critical factors in testing mram devices
TRANSCRIPT
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 !
Stevenson -- CYPRESS 3 SWTW – June 2003
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
Stevenson -- CYPRESS 4 SWTW – June 2003
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
Stevenson -- CYPRESS 5 SWTW – June 2003
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-
Stevenson -- CYPRESS 6 SWTW – June 2003
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
Stevenson -- CYPRESS 7 SWTW – June 2003
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
Stevenson -- CYPRESS 8 SWTW – June 2003
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
Stevenson -- CYPRESS 9 SWTW – June 2003
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
Stevenson -- CYPRESS 10 SWTW – June 2003
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 ++=
Stevenson -- CYPRESS 11 SWTW – June 2003
GAUSSMETERSGAUSSMETERS
F.W.Bell 1-axis, 2 AxisLakeshore 2-axis
As Easy As Voltmeters Hall Effect Devices
Stevenson -- CYPRESS 12 SWTW – June 2003
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
Stevenson -- CYPRESS 13 SWTW – June 2003
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
Stevenson -- CYPRESS 14 SWTW – June 2003
DYNAMIC MEASUREMENTSDYNAMIC MEASUREMENTS
Dynamic Measurements Made at 1000 HzAnalog-Out Signal UsedData Captured Using Test Point Software
Stevenson -- CYPRESS 15 SWTW – June 2003
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)
Stevenson -- CYPRESS 16 SWTW – June 2003
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
Stevenson -- CYPRESS 17 SWTW – June 2003
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)
Stevenson -- CYPRESS 18 SWTW – June 2003
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)
Stevenson -- CYPRESS 19 SWTW – June 2003
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
Stevenson -- CYPRESS 20 SWTW – June 2003
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
Stevenson -- CYPRESS 21 SWTW – June 2003
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
Stevenson -- CYPRESS 22 SWTW – June 2003
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)
Stevenson -- CYPRESS 23 SWTW – June 2003
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
Stevenson -- CYPRESS 24 SWTW – June 2003
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
Stevenson -- CYPRESS 25 SWTW – June 2003
FORCER SHIELDSFORCER SHIELDS
Fully Assembled Theta and Z-motor Shield
Stevenson -- CYPRESS 27 SWTW – June 2003
STATIC SAMPLING POINTSSTATIC SAMPLING POINTS
SIMULATED WAFER
PREALIGNER (17 test points) CHUCK (25 test points)
Stevenson -- CYPRESS 28 SWTW – June 2003
Prealigner Assy.
Probe Holder
Sypris SAF99-1802
XY fields
Simulated Wafer
Prealigner Cover
Sypris STF99-0402
XYZ fields
TEST FIXTURETEST FIXTURE
Stevenson -- CYPRESS 30 SWTW – June 2003
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 ++=
Stevenson -- CYPRESS 31 SWTW – June 2003
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)
Stevenson -- CYPRESS 32 SWTW – June 2003
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
Stevenson -- CYPRESS 33 SWTW – June 2003
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
Stevenson -- CYPRESS 34 SWTW – June 2003
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
Stevenson -- CYPRESS 35 SWTW – June 2003
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