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Thin Film Organic Photodiodes on Complementary Metal-Oxide-Semiconductor (CMOS) Materials Structured via Orthogonal Photolithography for Sensor Applications

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In this work we present an easy and cheap method to structure organic photodetectors integrated on an 200 mm silicon wafer in combination with a thin film encapsulation. A new top absorbing organic photodetector device is discussed, structured with the orthogonal photo-lithography, for light sensors and organic photodetector applications. Introduction The thin film technology based on organic semiconductor showed in recent years a great progress in research and development. Devices like OLED and OPD are mature for many applications such in sensor and microsystem technology. Advantages like flexibility, stretchability, transparency, light weight and easy integration sets OPDs in the focus of new developments for optical sensors. OPDs offer a wide variety of applications in the sensors such as in medical-or biotechnology, environmental analysis and industrial process monitoring are possible. Organic photodiodes are a good alternative to existing inorganic detector devices through their properties of simple construction and the easy integration. OPD can be deposited from the liquid phase or by physical vacuum deposition (PVD) processes and provide the advantage of cost-effectively against conventional semiconductor processes. In production shadow mask technology is the state of the art process to structure organic devices ,but is limited to feature sizes being larger than > 40 m. The technology of orthogonal photolithography to structure organic devices enables feature sizes to about 10 microns and below which generates new methods and applications.
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Thin Film Organic Photodiodes on Complementary Metal-Oxide-Semiconductor
(CMOS) Materials Structured via Orthogonal Photolithography for Sensor
Applications.
Matthias Jahnel, Matthias Schober, Karsten Fehse, Olaf Hild and Uwe Vogel
Fraunhofer Institute for Organic Electronics, Electron Beam and Plasma Technology FEP,
Maria-Reiche-Str. 02, Dresden 01199, Germany
Keywords: Organic OPD, Orthogonal photolithography, Sensors, Photodetetor, CMOS
Abstract
In this work we present an easy and cheap method to
structure organic photodetectors integrated on an 200 mm
silicon wafer in combination with a thin film encapsulation.
A new top absorbing organic photodetector device is
discussed, structured with the orthogonal photo-
lithography, for light sensors and organic photodetector
applications.
Introduction
The thin film technology based on organic
semiconductor showed in recent years a great progress in
research and development. Devices like OLED and OPD
are mature for many applications such in sensor and
microsystem technology. Advantages like flexibility,
stretchability, transparency, light weight and easy
integration sets OPDs in the focus of new developments
for optical sensors. OPDs offer a wide variety of
applications in the sensors such as in medical- or
biotechnology, environmental analysis and industrial
process monitoring are possible. Organic photodiodes are
a good alternative to existing inorganic detector devices
through their properties of simple construction and the
easy integration. OPD can be deposited from the liquid
phase or by physical vacuum deposition (PVD) processes
and provide the advantage of cost-effectively against
conventional semicon-ductor processes. In production
shadow mask technology is the state of the art process to
structure organic devices ,but is limited to feature sizes
being larger than > 40 m. The technology of orthogonal
photolithography to structure organic devices enables
feature sizes to about 10 microns and below which
generates new methods and applications.
Experimental details
The thin film technology based on organic
semiconductor showed in recent years a great progress in
research and development. Devices like OLED and OPD
are mature for many applications such in sensor and
microsystem technology. Advantages like flexibility,
stretchability, transparency, light weight and easy
integration sets OPDs in the of new developments for
optical sensors. OPDs offer a wide variety of applications
in the sensors such as in medical- or biotechnology,
Environmental analysis and industrial process monitoring
are possible. Organic photodiodes are a good alternativ to
existing inorganic detector devices through their properties
of simple construction and the easy integration. OPD can be
deposited from the liquid phase or by physical vacuum
deposition (PVD) processes and provide the advantage of
cost-effectively against conventional semicon-ductor
processes. In production shadow mask technology is the
state of the art process to structure organic devices ,but is
limited to feature sizes being larger than > 40 m. The
technology of orthogonal photolithography to structure
organic devices enables feature sizes to about 10 microns
and below which generates new methods and applications.
We show organic photodiodes structured with the
technology of orthogonal photolithography and protected
them with a thin-film encapsulation against environmental
influences. The processes of structural resolution by means
of orthogonal photolithography is based on the liquid of
patterning by etching of the organic material, to atmosphere.
[1]. Figure 1. illustrates the schematic process-flow of
structuring via orthogonal photolithography and Figure 2.
(a) and (b) exhibit the reference and structured OPD
device. After the manufacturing of the OPD anode by
thermal evaporation and the spin-coating with 1250 rpm of
absorption layer material “P3HT: PC61BM” the photo-resist
“Oscor 4000“, supplied by Orthogonal Inc., was spin-coated
with 900 rpm on top of the organic absorber material. The
thickness of the aluminum anode is 50 nm and the hole
transport layer consists of Mo / MoO3 with 6.5 nm. The
thickness of the absorption layer is about ~ 100 nm thick
and the photo-resist is about 1,5 mm. The Figure 3 (a)
shows the resolution test structures of photo-lithography.
Subsequently, the layout transfer from the photo-mask is
carried out on the photo-resist by the exposure to ultraviolet
light with a wavelength of 365 nm. Due to exposure of
wavelengths in the UV-range, the photons activate and by
the subsequent annealing for the photo-resist cross-linking.
The development of the photo-resist is performed with the
“Orthogonal developer 100”, supplied by Orthogonal Inc.,
and the rotation speed of 200 rpm with a continuous
material flow. By developing the photo-resist only the active
regions of the OPD are covered and the areas outside are
not protected by the resist. The next process step is the
patterning of the device via etching. The duration of the
etching process is 5 minutes O2-plasma etching.
FMC6 - 2
ISSN-L 1883-2490/23/0521 © 2016 ITE and SID IDW/AD ’16 521
Figure 1. Schematic overview of the orthogonal photolithography process.
and inhomogeneity of the HTL. We attribute the change in
MoO
3
thickness, towards the edge to be responsible
for the
decrease of the series resistance with decreasing film
thickness and thus the electron flow is less decreased in the
reverse direction. [2]
Table 1. OPD Layer architecture, 8 inch Wafer vs. Standard
OPD as reference both processed at a silicon substrate,
The absorption layer for OPDs at 8 inch Wafer was
processed by orthogonal photolithography and the reference
device which was manual structured by wipe away the
organic.
Layer Material 8 inch Reference
14 Glass no Yes
13 Al
2
O
3
40 no
12 s-NPB 100 no
11 Al
2
O
3
40 no
10 Polymer 400 no
9 Al
2
O
3
40 no
8 Polymer 400 no
7 Al
2
O
3
145 no
6 Ag 10 10
5 Ca 3 3
4 P3HT:PC
61
BM 100 100
3 MoO
3
5 5
2 Mo 1.5 1.5
1 Al 50 50
(a) (b)
Figure 2. OPD at silicon, (a) reference device with
glass and (b) use orthogonal photo-lithography and TFE.
“A” indicate the anode and “K” the cathode and the red
rectangle indicates the active area.
The duration of the etching process is 5 minutes at an
O
2
flow of 20 sccm and a power input of 200 W. The not
covered organic material is removed by the O
2
-plasma
etching and only the active regions of the OPD persist.
Next step of structuring is the removal of the photo-resist.
This is replaced with the “Orthogonal stripper 700” using
the spin-coater. The removal of the photo-resist was
repeated seven times in a sequence by rotation of 200
rpm and 30 seconds residence time. The final result is
shown in Figure 3 (b). To reduce the influence of O
2
and
H
2
O, all devices are annealed after structuring at 140 °C
in air. After the orthogonal photo-lithography and
structuring process the 8-inch wafers are transferred into
the ultra-high vacuum, in order to manufacture the
transparent calcium- / silver cathode. Following the thin
film encapsulation (TFE) was deposited as the last
element in the layer composite of OPD overlapping the
active regions. This encapsulation is based on an
alternating layer system of four times aluminum dioxide
(Al
2
O
3)
and two times acryl-polymer films. The first Al
2
O
3
layer consist of 145 nm thickness and the two others are
40 nm thick. The acryl-polymer films between the Al
2
O
3
layer is 400 nm thick and completed the TFE with a last
organic layer (s-NPB; 100 nm) covered by 40 nm Al
2
O
3.
Table 1. shows the layer sequence of OPD Device with
TFE compared to a reference device which was manually
structured by wiping away the organic.
Results and discussion
The Figure 4 (a) exhibit the JV-curve of the OPD in
comparison to the reference device and (b) characterize
the external quantum efficiency (EQE) over the 8-inch
wafer. If we compare the reference OPD with the device
which was structured by orthogonal photolithography we
can see a difference in performance, see Table 2 We
notice the difference in J
PH
, V
OC
and J
0
and see this
effect in lost EQE and R
Ȝ.
The dark current changes from
center to the edge in Figure 4 (b), especially we see in
the range of 0 V to - 4 V the dark current of the OPD at
the edge is significantly higher than in comparison to the
OPD in the middle. This may be due to the production
522 IDW/AD ’16
(a) (b)
Figure 3. (a) indicates the resolution of photo-lithography
and (b) shows the structured Layer P3HT:PC61BM via
orthogonal photolithography.
(a) (b)
Figure 4. (a) illustrate the current density-voltage curve of OPDs in comparison to reference devices. The figure (b) shows
the OPDs at 8-inch wafer by comparison of border to center position at the wafer.
layer thickness is shown in change of JPH and also
variation in optical cavity due to the TFE affects JPH.
Table 2. illustrate this behavior of different performance
in values from the center to the wafer border. The EQE
also shows changes in the comparison of the reference
Resulting the On/Off- ration decreases with an
increasing of dark current J0. Furthermore, the change
of the absorption layer thickness have an additional
impact on the reverse current and the On / Off-behavior.
We see a 5 % OPDs in relation to the OPDs on 8 inch
(a) and of the edge and center (b), see Figure 5.
increased thickness of the organic bulk material from
center to the edge of the wafer. This affect in decreasing
series resistance with decreasing layer thickness to the
edge of the wafer and becomes apparent in J0, see
Figure 4 (b). The absorption of the OPDs, which were
made on 8 inch wafer, over the entire spectral range
shows a lower absorption of light compared to the
reference Another effect of the change in the absorption
devices. The break of against the reference caused by the
orthogonal 12.5 % at 550 nm photolithography process
and a number of maxima is produced by the TFE by
changing OPD cavity. Moreover, the change of the
absorption layer on the surface of the wafer is also partly
responsible for the variations in absorption spectrum. The
same is reflected in the consideration of the responsivity.
The OPD are developed for a maximum sensitivity at 550
nm but they vary by the inhomogeneity of thin film
encapsulation and artificial cavity effects, see Figure 5.
and Figure 6. (a) and (b). The evaluation of sensitivity of
lithography to the reference OPD, see Figure 5 (a)
illustrates that three local maxima at 500 nm, 550 nm and
600 nm exist. The largest absorption is, as intended, at
about 550 nm. In the comparison of the OPD from the
edge to the center a shift of about 15 nm can be seen for
the wavelength. The maxima of the OPDs move to the
edge region to shorter wavelengths. Despite the
limitations, imposed by the orthogonal photolithography
and the influence of the inhomogeneity of the deposition
process, a positive conclusion can be considered. We
showed the transfer of the OPD technology on 200 mm
silicon wafer size (8-inch Wafer) and improved the
structuring of organic semiconductor to a new scale. Using
orthogonal photolithography for patterning P3HT: PC61BM
absorption layer one challenge regarding process flow and
O2-etching and we showed the whole process with
commercially available materials. Furthermore, a thin film
encapsulation over the OPD components has been
established. Thus, it is possible to realize sensor
applications directly without an influence of glass cavity on
industrial relevant wafer sizes.
IDW/AD ’16 523
(a) (b)
Figure 5. (a) exhibit the external quantum efficiency of the reference device vs. OPD structured via photolithography. (b)
illustrated the EQE over the 8-Inch wafer from center to border position.
(a) (b)
Figure 6. demonstrate the responsivity of the reference and via lithography structured OPD devices and (c) demonstrates a
comparison of responsivity over the 8 inch wafer.
Table 2. Overview of characteristic parameter of OPDs.
Jph [mA/cm
2
] J
0
[mA/cm
2
] V
OC
[V] EQE [%] R
Ȝ
[A/W]
Reference 5.10 0.06 0.59 37.6 0.165
Lithography 6.14 0.48 0.48 32.8 0.145
8-inch border 6.34 0.49 0.47 30.2 0.135
8-inch center 5.70 0.09 0.47 28.9 0.130
Acknowledgement
This project has received funding from the ECSEL joint
undertaking under grant agreement No 661796 as well as
from the German federal ministry of education and
research (BMBF) and the free state of Saxony under grant
No 16ESE0058S.
Corresponding Author
Matthias Jahnel, email: Matthias.jahnel@fep.fraunhofer.de
Phone: +49 351 8823-206; Fax. - 394
References
[1] Zakhidov, A. A., Lee, J.-K., Fong, H. H., DeFranco, J.
A., Chatzichristidi, M., Taylor, P. G., Ober, C. K. Malliaras,
G. G. Hydrofluoroethers as Orthogonal Solvents for the
Chemical Processing of Organic Electronic Materials. Adv.
Mater., 20, (2008) 3481–3484.
[2] Ning and Lassiter, Brian E. and Lunt, Richard R. and
Wei, Guodan and Forrest, Stephen R., Applied Physics
Letters, 94, (2009) 023307
524 IDW/AD ’16
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Full-text available
Article
A study was conducted to demonstrate a new approach for chemicalprocessing of organic electronic materials. It was demonstrated that the approach is based on the use of fluorous solvents, segregated hydrofluoroethers (HFE). The study also demonstrated that that processing organic electronics, using HFEs under extreme conditions, such as boiling temperatures, does not cause any dissolution, cracking, delamination,or other unfavorable physical or chemical change. The study also demonstrated that the use of fluorous solvents enables simple photolithographic patterning of organic electronic materials. It was shown that fluorous solvents are perfluorinated on very highly fluorinated liquids, which are immiscible with organic solvents and water.
  • A A Zakhidov
  • J.-K Lee
  • H H Fong
  • J A Defranco
  • M Chatzichristidi
  • P G Taylor
  • C K Ober
  • G G Malliaras
Zakhidov, A. A., Lee, J.-K., Fong, H. H., DeFranco, J. A., Chatzichristidi, M., Taylor, P. G., Ober, C. K. Malliaras, G. G. Hydrofluoroethers as Orthogonal Solvents for the Chemical Processing of Organic Electronic Materials. Adv. Mater., 20, (2008) 3481–3484.
  • Ning
  • Brian E Lassiter
  • Richard R Lunt
  • Guodan Wei
  • Stephen R Forrest
Ning and Lassiter, Brian E. and Lunt, Richard R. and Wei, Guodan and Forrest, Stephen R., Applied Physics Letters, 94, (2009) 023307