Highly Reliable Ring-Type Contact for High-Density Phase Change Memory

Abstract

An advanced bottom electrode contact (BEC) was successfully developed for reliable high-density 256 Mb phase-change random access memory (PRAM) using a ring-type contact scheme. This advanced ring-type BEC was prepared by depositing very thin TiN films inside a contact hole, after which core dielectrics were uniformly filled into the TiN-deposited contact hole. Using this novel contact scheme, it was possible to reduce reset current while maintaining a low set resistance and a uniform cell distribution. Thus, it has been clearly demonstrated that the use of the ring-type contact technology is very feasible for high-density PRAM beyond 256 Mb.

Phase change memory

“…Usually, a very high current is required to generate an adequate energy to switch the cell, especially for RESET operations. To make PCM operate at CMOS compatible voltages, various cell structures have been developed to improve electrical-to-thermal efficiency through device geometry optimization [16,[22][23][24][25][26][27][28]. One effective approach has been to create sub-lithographic features to minimize the volume of the phase change material in the current path through the PCM storage element.…”

“…One effective approach has been to create sub-lithographic features to minimize the volume of the phase change material in the current path through the PCM storage element. Depending on the implementation of the sub-lithographic aperture, PCM cell structures can be divided into two categories ( Figure 4): 1) contact-minimized cells [22][23][24]; and 2) volume-minimized cells [16, 26-29, 31, 32]. Figure 5 shows a mushroom cell, which is a contact-minimized cell [23].…”

The future of phase-change semiconductor memory devices

“…[12]). [17], line-type devices [18], and devices in which the phasechange alloy is confined within a small via formed in a dielectric surround [19]. The confined cell is particularly well suited for high-density memory arrays [20] because of its good scaling characteristics and reduced programming current.…”

Thermal strain imaging of chalcogenide in a phase change memory

“…Among nanofabricated devices, a phase change memory (PCM) switches high-resistive amorphous and low-resistive crystalline states of chalcogenide glasses for memory operation by Joule heating [3]. Rising temperature in the memory cell is an important factor for the device operation.…”

“…If large variations in resistivity were in active areas engaged in device operation or signal lines around the active areas, undesirable Joule heating at the low-resistive parts should degrade or destroy the devices. Signal lines down-sized to several-tens nanometers do not have enough margin for fluctuation in resistivity any longer.Among nanofabricated devices, a phase change memory (PCM) switches high-resistive amorphous and low-resistive crystalline states of chalcogenide glasses for memory operation by Joule heating [3]. Rising temperature in the memory cell is an important factor for the device operation.…”