Anisotropic Thermal Conductivity Measurement of Organic Thin Film with Bidirectional 3omega Method

TL;DR

This paper introduces a novel bidirectional 3omega method to measure anisotropic thermal conductivity in ultra-thin organic films, enabling separate evaluation of in-plane and cross-plane conductivities crucial for electronic applications.

Contribution

The study develops a new measurement system that accurately assesses anisotropic thermal conductivity in thin films by using patterned metal wires of different widths.

Findings

Measured in-plane thermal conductivity of PEDOT:PSS was 2.9 W/m·K.

Achieved anisotropy ratio of 10 in the thermal conductivity.

System can be adapted for even thinner films with smaller wire widths.

Abstract

Organic thin film materials with molecular ordering are gaining attention as they exhibit semiconductor characteristics. When using them for electronics, the thermal management becomes important, where heat dissipation is directional owning to the anisotropic thermal conductivity arising from the molecular ordering. However, it is difficult to evaluate the anisotropy by simultaneously measuring in-plane and cross-plane thermal conductivities of the film on a substrate, because the film is typically as thin as tens to hundreds of nanometers and its in-plane thermal conductivity is low. Here, we develop a novel bidirectional 3{\omega} system that measures the anisotropic thermal conductivity of thin films by patterning two metal wires with different widths and preparing the films on top, and extracting the in-plane and cross-plane thermal conductivities using the difference in their sensitivities to the metal-wire width. Using the developed system, the thermal conductivity of spin-coated poly(3,4-ethylenedioxythiophene) olystyrene sulfonate (PEDOT:PSS) with thickness of 70 nm was successfully measured. The measured in-plane thermal conductivity of PEDOT:PSS film was as high as 2.9 W m-1 K-1 presumably due to the high structural ordering, giving anisotropy of 10. The calculations of measurement sensitivity to the film thickness and thermal conductivities suggest that the device can be applied to much thinner films by utilizing metal wires with smaller width.