Parasitic capacitance effect on programming performance of phase change random access memory devices

Parasitic capacitance has increasing implications on the programming performance of phase change random access memory (PCRAM) devices due to increased scaling and high frequency operation. PCRAM devices with larger parasitic capacitance were found to require higher applied voltage to amorphize due to a larger leakage current. The quenching time is also increased due to a longer voltage fall time during amorphization, resulting in a partially crystallized amorphous state. This partial amorphous state requires a lower applied voltage for crystallization, which means improved crystallization performance at the expense of amorphization. Multilevel devices could be implemented by varying the parasitic capacitance to achieve different amorphous resistance.