PlainSite. Legal Document. United States Patent and Trademark Office Case No Self-compensating Thermal Expansion. Document.

PlainSite

Legal Document

®

United States Patent and Trademark Office

Case No. 10631940

Magnetic Hard Disk Recording Head With

Self-compensating Thermal Expansion

Document

View Document

Specification

MAGNETIC

HARD

DISK

RECORDING

HEAD

WITH

SELF-COMPENSATING

THERMAL

EXPANSION

5

FIELD

OF THE

INVENTION

The

inventionrelatesgenerallytomagnetic headsforhard diskdrives, and

more

particularly tomagneticheads with reduced thermalprotrusion attheairbearingsurface.

BACKGROUND

An

important goalofthe harddisk drive industryistodevelopmagnetic heads

10 with continuedincreases indisk drive capacityandperformance,andcontinueddecreases

inthe costofdiskdrives. Improvementsinmagnetic headsaresoughtthatprovide ever

fasterdata writing speeds, andthatallowdatatobewrittenwith everincreasingdata

density, thatis,with

more

data storedperunitofdiskarea.

Typicallywhile adisk driveisoperating, themagneticheadisseparatedfromthe

15 surfaceofthedisk

by

a smallgap,whichistermedtheairbearinggap.

The

airbearing

gapismaintained

by

aslideranda suspension system.

The

sliderincludes themagnetic

head andanairbearingsurface

(ABS)

thatis shaped suchthattherotation ofthedisk

past theslidercreatesanaerodynamicforcethattendstopushtheslider

away

fromthe

disk. Atthe

same

time, thesliderispushedtowardsthedisk

by

thesuspension.

The

net

20 effectistomaintain agenerallyuniformdistancebetweenthe diskandtheairbearing

The

sizeoftheairbearinggap,also

known

astheairbearingflyheight,isakey

parameterofthediskdrive. Smallerairbearing

g^s

allow magnetic headstohavefaster

writingspeedsandhigher datadensity.

On

theotherhand

when

thegapbecomestoo

small,itbecomestoolikely thatthemagnetichead

may

come

intocontactwiththe disk 5 surface,whichcan permanently

damage

themagnetichead, the disksurface,or both.

A

known

problemwithmagnetic headsisthatheat causesuneventhermal

expansionofcomponentswithin the head, thusdistortingthe airbearingsurfaceofthe

head.

The

distortiontakestheformof aprotrusionofpartofthemagneticheadintothe

airbearing gap,wherethesizeoftheprotrusioncanbeonthe orderof

20%

ofthe height

10 oftheairbearing gap.

The

protrusioncancontributetoimwantedcontactofthemagnetic

head withthesurfaceofthedisk, whichcan

damage

the head, thedisk,orboth.

SUMMARY

OF THE

INVENTION

The

inventionseekstoreducethe protrusionthat resultsfromthermal expansion

ofthemagnetic head duringitsoperation.

15 In

some

embodiments,theinvention providesa magneticheadforreadingand

writingahard magneticdisk.

A

read-headportionofthemagnetic headincludesoneor

more

read-headinsulation layers,andawrite-head portionofthemagneticheadincludes

oneor

more

write-head insulationlayers.

The

magnetichead

may

optionallyfurther

includeoneor

more

insulationlayersbetweentheread-headportionandthe write-head

20 portion.

One

or

more

oftheseinsulation layersincludesamaterialhaving anegative

V.

Suitablematerialsinclude,butarenotlimitedto: carbonfiber;carbonfiber inan

epoxy

matrix; carbonfiber inaphotoresistmatrix;zirconiumtungstate (Zr

W2

Og);

zirconiumtungstate in

an epoxy

matrix;zirconiumtungstate inaphotoresistmatrix,

hafhiumtungstate

(Hf

W2

Os), hafiiiumtungstate inan

epoxy

matrix,orhafiiiiun

5 tungstate inaphotoresistmatrix.

BRIEF DESCRIPTION

OF

THE

DRAWING

Objects, features

and

advantages ofthe inventionwill

become

apparent firom the

descriptions anddiscussionsherein,

when

readinconjunctionwiththe drawing.

Technologiesrelated totheinvention,

example embodiments of

theinvention,

and

10

example

uses ofthe invention areillustratedin thevariousfiguresofthe drawing.

The

drawingsaregenerally not

drawn

to scalesuchthat the relative sizes

of

the elements

shown

may

be distorted to clarify featuresofthe invention, thusthe shapes

shown

forthe elements

may

varysubstantially

from

their actual shapes.

Fig. 1 isatop

view

ofa diskdrive thatincludes amagnetic head accordingto an

15

embodiment

ofthe invention;

Fig.2is a crosssectional

view

ofapriorartmagnetichead;

Fig.3 isa crosssectional

view

of magnetic head accordingto an

embodiment of

the invention, in

which

the protrusionofthehead has

been

reduced

by

includinginthe

headmaterialswith anegativethermal expansioncharacteristic;

and

20

Fig.

4

isa crosssectional

view

of magnetic head accordingto another

by

using negativethermal expansionmaterialsand

by

addinga heat sink layertothe

head.

DETAILED

DESCRIPTION

OF THE PREFERRED EMBODIMENTS

The

descriptions,discussions andfigureshereinillustratetechnologiesrelated to

5 the invention,

show

examples

of

theinvention,andgive examples ofusing theinvention.

Known

methods,procedures, systems,circuits, orelements

may

beillustratedand

described without givingdetails soas to avoidobscxiring the principles

of

theinvention.

On

theother hand, detailsofspecific

embodiments

oftheinvention arepresented,

even

though suchdetails

may

notapplytoother

embodiments of

the invention.

10 Fig. 1 is a top plan

view

that depicts significant

components

ofahard disk drive

10 according to an

embodiment

of the invention.

The

hard disk drive 10 includes a

magnetic

media

hard disk 14 that isrotatably

mounted upon

amotorized spindle 18.

An

actuator

arm 22

is pivotally

mounted

within the hard disk drive 10.

A

slider

26

is

mounted upon

the distal

end

ofthe actuator

arm

22.

The

slider26 has a trailing surface

15 30 that includes a magnetic

head

34 according to an

embodiment

ofthe invention.

A

typical hard disk drive 10

may

include aplurality ofdisks 14 that are rotatably

mounted

upon

the spindle 18 and acorrespondingplurality

of

the actuatorarms 22, the shders 26,

andthe magnetic heads 34.

As

is

known

to those skilled in the art,

when

the hard disk

drive 10 isoperated, the hard disk 14rotates

upon

the spindle 18 andtheslider

26

gUdes

Fig. 2 isaside cross-sectional

view

taken alongline

2-2,

ofFig. 1 illustratinga

magnetic

head

38 accordingto the priorart,theharddisk 14,

and

anairbearinggap

42

between

the

head

38

and

theharddisk 14.

As

iswell

known,

theharddisk 14 includes a

layer

46

of aferromagnetic materialthatislayeredontoa disksubstrate 50.

5

The

prior art magnetic

head

38 includes: a

head

substrate 54;

and

an undercoat

layer 58 that is deposited

upon

a surface

62 of

the

head

substrate

54

when

the

head

substrate

54

is

form of

awafer

and

the surface

62

istheuppersurface ofthe wafer.

The

prior art magnetic

head

38 further includes aread

head

portionthat includes: a firstread

head

magnetic shield (SI) layer

66

that is fabricated

upon

the undercoat layer 58; a first

10 (II) insulation layer

70

that is fabricated

upon

the SI shield 66; a read

head

element 74

that is fabricated

upon

insulation layer 70; a second (12) insulation layer 78 that is

fabricated

upon

the read

head

74 and the II insulation layer 70; and a second magnetic

shield(S2) layer82 thatis fabricated

upon

the12 insulation layer 78.

A

fiirtherinsulation layer 86 is deposited

upon

the

S2

shield 82

and

serves to insulate the read-head

and

the

15 write-head portions

of

magnetic

head

3 8

.

Magnetic head

38 further includes the write

head

portion,

which

includes a first

magnetic pole (PI) layer

90

that is fabricated

upon

the insulation layer 86.

As

is well

known

to those skilled in the art, in a type of magnetic

head

termed a

merged

head, the

PI

pole layer

90 and

the

S2

shield layer 82 are

merged

into a single layer thatperforms

20

the fimctions ofthe

S2

shield 82

when

the magnetic

head

is reading data firom a hard

disk,

and

performsthefiinctionofthe

PI

pole layer

90

when

themagnetic

head

iswriting data to ahard disk.

The

insulation layer 86 is not present in such a

merged

head.

The

invention,as isdiscussed

below

indetail,

may

be embodied

inastandard magnetichead,

asdepictedin Fig. 2, or as a

merged

magnetichead, asdepictedin Fig.4.

The

write-head portion of the prior art magnetic

head 38

further includes: a

patterned write gap layer

94

that is fabricated

upon

the

PI

pole 90; a spiral, planar

inductioncoiltiiatincludes aplurality

of

innerturns

96 and

aplurality

of

outerturns 98;

and a second magnetic pole(P2) 102.

The

second magnetic pole 102 includes: asecond

magneticpole tip portion 110; a

yoke

portion 114;

and

a

back

gappiece 118.

The

inner

induction coilturns

96

aredisposed

above

the

PI

pole 90

and below

the

P2

yolkportion

'114,

and

are

formed

with coil insulation 106

between

the turns. Following the

fabrication

of

the induction coil, the second magnetic pole (P2) 102 is fabricated above

the inner inductioncoil turns 96.

The

P2

pole 102ismagneticallyconnected withthe

PI

pole

90

throughthe

back

gappiece 118. Followingfurther fabrication steps as are

known

to those skilled in the art, an overcoat layer 122 is deposited across the surface ofthe

head-substrate wafer,

and

thewaferisthereafter sliced intothe individualmagnetic heads

38.

The

magnetic heads are later fabricated to include a

pohshed

air bearing surface

(ABS)

126,asiswell

known

by

thoseskilled intheart.

Followingitsfabrication,themagnetic headisinstalled

on

the actuator

arm

22

of

aharddisk drive 10 proximatetothe surfaceofaharddisk,as isdepicted in Fig.2.

Significantly,

due

tothermalexpansion of headlayersand

components

duringnormal

operatingconditions,theairbearing surface 126willdevelop asubstantialprotrusion 130

of head

materialintotheairbearing gap. Thus, a magnetic

head

thatisdesignedto

gapduring usage.

The

protrasion 130iscaused

by

heat, including: heat generated within

themagnetic

head

during theoperation

of

thediskdrive;heat generatedelsewherewithin

thediskdrive; and ambientheatexternal to thediskdrive. Thisheatactsunevenly

on

the

variousmaterialsusedin fabricatingmagnetic

head

38. Materialstypicallyusedin

5 magnetic heads

and

slidersincludealumina(AI2 O3),

which

hasacoefficientofthermal

expansion

(CTE)

per degreeKelvin of approximately

7x10-6/

copper,

which

hasa

CTE

of approximately

2x10-5/

°K.

The

protrusionofa disk drivecan be analyzedin

two

categories:staticprotrusion

and

dynamic

protrusion. Staticprotrusionrefers to theprotrusiondueto the temperature

10 internal to anoperating diskdrivebeinghigher thanthetemperatureat

which

the

magnetic

head

was

designedto operate.

Dynamic

protrusionrefers to theprotrusion

caused

by

heat generatedin themagnetic headduringthewritingprocess.

Such

heat

includesbothJoule heatingthatoccurs within inductioncoilturns

96 and

98,

and eddy

currentheatingthatoccurs withinmagneticpoles

90

and 102.

Modem

diskdrives

15 operate with airbearinggapsintherange of10nanometers (nm), andcontinued

improvements

inmagnetic headsresult incontinued reductions

of

the airbearinggap42.

At

agap sizeof10

nm

the thermal expansion ofthemagnetic head

may

be

substantial,

forexample, aprior-artmagnetic

head

may

protrude

by

about 2

nm, which

is

approximately

20%

oftheairbearinggap42.

20

Fig.3 isacross-sectional

view

taken alongcutline2-_{2 of}Fig. 1 thatillustratesa

magnetic head 134accordingtoan

embodiment

oftheinvention. Exceptasdescribed

composition

and

alternatives tothe correspondingly

numbered

layers

and components

withinmagnetic head

38 of

Fig.2.

To

reducethe

unwanted

thermal expansion

and

protrusionofthemagnetichead,

one

or

more

of

theinsulation layers

of

magnetic

head 134

are

formed from

a material

5 havinga negativethermalexpansioncharacteristicsuchthatthe materialwillshrinkin

size

when

heated.

These

layers

may

include: thefirstinsulation layer70; thesecond

insulation layer78; theinsulationlayer86

between

theread-headportion

and

the

write-head

portionofthemagnetic head; thewritegap layer94; thecoil insulation 106; or the

overcoat layer 112.

Any

of,

any

combinationor

two

or

more

of,oralloftheinsulation

10 layersused

may

containthematerialwiththenegativethermal expansioncharacteristic.

As

can be seen

by

comparing

Figs. 2and3, theprotrusion 138 of magnetic

head

134 accordingto an

embodiment

ofthe inventionisreduced, as

compared

to the

protrusion

130

ofthemagnetic

head

38,becausethemagnetic

head

134contains

materialsthat

become

smallerastheyare heated.

As

is

known

to thoseskilled in theart,

15 thermal expansion ofmaterials,

and

ofstructures

composed

of conjoined elements

formed from

variousmaterials, canbe

modeled

by

computer

simulation.

Resultsof such a simulationperformed

by

theinventorsindicate thatthe static

thermalprotrusionofamagnetic

head

canbe reduced

by

approximately

50%

andthe

dynamic

thermalprotrusion

can

be

reduced

by

about

10%

by

changing onlythe

20

composition oftheovercoatlayer122. Inthis simulation, the overcoatlayer 122

was

10

microns

(^m)

thick

and

was

made

from

a hypothetical materialwithanet thermal

including theundercoatinsulation layer58

which had

a thickness

of

1.6 jxm.

The

SI

shield layer 66,the

S2

shieldlayer82, andthePIpole layer

90 were

2 thickand

were

made

from

80%

nickel (Ni)

and

20%

iron (Fe).

The

pole pedestal 154

was

2.7 |uimthick

and

was

also

made

from

20%

nickel

and

80%

iron.

The

P2

polelayer

90

includedbotha

5 poletip segment nearthe airbearing surface

42 and

a

yoke segment

that

was

joinedtothe

poletipsegment.

The

poletip

segment

was

1.4 [imthick

and

was

made

from

20%

nickel and

80%

iron.

The

yoke segment

was was

1.7

^m

thick

and

was

made

from

45%

nickel and

55%

iron.

Materialswitha negative thermalexpansioncharacteristic are

known

intheart;

10 see forexample, U.S. Patent

No.

5,514,360, issuedtoArthur

W.

Sleight. Materials

suitable foruseinvarious

embodiments

ofthe inventioninclude,butarenotlimitedto,

zirconiumtungstate(Zr

W2

Og), hafiiiumtungstate

(Hf

W2

Og),orcarbon fibers.

Zirconiumtungstate

may

be

preferred in

some

embodiments

ofthe inventionbecause its

coefficientofthermal expansion

(CTE)

perdegree Kelvinis approximately-8.8

x

10'^_/

15 °K,

which

iscomparable inabsolutemagnitudeto thatofalumina,

and

becauseits

thermal contractionisisotropic, thatis, itoccurs equallyinalldirections. Incontrast,

carbonfibers

have

alower

CTE

of

approximately-1

x

10'^/''K,

and

the negative thermal

expansioncharacteristic onlyapplies alongtheaxisofthefiber.

Embodiments of

the invention

may

usevariousforms

of

materialswitha negative

20

thermalexpansioncharacteristic,

and

thematerialsused

may

be

fabricated intomagnetic

headsaccordingtovarious techniques. Suitabletechniquesinclude,but arenotlimited

epoxy, andthenusing

known

techniquesforcoating awafer with an

epoxy

layer; a techniqueof

powdering

thematerial, then including the

powder

within a matrix

of

photoresist, andthen using

known

techniques forcoating awafer withaphotoresistlayer;

anda technique ofsputteringthe materialonto a wafer.

5 Fig.

4

is a schematic

view of

a cross sectional

view

ofamagnetic head

142

accordingtoafurther

embodiment

ofthe invention. Exceptasdescribedbelow,the

layersand

components

withinmagnetic

head

142 areequivalentinform,composition

andalternativestothe correspondingly

numbered

layers and

components

withinmagnetic

head'38 ofFig. 2

and

magnetic

head

134

of

Fig. 3.

10 In orderto furtherreducethe

unwanted

thermal expansion ofthemagnetic

head

142,a heattransfer layer 146

may

additionally

be

fabricatedwithinthe head.

The

protrusionofthemagnetic

head

142 islessthantheprotrusioninamagnetic

head

that

uses onlynegative thermal expansionmaterials withouttheuseoftheheattransferlayer

142,becausethetemperature buildup within theheadis reduced

by

theheattransfer

15 layer.

Such

heattransfer layers aredescribedindetailinU.S. Patent ApplicationSerial

No.

Docket No. SJ09-2002-0037US1,

entitled"Heat Sink fora

Magnetic Recording Head,"

by

Savas Gideretal,

which

isassignedtothe assigneeof

this appUcation

and

incorporated hereinasthoughsetforth infull.

The

incorporated

patentappUcation disclosesheattransfer layers,heatsinks andthehke,

any

orall

of

20

which

may

beincorporatedintovarious

embodiments

oftheinvention.

Unlike magnetic heads

38 and

134(as

shown

in Figs. 2 and3),themagnetic head

describedwithregardto Fig. 2above,

do

not contain asseparate elements the

S2

shield

82, the

PI

pole

90 and

the insulation layer 86. Rather, a

merged

ferromagneticlayer 150

is fabricated

upon

theupperinsulation layer 78.

The

merged

layer150 of magnetic head

142 performs thefunctionsofthe shield82

and

ofthe

PI

pole90.

5 Also, unlikemagnetic heads 38

and

134, themagnetic

head

142 has a two-layer

inductioncoil, in

which two

layersofinnerturns 96are

formed

afterthe

merged

layer

150

and

before the

P2

pole102.

A

dual-layermagnetichead,suchas

head

142,

may

also

include a pole pedestal 154 thatis

composed

ofa ferromagneticmaterial,

and

is

formed

upon

the

merged

layer 150atthe airbearing surface126.

The

pole pedestal 154extends

10 the magneticpole,thus allowingadditional

room

for

two

layersoftheinner induction

coil

tums 96

to

be

fabricatedafterthe

merged

layer *₁₅₀

_and

_{before the}second magnetic

polelayer '_{102. Various}

_embodiments

_{ofthe invention}useinduction_coilswithvarious

numbers

oflayersof tums, and

may

useoromitthepole pedestals 154.

Inthemagnetic head 142,aninsulation layer 158 isfabricated

upon

the

P2

pole

15 layer 102,

and

thenthe heattransfer layer146isfabricated

upon

the insulation layer 158.

The

heattransfer layer 146 isfabricatedwith an

end

160thatis

formed

nearairbearing

surface 126,

and

itextends

from

the

end

160 aroxmdthewrite-head portion

and

the

read-head

portionof magnetic

head

142to the

head

substrate54;thus, layer 146thermally

couplesandtransfersheat

from

themagnetic

head

142tothe

head

substrate 54.

An

20

insulationportion 162 oftheheattransfer layer 146is

formed

atthe airbearing surface

126.

The

insulationportion 162

may

be formed from

a materialhavinga negative

oftheheattransfer layer 146.

The

heattransfer layer 146ispreferablybut not

necessarily

formed from

a materialwith very high thermalconductivity, suchascopper.

When

copperisused, theinsulationportion 162 servestoprevent exposing coppertothe

airbearingsurface,

where

it

may

createcorrosionproblems.

5 Various

embodiments

oftheinventioncaninclude heattransferlayers that are

formed

in

one

or

more

of

variouslocationswithin ornear themagnetichead.

Such

locations include,butarenot limitedto:

between

theread-headportion

and

the

write-head

portion

of

themagnetichead;

between

two

or

more

layers

of

coil

tums 96

or 98; or

as

shown

inmagnetic

head

142,

between

thesecondmagnetic polelayer 102

and

the

10 overcoat layer 122.

Some

embodiments

oftheinventioncaninclude a heattransferlayer

orlayers that transferheat

away

from

airbearing surface 126 withouttransferringthe

heatto

any

particularelementorlocation. Inotherembodiments, theheat transferlayer

orlayers arethermallycoupledtovarious elementswithin themagnetic

head

or the

slider, includingbut not limitedto: a heat sink

on

a surface

of

the sliderotherthan theair

15 bearingsurface;or

head

substrate 54. Fijrther

embodiments

ofthe invention

may

include

various insulation layers thatare

composed

ofanegativethermalexpansion characteristic

material,includingbut not limitedtothose

shown

in

any of

Figs.2, 3, or4.

The

scope ofthe inventionisset forth

by

thefollowing claims

and

theirlegal

equivalents.

The

inventionissubject to

numerous

modifications, variations, selections

20

among

altematives,changesinform,

and

improvements,inlight

of

theteachingsherein,

the techniques

known

tothoseskilledinthe art,

and

advancesintheartyettobe

made.

specificdetails;theyarenotintendedto

be

exhaustive orto limitthe inventiontothe