Giant reduction in lateral thermal conductivity of thin nitride/silicon/oxide membrane measured with a suspended micro structure

A suspended micro structure, a thermal bridge, was developed for measurement of lateral thermal conductivity of membrane materials. Integration of several polysilicon thermal elements (heaters and temperature sensors) with a membrane in a thermal bridge makes direct and accurate measurement of lateral thermal conductivity possible. A multilayer membrane composed of a layer of silicon nitride, a layer of monocrystalline silicon and a layer of silicon oxide was tested. Two measuring methods, a small signal differential method and an equivalent circuit method, were employed for evaluation of the thermal conductivity. The two-dimensional thermal conductivity of the membrane was found Io be 0.34 × 10^-6 W / K. This yields a lateral thermal conductivity of less than 2.2 W / m K for the silicon layer sandwiched in the membrane. In contrast, the thermal conductivity for bulk silicon is 148 W / m K. The accuracy of the result is also discussed.