Highly sensitive scanning probes for nanoscale thermal microscopy – TIPTOP

The overall scientific and technological strategy of TIPTOP is divided into five R&D Tasks. It has been chosen to maximize the collaboration between partners.
Task 1 “Fabrication of the probe” addresses the optimization of the NbN thermometry for room temperature measurement, the design, the fabrication and the characterisation of the thermal nanosensor of the new probes. It also addresses a study consolidating the proposed innovative technology so that it leads to a real exploitation potential in terms of patents and for technology transfer.
Task 2 “Probe holder and TCU related to measurements” deals with the development of tools related to the integration of the new probe to the equipment of the industrial partner.
In Task 3 “Fabrication of specific samples for testing and metrology qualification”, focus is on the design, manufacturing and full characterisation of samples, dedicated to SThM tests, by means of various characterization techniques.
Task 4 “Characterization of the SThM measurements” addresses the SThM measurement by means of novel probes and the analysis of the experimental results obtained using modelling (probes and modelling being provided by Task1 and Sub-Task4.2 respectively). This includes the analysis of active samples developed in Task3 and also measurements using current commercial SThM modules for comparison.
The last phase of the project, embodied in Task 5 “Applications”, corresponds to selected application of the new completed SThM technique. This includes the in-depth study of the probe-sample interaction, the measurement of temperature field on active devices and the characterization of thermal properties of nanostructured materials.

After three years of project,
o a large new know-how regarding probe and active sample fabrication have been acquired and novel probes and samples dedicated for their calibration in temperature measurement are available and are currently tested by the consortium.
o Full electro-thermal three-dimensional models were developed for different types of commercially available probes and the novel probe. Based on comparison of simulation results made with such modelling tool with experimental dada we demonstrated the ballistic limit for air conduction.
o A new electrical and SThM probe holder was developed for use of the novel probe in an equipment of the industrial partner who has developed specific electronics and software for SThM measurement.
o The specimens devoted to the showcase of demonstration of the new technologies and then maximize the project impact through dissemination and exploitation are available.

TIPTOP will provide a novel Scanning Probe Microscopy method for thermal metrology at nanoscale. Various issues regarding the impact of nanometre-scale heat transfer on engineered systems justify the importance of developing new experimental methods with this purpose. As for project selected application: advanced thermoelectric converters based on CMOS materials, other key challenging areas of high industrial and fundamental importance include:
- Characterization of the thermal properties of new nanostructured materials with a view to enabling their optimization. Such materials have application as nanostructured solar cells, phase-change memory devices, thermoelectric generators, thermal barriers in nuclear, automotive, aeronautics and aerospace industries. Similarly nano-objects are used for integration as electronic components or in the next generation of Micro&Nano&Opto (possibly quantum) Electromechanical Systems (MEMS, NEMS, etc.).
- Filling of the lacks of understanding of failure mechanisms in micro- or nanoelectronic devices.
- Improvement of the accuracy and validity of prediction tools for the ultra-integrated technologies.
- Characterization of heat transfer between two objects at nanoscales (for MEMS, NEMS,...).
The development of a low-temperature SThM (LT-SThM) is also a very exciting perspective for this project. Indeed, the work done at room temperature for setting up the technology will be used as a solid background for implementing this technology for measurement versus temperature. As mentioned in the project, the performance of the NbN thermometry is even better as the temperature is lowered with TCR above 1K-1 at 1K. This will enable the development of ultra-highly sensitive LT-SThM, a tool that does not exist currently at cryogenic temperature. Measurements of local temperature and thermal conductance at the nanoscale will be possible down to very low temperature (below 10K).

1. R. Swami, J. Paterson, D. Singhal, G. Julié, S. Le-Denmat, J.-F. Motte, G. Hamaoui, A. Alkurdi, J. Yin, J.-F. Robillard, P.-O. Chapuis, S. Gomès, and O. Bourgeois, Highly Sensitive Resistive Thermal Probes for Nanoscale Thermometry, SFT Nanoscale Heat Transport Days, 30-31 janvier 2020, Paris.
2. G. Hamaoui, J. Yin, R. Swami, J. Paterson, J.-F. Robillard, O. Bourgeois, P.-O. Chapuis and S. Gomès, Thermometry via Scanning Thermal Microscopy: Investigation of a topography-free silicon sample with implanted resistive lines, SFT Nanoscale Heat Transport Days, 30-31 janvier 2020, Paris.
3. R. Swami, G. Julié, S. Le-Denmat, J.-F. Motte, J. Paterson, D. Singhal, A. Alkurdi, J. Yin, J.F. Robillard, P.-O. Chapuis, S. Gomès and O. Bourgeois. Development of Highly Sensitive Niobium Nitride Resistive Thermal Probes Nanoscale Scanning Thermal Microscopy, E-MRS Wasaw Poland (2019).
4. J. Yin et al., Nanometer-scale active thermal devices for thermal microscopy probe calibration, ISPM Louvain-La-Neuve, Belgium, 26-29 May 2019,
5. G. Hamaoui, A. Pic, W. Zhao, A. Alkurdi, J. Yin, S. Gallois-Garreignot, Th. Epicier, M. Bugnet, J.F. Robillard, S. Gomès, and P.-O. Chapuis, Nanothermometry by Means of Scanning Thermal Microscopy: Investigation of Electro-thermal Devices with Embedded Metallic Lines, 25th international workshop Thermla Investigation of ICs and Systems, Therminic 2019, Lecco, Italy (2019).
6. O. Bourgeois (Invited oral) Thermal transport at the nanoscale: from quantum transport to thermoelectrics applications, Workshop on Low-dimensional Thermoelectric Materials, Nancy, France (2018).
7. S. Gomès (Invited oral) Scanning Thermal Microscopy: state of the art, main challenges and application to the characterization of TE materials, Workshop on Low-dimensional Thermoelectric Materials, Nancy, France (2018).

Mastering heat transfer in micro and nanoscale materials or devices has become crucial, in particular due to increasing thermomechanical issues and the dependence of many phenomena involving an Arrhenius-type law on local temperature. Despite sustained effort over the two last decades to reach this objective, local thermal characterization at the nanoscale remains a challenge. Scanning Thermal Microscopy (SThM) is a technique derived from Atomic Force Microscopy (AFM) where a thermal sensor is located on the probe. This technique is expected to allow for sub-100 nm spatial resolution. However, the cost to reach such a spatial resolution is usually that the sensitivity of the thermal measurement is not as good as for other techniques.

The TIPTOP project is a 4-year collaborative project aiming at (i) developing a new resistive SThM probe for nanoscale quantitative thermal measurement, (ii) demonstrating the capabilities of the new technique on application-oriented micro and nanostructured materials and systems, (iii) developing an optimized technological French industrial solution.

The solution proposed in TIPTOP is based on the following novelties: (a) the use of a unique type of resistive thermometry using niobium nitride, which has been shown to possess a temperature coefficient of the electrical resistivity (thermal sensitivity) 5 to 10 times higher than competitors, will allow for a strong improvement of the capabilities of SThM. (b) A proper design of the SThM cantilever can also lead to an improvement of SThM, since currently-available cantilevers have not been optimized at all, which results in huge (>95%) thermal losses in SThM probes. (c) The electronics associated to the electrothermal measurements required by thermal characterization can be miniaturized, located closer to the tip, therefore becoming more reliable than solutions available up to now. In addition, SThM is currently a complicated technique with almost no efficient calibration setup and it requires long learning process which often discourages the potential user. In this project, (d) two channels will be followed to remedy this drawback. A set of nanometer-scale active thermal devices based on the electronics technology will be fabricated to facilitate the calibration of the technique. In addition, showcases involving world-class nanomaterials will demonstrate the potential of the TIPTOP SThM solution.

All the work is subtended by acknowledging that nanoscale thermal transport is an open field where many novel physical phenomena can be observed, involving e.g. ballistic transport, Kapitza resistances, adsorbed menisci or near-field thermal radiation. Novel scientific results on these topics are possible only if a strong improvement in the thermal sensitivity is demonstrated. Some results are targeted as an output of TIPTOP.
To reach its objectives, the project consortium gathers three academic research laboratories with complementary expertise in SThM, nanothermal modelling, resistive nanothermometry, instrumentation, metrology and micro and nanofabrication, and one industrial partner strongly involved in the development and manufacturing of Scanning Probe Microscopy (SPM) instruments.

The outputs of TIPTOP will be embodied in (a) the highly-sensitive SThM along with the necessary new instrumentation and (b) the showcase of demonstration on specimens that will be developed to maximize impact through dissemination and exploitation.