One-Dimensional Thickness Scaling Study of Phase Change Material $(\hbox{Ge}_{2}\hbox{Sb}_{2}\hbox{Te}_{5})$ Using a Pseudo 3-Terminal Device

To address the scalability of phase change memory (PCM), we study a 1-D thickness scaling effect on threshold switching voltage (<i>V</i>_th), <i>V</i>_th drift, high resistance state (RESET) resistance (<i>R</i>_RESET) drift, and crystallization temperature (<i>T</i>_crys). We use a pseudo three-terminal device to accurately correlate the amorphous region thickness to the observed characteristics. The pseudo 3-terminal device is a fully functional PCM cell and enables 1-D thickness scaling study down to 6 nm without the need for ultrafine lithography. <i>V</i>_th scales down to 0.65-0.5 V (at 25°C-75°C) for 6-nm-thick Ge₂Sb₂Te₅ (GST), showing that stable read operation is possible in scaled PCM devices. The <i>V</i>_th drift measurement suggests that <i>V</i>_th drift can be attributed to threshold switching field (<i>E</i>_th) drift, whereas <i>V</i>_th0, i.e., <i>V</i>_th at zero thickness, stays almost constant. <i>R</i>_RESET drift shows no dependence on the amorphous GST thickness. <i>T</i>_crys is ~175°C for the device with 6-nm-thick GST, compared with ~145°C of thick GST. From the 1-D scaling study, no significant hurdles against scaling are found down to 6 nm. Further study of scaling effect on endurance and development of scalable selection device is needed to assess the ultimate scalability of PCM.