Trident™ Thermal Conductivity Application Highlight: Measuring Thin Film Samples using Flex TPS Sensor

The following Application Highlight addresses the measurement of polymeric thin films using the Flex Transient Plane Source (TPS) sensor and the Thin Films utility available on Trident.  

Thin Films are used for a variety of applications in protective optical and electric coatings, thin-film photovoltaic cells and thin film batteries (Figure 1). While thin film materials have existed for decades, thermal conductivity measurement methodologies have traditionally been focused on exploring bulk samples, and the capability to characterize these specialty materials has generally lagged. In recent years, the knowledge gap has shrunk, prompted by new and exciting markets in nano and microscale fabrications where thermal management is significantly important. A novel tool for such characterization is the Transient Plane Source (TPS) adaptation for testing thin films as outlined in ISO 22007-2. 

Figure 1. Thin Films have many applications ranging from flexible electronics, optics, and photovoltaics each with thermal management problems to solve. In this example photo, electronic components are embedded in a thermally insulative and electrically insulative material called Kapton. (Copyright: Wikipedia Commons, 2020).

Using a C-Therm FLEX TPS thermal conductivity sensor and Trident’s Thin Films Utility, the measurement involves testing initially with just the selected backing material. The backing material is selected based on the type of sample being tested - according to the ISO guidance document it should be at least 10 times greater thermal conductivity than the test material.i This is followed by testing 1 layer of the thin film and then 2 layers of the thin film (in some cases up to 3 layers may be required). The successive addition of the thin film is used to generate a linear regression of temperature rise vs film thickness, which is then used to determine thermal conductivity (k). A general rule of thumb for the number of tested layers is to have a total layered thickness less than 1000 mm for best results. Measurement validation is determined by the line of best fit and an R2 value of at least 0.999 is required. The TPS method requires only a few layers of film to achieve a valid result, making it appealing for such characterization. The procedure does require an accurate measurement of the film thickness (± 1 µm) to achieve a high-quality result. 

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