Electronic Displays Conference February 2014

20/05/2015

1

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

van

tag

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Issu

es

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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