Critical Factors in Testing MRAM Devices

Critical Factors in Testing MRAM Critical Factors in Testing MRAM DevicesDevices

W. StevensonW. StevensonCypress Semiconductor, IncCypress Semiconductor, Inc

G. G. AsmeromAsmeromC. TaylorC. Taylor

ElectroglasElectroglasInc.Inc.

Southwest Test Workshop

June 2003

Stevenson -- CYPRESS 2 SWTW – June 2003

AGENDA / OBJECTIVEAGENDA / OBJECTIVE

MRAM Device ?Nomenclature, Advantages, Applications

MRAM Principles ?Logic States, Read Ops, Write Ops

Testing Challenges ?KGD Test FlowDevice Tuning, Stray Mag FieldsHow overcome?

(EG Prober, External Field Control Measures)

Summary / Conclusions !


MRAM KEY POINTSMRAM KEY POINTS

Magnetoresistive Random Access Memory Technology Marriage [CMOS + Mag Spin Layer]DRAM Density SRAM Speed NVRAM Data Retention

Key Aspects Competitive Cell SizeHigh Write-cycle EnduranceFast Write/Read CyclesData Retention Without Standby Power


EMERGING MEMORIESEMERGING MEMORIESPerfect Memory ?

Low Cost (dense), Fast Data Access / Write, Low Power, Non-Volatile, CMOS compatible, Reliable

New Technologies: FRAM, MRAM, OUMMRAM = Ideal Choice

ENDURANCE

NON-VOLATILE

STANDBY

ACTIVE POWER

WRITE TIME

ACCESS TIME/ COST

OUMMRAMFRAMFLASHSRAMDRAMBESTGOODWORST


MTJ MTJ –– SPINTRONIC STATESSPINTRONIC STATES

Al2O3 INSULATING BARRIER

PINNED (HARD) LAYER

FREE (SOFT) LAYER

PARALLELRp (Low)

Logic State 0

S

H

m+

m+

e-

MR = 24.8%

11.5

12.5

13.5

14.5

15.5

-50 -25 0 25 50FIELD (Oe)

R (O

hm)

ANTI- PARALLELRap (High)

Logic State 1

S

H

m+

m-

e-


NONNON--DESTRUCTIVE READDESTRUCTIVE READ

Read Resistance OfSelected 1T1R

Compare Resistance To Reference 1T1R*

"Data" "0""1"

Dummy"1"

Dummy"0"

Output

Vcc

Bit Line

Vref

WL

Gnd

BIT LINE

W L

XTOR

MTJELECTRODE

& CONTACT

D S

DIGITLINE


NONNON--DESTRUCTIVE DESTRUCTIVE WRITEWRITE

...(n) Ipd digit-lines

...(n-1) ...(n) ...(n+1) Ipb bit-lines

...

...(n+1)

Operating Region

0

5

10

15

20

25

30

35

40

0 5 10 15 20 25 30 35 40

Ipd Digit Line Field (Oe)

Ipb

Bit

Line

Fie

ld (O

e)

Ipb, Ipd Write Current IntersectionX Ipd

Y Ipb

Ipb => Easy Axis (bitline)

Ipd => Hard Axis (digit line)

Resultant Current = Ipd +Ipb

Only Intersection Gets Full Current


SORT MAG FIELD COILSSORT MAG FIELD COILS

RING CARRIER

CARD TOWER

PROBE CARD

COIL HOUSING

X-Y MAG COILS

HEAT SINK

X DISTURB

Y DISTURB

Find Hyper-sensitive Bits –Sweep External XY Fields to Find > Repair / Kill


TEST CHALLENGESTEST CHALLENGES

Scribeline Test Standard IC tests: Transistor, Resistor, Contact, etc.MRAM Adds Magnetic Switching

Wafer Sort Testing MRAM Is Similar to Testing SRAMAdds Current Tuning & Disturb Tests at Sort-1

(Before Repair & Shielding)Requires a Magnetically Neutral Environment

(< +/-1.0 Oe)Produces a KGD device (WLBI, Class, etc.)

Key ChallengeMagnetically Neutral Environment for Prober


MEASUREMENT UNITSMEASUREMENT UNITS

H Magnetic Field StrengthCGS 1 oersted [Oe] – 2 poles @ 1cm -> 1 dyne

B – Flux Density# Flux Lines Passing Perpendicular to Given AreaCGS 1 gauss [G] – 1 flux lines / 1 cm2SI 1 Tesla [T] – 10K flux lines / 1cm2 1 G = 1 Oe in free space (air)Earth’s Magnetic Field ~ 0.7 GaussTotal Flux Density is RSS of X, Y, Z components

222zyx BBBB ++=


GAUSSMETERSGAUSSMETERS

F.W.Bell 1-axis, 2 AxisLakeshore 2-axis

As Easy As Voltmeters Hall Effect Devices


GAUSSMETERSGAUSSMETERS

Sources of ErrorDrift - 1 Hour Warm upZeroing – Null in Zero Flux Chamber < -.004 G Positioning – Probe Perpendicular to SurfacesTemperature - Avoid High Temperature Areas Interference – Lab Equipment Audited, Max < .21G

AxialProbe

Transverse


MAGNETIC FIELD MAGNETIC FIELD MEASUREMENTSMEASUREMENTS

Engineering the Electroglas 4090µ Prober for a Neutral Magnetic Environment

Dynamic AnalysisGaussmeter NoiseZ MotionX,Y MotionTemperature Transition

Static AnalysisChuckQuick LoaderTransfer ArmPre-alignerLift Pins


DYNAMIC MEASUREMENTSDYNAMIC MEASUREMENTS

Dynamic Measurements Made at 1000 HzAnalog-Out Signal UsedData Captured Using Test Point Software


NOISE LEVEL ANALYSIS

Measured with probe in zero flux chamberZero Flux Chanber

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0 2000 4000 6000 8000 10000 12000

time (ms)

B (g

auss

)

Time (ms)

Zero Flux ChamberFi

eld

(Gau

ss)


MOTION ANALYSISMOTION ANALYSIS

Probe on Chuck Top (Wafer Plane on Forcer) Proximal to Vacuum PinField Component Normal to the Chuck Top

Measurements Made for Z Motions:5 Mils,10 Mils, 20 Mils50 Mils, 200Mils – Data Shown

Measurements Made for XY Platen Motions:X-fast, X-slow, Y-fast, Y-slow

Measurements Made for Temperature Change:Ambient to Hot (25C to 125C) Peltier


Z MOTION DATA Z MOTION DATA –– 50 MILS50 MILSZ motion - 50 mils

-1.35

-1.3

-1.25

-1.2

-1.15

-1.1

-1.05

-10 1000 2000 3000 4000 5000 6000

time (ms)

B (g

auss

)

Time (ms)

Fiel

d (G

auss

)Z Motion (50 mils)


Z MOTION DATA Z MOTION DATA –– 200 MILS200 MILSZ motion - 200 mils

-1.5

-1.45

-1.4

-1.35

-1.3

-1.25

-1.2

-1.15

-1.1

-1.05

-10 1000 2000 3000 4000 5000 6000

time (ms)

B (g

auss

)

z down

z downz up

z up

Time (ms)

Fiel

d (G

auss

)

Z Motion (200 mils)


X MOTION SLOW SCANX MOTION SLOW SCANSlow Scan in x axis

-1.4

-1.3

-1.2

-1.1

-1

-0.9

-0.80 1000 2000 3000 4000 5000 6000

Time (ms)

B (g

auss

)

begin motion

Time (ms)

Fiel

d (G

auss

)

Slow Scan in X-axis

Begin motion


X MOTION FAST SCANX MOTION FAST SCANFast scan - x axis

-1.7

-1.6

-1.5

-1.4

-1.3

-1.2

-1.1

-1

-0.9

-0.80 1000 2000 3000 4000 5000 6000

time (ms)

B (g

auss

)

start motion

stop motion

Time (ms)

Fiel

d (G

auss

)Fast Scan X-axis

start

stop


Y MOTION SLOW SCANY MOTION SLOW SCAN

Slow scan in y axis

-1.45

-1.4

-1.35

-1.3

-1.25

-1.2

-1.15

-1.1

-1.05

-10 1000 2000 3000 4000 5000 6000

time (ms)

B (g

auss

)

begin motion

Time (ms)

Fiel

d (G

auss

)

Slow Scan in Y-axis

begin motion


TEMPERATURE TRANSITION TEMPERATURE TRANSITION ANALYSISANALYSIS

Initial Transition (10 Seconds) Ambient to HotTemperature ramp up

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0 2000 4000 6000 8000 10000 12000

time (ms)

B (g

auss

)

Time (ms)

Fiel

d (G

auss

)Temperature Ramp (ambient to

hot)


DYNAMIC RESULTSDYNAMIC RESULTS

OK0.470.320.17Temp

OK, Delta 0.18, -1.03-----1.38Y Scan

OK-1.07-1.22-1.42X-Fast Scan

OK-0.89-1.08-1.30X-Slow Scan

Shield-1.00-1.23-1.48Z – 200 mils

Shield-1.09-1.15-1.32Z - 50 mils

OK – Negligible------------Z - 5, 10, 15 mils

Noisy – Needs Improvement 0.04Zeroing

IMPACTMAXAVEMINMeasurement

Spec < 5 G for Dynamic


FIELD CONTAINMENT STEPSFIELD CONTAINMENT STEPS

Retrofitted Magnetic Shielding KitsReplaced Shafts / Pins With Non-magnetic MaterialsDesigned Shields for Containment Repositioned Components

Improved Metrology –Reduced Noisy MeasurementsImproved Gaussmeters, Probes, and Sampling Jigs

Completed Measurement Matrix


FORCER SHIELDSFORCER SHIELDS

Fully Assembled Theta and Z-motor Shield


PREPRE--ALIGNER SHIELDSALIGNER SHIELDS

Pre-Aligner Shield


STATIC SAMPLING POINTSSTATIC SAMPLING POINTS

SIMULATED WAFER

PREALIGNER (17 test points) CHUCK (25 test points)


Prealigner Assy.

Probe Holder

Sypris SAF99-1802

XY fields

Simulated Wafer

Prealigner Cover

Sypris STF99-0402

XYZ fields

TEST FIXTURETEST FIXTURE


CHUCK FORCER POSITIONCHUCK FORCER POSITION


STATIC FIELD STATIC FIELD -- CHUCKCHUCK

Measured (X, Y, and Z Axes)Field Magnitude Is the Resultant Vector:

Results:1st Pass – Original Pins – 2.6 G Maximum

Pins Coupled Z, θ Motors to Wafer SurfaceReplaced Pins With Non-magnetic Composition

2nd Pass – SS 304 Pins – 1.84 G Maximum3rd Pass – New Mat’l Pins – 1.18 G Maximum4th Pass – Add Shields < 0.6 G Maximum

222zyx BBBB ++=


PIN MATERIAL EXPERIMENTPIN MATERIAL EXPERIMENT

None Z- θ Z- θCoupling Impact

Decision:Pins alone don’t meet spec, shield Z-theta motors

After Shielding: Wafer Plane < 0.6 G, Meets Spec !

1.051.841.53B-0.301.761.24Bz1.000.460.70By0.08-0.240.55Bx321

ss 304 pins (2nd Gen)

1.180.880.50B-0.950.640.25Bz0.700.480.33By0.060.370.28Bx321

New Pins (3rd Gen)


PREPRE--ALIGNERALIGNER4090µ Pre-aligner XY and Z Fields

-1.00

-0.80

-0.60

-0.40

-0.20

0.00

0.20

0.40

0.60

0.80

1.00

1 3 5 7 9 11 13 15 17

Location Number

Z

XYRange: 0.16 to

0.78


FORCER FORCER –– PROBE AREAPROBE AREA4090µ Probe Area XY And Z Averages

at Chuck Up And Down Position

-1.00

-0.80

-0.60

-0.40

-0.20

0.00

0.20

0.40

0.60

0.80

1.00

1 3 5 7 9 11 13 15 17 19 21 23 25

Location Number

Avg XY Up

Avg Z Up

Avg XY Down

Avg Z Down

Range: -0.68 to 0.59


MATERIAL HANDLERMATERIAL HANDLER

Static Analysis (measured over wafer surface)

0.58.0Lift pins0.81.3Pre-aligner0.50.5Transfer arm 0.50.5Quick Loader 0.68.0Chuck

After, Max

Before, MaxSite


CONCLUSION / SUMMARYCONCLUSION / SUMMARY

New Memory – New Requirements

MRAM AdvantagesTarget applications - cellular phones, portable devices, and personal computers. Instant-on computing, indefinite standby without power.

Test ChallengesAccurate magnetic measurementsControl of stray magnetic fields


APPRECIATIONAPPRECIATION

ElectroglasSteve LugosiLarry HendlerRobert BerganHardip Singh

Test Point SoftwareLarry Hendler

Cypress - SMSNarayan PirohitFred Jenne

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Critical Factors in Testing MRAM Devices

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