25-04-2012, 04:57 PM
POLY FUSE
POLY-FUSE.pptx (Size: 1.51 MB / Downloads: 98)
INTRODUCTION
A Polyfuse is a one-time-programmable memory component used in semiconductor circuits for storing unique data like chip identification numbers or memory repair data.
Polyfuses were developed as a replacement of laser fuses.
HISTORY AND BASICS
The first polyfuses consisted of a polysilicon line, which was programmed by applying a high (10V-15V) voltage across the device.
The resultant current physically alters the device and results in an increase in electrical resistance.
This change in resistance can be detected and registered as a logical one.
An unprogrammed Polyfuse would be registered as a logical zero.
These early devices had severe drawbacks like a high programming voltage and unreliability of the programmed devices.
MODERN POLYFUSE
Modern polyfuses consist of a siliced polysilicon line, which is also programmed by applying a voltage across the device.
the resultant current physically alters the device and results in an increase in resistance.
The silicide 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
PRINCIPLE ELECTRONIC CIRCUIT
Principle schematic have:
Polyfuse Element
Programming Transistor
Current Mirror
Testmodes
Principle Layout
PROM Storage
RAM Access
LOADing Mode
PROGramming Mode
Optional Parallel Out
PROGRAMMING FEATURES
Programming in standard
CMOS process
Current programming
Infield programming
possible
PROGRAMMING CHARACTERISTICS
Ilinear: Linear resistor characteristics
Iheat: Temp. is raising
Imelt: Tungsten Silicide is melting
Imax: Maximum current of minimum resistance
Imin: Local current min.
Iosc: Oscillation because of break
Ialloy: No autonomous current pinch off
CROSS SECTION
Typical Current Programmed Poly Fuse
Active PolyFuse region no longer
has Tungsten included
High ohmic stable alloy
Local break of a few nm
Minimal lifetime drift of the resistance value
Low Current Programmed Poly Fuse
Inhomogenious temperature gradient during programming
Low ohmic resistor
Lifetime drift to higher resistor values
Higher Current Programmed Poly Fuse
High energy is forcing the Tungsten seperation
Break before Tungsten completely removed