 100% yield rate for various components.
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Key Findings |
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Potential use in non-academic contexts |
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Impacts |
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| Description |
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Sectors submitted by the Researcher |
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This information can now be found on Gateway to Research (GtR) http://gtr.rcuk.ac.uk
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