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We characterized resistance drift in phase change memory devices in the 80 K to 300 K temperature range by performing measurements on 20 nm thick, ∼70–100 nm wide lateral Ge₂Sb₂Te₅(GST) line cells. The cells were amorphized using 1.5–2.5 V pulses with ∼50–100 ns duration leading to ∼0.4–1.1 mA peak reset currents resulting in amorphized lengths between ∼50 and 700 nm. Resistance drift coefficients in the amorphized cells are calculated using constant voltage measurements starting as fast as within a second after amorphization and for 1 h duration. Drift coefficients range between ∼0.02 and 0.1 with significant device-to-device variability and variations during the measurement period. At lower temperatures (higher resistance states) some devices show a complex dynamic behavior, with the resistance repeatedly increasing and decreasing significantly over periods in the order of seconds. These results point to charge trapping and de-trapping events as the cause of resistance drift. 

We model the current density in a semiconductor based on the drift-diffusion transport of the charge carriers to accurately determine the thermoelectric effects in the bulk material (Thomson effect) and material junctions (Peltier effect). We utilize the model to perform 2-D finite element simulations of mushroom phase change memory cell with a critical dimension of 20 nm using temperature and electric field dependent material parameters and analyze the contributions of symmetric Joule heating and asymmetric thermoelectric heats during reset and set operations. We investigate the effect of altering the direction of current flow by changing the connection point between the cell and the access device and observe that, corresponding change in thermoelectric effects cause significant difference in operation dynamics, temperature distribution profiles, amorphous volume, energy requirement and resistance contrast between reset and set states. 

We calculate critical electronic conduction parameters of the amorphous phase of Ge 2 Sb 2 Te 5 (GST), a common material used in phase change memory. We estimate the room temperature bandgap of metastable amorphous GST to be E g (300K) = 1.84 eV based on a temperature dependent energy band model. We estimate the free carrier concentration at the melting temperature utilizing the latent heat of fusion to be 1.47 x 10 22 cm -3 . Using the thin film melt resistivity, we calculate the carrier mobility at melting point as 0.187 cm 2 /V-s. Assuming that metastable amorphous GST is a supercooled liquid with bipolar conduction, we compute the total carrier concentration as a function of temperature and estimate the room temperature free carrier concentration as p(300K) ≈ n(300K) = 1.69×10 17 cm -3 . Free electrons and holes are expected to recombine over time and the stable (drifted) amorphous GST is estimated to have p-type conduction with p(300K) ≈ 6×10 16 cm -3 .