Three-Dimensional Nanothermistors for Thermal Probing

Accessing the thermal properties of materials or even full devices is a highly relevant topic in research and development. Along with the ongoing trend toward smaller feature sizes, the demands on appropriate instrumentation to access surface temperatures with high thermal and lateral resolution also increase. Scanning thermal microscopy is one of the most powerful technologies to fulfill this task down to the sub-100 nm regime, which, however, strongly depends on the nanoprobe design. In this study, we introduce a three-dimensional (3D) nanoprobe concept, which acts as a nanothermistor to access surface temperatures. Fabrication of nanobridges is done via 3D nanoprinting using focused electron beams, which allows direct-write fabrication on prestructured, self-sensing cantilever. As individual branch dimensions are in the sub-100 nm regime, mechanical stability is first studied by a combined approach of finite-element simulation and scanning electron microscopy-assisted in situ atomic force microscopy (AFM) measurements. After deriving the design rules for mechanically stable 3D nanobridges with vertical stiffness up to 50 N m^-1, a material tuning approach is introduced to increase mechanical wear resistance at the tip apex for high-quality AFM imaging at high scan speeds. Finally, we demonstrate the electrical response in dependence of temperature and find a negative temperature coefficient of -(0.75 ± 0.2) 10^-3 K^-1 and sensing rates of 30 ± 1 ms K^-1 at noise levels of ±0.5 K, which underlines the potential of our concept.