Extracting the temperature distribution on a phase-change memory cell during crystallization

Phase-change memory (PCM) devices are enabled by amorphization- and crystallization-induced changes in the devices' electrical resistances. Amorphization is achieved by melting and quenching the active volume using short duration electrical pulses (∼ns). The crystallization (set) pulse duration, however, is much longer and depends on the cell temperature reached during the pulse. Hence, the temperature-dependent crystallization process of the phase-change materials at the device level has to be well characterized to achieve fast PCM operations. A main challenge is determining the cell temperature during crystallization. Here, we report extraction of the temperature distribution on a lateral PCM cell during a set pulse using measured voltage-current characteristics and thermal modelling. The effect of the thermal properties of materials on the extracted cell temperature is also studied, and a better cell design is proposed for more accurate temperature extraction. The demonstrated study provides promising results for characterization of the temperature-dependent crystallization process within a cell. � 2016 Author(s)

Understanding the Structure and Reactivity of Mixed Titanium(IV) Alkoxide and Tin(II)/(IV) Carboxylates as Esterification Catalysts

A set of new compounds are formed upon mixing of titanium­(IV) alkoxides with tin­(II) dicarboxylates or tin­(IV) dialkyl dicarboxylates. These mixed Ti/Sn catalysts outperform titanium alkoxides or tin complexes alone as polyesterification catalysts. However, the tin complexes employed are toxic, and efforts are underway to remove them from environmental circulation. This study elucidates the structures generated of mixed Ti/Sn complexes and how they lead to improved reactivity. A suite of characterization techniques was utilized in structural elucidation including 1H, 13C­{1H}, and 119Sn NMR, as well as 13C–1H HSQC, 1H–1H COSY, 119Sn–1H HMQC (heteronuclear multiple quantum coherence), DOSY (diffusion-ordered spectroscopy) NMR, and ASAP-MS (atmospheric solids analysis probe–mass spectrometry). These characterization techniques led to the identification of Sn–Ti heterobimetallic dimers, regardless of the tin source (viz., Sn­(II) or Sn­(IV)). The greater stability of the catalysts to agglomeration was identified ex situ by UV–vis spectroscopy by observing colloid formation. Probe reactions of Fischer esterification and transesterification were used to characterize catalyst robustness under reaction conditions and catalyst activity relative to pure Ti or Sn complexes. This set of techniques allows for characterization of nontrivial mixed esterification catalysts and will be able to be applied to nontoxic mixtures in the future as a step toward improving sustainable catalysis