Nanolink-based thermal devices: integration of ALD TiN thin films

In this work, a new fabrication process is investigated for ultralow power, microelectronic hotplates. These hotplates are based on a small surface (0.0012-0.12 mm2) that is heated by a heater to temperatures in the range of 300-400 °C. These hotplates can be used for instance as gas or flow sensors. Applied as gas sensor, an (exothermic) combustion reaction will take place at the (catalytic) surface in the presence of a flammable gas during which heat is generated. This reaction heat is detected by a change in the (temperature dependent) heater resistance. This means that in a hotplate the heater simultaneously acts as a heat source and thermal sensor. The research, discussed in this work, is part of the ‘Hot Silicon’ project in which ultralow power (10-6 W) hotplates are studied; the power consumption is a factor 1000 less than state-of-the-art ‘low power’ heaters. The ultralow power enables integration of hotplates as for instance gas sensors in portable (battery powered) systems for industrial or domestic applications, for instance for the detection of hazardous (harmful and/or flammable) gases. A combination of various sensors (in a ‘sensor array’ for instance) can be used for the detection of multiple gases. Furthermore, low power gas sensors are generally safer. In this work, the hotplate is based on a small high ohmic conducting cylinder (the ‘link’). The link is embedded in an insulating (glass) layer and positioned between two crossing electrodes. Fabrication of the link is based on etching a hole in the glass layer and coating it with an ultrathin (7-15 nm) titanium nitride (TiN). Due to the excellent step coverage of the ALD process, a perfectly hollow and conducting cylinder is created.