POLY FUSEA N EW STANDARD OF CIRCUIT PROTECTION

BY- TARUN SHARMA

0814331052

OUTLOOK

INTRODUCTION HISTORY AND BASICS MODERN POLY FUSE PRINCIPLE ELECTRONIC CIRCUIT PROGRAMMING FEATURES AND CHARACTERISTICS CROSS SECTION RELIABILITY INVESTIGATION PROCESS CONTROL DESIGN ISSUE DESIGN REQUIREMENT APPLICATION CONCLUSION REFERENCES

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.

Contacts

ContactBarrier

Tungsten SilicidePoly Silicon

Polyfuse used as an OTP base element Poly Silicon with Tungsten Silizide Low ohmic standard resistance

(<100W) High ohmic after programming

(>10kW)

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

NMOSCurrentMirror

Supply

PolyFuse

DifferentBias Currents

Programming Part Reading Part

DigitalLevelControl

VoltageLevel

Detector

Principle Layout PROM Storage RAM Access LOADing Mode PROGramming Mode Optional Parallel Out

RAM PROM

LOGIC

Parallel Out

LOAD PROG

WRITE READ

PROGRAMMING FEATURES

Programming in standard

CMOS process

Current programming

Infield programming

possible

A

Poly FuseArea

Poly SiliconTungsten Silicide

Tungsten Plug (Contact)

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

IprogmA

VprogV

tprog 0µs 1µs 2µs 3µs

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

Substrate

Field Oxide

Poly Silicon

Tungsten Silicide

Tungsten Plug Field Oxide

Poly Silicon

approx. 40nm

Low Current Programmed Poly Fuse

Inhomogenious temperature gradient during programming

Low ohmic resistor Lifetime drift to higher

resistor valuesTungs

Tungsten PlugTungsten PlugTungsten Plug

Tungsten SilicideField Oxide

Poly Silicon

Field Oxide

Substrate

Tungsten Plug

Tungsten Silicide

Poly Silicon

Higher Current Programmed Poly Fuse

High energy is forcing the Tungsten seperation

Break before Tungsten completely removed

Relatively high ohmic resistor

Lifetime drift to lower resistor 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 transistor

Special Test Function- to guarantee lifetime stability- for infield programming

PROCESS CONTROL

WAT Structure- PolyFuse Element- Burning NMOS Transistor

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

DESIGN REQUIREMENT

Requirements For Lifetime Stability- A programmed PolyFuse resistance must be

larger than 10k W after programming - The resistance of a programmed PolyFuse is

checked at 1k W during lifetime operation- This margin ensures proper operation of

programmed PolyFuses over lifetime

Requirement for Infield Programming- Testmode to measure the unprogrammed

PolyFuse resistance (<100 )W

APPLICATION

Used in : Automobiles Batteries Computers Peripherals Industrial control Consumer electronics Medical electronics Lightening Security and fire alarm system Telecommunication 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; United States Patent 4,413,272; November 1983 M. Alavi, M. Bohr, J.Hicks; A PROM Element based on Salicide

Agglomeration of Poly Fuses in a CMOS Logic Process; IEEE International Electron Device Meeting; December 1997

W.R. Tonti, J.A. Fifield, J. Higgins, W.H. Guthrie, W. Bery,C. Narayan; Product Specific Sub-Micron E-Fuse Reliability and Design Qualification; IEEE 2003 IRW Final Report

J.Simader; Entwicklung von Polyfuses als PROM Element für den CSD (0,35 μm CMOS) Prozess; Diploma Thesys, September 2002

Research Institute for Electron Microscopy and Fine Structure Research (FELMI); TU-Graz