Property of Cover Glass in Capacitive Touch Screen
Transcript of Property of Cover Glass in Capacitive Touch Screen
Property of Cover Glass in CapacitiveTouch Screen
2© Corning Incorporated 2008Technical Materials
Corning Incorporated
Founded:1851
Headquarters:Corning, New York
Employees:Approximately 25,000 worldwide
2007 Sales:$5.86 Billion
Fortune 500 Rank:417
• Corning is the world leader in specialty glassand ceramics.
• We create and make keystone componentsthat enable high-technology systems forconsumer electronics, mobile emissionscontrol, telecommunications andlife sciences.
• We succeed through sustained investmentin R&D, over 150 years of materials scienceand process engineering knowledge, and adistinctive collaborative culture.
3© Corning Incorporated 2008Technical Materials
Corning market segments and additional operations
DisplayTechnologies
Telecom EnvironmentalTechnologies
LifeSciences
SpecialtyMaterials
OtherProducts
& Services
•LCD GlassSubstrates
•LTPS-LCD GlassSubstrates
•Optical Fiber &Cable
•Hardware &Equipment
CoaxialConnectivityProducts
•EmissionsControl Products
– Automotive– Diesel– Stationary
•Cell Culture &Bioprocess
•GeneralLaboratoryProducts
•Advanced Optics &Materials
•Display Optics &Components
•SemiconductorOptics &Components
•Aerospace•Astronomy•Optical Metrology•Ophthalmic•Telecom
Components•Specialty Glass
•Display Futures
•New BusinessDevelopment
•Drug DiscoveryTechnology
•Steuben Glass
•Equity Companies– Dow Corning Corp.– Eurokera, S.N.C– Samsung Corning
Precision GlassCompany, LTD(SCP)
GorillaTM Glass
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A culture of innovation
Processes for massproducing thetelevision bulb
19471879
Glass envelope forThomas Edison’slight bulb
1915
Heat-resistantPyrex® glass
First low-lossoptical fiber
1970 1984
AMLCD glass forcomputers andlarge screen TVs
1972
Ceramic substratesfor automotivecatalytic converters
Dow Corningsilicones
1934
Glass ceramics
1952 2006
High-throughputlabel-free screeningplatform fordrug discovery
Fusion drawprocess
1960
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Capacitive Touch ScreenStructure
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Current Tech
Surface Capacitive is currently the 2nd largest technology
Source: 3M
•How it works– ITO conducts a continuous electrical
current across the sensor– Finger touch alters the capacitance field– The resulting distortion is measured by
circuits at each corner of the screen
•Advantages: durability
•Disadvantages: requires finger touch
•Applications: retail, game/entertainment,industrial/financial
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Current Tech
Projected Capacitive becomes more popular due toiPhone, and can be used for both small and large panels
Source: Elo
•How it works– Consists of a sensor grid of micro-fine wires
laminated between two layers of protectiveglass
– Touch location calculated from changingelectrical characteristics of the sensor grid
– Can be installed behind other materials, e.g.vandal-resistant glass
– Finger does not have to be in physicalcontact
•Advantages: durability, environmental tolerance
•Disadvantage: high cost
•Applications: mobile phone, retail
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Design Considerationsfor
Cover Glass
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Typical glass surface damage from “used”devices
~ 20 micron depth
~ 40 micron depth
Scratch with Lateral Cracks
Scratches
Impacts
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Surface damages cause glass failureSummary of Failure Analysis of Broken Devices (Field-returned and drop tested):
• Major cause of fracture – Impact damage– Sharp impacts create flaws that cause failure
• Keys, pens, gravel, etc.
• Second major cause - Scratch-related damage– Fracture initiated from a flaw within the scratch
• Over-stress alone does not cause failure– Strengthened glass deflects substantially before failure
• Devices do not have room for so much deflection– Failure stresses are never reached
Origin
Depth of damage 15 µm
Impact event
Depth of scratch 25-40µm
Scratch event
Impact
Scratch
Other
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1st Qtr
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Design considerations• Define “Design strength”
• Strength of glass decreaseswhen damaged– In-use strength measured by
Abraded Strength– Abrasion per ASTM C158
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100
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Glass and IX Condition
Stre
ngth
, MPa
IG3NS
IG3 Corning18
Corning31
Corning45
Corning57
only enoughspecimens forabrasion at tmeof testing
Unabraded
abraded
• Strength of brittle materialsrepresented by Weibull statistics– Select low (1%?) probability of
failure strength– Apply a factor of safety
Strength, MPa
Failu
re P
roba
bilit
y, %
100 10001
5
10
50
90
99
Soda limeglass
Gorillaglass
• Input requirements from failure-mode analysis
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Requirements for glass in mobile devices
1. Tight Strength distributions
2. High retained (abraded) strength
3. Increased resistance to impact damage
4. Greater resistance to scratching
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Gorilla™ Glass
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What is Corning Gorilla™ Glass?
• Alumino-silicate thin sheet glass– Capable of high strength and reliability when chemically
tempered with an ion-exchange process
• Formed using Corning’s proprietary fusion draw process– Highest quality of as-drawn glass sheets in the world– Thickness 0.7 mm –2.0 mm as drawn
• Corning glass is ideal for display cover windows– Touch screens– Mobile phones– Other mobile electronic devices
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Key benefits
• Glass designed for deep, protective, ion-exchange layer
• High strength and reliability
• Ability to sustain impacts without damage
• Retains high strength after use and abuse
• Pristine glass sheet surface
• Scalable sheet sizes for optimal throughput
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Gorilla™ Glass combines unique capabilities
Proprietary fusionforming process:superior surface,
scalability,reliability
Innovative glasscompositionoptimized for
chemicaltempering
Gorilla Glass
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Fusion-formed for a pristine surface
Roughness Measurement ResultsArea 1 Area 2
RMS 0.29 nm 1.46 nmRa 0.23 nm 1.13 nmZ-Range 4.23 nm 33.7 nm
5 um 5 m
Fusion Lap & polish10 nm
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What properties of glass provide these requirements?
• Flaws, damages andscratches on the surfacereduce strength
• Enveloping compression layerof Gorilla™ Glass providestight strength distributions
Flaw populations in the surface
Competition GorillaCross section of a chip
Competition GorillaCross section of a scratch
Competition Gorilla
DOL
DOL
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Gorilla™ Glass –ideally suited for protective covers formobile displays
• Highest degree of chemical strengthening
• Tightest strength distribution
• Highly tolerant to in-use damage (high retained strength)
• Highest impact resistance
• Highest resistance to scratch
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The ion-exchange process
O2
Si
AlNa: 0.97Å
K:1.33Å
KNO3bath
glass
Glasssurface
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What is chemical strengthening?
• Compressive stress and depthof layer (DOL) define thecharacteristics of chemicalstrengthening
• Stress equilibrium will inducea tensile stress in the centerof the sheet
• Overcoming the compressivestress at the crack tip isnecessary to initiate failure
CS
TS
DOL
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Gorilla™ Glass has the highest depth of layer (DOL)
• Degree of chemicalstrengthening is thedevelopment of thedesired level ofcompressive stress(CS) over desiredDOL
• Gorilla Glass canachieve DOLgreater than typicaldamages/flawsdepth
• Gorilla glass isdesigned for lowerstress relaxation,higher DOL andhigh CS
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
300.0 400.0 500.0 600.0 700.0 800.0 900.0Compressive stress (MPa)
DO
L ( µ
m)
E
A
I
Gorilla
Compressive Stress (MPa)
Gorilla
DO
L (µ
m)
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300
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E A I Gorilla
Com
pres
sive
Str
ess
(MPa
) DOL = 15DOL = 25
Gorilla™ Glass has the highest CS at given DOL
• The predicted CS at15 um and 25 umDOL is shown
• At deeper DOL,compressivestresses aresignificantly lowerfor the soda-limeglassesC
ompr
essi
ve S
tress
(MP
a)
Gorilla
Extrapolated
24© Corning Incorporated 2008Technical Materials
Gorilla™ Glass –ideally suited for protective covers formobile displays
• Highest degree of chemical strengthening
• Tightest strength distribution
• Highly tolerant to in-use damage
• Highest impact resistance
• Highest resistance to scratch
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Gorilla™ Glass has tighter strength distribution
A
Gorilla
Strength, MPa
Failu
re P
roba
bilit
y, %
100 10001
5
10
50
90
99
• Gorilla Glassshows thehighest overallstrength
Note: Edge strength is measured using 4-pt bend test
26© Corning Incorporated 2008Technical Materials
Gorilla™ Glass –ideally suited for protective covers formobile displays
• Highest degree of chemical strengthening
• Tightest strength distribution
• Highly tolerant to in-use damage
• Highest impact resistance
• Highest resistance to scratch
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Flaws induced during in-service life
Gorilla™ Soda Lime
• “In Use Flaws”canbe simulated byabrading thesurface
– ASTM C158
• Measure strengthafter increasinglevels of abrasionof glass surface– Ring-on-ring test
method
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• “Contact force factor”combines abrasionpressure with gritdiameter
• A deeper DOL protectsthe glass surface fromin-use damage
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0 5 10 15 20Contact Force Factor
Stre
ngth
(MPa
)
GorillaAEI
Gorilla™ Glass retains significant strength after use
Gorilla
Stre
ngth
(MPa
)
Contact Force Factor
Higher “In Use”Strength
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High retained strength is directly related to DOL
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Glass and IX Condition
Stre
ngth
, MPa
IG3NS
IG3 Corning18
Corning31
Corning45
Corning57
only enoughspecimens forabrasion at tmeof testing
Unabraded
abraded
30© Corning Incorporated 2008Technical Materials
Gorilla™ Glass –ideally suited for protective covers formobile displays
• Highest degree of chemical strengthening
• Tightest strength distribution
• Highly tolerant to in-use damage
• Highest damage resistance
• Highest resistance to scratch
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Gorilla™ has increased resistance to impact damage
4500 g load 1500 g load
IOX Gorilla Glass IOX Soda Lime
Vickers indenter: a = 68.00°
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Gorilla™ Glass can bear up to 6X more load
Gorilla glass withstands 6X higher loads before radial cracks form- Sharp object impact
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7000
A I E Gorilla
Crit
ical
Loa
d (g
)
Gorilla
Crit
ical
Loa
d (g
)
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Gorilla™ Glass is more resistant to lateral cracking
No lateral cracks were initiated in Gorilla glass for loads up to 6500 grams
Load Required to Initiate Lateral CracksLoad required to initiate lateral cracks
14.81214.2
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A C E 1317
Cri
tical
Loa
d (g
)
no cracks
I
DOL
Gorilla
Crit
ical
Loa
d (g
)
Load Required to Initiate Lateral Cracks
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Gorilla™ Glass is more resistant to chipping
Gorilla glass inhibits formation of chips associated with indentation
Load required to initiate chipping
14.812
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Cri
tical
Loa
d (g
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no chips
I
Load Required to Initiate Chipping
DOL
Gorilla
Crit
ical
Loa
d (g
)
35© Corning Incorporated 2008Technical Materials
Gorilla™ Glass –ideally suited for protective covers formobile displays
• Highest degree of chemical strengthening
• Tightest strength distribution
• Highly tolerant to in-use damage
• Highest impact resistance
• Highest resistance to scratch
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Gorilla™ Glass shows minimum collateral damageafter scratch event
A20
400
Load
(g)
lateral cracks
scratch groovechipping
I20
400
Load
(g)
chipping scratch groove
Gorilla20
400
Load
(g)
E
Loadchart notto scale
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Gorilla™ Glass is designed for mobile devices
Minimum collateralDamage after scratch
event
Highest DamageTolerance
Greatest RetainedStrength
Tightest StrengthDistribution
DeepestDepth of Layer
Maximum SurfaceCompressive Stress
OptimalMobile DevicePerformance
Thank You