A polyfuse is a one-time-programmable memory component used in

semiconductor A semiconductor is a material which has an electrical resistivity and conductivity, electrical conductivity value falling between that of a electrical conductor, conductor, such as copper, and an insulator (electricity), insulator, such as glas ...

circuits for storing unique

data In the pursuit of knowledge, data (; ) is a collection of discrete values that convey information, describing quantity, quality, fact, statistics, other basic units of meaning, or simply sequences of symbols that may be further interpreted ...

like chip identification numbers or memory repair data, but more usually small to medium volume production of read only memory devices or microcontroller chips. They were also used as to permit programming of

Programmable Array Logic Programmable Array Logic (PAL) is a family of programmable logic device semiconductors used to implement logic functions in digital circuits introduced by Monolithic Memories, Inc. (MMI) in March 1978. Introductory advertisement on PAL (Progra ...

. The use of fuses allowed the device to be programmed electrically some time after it was manufactured and sealed into its packaging. Earlier fuses had to be blown using a

laser A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word "laser" is an acronym for "light amplification by stimulated emission of radiation". The fir ...

at the time memory was manufactured. Polyfuses were developed to replace the earlier nickel-chromium (ni-chrome) fuses. Because ni-chrome contains nickel, the ni-chrome fuse, once blown had a tendency to grow back and render the memory unusable.

History

The first polyfuses consisted of a polysilicon line, which was programmed by applying a high (10V-15V)

voltage Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge to m ...

across the device. The resultant current physically alters the device and increases its

electrical resistance The electrical resistance of an object is a measure of its opposition to the flow of electric current. Its reciprocal quantity is , measuring the ease with which an electric current passes. Electrical resistance shares some conceptual parallels ...

. This change in resistance can be detected and registered as a logical zero. An unprogrammed polyfuse would be registered as a logical one. These early devices had severe drawbacks like a high programming voltage and unreliability of the programmed devices.

Modern polyfuses

Modern polyfuses consist of a silicided

polysilicon Polycrystalline silicon, or multicrystalline silicon, also called polysilicon, poly-Si, or mc-Si, is a high purity, polycrystalline form of silicon, used as a raw material by the solar photovoltaic and electronics industry. Polysilicon is produce ...

line, which is also programmed by applying a voltage across the device. Again, the resultant current permanently alters the resistance. The

silicide A silicide is a type of chemical compound that combines silicon and a (usually) more electropositive element. Silicon is more electropositive than carbon. Silicides are structurally closer to borides than to carbides. Similar to borides and carb ...

layer covering the polysilicon line reduces its resistance (before programming), allowing the use of much lower programming voltages (1.8V–3.3V). Polyfuses have been shown to reliably store programmed data and can be programmed at high speed. Programming speeds of 100ns have been reported.

History

Modern polyfuses

See also

References