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MSE 542 Flexible Electronics• Materials Characterization

• dielectrics • semiconductors

• Examples• Embedded active and passive devices

(dielectric and resistive materials) • Active matrix thin film transistor (TFT)

(semi-conducting materials)

Jan Obrzut, NIST Polymers Division (jan.obrzut@nist.gov)

Radio Freq IDsMotorola, iNEMI 2006

Energy sourcesKonarka, PowerPaper, Thin Battery Technology

Passive R, L, C (PCB industry)

Organic Flexible, Transparent, Printable, Embedded Electronic Devices

Methodologies for characterization of organic electronic materials at high microwave frequencies

Improved high frequency performance of dielectrics , resistors, ferrooelectrics

2006 Roadmap

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3

SM-Discrete capacitance, one per IO, ineffective at frequencies approaching 1 GHz

Power plane. Impedance decreases 3 X per 2X increase in clock speed

New thin film organic materials and fabrication processes that are compatible with FR-4 and flex printed circuit boards

Resistors - RLC cells, terminations (high- k, controlled HF loss)

Capacitors - RCL cells, decoupling (high- k, controlled HF loss)

Power planes VDD, power bus noise(high- k, controlled HF loss)

Dielectrics - Interconnects, microstrips(low - k, low loss)

Broadband testing 0.5 to 10 GHz

Integrated Passive Technology for Microwave and High Speed Electronics

0.1

1.

10.

100.

1 MHz 100 MHz0.1 MHz 1 GHz10 MHz

Bare Board

Board withdecoupling What happens

> 1 GHz

After T. Hubbing, NCMS Workshop, NIST 08/02

High-k organic thin dielectrics substrates, Z → 0

Z = 1/ωC + ωL

Integrated Power Plane

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Impedance of embedded power-ground planes (a) - 50 μm thick Fr-4, 0.07nF/cm2

(b) - 100 μm thick high-k epoxy, 0.34 nF/cm2

both (a) and (b) have the same 50 μm copper clad

Resonance dumping is more effective in the high k layer (b)why? see page 13

G-S-G Network Analyzer

1 port , S11 measurements

testing probe HF coax cable

Power-ground plane

High frequency impedance testing of power-ground planes

½ oz copper foil + copper plating 0.020“ +/- 0.002” Tetra II core

0.020“ +/- 0.002” Tetra II core ½ oz copper foil + copper plating

½ oz copper foil

1 oz copper foil 1 oz copper foil

0.005“ +/- 0.001” Tetra II prepreg 0.005“ +/- 0.001” Tetra II prepreg

0.005“ +/- 0.001” Tetra II prepreg

½ oz copper foil Layer 1 Layer 2 Layer 3 Layer 4 Layer 5 Layer 6

Component Signal Power Ground Signa Solder

TV-1-1-Y 6-layer stack-up

Teast board and the stack-up, NCMS EDC Project 08/01

J.Obrzut and A. Anopchenko ., IEEE Trans. Instrum. Meas., 52, 1120-1124, (2003)

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side view

top view

Microstrip, Zo

ZL

Via to GNP

G

S

G

Embedded Passive Device

Signal

Microstrip, Zo 1st level, S

2nd level, GNP 3rd level, S

4th level

Impedance, Zl , of Embedded Passive Devices

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l0

cl/l rε

υτ 000 ==

τ0 - propagation time in the microstrip

εr - dielectric constant

Z0 - microstrip characteristic impedance

Zl - device impedance

Impedance measurements using TDR

time delay

Refle

c ted v

ol ta g

e

Vo

time delay

Zl = 1/2 Zo

-1/3 Vo

Open, Zl = ∞

Refle

c ted v

ol ta g

e

Vo

Vr=Vo

Short, Zl = 0

Refle

c ted v

ol ta g

e

Vr = -V0

time delay

Vo

Reflected pulse is in phase, Vr = V0

Reflected pulse is out of phase, Vr = -V 0

For a matched impedance Zl = Zo Vr = Vo , no reflection

Refle

c ted v

ol ta g

e

Vr =+1/3 Vo

time delay

Vo

Resistor

Terminating standards

6

Resistive Load

2τo

2τo

2τo

2τo

l

l

ZZZZ

+−

=Γ0

0

0VVr=Γ

Γ−Γ+

=11

0ZZl

1−=Γ

1=Γ

31

=Γ

02ZZl =

31

−=Γ

021 ZZl =

Time Domain Application Theory, Agilent Application Note 1304-2

4

Refle

c ted v

ol ta g

e

Refle

c ted v

ol ta g

e2τo

2τo

2Vo

Vo Vo

R L

R

L

)1(0

00 ZR

ZRV+−

+

2Vo

)ZRZR(V

0

00 1

+−

−

]e)ZRZR[(V)(V T/

rττ −

+−

+=0

00 1 ])1()1[()( /

0

0

0

00

Tr e

ZRZR

ZRZRVV ττ −

+−

+++−

−=

Shunt R-L Series R-L

LRZ

ZRT )(0

0+=

0ZRLT+

=

7

Impedance measurements using TDR

time delay τ time delay τR values and materials resistive properties can be extracted

from the TDR traces

Vo

2Vo

2τoVo

2τoRefle

c ted v

ol ta g

e

Refle

c ted v

ol ta g

e

time delay τ time delay τ

R C RC

)1(0

00 ZR

ZRV+−

+2Vo)(

0

00 ZR

ZRV+−

])(2[)( /

0

00

Tr e

ZRZRVV ττ −

+−

−=

Shunt R-C Series R-C

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Impedance measurements using TDR

)]e)(ZRZR[(V)(V T/

rττ −−

+−

+= 110

00

C)ZR

RZ(T0

0

+= C)ZR(T 0+=

C values and materials dielectric properties can be extracted from the TDR traces

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Gauss lawε0εr E = Q/AC = Q/V= ε0εr A/d [F]

D = P0 + ε1 E+ ε2 EE+ ε3 EEE + …

CapacitanceDielectric displacement D ∼ Q

in a linear V sweepi = dQ/dt =C (dV/dt) = a C

V= a t

time t

c urr e

n t i

v olta

ge V

Vmax

leakage

saturationd is

p lace

men t

D P 0+ε 1E

electric field E = V/d

saturationI=a C

Measure capacitance, C, and then calculate εr Charge storage, Nonlinear dielectric effects ( C = f (V))

Materials static dielectric constant, εr

d

Q = σfree A

V

+ + + + + + + + + + + + + + +

- - - - - - - - - - - - - - -+ + + + + + + + + +

ε0 E = σfree - P P=σpol

- - - - - - - - - - - - -

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Effective dielectric constant measured by using TDR (propagation quasi static)

τΔc

l/l rευτ

002==

Δ

),w/(h(fZ rl ε=

l

w

εr

h

50 Ω

measure Zl and Δτ ⇒ εr

More advanced analysis from the shape of a pulse, group and phase velocity 10

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measurements in time domain and in frequency domain

ω1 ω2

τ

V0 - amplitudeφ=ωτ - phase

t

f

Frequency DomainV=V0 exp(i(ωt+φ))

Time Domainv(t)=V0 sin (ωt+φ)

v(t)

•Time domain - transient response, visualization

•Frequency domain - steady state phasor transformsconvenient for calculating materials property -complex impedance

ZR = R

ZC = - j 1/ωC

ZL = j ωL

|Z|= Sqrt (R2 +(ZL-ZC)2)

Z ZCZR

ω Re

Im

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k <= 100, d - 1 μm to 100 μm , f 100 MHz to 12 GHz

At higher frequencies the dielectric represents a network of a transmission line with capacitance and inductance (wave propagation)

0 . 1 1 1 0

0 . 0 1

0 . 1

1

1 0

1 0 0

- 1 0 0

- 8 0

- 6 0

- 4 0

- 2 0

0

2 0

4 0

6 0

8 0

1 0 0

|Z |= 0 . 0 5 Ω

|Z |= 5 Ω

|Z|

(Ω)

F re q u e n c y, G H z

Phas

e (d

egre

e)

NIST test methodSECTION B

SECTION A

APC-7 Mount Test Specimen

Center Conductor Pin

APC-3.5 Port

to Network Analyzer, S11

Short Standard with a gapSECTION B

SECTION A

APC-7 Mount Test Specimen

Center Conductor Pin

APC-3.5 Port

to Network Analyzer, S11

Short Standard with a gap

IPC Standard TM650-2.5.5.10

))1()1(()cot(

11110

*

spr LjZCj

xxωω

ε−−+

=SS

clx r 2∗= εω

Zin= Z0 (1+S11)/(1−S11)

Broadband dielectric constant measurements, in frequency domain, measure Si,j, impedance

J.Obrzut and A. Anopchenko ., IEEE Trans. Instrum. Meas., 53, 1197-1201 (2004) 12

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1

10

100

1000

0 10 20 30 40 50 60 70 80 90 100

BaTiO3 Concentration [vol%]

Die

lect

ric C

onst

ant

CR-SPEGDATMPTAEmCap

εBaTiO3

51%,130

Macromol. 34, 5910 (2001)

High frequency dielectric loss in in high k composites is beneficial for embedded capacitance applications, Z ≈ 0

Broadband dielectric constant of composite materials

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a) l =164 mm, ε1 = 36.3 at 151 MHz, b) l=29.5 mm, ε1 = 36.4 at 842 MHz, c) l=8 mm, ε1 = 35.9 at 3.122 GHz

Dielectric constant measurements in frequency domain, measure S2,1 or S1,1 , resonant frequency

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2

212

⎟⎠⎞

⎜⎝⎛+⎟

⎠⎞

⎜⎝⎛=

=⋅=

−= ⋅⋅−

wn

lmcf

nl/

)ee(EE

rn,m

gg

tto

ε

λλπβ

ββ

GSG

GSG

Z0 Z0ZR ≈ 1/2 Z0

a b c

NCMS EDC Project, 2000

l

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8

• Low impedance power planes, R, L, C• TDR measurements, Z, Δτ ⇒ εr

• Static εr from charge/voltage capacitance• High frequency broadband ε* (to 12 GHz)

high k composites• Microstrip resonators, resonant frequency ⇒ ε*

• Nonlinear effects in organic dielectrics and semiconductors

Summary of dielectric materials characterization (Compared SMT ceramic passives vs embedded organic)

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• has a non-volatile memory function that keeps its image stable.the screen image doesn't require repetitive updates to be maintained

• low power consumptionchanging content uses about the same amount of electricity as the weak radio waves found in some security badges.

• Uses TFT, Ferroelectric memory cell

Active matrix thin film transistor (TFT)

Tokyo International Forum 2005

Fujitsu bendable RGB color electronic paper

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1. A twisted nematic LC cell

2. Under voltage V, LC molecules align with the electric field

LCD BW pixel

1

2

In TFT LCD each LCC is stimulated individually by a dedicated transistor or diode

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a-Si TFT based pixel array with independent storage capacitor

TFT displays use active matrix addressing, which allows for quick refreshing of stored charge at each pixel

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10

Typical TFT configuration

substrate

semiconductordrainsource

gatedielectric

t2W t3

t1

L

Critical materials properties:• charge carriers mobility• gate dielectric constant

Sip-S

ia-S

i

Pentac

ene

o-thio

phen

e

Polythi

ophe

ne F8T2

Nanow

ires

Nanotu

bes

Chalco

genid

e

1E-3

0.01

0.1

1

10

100

1000

Mob

ility

(cm

2 /Vs)

DTGGFET)linear(D V)VV(ClwI −=μ

μ - mobility (cm2/Vs)CG -gate capacitance (ε0εrA/t1)VG - gate voltageVD - drain voltageVT - threshold voltaget1 - 10 μm to 100 μmt2 0.1 μm to 1μm

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TFT active matrix technologyY. Kuo et al, IBM J. Res Dev. 43, pp. 73 (1999)

Thin-film materials deposition methodsa-Si:H, polysilicon, CdSe, etc.PECVD, LPCVD, evaporation, etc.

SiNx, SiO2, SiOxNy, Ta2O5, Al2O3 dual dielectrics PECVD, APCVD, sputtering, anodization, etc.

Mo, Ta, Cr, Ti, Al, Cu, Ta-Mo, Mo-W, Cr-Ni, ITO. Sputtering, evaporation, etc.

a-Si or polycrstalline n+ Si, (for ohmic contacts) PECVD, ion-shower doping, etc. Low-temperature, low-Na glass (substrates)

higher mobility increases speed and decreases operational voltage

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Organic Electronic Materials

Poly( 3-hexyl tiophene ) (P3HT) ( Aldrich, custom synthesized)

s s s ss s s s s s Forms ordered lamellar structure with π-stacking. Doped by air.

Poly[5,5’-bis(3-dodecyl-2-thienyl)-2-2’-bithiophene] (PQT-12), (Xerox)

Polymer is more stable with similar characteristics to P3HT.

R= C12H25

μ ≈ 0.1 cm2/Vs

μ ≈ 0.1 cm2/Vs

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Organic Electronic Materials

Pentacene from soluble precursor (IBM)

Weig

ht (%

)

temp (°C)

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12

Silicon Wafer

Cr/Au depositions and photolithography

Spin coat with polymer

Spin coat fabrication Process

Std chemical cleaning

Thermal oxidation (SiO2) orPulsed laser deposition (HfO2)

gate dielectric100 nm SiO2 or100 nm HfO2

Electrode pattern

(O2) plasma cleanHMDS

Contact angle 50°- 60°

Gate dielectric surface

preparation

0.5% solution in toluene

20 nm to 10 nm

Thermal treatment

Electrical Testing

Organic- TFT

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100 nm SiO2Si-substrate

n+

Au AuP3HT

VG

VD Is

20 nm to 60 nm

Organic- TFT Output Characteristic

P3HT FET

0 -40 -80

0.0

-50.0µ

-100.0µ

-150.0µ

-200.0µ

-250.0µ

I D (A

)

drain voltage (V)

- 80V - 70 V - 60 V - 50 V - 40 V - 30 V - 20 V - 10 V 0 V

gate voltage

μ = 3 x10-3 cm2/Vs

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13

Vacuum deposited pentacene TFTμFET - 0.2 cm2/Vs

Charge carriers mobility increases with increasing molecular order

Organic- TFT

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In organic semiconductors, both the properties of the individualmolecules and the structural order of the molecules in the film determine the macroscopic properties of the material.

These properties can be controlled by using molecular engineering to synthesize molecules with optimal characteristicsand by controlling the conditions under which these molecules assemble to form the solid.

Organic - TFT

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Next Step: New Materials and Metrology for Organic Electronics

Challenges: operational voltage, speed• Materials

– dielectric to semiconducting transition– structure at the interface– gate dielectric

•Metrology– thin film structures ( < 100 nm)– nonlinear dielectric effects (E > 105 V/cm) wave vector π/a

ener

g y

0 10 20 30 40 500.0

2.0x10-54 .0x10-56 .0x10-58 .0x10-51 .0x10-41 .2x10-41 .4x10-41 .6x10-41 .8x10-42 .0x10-42 .2x10-4

σ (Ω

−1cm

−1)

G ate Voltage (V )

L= 5 μm L= 10 μm L= 20 μm L= 50 μm

V d=-7 .5V

NIST FET Test structure scales linearly with dimensions10 1 10 2 10 3 10 4 10 5 10 6 10 7 10 8 10 9 10 10

3456789

101112

ε'

frequency (H z )

1.8 eV

Eg<

1 eV

We are here

ωp

Need to decrease band gap (Eg)

and increase frequency of the dielectric-to-sem.conducting transition( ωp)

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Summary Plasma deposition and etching are used extensively in the fabrication of large-area a-S:H TFT arrays. The PECVD process can supply materials with varying characteristics to fit the unique structure and materials requirements of TFTs.

Organic TFTs are close to passage from the research laboratory to product development and then to manufacturing of new products based on organic semiconductors.

Organic materials with enhanced electromagnetic properties are increasingly used in advanced electronic packaging AMLCD, Embedded Devices, Flexible and Transparent Electronics

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