相变存储器 Phase-Change Memory (PCM)

转自：https://www.st.com/content/st_com/zh/about/innovation---technology/PCM.html

(嵌入式内存技术正处于十字路口。在FD-SOI和FinFET高级CMOS技术中，传统浮栅嵌入式非易失性存储器（eNVM）的集成在28nm和更小的硅几何结构上是一个重大的技术挑战。新的NVM技术基于特殊外来材料的功能特性，采用了与Flash存储器技术完全不同的物理机制，并为28纳米CMOS转变带来的工艺集成困难提供了更有效的解决方案。在这些常被称为“新兴存储器”的新型NVM技术中，最成熟的是相变存储器（PCM）。

相变记忆的基本机制是由斯坦福·罗伯特·奥夫斯基在20世纪60年代发明的。ST持有原始开发的专利许可证，并在这项突破性工作的基础上发展了15年多，开发了嵌入式PCM解决方案（ePCM），该解决方案如今已集成到我们的28nm FD-SOI技术平台中。

相变存储器是用锗锑碲（GST）合金制成的，它利用了材料在非晶态和晶态之间物理性质的快速热控变化。对应于逻辑0和1的这些状态通过非晶态（逻辑0）中的高电阻和晶态（逻辑1）中的低电阻进行电区分。PCM在低电压下读写，与Flash和其他嵌入式存储器技术相比，它具有许多显著的优势。)

Embedded Memory technologies are at a crossroads. The integration of conventional floating gate embedded Non-Volatile Memories (eNVM) represents a significant technical challenge at 28nm and smaller silicon geometries in both FD-SOI and FinFET advanced CMOS technologies. New NVM technologies, based on the functional properties of particular exotic materials, employ radically different physical mechanisms than those used with Flash memory technologies and provide a more effective solution to the process integration difficulties raised by the disruptive 28nm CMOS transition. Among these new NVM technologies, often called “emerging memories,” the most mature is Phase-Change Memory (PCM).

The fundamental mechanism for Phase-Change Memory was invented in the 1960s by Stanford Robert Ovshinsky. ST holds a license to the patents that resulted from that original development and has built onto that ground-breaking work for more than 15 years, developing the embedded PCM solution (ePCM) that is today integrated into our 28nm FD-SOI technology platform.

Phase-Change Memory is made using a Germanium Antimony Tellurium (GST) alloy, and takes advantage of rapid heat-controlled changes in the material’s physical property between amorphous and crystalline states. These states, which correspond to logic 0 and 1, are electrically differentiated by high resistance in the amorphous state (logic 0) and low resistance in the crystalline state (Logic 1). PCM, which reads and writes at low voltage, offers several substantial advantages over Flash and other embedded memory technologies.

Phase-Change Memory Technology Architecture

Phase-Change Memory (PCM) array

A cross section of the embedded-PCM bitcell integrated in the 28nm FD-SOI technology shows the heater that quickly flips storage cells between crystalline and amorphous states.

Phase-Change Memory Advantages

Write Performance / Data Retention

With single-bit alterability, PCM technology delivers significantly better write and comparable read performance than Flash-based memories that require at least a byte- or sector-erase cycle before reprogramming. This single-bit alterability simplifies software handling of data storage. ST’s implementation benefits from patented technology related to the memory cell and to the GST alloy to support high-temperature data retention, including during solder reflow, so firmware can be uploaded to ePCMs before mounting and soldering.

High Density / Low Power Roadmap

The speed/power characteristics of the ePCM macro-cell and its roadmap at smaller geometries offer a scalable solution for large embedded memories.

Robust Performance

ST’s PCM technology has been developed and tested to operate within the most stringent automotive requirements for robust high-temperature operation, radiation hardening, and data retention. ePCM achieves automotive requirements for AEC-Q100 Grade 0 with an operating temperature up to +165°C.

Flexible Back-end Process

ePCM is a back-end technology which separates the non-volatile memory-cell process module from the complex logic-transistor modules built in the Front-End. As a Back-End, metallization-based process, ePCM is technology-independent, so it can be embedded in virtually any technology node.

FD-SOI and PCM Combined

Fully Depleted Silicon On Insulator, or FD-SOI, another technology that ST pioneered, is a planar process technology that delivers the benefits of reduced silicon geometries while actually simplifying manufacturing. Combining 28nm FD-SOI and PCM enables memory array sizes that are 4-5 times larger than what Flash on bulk 40nm CMOS can achieve.

Phase-Change Memory Applications

Ever more demanding applications are pushing the limits of MCU architectures due to their need for more processing power, lower power consumption, and larger memory sizes. One of the most challenging demands is for larger embedded memories to hold bigger and more complex firmware.

ePCM presents a solution to these chip- and system-level challenges, while meeting automotive requirements for AEC-Q100 Grade 0, operating at temperature up to +165°C. In addition, ST’s technology assures firmware/data retention through high-temperature soldering reflow processes and immunity to radiation, for additional data safety.

ST presented an update on the architecture and performance of a 16Mb ePCM array for a 28nm FD-SOI automotive MCU at the 2018 International Electron Devices Meeting (IEDM) in San Francisco on December 4, 2018.

Truly Innovative 28nm FDSOI Technology for Automotive Microcontroller Applications embedding 16MB Phase Change Memory：https://www.st.com/content/ccc/fragment/multimedia/e-presentation/technology_pres/group0/63/51/83/98/d4/11/40/7b/IEDM_conference_Dec2018_ARNAUD/files/IEDM_conference_Dec2018_ARNAUD.pdf/jcr:content/translations/en.IEDM_conference_Dec2018_ARNAUD.pdf