Micron has own take on novel selector-only memory

Technology News | March 25, 2024

By Peter Clarke

Analog Materials & processes Memory & Data Storage

Micron Technology Inc. (Boise, Idaho) has developed its own version of a novel type of memory based on Ovonic Threshold Selector (OTS) devices.

Micron discussed the technology, which it calls Single-chalcogenide X-Point Memory (SXM), in an invited paper at the International Electron Devices Meeting held in December, 2023. The paper is entitled Status and Perspectives of Chalcogenide-based Cross-Point Memories.

The technology reported on is similar to developments at SK Hynix, dubbed selector-only memory (SOM), and at Samsung, called self-selecting memory (SSM), which were presented in the same session at IEDM (see Selector-only memory gains advocates, including SK Hynix).

The selector-only memory (SOM, SSM or SXM) is based on chalcogenide phase-change material in Ovonic Threshold Selector devices (OTS) that were used in 3D XPoint phase-change memories and that are used for various ReRAM devices.

Conventionally a transistor or diode “selector” device is used to select a memory cell within an array and to prevent “sneak paths” through the array that would bypass the selected cell. However, researchers at Micron and elsewhere have observed that an OTS device could show a variable threshold voltage depending on the polarity of a previous voltage pulse. This memory effect in the diode allows the device to perform the tasks of both memory cell and selector and promises the development of a simpler and lower power crosspoint memory. This could combine something close to the areal density and read latency of DRAM with the non-volatility of phase-change memory.

3D XPoint experience

Micron already has extensive experience of working with chalcogenide phase change materials having collaborated with Intel on the manufacturing of 3D XPoint phase-change memory. However that memory met with limited success and was eventually dropped.

It is now revealed that Micron has also been working on the selector-only SXM technology since before it announced the decision to cease development of 3D XPoint memory in March 2021 (see Micron turns its back on 3D-XPoint, puts fab up for sale). At that time Micron said “With immediate effect, Micron will cease development of 3D XPoint and shift resources to focus on accelerating market introduction of CXL-enabled memory products.”

256Gbit 4-deck SXM on a 20nm half-pitch. Source: Micron Technology.

In the invited paper at IEDM Micron researchers reported on a 4-deck 256Gbit SXM component on a 20nm half-pitch and referenced patents on the technology dating back to 2018. An endurance reliability of 15 million cycles is reported as well as a retention of 7 years at 40 degrees C. It is notable that the cross-sectional scanning electron micrography of the 256Gbit component is dated August 2019.

While there is no indication that Micron is committed to manufacturing such a memory commercially, the company did discuss the market introduction of CXL-enabled memory products in its 2021 press release. Selector-only memories have been described as being suited to meeting CXL memory requirements.

The Micron researchers make the point that the simplified cell structure of SXM that requires a single thin chalcogenide layer placed in between two electrodes could ease a transition from the planar multi-deck cross-point architecture of 3D XPoint to a 3D-NAND-like multi-tier vertical architecture thereby increasing the competitiveness of SXM.

The authors conclude in the paper that the technology has “a very high potential for future market opportunities.”