Oxide-based Electric Devices :
Flexible Transparent Thin Film Transistors
By Yu-Lin Wang
Fall 07
A PROPOSAL PRESENTED TO THE GRADUATE COMMITTEE IN PARTIAL
FULFILLMENT OF THE REQUIREMENTS OF THE DOCTARAL QUALIFYING
EXAM
Materials Science and Engineering
University of Florida
TABLE OF CONTENTS
1.0 Introduction
…………………………………………………………………3
1.1 Motivations …………………………………………………………………..3
1.2 Objectives of research ………………………………………….……………4
2.0 Literature review
………………………………………………………………5
2.1 Comparisons of materials for TFTs used in display applications…………5
2.2 Amorphous transparent conducting oxides (ATCOs)….......………………6
2.3 Transparent thin film transistors on flexible substrate (TFTs) …………8
3.0 Research Plan
………………………………………………………………… 9
3.1 Experiments……………………………………………………………….......9
3.1.1 Depletion mode field effect transistors fabricated in a room temperature
process by using α-IZO and α-IGZO as the channel layer ….…… 9
3.1.2 Enhance mode field effect transistors fabricated in a room temperature
process by using α-IZO and α-IGZO as the channel layer……..…10
3.1.3 Transparent conductive oxide film growth at room temperature…..10
3.1.3.1 N2/O2 gas effect………………………………………………..10
3.1.3.2 SiO2 and IZO co-sputtering ………………………………….11
3.1.4 Gate dielectrics …………………………………………………………12
3.1.5 Surface treatment by O2 plasma and H2 plasma…………………….13
3.1.6 Ring Oscillator…………………………………………………….…….13
3.1.7 Reliability test……………………………………………………….…..13
3.1.8 Device simulation…………………………………………………….....13
3.2 Characterization………………………………………………………….…..13
4.0 Initial Results
………………………………………………………………....14
4.1 Depletion mode IZO thin film transistors…………………………….…….14
4.1.1 Large gate area TFTs…………………………………………………….14
4.1.2 Small gate length FETs and the frequency response………………...15
4.2 Enhance mode IZO thin film transistors…………………………………....17
5.0 Summary ………………………………………………………………………....18
6.0 Timeline……………………………………………………………………..….....19
7.0 References
…………………………………………………………………20
2
1.0 Introduction
1.1 Motivations
Flexible electronics is emerging rapidly(1,2). Theses devices have the advantages such
as low profile, light weight, small size, and better performance. In displays, thin film
transistors (TFTs) are used as switching components in the active-matrix over a large
area. Currently, liquid crystal displays (LCDs) mostly use amorphous Si as the channel.in
TFTs. However, due to the low mobility (<1 cm2/Vs)(40) and high process temperature
(350℃)(40), amorphous Si-TFTs are not available for high resolution displays on cheap
plastic substrates. Organic TFTs have very low mobility (< 1 cm2/Vs)(40) and may have
reliability concerns(40). Oxide-based TFTs have at least 1 order higher mobility (10~50
cm2/Vs)(34,35) than amorphous Si-TFTs and organic TFTs and can be deposited at room
temperature. The high mobility of oxide-based TFTs, make them available for high
resolution displays and can integrate switching TFTs in the active-matrix and driverintegrated circuits (driver ICs) on the same plastic substrate, which can reduce cost and
provide a more compact display. Besides, oxide-based TFTs have other advantages such
as room temperature deposition, higher transparency, better smoothness, etc.(31~33). The
oxide-based TFTs have a great potential to realize a roll-to-roll display. If this technology
can be realized, it may not only replace the current amorphous Si-TFTs for LCDs, but
will also create new applications on various sets such as heads-up, windshield, electronic
books or light weight computers for soldiers in the battle field and eventually change the
whole display industry.
3
1.2 Objectives of research
In this study, I propose to fabricate TFTs by sputtering InZnO and InGaZnO on hard
(glass) and flexible (plastic) transparent substrates. Depletion mode and enhancement
mode field effect transistors will be fabricated. The study will include device designs,
materials tuning, process developments, device characterization, device simulation,
device reliability test, and device circuit demonstration. The study will cover the whole
course of the device development.
Transparent conductive oxides (TCOs) were applied in many areas, such as the
transparent electrodes used in liquid crystal displays, solar cells, and light emitting diodes
because of their high electrical conductivity and high optical transparency(3~5). Oxidebased thin film transistors attract much attention due to their advantages such as high
mobility, high electrical conductivity, and high visible transmittance(6~9). Amorphous or
nano-crystalline n-type oxide semiconductors such as zinc oxide, zinc tin oxide, indium
gallium oxide, and indium gallium zinc tin oxide displays demonstrate surprisingly high
carrier mobilities (~10 cm2 /Vs)
temperature
even for amorphous films deposited at room
(9-26)
. Many transparent thin film transistors (TTFTs) were reported using
crystalline ZnO(27,28), or polycrystalline SnO2(29), and In2O3(30). However, to realize the
transparent thin film transistor for flexible electronics, amorphous films are more suitable
than crystalline type, because amorphous type oxide films have extra advantages such as
low temperature deposition, good film smoothness, low compressive stress, and large
area deposition by sputtering(31, 32, 33). An amorphous conductive oxide, InZnO (IZO),
with a high carrier mobility (10~50 cm2/Vs)(34,35), was proved a promising TCO due to its
good electrical properties and thermal stability, and has been fabricated as TFTs(36,38). A
4
similar material, InGaZnO (IGZO), was also reported as being used as the channel layer
in a TFT with a good electrical stability and a high carrier mobility (1~10 cm 2/Vs)(39,31)
which may be another choice to replace a-Si in display applications.
2.0 Literature review
2.1 Comparisons of materials for TFTs used in display applications
An amorphous or polycrystalline Si:H layer as the channel have been commonly
used for most conventional TFTs in display applications. The standard Si-based TFTs
have drawbacks such as light sensitivity, light-induced degradation and low field effect
mobility (<1 cm2/Vs)(40). Therefore, Si:H TFT devices reduce the efficiency of light
transmittance and brightness. Besides, both amorphous and polycrystalline Si:H TFTs
require relatively high process temperatures (350℃ and 450℃, respectively)(40) making it
difficult to fabricate these TFTs on plastics. One of the methods to increase the efficiency
and avoid high temperature is to use amorphous transparent oxides for the channels and
electrodes, and fabricate TFTs at room temperature. Table 1 shows the major differences
among α-IZO, α-Si, and polycrystalline Si. Obviously, α-IZO has the advantages of
high field effect mobility, high transparency, room temperature compatible processing,
large area deposition by sputtering, plastics substrate available, and is a cheaper
process(40).
Table 1. Materials for TFTs used in display applications
5
2.2. Amorphous transparent conducting oxides (ATCOs)
TCOs are composed of post-transition metal oxides with outer major quantum
number n ≧ 4(39,41). These TCOs exhibit n-type carriers(39,41). Oxygen vacancies
dominate the carrier concentration in these TCO films. For these TCOs, the mobility is
still close to that of the polycrystalline even in the amorphous material. It is very different
fromα-Si, which has a extremely low mobility (<1 cm2/Vs)(40) in amorphous type
comparing to the several orders higher mobility in polycrystalline (30~300 cm2/Vs)(40) or
crystalline (>1000 cm2/Vs)(40). Table 2 shows some commonly used TCOs have this
feature. Although there is more than one mechanism explaining the conduction behavior
for these TCOs, the most widely accepted theory of carrier transport is the s orbitals
overlapping of these transition metal atoms(39,41).
Table 2 Comparisons of various TCOs
Among various conductive oxides, the IZO system exhibits many advantages for the
flexible transparent TFTs such as high field effect mobility, high transparency, room
6
temperature compatible process, large area deposition by sputtering, plastic substrates
available, and is a cheaper process(8,34~36,38). Other conductive oxides may not fit all the
requirements for the flexible transparent TFTs. The first requirement is the film has to be
transparent in visible region which means the bandgap Eg > 3 eV. CdO-PbO and AgSbO3
systems have a bandgap smaller than this requirement(42,43). The second requirement is
the film must be amorphous and conductive as deposited in room temperature. CdOCeO2 is very resistive (resistivity ~1x104 ohm-cm)(44) as deposited if no dopants are
added in. In addition, Cd2+ ions is toxic against the environment(39). Amorphous In2O3
looks like a good candidate, however, when the oxygen ratio increases a little bit, it
becomes polycrystalline(41,46). ZnO is always polycrystalline as deposited(38). In2O3-ZnO
systems have a wide range of amorphous materials in In/Zn ratio and various oxygen
partial pressure (37,39). Note that the change in oxygen ratio is very important because the
carrier concentration can be adjusted by controlling the oxygen partial pressure or the
O2/Ar ratio. α-IZO has a considerable high mobility (10~50 cm2/Vs)(34,38,40) as deposited
at room temperature which is at least one order higher than amorphous Si(40). Ga2O3-ZnO
(GZO) system has a little bit lower mobility than IZO(38). GaInZnO (GIZO) also has a
little bit lower mobility compared to IZO(39). The last candidate is ITO, which is widely
used as electrodes in LEDs, solar cells and LCDs(60~62). Compared to ITO, IZO has a
higher work function(10,51,57), higher transmittance in the infrared region(58), and lower In
concentration than ITO(51). A higher In concentration means higher price(51). Accordingly,
the IZO will be used as channels and electrodes to fabricate the flexible transparent TFTs
in this research. GIZO-TFTs were reported having a better stability than IZO-TFTs(53).
Thus, GIZO-TFTs will also be included in this study.
7
2.3 Transparent thin film transistors on flexible substrates
Many groups reported oxide based TFTs using IZO, GZO, ZnO, SnO2, In2O3 as
channel layers fabricated on glass(8,29,31,30,34,38, 40). However, few of them are reported on
organic flexible transparent substrates. In recent years, α-Si TFTs have been fabricated
a lot on organic substrate such as PET (polyethylene terephthalate)(59). Recently, an
enhancement mode TTFT using IGZO as the channel layer and Y2O3 as the gate
dielectric fabricated on a PET substrate was reported (39,52,53). The TFT has a field effect
mobility of 10 cm2/Vs, threshold voltage 1.2V, on-off ratio >106 , subthreshold voltage
swing ~0.2V/decade. It shows the TCO type TFTs have great potential to beat theα-Si
TFTs (low mobility < 1cm2/Vs, high temperature 350℃ ) and organic TFTs (low
mobility < 1 cm2/Vs)(40) not only in electrical properties, but also in optical properties,
ease of processing, and cost.
Currently, two different technologies are used to fabricate TFTs on plastics. The first
one is to deposit films and do processes directly on the plastics(54,59). The other one is to
fabricate TFTs on rigid glass first, then etch off the substrate glass and paste the flexible
plastics onto the TFTs(55). The second one can avoid high temperature and stress caused
by film deposition. However, our IZO and IGZO TFTs are fabricated in a room
temperature process, so we can use the direct process approach.
8
3.0 Research Plan
3.1 Experiments
3.1.1 Depletion mode field effect transistors fabricated in a room temperature
process by using α-IZO and α-IGZO as the channel layer
I plan to fabricate the depletion mode TTFTs as shown in figure 1(a). The gate
dielectrics will be SiO2 , SiNx or Sc2O3. Channel layers will be IZO or InGaZnO. Device
performance will be compared for different structures. Eventually, a fully transparent
TFT will be fabricated on a flexible transparent substrate, PET.
(a)
(b)
Figure 1(a) Schematics of the fully transparent D-Mode TFTs on flexible transparent
substrate. (b) D-Mode TFTs on glass.
We have already fabricated depletion mode thin film transistors using IZO as the
channel layer on glass substrates as depicted in figure 1(b). This is the first report of
depletion mode TFTs made of IZO film in channel layer(36). The IZO films were
deposited near room temperature by rf magnetron sputtering using 4 inch diameter targets
of In2O3 and ZnO(37). The working pressure was varied from 2-15 mTorr in a mixed
ambient of O2/Ar. The percentage of O2 in the mixture was varied from 0-3%. At a
percentage of 2.5 %, we obtained films with carrier concentration of ~1018 cm-3 and
electron mobility of 17 cm2.V-1.s-1 obtained from Hall measurements. The partial pressure
of oxygen during the sputter deposition was found to be the dominant factor controlling
the conductivity of the films. The sputtering power on the targets was held constant at
9
125W, leading to compositions of the films measured by x-ray fluorescence spectroscopy
of In/Zn=0.5 in atomic ratio. The typical thickness of the IZO films deposited was 150
nm, with a root mean square roughness of 0.4 nm measured over a 10x10 μm2 area by
Atomic Force Microscopy. The films were amorphous as determined by x-ray diffraction
and showed optical transmittance of ~80% in the visible range.
3.1.2 Enhance mode field effect transistors fabricated in a room temperature
process by using α-IZO and α-IGZO as the channel layer
The enhance mode TFT structure is shown in figure 2(a). Here I also plan to use
IZO and IGZO as the channel layers and design structures for the channel. Recently, we
successfully fabricated enhance mode thin film transistors using IZO as the channel layer
as depicted in figure 2(b). The device has very good performance which will be described
in a later chapter.
(a)
(b)
Figure 2(a) Schematics of the fully transparent E-Mode TFTs on flexible transparent
substrate. (b) E-Mode TFTs on glass.
3.1.3 Transparent conductive oxide film growth at room temperature
3.1.3.1 N2/O2 gas effect
As described in the previous section, the IZO film was deposited in the sputtering
machine with two targets, ZnO and In2O3, together with O2 and Ar gas in the chamber.
The O2/Ar ratio decides the carrier concentration in the IZO film. Here I plan to use
10
N2/O2/Ar gas mixture to deposit IZO film. The reasons I use N2 is because in the plasma,
N2 will convert to N2+, which may replace O and bond with In. This was investigated in
forming p-type ZnO(56). We know the carriers in the IZO result from the nonstoichiometry, which means the lack of oxygen allows some In atoms that are not bonded
with oxygen atoms to release electrons to the conduction band. That is why when the
O2/Ar ratio change during IZO film deposition, the carrier concentration will also change.
Higher O2/Ar ratio leads to a decrease in the number of oxygen vacancies, which also
means the carrier concentration decreases(37). When removing one oxygen atom from the
In, one oxygen vacancy is created. In is a big atom and tends to lose electrons. Oxygen is
a small atom and tends to get electrons from the In. ZnO acts as a stabilizer in the In2O3
matrix (38). That’s why IZO and (GaZnO) GZO both have lower sensitivity of O2/Ar ratio
to carrier concentration than ZnO (38). Since the oxygen has a higher electronegativity
than nitrogen, oxygen can form a strong ionic bond with In. This means when removing
or adding a certain amount of oxygen or nitrogen bonded with In, oxygen will produce a
larger change in carrier concentration than nitrogen. This means nitrogen can reduce the
sensitivity of O2/Ar ratio to carrier concentration. The second reason is, due to the
previous reason, nitrogen may improve the device reliability. A reliability issue is one of
the reasons why GaInZnO was developed(53). We may provide another view to do the
same thing by an easier method.
3.1.3.2 SiO2 and IZO co-sputtering (SIZO)
Ga2O3 introduced into the In2O3-ZnO system to form the InGaZnO was reported
as providing a better stabilization in TFTs than IZO(53). Ga was chosen because it has an
atomic radius close to In(39). The introduction of Ga into the IZO reduces the electron
11
concentration and mobility(39). The highest carrier concentration of IGZO is around ~
1019 cm-3 (39,41) which is smaller than that of IZO (~1021 cm-3)(35,38). The reduction in
carrier concentration is not bad because for the channel layer, 1018 ~1016 cm-3 is enough
for both depletion and enhancement mode TFTs. Although carrier concentration in IZO
can also be adjusted by O2/Ar ratio, the carrier concentration change in the IZO film is
dramatic ranging from 1018 to 1016 cm-3 in a small O2/Ar ratio region(37). Ga not only
reduces carrier concentration, but also reduces the sensitivity of the carrier concentration
to the O2/Ar ratio(38,39). It is good for controlling the carrier concentration. However, in
the mean time, the reduction in mobility is not welcome. It is interesting to introduce
another oxide into the IZO system to stabilize the oxide system and the mobility . The
idea is to incorporate a smaller atom and in the mean time, oxide formed by this atom has
Eg > 3eV. SiO2 fits these requirements. Si can easily bond with oxygen to reduce
sensitivity of the carrier concentration to the O2/Ar ratio during film deposition. Also, due
to the smaller radius of Si than Ga, In atoms still can keep their s orbitals overlapped.
This means the mobility may not be degraded too much.
3.1.4 Gate dielectrics
Due to the different interfaces that may form between IZO and various dielectrics, it
is necessary to use different dielectrics such as SiO2, SiN, and Sc2O3 as the gate
dielectrics in the TFTs and compare the device performance.
3.1.5 Surface treatment by O2 plasma and H2 plasma
O2 plasma can obviously decrease the surface carrier concentration of the IZO film
due to the annihilation of the oxygen vacancies. This might help to reduce the surface
leakage and then improve on/off ratio if the surface leakage dominates the leakage
12
current, especially for the depletion mode FET. H+ was reported to be implanted into the
CdO-CeO2 film and act as a shallow donor(44). I believe H2 plasma can also create a
donor in IZO film. One very interesting experiment is that if we introduce hydrogen into
an IZO film, which had been deposited under a high O2/Ar ratio, will it be easier to
control the carrier concentration by hydrogen plasma? Due to the very small size of the
hydrogen, it should not reduce the hall mobility of the IZO film because it will not inhibit
the overlap of the 5s orbitals of In .
3.1.6 Ring Oscillator
After we successfully fabricate the D-mode and E-mode FETs, we can start to make
a ring oscillator using these TFTs.
3.1.7 Reliability test
The reliability test will include (i) current stress in room temperature and high
temperature (ii) thermal shock and bending test. These tests will be applied to the TCO
films and devices on both glass and PET.
3.1.8 Device simulation
The device will also be measured for the s parameters and be simulated to extract
the parasitic parameters of the D-mode and E-mode FETs. We have already performed
the simulation for the D-mode IZO TFTs, which will be mentioned in the latter section.
TFTs made of IZO, IGZO or SIZO will be compared and discussed.
3.2 Characterization
SEM, SIMS, XRD, XPS, AFM, Transmittance, photoluminescence will be used to
characterize the films. An Agilent 4156 parameter analyzer and Agilent E8361 network
analyzer will be used to characterize the device dc and rf performance, respectively.
13
4.0 Initial Results
4.1 Depletion mode IZO thin film transistors
4.1.1 Large gate area TFTs
Top-gate-type TFTs using a-IZO channels and 50 or 95-nm-thick SiO2 gate
insulators deposited by plasma enhanced chemical vapor deposition were fabricated as
shown schematically in Figure 1(a). Figure 3 shows the top-view of the TFT. The gate
dimension is 36 µm × 100 µm. The IZO film deposited in 2.5% O2/Ar ratio has a carrier
concentration about 1018 cm-3(37). The whole process was done without heating the
substrates, making the entire process consistent with typical continuous-use temperatures
of commercial plastic films for electronic devices.
Figure 4 shows IDS-VDS characteristics from IZO transistors with 50 nm thick SiO2
gate dielectric. The transistor operates in depletion-mode with an appreciable drain
current at zero gate voltage and exhibits excellent drain current saturation.
Figure 5 shows IDS and gm as a function of VGS for a device with 50 nm SiO2 gate.
The sub-threshold voltage swing was 1.9 V/decade and the device had a threshold voltage
of -6.5V.The latter is the gate voltage at the onset of the initial sharp increase in current in
a log(ID)-VGS characteristic. The drain current on-to-off ratio was >106. These results are
competitive with past results on TFTs using room temperature sputter deposited
amorphous InGaZnO4 as the channel material (31). The field-effect mobility was of ~4.5
cm2.V-1.s-1. The gate I-V characteristics from devices with two different gate dielectric
thicknesses are shown in Figure 6. The leakage current is very small, in the 10-10A range,
for both gate thicknesses and demonstrates that the low temperature deposition process
produces acceptable quality SiO2 for TFT applications. The threshold voltage was
14
decreased to -5.5V for the thicker dielectric and the slope of the sub-threshold voltage
swing was 0.87V/decade for the 95 nm thick dielectric.
Figure 3. Top-view of the TFT
Figure 5. IDS, gm, as a function of VGS
Figure 4. IDS vs. VDS
Figure 6 Gate leakage current
4.1.2 Small gate length FETs and the frequency response
Top-gate TFTs using 50 nm of -IZO channels and 12.5 nm-thick SiNx gate
insulators deposited by plasma-enhanced chemical vapor deposit ion (PECVD) were
fabricated as shown similarly in Figure 1(b). The gate dimension is 1 µm × 200 µm. The
SiNx layer was deposited without heating the substrates. In addition, the SiNX gate
dielectric provided superior stability of device performance relative to SiO2 deposited
under the same conditions(36). Specific contact resistance and sheet resistance from the
linear transmission line measurements were 7 × 10-5 Ω.cm2 and 0.9 MΩ/sq, respectively.
15
Figure 7. IDS vs. VDS
Figure 8. IDS, gm, as a function of VGS
Figure 7 shows typical drain current versus drain voltage, IDS-VDS, characteristics
from the IZO transistors. Figure 8 shows drain current, IDS, and transconductance, gm, as
a function of VGS for an IZO TFT. An inset plot shows log(IDS), drain current, and log(Ig),
gate current, as a function of VGS. A maximum transconductance of 7.5 mS/mm was
obtained at IDS=1.35mA ,Vg=0V and Vd=5V. This is the highest transconductance ever
reported for IZO based TFTs. The transistor has a low threshold voltage of -2.5V. The
drain current on-to-off ratio was >105. The gate leakage is about 10-10A ~10-11A. The
field-effect mobility is 14.5 cm2.V-1.s-1.
Figure 9. S-parameters
Figure 10. h21 and U gain
The measured s-parameters, estimated h21 and unilateral power gain of a typical IZO
TFT are illustrated in Figure 9 and figure 10 respectively. The TFT was biased at drain
16
and gate voltage of 3V and 0V, respectively during the s-parameter measurements. Unity
gain cut-off frequency and maximum frequency of oscillation of 180 and 155 MHz,
respectively, were achieved. A simplified equivalent T-model for the IZO TFT, as shown
in Figure 11, was used to extract the device parameters. The extracted device parameters
are listed in Table 1. The extracted source and drain resistance were consistent with the
estimated resistance based on the transmission line measurements and drain I-V
characteristics. The simulated intrinsic transconductance was very close to the measured
extrinsic transconductance. The low cut-off frequency of the IZO was limited by the
fairly long transit time, 16 ps, low transconductance, and high parasitic resistances, which
were results of the low mobility and saturation velocity of the -IZO channel layer.
However, this MHz-range switching performance is sufficient for many display
applications(ref).
Figure 11. T-model
Table 3. Extracted device parameters
4.2 Enhance mode IZO thin film transistors
Recently, enhancement mode top-gate TFTs using 20 nm of a-IZO channels and 100
nm-thick SiO2 gate insulators deposited by plasma-enhanced chemical vapor deposit ion
17
(PECVD) were fabricated. Figure 2(b) shows the cross-section structure of the TFT with
a gate dimension of 1 µm × 100 µm. The IZO film was deposited in 3.1% of O2/Ar ratio
has a carrier concentration about 1.5x1016 cm-3. The SiO2 layer was deposited without
heating the substrates, making the entire process consistent with typical continuous-use
temperatures of commercial plastic films for electronic devices..
Figure 12 shows typical drain current versus drain voltage, IDS-VDS, characteristics
from the IZO transistors. The transistor operates in enhancement-mode showing excellent
pinch-off. Figure 13 shows drain current, IDS, and transconductance, gm, as a function of
VGS for an IZO TFT. An inset plot shows log(IDS), drain current, and log(Ig), gate current,
as a function of VGS. A transconductance of 10 mS/mm was obtained at drain current of
0.3mA at 0.85V gate voltage and 3V drain voltage. The transistor has a low threshold
voltage of 0.5V and an excellent sub-threshold voltage swing of 0.135 V/decade. The
drain current on-to-off ratio was ~105. The gate leakage is about 10-10A ~10-9A.
Figure 12. IDS vs. VDS
Figure 13. IDS, gm, as a function of VGS
5.0 Summary
In this proposal, IZO and IGZO will be used as channel layers to fabricate depletion
mode and enhancement mode TFTs and ring oscillators on glass and flexible transparent
18
substrate (PET). The SiO2-In2O3-ZnO system and N2 plasma incorporated IZO film will
be grown to get a better controllability of the carrier concentration during the film growth.
Hydrogen plasma and oxygen plasma effects on the TCO films and the TFTs will be
investigated. The device reliability will be tested to compare the effects from different
TCO films and process treatments. Devices will be simulated in a device model to extract
the parasitic parameters. Devices will be characterized in dc and rf performance. The
depletion and enhancement mode TFTs have been fabricated successfully on glass by
using IZO films as the channel layers.
6.0 Timeline
19
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