New insights on crystalization in PCM materials revealed by in situ TEM

Original article by Kun Ren, Yan Cheng, Mengjiao Xia, Shilong Lv, Zhitang Song. Published in Ceramics International, volume 45, issue 15.

In this work the DENSsolutions in situ TEM Lightning system (8 contact, heating and biasing) has been employed by customers from Hangzhou Dianzi University and East China Normal University, China to study the temperature induced nucleation behavior in Ge₂Se₂Te₅ samples In Situ. This material is used as Phase Change Memory (PCM) and the knowledge of the amorphous-to-crystallize transition and the crystallization behavior is essential to its application, especially in nanometer or sub-nanometer modern and future electronics.

Fig. 1. (a) Temperature profile of the thermal pulse applied on the sample, the maximum temperature is 204 °C. (b)–(j) TEM images of the sample at different stages of the heating pulse, with the timestamp shown in the lower right. The scale bar denotes 100 nm. Crystallization directions are marked by red arrows. 

TEM images of the sample at different stages of the heating pulse, with the timestamp shown in the lower right. The scale bar denotes 100 nm. Crystallization directions are marked by red arrows. 

Using fast thermal pulses of 185 °C – 204 °C applied to a FIB lamella, placed on the MEMS-based Nano-chip it was possible to follow the nucleation dynamics in real time and reveal the heterogeneous nature of the nucleation, e.g. crystallization at the interface and the interior of the sample. This distinguished behavior of Ge₂Se₂Te₅ is caused by in-situ deposition of the sample thus avoiding the formation of the covalent bonds between the PCM material and the substrate. Formation of a passivation layer at the PCM-substrate interface can lead to an enhancement of the switching speed in memory with decreasing the cell size.

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