Quantitative nanoscale thermal characterization of nano materials and devices by enabling low-noise null-point scanning thermal microscopy

다국어 초록 (Multilingual Abstract)

The application of conventional scanning thermal microscopy (SThM) is severely limited by three major problems: (i) distortion of the measured signal due to heat transfer through the air, (ii) the unknown and variable value of the tip-sample thermal contact resistance, and (iii) perturbation of the sample temperature due to the heat flux through the tip-sample thermal contact. Recently, we proposed null-point scanning thermal microscopy (NP SThM) as a way of overcoming these problems in principle by tracking the thermal equilibrium between the end of the SThM tip and the sample surface. However, in order to obtain high spatial resolution, which is the primary motivation for SThM, NP SThM requires an extremely sensitive SThM probe that can trace the vanishingly small heat flux through the tip-sample nano-thermal contact. Herein, we derive a relation between the spatial resolution and the design parameters of a SThM probe, optimize the thermal and electrical design, and develop a batch-fabrication process. We also quantitatively demonstrate significant sensitivity improvement, lower measurement noise, and higher spatial resolution of the fabricated SThM probes. By utilizing the exceptional performance of these fabricated probes, we show that NP SThM can be used to obtain a quantitative temperature profile with nanoscale resolution independent of the changing tip-sample thermal contact resistance and without perturbation of the sample temperature or distortion due to the heat transfer through the air.
we rigorously re-derived the principal equation of null-point scanning thermal microscopy (NP SThM) in terms of measuring the thermal properties to explain how this technique, which has already been proven to resolve the major problems of conventional SThM and be able to quantitatively measure the temperature profile, can be effectively utilized for quantitatively measuring the local thermal resistance with a nanoscale spatial resolution. Using NP SThM, we measured the relative change in the thermal conductivity of suspended chemical vapor deposition (CVD)-grown graphene disks with radii of 50?3680 nm and estimated the absolute value of the thermal conductivity of these disks in a diffusive regime. We performed a theoretical analysis to demonstrate that the relative changes and absolute values of the thermal conductivity of the graphene disks were consistent.
Finally, by using the NP SThM, we profile the undisturbed temperature distribution around the electrically heated 100 nm-wide platinum nano-heater patterned on SOI wafer and the local spreading thermal resistance qualitatively at the same time. Comparison of the experimental temperature and thermal resistance profiles with those obtained from diffusion equation explains why the local temperature gradient as well as the absolute temperature is higher than the modeling results around the nano-heater. The quantitative data obtained in this study would be an essential reference data for the validation of the theoretical model for thermal analysis in nanoelectronic devices. Furthermore, since NP SThM can profile φ simultaneously as well as the undisturbed temperature, NP SThM would be widely applicable in the analysis of the energy transport/conversion in the nano-devices and nano-materials.

목차 (Table of Contents)

• 1. INTRODUCTION ........................................................................................................................... 1
• 2. ENABLING LOW-NOISE NULL-POINT SCANNING THERMAL MICROSCOPY BY THE OPTIMIEZATION OF SThM PROBE THROUGH A RIGOROUS THEORY OF QUANTITATIVE MEASUREMENT .............................................................................................................................. 5
• 2.1 Spatial resolution of a SThM probe based on a rigorous theory of quantitative
• measurement ........................................................................................................................... 5
• 2.2 Design and fabrication of a SThM probe with high spatial resolution and
• low noise based on a rigorous theory of quantitative measurement ....................................... 9
• 2.3 Evaluation of the performance of the fabricated probe ......................................................... 17
• 2.4 Enabling low-noise, high-resolution NP SThM using fabricated probes .............................. 22
• 3. APPLICATION OF LOW NOISE, HIGH RESOLUTION NULL-POINT SCANNING THERMAL MICROSCOPY ............................................................................................................. 28
• 3.1 Measuring size dependence of thermal conductivity of suspended graphene using
• null-point scanning thermal microscopy ............................................................................... 28
• 3.1.1 Background ................................................................................................................. 28
• 3.1.2 Principle of measuring thermal resistance by NP SThM ............................................ 29
• 3.1.3 Observing the size effect on the thermal conductivity of graphene disk .................... 34
• 3.1.4 Experimental setup and sample fabrication ................................................................ 35
• 3.1.5 Measurement results ................................................................................................... 38
• 3.2 Quantitative temperature profiling across a nano-heater on SOI using
• null-point scanning thermal microscopy ............................................................................... 49
• 3.2.1 Background ................................................................................................................. 49
• 3.2.2 Experimental setup and sample fabrication ................................................................. 51
• 3.2.3 Measurement results and discussion ........................................................................... 54
• 4. CONCLUSION ............................................................................................................................. 61
• APPENDIX A ................................................................................................................................... 65
• APPENDIX B ................................................................................................................................... 68
• APPENDIX C ................................................................................................................................... 70
• APPENDIX D ................................................................................................................................... 73
• APPENDIX E ................................................................................................................................... 74
• REFERENCES .................................................................................................................................. 77
• ABSTRACT (in Korean) ................................................................................................................... 87