The design and thermal measurement of III-V integrated micro-coolers for thermal management of microwave devices

Modern high frequency electronic devices are continually becoming smaller in area but capable of generating higher RF power, thereby increasing the dissipated power density. For many microwave devices, for example the planar Gunn diode, standard thermal management may no longer be sufficient to effectively remove the increasing dissipated power. The work has looked at the design and development of an active micro-cooler, which could be fully integrated with the planar Gunn diode at wafer level as a monolithic microwave integrated circuit (MMIC). The work also resulted in the further development of novel thermal measurement techniques, using micro-particle sensors with infra-red (IR) thermal microscopy and for the first time to measure thermal profiles along the channel of the planar Gunn diode. To integrate the gallium arsenide (GaAs) based planar Gunn diode and micro-cooler, it was first necessary to design and fabricate individual GaAs based planar Gunn diodes and micro-coolers for thermal and electrical characterisation. To obtain very small area micro-coolers, superlattice structures were investigated to improve the ratio between the electrical and thermal conductivities of the micro-cooler. To measure the specific contact resistivity of the superlattice based micro-cooler contacts, the Reeves & Harrison TLM (transmission line method) was used as it included both horizontal and vertical components of the contact resistance. It was found, for the GaAs based micro-cooler, only small amounts of cooling (1 ºC. A novel approach of determining if the measured cooling temperature was due to cooling or probe loading was developed. A 1D model for the integrated micro-cooler was developed and the results indicated that when the micro-cooler was used as a cooling element in a monolithic microwave integrated circuit, the supporting substrate thickness was very important. Simulation showed to obtain cooling the substrate thickness had to be very thin (