Using near-infrared thermography microscopy and a low-cost charge-coupled device (CCD) camera, we have designed a system which is able to deliver quantitative submicronic thermal images. Using a theoretical model based on Planck's law and CCD sensor properties allowed us to determine a minimal theoretical detection temperature and an optimal temperature sensitivity of our system. In order to validate this method, we show a good relationship between a theoretical study and a thermal measurement of a microsample.

Conducting polyaniline-based chemiresistors on printed polymeric micro-hotplates were developed, showing sensitive and selective detection of ammonia vapor in air. The devices consist of a fully inkjet-printed silver heater and interdigitated electrodes on a polyethylene naphthalate substrate, separated by a thin dielectric film. The integrated heater allowed operation at elevated temperatures, enhancing the ammonia sensing performance. The printed sensor designs were optimized over two different generations, to improve the thermal performance through careful design of the shape and dimension of the heater element. A vapor-phase deposition polymerization technique was adapted to produce polyaniline sensing layers doped with poly(4-styrenesulfonic acid). The resulting sensor had better thermal stability and sensing performance when compared with conventional polyaniline-based sensors, and this was attributed to the polymeric dopant used in this study. Improved long-term stability of the sensors was achieved by electrodeposition of gold on the silver electrodes. Response to sub-parts-per-million concentrations of ammonia even under humid conditions was observed.

The design of ultra-low power micro-hotplates on a polyimide (PI) substrate supported by thermal simulations and characterization is presented. By establishing a method for the thermal simulation of very small scale heating elements, the goal of this study was to decrease the power consumption of PI micro-hotplates to a few milliwatts to make them suitable for very low power applications. To this end, the mean heat transfer coefficients in air of the devices were extracted by finite element analysis combined with very precise thermographic measurements. A simulation model was implemented for these hotplates to investigate both the influence of their downscaling and the bulk micromachining of the polyimide substrate to lower their power consumptions. Simulations were in very good agreement with the experimental results. The main parameters influencing significantly the power consumption at such dimensions were identified and guidelines were defined allowing the design of very small (15 × 15 μm) and ultra-low power heating elements (6 mW at 300 • C). These very low power heating structures enable the realization of flexible sensors, such as gas, flow or wind sensors, for applications in autonomous wireless sensors networks or RFID applications and make them compatible with large-scale production on foil such as roll-to-roll or printing processes.

Since local thermal probing has become a major tool for studying transport phenomena at micro- and nanoscale levels, the fundamental aspect of the interaction between the tip of the probe and the sample has remained the key point on which any quantitative measurement relies. In this paper, we present results on thermal resistances involved in the contact mechanism of a microthermocouple cantilever probe that is used to scan the surface of a microhotplate at different levels of temperature. We point out the potential of such an active microsystem as an efficient calibration tool for near-field thermal probes.

A novel probe for scanning thermal microscope using a micro-thermocouple probe placed on a Quartz Tuning Fork (QTF) is presented. Instead of using an external deflection with a cantilever beam for contact detection, an original combination of piezoelectric resonator and thermal probe is employed. Due to a non-contact photothermal excitation principle, the high quality factor of the QTF allows the probe-to-surface contact detection. Topographic and thermal scanning images obtained on a specific sample points out the interest of our system as an alternative to cantilevered resistive probe systems which are the most spread.

We report on the dynamic and static thermal characterization of microsystems using a visible and near-infrared (NIR) thermography system based on a low-cost standard CCD sensor. The interest of this method is that it is possible to obtain a true spatial resolution better than 500 nm, which is necessary in high spatial resolution applications (microsystem applications). Another interesting point of this optical method is that the temperature error versus the emissivity error is always very low (compared to infrared thermography). We show, in this study, that this behavior originates in the high sensitivity of Planck's law in this wavelength range (compared to infrared range). Thus, we demonstrate the principal advantages of this method for micromachined heater application. Thermal measurements (in dynamic and static modes) were performed on micro-heaters commonly used in microsystems, platinum-and silicon-based micromachined heaters. The results show the capability of the method in terms of the thermal resolution and spatial resolution as well as the capacity to quickly obtain static and dynamic thermal images of the studied sample.

A scanning thermal microscope working in passive mode using a micronic thermocouple probe is presented as a quantitative technique. We show that actual surface temperature distributions of microsystems are measurable under conditions for which most of usual techniques cannot operate. The quantitative aspect relies on the necessity of an appropriate calibration procedure which takes into account of the probeto-sample thermal interaction prior to any measurement. Besides this consideration that should be treated for any thermal contact probing system, the main advantages of our thermal microscope deal with the temperature available range, the insensitivity to the surface optical parameters, the possibility to image DC and AC temperature components up to 1 kHz typically and a resolution limit related to near-field behavior.

No abstract