Stéphane Grauby

Calibration procedure for temperature measurements by thermoreflectance under high magnification conditions

We show that, in thermoreflectance measurements under high focusing conditions, the signal is not only due to the surface temperature variations. Indeed, the reflected light from the device under test interferes with the incoming one, making a parasitic Fabry-Perot. Besides, the motion of the sample surface induced, for example, by Joule heating, can produce an additional signal superimposed on the thermoreflectance one. Consequently, reliable thermoreflectance measurements under high focusing conditions, and particularly their calibration, demand a control of the distance between the objective and the sample. Using a servo loop to maintain the distance between the objective and the device constant, thermoreflectance measurements have been made in transient regime on an electronic device and the thermoreflectance coefficient of gold has been deduced.

Scanning thermal microscopy of individual silicon nanowires

Thermal imaging of individual silicon nanowires (Si NWs) is carried out by a scanning thermal microscopy (SThM) technique. The vertically aligned 1.7 μm long Si NWs are fabricated combining nanosphere lithography and metal-induced wet chemical etching. A thermal model for the SThM probe is then presented with two steps: a model out of contact which enables a calibration of the probe, and a model in contact to extract thermal parameters from the sample under study. Using this model and the experimental thermal images, we finally determine a mean value of the tip-to-sample thermal contact resistance and a mean value of the Si NWs thermal conductivity. No significant thermal conductivity reduction in comparison with bulk Si is observed for Si NWs with diameters ranging from 200 to 380 nm. However, the technique presented here is currently the only one available to perform thermal measurements simultaneously on an assembly of individual one-dimensional nanostructures. It enables to save time and to make a sta...

Four different approaches for the measurement of IC surface temperature: application to thermal testing

Silicon die surface temperature can be used to monitor the health state of digital and analogue integrated circuits (IC). In the present paper, four different sensing techniques: scanning thermal microscope, laser reflectometer, laser interferometer and electronic built-in differential temperature sensors are used to measure the temperature at the surface of the same IC containing heat sources (hot spots) that behave as faulty digital gates. The goal of the paper is to describe the techniques as well as to present the performances of these sensing methods for the detection and localisation of hot spots in an IC.

Fabrication of Bi2Te3 nanowire arrays and thermal conductivity measurement by 3ω-scanning thermal microscopy

Bi2Te3 is well-known for its utility in thermoelectrical applications and more recently as topological insulator. Its nanostructuration has attracted plenty of attention because of its potential capacity to reduce thermal conductivity. Here, we have grown a composite sample made of a Bi2Te3 nanowires (NWs) array embedded in an alumina matrix. We have then performed scanning thermal microscopy (SThM) in a 3ω configuration to measure its equivalent thermal resistance. Using an effective medium model, we could then estimate the mean composite thermal conductivity as well as the thermal conductivity of the NWs to be, respectively, (λC) = (1.68 ± 0.20) W/mK and (λNW) = (1.37 ± 0.20) W/mK, showing a slight thermal conductivity reduction. Up to now, there have been two main techniques reported in literature to evaluate the thermal conductivity of nanostructures: the use of a thermal microchip to probe a single NW once its matrix has been dissolved or the probing of the whole NWs array embedded in a matrix, obtai...

Thermal exchange radius measurement: Application to nanowire thermal imaging

In scanning thermal microscopy (SThM) techniques, the thermal exchange radius between tip and sample is a crucial parameter. Indeed, it limits the lateral spatial resolution but, in addition, an accurate value of this parameter is necessary for a precise identification of thermal properties. But until now, the thermal exchange radius is usually estimated but not measured. This paper presents an experimental procedure, based on the 3omega-SThM method, to measure its value. We apply this procedure to evaluate the thermal exchange radius of two commercial probes: the well-known Wollaston one and a new probe constituted of a palladium film on a SiO(2) substrate. Finally, presenting silicon nanowire images, we clearly demonstrate that this new probe can reach a spatial resolution better than 100 nm whereas the Wollaston probe hardly reaches a submicronic spatial resolution.

Nanoscale Block Copolymer Ordering Induced by Visible Interferometric Micropatterning: A Route towards Large Scale Block Copolymer 2D Crystals

We have overcome the cost and time consumption limitations of common lithography techniques used to control the self-assembly of block copolymers into highly ordered 2D arrays through the use of a guiding pattern created from a polymeric sub-layer. The guiding pattern is a sinusoidal surface-relief grating interferometrically inscribed onto an azobenzene containing copolymer sub-layer leading to a defect-free single grain of block copolymer domains.

Imaging setup for temperature, topography, and surface displacement measurements of microelectronic devices

We present an imaging system that enables the extraction of three different types of information: First, the topography measurement of an electronic device at rest; then, two other informations are obtained when the same device is submitted to a transient current: on one hand, the induced surface displacement and on the other hand, the qualitative surface temperature variations field. The same bench includes two imaging techniques, one based upon interferometry, the other upon thermoreflectance, both of them using a light-emitting diode as a source of light. Results on a microheater are presented.

Strategies for built-in characterization testing and performance monitoring of analog RF circuits with temperature measurements

This paper presents two approaches to characterize RF circuits with built-in differential temperature measurements, namely the homodyne and heterodyne methods. Both non-invasive methods are analyzed theoretically and discussed with regard to the respective trade-offs associated with practical off-chip methodologies as well as on-chip measurement scenarios. Strategies are defined to extract the center frequency and 1 dB compression point of a narrow-band LNA operating around 1 GHz. The proposed techniques are experimentally demonstrated using a compact and efficient on-chip temperature sensor for built-in test purposes that has a power consumption of 15 μW and a layout area of 0.005 mm 2 in a 0.25 μm CMOS technology. Validating results from off-chip interferometer-based temperature measurements and conventional electrical characterization results are compared with the on-chip measurements, showing the capability of the techniques to estimate the center frequency and 1 dB compression point of the LNA with errors of approximately 6% and 0.5 dB, respectively.

Heterodyne picosecond thermoreflectance applied to nanoscale thermal metrology

Picosecond thermoreflectance is an unprecedented powerful technique for nanoscale heat transfer analysis and metrology, but different sources of artifacts were reported in the literature making this technique difficult to use for long delay (several ns) thermal analysis. We present in this paper a new heterodyne picosecond thermoreflectance (HPTR) technique. As it uses two slightly frequency shifted lasers instead of a mechanical translation stage, it is possible to avoid all artifacts leading to erroneous thermal parameter identifications. The principle and set-up are described as well as the model. The signal delivered by the HPTR experiment is calculated for each excitation configurations, modulating or not the pump beam. We demonstrate the accuracy of the technique in the identification of the thermal conductivity of a 50 nm thick SiO2 layer. Then, we discuss the role of the modulation frequency for nanoscale heat transfer analysis.

Thermoreflectance calibration procedure on a laser diode: application to catastrophic optical facet damage analysis

In this letter, we present a thermoreflectance setup specially designed for the study of the temperature variations of the output facet of a laser diode. Indeed, the temperature of the laser diode is controlled by a Peltier element and the device under test is used as a temperature sensor. We propose a calibration procedure based on electrical measurements combined with optical ones; it leads to the determination of thermoreflectance coefficients and then to absolute temperature variations on a running laser diode. We can hence ensure a proper running of the diode and avoid its catastrophic optical facet damage.