One-dimensional thickness scaling study of phase change material (Ge ₂Sb₂Te₅ using a pseudo 3-terminal device

Abstract

To address the scalability of phase change memory (PCM), we study a 1-D thickness scaling effect on threshold switching voltage Vth), V th drift, high resistance state (RESET) resistance (R RESET) drift, and crystallization temperature (Tcrys). 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. Vth scales down to 0.650.5 V (at 25 °C75°C) for 6-nm-thick Ge2Sb 2Te5 (GST), showing that stable read operation is possible in scaled PCM devices. The Vth drift measurement suggests that Vth drift can be attributed to threshold switching field E th drift, whereas Vth0, i.e., Vth at zero thickness, stays almost constant. RRESET drift shows no dependence on the amorphous GST thickness. Tcrys 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. © 2010 IEEE.