Programmable ROM: Difference between revisions

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{{Memory types}}

{{short description|TypeWrite of solid stateonce computer memory that becomes read only after being written once}}

A '''programmable read-only memory''' ('''PROM''') is a form of digital memory where the contents can be changed once after manufacture of the device. The data is then permanent and cannot be changed. It is one type of [[read-only memory]] (ROM). PROMs are usually used in digital electronic devices to store low level programs such as [[firmware]] or [[microcode]]. PROMs may be used during development of a system that will ultimately be converted to ROMs in a mass produced version. These types of memories are used in [[microcontroller]]s, [[video game console]]s, mobile phones, radio-frequency identification ([[RFID]]) tags, implantable medical devices, high-definition multimedia interfaces ([[HDMI]]), and in many other consumer and automotive products.

PROMs are manufactured blank and, depending on the technology, can be programmed at the wafer, final test, or system stage. Blank PROM chips are programmed by plugging them into a device called a ''PROM programmer''. A typical PROM device has an array of memory cells. The [[bipolar transistor]]s in the cells have an emitter that is connected to a [[Fuse (electrical)|fuse]] called a [[polyfuse (PROM)|polyfuse]]. To program a PROM is to strategically blow the polyfuses.<ref>{{cite book | url=https://books.google.com/books?id=9VHMBQAAQBAJ&dq=prom+fuse&pg=PA760 | title=The Electronics Handbook | isbn=978-1-4200-3666-4 | last1=Whitaker | first1=Jerry C. | date=3 October 2018 | publisher=CRC Press }}</ref>

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=== One time programmable memory ===

OTP (one time programmable) memory is a special type of [[non-volatile memory]] (NVM) that permits data to be written to memory only once. Once the memory has been programmed, it retains its value upon loss of power (i.e., is non-volatile). OTP memory is used in applications where reliable and repeatable reading of data is required. Examples include boot code, encryption keys and configuration parameters for analog, sensor or display circuitry. OTP NVM is characterized, over other types of NVM like [[eFuse]] or EEPROM, by offering a low power, small area footprint memory structure. As such, OTP memory finds application in products from microprocessors & display drivers to power management ICs (PMICs).

Commercially available semiconductor antifuse-based OTP memory arrays have been around at least since 1969, with initial antifuse bit cells dependent on blowing a capacitor between crossing conductive lines. [[Texas Instruments]] developed a MOS [[gate oxide]] breakdown antifuse in 1979.<ref>See [http://patimg2.uspto.gov/.piw?Docid=4184207&idkey=NONE US Patent 4184207] {{Webarchive|url=https://web.archive.org/web/20180427183945/http://patimg2.uspto.gov/.piw?Docid=4184207&idkey=NONE |date=2018-04-27 }} - High density floating gate electrically programmable ROM, and [http://patimg2.uspto.gov/.piw?Docid=4151021&idkey=NONE US Patent 4151021] {{webarchive|url=https://web.archive.org/web/20180427092847/http://patimg2.uspto.gov/.piw?Docid=4151021&idkey=NONE |date=2018-04-27 }} - Method of making a high density floating gate electrically programmable ROM</ref> A dual-gate-oxide two-transistor (2T) MOS antifuse was introduced in 1982.<ref>[http://www.chipestimate.com/techtalk/techtalk_071218.html Chip Planning Portal]. ChipEstimate.com. Retrieved on 2013-08-10.</ref> Early oxide breakdown technologies exhibited a variety of scaling, programming, size and manufacturing problems that prevented volume production of memory devices based on these technologies.