Electronic Displays Conference February 2014
Transcript of Electronic Displays Conference February 2014
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The Future of Capacitive Touch
In Mission Critical Applications
Electronic Displays Conference
February 2014
Chris Ard, Steve Roberts, Peter Sleeman
Agenda
• Capacitive touchscreens – from novelty to commodity
– Design Stepping Stones
– Limitations of projected capacitive touch
• Projected capacitive touch is here to stay
– Market adoption of capacitive touchscreens
– Consumer vs industrial touchscreens
• Current best practice
– Simulating & designing capacitive touchscreens
– Building & qualifying touchscreens
– Current state of the art
• Technology evolution
– New materials & manufacturing methods
– New features and their possible impact
• Conclusions
LG
Chocolate
LG
Prada
Samsung
F700
Apple
iPhone
The Birth of Capacitive
Touch in Mobile Handsets
Motorola
V6 Maxx
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Wall ovens
Microwave ovens
Inductive cooktops
Automotive keyless
Deskphones
MP3 players
PC button bars
Buttons & wheels on handsets
Self cap TS on handsets
Mutual cap TS on handsets
Design & Market Stepping Stones
Mutual Cap TS Now Commoditised in Consumer Electronics
What We
Learned
Ovens & cooktops – EMC
Automotive keypad – water
Phones – thin stack
BT headset – floating
Limitations of Capacitive Touchscreens
Projected Capacitive
• Durability of glass surface
• Excellent optical properties
• Good OS support
• Light touch / multi-touch (gestures)
• Meets user expectations
• Possibility for ‘prox’ sensing
• Difficult to integrate / tune
• ‘Works’ with dirt & liquids
• ‘Works’ with gloves
• ‘Good’ noise tolerance
• Cost higher than basic resistive
• Conductive touch ‘digit’ required
Analog Resisitive
• Small stylus of any material works
• Works with gloves & fingernails
• Very dirt & liquid tolerant
• Positive press action
• Excellent noise tolerance
• Large supplier base / easy to integrate
• Multi-touch is ‘available’
• Light / multi-touch gestures poor
• Wear-out inevitable
• Optical properties poor
• Calibration needed
Ad
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About TouchNetix
November 2009
Atmel supplies true
multitouch mutual
capacitance
solution
October 2008
Atmel launch
QTwo and QField
single touch and
dual touch
touchscreens
1996 1.. 2007 2008 2009 2010 2011 2012 2013 2014
Initial capacitive
touch products
developed by
Quantum
Research
2007
First capacitive
touchscreen
design win
February 2010
Samsung
Wave, first on-
cell design
using
maXTouch2005
First fixed
key
capacitive
touchscreen
Driving the Evolution of Capacitive Touchscreens
2012
Appliance
touchscreen2013
True single
layer ITO
2012
Marine
touchscreen
2014
Industrial
touchscreen
2014
True single
layer metal
Touchscreen Markets
• Projected touchscreen market 2018
• Three distinct volume segments:Orders of magnitude volume difference
Consumer: 2.4Bn, Auto: 42M, Non-Consumer: 7M
• Capacitive penetration in 2018:Consumer 99%, Auto 60%, Non-consumer 44%
Remainder is mostly Resistive
• Consumer business mostly 4.5” – 12”
• Non-consumer touchscreen markets
• Capacitive penetration 2014-2018:2014 is 22% >> 2018 is 44%
Remainder is mostly Resistive, IR, Surface Cap
• Majority of business >10” diagonal
• Barriers to adoption of capacitive are
disappearing fast
Market Data – DisplaySearch (2014)
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Consumer vs Industrial
Consumer Grade Touchscreens
• Built for yield & price; performance is
secondary
• Almost all suppliers ‘build to print’
• Design ‘print’ is typically provided by
driver IC vendor
• More than 200 global suppliers
• Testing usually for ‘function only’
• Often not tested to save cost
• No end user integration support for
volumes below 500K per year
• Product lifetime expectation is a few
years at most
Industrial Grade Touchscreens
• Flawless performance is expected
• Full parametric testing needed to
guarantee performance
• All suppliers are ‘build to print’ or
manufacture in partnership with
specialist design house
• Specialist design capability needed to
achieve required performance
• Expert integration support required
to guarantee performance in end
product
• Less than 10 capable global suppliers
• Lifetime expectation 20+ years
Long Product Life – Almost Always ‘On’
High duty cycle, multiple shift operation
Short Product Life - Usually Turned ‘Off’
Devices designed to ‘sleep’ to save power
Sensor – AFE – Processing – Tuning
• >90% of theoretical performance needed for industrial applications
• Tuning uses register settings – mostly no longer firmware driven
• Significant interaction between various IC register settings
• Importance of the sensor design cannot be over emphasized
• Deep knowledge of IC functionality is important to deliver best performance
System level testing essential – tuning examples below – IC vendor approach varies
sensor array
measurement
system
AFE / CTE
Data Acquisition
background
touch
algorithms
Frame Processing
post-process,
classify, report
(system tuning)
Object Processing
Housekeeping Functions – Drift Compensation etc
Touch
Event
Driven
Output
• Usability parameters
• Water suppression
• Small object detection (stylus)
• Gloved object detection
• Large object suppression
• Basic configurations
• clipping, channels
• sleep, electrical drive
parameters
• linearity, report rate
• Noise avoidance (desirable)
• frequency hopping
• higher voltage
• Noise mitigation (less desirable)
• several software filters
• common mode noise rejection
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Performance Simulation & Designing Sensors
• Optimal sensor design is key for larger
touchscreens – much better performance
• Chip vendor design guides have limitations
• Touch delta, signal crosstalk, floating
behaviour, noise tolerance are all strongly
design driven
• TouchNetix design process is significantly
automated to provide complete production
DXF including edge wiring design and optical
modifier algorithms
• New materials & stacks easily evaluated
before building sensors
Unintended Touch
Delta
Main Touch DeltaSignal crosstalk example
from performance
simulation
(Single layer metal design)
DITO SITO
Node Size / Pitch
Sensor Size (15")
Pattern type Flooded-X Diamond w/bridges
Connection
ITO
Edge track resistance
Bridge insulator N/A 1.5µm @ εr=3.0
Bridge width N/A 0.2 mm
Rx spines 0.25 mm N/A
Node capacitance (3D FEM) 1.0pF 1.9pF
Node resistance (2D FEM) Tx: 50 Ω / Rx: 1000Ω Tx & Rx: 317 Ω
Touch Delta (3D FEM) 4.6% 3.1%
90% charge time (SPICE) 0.91 µs 1.53 µs
ST
RU
CT
UR
ES
IMU
LA
TIO
N
5mm x 5mm
40Tx x 70Rx Electrodes
All four edges
50 Ohm/sq
200 Ohm
• 1/3 of performance potential lost using SITO
• Large surface area receivers in diamond
pattern significantly degrade noise tolerance
SITO vs DITO Comparison
Building Good Sensors
• Building & diagnosing sensors is instructive
• Almost all sensors ‘work’ off the production line
– some are not suitable for industrial markets
• Must measure corner cases on all time constants
to be sure of performance
References
Map (note
some sensor
problems)
Visualisation Tool
TouchHub Characterisation & Test Toolset
Production Test Tool
Y Line
Isola
tion
Isola
tion
Isola
tion
Gro
und
20µm cuts
High Impedance Y Short to Gnd
Y line not fully connected both ends
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Qualifying Industrial Touchscreens
• Surviving (powered) damp heat is a key test• 60⁰C/90%RH or 85⁰C/85%RH
• Not a simple system to analyse• Chip drive mechanism is important
• High duty cycle of industrial systems
• ALWAYS on & working
• Several materials / interfaces involved
• Sensor constraints• Narrow edge margins >> higher field strength
• Low resistance ITO >> glass substrates
• Higher IC drive voltages (40V!) to improve SNR
• Risks from electric fields• Can enhance migration of edge wiring (silver)
• Corrosion of ALL materials
• Damage to dielectric materials (breakdown)
• Sensors often still functional BUT• Degraded performance, susceptible to noise Breakdown Damage to OCA
Silver Migration
State of the Art
Full Multi-Touch Capacitive Touchscreens for Industrial Applications• Up to 24” diagonal with 3-4mm front lens typical
• Node pitch – ideal is <5mm for tight pinch, linearity degrades when larger
• 10V RMS injected noise immunity (during operation)
• Palm & wipe-down suppression
• Glove operable (thick industrial)
• ‘Noisy’ display compatible
• Harsh Environmental spec
• >500Hrs (operating) at 60⁰C / 90%RH
• Works well with ‘some’ water on surface
Future Requirements• Secondary confirmation from ‘press’
• Lower cost
• Further improvements to water tolerance
• Controlled introduction of new materials / structures
Typical industrial gloves
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The Future – Touch Qualification
• Press qualification of XY touch data - important for industrial, medical &
automotive applications
– physical press of the cover lens to trigger an activation
– effective press detection also enables realistic haptic effects
• Capacitive touch panels already output a “Z” component >> touch ‘intensity’
– not user independent, relies on finger squash, data unreliable
• A new ‘press sensing’ technique has been developed by TouchNetix
– custom touch panel and measurement system
– detects tiny ‘relative’ changes in cover lens position (microns of displacement)
– works in any orientation, generates substantially uniform output across entire
surface, fully scalable
• Combine in OS (or elsewhere) to qualify &
enhance XY touch data
• Application example: press to zoom
• Come to exhibit 1-158 to try
Press Sensing Output Streams
Touch event data
Press event data
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Capacitive pressScreen
• Uniform surface response for good usability
• Press data delivered to Windows or Linux OS
• Multi-point capacitive touch – integrated press
• Aggregate pressure with around 8-bits range
• Works with any lens thickness or material
0-40g ~140g ~400g
15” Diagonal Capacitive pressScreen
Dynamic ‘Tap’ pressure
response is important
Touch surfaceTouch sensor
Press
sensor
Mounting
/sealing
gasket
Frame Display
Light tap
Medium tap
Heavy tap
Approx10µm
displacement
for 200g press
Touch Only
The Future - New Materials & Structures
• Why move away from ITO?
– Commercially OK, availability & quality remain good
– ITO is OK out to ~24” diagonal screens (glass sensor substrate)
• Lower resistance materials are desirable beyond ~18”
• Alternatives to ITO (Not for reasons of cost)
– Metal (mesh) sensors – good option
• Good performance advantages
– Silver nanowire – sensor performance OK
• Optical properties now acceptable for many applications
• Reliability needs further confirmation
– Carbon based sensors
• Maturing but not all aspects ready yet
• Single layer structures will find a place
– Simulation essential to achieve required performance
Single layer sensor
metal structure
Moiré effect
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Conclusions
• The market for non-consumer applications is developing rapidly
– Different focus – flawless performance over many years needed in most applications
– Trouble free implementation and competitive low volume availability (low tooling costs)
are important to fully enable these markets
– Deployment methodologies improving but will not be as easy as resistive any time soon
• ITO is adequate for existing requirements if you know the pitfalls
– Film sensors OK up to 10” diagonal, glass sensors OK up to 24” diagonal
– Care needed with higher voltage drive - there may be side effects
• New materials & stacks show promise to supplement ITO
– Need to design to the strengths of these materials, metal is particularly promising
– True single layer film sensors will earn their place up to 10” diagonal
• What do we still need to work on?
– Use with gloves and with water can always be improved – variable results with dual
(self, mutual) mode on larger screens
– Press sensing - highly interesting ‘qualification’ UI layer – new applications & HAPTICS
will be enabled by work in this area