Measurement of the thermal conductivity anisotropy in polyimide films

Abstract

Polymer films are playing an important role in the development of micromachined sensors and actuators, fast logic circuits, and organic optoelectronic devices. The thermal properties of polyimide films govern the temporal response of many micromachined thermomechanical actuators, such as ciliary arrays. This work develops three experimental techniques for measuring both the in-plane and the out-of-plane thermal conductivities of spin-coated polyimide films with thicknesses between 0.5 and 2.5 m, which are common in MEMS. Two of the techniques use transient electrical heating and thermometry in micromachined structures to isolate the in-plane and outof-plane components. These techniques establish confidence in a third, simpler technique, which measures both components independently and uses IC-compatible processing. The data illustrate the anisotropy in the thermal conductivity of the polyimide films investigated here, with the in-plane conductivity larger by a factor between four and eight depending on film thickness and temperature. The anisotropy diminishes the time constants of thermal actuators made from polyimide films. [375]

Experimental Verification of the Formation Mechanism for Pillar Arrays in Nanofilms Subject to Large Thermal Gradients

“…The solid (black) curve is the TC model with fitting constant k p ¼ 0:68 W=m K, which produces excellent agreement. (The value of k p is not expected to change significantly over the film thickness and temperature ranges used in this study [14].) Similar fits for 1:3 kg=mol PS films can be found in the supplemental section [15].…”

“…Birefringence measurements of spun coat and annealed PS films (150 kg=mol, 2:3 m) have established out-ofplane alignment on oxide coated wafers [16]. Additional studies have shown that the thermal conductivity of polymer microscale films can increase by a factor 4-8 in the direction of alignment [14]. Chain alignment is also observed to increase with decreasing molecular weight and decreasing film thickness [17].…”

A review on thermally conductive polymeric composites: classification, measurement, model and equations, mechanism and fabrication methods

“…The λ value of PPy and polythiophene is 5.0 and 3.8 W/mK, respectively, 20-30 times higher than that of non-conjugated polymers. (b) By directional stretching and external electric or magnetic field [108,109], small molecule monomers can form an orderly arrangement via polymerization, increasing order and crystallinity of the polymers, as well as the free path of phonon propagation, finally to realize high λ value of the polymers. Shen [110] reported a polyethylene (PE) material with ultrahigh λ value of 104 W/mK, ascribed to be stretched into PE fibers with the diameter between 50 and 500 nm, far above that of the original PE matrix, also more than some metals.…”

Thermal Characterization of Thin Films for MEMS Applications

“…The method upon which this work is based involves a micromesa test structure, seen in figure 2 and developed by Kurabayashi, et al (1). The geometry that these mesa structures employ limits the heat path to conduction perpendicular to the surface of the substrate with very little excess heat lost from the sides or top of the structures.…”