FABRICATION of ORGANIC LIGHT-EMITTING DEVICES
Jennifer Reinig, Junior Physics/Math Major at Drake University
Physics REU: IA State University, Summer 2001
FORWARD
This manual is prepared for the purpose of providing knowledge about OLED
fabrication, the theory behind the operation of OLED’s, as well as classifying the
substances and types of observations that are made during OLED fabrication and testing.
A significant portion of the text is devoted towards explaining the procedure of OLED
fabrication as observed during the summer of 2001 in rooms A216, A217, and A218 in
the Physics Hall at IA State University. Several detailed diagrams are included as
audiovisuals. In most cases, the text is formatted in column style for easier reading.
Although the procedure and apparatus descriptions are as detailed as possible, it is
not expected that this document gives all the necessary information needed for the
beginner. Anyone wishing to thoroughly become involved with OLED research should
follow an experienced graduate student in the lab for a couple of weeks before taking
upon any independent work.
Special thanks must be given to Joseph Shinar, who supervised this research, as
well as the graduate students with whom I worked with. My associates included Bhaskar
Choudhury, and Moon-Ky Lee.
33
1
TABLE OF CONTENTS
I N T R O D U C T I O N ______________________________________________
Basic Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
The p-n Junction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-6
Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Factors Influencing Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
HOMO and LUMO levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-10
Electron Mobility. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
OLED Materials and Their Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Hole Transporting Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Electron Transporting Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
G E O M E T R Y __________________________________________________
Dot Array . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-16
Combinatorial Factorization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-17
A P P A R A T U S _________________________________________________
The Fume Hood . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The Loadlock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The Glove box . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Equipment Used During Thin Film Deposition . . . . . . . . . . . . . . . . . . . . .
18-19
20-21
. 22-23
24-26
P R O C E D U R E_________________________________________________
I. General Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
II. Preparation of Striped ITO Substrate . . . . . . . . . . . . . . . . . . . . . . . .. . . . 29-30
III. Preparation of ITO Substrate: Partial Etching of ITO . . . . . . . . . . . . . . 31
IV. Thin Film Deposition in the Glove box . . . . . . . . . . . . . . . . . . . . . . . . . 32-33
33
2
TABLES
Table 1: LUMO and HOMO levels for various organic materials . . . . . . . . . . . . . 10
Table 2: Electron Mobility of various HTL and ETL layers . . . . . . . . . . . . . . . . . 11
Table 3: Materials Used in OLED Fabrication . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Table 4: Thickness Monitor Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
V-P Conversion Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
DIAGRAMS
Figure 1: Basic Structure of a bilayer OLED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Figure 2: Light Emission from a Semiconductor . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Figure 3: I-V Curve for a Real Diode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Figure 4: Basic Operation of an OLED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Figure 5: Energy Diagram for Multilayer OLED . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Hole Transporting Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Electron Transporting Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Figure 6: Dot Array Geometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15
Figure 7: Varied Thicknesses for a Dot Array OLED . . . . . . . . . . . . . . . . . . . . . . .16
Figure 8: Combinatorial Factorization Geometry . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Figure 9: Light Emission from a Combinatorial Factorization OLED . . . . . . . . . . . 17
Figure 10: The Fume hood . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Figure 11: The Load lock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Figure 12: The Glove box . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Figure 13: Equipment Used During Thin Film Deposition . . . . . . . . . . . . . . . . . . . 24
33
3
______________INTRODUCTION____ ___ __
Figure
1
shows
the
basic
and electron transporting layers, as well
structure of an OLED (Organic Light
as a buffer between the ETL and
Emitting Device) in its simplest form.
cathode. Different geometries other than
Most OLED’s generally contain more
the plane geometry may also be used for
than one layer in the hole transporting
the ITO and cathode layer.
Figure 1: Basic Structure of a bilayer OLED
1
1
Shinar, Joseph, and V. Savvateev. Chapter 1. Introduction to Organic Light Emitting Devices. Ames,
IA: Iowa State University. p. 33.
33
4
Figure 2: Light Emission from a Semiconductor
The p-n Junction
An OLED is a type of p-n
junction that generates light output from
electrical
2
The
the
two
layers
are
connected in circuit to form a p-n
p-type
junction, the electrical current causes the
semiconductors have positive charge
electrons from the ETL to move across
carriers (also called holes), and an n-type
the energy gap and recombine with
semiconductor
carriers
input.
When
has
(electrons).
3
negative
charge
holes, emitting photons with energy hf =
The
p-type
E g (Figure 2) .
4
The energy gap is the
semiconductor refers to the HTL, while
difference
the n-type semiconductor refers to the
LUMO level of the emitting layer, and it
ETL.
is largely responsible for the observed
between
the
HOMO
and
color of the light.
2
Serway, Raymond A., et al. “Light-Emitting
and –Absorbing Diodes: LEDs and Solar Cells.”
Modern Physics, Second Edition. Fort Worth,
Texas: Harcourt Brace College Publishers,
1997. p. 446.
3
Serway, Raymond A., et al. “The p-n
Junction.” Modern Physics, Second Edition. P.
443.
33
4
Serway, Raymond A., et al. “Light-Emitting
and –Absorbing Diodes: LEDs and Solar Cells.”
Modern Physics, Second Edition p. 446.
5
At
the
junction
of
the
two
The equation for an ideal diode is,
regions, a new region forms, which is
depleted of moving charges. An electric
3
I =I 0 (e
qV/kBT
– 1)
5
field of about 10 -10 V/cm exists in this
depletion region, and it prevents the
Where I is the current, q is the charge of
diffusion of holes and electrons across it
an electron, Vies the voltage, kB is
in the absence of an external voltage.
Boltzmann’s constant, and T is the
Current can flow in only one
temperature in Kelvin’s.
direction—from the n-type region to the
p-type region (also called reverse bias).
In forward bias, the current increases
exponentially with increasing voltage,
because
the
increased
forward
bias
decreases the barrier between the two
regions. However, with reverse bias, the
current quickly reaches a maximum
value I o because the increased voltage
increases the barrier
between the two
Figure 3: I-V curve for a Real Diode
5
regions (See Figure 3).
5
Serway, Raymond A., et al. “Semiconductor
Devices.” Modern Physics, Second Edition.
Fort Worth, Texas: Harcourt Brace College
Publishers, 1997. P. 443-445.
33
6
Operation
An
electrical
current
causes
characteristic of the HOMO and LUMO
electrons to move from the cathode and
levels of the emitting layer. In Figure 3,
through the consecutive layers beneath
an increase in voltage increases the slope
it, while the holes (positive charges)
along the HOMO and LUMO lines,
move in the opposite direction (Figure
increasing
the
transfer
of
charges.
4). When the holes and electrons meet,
they emit a quantum of light that is
Figure 4: Basic Operation of an OLED
6
6
Shinar, Joseph and V. Savvateev. Chapter 1. Introduction to Organic Light Emitting Devices. Ames, IA:
Iowa State University. P. 34.
33
7
While the general mechanism
Factors Influencing Performance
Various
the
responsible for the operation of OLED’s
quality of the OLED, including the
is well understood, it generally takes
choice
several months of laboratory work to
of
geometry,
factors
influence
materials,
purity
of
thicknesses,
samples,
and
become skilled in OLED fabrication.
contamination from air or other sources.
However, there are several variables that
The factors that are most responsible for
can be analyzed to predict the success of
the quality are the choice of materials in
an OLED and/or understand why a
the ETL and HTL layer.
particular combination produces better
Different
combinations will emit different colors
than usual results.
and
important factors are electron mobility
have
different
lifetimes.
The
The two most
emission from OLED’s is generally
and
desired in the blue-ultraviolet range, due
unoccupied molecular orbital (HOMO)
to the high energy of this portion of the
and the lowest unoccupied molecular
light
orbital
spectrum.
However,
energy
levels
(LUMO).
of
the
highest
Materials
are
OLED’s that emit other colors can also
generally chosen so that the energy
be made (red, green, white, etc). Some
levels of the HOMO and LUMO levels
desirable factors are a long lifetime and
“match” as electrons and holes travel
a strong intensity of the device.
from one side to another (Figure 4).
Their
envisioned ranges from the replacement
of fluorescent lights to sensors that
detect the levels of a chemical in the
environment.
33
HOMO/LUMO Levels
As electrons travel from the
cathode,
they
must
jump
from
the
8
LUMO of one material to the LUMO of
flow
the next material (Figure 3).
A small
between the LUMO-LUMO levels and
energy gap enhances the conditions for
HOMO-HOMO levels of the materials
electron flow. The same is true for the
in sequence is the major reason for the
holes as they travel in the opposite
use of more than one material layer in
direction. The need to facilitate electron
the HTL and ETL.
by
reducing
the
energy
gaps
Figure 5: Energy Diagram for a Multilayer OLED
Figure 5 represents the flow of
LUMO levels. When they meet, they
positrons and electrons for a multilayer
emit a quantum of light or travel as an
OLED. The energy gap between
exciton. In the diagram, if perilene was
successive levels is on the order 0.2 eV.
removed, the light would be of a
The positron falls into consecutively
different color because the emitting layer
lower HOMO energy levels, while the
would be CBP. (Energy levels not
electron falls into consecutively lower
drawn to scale).
33
9
Table I is a list of the LUMO
Materials are chosen so that the
(Lowest Unoccupied Molecular Orbital)
energy levels “match” in going from one
and
Unoccupied
level to another (See Figures 4 and 5).
Molecular Orbital) energy levels for
In general, the absolute value of the
various organic materials.
Literature
energy level increases in going from the
values of the HOMO and LUMO energy
anode to the to HTL and in going from
levels vary from source to source, and so
the cathode to the ETL (including any
the values reported in Table 1 are either
layers in between).
the most reported result, the mean, or
jump in the HOMO or LUMO energy
HOMO
(Highest
some average calculation thereof.
7
from
one
layer
to
Minimizing the
another
greatly
facilitates the motion of electrons and
Table 1: LUMO and HOMO levels for
various organic materials
holes (positrons).
Often buffer layers
are placed between two layers (between
LUMO
(-eV)
Alq3
3.00
2.56
α−NPB
Butyl-PBD 2.60
CBP
2.90
CuPc
3.00
Perilene
3.10
HOMO
(-eV)
6.00
5.40
6.20
6.00
5.00
5.80
the cathode and ETL). The buffers work
by the same mechanism, aiding electron
flow.
7
The fact that exact values are not consistent
from source to source does not greatly matter,
since what is most important is not the exact
value but a meaningful way of determining
whether a given energy level is below or above
that of another material.
33
10
Hole and Electron Mobility
Another major factor influencing
performance
is
hole
and
as materials in an ETL layer.
Table 2
electron
has some electron and hole mobilities for
mobility. The low electron mobility of
a few of the organic materials used in the
most organic materials prevents their use
ETL and HTL layers.
Table 2: Electron Mobility of Various HTL and ETL Layers
CuPc
TPD
NPB, NPD
Alq 3
Electron Mobility
2
(cm /Vs)
1.5E-07-1.5E-06
Hole Mobility
2
(cm /Vs)
1.5E-05-1.5E-04
1.4E-06
1.25E-03
3E-04
2E-8
8
8
Shinar, Joseph, and V. Savvateev. Chapter 1. Introduction to Organic Light Emitting Devices. Ames,
Iowa: Iowa State University. p. 27.
33
11
Table 3: Materials Used in OLED Fabrication
Alq 3
Bu-PBD
Perilene
CuPc
TPD
(α)NPB, ( α)NPD
DPVBi
CBP
Aluminum
Al 2 O 3
CsF (or Cs Acetate)
ITO
Function
Thickness
(Å)
ETL
ETL
ETL/emitting
HTL
HTL
HTL
HTL/emitting
HTL/emitting
Anode
Buffer
Buffer
Cathode
100-400
100
*
400
100-400
400
400
100-200
400
1000-3000
20
20
1000
Current
(Amps)
13
9
12
15
12
12
13
35-40
20
—————
Color
Green
Blue
Blue
Blue
Blue
Blue
Blue
Blue
—————
—————
—————
—————
The materials chosen for the HTL and ETL layers are organic materials that
contain several hexagonal and/or pentagonal π -conjugated rings. The success of their
performance is due to the behavior of the π -bonds. They behave as semiconductors, due
to the small energy gap between the highest unoccupied π-orbital and the lowest
unoccupied π -orbital. Within the ring structures, the π -orbitals overlap one another. This
overlap of the adjacent π -orbital wave functions makes the electrons relatively
9
delocalized, i.e., capable of mobility, a property contributing to their performance as
semiconductors.
*
Perilene is typically deposited with ( α)NPB: ~ 400 Å, 2% perilene, 98% ( α)NPB.
Shinar, Joseph, and V. Savvateev. Chapter 1. Introduction to Organic Light Emitting Devices. Ames,
Iowa: Iowa State University. p. 2.
9
33
12
Hole Transporting Materials
TPD
10
CuPc
DPVBi
CBP
11
( -)NPB, ( -) NPD
10
Shinar, Joseph, and V. Savvateev. Chapter 1. Introduction to Organic Light Emitting Devices. Ames,
Iowa: Iowa State University. p. 30.
11
Zou, L., et al. Combinatorial Fabrication and Studies of Intense Efficient Ultraviolet-Violet Organic
Light Emitting Device Arrays. Ames Laboratory-USDOE, and department of Physics and Astronomy,
Iowa State University, Ames, IA. P. 8.
33
13
Electron Transporting Materials
Alq 3
12
Bu-PBD
13
12
Shinar, Joseph, and V. Savvateev. Chapter 1. Introduction to Organic Light Emitting Devices. Ames,
Iowa: Iowa State University. p. 30.
13
Zou, L., et al. Combinatorial Fabrication and Studies of Intense Efficient Violet-Violet Organic Light
Emitting Device Arrays. Ames Laboratory-USDOE, and department of Physics and Astronomy, Iowa
State University, Ames, IA. P. 8.
33
14
__________________GEOMETRY__________________
There are two basics of types of
by using a special shutter during thin
geometry that are useful in OLED’s.
film deposition. The technique is useful
They are the dot array and striping
in determining which combination of
(combinatorial factorization). The dot
thicknesses produces the best results. It
array geometry has planar ITO, HTL,
is also used when several OLED’s are
and ETL layers, while the aluminum
needed, since each plate is a 21 x 21
layer is deposited as “dots” (See Figure
matrix of OLED’s. (Typically, only the
6).
center ones are used). The disadvantage
As
shown
in
Figure
7,
the
is
that
each
“dot”
must
be
tested
thickness of the HTL and ETL layers
separately, since there is no conducting
can be made to vary.
material
The example
shown is with CuPc as HTL and BuPBD as the ETL.
between
the
aluminum
cylinders.
This is accomplished
Figure 6: Dot Array Geometry
33
15
Figure 7: Varied Thicknesses of a Dot Array OLED
In a process called combinatorial
factorization (Figure 8), virtually any
upper left hand corner to light up (n
2
circuits → n OLED’s).
combination of the various junctions
One problem that makes this type
between anode and cathode may be
of
made to lit up. The OLED is made by
seepage of the HTL layer in between the
putting a layer of ITO striping on the
gaps of the ITO striping.
This can be
bottom, smooth ETL and HTL layers,
avoided
solution
and aluminum striping on the top that
polystyrene (from a Styrofoam cup) in
crisscrosses
toluene within the gaps between the
the
ITO
striping
when
fabrication
by
less
painting
desirable
a
is
the
of
viewed from above.
In Figure 9, putting only two
circuits causes the four junctions in the
33
16
Figure 8: Combinatorial Factorization
ITO stripes.
When painting the
stripes; however, experimental testing at
polystyrene solution, some of it may
Ames Lab has shown that this does not
inevitably spill over on top of the ITO
greatly affect the performance of the
OLED.
Figure 9: Light Emission from a Combinatorial Factorization OLED
33
17
_________________APPARATUS_________________
Figure 10: The Fume Hood
Figure 10 is a diagram of the
laboratory fume hood. It is used when
fountains are immediately outside of
Room A216 to the right.
removing a strip of ITO (Part II of the
In the back right corner are
procedure), partial etching of the ITO
several
(Part III of the procedure), and general
chemicals (A) and a wastebasket for
cleaning purposes. Eye goggles should
glass
be worn when working in the fume
waste (B).
hood, as well as protective clothing and
propanol, methanol, acetone, aquilegia,
closed-toe shoes.
toluene, and ITO surfactant.
In the event of eye
glass
and
other
bottles
of
various
miscellaneous
solid
The chemicals include 2-
contamination, a shower and eye wash
33
18
In the middle of the fume hood
ultrasonicator is filled halfway with
(C) are several small glass containers
water, and a circular Styrofoam buoy is
used to hold the OLED’s and chemicals
placed around the container. The buoy
while carrying out the steps of the
prevents the container from sinking, thus
procedure.
avoiding water contamination.
coded.
Each container is color-
Green is for 2-propanol, light
In front of the ultrasonicator is a
pink is for demonized water, yellow is
cylinder of compressed argon (E). It is
for aquilegia, red is for acetone, and
used to blow dry the OLED’s.
light blue is for ITO surfactant.
The
Deionized water flows from the
containers are filled halfway with the
right faucet, and regular tap water flows
needed chemical, and then rinsed with
from
deionized water after use.
containers for toluene and acetone are
the
left
(F).
Special
waste
The ultrasonicator sits in the
also in the sink. Chemicals other than
front right corner (D). The glass dishes
acetone and toluene should never be
containing chemicals and OLED’s are
poured directly into the sink but should
put in the ultrasonicator to ensure that a
be placed beneath the deionized water
reaction occurs uniformly on the surface
faucet and diluted with running water for
of
a couple of minutes.
33
the
OLED.
Before
use,
the
19
Figure 11: The Load lock
Figure 11 is a diagram of the
completely evacuated, at which point the
load lock where the OLED’s are loaded
pressure gauge will have reached its
into the glove box.
lowest point.
To open the load
Refill the chamber by
lock, pull out the lever at A, and lift up
turning the lever at D a few degrees
the bar. The circular cover should rotate
counterclockwise.
clockwise towards the back.
Place the
chamber, watch the lights along the top
plastic container with the OLED’s into
row of the gauge at E. Approximately 4-
the slide drawer and close the lid.
5 lights will light up at first, but as the
Evacuate the chamber by pulling the bar
argon flows into the chamber, the lights
at C 90 ° to the right.
will go off.
The sound of a
motor will be heard until the chamber is
33
While refilling the
Once there are one-two
lights left on, turn the refill lever back to
20
its starting position and wait until some
At the back of the chamber there
of the lights light up. Continue in this
is a door similar to the one on the
manner until the pressure gauge at C
outside (not shown). This is opened in
reads reaches the equilibrium value (0).
the same manner, except from the inside
The gauge at B monitors the
oxygen level inside the chamber.
It
of the glovebox.
The
chamber
should
be
should be at about 4 parts per million or
evacuated and backfilled twice when
less.
loading OLED’s from the laboratory into
If
immediately
it
becomes
evacuate
the
two
high,
chamber.
the glove box.
It should be evacuated
Never remove the OLED’s from the
and backfilled once after taking out
loadlock and put them in the glovebox if
OLED’s from the glove box.
the oxygen level is too high.
33
21
Figure 12: The Glove box
The thin film deposition takes
in an airtight, clear, plastic container and
place in the glove box (Figure 12). It is
are loaded in the load lock (A) (See
a sealed chamber filled with argon gas.
Figure 6 for operation of the load lock).
Its purpose is to prevent exposing the
OLED’s
OLED’s to oxygen. OLED’s are placed
directly, even with latex gloves. Always
33
should
never
be
touched
22
pick
them
up
with
a
tweezers
or
monitor.
The pressure monitor (G)
transport them by placing them on one
displays the pressure inside the vacuum
of the plastic dishes.
chamber. The samples to be deposited
All of the equipment in the glove
are located in the various drawers along
box is operated from the outside by
the far right hand side (E). (See Figure 8
putting one’s hands in the various gloves
and the explanation that follows for
and inverting them towards the inside
more information on operation of the
(B). Latex gloves should always be put
vacuum chamber and the equipment
on first before working inside the glove
associated with it). The spin-coater (I) is
box.
used to deposit a thin layer of a polymer
All watches, rings, bracelets, etc.
should also be removed. A lab coat is
(or other solution) on an OLED.
recommended.
OLED’s are stored in container’s along
The vacuum chamber (C) is
the far left (J).
The
Miscellaneous objects
hooked up to the vacuum pump (D) and
are also inside the glove box (K),
the two power sources (H).
including tweezers, markers, clips, metal
To the left
of the vacuum pump is the thickness
33
gratings and coverings, etc.
23
Figure 13: Equipment Used During Thin Film Deposition
Figure 13 is a diagram of the
equipment
used
film
grating is then clipped to the aluminum
deposition. The main component is the
bar on top of the supporting rods (near
vacuum
K).
chamber
deposition,
the
during
(A-F).
metal
thin
or placed in an appropriate grating. This
During
cylinder
Aluminum
coils
are
mounted
(A)
between washers (E) by loosening and
encloses the components on top of the
tightening the bolts on either side of the
vacuum chamber base.
supports with a small wrench.
The OLED(s)
are clipped onto an aluminum plate (B)
33
The
sample to be deposited is placed in the
24
spring portion of the coils.
A cover (C)
monitor (J).
A list of both the V-P
is often used to prevent deposition until
conversions and the acoustic impedances
the deposition rate has been sufficiently
and material densities are located near
stabilized.
A small sensor (K) records
the top and towards the middle of the
the deposition rate, as well as the
glovebox for easy reference. (See also
thickness deposited.
the tables that follow of this report ).
Once deposition
has stabilized, the cover can be moved
To start deposition, the power
by rotating the lever (D) beneath the
source is turned on (H), and the current
base of the vacuum chamber.
is slowly increased to the desired value
Once the setup has been properly
(See
Table
4
for
the
approximate
enclosed, the vacuum can be turned on.
currents associated with each value).
This is done by undepressing button two
The increase in the current heats the
and
aluminum coils and the materials in the
depressing
button
one
on
the
vacuum pump (G). Plan for at least two
middle
hours to allow the vacuum to become
material to evaporate. In most cases, a
completely established.
deposition
The pressure
spring
portion,
rate
of
causing
about
the
1
inside the chamber is monitored by the
angstrom/second is desired. During this
device at (I).
part of the procedure, the deposition rate
completely
When the vacuum is
the
reading
should be 3.500 – 3.700 V.
Before
current
depositing
correct
quantity of the substance may quickly
material
evaporate and be deposited at once. If
densities must be set on the thickness
this happens, the current should be
acoustic
33
established,
the
material,
impedance
the
and
should be carefully watched. If the
becomes
too
high,
a
large
25
decreased, and the rate should stabilize.
( Å/s), as well as the amount of sample
With all materials, there is a very narrow
that has been deposited (kÅ).
range of currents within which the rate
thickness of the sample to be deposited
will be at the desired level.
varies (see Table for some approximate
The
thickness monitor is closely watched for
The
values).
information about the rate of deposition
Table 4: Thickness Monitor Settings
14
Substance
Material Density Acoustic Impedance
Al
2.70
8.17
Mg
1.74
5.48
Au
19.30
23.18
LiF
2.64
11.41
CuPc/3AS/TPD/Alq
1.38
1.50
Y
4.34
10.57
Ag
10.50
16.69
Ca
1.55
8.83
CsF
4.12
8.83
In
7.31
6.54
14
This table is a copy of the table on the west side of the glove box in room A216 of the Physics Hall at
Iowa State University, Ames, IA. Summer 2001.
33
26
__________________
V-P Conversion Tables15_
Balzer Conversion :
Voltage (V) Pressure (Torr)
2.5
5.10E-08
2.7
1.10E-07
2.9
2.37E-07
3.1
5.10E-07
3.3
1.10E-06
3.5
2.37E-06
3.7
5.10E-06
3.9
1.10E-05
4.1
2.37E-05
4.3
5.11E-05
4.5
1.10E-04
4.7
2.37E-04
4.9
5.11E-04
5.1
1.10E-03
5.3
2.37E-03
5.5
6.39E-04
5.7
1.10E-02
5.9
2.37E-02
6.1
5.11E-02
6.3
1.10E-01
6.5
2.37E-01
6.7
5.12E-01
6.9
1.10E+00
7.1
2.38E+00
7.3
5.12E+00
7.5
1.10E+01
7.7
2.38E+01
7.9
5.12E+01
8.1
1.10E+02
8.3
2.38E+02
8.5
5.12E+02
8.7
1.10E+03
8.9
2.38E+03
9.1
5.13E+03
_______
P(torr) = 10^(1.66V-11.46)
Voltage (V) Pressure (Torr)
3.80
7.49E-06
3.81
7.79E-06
3.82
8.09E-06
3.83
8.41E-06
3.84
8.74E-06
3.85
9.08E-06
3.86
9.43E-06
3.87
9.80E-06
3.88
1.02E-05
3.89
1.06E-05
3.90
1.10E-05
3.91
1.14E-05
3.92
1.19E-05
3.93
1.23E-05
3.94
1.28E-05
3.95
1.33E-05
3.96
1.38E-05
3.97
1.44E-05
3.98
1.50E-05
3.99
1.55E-05
4.00
1.61E-05
4.01
1.68E-05
4.02
1.74E-05
4.03
1.81E-05
4.04
1.88E-05
4.05
1.96E-05
15
The tables are copies of the ones found on the west side of the glove box in room A216 of the Physics
Hall at Iowa State University, Ames, IA. Summer, 2001.
33
27
_____________________ P R O C E D U R E______________
I. GENERAL INSTRUCTIONS
Experience should be gained by
working
with
one
of
the
graduate
students for a week or more before
undertaking
The oxygen monitor should be
checked periodically. If the level rises
Vinyl gloves should be worn at all times,
above 4 ppm, evacuate the chamber and
and a lab coat is recommended. In the
purify it with argon.
case
should be replaced if the pressure falls
an
independent
back of the room.
work.
of
any
manuals are in the filing cabinet in the
emergency,
follow
the
directions on the door of room A216. In
Argon cylinders
below 300 psi.
case of problems or questions, operating
33
28
II. PREPARATION OF STRIPED ITO SUBSTRATE
layer
Several glass plates coated with a
razor. Do this for the rest of the marks
of
as well.
ITO
are
already
in
the
laboratory. Put on a pair of latex gloves
Starting from the right side and
and pick out the appropriate size (either
leaving the first strip of tape on the ITO,
1” x 1” or 2” x 2”). Pick up the glass
remove every other strip of tape. This is
plate with a tweezers and place it on a
best done by recutting the tape along the
Kimwipe. Determine which side is the
slit near the edge of the plate and using a
ITO side by placing both terminals of an
tweezers to lift up the tape from bottom
ohmmeter on one side of the glass plate.
to top. Place the glass plate on a dish
The side with the ITO will register a
and take it to the eastern fume hood.
resistance (typically 20 – 40 ohms),
Spray with Krylon spray paint. Allow to
while the glass plate will not.
dry for 15-20 minutes.
Place the glass plate on an
aluminum plate.
Cover the ITO side
completely with tape (typically black
Once it is
completely dry, take the glass plate back
to the working counter and remove the
remaining pieces of tape.
electrical tape, or some other thick tape).
The glass plate should now have
Place a ruler horizontally across the top
2 mm stripes of Krylon spray paint
and
two
across the whole surface of the ITO side.
millimeters. Next, place a straight edge
Place the ITO side face up into aqua
vertically in line with one of the marks
regia (in the western fume hood). Aqua
and cut along the straight edge with a
regia is 25% HNO 3 , 75% HCl. If
33
make
markings
every
29
necessary, this may be prepared by
diamond cutter. Hold on either side and
pouring the correct ratio of HNO 3 slowly
gently break in two. Draw horizontally
16
Aqua regia removes the ITO
across the middle of these two pieces
layer along the bare strips of the glass
with a diamond cutter, and break into.
plate.
Allow the plate to sit for
The glass plates are now ready to be
approximately 10 minutes. Take out the
cleaned, i.e., removal of thin film of
glass plate with a tweezers and blow dry
remaining paint and debris.
into HCl.
Check the surface in
Ultrasonicate in a petrie dish
between the stripes of paint to make sure
with ITO surfactant for approximately
all of the ITO has been removed (It
15 minutes. Place the dish beneath the
should register zero resistance).
distilled water faucet and wash with
with argon.
The paint can now be removed
flowing distilled water for approximately
by submerging the plate in acetone.
15 minutes. Take out the plates and put
Take a Q-tip and rub the face of the plate
them into isopropanol (2-propanol) for
to remove the paint. Pick up the plate
2-3
and rinse it in distilled water for a few
ultrasonicate
seconds.
Remove the plates from the acetone and
Dump the acetone into the
appropriate waste container in the sink.
If 2” x 2” plates have been used,
minutes.
Put
for
in
~
acetone
3-5
and
minutes.
submerge them in isopropanol for ~ 2
minutes. Blow dry with argon.
17
they must be broken into 1” by 1” plates.
With a straight edge, draw a line down
the middle of the glass plate with a
16
Shinar, Joseph. Organic Device Fabrication in
Rm A216, Physics. Ames, Iowa: Iowa State
33
University, June 1997. p. 1.
17
Shinar, Joseph. Organic Device Fabrication in
Rm A216, Physics. Ames, Iowa: Iowa State
University, June 1997. p. 2.
30
III. PREPARATION OF ITO SUBSTRATE: PARTIAL ETCHING OF ITO
Partial etching of the remaining
regia bath of 1 part aqua regia and 3-4
IT smoothes the surface of the ITO
parts water. Ultrasonicate for at least 10
substrate.
minutes.
If
the
combinatorial
Etch past golden to golden –
18
factorization method is not desired, this
green reflection, for 3-AS.
step should be performed before thin
the plate from the aqua regia solution,
film deposition.
rinse, and place in distilled water for 5-
If the striped ITO
Remove
method is used, this step may or may not
10 minutes.
be taken, depending on the quality of
Transfer to an isopropanol bath for a few
results desired.
One indicator that
seconds. Ultrasonicate in acetone for ~
factors into the decision is the resistance
5 minutes. Completely dry a container
of the ITO substrate.
with a heat gun, and then fill the dried
A resistance
between 20 and 30 ohms indicates that
container with isopropanol.
the surface is very rough. A resistance
the plates in isopropanol for ~ 2 minutes.
of 30-40 ohms is desired, and partial
Blow-dry with argon. Put the plates into
etching of the ITO layer will smooth the
a plastic container and load them into the
surface, increasing the resistance.
glove box load lock. Pump and backfill
To
partially
etch
the
ITO
the load lock twice.
Submerge
19
substrate, first mark the glass side of the
plate and place the plate into an aqua
18
Shinar, Joseph. Organic Device Fabrication in
Rm A216, Physics. Ames, Iowa: Iowa State
University, June 1997. p. 2.
19
Shinar, Joseph. Organic Device Fabrication in
Rm A216, Physics. Ames, Iowa: Iowa State
University, June 1997. p. 2-3.
33
31
IV. THIN FILM DEPOSITION IN THE GLOVE BOX
Put on latex gloves and insert
in the cylinder, refill it. (The cabinet also
both hands into the rubber gloves of the
contains jars of the different materials
glove box. Set the appropriate values of
for use in refilling).
the
material
density
acoustic
Clip the OLED’s onto the desired
impedance on the thickness monitor for
metal plate or grating, and clip the plate
the material to be deposited. Make sure
to
that the vacuum inside the vacuum
deposition
chamber is off. Remove the lid of the
should be directly above the heater coils.
vacuum chamber and the metal cylinder
Put the shutter in the desired position.
surrounding
components.
Bring the metal cylinder over the top to
Loosen the bolts on top of the supports
enclose the setup, and put the lid on top.
that hold the heater coils. Load a heater
Turn on the vacuum pump and wait for
coil from the inside, in between the large
the vacuum to be established (This takes
washer and the smaller one beneath it.
about 2 hours).
the
inside
and
Tighten the bolts. The coil should be in
the
top
horizontal
chamber.
Once
the
post
The
vacuum
in
the
OLED’s
has
been
the center of the support, and balanced
established (the pressure gauge should
symmetrically.
Using a tweezers, take
be between 3.5 and 3.7), turn on the
out the material to be deposited from the
power supply and increase the current to
materials drawers. Load a cylinder that
the
is approximately 1/3 – 1/2 full into the
thickness
heater coil. If there is not much sample
deposition, as well as the thickness
33
desired
position.
monitor
for
Watch
the
rate
the
of
32
deposited. Once the thickness level has
minutes.
been
before),
deposit again in the same manner. (See
decrease the current to zero. Close the
Tables 3 and 4 of this report for the
shutter if deposition continues above the
values
desired level. Wait ~ 10 minutes. Turn
material density, and current associated
the vacuum off and wait a couple of
with each material).
33
reached
(or
slightly
Load the next material and
of
the
acoustic
impedance,
33