# Thin Film

## Measurement of coatings and stand-alone films

When measuring thermal transport properties of a thin-film of coating a special thin-film sensor is used. It is a plane sensor consisting of a resistive pattern etched out of a 10 µm thick Nickel foil. The pattern is covered on both sides by an insulation material to give mechanical strength to the sensor and to allow measurements on electrical conducting materials.

Given a certain output of power in the sensor, the temperature increase of the ”sensing”, nickel pattern can be divided into two parts, which is particularly obvious if a metallic sample with high thermal conductivity is being studied. One part of the temperature increase is the temperature drop across the insulating layer and the other part is the transient increase of the temperature of the metal surface.

The temperature drop across the insulating layer becomes constant after a short initial period
of the transient. The reason is that a) the output of power from the ”sensing” material, b) the thickness and c) the area of the insulating material all are constant. The reason why it takes a short period of time for the temperature drop across the insulating layer to become constant is that the sensor has a small but finite heat capacity. The details of the theory are given in the reference below.

According to the theory given in this reference the thermal conductivity of the thin sample material can then be extracted from the following formula:

where P is the total output of power, A is the area of the conducting pattern, Lambda is the thermal conductivity of the thin sample, ΔT is the fully developed temperature difference across one of the insulating layers and Δx is the thickness of the thin sample pieces.

Equation 1 shows the importance of determining all the parameters accurately in order to receive satisfactory results. Before running an experiment, the software will request the user to specify the thickness of the thin sheet sample material. For optimum results, an accuracy of +/- 0.5 µm is required.

## Specifications

### TPS 3500

 Thermal Range: 0.01 to 5 W/mK Temperature: -160°C to 300°C Thickness Range: 0.01 to 1 mm Minimum Dimensions: 22 mm diameter or square

### TPS 2500 S

 Thermal Range: 0.01 to 5 W/mK Temperature: -160°C to 300°C Thickness Range: 0.02 to 1 mm Minimum Dimensions: 22 mm diameter or square

### TPS 2200

 Thermal Range: 0.01 to 5 W/mK Temperature: -160°C to 300°C Thickness Range: 0.02 to 1 mm Minimum Dimensions: 22 mm diameter or square