L. Thiery

Development of a New Generation of Ammonia Sensors on Printed Polymeric Hotplates

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.

Quantitative thermal microscopy using thermoelectric probe in passive mode

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 probe-to-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.

Characterization and fabrication of fully metal-coated scanning near-field optical microscopy SiO2 tips

The fabrication of silicon cantilever‐based scanning near‐field optical microscope probes with fully aluminium‐coated quartz tips was optimized to increase production yield. Different cantilever designs for dynamic‐ and contact‐mode force feedback were implemented. Light transmission through the tips was investigated experimentally in terms of the metal coating and the tip cone‐angle. We found that transmittance varies with the skin depth of the metal coating and is inverse to the cone angle, meaning that slender tips showed higher transmission. Near‐field optical images of individual fluorescing molecules showed a resolution < 100 nm. Scanning electron microscopy images of tips before and after scanning near‐field optical microscope imaging, and transmission electron microscopy analysis of tips before and after illumination, together with measurements performed with a miniaturized thermocouple showed no evidence of mechanical defect or orifice formation by thermal effects.

Scanning thermal microscopy based on a quartz tuning fork and a micro-thermocouple in active mode (2ω method)

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.

Évolution des techniques de micromesures thermiques au travers de quelques applications

Abstract The thermoelectric sensors made at present in our laboratory have junction dimensions from a few micrometers to 0.5 μm. Two techniques are used: welding of ultra-thin wires and vacuum deposition (PVD). Two applications related to the first one will be presented: the detection of periodic field of temperature for photothermal microscopy and acoustic resonator characterization. In the latter, the comparison of simultaneous pressure and temperature will lead us to improve the knowledge of thermoacoustic phenomena. The deposition technique allows us to create either simple thermoelectric couples, multiple as thermopiles; or heat (and light) flow sensors. Our work is presented in that field, with the development of a laser light sensor designed to image its light profile for large emission bandwidth and power densities. Finally, the description followed by an example of application is shown in the case of the heat flow measurement between a laminar gaseous flow and a wall. By comparison, we show that the use of such sensors could be worthwhile to replace the usual temperature sensors in the estimation of the heat transfer coefficient at the gas-wall boundary.

Photo-thermal quartz tuning fork excitation for dynamic mode atomic force microscope

A photo-thermal excitation of a Quartz Tuning Fork (QTF) for topographic studies is introduced. The non-invasive photo-thermal excitation presents practical advantages compared to QTF mechanical and electrical excitations, including the absence of the anti-resonance and its associated phase rotation. Comparison between our theoretical model and experiments validate that the optical transduction mechanism is a photo-thermal rather than photo-thermoacoustic phenomenon. Topographic maps in the context of near-field microscopy distance control have been achieved to demonstrate the performance of the system.

Precise Thermography of Microsystems in the Visible Region using a Standard CCD Camera

This communication reports on the thermal characterisation of microsystems using a visible thermography system based on a low cost standard CCD sensor. The interest of such a method in low spatial resolution applications, with the possibility to reach a true spatial resolution inferior to 500 nm, is demonstrated. One interesting point of this optical method is that it is not very sensitive to the optical properties of the object, contrary to thermoreflectance and infrared (IR) thermography. Thermal measurements were performed on micro-heaters commonly used in microsystems, platinum and silicon based micromachined heaters. The paper presents the capability of the method in terms of thermal resolution and spatial resolution, as well as the capacity to quickly obtain static and dynamic thermal images of the studied samples.

Investigations of room temperature bolometers for THz applications

We investigate in this work the performance of two configurations of room temperature bolometers dedicated to THz applications. Fabrication processes, noise level, sensitivity and resolution characterizations are presented. Results emphasize the efficiency of the proposed approach.

Micromachined temperature calibration tool for contact Scanning Thermal Microscope probes

Local thermal probing has become a major tool for studying transport phenomena at micro and nanoscale levels, detecting hot spots and failures of microelectronic devices or measuring surface temperature distribution at these scales. If contact point measurement of a local tip is expected to provide the best spatial resolution, the fundamental aspect of the interaction between the probe tip and the sample remains the key point on which any quantitative measurement relies. We focus on the calibration procedure that will allow measuring the thermal response (error) of a contact probe used for temperature measurement on a surface. For this purpose, a micro-hotplate made of platinum heater suspended on thin silicon nitride (SiN) membrane represents an interesting tool. The objective is to develop heated reference samples with localized temperature sensors embedded on its surface to probe the temperature during the probe contact. We report on the thermal design of low-power calibration chip and the first results obtained when contacting wire based micro-thermocouple Scanning Thermal Microscope (SThM) probes.

Aerosol jet printing of miniaturized, low power flexible micro-hotplates

We report on printed flexible micro-hotplates operating at high temperature at lower power consμmption than ever reported using aerosol jet printing of fine metallic conductor features. Efficient heating (i.e., 40 mW at 325 °C) was produced by reducing the effective heating area and substrates thickness. Gold (Au) nanoparticles solution was used for printing micro-hotplates of two different sizes, i.e., 500 × 500 μm2 and 300 × 300 μm2, on 50 μm- and 13 μm-thick PI substrates, respectively. Comsol simulations were used to optimize the thermal design of micro-hotplates. Their power consμmption at 325 °C was of 54 mW for the large hotplate and of 40 mW for the smaller design. These results validate the simple manufacturing of high temperature and power efficient flexible micro-hotplates for applications such as in portable gas and chemical sensors, thermal metrology, etc.