EFuse

In computing, an eFuse (electronic fuse) is a microscopic fuse put into a computer chip. This technology was invented by IBM in 2004{{Cite web |title=IBM’s eFuse technology portends adaptable chips |url=https://www.eetimes.com/ibms-efuse-technology-portends-adaptable-chips-2/}} to allow for the dynamic real-time reprogramming of chips. In the abstract, computer logic is generally "etched" or "hard-wired" onto a chip and cannot be changed after the chip has finished being manufactured. By utilizing a set of eFuses, a chip manufacturer can allow for the circuits on a chip to change while it is in operation.{{cite web |author=DCC |title=Method and apparatus for causing an open circuit in a conductive line |date=1989-03-14 |url=http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=4,962,294.PN.&OS=PN/4,962,294&RS=PN/4,962,294 |archiveurl=https://web.archive.org/web/20170211141010/http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1 |archivedate=2017-02-11 }}

Mechanism of action

eFuses can be made out of silicon or metal traces. In both cases, they work (blow) by electromigration, the phenomenon where electric flow causes the conductor material to move. Although electromigration is generally undesired in chip design as it causes failures, eFuses are made of weak traces that are designed to fail before others do.{{cite web |last1=Smith |first1=Tony |title=IBM eFuse to yield self-repairing, self-regulating CPUs |url=https://www.theregister.com/2004/08/02/ibm_efuse/ |website=The Register |language=en}}{{cite web |title=Examining metal eFuses |url=https://archive.eetasia.com/www.eetasia.com/ART_8800717286_499485_TA_9b84ce1d.HTM |website=EETAsia |access-date=2020-12-30 |archive-date=2021-06-14 |archive-url=https://web.archive.org/web/20210614125738/https://archive.eetasia.com/www.eetasia.com/ART_8800717286_499485_TA_9b84ce1d.HTM |url-status=dead }}

Uses

eFuses were initially marketed by IBM as a way to provide in-chip performance tuning. If certain sub-systems fail, or are taking too long to respond, or are consuming too much power, the chip can instantly change its behavior by blowing an eFUSE.{{cite web |publisher=IBM |title=IBM introduces chip morphing technology |date=2004-07-30 |accessdate=2009-09-17 |url=http://www-304.ibm.com/jct03001c/press/us/en/pressrelease/7246.wss |archive-url=https://web.archive.org/web/20100724095358/http://www-304.ibm.com/jct03001c/press/us/en/pressrelease/7246.wss |archive-date=2010-07-24 |url-status=dead }}{{cite journal |first=Otis |last=Port |journal=BusinessWeek |title=Mighty Morphing Power Processors |date=2005-06-06 |url=http://www.businessweek.com/magazine/content/05_23/b3936081_mz018.htm|archive-url=https://web.archive.org/web/20050529023836/http://www.businessweek.com/magazine/content/05_23/b3936081_mz018.htm|url-status=dead|archive-date=May 29, 2005}} Today, most eFuses are used to etch serialization or calibration data onto a chip thus making it a read-only value.{{cite web |publisher=Espressif |title=Espressif ESP-IDF esp_mac.h |date=2023-06-08 |accessdate=2023-11-07 |url=https://github.com/espressif/esp-idf/blob/master/components/esp_hw_support/include/esp_mac.h}}

Descriptive term

eFuses are perhaps more commonly used as a one-time programmable ROM or write-restricted memory, and not actual physical electric fuses. This ranges from writing unique information onto CPUs, or in the case of game consoles and other restricted hardware, preventing downgrades by permanently recording a newer version. The Xbox 360, Nintendo Switch, Pixel 6 and Samsung Galaxy S22 are known for using eFuses this way.{{Cite web |last=Amadeo |first=Ron |date=2022-08-31 |title=Google gives developers a way to sidestep Android 13’s one-way update |url=https://arstechnica.com/gadgets/2022/08/google-gives-developers-a-way-to-sidestep-android-13s-one-way-update/ |access-date=2022-09-04 |website=Ars Technica |language=en-us}}

Implementations

eFuses used for performance adjustment or unique IDs:

IBM POWER5 and POWER6 high-end RISC processors; probably all newer models
IBM System z9 and System z10 mainframe processors{{cite journal |last1=Rizzolo |first1=R. F. |last2=Foote |first2=T. G. |title=IBM System z9 eFUSE applications and methodology |journal=IBM Journal of Research and Development |date=2007-02-13 |volume=51 |pages=65–75 |accessdate=2007-02-28 |url=http://www.research.ibm.com/journal/rd/511/rizzolo.html |doi=10.1147/rd.511.0065|display-authors=etal|url-access=subscription }}
Sony/Toshiba/IBM Cell used in PlayStation 3. Not claimed to be used for downgrade prevention.
Intel Westmere CPUs; probably all newer models
TI MSP430 MCU family for Unique IDs.
TI FPD-Link SERDES for a variety of different settings.

eFuses known to be used for hardware restriction:

IBM/Microsoft Xenon CPU in the Xbox 360 game console. 768{{nbsp}}bits of fuses.{{cite web |title=Understanding the Xbox 360's Fusesets |url=https://free60.org/Hardware/Fusesets/ |website=Free60 Wiki}}{{cite web |author=Speedy22|title=XBOX 360 CPU Datasheet. Version 1.5. |date=2006-03-07 |accessdate=2007-02-28 |url=http://dwl.xbox-scene.com/tutorial/XBOX360cpu15data.pdf |archiveurl=https://web.archive.org/web/20060315071537/http://dwl.xbox-scene.com/tutorial/XBOX360cpu15data.pdf |archivedate=2006-03-15 }}{{cite web |publisher=IBM |title=IBM delivers Power-based chip for Microsoft Xbox 360 worldwide launch |date=2005-10-25 |accessdate=2007-02-28 |url=http://www-03.ibm.com/chips/news/2005/1025_xbox.html |archiveurl=https://web.archive.org/web/20070311071013/http://www-03.ibm.com/chips/news/2005/1025_xbox.html |archivedate=2007-03-11 }}
Samsung Knox devices use an eFuse to detect if a non-Samsung boot path has ever been run. {{Cite web |title=What is a Knox Warranty Bit and how is it triggered? |url=https://docs.samsungknox.com/admin/knox-platform-for-enterprise/faq/#what-is-a-knox-warranty-bit-and-how-is-it-triggered |access-date=2024-07-16 |website=docs.samsungknox.com}}

Variants

Resettable eFuses are used for protecting circuits. They act similarly to resettable fuses, and are generally shipped as a standalone chip package.{{cite web |title=E-fuses |url=https://www.st.com/en/power-management/e-fuses.html |website=STMicroelectronics |language=en}}

There are several ways of implementing an antifuse in silicon: see {{section link|Antifuse|Antifuses in integrated circuits}}.

References

Category:IBM computer hardware