Memories, both volatile and non-volatile are a critical element in various computing and logic devices, since that is where the data lives that is being processed. The mass market for memory technologies serves consumer, industrial and enterprise applications (including in data centers), but computing at temperature extremes, both very cold temperatures and very high temperatures are important for quantum computing (generally at very cold temperatures) and for extreme temperature and environmental applications.
I have written in the past about possible technologies to enable quantum computing memories. In this article we will talk about memories for extreme temperature applications.
This article is based upon a recently published Nature Reviews Materials article, Materials for High Temperature Digital Electronics. This review article goes into depth on the various factors that to into creating volatile and non-volatile memories for extreme temperature applications, particularly for high temperature applications.
Consumer memories begin to lose performance around 85C, begins to degrade around 150C and rapidly degrades at 210C. These temperatures are acceptable for most computer applications, but not in extreme environments.
The table below, from the article, gives some insights into applications with temperatures up to 1,000C. Electronic packaging with organic materials is only good up to about 150C, beyond that temperature various ceramic packaging technologies are required. These applications include logic and computing devices for automotive, oil exploration and geothermal applications, interplanetary exploration, nuclear reactors and aerospace applications.
Regarding non-volatile memory, NVM, for very high-temperature applications, the figure below shows several important memory characteristics as a function of temperature for the mostly likely memory technologies for higher temperatures. These are data retention, in seconds), read endurance, in cycles and on/off ratio.
Magnetic random-access memory (MRAM) and phase change memories are limited by their Curie temperatures and phase change temperatures, although MRAM products are now available as embedded memory for automotive applications. The best non-volatile memory candidates for high temperatures, the green regions in the figures below are special types of NOR flash, ferroelectric memories and resistive memories.
In particular, nitride ferroelectric NVM, particularly in wurtzite-structured nitrides and oxides, appears to be the most promising technology. However more work needs to be done with these memories, particularly in the on/off ratio.
It should be noted that for these high temperature applications traditional silicon substrates won’t work. For these applications wide bandgap semiconductor materials are required such as SiC and GaN, especially to support device operation at 850C or higher.
The chart below shows feature size scaling trends for regular commercial semiconductors and high temperature semiconductor devices. Packaging and interconnect as well as technical issues and particularly the low demand for high temperature electronic devices limit the feature size and thus the achievable density for semiconductors operating at very high temperatures.
It is obvious that high temperature devices tend to lag silicon devices operating at lower temperatures, on a logarithmic scale. The various issues in making high temperature semiconductor devices limits their use to aerospace, avionics, automotive, oil/gas exploration and nuclear power applications. The low volume of these applications slows the miniaturization and performance of these applications compared to higher volume applications.
High temperature volatile and non-volatile memories are important for aerospace, avionics, automotive, oil/gas exploration and nuclear power applications but these applications require new materials, interconnects, packaging and manufacturing processes
