Thermo-Electric Modeling of Nanotube-Based Environmental Sensors

Free-standing electrically conductive nanotube and nano-bridge structures offer a simple, small-scale, low-power option for pressure and temperature sensing. To sense pressure, a constant voltage is applied across the bridge. At small scales, the heat transfer coefficient is pressure-dependent. The change in the heat transfer coefficients result in the circuit operating at higher temperatures, with different resistances, at low pressures. This in turn will lead to a change in the electrical resistivity of the system. If the system is held at constant voltage, this can be measured as a change in the current in such systems, representing a simple alternative to existing Pirani gauges. The current work simulates the Joule heating, conduction and convection heat transfer of a 5 micron long suspended single-wall carbon nanotube, incorporating temperature-sensitive material properties. The simulation allows prediction of the thermo-electrical response of the systems. The results agree with the trends observed in existing devices. Additional results look at the effects of system length, temperature, and contact resistances between the substrate and the device.