POLY FUSEA NEW STANDARD OF CIRCUIT

PROTECTION

BY- TARUN SHARMA0814331052

OUTLOOK

INTRODUCTIONHISTORY AND BASICSMODERN POLY FUSE

PRINCIPLE ELECTRONIC CIRCUITPROGRAMMING FEATURES AND CHARACTERISTICSCROSS SECTION

RELIABILITY INVESTIGATIONPROCESS CONTROLDESIGN ISSUEDESIGN REQUIREMENTAPPLICATIONCONCLUSIONREFERENCES

INTRODUCTION

A Polyfuse is a one-time-programmablememorycomponentused in semiconductorcircuits forstoringunique data like chip identificationnumbersor memory repair data.

Polyfuseswere developed as a replacement of laserfuses.

Contacts

ContactBarrier

Tungsten SilicidePoly Silicon

Polyfuse used as an OTP base element

Poly Silicon with Tungsten SilizideLow ohmic standard resistance (<100W)High ohmic after programming (>10kW)

HISTORY AND BASICS

The first polyfusesconsisted of a polysiliconline,which was programmedby applying a high (10V-15V) voltage across the device.

The resultant current physicallyalters the device andresults in an increase in electrical resistance.

This change in resistance can be detected andregistered as a logical one.

An unprogrammed Polyfuse would be registered asa logical zero.

These early devices had severe drawbacks like ahigh programming voltage and unreliability of theprogrammed devices.

MODERN POLYFUSE

Modern polyfuses consist of a siliced polysilicon line,which is also programmed by applying a voltageacross the device.the resultant current physically alters the device andresults in an increase in resistance.

The silicide layer covering the polysilicon linereduces its resistance (before programming),allowing the use of much lower programmingvoltages (1.8V-3.3V).

Polyfuses have been shown to reliably storeprogrammed data and can be programmed at highspeed.

Programming speeds of 100ns have been reported

PRINCIPLE ELECTRONIC CIRCUIT

Principle schematic have:Polyfuse Element

Programming Transistor

Current Mirror

Testmodes

NMOSCurrentMirror

Supply

PolyFuse

Programming Part

DifferentBias Currents

Reading Part

DigitalLevelControl

VoltageLevel

Detector

PROGPROM

LOGIC

LOADRAM

Principle LayoutPROM Storage

RAM Access

LOADing Mode

PROGramming Mode

Optional Parallel Out ParallelOut

WRITEREAD

PROGRAMMING FEATURES

Programming in standard

CMOS process

Current programming

Infield programming

possible

A

Poly FuseArea

T ngst n Pl g ( ont ct)T ngst n ilici

Pol

ilicon

tpr g 0

µs 1 µ

s2 µs 3

µs

Ialloy: No autonomous currentpinch off

PROGRAMMING CHARACTERISTICS

Ilinear: Linear resistor characteristicsIpr g

mAImelt: Tungsten Silicide is melting

Imax: Maximum current ofminimum resistance

Imin: Local current min.

Iosc: Oscillation because of break

Vpr gV

CROSS SECTION

Typical Current ProgrammedPoly Fuse

Active PolyFuse region no longer

has Tungsten included

High ohmic stable alloy

Local break of a few nm

Minimal lifetime driftof the resistance value

Field Oxide

Substrate

Tungsten Silicide

Poly Silicon

Tungsten Plug Field Oxide

Poly Silicon

approx. 40nm

Low Current ProgrammedPoly Fuse

Inhomogenious temperaturegradient during programming

Low ohmic resistor

Lifetime drift to higher

n PlTungs te ug

n

resistor valuessgnuT

Field OxideTungs te Silicide

Poly Silicon

u s

Field Oxide

S b trate

n PlTungs te ug

nTungs te Silicide

Poly Silicon

Higher Current Programmed

Poly FuseHigh energy is forcing the Tungstenseperation

Break before Tungsten completelyremoved

Relatively high ohmicresistorLifetime drift to lowerresistor values possible

Tungsten Plug

Tungsten Silicide

Poly Silicon

TungstenHALO

Tungsten

Field Oxide

Field Oxide

Substrate

Tungsten Plug

Tungsten Silicide

Poly Silicon

RELIABILITY INVESTIGATIONS

Lifetime Drift over Time

2000h BurnIn@125 °C

HTOL Test JESD22-108

Lifetime Drift Investigated for

typical current programmed PolyFuses

low current programmed PolyFuses

high current programmed PolyFuses

DESIGN ISSUE

IP Blocks with PolyFuses Designed

- 32 bit- 128bit

Optimized Programming Path

- PolyFuse

- Related programming transistorSpecial Test Function

- to guarantee lifetime stability- for infield programming

PROCESS CONTROL

WAT Structure

- PolyFuse Element- Burning NMOS TransistorMeasurements

- Resistor of unprogrammed PolyFuse- Resistor of programmed PolyFuse- Current of Burning Transistor

DESIGN REQUIREMENT

Requirements For Lifetime Stability

- A programmed PolyFuse resistance must belarger than 10k; after programming

- The resistance of a programmed PolyFuse ischecked at 1k; during lifetime operation

- This margin ensures proper operation ofprogrammed PolyFuses over lifetime

Requirement for Infield Programming

-Testmode to measure the unprogrammedPolyFuse resistance (<100;

APPLICATION

Used in :AutomobilesBatteriesComputersPeripherals

Industrial controlConsumer electronicsMedical electronicsLighteningSecurity and fire alarm systemTelecommunication equipment

CONCLUSION

Reliable Programming Conditions

Programmable over whole Process Range

Lifetime Stability

High Programming Yield

Process Control

Infield Programming Option

REFERENCES

Mochizuki; Semiconductor devices having fuses; UnitedStates Patent 4,413,272; November 1983

M. Alavi, M. Bohr, J.Hicks; A PROM Element based on SalicideAgglomeration of Poly Fuses in a CMOS Logic Process; IEEEInternational Electron Device Meeting; December 1997W.R. Tonti, J.A. Fifield, J. Higgins, W.H. Guthrie, W. Bery,C.Narayan; Product Specific Sub-Micron E-Fuse Reliability andDesign Qualification; IEEE 2003 IRW Final Report

J.Simader; Entwicklung von Polyfuses als PROM Element für denCSD (0,35 m CMOS) Prozess; Diploma Thesys, September2002Research Institute for Electron Microscopy and Fine StructureResearch (FELMI); TU-Graz