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Pyroelectric Technique for Measurement of Thermal Conductivity

IP.com Disclosure Number: IPCOM000049466D
Original Publication Date: 1982-Jun-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 4 page(s) / 40K

Publishing Venue

IBM

Related People

Melcher, RL: AUTHOR [+2]

Abstract

Use is made of pyroelectric sensors to measure thermal conductivity while avoiding the need for small temperature sensors which are easily adapted to measurement of thin films and layers. Other techniques do not appear to exist at room temperature.

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Pyroelectric Technique for Measurement of Thermal Conductivity

Use is made of pyroelectric sensors to measure thermal conductivity while avoiding the need for small temperature sensors which are easily adapted to measurement of thin films and layers. Other techniques do not appear to exist at room temperature.

The progress of modern integrated circuit technology is limited more by the removal of heat from chips and packages than by the ability to construct densely packed circuits. In optimizing heat removal, knowledge concerning the thermal properties of thin films and layered structures is exceedingly important. Similarly in the aerospace industry the thermal properties of paints, coatings and layers are important. In developing new sources of energy (e.g., solar cells) as well as in more efficiently utilizing existing sources, the thermal properties of thin sheets, layers, coatings or layered structures play an important role.

Numerous techniques exist for measuring the thermal conductivity and diffusivity of bulk materials. These include steady-state, transient and thermal wave techniques. A thorough review of techniques for measurement of thermal conductivity and diffusivity as well as experimental data may be found in (*).

In this article we describe how pyroelectric sensors can be used to measure the thermal properties, particularly the thermal diffusivity, of thin films, layers, etc. In Fig. 1A, we show an embodiment of our technique. Here, a thin layer of material 2 is in intimate thermal contact with a pyroelectric crystal or ceramic substrate 3 which has very thin conducting electrodes 4 on either side. The material 2 is heated by a short burst of energy 1, which is illustrated in Fig. 1B. As the heat absorbed in material 2 diffuses into the pyroelectric substrate 3, a charge is produced on the electrodes 4 which then flows through the load resistor (R(L)) 5 to create a voltage V at terminal 6 which is monitored on a suitable device, such as a digital oscilloscope or other transient recording media. Fig. 2 shows a typical curve of voltage versus time recorded in this way by the pulse in Fig. 1B, both starting at time zero. Analysis of the shape of this curve yields a value for the thermal diffusivity, alpha, of the sample where alpha=k/pC, where k is the thermal conductivity, p the density, and C the heat capacity of the sample. The amplitude of the curve or the area under the curve gives a value for the heat capacity.

Although over-simplified when applied to the present case, the nature of the curve in Fig. 2 is understood from the solution to the thermal diffusion equation in one dimension (see original).

As a function of time this equation is qualitatively of the same form as Fig. 2. The maximum temperature for fixed x occurs at t (max)= (max)=x/2/ /2 alpha. Interpreting x to be the thickness of the sample and alpha its to be thermal diffusivity, one sees that the curve scales as x2/2 alpha.

Numerous experiments have...