An Improved Electrical Switching and Phase-Transition Model for Scanning Probe Phase-Change Memory

Abstract

Scanning probe phase-change memory (SPPCM) has been widely considered as one of the most promising candidates for next-generation data storage devices due to its fast switching time, low power consumption, and potential for ultra-high density. Development of a comprehensive model able to accurately describe all the physical processes involved in SPPCM operations is therefore vital to provide researchers with an effective route for device optimization. In this paper, we introduce a pseudo-three-dimensional model to simulate the electrothermal and phase-transition phenomena observed during the SPPCM writing process by simultaneously solving Laplace’s equation to model the electrical process, the classical heat transfer equation, and a rate equation to model phase transitions. The crystalline bit region of a typical probe system and the resulting current-voltage curve obtained from simulations of the writing process showed good agreement with experimental results obtained under an equivalent configuration, demonstrating the validity of the proposed model.

Amorphization Optimization of Ge2Sb2Te5 Media for Electrical Probe Memory Applications

“…In addition to multi-bit recording, the erasure of a previously written amorphous bit (i.e., recrystallization) was also simulated, leading to Figure 7 . Clearly, such an erasing process involves crystallization kinetics which can be accurately modelled by simultaneously solving a set of coupled equations, including the Laplace equation, the heat conduction equation, and the crystallization rate equation, all of which have been previously proposed for the optimization in the writing of crystalline bits [ 10 ] and, consequently, have not been repeated here. According to Figure 7 , by choosing the appropriate erasing pulse (4 V of 100 ns here), the previously written amorphous bit could be completely recrystallized without adversely re-amorphizing the surrounding crystalline background (i.e., the temperature inside the surrounding crystalline region did not exceed the melting point).…”

“…Accordingly, a typical electrical probe memory consists of a conductive probe and a trilayer stack, which is made up of a Ge 2 Sb 2 Te 5 layer sandwiched by a diamond-like carbon (DLC) layer and a titanium nitride (TiN) bottom electrode, as illustrated in Figure 2 . Such an architecture has been previously used to optimize the writing of crystalline bits [ 9 , 10 ]. A commercial software package based on the finite-element method, i.e., Comsol Multiphysics TM , was deployed to imitate the electrical, thermal, and phase-transformation kinetics which occurred inside the device.…”

“…The advantageous features of the electrical probe memory derive from the use of the nanoscale probe tip, leading to the possibility of securing ultra-high recording density; additionally, the Chalcogenide alloy acts as storage media to provide super-fast phase transition, long data retention, low energy consumption, excellent scalability, and high On/Off resistance contrast [ 3 , 4 ]. Given its performance superiorities over conventional storage devices, the electrical probe memory has recently received considerable attentions from worldwide researchers in the aspects of the experimental fabrication [ 2 , 3 , 4 , 5 , 6 , 7 ] and the theoretical simulation [ 8 , 9 , 10 ]. It should be noted that the majority of previous research concentrated on the phase transition from amorphous to crystalline phases while ignoring the writing of amorphous marks from the crystalline background.…”

Overview of Probe-based Storage Technologies

“…Depending on the adopted architecture of phase-change probe memory, a variety of resulting bit size from 80 to 20 nm has been reported [ 94 – 100 ]. By the time of writing, the maximum areal density of phase-change probe memory that can be achieved experimentally is up to 1 Tbit/in 2 [ 94 ] with corresponding power consumption of 100 PJ per bit [ 95 ], much lower than the thermo-mechanical probe memory.…”