Antifuse
Encyclopedia
An antifuse is an electrical device that performs the opposite function to a fuse
. Whereas a fuse starts with a low resistance and is designed to permanently break an electrically conductive path (typically when the current
through the path exceeds a specified limit), an antifuse starts with a high resistance and is designed to permanently create an electrically conductive path (typically when the voltage across the antifuse exceeds a certain level). This technology has many applications.
s (ICs). ICs that use antifuse technology employ a thin barrier of non-conducting amorphous silicon
between two metal
conductors. When a sufficiently high voltage is applied across the amorphous silicon it is turned into a polycrystalline
silicon-metal alloy
with a low resistance
, which is conductive.
Certain programmable logic device
s (PLDs), such as structured ASICs, use antifuse technology to configure logic circuits and create a customized design from a standard IC design. Antifuse PLDs are one time programmable in contrast to other PLDs that are SRAM
based and which may be reprogrammed to fix logic bugs or add new functions. Antifuse PLDs have advantages over SRAM based PLDs in that like ASIC
s, they do not need to be configured each time power is applied. They may be less susceptible to alpha particle
s which can cause circuits to malfunction. Also circuits built via the antifuse's permanent conductive paths may be faster than similar circuits implemented in PLDs using SRAM technology. QuickLogic Corporation
refers to their antifuses as "ViaLinks" because blown fuses create a connection between two crossing layers of wiring on the chip in the same way that a via
on a printed circuit board
creates a connection between copper layers.
Antifuses may be used in programmable read-only memory (PROM
). Each bit contains both a fuse and an antifuse and is programmed by triggering one of the two. This programming, performed after manufacturing, is permanent and irreversible.
The antifuse is usually triggered using an approximately 5 mA
current. With a poly-diffusion antifuse, the high current density creates heat
, which melts a thin insulating layer between polysilicon and diffusion electrodes, creating a permanent resistive silicon link.
s, street light
circuits using incandescent light bulb
s were often operated as high-voltage series circuits. Each individual street-lamp was equipped with a film cutout; a small disk of insulating film that separated two contacts connected to the two wires leading to the lamp. In the same fashion as with the Christmas lights described above, if the lamp failed, the entire voltage of the street lighting circuit (thousands of volts) was imposed across the insulating film in the cutout, causing it to rupture. In this way, the failed lamp was bypassed and illumination restored to the rest of the street. Unlike Christmas lights, the circuit usually contained an automatic device to regulate the electrical current flowing in the circuit, preventing the current from rising as additional lamps burned out. When the failed lamp was finally changed, a new piece of film was also installed, once again separating the electrical contacts in the cutout. This style of street lighting was recognizable by the large porcelain
insulator that separated the lamp and reflector from the light's mounting arm; the insulator was necessary because the two contacts in the lamp's base may have routinely operated at a potential of several thousands of volts above ground/earth.
Fuse (electrical)
In electronics and electrical engineering, a fuse is a type of low resistance resistor that acts as a sacrificial device to provide overcurrent protection, of either the load or source circuit...
. Whereas a fuse starts with a low resistance and is designed to permanently break an electrically conductive path (typically when the current
Electric current
Electric current is a flow of electric charge through a medium.This charge is typically carried by moving electrons in a conductor such as wire...
through the path exceeds a specified limit), an antifuse starts with a high resistance and is designed to permanently create an electrically conductive path (typically when the voltage across the antifuse exceeds a certain level). This technology has many applications.
Christmas tree lights
Antifuses are best known for their use in mini-light (or miniature) style low-voltage Christmas tree lights. Ordinarily (for operation from mains voltages), the lamps are wired in series. (The larger, traditional, C7 and C9 style lights are wired in parallel and are rated to operate directly at mains voltage.) Because the series string would be rendered inoperable by a single lamp failing, each bulb has an antifuse installed within it. When the bulb blows, the entire mains voltage is applied across the single blown lamp. This rapidly causes the antifuse to short out the blown bulb, allowing the series circuit to resume functioning, albeit with a larger proportion of the mains voltage now applied to each of the remaining lamps. The antifuse is made using wire with a high resistance coating and this wire is coiled over the two vertical filament support wires inside the bulb. The insulation of the antifuse wire withstands the ordinary low voltage imposed across a functioning lamp but rapidly breaks down under the full mains voltage, giving the antifuse action. Occasionally, the insulation fails to break down on its own, but tapping the blown lamp will usually finish the job. Often a special bulb with no antifuse and often a slightly different rating (so it blows first as the voltage gets too high) known as a "fuse bulb" is incorporated into the string of lights to protect against the possibility of severe overcurrent if too many bulbs fail.Antifuses in integrated circuits
Antifuses are widely used to permanently program integrated circuitIntegrated circuit
An integrated circuit or monolithic integrated circuit is an electronic circuit manufactured by the patterned diffusion of trace elements into the surface of a thin substrate of semiconductor material...
s (ICs). ICs that use antifuse technology employ a thin barrier of non-conducting amorphous silicon
Amorphous silicon
Amorphous silicon is the non-crystalline allotropic form of silicon. It can be deposited in thin films at low temperatures onto a variety of substrates, offering some unique capabilities for a variety of electronics.-Description:...
between two metal
Metal
A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...
conductors. When a sufficiently high voltage is applied across the amorphous silicon it is turned into a polycrystalline
Polycrystalline
Polycrystalline materials are solids that are composed of many crystallites of varying size and orientation. The variation in direction can be random or directed, possibly due to growth and processing conditions. Fiber texture is an example of the latter.Almost all common metals, and many ceramics...
silicon-metal alloy
Alloy
An alloy is a mixture or metallic solid solution composed of two or more elements. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may or may not be homogeneous in distribution, depending on thermal history...
with a low resistance
Electrical resistance
The electrical resistance of an electrical element is the opposition to the passage of an electric current through that element; the inverse quantity is electrical conductance, the ease at which an electric current passes. Electrical resistance shares some conceptual parallels with the mechanical...
, which is conductive.
Certain programmable logic device
Programmable logic device
A programmable logic device or PLD is an electronic component used to build reconfigurable digital circuits. Unlike a logic gate, which has a fixed function, a PLD has an undefined function at the time of manufacture...
s (PLDs), such as structured ASICs, use antifuse technology to configure logic circuits and create a customized design from a standard IC design. Antifuse PLDs are one time programmable in contrast to other PLDs that are SRAM
Static random access memory
Static random-access memory is a type of semiconductor memory where the word static indicates that, unlike dynamic RAM , it does not need to be periodically refreshed, as SRAM uses bistable latching circuitry to store each bit...
based and which may be reprogrammed to fix logic bugs or add new functions. Antifuse PLDs have advantages over SRAM based PLDs in that like ASIC
Application-specific integrated circuit
An application-specific integrated circuit is an integrated circuit customized for a particular use, rather than intended for general-purpose use. For example, a chip designed solely to run a cell phone is an ASIC...
s, they do not need to be configured each time power is applied. They may be less susceptible to alpha particle
Alpha particle
Alpha particles consist of two protons and two neutrons bound together into a particle identical to a helium nucleus, which is classically produced in the process of alpha decay, but may be produced also in other ways and given the same name...
s which can cause circuits to malfunction. Also circuits built via the antifuse's permanent conductive paths may be faster than similar circuits implemented in PLDs using SRAM technology. QuickLogic Corporation
QuickLogic
QuickLogic Corporation is a manufacturer of Customer Specific Standard Products, or CSSP.Until 2007 they were a supplier of Field-Programmable Gate Arrays based on antifuse technology, making the devices one-time programmable...
refers to their antifuses as "ViaLinks" because blown fuses create a connection between two crossing layers of wiring on the chip in the same way that a via
Via (electronics)
A via is a vertical electrical connection between different layers of conductors in a physical electronic circuit.- In IC :In integrated circuit design, a via is a small opening in an insulating oxide layer that allows a conductive connection between different layers. A via on an integrated circuit...
on a printed circuit board
Printed circuit board
A printed circuit board, or PCB, is used to mechanically support and electrically connect electronic components using conductive pathways, tracks or signal traces etched from copper sheets laminated onto a non-conductive substrate. It is also referred to as printed wiring board or etched wiring...
creates a connection between copper layers.
Antifuses may be used in programmable read-only memory (PROM
PROM
PROM may refer to:*Phosphate rich organic manure*Premature rupture of membranes, an obstetric term*PROM-1 land mine*Programmable read-only memory, related to electronics...
). Each bit contains both a fuse and an antifuse and is programmed by triggering one of the two. This programming, performed after manufacturing, is permanent and irreversible.
The antifuse is usually triggered using an approximately 5 mA
Ampere
The ampere , often shortened to amp, is the SI unit of electric current and is one of the seven SI base units. It is named after André-Marie Ampère , French mathematician and physicist, considered the father of electrodynamics...
current. With a poly-diffusion antifuse, the high current density creates heat
Heat
In physics and thermodynamics, heat is energy transferred from one body, region, or thermodynamic system to another due to thermal contact or thermal radiation when the systems are at different temperatures. It is often described as one of the fundamental processes of energy transfer between...
, which melts a thin insulating layer between polysilicon and diffusion electrodes, creating a permanent resistive silicon link.
Street-lighting (obsolete)
In a similar fashion to that of Christmas tree lights, before the advent of high-intensity discharge lampHigh-intensity discharge lamp
High-intensity discharge lamps are a type of electrical lamp which produces light by means of an electric arc between tungsten electrodes housed inside a translucent or transparent fused quartz or fused alumina arc tube. This tube is filled with both gas and metal salts. The gas facilitates the...
s, street light
Street light
A street light, lamppost, street lamp, light standard, or lamp standard is a raised source of light on the edge of a road or walkway, which is turned on or lit at a certain time every night. Modern lamps may also have light-sensitive photocells to turn them on at dusk, off at dawn, or activate...
circuits using incandescent light bulb
Incandescent light bulb
The incandescent light bulb, incandescent lamp or incandescent light globe makes light by heating a metal filament wire to a high temperature until it glows. The hot filament is protected from air by a glass bulb that is filled with inert gas or evacuated. In a halogen lamp, a chemical process...
s were often operated as high-voltage series circuits. Each individual street-lamp was equipped with a film cutout; a small disk of insulating film that separated two contacts connected to the two wires leading to the lamp. In the same fashion as with the Christmas lights described above, if the lamp failed, the entire voltage of the street lighting circuit (thousands of volts) was imposed across the insulating film in the cutout, causing it to rupture. In this way, the failed lamp was bypassed and illumination restored to the rest of the street. Unlike Christmas lights, the circuit usually contained an automatic device to regulate the electrical current flowing in the circuit, preventing the current from rising as additional lamps burned out. When the failed lamp was finally changed, a new piece of film was also installed, once again separating the electrical contacts in the cutout. This style of street lighting was recognizable by the large porcelain
Porcelain
Porcelain is a ceramic material made by heating raw materials, generally including clay in the form of kaolin, in a kiln to temperatures between and...
insulator that separated the lamp and reflector from the light's mounting arm; the insulator was necessary because the two contacts in the lamp's base may have routinely operated at a potential of several thousands of volts above ground/earth.
External links
- Information on use of antifuses in Christmas lights - Note that they avoid use of the term antifuse presumably because of their non-technical audience.
- More information on the types of Christmas lights