Thermocompression bonding of vertically aligned carbon nanotube turfs to metalized substrates.

Vertically aligned carbon nanotube turfs (VACNTs), consisting of entwined, nominally vertical carbon nanotubes, are being proposed for use as electrical and thermal contact materials. Issues in their implementation include high contact resistance, the van der Waals interactions of carbon nanotubes, and a low temperature limit during processing. One route for circumventing the 750 degrees C temperatures required for VACNT growth using chemical vapor deposition is for the VACNTs to be grown separately, and then transferred to the device. A method of mechanical transfer, using thermocompression bonding, has been developed, allowing dry mechanical transfer of the VACNTs at 150 degrees C. This method can be used for the construction of both a thermal switch or a permanent conducting channel. The conductivity of the bonded structure is shown to be independent of the imposed strain, up to strains in excess of 100%.

A facility for characterizing the steady-state and dynamic thermal performance of microelectromechanical system thermal switches.

A facility to characterize microelectromechanical system (MEMS) thermal switches by measuring two pertinent figures of merit is described. The two figures of merit measured are the ratio of thermal resistance of the switch in the off and on states, Roff/Ron, and the time required to switch from the off to the on state, tauswitch. The facility consists of two pieces of equipment. A guard-heated calorimeter is used to measure heat transfer across the thermal switch under steady-state conditions. Measuring heat transfer across a thermal switch in both the off and on states then gives the thermal resistance ratio Roff/Ron. A thin-film radial heat-flux sensor is used to measure heat transfer across the thermal switch under dynamic conditions. Measuring heat transfer across a thermal switch as the switch changes from the off to the on state gives the thermal switching time tauswitch. The test facilities enable the control of the applied force on the thermal switch when the thermal switch is on, the thickness of the gas gap when the thermal switch is off, and the gas species and pressure in the thermal switch gas gap. The thermal performance of two MEMS thermal switches employing two different thermal contact materials, a polished silicon surface and an array of liquid-metal microdroplets, is characterized and compared.