We investigate intermediate states of Ge‐rich GeSbTe phase‐change memory (PCM) cells by electrical impedance spectroscopy (EIS) after partial SET and RESET programming. The electrical impedance response is well described by a series resistor and a parallel RC circuit, allowing extraction of state‐dependent resistance and capacitance values. A resistance ratio of ∼250 and a capacitance reduction of ∼85% are observed between RESET and SET states. While resistance can be continuously tuned, capacitance major variation remains confined near the SET state, with crystalline‐dominated cells exhibiting the highest values. Technology computer‐aided design simulations confirm the equivalent circuit and reveal that conduction mainly occurs along the amorphous–crystalline interface. Cells with embedded Ge or Sb grains display the largest capacitances, as these inclusions provide extra conduction pathways and localized charge storage sites that jointly influence the device's resistance and capacitance. Overall, this work demonstrates that the electrical properties of inhomogeneous multiphase PCMs are governed by the complex network of nanoscale heterostructures present in their active regions. It also demonstrates that EIS is a suitable, nondestructive technique for characterizing PCM devices.
Delpoux et al. (Wed,) studied this question.