Three-Dimensional Nanothermistors for Thermal Probing

Abstract

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, selfsensing 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.

Mechanical Properties of 3D Nanostructures Obtained by Focused Electron/Ion Beam-Induced Deposition: A Review

“…A more recent example of nanomechanical measurements was demonstrated by Sattelkow et al [128], who used 3D FEBID for the fabrication of freestanding 3D nanoarchitectures in the frame of AFM-based thermal nanoprobes. The authors used a combined approach between finite element simulations and SEM assisted, in situ AFM compression experiments, which revealed the strong implications of the overall design and the fabrication accuracy.…”

“…As for the upper row, these experiments reveal the high demands on nanofabrication to fully exploit the intended mechanical properties. Images were reproduced with permission from reference [128].…”

“…For further studies, ∆α was defined as indicated in blue. Then, this parameter was varied in finite-element simulations, while vertical stiffnesses were calculated as shown in (f) and further validated by experiments (see ref [128]). As evident, even a small ∆α of 5 • implies a four-fold decrease in stiffness, which decays quickly with larger ∆α.…”

Focused Electron Beam-Based 3D Nanoprinting for Scanning Probe Microscopy: A Review

“…As can be seen in Figure 1a, freestanding wires can reveal a blade-like character with the longer dimension of the vertical cross-section being oriented along the electron beam axis. Such non-circular shapes entail spatially inhomogeneous mechanical stiffness, which can become detrimental during AFM measurements, where the structure twisting or inhomogeneous bending convolutes the final image [66]. Perfectly circular shapes only arise for vertical pillars deposited via stationary exposure, while conversely, inclined segments reveal a non-linear variation of its thickness-to-width aspect ratio.…”

“…This topic is reviewed in great detail by Utke et al in another article of this special issue, which gives a comprehensive insight into mechanical properties, and their dependency on fabrication and on post-growth treatment approaches [92]. In brief, FEBID pillars are much stiffer along the main axis compared to situations where lateral forces become relevant [66]. As the latter depends on the pillar lengths as well, single-pillar-like FEBID structures should be as long as needed, but as short as possible.…”