A method for tailoring amorphous and crystalline states of phase-change memory cells based on digital bidirectional pulses

Abstract

The invention discloses a phase change storage unit amorphous state and crystalline state cutting method based on digital bidirectional pulses. Through application of a RESET pulse and a SET pulse with different polarities on two electrodes of a phase change storage unit, the volume of the non-crystallizing region in the phase change storage unit changes under action of the pulse modulation effect, and the shape is similar to a cylinder. Through adjustment of amplitudes, widths, intervals and polarities of two electric pulses, the resistance and the pulse modulation mode of the phase change storage unit are in a linear relation. The RESET pulse and the SET pulse with different polarities are employed to apply on two electrodes of the phase change storage unit respectively or at the same time to achieve a cylindrical non-crystallizing region, thus the non-crystallizing resistance and the pulse modulation mode are in a linear relation, and accurate control of the non-crystallizing resistance is achieved. The generated temperature gradient extends to the temperature of the non-crystallizing region and is less than the crystallization temperature, annealing processing of the non-crystallizing region can be achieved, and the problems of resistance drift and random fluctuation are reduced effectively.

Description

technical field [0001] The invention belongs to the field of microelectronics, and more specifically relates to a method for tailoring the amorphous state and the crystalline state of a phase-change memory unit based on digital bidirectional pulses. Background technique [0002] Since Stanford R. Ovshinsky discovered in 1968 that phase change materials can reversibly change between crystalline and amorphous states, phase change materials have been successfully applied in optical storage CD-RW and DVD. Phase-change materials use the Joule heat generated by the applied electric pulse to control the transition of phase-change materials from crystalline to amorphous states, and the difference in resistance between the two forms makes them useful for storing information. From the material's point of view, the applied electrical pulse is actually a tailoring of the material's crystalline or amorphous state. [0003] At present, the methods of electric pulse tailoring of phase cha...

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Problems solved by technology

According to the resistance formula R=ρL / A (ρ is the resistivity of the bulk material, L is the length of the block, and A is the cross-sectional area of ​​the block), it can be seen that the estimation of the amorphous state resistance is more complicated, because the mushroom along the direction from the bottom to the top electrode The cross-sectional area at different positions of the shape gradually decreases. As the mushroom shape grows, both L and A are changing. The amorphous resistance will be affected by the length and the cross-sectional area at the same time. In addition, the cutting near the heating end and far away from the heating end The choice of the applied pulse parameters is very different, which also adds difficulties to the optimization of the pulse

In particular, the starting point of this type of pulse application is to tailor the amorphous or crystalline state, and the problem of resistance drift suppression is not considered at all.

[0004] Therefore, it is difficult to precisely control the amorphous resistance by the above-mentioned tailoring method, and it is even more difficult to control its linear change at the nanoscale.

On the other hand, the relaxation of the amorphous structure formed by the Joule heat generated by the unipolar pulse will also have a negative impact on the performance of the phase change memory cell.

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