Abstract
Crystal–amorphous transformation achieved via the melt-quench pathway in phase-change memory involves fundamentally inefficient energy conversion events; and this translates to large switching current densities, responsible for chemical segregation and device degradation. Alternatively, introducing defects in the crystalline phase can engineer carrier localization effects enhancing carrier–lattice coupling; and this can efficiently extract work required to introduce bond distortions necessary for amorphization from input electrical energy. Here, by pre-inducing extended defects and thus carrier localization effects in crystalline GeTe via high-energy ion irradiation, we show tremendous improvement in amorphization current densities (0.13–0.6 MA cm−2) compared with the melt-quench strategy (∼50 MA cm−2). We show scaling behaviour and good reversibility on these devices, and explore several intermediate resistance states that are accessible during both amorphization and recrystallization pathways. Existence of multiple resistance states, along with ultralow-power switching and scaling capabilities, makes this approach promising in context of low-power memory and neuromorphic computation.
Highlights
Crystal–amorphous transformation achieved via the melt-quench pathway in phase-change memory involves fundamentally inefficient energy conversion events; and this translates to large switching current densities, responsible for chemical segregation and device degradation
These approaches illustrate intelligent device designs based on geometry and chemical doping, none of them have been able to reduce the high amorphization current densities (B50 MA cm À 2)[7] that are responsible for device degradation issues owing to chemical segregation and heat[11], precluding the widespread commercialization of Phase-change materials (PCMs) technology
Resistivity was evaluated as r 1⁄4 RNWA/ld, where RNW is the resistance of the nanowire obtained by subtracting the contact resistance measured in a multiple probe configuration (Fig. 1a, inset) from the total device resistance. ld and A are the length and cross-sectional area of the nanowire device, respectively
Summary
Crystal–amorphous transformation achieved via the melt-quench pathway in phase-change memory involves fundamentally inefficient energy conversion events; and this translates to large switching current densities, responsible for chemical segregation and device degradation. By pre-inducing extended defects using high-energy He þ ion irradiation, we show for GeTe devices in the crystalline phase that the carriers at EF can be localized, and strongly couple with the lattice[14,15]. These devices transformed to an amorphous phase via the defect-based pathway[13,18], at current densities (js) of 0.13–0.5 MA cm À 2 significantly lower than js 1⁄4 50 MA cm À 2 observed in the melt-quench pathway[6,7]. We illustrate scaling of switching currents with device volumes, and reversible and repeatable low-power switching from defect-engineered crystalline states to amorphous phase
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