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A

SEMINAR REPORT

ON

Flexible Electronics

Submitted

in Partial Fulfillment

for the Award of the Degree of

Bachelor of Technology

In Department of Electronics & Communication Engineering

Session-2013-2017

Submitted To:- Submitted By:-

Mrs. Shumaila Akbar SOURABH KUMAR

(H.O.D of ECE Department) (13ECIECOO8)

DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING

COMPUCOM INSTITUTE OF TECHNOLOGY AND MANAGEMENT

SP-5,EPIP RIICO INDS. AREA SITAPURA, JAIPUR-302022

RAJASTHAN TECHNICAL UNIVERSITY KOTA

FEBRUARY, 2017

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Candidate Deceleration

I hereby declare that the work, which is being presented in the Seminar report, entitled

“Flexible Electronics” in partial fulfillment for the award of the Degree of “bachelor of technology” in

Electronics and Communication Engineering submitted to the Department of EC Engineering,

I have not submitted the matter presented in this technical report anywhere for the award of my other Degree.

SOURABH KUMAR

Branch: EC

Enrolment No: 13E1CIECM3XP008

Roll No: 13ECIEC008

CIITM, Jaipur, Rajasthan, India

Head Of Department:

Mrs. Shumaila Akbar

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ACKNOWLEDGEMENT

Inspiration and guidance are valuable in all aspects of life, especially what is academic. “Experience is the best

teacher”, is an old age. The satisfaction and pleasure that accompany the gain of experience would be

incomplete without mentioning the people who made it possible.

I am extremely thankful and grateful to our guide Mr. AJAY JANGID Dept. of Electronics and

Communication Engineering, CITM. He is being our guide has taken keen interest in the progress of the

seminar work by providing facilities and guidance. I am indebted to my guide and co-ordinator for his

inspiration, support and kindness showered on us throughout the course. I express my profound sense of

gratitude to SHUMAILA AKBAR, HOD, Dept. of Electronics and Communication Engineering, CITM for

giving me the opportunity to pursue my interest in this Seminar.

Lastly, heartfelt thanks to my parents, friends and teaching and non-teaching staff of my college for their

encouragement and support.

SOURABH KUMAR

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COMPUCOM INSTITUTE OF TECHNOLOGY AND

MANAGEMENT

CERTIFICATE

This is to certify that the Seminar entitled “Flexible Electronic Paper ” is bonafied work carried

out by SOURABH KUMAR (13ECIEC008) in partial fulfillment of VIII Semester to award the

Bachelor Degree in Electronics and Communication Engineering of the COMPUCOM

INSTITUTE OF TECHNOLOGY AND MANAGEMENT under RAJASTHAN TENCHNICAL

UNIVERSITY,KOTA during the year 2016-17. It is certified that all corrections/suggestions

indicated for Internal Assessment have been incorporated in the Report and deposited in the

department library. The Seminar Report has been approved as it satisfies all the academic

requirements in respect of Seminar prescribed for the Bachelor of Engineering Degree.

Mrs. Shumaila Akbar

Project Guide & Project Coordinator

(Head of the Department ECE)

Place: Jaipur

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Abstract

Flexible electronics is a new trend in electronics industry to handle the increasing burden on

chips. It is a technology for assembling electronic circuits by mounting electronic devices on

flexible plastic substrate. This technology is increasingly being used in a number of applications

which benefit from their light weight, favourable dielectric properties, robust, high circuit

density and conformable nature. Flexible circuits can be rolled away when not required. To

replace glass, plastic substrate must offer properties like clarity, dimensional stability, low

coefficient of thermal expansion, elasticity etc. Recent advances in organic and inorganic based

electronics proceeds on flexible substrate, offer substantial rewards in terms of being able to

develop displays that are thinner , lighter and can be rolled when not in use. This paper will

discuss about the properties, preparation methods, applications and challenges in this rapidly

growing industry.

Keywords : Electronics, Flexible, Circuits, Silicon, Substrates

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CONTENTS

CONTENTS PAGE NO

Candidate Deceleration ……………………………………….. 2

Acknowledgement ………………………………………… 3

Certificate ……………………………………………. 4

Abstract …………………………………………………. 5

1.Flexible Electronics

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Chapter 1

Flexible Electronics

1.1 Introduction

Flexible electronics, also known as flex circuits, is a technology for assembling electronic

circuits by mounting electronic devices on flexible plastic substrates, such

as polyimide, PEEK or transparent conductive polyester film. Additionally, flex circuits can

be screen printed silver circuits on polyester. Flexible electronic assemblies may be

manufactured using identical components used for rigid printed circuit boards, allowing the

board to conform to a desired shape, or to flex during its use. An alternative approach to flexible

electronics suggests various etching techniques to thin down the traditional silicon substrate to

few tens of micrometers to gain reasonable flexibility, referred to as flexible silicon (~ 5 mm

bending radius).

Flexible electronics have recently attracted much attention since they enable many promising

applications such as RFID tags, solar cells ,bio-sensors, wireless power and signal transmission

sheets ,e-skin, e-paper and flexible display. The characteristic of flexible electronics is not only

reduced cost and they have light weight, thinner, non-breakable & new forms to create many

new applications. It is an attractive candidate for next-generation consumer electronics and they

will soon be part of our daily lives. Development strategy of flexible electronics is dependent on

global technology progresses and market forecasts. Currently, it has been estimated that there

are about 1500 worldwide research units working on various aspects of flexible electronics.

Market analysis estimates the revenue of flexible electronics can reach 30 billion USD in 2017

and over 300 billion USD in 2028

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1.2 History

Patents issued at the turn of the 20th century show that early researchers were envisioning ways

of making flat conductors sandwiched between layers of insulating material to layout electrical

circuits to serve in early telephony switching applications. One of the earliest descriptions of

what could be called a flex circuit was unearthed by Dr Ken Gilleo[13]and disclosed in an

English patent by Albert Hansen in 1903 where Hansen described a construction consisting of

flat metal conductors on paraffin coated paper. Thomas Edison’s lab books from the same

period also indicate that he was thinking to coat patterns cellulose gum applied to linen paper

with graphite powder to create what would have clearly been flexible circuits, though there is

no evidence that it was reduced to practice. In the 1947 publication "Printed Circuit

Techniques" by Cledo Brunetti and Roger W. Curtis[14] a brief discussion of creating circuits on

what would have been flexible insulating materials (e.g. paper) indicated that the idea was in

place and in the 1950s Sanders Associates' inventors (Nashua, NH) Victor Dahlgren and

company founder Royden Sanders made significant strides developing and patenting processes

for printing and etching flat conductors on flexible base materials to replace wire harnesses. An

advertisement from the 1950 placed by Photocircuits Corporation in New York demonstrated

their active interest in flexible circuits also.

Today, flexible circuits which are also variously known around the world variously as flexible

printed wiring, flex print, flexi circuits, are used many products. Large credit is due to the

efforts of Japanese electronics packaging engineers who have found countless new ways to

employ flexible circuit technology. For the last decade, flexible circuits have remained one of

the fastest growing of all interconnection product market segments. A more recent variation on

flexible circuit technology is one called "flexible electronics" which commonly involves the

integration of both active and passive functions in the processing.

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Chapter 2

Flexible circuit structures

2.1 Introduction

There are a few basic constructions of flexible circuits but there is significant variation between

the different types in terms of their construction. Following is a review of the most common

types of flexible circuit constructions

2.2 Types of Flex Circuits

2.2.1 Single-sided flex circuits

Single-sided flexible circuits have a single conductor layer made of either a metal or conductive

(metal filled) polymer on a flexible dielectric film. Component termination features are

accessible only from one side. Holes may be formed in the base film to allow component leads

to pass through for interconnection, normally by soldering. Single sided flex circuits can be

fabricated with or without such protective coatings as cover layers or cover coats, however the

use of a protective coating over circuits is the most common practice. The development

of surface mounted devices on sputtered conductive films has enabled the production of

transparent LED Films, which is used in LED Glass but also in flexible automotive lighting

composites.

2.2.2 Double access or back bared flex circuits

Double access flex, also known as back bared flex, are flexible circuits having a single

conductor layer but which is processed so as to allow access to selected features of the

conductor pattern from both sides. While this type of circuit has certain benefits, the specialized

processing requirements for accessing the features limits its use.

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2.2.3 Sculptured flex circuits

Sculptured flex circuits are a novel subset of normal flexible circuit structures.

The manufacturing process involves a special flex circuit multi-step etching method which

yields a flexible circuit having finished copper conductors wherein the thickness of the

conductor differs at various places along their length. (i.e., the conductors are thin in flexible

areas and thick at interconnection points.).

2.2.4 Double-sided flex circuits

Double-sided flex circuits are flex circuits having two conductor layers. These flex circuits can

be fabricated with or without plated through holes, though the plated through hole variation is

much more common. When constructed without plated through holes and connection features

are accessed from one side only, the circuit is defined as a "Type V (5)" according to military

specifications. It is not a common practice but it is an option. Because of the plated through

hole, terminations for electronic components are provided for on both sides of the circuit, thus

allowing components to be placed on either side. Depending on design requirements, double-

sided flex circuits can be fabricated with protective coverlayers on one, both or neither side of

the completed circuit but are most commonly produced with the protective layer on both sides.

One major advantage of this type of substrate is that it allows crossover connections to be made

very easy. Many single sided circuits are built on a double sided substrate just because they

have one of two crossover connections. An example of this use is the circuit connecting

a mousepad to the motherboard of a laptop. All connections on that circuit are located on only

one side of the substrate, except a very small crossover connection which uses the second side

of the substrate.

2.2.5 Multilayer flex circuits

Flex circuits having three or more layers of conductors are known as multilayer flex circuits.

Commonly the layers are interconnected by means of plated through holes, though this is not a

requirement of the definition for it is possible to provide openings to access lower circuit level

features. The layers of the multilayer flex circuit may or may not be continuously laminated

together throughout the construction with the obvious exception of the areas occupied by plated

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through-holes. The practice of discontinuous lamination is common in cases where maximum

flexibility is required. This is accomplished by leaving unbonded the areas where flexing or

bending is to occur.

2.2.6 Rigid-flex circuits

Rigid-flex circuits are a hybrid construction flex circuit consisting of rigid and flexible

substrates which are laminated together into a single structure. Rigid-flex circuits should not be

confused with rigidized flex constructions, which are simply flex circuits to which a stiffener is

attached to support the weight of the electronic components locally. A rigidized or stiffened flex

circuit can have one or more conductor layers. Thus while the two terms may sound similar,

they represent products that are quite different.

The layers of a rigid flex are also normally electrically interconnected by means of plated

through holes. Over the years, rigid-flex circuits have enjoyed tremendous popularity among

military product designer, however the technology has found increased use in commercial

products. While often considered a specialty product for low volume applications because of the

challenges, an impressive effort to use the technology was made by Compaq computer in the

production of boards for a laptop computer in the 1990s. While the computer's main rigid-flex

PCBA did not flex during use, subsequent designs by Compaq utilized rigid-flex circuits for the

hinged display cable, passing 10s of 1000s of flexures during testing. By 2013, the use of rigid-

flex circuits in consumer laptop computers is now common.

Rigid-flex boards are normally multilayer structures; however, two metal layer constructions

are sometimes used.

2.2.7 Polymer thick film flex circuits

Polymer thick film (PTF) flex circuits are true printed circuits in that the conductors are actually

printed onto a polymer base film. They are typically single conductor layer structures, however

two or more metal layers can be printed sequentially with insulating layers printed between

printed conductor layers. While lower in conductor conductivity and thus not suitable for all

applications, PTF circuits have successfully served in a wide range of low-power applications at

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slightly higher voltages. Keyboards are a common application, however, there are a wide range

of potential applications for this cost-effective approach to flex circuit manufacture.

2.3 Manufacturing

Flexible printed circuits (FPC) are made with a photolithographic technology. An alternative

way of making flexible foil circuits or flexible flat cables (FFCs) is laminating very thin

(0.07 mm) copper strips in between two layers of PET. These PET layers, typically 0.05 mm

thick, are coated with an adhesive which is thermosetting, and will be activated during the

lamination process. FPCs and FFCs have several advantages in many applications:

Tightly assembled electronic packages, where electrical connections are required in 3 axes,

such as cameras (static application).

Electrical connections where the assembly is required to flex during its normal use, such as

folding cell phones (dynamic application).

Electrical connections between sub-assemblies to replace wire harnesses, which are heavier

and bulkier, such as in cars, rockets and satellites.

Electrical connections where board thickness or space constraints are driving factors.

2.4 Advantage and Disadvantage of FPSs

2.4.1 Advantage of FPCs

Potential to replace multiple rigid boards and/or connectors

Single-Sided circuits are ideal for dynamic or high-flex applications

Stacked FPCs in various configurations

2.4.2 Disadvantages of FPCs

Cost increase over rigid PCBs

Increased risk of damage during handling or use

More difficult assembly process

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Repair and rework is difficult or impossible

Generally worse panel utilization resulting in increased cost

2.5 Applications

Flex circuits are often used as connectors in various applications where flexibility, space

savings, or production constraints limit the serviceability of rigid circuit boards or hand wiring.

A common application of flex circuits is in computer keyboards; most keyboards use flex

circuits for the switch matrix.

In LCD fabrication, glass is used as a substrate. If thin flexible plastic or metal foil is used as

the substrate instead, the entire system can be flexible, as the film deposited on top of the

substrate is usually very thin, on the order of a few micrometres.

Organic light-emitting diodes (OLEDs) are normally used instead of a back-light for flexible

displays, making a flexible organic light-emitting diode display.

Most flexible circuits are passive wiring structures that are used to interconnect electronic

components such as integrated circuits, resistor, capacitors and the like, however some are used

only for making interconnections between other electronic assemblies either directly or by

means of connectors.

In the automotive field, flexible circuits are used in instrument panels, under-hood controls,

circuits to be concealed within the headliner of the cabin, and in ABS systems. In computer

peripherals flexible circuits are used on the moving print head of printers, and to connect signals

to the moving arm carrying the read/write heads of disk drives. Consumer electronics devices

make use of flexible circuits in cameras, personal entertainment devices, calculators, or exercise

monitors.

Flexible circuits are found in industrial and medical devices where many interconnections are

required in a compact package. Cellular telephones are another widespread example of flexible

circuits.

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Flexible solar cells have been developed for powering satellites. These cells are lightweight, can

be rolled up for launch, and are easily deployable, making them a good match for the

application. They can also be sewn into backpacks or outerwear.

Fig 1.Row to Row Process of Manufacturing

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Chapter 3

Manufacturing Techniques

3.1 Introduction:-

Polydimethylsilioxane (PDMS) is ideal substrate and composite matrix material for flexible

electronics. It is optically transparent, viscoelastic, chemically and thermally stable, highly

flexible ,hydrophobic and can easily be moulded with high resolution and aspect ratio. To avoid

metallization Electrically Conductive Adhesive (ECA)are used. ECAs are conductive

composites composed of metallic fillers within a polymeric matrix. This technology is coined as

PDMS-in-PDMS electronics. Basically, flexible electronics deals with circuits developed using

Thin Film Transistors (TFT). Different TFT technologies are available today to develop

circuits.

3.2 Types of Manufacturing Technology

3.2.1 Amorphous Silicon Technology

Hydrogenated amorphous silicon(a Si:H)TFTs are the workforce of today’s active matrix LCD

displays [2-4]. The main driving force for OLED display is its emissive characteristics, good

colour saturation and clarity. It is also sunlight readable. This technology is suitable for the bi-

stable displays such as electrophoretic and cholesteric displays, a Si:H TFT based integrated

drivers can be used in application which require only occasional image updates such as

advertising, map applications, point of sale labels etc.

3.2.2 Polysilicon Technology

Polysilicon TFTs are processed at higher temperature using laser re-crystallisation of a Si:H

material and can have mobilities greater than 100cm2v-1s-1. The threshold voltages of these of

TFTs are very stable. Poly-Si TFTs can be used to develop display backplanes as well as

CMOS digital circuits [5]. However, the process and substrate costs are comparatively higher

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and thus restrict the use of these TFTs in high resolution displays in smart phones and high end

radio frequency tags.

3.2.3 Organic Thin Film Transistors

Organic TFTs can be manufactured using a number of organic semiconductors such as

Pentacene, TIPS Pentacene etc. These semiconductors can be processed at low temperatures

using solution processes or vacuum evaporated processes such as spin coating and ink-jet

printing [6]. Roll-to-Roll processing may bring down the cost of production. The OTFT is

sensitive to air and hence its performance degrades over time when exposed to the environment

.Barrier coating is required to protect it from exposure.

3.2.4 Single Crystal Silicon on Flexible Substrates

It is possible to develop single crystal silicon circuits on flexible substrates with mobilities

greater than 500cm2v-1 s-1 and response frequencies greater than 500MHz.In this techniques, a

semiconducting micro/nanomaterial known as microstructural silicon is printed using dry

transfer or solution based techniques onto plastic substrates to produce high performance TFTs .

3.2.5 Mixed Oxide Thin Film Transistors

Mixed oxide thin film transistors such as IZO,IGZO provide better mobility, higher current

densities and better stability compared to a Si:H TFTs. Another feature of mixed oxide TFT is

that they are transparent. Hence, there is much interest to develop transparent electronics on

large area flexible substrate.

3.2.6 Hybrid (CMOS) Technology CMOS technology has several advantages over nMOS or

pMOS only technologies. Speed of CMOS technology is considerably faster than anyother

technology with much lesser power loss. By including n-type and p-type TFTs on the same

substrate, it is possible to implement CMOS circuits which reduce power consumption, leakage

currents and improve the gain of the digital logic circuits [12-13]. Research done at Flexible

Display Centre in collaboration with University of Texas at Dallas shows that these CMOS

logic circuits are more stable compared to a Si:H TFT circuits. This is because the V(t) of the a

Si:H TFT shifts in positive direction with electrical stress while that of organic TFTs shift

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negative as shown in fig. 1. In this technology, a Si-H TFTs and Pentacene TETs on PEN

substrate and successfully demonstrated a CMOS column driver for electrophoretic displays.

Fig. 2: V(t) shift- a –Si:H nMOS and pentacene pMOS

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Chapter 4

Flexible circuit materials

4.1 Introduction

Each element of the flex circuit construction must be able to consistently meet the demands

placed upon it for the life of the product. In addition, the material must work reliably in concert

with the other elements of the flexible circuit construction to assure ease of manufacture and

reliability. Following are brief descriptions of the basic elements of flex circuit construction and

their functions.

4.1.1 Base material

The base material is the flexible polymer film which provides the foundation for the laminate.

Under normal circumstances, the flex circuit base material provides most primary physical and

electrical properties of the flexible circuit. In the case of adhesiveless circuit constructions, the

base material provides all of the characteristic properties. While a wide range of thickness is

possible, most flexible films are provided in a narrow range of relatively thin dimension from

12 µm to 125 µm (1/2 mil to 5 mils) but thinner and thicker material are possible. Thinner

materials are of course more flexible and for most material, stiffness increase is proportional to

the cube of thickness. Thus for example, means that if the thickness is doubled, the material

becomes eight times stiffer and will only deflect 1/8 as much under the same load. There are a

number of different materials used as base films including: polyester (PET), polyimide (PI),

polyethylene naphthalate (PEN), polyetherimide (PEI), along with various fluropolymers (FEP)

and copolymers. Polyimide films are most prevalent owing to their blend of advantageous

electrical, mechanical, chemical and thermal properties.

4.1.2 Bonding adhesive

Adhesives are used as the bonding medium for creating a laminate. When it comes to

temperature resistance, the adhesive is typically the performance limiting element of a laminate

especially when polyimide is the base material. Because of the earlier difficulties associated

with polyimide adhesives, many polyimide flex circuits presently employ adhesive systems of

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different polymer families. However some newer thermoplastic polyimide adhesives are making

important in-roads. As with the base films, adhesives come in different thickness. Thickness

selection is typically a function of the application. For example, different adhesive thickness is

commonly used in the creation of cover layers in order to meet the fill demands of different

copper foil thickness which may be encountered.

4.1.3 Metal foil

A metal foil is most commonly used as the conductive element of a flexible laminate. The metal

foil is the material from which the circuit paths are normally etched. A wide variety of metal

foils of varying thickness are available from which to choose and create a flex circuit, however

copper foils, serve the vast majority of all flexible circuit applications. Copper’s excellent

balance of cost and physical and electrical performance attributes make it an excellent choice.

There are actually many different types of copper foil. The IPC identifies eight different types

of copper foil for printed circuits divided into two much broader categories, electrodeposited

and wrought, each having four sub-types.) As a result, there are a number of different types of

copper foil available for flex circuit applications to serve the varied purposes of different end

products. With most copper foil, a thin surface treatment is commonly applied to one side of the

foil to improve its adhesion to the base film. Copper foils are of two basic types: wrought

(rolled) and electrodeposited and their properties are quite different. Rolled and annealed foils

are the most common choice, however thinner films which are electroplated are becoming

increasingly popular.

In certain non standard cases, the circuit manufacturer may be called upon to create a specialty

laminate by using a specified alternative metal foil, such as a special copper alloy or other metal

foil in the construction. This is accomplished by laminating the foil to a base film with or

without an adhesive depending on the nature and properties of the base film.

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Chapter 5

Flexible Electronic Components

5.1 Introduction

Fast flexible electronics operating at radio frequencies (>1 GHz) are more attractive than

traditional flexible electronics because of their versatile capabilities, dramatic power savings

when operating at reduced speed and broader spectrum of applications. Transferrable single-

crystalline Si nanomembranes (SiNMs) are preferred to other materials for flexible electronics

owing to their unique advantages. Further improvement of Si-based device speed implies

significant technical and economic advantages. While the mobility of bulk Si can be enhanced

using strain techniques, implementing these techniques into transferrable single-crystalline

SiNMs has been challenging and not demonstrated.

Fig. 3 Flexible Electronic Components

5.2 Resistors and Capacitors

The past approach presents severe challenges to achieve effective doping and desired

material topology. Here we demonstrate the doping techniques with self-sustained strain sharing

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by applying a strain-sharing scheme between Si and SiGe multiple epitaxial layers, to create

strained print-transferrable SiNMs. We demonstrate a new speed record of Si-based flexible

electronics without using aggressively scaled critical device dimensions.

Fig. 4 Structure of resistor Fig. 5 Structure of capacitor

The given figure aboves shows the structures of thin flim resistors and capacitors which

are constructed on flexible substrate and the conductive paths are made up of flexible materials

such as silicon nanomembranes, grapheme, carbon nanotubes etc. Nanotechnology is to a large

extent for the manufacturing of electronic components

5.3 Memory, Amplifiers and Ring Oscillators

At the International Electron Devices Meeting (IEDM) last fall IBM researchers

demonstrated CMOS circuits —including SRAM memory and ring oscillators—on a flexible

plastic substrate. The extremely thin silicon on insulator devices had a body thickness of just 60

angstroms. IBM built them on silicon and then used a room-temperature process called

controlled spalling, which essentially flakes off the Si substrate. Then they transferred them to

flexible plastic tape. The devices had gate lengths of <30 nm and gate pitch of 100 nm. The ring

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oscillators had a stage delay of just 16 ps at 0.9 V, believed to be the best reported performance

for a flexible circuit.

In a recent edition of the journal Nature Communications a team of researchers from the

University of Pennsylvania showed that nanoscale particles, or nanocrystals, of the

semiconductor cadmium selenide can be "printed" or "coated" on flexible plastics to form high-

performance electronics. Because the nanocrystals are dispersed in an ink-like liquid, multiple

types of deposition techniques can be used to make circuits, wrote the researchers. In their

study, the researchers used spin coating, where centrifugal force pulls a thin layer of the

solution over a surface, but the nanocrystals could be applied through dipping, spraying or ink-

jet printing as well, they report.

Using this process, the researchers built three kinds of circuits to test the nanocrystal’s

performance for circuit applications: an inverter, an amplifier and a ring oscillator. All of these

circuits were reported to operate with a couple of volts, according to the researchers an

important point since If you want electronics for portable devices that are going to work with

batteries, they have to operate at low voltage or they won’t be useful.

Fig. 6 Flexible memories

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5.4 Batteries

One of the things seemingly hampering advances in bendable electronics research is

uncertainty surrounding a product’s power source. At the University of Delaware, Bingqung

Wei and his colleagues are researching energy sources that are scalable and stretchable. In a

report published in Nano Letters, a journal of the American Chemical Society, Wei’s research

team reported significant progress in developing scalable, stretchable power sources using

carbon nanotube macrofilms, polyurethane membranes and organic electrolytes. According to

Wei, the supercapacitor developed in his lab achieved excellent stability in testing and the

results will provide important guidelines for future design and testing of this leading-edge

energy storage device.

Also in Nano Letters researchers from the Korea Advanced Institute of Science and

Technology (KAIST) in Daejeon, South Korea published a study on a new bendable Li-ion

battery for fully flexible electronic systems.

Although the rechargeable lithium-ion battery has been regarded as a strong candidate for

a high-performance flexible energy source, compliant electrodes for bendable batteries are

restricted to only a few materials, and their performance has not been sufficient for them to be

applied to flexible consumer electronics including rollable displays.

Fig. 7 Flexible lithium ion battery

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The researchers presented a flexible thin-film lithium ion battery that enables the

realization of diverse flexible batteries regardless of electrode chemistry. The result is a flexible

Li-ion battery that can be made with almost any electrode material. Here, the researchers used

lithium cobalt oxide as the cathode material, which is currently the most widely used cathode in

non-flexible Li-ion batteries due to its high performance. For the anode, they used traditional

lithium.

Fig 8 . Technology Integration,Applications

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Chapter 6

Flexible Display

6.1 Histroy

The era of mobile devices began in the second half of the 1990s. As cell phones became

widely used, the market for mobile equipment grew at a rapid rate. The main area of

competition was in making devices smaller and improving call quality. Once the ideal size and

call quality was achieved it became harder to differentiate the products in the early 2000s.As a

result, companies started competing to develop simple wireless telecom devices and added

value for customers by offering colour display, MP3 and camera functions. The landscape of

the market changed quickly as GSM and CDMA combined to form WCDMA or 3G.The market

became more operator-driven as telecom companies used a variety of marketing methods,

including providing customers with subsidies and two-year contracts. By the second half of

2005, most phones had similar design and functions (camera, colour display, 3G) and with

differentiation becoming more difficult, commoditisation started and competitors focused on

lowering production costs.

Table 1 The History Of Handset Industry

After 2005, competitors turned their attention to making cell phones essential in everyday

life. As a result, products with differentiated form factors, such as casing, keypad and slim form

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factor, were designed. The market for high-end phones started to take off. Consumer

interest in design was an opportunity for Samsung and LG to strengthen their positions in a

market dominated by cost efficient companies, such as Nokia.Then Apple’s iPhone arrived,

providing completely new experiences, such as entertainment features and a highly distinctive

design and customization options. The handset market went through rapid change as Wi-Fi

internet revolutionised the data side of the business. Apple was the dominant force until the

advent of Android-based phones. Differentiation has become even harder with most companies

using full HD panels, a standardized quad-core application process, touch screen and the

Android operating system. In a commoditised market, design is the high-end market’s main

differentiating point. They believe flexible display will take this to a new level as the new

technology will see handheld digital devices become lighter ,thinner and more convenient for

users. Display technology is advancing in four directions: 1) improving the sense of reality

through 3D TV, 2) adopting additional functions, such as touch and internet connectivity, 3)

enabling greater mobility via lighter and thinner products, such as in smartphones and tablet

PCs, and 4) expanding adaptability for displays in homes and industries via thinner, larger

products, such as UHD TV. Until recently, progress on flexible display technology has been

slow. The main reason is that companies have already made heavy investments in LCD, the

technology used in flat display panels.

Fig 9 Display Development

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6.2 Flexible Displays

The desire for a display that has the flexibility and even “foldability” of paper, but with

the capability to update the information on the page almost instantly is what drives the interest

and commercial funding of flexible electrophoretic devices. Though the electronic paper

application is probably in our near future, with some prototypes already available, it is likely

that other applications will be more interesting from a commercialization and social acceptance

point of view. Large area displays,smart cards, mobile phones, and automotive applications will

be some of the targets for flexible electrophoretic displays.

For large area signage and displays, flexible elecrtrophoretic display technology holds

promise for several reasons. First, for applications where flexibility or even conformability is

desired or useful, the strong optical contrast at nearly all viewing and illumination angles is of

interest. The compartmentalization of the ink and the drive electronics into physically separated

pixels also allows for greater flexibility than polycrystalline or polymeric materials.

Additionally this technology holds promise for remote or mobile display applications due to its

low power usage and relative toughness when built with polymeric substrates. The slow refresh

time in these applications is a minimal issue because most signs are updated on much longer

time scales. At the same time, companies are making significant strides towards higher refresh

rates, nearing video speed.

Finally, the electrophoretic display technology is the only technology with which large

area (up to 30 inches wide) flexible displays have already been realized and are in the process of

commercialization, giving this technology a market lead. With a higher refresh rate,

electrophoretic displays will be able to break into the low end automotive and mobile phone

markets.

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Fig. 10 Illusion of flexible display Fig. 11 flexible display by Sony

While stability and environmental sensitivity are of much lower concern than for organic

display materials, the addition of color capabilities, either through novel multi-filter stacking or

through novel colored particle technology is more challenging than with the organic display

materials. The automotive and mobile phone markets are likely to fully embrace the

electrophoretic display when color becomes widely available due to its wide viewing angles,

robustness and flexibility as well as the fact that the displays may be made in large volume with

large active areas and have relatively low weight. Color capabilities will be the largest

challenge for electrophoretic displays, requiring innovative approaches to overcome the

inherent bi-color, bi-stable paradigm that the display technology has grown to embrace. E-Ink

has already made some progress toward this end by partnering with the Toppan Printing

Company to make color filters to overlay the electrophoretic display layer.

6.3 Features

Rigid Graphical User Interfaces (GUIs) often feature input that is indirect, one-handed, and

dependent on visual cues. By contrast, paper documents, and presumably flexible displays,

may: 1. Be very thin, low-weight, yet rugged, allowing superior portability over any current

mobile computing form factor. 2. Have many form factors. This allows for distinct physical

affordances that relate to specific functionalities: reading a newspaper serves a different purpose

than reading a product label, and implies a different form factor. 3. Provide variable screen real

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estate that fits the current context of use. 4. Have many physical pages, each page pertaining

only to a specific and physically delineated task context. 5. Use physical bend gestures with

strong tactile and kinesthetic feedback for efficient navigation.

Prior simulations of flexible displays have already produced a library of paper-like interaction

styles, most of which focus on the use of bend gestures. A bend gesture is the physical, manual

deformation of a display to form a curvature for the purpose of triggering a software action. In

this paper, we present an evaluation of user preferences for bend gestures in executing a real set

of tasks, using an actual flexible display. We designed a study in which users were asked to

design their own bend gesture using a thin film E Ink display with integrated bend sensors. This

approach has two distinct advantages over prior work:(1) visual feedback is provided directly

on the display itself, and (2) dynamic material characteristics of bending layers of sandwiched

flexible electronics were included. In the first part of our study, we asked participants to define8

bend gesture pairs. In the second part, we asked them to evaluate the appropriateness of their

bend gestures for us with multiple actions. Finally, users were asked to use and evaluate bend

gestures in the context of complete tasks(e.g., operating a music player). Results showed that

users selected individual bend gestures and bend gesture pairs that were conceptually simpler

and less physically demanding. There was a strong agreement among participants touse 3 bend

gesture pairs in applications: (1) side of display,up/down (2) top corner, up/down (3) bottom

corner, up/down. There was also strong consensus on the polarity(physical bend direction: up or

down) of bend gesture pairs for actions with clear directionality (e.g., navigating left and right

to select an icon). In the early stages, flexible display will be used in small displays, such as

watches, which can be mass produced. Then, depending on how the technology matures, it will

be applied in smartphones and tablets.

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Chapter 7

WORKING PRINCIPLE OF E-PAPER

7.1 Introduction

E-paper comprises two different parts: the first is electronic ink, sometimes referred to as the

―frontplane‖; and the second is the electronics required to generate the pattern of text and

images on the e-ink page, called the ―backplane‖.

Over the years, a number of methods for creating e-ink have been developed. The Gyricon e-ink

developed in the 70s by Nick Sheridon at Xerox is based on a thin sheet of flexible plastic

containing a layer of tiny plastic beads, each encapsulated in a little pocket of oil and thus able

to freely rotate within the plastic sheet. Each hemisphere of a bead has a different color and a

different electrical charge. When an electric field is applied by the backplane, the beads rotate,

creating a two-colored pattern. This method of creating e-ink was dubbed bichromal frontplane.

Originally, bichromal frontplane had a number of limitations, including relatively low

brightness and resolution and a lack of color. Although these issues are still being tackled, other

forms of eink, with improved properties compared to the original Gyricon, have been developed

over the years.

One such technology is electrophoretic frontplane, developed by the E Ink Corporation.

Electrophoretic frontplane consists of millions of tiny microcapsules, each approximately 100

microns in diameter—about as wide as a human hair. Each microcapsule is filled with a clear

fluid containing positively charged white particles and negatively charged black particles. When

a negative electric field is applied, the white particles move to the top of the microcapsule,

causing the area to appear to the viewer as a white dot, while the black particles move to the

bottom of the capsule and are thus hidden from view. When a positive electric field is applied,

the black particles migrate to the top and the white particles move to the bottom, generating

black text or a picture.

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The brightness and resolution of electrophoretic-based e-ink is better than that of

bichromalbased e-ink, but both are monochromatic in nature. To create color, E Ink joined

hands with the Japanese company Toppan Printing, which produces color filters.

Another drawback of electrophoretic e-ink is its low refresh rate, making electrophoretic e-ink

unsuitable for displaying animation or video. Since it takes time for the particles to move from

one side of the microcapsule to the other, drawing a new text or image is too slow and creates a

flicker effect.

7.2 APPLICATIONS OF E-PAPER

1. Clearly, great progress has been made in the field of e-paper since the invention of Gyricon.

Companies such as E Ink, SiPix, and Polymervision, as well as such giants as Sony, IBM,

Hewlett-Packard, Philips, Fujitsu, Hitachi, Siemens, Epson, and many others, are continuing to

develop e-paper technology. Founded in 1997 and based on research begun at the

Massachusetts

Institute of Technology’s Media Lab, E Ink developed proprietary e-paper technology that

already has been commercialized by a number of companies, including iRex Technologies and

Sony, both of which already have commercial e-paper readers on the market.

At this stage, some of the products based on E Ink’s technology are little more than expensive

gimmicks, such as Seiko’s limited-edition e-paper watch (priced at over $2,000).Other products

to be marketed have more substantial applications. E-paper thin color displays for packaging,

currently under advanced development at Siemens, could display prices on products

dynamically, instantly altering a product’s price when necessary (using such low-power

wireless technology as radio-frequency identification, or RFID, for example). A dynamic

expiration date, which would graphically display the amount of time remaining for food and

drug consumption, is another potential application.

A completely different solution for creating e-paper, known as cholesteric liquid crystal

(ChLCD), is being developed by such companies as IBM and Philips, as well as HP and Fujitsu,

which have demonstrated actual devices. ChLCD technology is based on the well-known and

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widespread technology of liquid crystal displays (LCDs), which work by applying a current to

spiral-shaped liquid-crystal molecules that can change from a vertical to a horizontal position.

Although other potential technologies for developing advanced color electronic paper exist such

as photonic crystals (P-ink) recently covered by TFOT, many analysts believe that ChLCD

technology could become the dominant e-paper technology of the next decade. This assessment

relates to the high level of maturity exemplified by the current LCD industry, as well as to the

fact that ChLCD technology currently offers what many analysts see as the ideal list of features

for e-paper: flexibility and even bend ability; thinness, at approximately 0.8 millimeters;

lightness; a bi-stable nature, requiring no power to maintain an image and very little power to

change it; good brightness, contrast, and resolution; as well as vivid color and a decent refresh

rate capable of displaying animation and possibly even video.

2. Potential applications of e-paper technology is staggering. In addition to a new method for

labeling foods and drugs, it could be used to label anything from shelves to office binders. One

of the original uses of the Gyricon e-ink was in advertising and billboards; the bi-stable nature

of the technology made the Gyricon a useful and cost-effective billboard technology. E-paper

displays can also be used as low-power digital screens for a variety of electronic appliances,

from microwaves to MP3 players.

Fig 12 Citizen E-Ink Clock

3. Although many potential applications for e-paper technology exist, one of the more exciting

products is the e-paper reader, which may soon replace the age-old newspaper and possibly

even certain types of books; some technical literature may be perfectly suited for e-paper. The

next generation of e-paper readers will add color, include improved hardware that can refresh

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pages more quickly, and have more advanced wireless capabilities.Existing readers from Sony,

iRex, and a number of other companies are still quite expensive and suffer from some of the

problems that plague early technology models. The next generation of readers will also be

flexible, making such applications as digital maps an attractive option, especially when

connected to GPS hardware and software. Although e-paper readers like iRex’s iLiad, are

already equipped with wireless Internet communication, they are not well suited as general-

purpose Web-surfing devices. Electronic readers of the future will one day become the ultimate

handheld devices.Having mentioned in this article a number of potential applications for e-

paper, it is possible that the most important applications of this technology have not yet been

invented.

7.3 Future Of E-Paper

The initial Gyricon technology proved expensive and had poor resolution; it was really only

usable in the sort of message-board-display systems that were produced by Gyricon Media. The

development of true e-paper really only dates from about 1998, when E Ink first demonstrated

their electrophoretic front plane display technology; this gave a higher resolution and was

potentially much cheaper.

Since then, other companies, such as SiPix, have come out with electrophoretic display

technologies. In the last four years, we have also seen companies like HP and Fujitsu bring out

flexible displays that use cholesteric LCD technology. (Cholesteric refers to the phase of a

liquid crystal in which the molecules are aligned in a specific manner. In Fujitsu’s case, for

example, up to 50 percent of incident light in specific wavelengths and colors is reflected). E-

paper has to be a cheap, reflective, low power, and preferably bendable, or have rollable display

technology, and we are only just seeing the development of the technologies that can deliver

this, namely an electrophoretic front plane bonded to a flexible organic electronic backplane.

These are the displays currently on the verge of being launched by Plastic Logic and Polymer

Vision.

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Chapter 8

Applications of Flexible Electronics

A large number of applications have been developed including displays, computational systems,

in energy storage and generation, health care, e-textiles etc. Fig. 13

Fig. 13: Next Generation Flexible Electronics Systems and the Key Relevant Sectors

A. Healthcare

Flexibility in electronic materials is very attractive for medical and bioengineering. Some

electronics have been integrated into human bodies . For example ,bionic eye, bionic ear,

optic nerve etc .heat, humidity ,salt or pressure sensor arrays can be used as bed sheet and

monitor a patient in real time. Flexible thin films could also play a key role in

deciphering the thought processes occurring in the brains.

B. Automotive Industry Intelligent roads will be engineered with the aim of improving

road safety, lowering road congestion and energy consumption. The road and vehicle will

also be able to interact dynamically, adjust either party to energetically optimize their

systems.

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C. Displays and Human-Machine Interactivity As a user slide fingers on the

surface, the applied time varying potential includes intermittent attractive and repulsive

electrostatic forces between the buried conducting layer and the finger. This electrostatic

attraction varies the normal contact forces between the user’s skin and surface and in

turn, modulates the dynamic friction and touch perception.

D. Smart Textiles Recently, there is increase interest in smart textiles for health

monitoring, entertainment and display applications. These smart textiles can be

embedded with multiple sensors and display devices for monitoring stress, toxic gases in

environment. Each smart thread is basically a shift register with a small display pixel and

possibly a sensor ,which can be used to transfer data from one end to other.

E. Wireless Networking Stretchable antennas have been fabricated using PDMS, which

is usually cast on a photo-resist mould with the desired design. The PDMS structure is

then peeled away and holes introduced for injection of a liquid eutectic

(Galinston:68.5%Ga,21.5%In, 10%Sn),to form the radiating elements. Another recently

explored route for fabrication of stretchable PIFA antennas uses direct deposition of thin-

film gold onto elastomeric substrate.

F. Electronic Paper Currently, the most successful technology and industry is electronic

paper, the main applications are e-Readers, electronic shelf labels, smart cards, electronic

posters and so on . Currently, the e-Reader is not really flexible because it use a glass

backplane. E-Ink Holdings and ITRI includes organic conductor and printing process,

substrate is PET films which only can be processed at low temperature. ITRI also

develops a passive technology of cholesterol liquid crystal which can be manufactured

using a fully roll-to-roll technology.

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Chapter 9

Challenges

There are some challenges that still need improvement.

A. Electrical Instability Reliability is critical for flexible circuit design to ensure that the

circuit would operate reliably throughout its lifetime. Thin film transistor(TFTs)often

suffers from electrical instability, but threshold voltage shift of a single TFT can be

modelled by analyzing its operating conditions and circuit lifetime can be predicted

accordingly using SPICE simulation.

B. Flexible Substrate Handling and Alignment The dimensional control of plastic

substrate is very difficult due to temperature, humidity and tension variation, special roll-

to roll operation.

C. Flexible Conductor Conductivity and Work Function The operation for flexibility

and conductivity are the trade-off parameters and work function always needs to modify.

D. Printing Quality The printing qualities are not easy to control due to liquid off-set or

jetting operations, special multilayer or large area film printing.

E. Flexibility Operation The most practiced flexible operations like bending, folding or

rolling is not easy guarantee due to multilayer structure. Research is going on to provide

more reliable flexibility to the circuits.

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Chapter 10

Advantage and Disadvantage of Flexible Electronics

A D VA N TA G E S

light weight Smaller dimensions required Space saving Foldable and bendable Increased circuitry density Wide Viewing Angle

DISADVANTAGES

Initial investment may be expensive Integration of components would be challenge for engineers Precision machines required Lifetime Manufacturing

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Chapter 11

Future Aspects

Development strategy of flexible electronics is dependent on global technology progresses and

market forecasts. The research and development is focused on big markets. Flexible electronics

covers a wide spectrum of applications including flexible display, flexible solar cell, printed

RFID, flexible lighting and others. Currently, it has been estimated that there are about 1500

worldwide research units working on various aspects of flexible electronics. Market analysis

estimates the revenue of flexible electronics can reach 30 billion USD in 2017 and over 300

USD in 2028 [19]. Region wise, the research activities in Europe cover a wide range of topic-

from materials, process, to system and applications. In the US, research is primarily driven by

military applications. Asian companies invest heavily in flexible display. Today, flexible

circuits which are also known around the world as flexible printed wiring, flex print, flexi

circuits are used many products. Large credits goes to the efforts of Japanese electronics

packaging engineers who have found a countless new ways to employ a flexible circuit

technology [20]. For the last decade, flexible circuits have remained one of the fastest growing

of all interconnection product market segments. A more recent variation on flexible circuit

technology is one called flexible electronics which commonly involve the integration of both

active and passive functions in the processing.

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Conclusion

In this report, we have discussed some of the fabrication techniques, applications, challenges

and future socioeconomic trends of thin –film technology are likely to enhance the performance

of the devices. Although this field is growing and getting matured, it has been expanding

rapidly and dynamically. The keys to success include grasping the tempo, building up a

complete value chain ,and attracting the necessary entities to join the efforts and cooperate. This

paper gives a brief overview of how the field of flexible electronics has evolved over the years

and what the future holds for the large area, rugged, low power electronics. Some of the

applications which can be developed on flexible substrates have been introduced.

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