Abstract
This article presents three photothermal methods dedicated to the measurement of the thermal properties of chalcogenide alloys, used as a central element in the new generations of non-volatile memory. These materials have two phases, amorphous and crystalline, possessing a sharp contrast in their electrical and thermal properties. In the crystalline phase, the properties also change very significantly with temperature. The control of the temperature of the samples, the choice of transducers, and the time or frequency characteristic values of the photothermal excitation are thoroughly discussed. Each photothermal technique is described from the experimental point of view as well as from the inverse method, performed to identify the parameters of interest. The identified thermal properties mainly concern the thermal conductivity and the thermal resistance at the interfaces between the phase-change materials and the materials in contact as encountered in the production of the microelectronic memory device. Assessing various photothermal techniques, the study suggests that pulsed photothermal radiometry is the most effective method for sensitive high-temperature measurements of thermal properties of the phase-change materials.
Highlights
The phase-change materials (PCMs) have been largely studied for several years because of their useful implementation within the field of non-volatile memories,[1,2,3,4] leading to the phase-change RAM or PCRAM
We proposed a review of the latest developments achieved for three photothermal radiometry methods used for the measurement of thermal properties as the thermal conductivity of phase-change chalcogenide alloys and related thermal boundary resistances
Those methods are complementary in terms of improving the accuracy of the seek parameters and to discriminate the thermal resistance at the interfaces between the PCM and the adjacent layers that are the metallic dielectrics and electrodes of the PCRAM cell. These methods are much more effective than contact methods (3ω and scanning thermal microscopy (SThM)) when we want to measure the changes in these thermal properties at high temperatures, above the phase-change temperature
Summary
The phase-change materials (PCMs) have been largely studied for several years because of their useful implementation within the field of non-volatile memories,[1,2,3,4] leading to the phase-change RAM or PCRAM. It allows for the design of the memory cell in order to avoid the thermal crosstalk effects with neighboring cells.[19,20] The measurement of PCM thermal conductivity must be performed over the entire temperature range including the amorphous-crystalline phase transition and up to the melting temperature It is well-established that the thermal boundary resistance (TBR) at the interfaces between the PCM microvolume and neighboring materials, such as the dielectrics and metal electrodes, has a comparable influence than that of the thermal conductivity on the heat transfer within the device.[19,21,22,23] It must be emphasized that, when the characteristic dimension of the system becomes comparable to or less than the average mean free path of the elementary heat carriers (phonons and electrons), the thermal conductivity has no longer physical meaning from the point of view of Fourier’s law. A typical case for the PCRAM application is the stack formed by the metal electrode, the PCM layer, and the dielectrics material that ensures electrical and thermal insulation of the operating cell
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