Bachelor Thesis Presentation Slides

Outline

PMMA-thin films as dielectric layer for printable field effect transistors Levon Altunyan Fakult¨ at f¨ ur Ingenieurwissenschaften Nanostrukturtechnik Universit¨ at Duisburg-Essen

April 28, 2009

Levon Altunyan

Universit¨ at Duisburg-Essen - Fakult¨ at f¨ ur Ingenieurwissenschaften, Nanostrukturtechnik

PMMA-thin films as dielectric layer for printable field effect transistors

Aim of the Work MIM Development Measurements Transistor Summary

Outline 1

Aim of the Work

2

MIM Development Spin Coating Process I-V measurements

3

Measurements C-V measurements; Static dielectric constant, Part I Measurements of the static dielectric constant, Part II Breakdown voltage Breakdown field strenght

4

Transistor MISFET devices

5

Summary Results Future Work

Levon Altunyan

Universit¨ at Duisburg-Essen - Fakult¨ at f¨ ur Ingenieurwissenschaften, Nanostrukturtechnik

PMMA-thin films as dielectric layer for printable field effect transistors

Aim of the Work MIM Development Measurements Transistor Summary

Objectives

The main aims of this work are: PMMA as gate dielectric Development of a metal insulator metal (MIM) structure I-V and C-V measurements of the MIM structures Measurement of the static dielectric constant ( PMMA ) Measurement of the breakdown voltage and breakdown field strenght of PMMA Realization of MISFET devices (PMMA as gate dielectric)

Levon Altunyan

Universit¨ at Duisburg-Essen - Fakult¨ at f¨ ur Ingenieurwissenschaften, Nanostrukturtechnik

PMMA-thin films as dielectric layer for printable field effect transistors

Aim of the Work MIM Development Measurements Transistor Summary

Spin Coating Process I-V measurements

Set of the initial spin coating procedure parameters

Use of 2 phases: Film thickness, h [nm] →

First Spin parameters: PMMA Layer Thickness (nm) vs. Spin Speed (rpm)

650

h = k1ωα

600

Second Spin parameters: ω ∈ [1000(rpm); 7000(rpm)] stepsize = 500(rpm) a = 500(rpm/s 2 ) t = 60(s)

550 500 450

Baking Conditions:

400 1000

ω = 1000(rpm) a = 500(rpm/s 2 ) t = 20(s)

2000

Levon Altunyan

3000 4000 5000 Spin Speed, ω [rpm] →

6000

7000

Tannealing = 120(◦ C ) tannealing = 50(min)

Preparation of 1 sample/step size PMMA layer thickness measured at 8 points/sample

Universit¨ at Duisburg-Essen - Fakult¨ at f¨ ur Ingenieurwissenschaften, Nanostrukturtechnik

PMMA-thin films as dielectric layer for printable field effect transistors

Aim of the Work MIM Development Measurements Transistor Summary

1 spin only tspin = 25(s) Max acc., a = 10000(rpm/s 2 ) tannealing = 30(min) Tannealing = 160(◦ C )

900 Film thickness, h [nm] →

Optimized Spin Coating process for the low viscosity PMMA supplied by Evonik:

Spin Coating Process I-V measurements

800 700

PMMA Layer Thickness (nm) vs. Spin Speed (rpm) h = k1ωα

600 500 400 300 1000

2000

3000 4000 5000 Spin Speed, ω [rpm] →

6000

Conclusions: The fit curve d(ω) = k1 ∗ (ω (−α) ) [1] should be seen only as a good reference for the general behavior of the measured set of data points.

Less scatering in the layer hights (ω > 1700(rpm)).

Results correspond better to the thicknesses given by the material data provided by Evonik for wt% = 4, 5(%).

Levon Altunyan

Universit¨ at Duisburg-Essen - Fakult¨ at f¨ ur Ingenieurwissenschaften, Nanostrukturtechnik

PMMA-thin films as dielectric layer for printable field effect transistors

Aim of the Work MIM Development Measurements Transistor Summary

Spin Coating Process I-V measurements

I-V measurements 6

Current, I [nA] →

1.5

x 10

1 0.5 0 −0.5 −1 −1.5 −1

−0.5

0 Voltage, V [V] →

0.5

1

Critical issue when using the initial MIM structure - High leackage currents have been observed.

Different scenarios for the possible reasons have been taken into consideration: Diffusion of the Silver contacts inside the PMMA layer; Probability that during measurements, the top contact’s electrode probe penetrates through, and touches the bottom contact;

Levon Altunyan

Universit¨ at Duisburg-Essen - Fakult¨ at f¨ ur Ingenieurwissenschaften, Nanostrukturtechnik

PMMA-thin films as dielectric layer for printable field effect transistors

Aim of the Work MIM Development Measurements Transistor Summary

Spin Coating Process I-V measurements

New Contacts Arrangement

To decrease the probability that during measurements, the top contact’s probe penetrates through, and touches the bottom contact and causes high leackage currents, a special design has been taken into cosideration.

High leakage current problems persisted.

Conclusion - Silver is dissolving inside the PMMA layer, which is the reason for the high leakage currents observed.

Levon Altunyan

Universit¨ at Duisburg-Essen - Fakult¨ at f¨ ur Ingenieurwissenschaften, Nanostrukturtechnik

PMMA-thin films as dielectric layer for printable field effect transistors

Aim of the Work MIM Development Measurements Transistor Summary

Spin Coating Process I-V measurements

Current/Voltage Characteristic

Current/Voltage Characteristic 0.01

Current [nA] →

Current [nA] →

500

0

0.005

0

−0.005

−500 −10

−8

−6

−4

−2

0 2 Voltage [V] →

4

6

8

10

−0.01 −10

−8

−6

−4

−2

0 2 Voltage [V] →

4

6

8

10

Material for the bottom and top contacts changed to Aluminium. ”Crossed” contacts design + Aluminium = low leakage currents.

The structure of the sucesfully eliminating contacts interconnections MIM structure can be summarized as follows: Use of aluminium metalized contacts: 25(nm) ≤ Albottom ≤ 50(nm) 50(nm) ≤ Altop ≤ 75(nm)

Use of the ”crossed contacts” design type

Levon Altunyan

Universit¨ at Duisburg-Essen - Fakult¨ at f¨ ur Ingenieurwissenschaften, Nanostrukturtechnik

PMMA-thin films as dielectric layer for printable field effect transistors

Aim of the Work MIM Development Measurements Transistor Summary

C-V measurements; Static dielectric constant, Part I Measurements of the static dielectric constant, Part II Breakdown voltage Breakdown field strenght

Capacitance, C [pF] →

80 70 60 50 40

Dielectric Constant, εPMMA [−] →

200

90

400

25 20 15 10 5 400

Levon Altunyan

100

450 500 550 600 PMMA Layer Thickness, dPMMA [nm] →

50 0

450 500 550 600 PMMA Layer Thickness, dPMMA [nm] →

30

0

150

Dielectric Constant, εPMMA [−] →

Capacitance, C [pF] →

100

400

450 500 550 600 PMMA Layer Thickness, dPMMA [nm] →

400

450 500 550 600 PMMA Layer Thickness, dPMMA [nm] →

50 40 30 20 10

Universit¨ at Duisburg-Essen - Fakult¨ at f¨ ur Ingenieurwissenschaften, Nanostrukturtechnik

PMMA-thin films as dielectric layer for printable field effect transistors

Aim of the Work MIM Development Measurements Transistor Summary

Levon Altunyan

C-V measurements; Static dielectric constant, Part I Measurements of the static dielectric constant, Part II Breakdown voltage Breakdown field strenght

Universit¨ at Duisburg-Essen - Fakult¨ at f¨ ur Ingenieurwissenschaften, Nanostrukturtechnik

PMMA-thin films as dielectric layer for printable field effect transistors

[−] →

3 2 1 0.04

0.06 0.08 0.1 Area, A [mm2] →

0.12

0.14

6

3 2 0

5 4.5 4 3.5 3 0.02

0.04

0.06 0.08 0.1 2 Area, A [mm ] →

0.12

0.14

0.02

0.04

0.06 0.08 0.1 Area, A [mm2] →

0.12

0.14

5

PMMA

5.5

5 4

[−] →

0.02

Dielectric Constant, Îľ

4

2.5 0

6

PMMA

5

0

C-V measurements; Static dielectric constant, Part I Measurements of the static dielectric constant, Part II Breakdown voltage Breakdown field strenght

Dielectric Constant, Îľ

Dielectric Constant, ÎľPMMA [−] →

Dielectric Constant, ÎľPMMA [−] →

Aim of the Work MIM Development Measurements Transistor Summary

4 3 2 1

0 350

400 450 500 550 600 650 PMMA Layer Thickness, dPMMA [nm] →

700

Figure: Dielectric Constant ( ) vs. Contacts Area, dPMMA ≈ a.)375; b.)475; c.)700 (nm) Levon Altunyan

Universit¨ at Duisburg-Essen - Fakult¨ at f¨ ur Ingenieurwissenschaften, Nanostrukturtechnik

PMMA-thin films as dielectric layer for printable field effect transistors

Aim of the Work MIM Development Measurements Transistor Summary

C-V measurements; Static dielectric constant, Part I Measurements of the static dielectric constant, Part II Breakdown voltage Breakdown field strenght

Dielectric Constant, Results and Discussion

Results: Higher capacitance values for lower PMMA layer hight observed.

Low frequency dependency (< 1%) of the (C-V) characteristics (f=100 kHz, f=1 MHz).

A few values deviate highly from the majority of points.

Consequence of the lower PMMA thicknesses at some areas of the MIM structures.

Not so precise implementation by the responsible company of the shadow maskâ&#x20AC;&#x2122;s contacts areas

The computed average value PMMAaverage â&#x2030;&#x2C6; 3, 72 corresponds well to the values given in different sources [2, 3, 4, 5].

Levon Altunyan

Universit¨ at Duisburg-Essen - Fakult¨ at f¨ ur Ingenieurwissenschaften, Nanostrukturtechnik

PMMA-thin films as dielectric layer for printable field effect transistors

Aim of the Work MIM Development Measurements Transistor Summary

C-V measurements; Static dielectric constant, Part I Measurements of the static dielectric constant, Part II Breakdown voltage Breakdown field strenght

−6

5

−6

x 10

5 4 Current, I [A] →

Current, I [A] →

4

x 10

3 2 1

3 2 1

0

0

−1 0

−1 0

10

20

30 40 Voltage, V [V] →

50

60

70

10

20

30 40 Voltage, V [V] →

50

60

70

−5

Current, I [A] →

3

x 10

2 1 0 −1 0

10

20

30 40 Voltage, V [V] →

50

60

70

Figure: Breakdown Voltage, dPMMA ≈ a.)700; b.) 475; c.)375 (nm) Levon Altunyan

Universit¨ at Duisburg-Essen - Fakult¨ at f¨ ur Ingenieurwissenschaften, Nanostrukturtechnik

PMMA-thin films as dielectric layer for printable field effect transistors

Aim of the Work MIM Development Measurements Transistor Summary

C-V measurements; Static dielectric constant, Part I Measurements of the static dielectric constant, Part II Breakdown voltage Breakdown field strenght

Breakdown Voltage, Results and Discussion

Results: After reaching Vcrit , a sudden flow of current, within very short time is observed.

Completely destruction of the dielectric to a smoking hot mass of undefinable structure was not detected.

An unexpected, fluctuating behaviour is observed.

The PMMA dielectric can recover its full dielectric strength once current flow has been externally interrupted. This ”self-healing” property of PMMA thin films corresponds to the reported in literature behaviour [7].

Levon Altunyan

Universit¨ at Duisburg-Essen - Fakult¨ at f¨ ur Ingenieurwissenschaften, Nanostrukturtechnik

PMMA-thin films as dielectric layer for printable field effect transistors

Aim of the Work MIM Development Measurements Transistor Summary

C-V measurements; Static dielectric constant, Part I Measurements of the static dielectric constant, Part II Breakdown voltage Breakdown field strenght

Thickness(nm): Altop ≈ 150 PMMA∈ [575; 625] Albottom ≈ 70

Breakdown Voltage: V11 ≈ 13, 7(V ) V12 ≈ 18, 0(V ) V13 ≈ 16, 0(V )

Altop ≈ 150 PMMA∈ [450; 500] Albottom ≈ 70

V21 ≈ 12, 5(V ) V22 ≈ 27, 0(V ) V23 ≈ 27, 0(V ) V24 ≈ 10, 5(V ) V31 ≈ 13, 0(V ) V32 ≈ 7, 0(V ) V33 ≈ 11, 0(V )

Altop ≈ 150 PMMA∈ [370; 420] Albottom ≈ 70

Levon Altunyan

Electric Field(MV/m): E11 ∈ [21, 92; 23, 82] E12 ∈ [25, 60; 27, 82] E13 ∈ [20, 74; 22, 54] E21 E22 E23 E24 E31 E32 E33

∈ [25, 00; 27, 77] ∈ [54, 00; 60, 00] ∈ [54, 00; 60, 00] ∈ [21, 00; 23, 33] ∈ [30, 95; 35, 13] ∈ [16, 66; 18, 91] ∈ [26, 19; 29, 72]

Universit¨ at Duisburg-Essen - Fakult¨ at f¨ ur Ingenieurwissenschaften, Nanostrukturtechnik

PMMA-thin films as dielectric layer for printable field effect transistors

Aim of the Work MIM Development Measurements Transistor Summary

C-V measurements; Static dielectric constant, Part I Measurements of the static dielectric constant, Part II Breakdown voltage Breakdown field strenght

Breakdown Field Strenght, Results and Discussion

Results Majority of values are in the range between 25 to 30 (MV/m).

The critical field strength ranges correspond to the typical for polymers [6].

Ecrit ≈ 34, 73 (MV/m) fits exactly to values reported in literature [8, 9].

Levon Altunyan

Universit¨ at Duisburg-Essen - Fakult¨ at f¨ ur Ingenieurwissenschaften, Nanostrukturtechnik

PMMA-thin films as dielectric layer for printable field effect transistors

Aim of the Work MIM Development Measurements Transistor Summary

W

Source

MISFET devices

L

Al

Drain UD Drain Contact Source Contact Semiconductor Insulator U Gate Contact Gate G Substrate

−6

x 10 Vg=0[V]

10

Vg=10[V]

5

Vg=30[V]

x 10 Vg=0[V]

10

Vg=20[V] Vg=40[V]

0 −5 0

C60 PMMA Al Glass

−6

15

ID [A] →

ID [A] →

15

Al

Vg=40[V]

5 0

10

20 VDS [V] →

30

40

−5 0

10

20 VDS [V] →

30

40

Figure: Al/PMMA/C60/Al MISFET Structure; Characteristic Curves

Levon Altunyan

Universit¨ at Duisburg-Essen - Fakult¨ at f¨ ur Ingenieurwissenschaften, Nanostrukturtechnik

PMMA-thin films as dielectric layer for printable field effect transistors

Aim of the Work MIM Development Measurements Transistor Summary

MISFET devices

W

L Drain UD Drain Contact Source Contact Semiconductor Insulator U Gate Contact Gate G Substrate

Al

2

100

0

0 g

V =−10[V] g

−4

V =−20[V]

D

V =0[V]

−2

I [nA] →

ID [nA] →

Source

Pentacene PMMA Al Glass

Vg=0[V] Vg=−10[V] Vg=−20[V]

−100

V =−30[V] g

Vg=−40[V]

−200

Vg=−50[V]

g

Vg=−30[V]

−6

−300

Vg=−60[V]

V =−40[V] −8 −40

g

−30

−20 VDS [V] →

−10

0

Al

−400 −60

−50

−40

−30 −20 VDS [V] →

−10

0

Figure: Al/PMMA/C60/Al MISFET Structure; Characteristic Curves Levon Altunyan

Universit¨ at Duisburg-Essen - Fakult¨ at f¨ ur Ingenieurwissenschaften, Nanostrukturtechnik

PMMA-thin films as dielectric layer for printable field effect transistors

Aim of the Work MIM Development Measurements Transistor Summary

MISFET devices

MISFET, Results and Discussion I

Results: C60 n-type; pentaceneâ&#x20AC;&#x2122;s p-type behaviour.

Some field effect is noticed.

Capacitance and a respective dielectric constant ( PMMA ), similar to silicon dioxideâ&#x20AC;&#x2122;s, has been measured. Therefore, it can be concluded that PMMA is a suitable gate dielectric for MISFET structures, but additional studies for the reasons causing the observed characteristic behaviour should be carried out.

Levon Altunyan

Universit¨ at Duisburg-Essen - Fakult¨ at f¨ ur Ingenieurwissenschaften, Nanostrukturtechnik

PMMA-thin films as dielectric layer for printable field effect transistors

structure, charges are directly injected into the channel inte of accumulated charges at the semiconductordielectric Aim of the Work MIM Development charges at the semiconductordielectric interMeasurements MISFET devices face.accumulated In the other two structures, the source/drain electrode In theTransistor other two structures, the source/drain electrodes Summary andface. the channel are separated by the semiconducting laye and the channel are separated by the semiconducting layer.

MISFET, ResultsThus, and Discussion II have to travel through several tens o charges first Thus, charges first have to travel through several tens of

a.)

b.)

Figur Commonfield-effect field-effect transistor transistor configurations: Figur e 4.e 4.Common configurations:(a) ( Figure:contact, Common bottom topFET gateConfigurations (BC/TG); (b) bottom contact, bottom gate bottom contact, top gate (BC/TG); (b) bottom contact, bottom ga (BC/BG); (c) top contact, bottom gate (TC/BG).

(BC/BG); (c) top contact, bottom gate (TC/BG).

Results: It is important that the roughness of the channel interface is additionally examined.

Moreover, implementation of the structures a.) bottom contact/top gate and b.) bottom contact/bottom gate could be a more beneficial choice with respect to the materials in use.

Lower channel roughness, increased gate voltage effect

Levon Altunyan

Universit¨ at Duisburg-Essen - Fakult¨ at f¨ ur Ingenieurwissenschaften, Nanostrukturtechnik

PMMA-thin films as dielectric layer for printable field effect transistors

Aim of the Work MIM Development Measurements Transistor Summary

Results Future Work

Summary

Summary The spin process is optimized.

Several structures are realized.

Current leackage problem is solved.

A mask with variable area for capacitance measurements has been designed.

C-V measurements are carried out.

Estimation of dielectric constant is achieved.

Breakdown voltage and breakdown field strenght are studied.

An attempt to realize MISFET structures utilizing PMMA as gate dielectric is made.

The characteristic curves of the designed devices are examined.

Levon Altunyan

Universit¨ at Duisburg-Essen - Fakult¨ at f¨ ur Ingenieurwissenschaften, Nanostrukturtechnik

PMMA-thin films as dielectric layer for printable field effect transistors

Aim of the Work MIM Development Measurements Transistor Summary

Results Future Work

Proposals for Future Work Capacitance measurements could be done on the MIS structures.

Implementation of bottom contact/bottom gate or bottom contact/top gate structure.

Further investigation of the field effect dependence.

Levon Altunyan

Universit¨ at Duisburg-Essen - Fakult¨ at f¨ ur Ingenieurwissenschaften, Nanostrukturtechnik

PMMA-thin films as dielectric layer for printable field effect transistors

References Abbreviations

C. Lawrence The mechanics of spin coating of polymer films.

Phys. Fluids, 31(10):2786, 1988.

Boedeker Plastics, Inc. http : //www .boedeker .com/acryl p.htm Accessed 08.03.2009.

J. Kronjaeger.

Electrical properties of Insulators. http : //www .kronjaeger .com/hv − old/hv /tbl/prop.html, Accessed 08.03.2009.

N. Friction, S. Kuehn, J. Marohn and R. Loring.

Noncontact Dielectric Friction.

J. Phys. Chem. B, 14525 - 14528, 110, 30, 2006.

S. Gross, D. Camozzo, V. Di Noto, L. Armelao and E. Tondello.

PMMA: A key macromolecular component for dielectric low-kappa hybrid inorganic-organic polymer films.

Eur. Polym. J., 43, 3, 2007.

Levon Altunyan

Universit¨ at Duisburg-Essen - Fakult¨ at f¨ ur Ingenieurwissenschaften, Nanostrukturtechnik

PMMA-thin films as dielectric layer for printable field effect transistors

References Abbreviations

H. Foll.

Electronic Materials - Skript.

University of Kiel, Faculty of Engineering, http : //www .tf .uni − kiel.de/matwis/amat/elmat en/index.html, Accessed 28.March 2009.

K. Miyairi and E. Itoh.

AC Electrical Breakdown and Conduction in PMMA Thin Films and the Influence of LiC104 as an Ionic Impurity.

International Conference on Solid Dielectrics, Toidorrse, France, July 5-9, 2004.

Evonik Industries.

R GS / PLEXIGLASB R XT. PLEXIGLASB http : //www .plexiglas.de/NR/rdonlyres/5FDB46EB − 8AB7 − 486C − AC 14 − 448B2D893034/0/2111PLEXIGLASGS XT en.pdf , July 2008, Accessed 28.March 2009.

Levon Altunyan

Universit¨ at Duisburg-Essen - Fakult¨ at f¨ ur Ingenieurwissenschaften, Nanostrukturtechnik

PMMA-thin films as dielectric layer for printable field effect transistors

References Abbreviations

Wikipedia - Die freie Enzyklop¨ adie.

Polymethylmethacrylat, Aufbau und Eigenschaften. http : //de.wikipedia.org /wiki/PlexiglasAufbau und Eigenschaften, Last modification 19. February 2009, Accessed on 28.March 2009

Levon Altunyan

Universit¨ at Duisburg-Essen - Fakult¨ at f¨ ur Ingenieurwissenschaften, Nanostrukturtechnik

PMMA-thin films as dielectric layer for printable field effect transistors

References Abbreviations

Explanation of Different Abbreviations

Metal Insulator-Metal.

Poly Methyl Metha Acrylate Indium Tin-Oxide.

Field Effect-Transistor.

Metal Insulator-Semiconductor.

Metal Insulator-Semiconductor Field Effect-Transistor.

Organic Field Effect-Transistor.

Table: Explanation of what different abbreviations mean.

Levon Altunyan

Universit¨ at Duisburg-Essen - Fakult¨ at f¨ ur Ingenieurwissenschaften, Nanostrukturtechnik

PMMA-thin films as dielectric layer for printable field effect transistors