HiTUS – an enabling technology for the

plastic electronics industry

19th March 2012

Dr. Steve Wakeham

Senior Development Engineer

Background to Plasma Quest Limited

PQL is a R&D company founded in 1998, 9 staff, 5 PhD’s. Based in Hook, Hampshire

Specialises in sputter deposition using a remote plasma

Novel generation provides greater control of deposition variables

Near ideal physical properties

“An enabling technology”

Introduction

Sputtering basics and the development of HiTUS

Key advantages of HiTUS, specifically for the plastic electronics industry

Large area capability – role to role compatible

Transparent conducting materials on plastic substrates (specifically ITO and ultra-thin gold).

Multitude of high deposition rate dielectrics can be deposited onto plastic substrates

Dielectric mirrors/colour filters

TFT’s and EL devices also possible

Sputter Deposition

Method for depositing a very thin film onto a bulk material using plasma

Generation of plasma by applying energy to a gas at reduced pressure

Positive ions in plasma are attracted to negative target and ‘sputter’ target atoms

These atoms form a thin film on any surface they come into contact with

PQL use a proprietary launch system to generate ions remotely Magnetron Sample with Race Track

Sputter system comparison

Gnd

Diode Sputtering(no magnetic field)

Low ionisation efficiency

= low sputter rates, high pressure

Target current density0.1 – 2.0 mA/cm2

Target : -ve bias

Gnd

‘Magnetron’ -confinement at target

High local ionisation efficiency

= high local sputter rates (‘racetrack’)

Target current densityup to 100 mA/cm2

locally

Target : -ve bias

Gnd

Remote Plasma

High remote ionisation efficiency= high sputter rates

over full targetTarget current density

up to 100 mA/cm2

over full target

Target : -ve bias

Remote generation

RF antenna generates plasma, magnets confine and amplify plasma density (from ~1010 ions/cm3 at antenna to ~1013 ions/cm3 near PLS exit)

High ion densities (but low energy) are achieved over whole target, no race track

No sputtering without target bias

Independent control of plasma density and ion energy

Large deposition parameter space

Reactive Sputtering

Used to deposit an oxide (or other compound) from a metal target

Reactive gas is injected at substrate and combines with sputtered metal particles

Magnetrons exhibits poor control due to target poisoning

PQL Systems sputter the whole target leading to greater control

HiTUS Reactive SputteringMagnetron Reactive Sputtering

System Configuration

Launch and steering electromagnets control ‘direction’ of plasma

Multi-Target system

– E.g. In:Sn, Hf, Al, Zn:Mn

– Complete devices without breaking

vacuum

Reactive gases are fed close to substrate and argon is fed close to target → help to prevent target poisoning

Glass, Si and flexible substrates secured to rotating platform

Key Advantages

Low Temperature Processes

Compatible with Plastics

High Deposition Rates

Controllable Stress

Increased Adhesion

Increased DensificationExample: Gold onto planarised PEN

Multi-target, multi substrate

ILH550First inline large area ‘HiTUS’

system, using proven ‘Linear’ version of the PQL technology

ILH 550

Key Attributes:

14” long, 3” diameter target

12” x 12” substrate coating

2 substrates simultaneously

peak deposition rate of 250nm/min

low temperature processes (<50 °C)

Expansion capability:

20” long target, 18” x 18”substrates

Role to role processing

No external substrate heating

Average of > 90 % visible transmission

Resistivity = 3.5 × 10-4 Ωcm

Low stress

Sheet resistance = 9 Ω/ for 400 nm film

Deposition rate > 70 nm/min

Properties retained when flexed

ITO on plastic substrates

200 nm ITO deposited by HiTUS

0

20

40

60

80

100

400 600 800 1000Wavelength (nm)

Tra

nsm

issio

n (

%)

HiTUS ITO on planarised PEN

HiTUS ITO on PET

Ultra-thin Gold

Thickness: between 40 and 80 Å

Conductivity: 16 ohms/square

Optical transmittance: 75% peak

Temperature: Ambient Ultra-thin gold on PEN

0

20

40

60

80

100

300 500 700 900 1100Wavelength (nm)

Tra

nsm

issio

n (

%)

Uncoated planarised PEN

Gold coated - 16 Ohm/sq.

Process time: 25 seconds

Substrates: PET/PEN/BOPP/Glass

One single processing step

High deposition rate dielectrics

Dispersion profiles for Hafnia

1.5

2

2.5

3

3.5

200 400 600 800 1000Wavelength (nm)

Ra

fra

cti

ve

in

dex IAD

HiTUS

Transmission data for HiTUS HfO2

0

20

40

60

80

100

250 500 750 1000 1250 1500 1750 2000 2250 2500

Wavelength (nm)

Tra

ns

mis

sio

n (

%)

Measured

Theoretical model357.8nm HfO2n = 2.06 at 550nm

Deposition rate > 20 nm/min on plastic

Higher R.I. than IAD deposited HfO2

Independently measured

Similar results seen for other coatings

Dielectric mirrors on PEN

23 Layer Calibration filter (SiO2/HfO2)

0

20

40

60

80

100

300 500 700 900 1100Wavelength (nm)

Tra

nsm

issio

n (

%)

Theory (dispersion datafrom AJTF)

Measured

Colour filters on PEN

Multi-layers of HfO2 and SiO2

Structure is HLHL…HLH (QW)

Layer count = 19 to 25

Overall thicknesses are between 1.2 and 2.0 µm

Vary the colour by adjusting the reference wavelength and hence changing thickness of individual layers

Higher R.I. = lower physical thickness (optical thickness = λ/4)

Photoluminescence on glass

HiTUS ZnS:Mn thin film exposed to UV light source

– Thickness = 620 nm– Target power = 200 W– Deposition rate = 55 nm/min

Substrate

Bottom electrode (e.g. ITO)

EL phosphor (ZnS:Mn

Top electrode

Dielectric

Dielectric

Fabrication of EL devices using HiTUS

All layers deposited with no

substrate heating

Working devices fabricated with no

post deposition annealing

Excellent transparency

– ITO used for front and back contacts

Complete structures deposited onto:

– Silicon and glass

– Planarised PET and PEN

substrates

EL device with double insulating layer structure

)

Electroluminescence on glass

Plastic compatible TFT’s

Channel layers:

– InZnO µFE ~ 10 cm2/V.sSwitching ratio > 106

– ZnO µFE ~ 0.4 cm2/V.sσins = 3.0 x 10-9 Ω-1m-1

σcon= 3.0 x 104 Ω-1m-1

High K(~30) Dielectrics:

– HfO2*:ρ=1014 Ωcm

breakdown > 3 MVcm-1

– AlN: ρ=2.7x1013 Ωcmbreakdown > 3 MVcm-1

Transparent devices at plastic compatible temperatures

1.E-12

1.E-11

1.E-10

1.E-09

1.E-08

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

-20 -10 0 10 20 30

Vg [V]

Ids [A

]

Vd = 5

Vd = 2

Vd = 0.2

* Flora M. Li et al, Applied Physics Letters 98, 252903 (2011)

Conducting ZnO

IZO channel

Cr/ITO gate contact

HfO2/Al2O3 gate insulator

IZO channel

S D S

Polymeric substrate

D

Summary

HiTUS is ABLE TO DEPOSIT THIN FILM COATINGS ONTO TEMPERATURE SENSITIVE PLASTICS because the substrates can be located away from the plasma.

Deposition ‘through’ high density plasma offers significant benefits as high energy is provided in an alternative way to heating the substrates.

Films are deposited with properties close to the bulk material (R.I. measurements of both HfO2 and Nb2O5 have demonstrated this)

Stress can be controlled by varying the process pressure during deposition

Hence low stress, fully densified thin films can be deposited onto plastic substrates at high rate.