Thermal Conductivity Measurements on Polycrystalline Silicon Microbridges Using the 3ω Technique

Abstract

The thermal performance of microelectromechanical systems devices is governed by the structure and composition of the constituent materials as well as the geometrical design. With the continued reduction in the characteristic sizes of these devices, experimental determination of the thermal properties becomes more difficult. In this study, the thermal conductivity of polycrystalline silicon (polysilicon) microbridges are measured with the transient 3 technique and compared with measurements on the same structures using a steady state Joule heating technique. The microbridges with lengths from 200 m to 500 m were designed and fabricated using the Sandia National Laboratories SUMMiT V™ surface micromachining process. The advantages and disadvantages of the two experimental methods are examined for suspended microbridge geometries. The differences between the two measurements, which arise from the geometry of the test structures and electrical contacts, are explained by bond pad heating and thermal resistance effects.

Comparison of Thermal Conductivity and Thermal Boundary Conductance Sensitivities in Continuous-Wave and Ultrashort-Pulsed Thermoreflectance Analyses

“…PSTR is not sensitive to G at the Al/SiO 2 interface at any frequencies, and the sensitivity to G at the Al/Si interface is independent of frequency. This is the same result found in studies utilizing the 3ω method [8,29]. The TTR technique is slightly sensitive to G at the Al/SiO 2 interface and shows dynamic sensitivity over the delay time to G at the Al/Si interface.…”

“…When calculating S Λ , it is assumed that G = 100 MW · m −2 · K −1 and C = 1 MJ · m −3 · K −1 ; when calculating S G , Λ is assumed as 100 W · m −1 · K −1 and C is assumed as 1 MJ · m −3 · K −1 (i.e., the thermal diffusivity is assumed as 1 × 10 −4 m 2 · s −1 ). This value of G is assumed when calculating S Λ since it represents an average value commonly observed between nanofilms [1,30], and this value of Λ is assumed when calculating S G since it roughly G is inherently insensitive in the frequency domain (PSTR) for Al/Si and Al/SiO 2 , which follows previous results [8,29] corresponds to the thermal conductivity of Si, which is the most common material used in nanodevices. Over the frequency domain of interest in PSTR and the time domain of interest in TTR, the thermal properties of the Al film do not drastically affect the sensitivity calculations in this work.…”

“…Equation 8 gives the change in temperature as a function of the heating event modulation frequency at the surface of the film.…”

“…However, decreasing length scales increase experimental challenges in thermal measurements [2,3]. For example, traditional electrical contact-based experimental techniques for measuring thermal transport, such as steady-state Joule heating [4,5] or the 3ω method [6,7], are subject to contact resistances that can greatly complicate analyses of thermal transport in nanostructures [8][9][10]. Therefore, optical-based measurement techniques have an advantage over electrical contact-based techniques due to their non-contact nature.…”

Measurement of Thermal Conductivity of PbTe Nanocrystal Coated Glass Fibers by the 3ω Method

“…8−11 The 3ω method has experienced particularly widespread use on samples with high thermal conductivity, such as carbon nanotube bundles, 3 carbon fibers 12 and yarns, 13 platinum wires, 14 and polycrystalline silicon microbridges. 15 However, the 3ω method has not yet been applied to low thermal conductivity wire-like materials such as PbTe-coated glass fibers. Furthermore, while the 3ω method employing a line heater on a substrate has been extended to layered composite planar samples, 16−18 the selfheated wire 3ω technique has not yet been employed to determine the thermal properties of composite fibers.…”