Active solid-state devices (e.g. – transistors – solid-state diode – Organic semiconductor material
Reexamination Certificate
2000-11-01
2002-02-05
Crane, Sara (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Organic semiconductor material
C257S289000, C257S310000
Reexamination Certificate
active
06344662
ABSTRACT:
Notwithstanding the specific mechanism of how the characteristics are achieved, we claim that we have demonstrated a structure and a process to fabricate the same to achieve high field effect mobilities and high current modulation in organic-inorganic hybrid perovskite-based TFTs. While the present invention has been described with respect to preferred embodiments, numerous modifications, changes, and improvements will occur to those skilled in the art without departing from the spirit and scope of the invention. All references cited herein are incorporated herein by reference and all references cited by the reference cited herein are incorporated herein by reference.
FIELD OF THE INVENTION
This invention pertains to the field of organic-inorganic hybrid materials as the semiconducting channels in thin film field effect transistors (TFT), and in particular to the low-voltage operation of such transistors, using high dielectric gate insulators, in applications such as flat panel displays.
BACKGROUND
Thin film field effect transistors (TFT) used in liquid crystal display (LCD) and other flat panel applications typically use amorphous silicon (a-Si:H) or polycrystalline silicon as the semiconductor and silicon dioxide and/or silicon nitride as the gate insulator. Recent developments in materials have led to the exploration of organic oligomers such as hexathiophene and its derivatives, and organic molecules such as pentacene (G. Horowitz, D. Fichou, X. Peng, Z. Xu, F. Garnier,
Solid State Commun.
Volume 72, pg. 381, 1989; F. Garnier, G. Horowitz, D. Fichou, U.S. Pat. No. 5,347,144) as potential low-cost and/or low-temperature replacements for amorphous silicon as the semiconductor in thin-film field-effect transistors. Field effect mobility in the range of 1 cm
2
V
−1
sec
−1
has been achieved in pentacene based TFT's with SiO
2
as the gate insulator (Y. Y. Lin, D. J. Gundlach, S. F. Nelson, T. N. Jackson,
IEEE Electron Device Lett.
Vol. 18 pp. 606-608 1997), making them potential candidates for such applications. A major drawback of these pentacene-based organic TFTs is the high operating voltage that is required to achieve high mobility and simultaneously produce high current modulation (typically about 100 V when 0.4 &mgr;m thick SiO
2
gate insulator is used). Reducing the thickness of the gate insulator would improve the above mentioned characteristics but there is a limit to the decrease of the insulator thickness, which is imposed by manufacturing difficulties and reliability issues. For example in the current generation of TFT LCD devices the thickness of the TFT gate insulator is typically 0.3 to 0.4 &mgr;m. Recently, it was shown that high mobility can be achieved in pentacene devices comprising a high dielectric constant (∈) gate insulator, at lower voltages than pentacene TFTs using a comparable thickness of SiO
2
(C. D. Dimitrakopoulos, P. R. Duncombe, B. K. Furman, R. B. Laibowitz, D. A. Neumayer, S. Purushothaman, U.S. Pat. No. 5,981,970 and 5,946,551, C. D. Dimitrakopoulos, S. Purushothaman, J. Kymissis, A. Callegari, J. M. Shaw,
Science,
283, 822-824, (1999); C. D. Dimitrakopoulos, J. Kymissis, S. Purushothaman, D. A. Neumayer, P. R. Duncombe, R. B. Laibowitz,
Advanced Materials,
Vol. 11, 1372-1375, (1999)).
Recently a new class of TFT was demonstrated, one that comprised an organic-inorganic hybrid material as the semiconductor such as the organic-inorganic perovskite (C
6
H
5
C
2
H
4
NH
3
)
2
SnI
4
. This class of organic-inorganic hybrid materials can be defined as “molecular scale composites” (K. Chondroudis, C. D. Dimitrakopoulos, C. R. Kagan, I. Kymissis, D. B. Mitzi; “Thin Film Field Effect Transistors With Organic-Inorganic Hybrid Materials As Semiconducting Channels”; Ser. No. 09/245,460; Filed on Feb. 5, 1999; “Organic-Inorganic Hybrid Materials as Semiconducting Channels in Thin-Film Field-Effect Transistors”, C. R. Kagan, D. B. Mitzi, C. D. Dimitrakopoulos,
Science
Vol. 286, 945-947, (1999).). These transistors have problems similar to the ones described above for pentacene: high operating voltage is required to achieve high mobility and simultaneously produce high current modulation (typically about 60 V when 0.5 &mgr;m thick SiO
2
insulator is used). Reducing the thickness of the gate insulator lowers the required operating voltages to achieve the above mentioned characteristics. Again there is a limitation to the decrease in insulator thickness, which is imposed by manufacturing constraints and reliability issues, especially for large area applications such as flat panel displays, where the gate insulator is not thermally grown on Si single crystals but is deposited on top of a gate electrode. Using a high dielectric constant gate insulator to achieve high mobility at lower voltages, as was shown in organic TFTs, is not an obvious solution since such an insulator should not be expected to have an effect on the mobility measured from a crystalline inorganic semiconductor, where mobility is considered a constant parameter. In the organic-inorganic perovskite (C
6
H
5
C
2
H
4
NH
3
)
2
SnI
4
) conduction takes place in the inorganic component and the organic component is insulating (D. B. Mitzi, C. A. Feild, W. T. A. Harrison, A. M. Guloy, Nature, Vol. 369, 467-469 (1994); K. Chondroudis, C. D. Dimitrakopoulos, C. R. Kagan, I. Kymissis, D. B. Mitzi; “Thin Film Field Effect Transistors With Organic-Inorganic Hybrid Materials As Semiconducting Channels”; Ser. No. 09/245,460, Filed on Feb. 5, 1999). While this is true for C
6
H
5
C
2
H
4
NH
3
)
2
SnI
4,
other hybrid materials can be designed in which the organic part consists of conjugated organic molecules, such as an oligothiophene containing molecule for example, and the inorganic part is insulating and is used to template the organization of the conjugated organic molecules, thus increasing their conductivity and/or mobility.
The electrical characteristics of TFTs having the organic-inorganic hybrid perovskite (C
6
H
5
C
2
H
4
NH
3
)
2
SnI
4
as the semiconductor, a heavily doped Si-wafer as the gate electrode, 500 nm thick thermally grown SiO
2
as gate insulator, and Pd source and drain electrodes, are adequately modeled by standard field effect transistor equations (S. M. Sze “
Physics of Semiconductor Devices”,
Wiley, New York., 1981, pg. 442), as shown previously (K. Chondroudis, C. D. Dimitrakopoulos, C. R. Kagan, I. Kymissis, D. B. Mitzi; “Thin Film Field Effect Transistors With Organic-Inorganic Hybrid Materials As Semiconducting Channels”; Ser. No. 09/245,460; Filed on Feb. 5, 1999; “Organic-Inorganic Hybrid Materials as Semiconducting Channels in Thin-Film Field-Effect Transistors”, C. R. Kagan, D. B. Mitzi, C. D. Dimitrakopoulos,
Science
Vol. 286, 945-947, (1999)). The organic-inorganic perovskite (C
6
H
5
C
2
H
4
NH
3
)
2
SnI
4
used in these devices behaves as a p-type semiconductor.
FIG. 1
, cited from “Organic-Inorganic Hybrid Materials as Semiconducting Channels in Thin-Film Field-Effect Transistors”, C. R. Kagan, D. B. Mitzi, C. D. Dimitrakopoulos,
Science
Vol. 286, 945-947, (1999)), shows the dependence of the current flowing between the source and drain electrodes (I
D
) on the voltage applied to the drain electrode (V
D
), at discrete voltages applied to the gate electrode (V
G
). When the gate electrode is biased negatively with respect to the grounded source electrode, (C
6
H
5
C
2
H
4
NH
3
)
2
SnI
4
-based TFTs operate in the accumulation mode and the accumulated carriers are holes. At low V
D
, I
D
increases linearly with V
D
(linear region) and is approximately given by the equation:
I
D
=
WC
i
L
μ
(
V
G
-
V
T
-
V
D
2
)
V
D
(
1
)
where L is the channel length, W is the channel width, C
i
is the capacitance per unit area of the insulating layer, V
T
is a threshold voltage, and &mgr; is the field effect mobility. &mgr; can be calculated in the linear region from the transconductance:
g
m
=
(
∂
I
D
∂
V
G
)
V
D
=
const
=
WC
i
L
μ
V
D
,
(
2
)
by pl
Dimitrakopoulos Christos Dimitrios
Kagan Cherie Renee
Mitzi David Brian
LandOfFree
Thin-film field-effect transistor with organic-inorganic... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Thin-film field-effect transistor with organic-inorganic..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Thin-film field-effect transistor with organic-inorganic... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2973423