films are currently under way, such as changing the solvent
systems, modifying the surface of supporting plates, as well as
crystal reorientation by thermal annealing.
In summary, we have prepared a stable and soluble pentacene
precursor which extrudes a unit of CO upon heating at 150 uC.
Pentacene films can be prepared by the spin-coating technique
followed by thermal annealing. The yield of thermal fragmentation
was nearly quantitative, and the pentacene film thus produced is
stable up to ca. 360 uC. Fabrication of OTFT devices using this
precursor has been demonstrated. Further improvement of film
morphology for devices is actively under way in our laboratory.
Financial support from a theme project of Academia Sinica is
gratefully acknowledged.
Notes and references
1
C. D. Dimitrakopoulos and P. R. L. Malenfant, Adv. Mater., 2002, 14,
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9
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Fig. 5 (a) Plot of drain current I
gate voltages VGS obtained from an OTFT with a channel width of 20 cm
and a channel length of 10 mm. (b) log(I ) vs. VGS for VDS = 260 V, and
vs. VGS in the saturation mode.
D
vs. drain-source voltage VDS at various
D
!I
D
Owing to the limited solubility of compound 1, the thin films
prepared by the spin-coating process were not entirely contiguous.
Nevertheless, OTFTs prepared using 1 exhibited typical FET
characteristics. The OTFT devices were fabricated using a heavily
˚
n-doped Si wafer as the substrate and the gate and using a 2000 A
thermally grown SiO film as the gate insulator. Au (30 nm) was
deposited and lithographically patterned on top of the SiO as
2
7
8
2
128, 9612.
the interdigitated source/drain electrodes. Compound 1 was then
spin-coated over the structure and was thermally converted to
pentacene. The output characteristics [i.e. the plot of drain current
C.-H. Lai, E. Y. Li, K.-Y. Chen, T. J. Chow and P.-T. Chou, J. Chem.
Theory Comput., 2006, 2, 1078; T. Irie and H. Tanida, J. Org. Chem.,
1979, 44, 1002.
9
H. K. Patney and M. N. Paddon-Row, Synthesis, 1986, 326;
M. N. Paddon-Row and H. K. Patney, Synthesis, 1986, 328.
D
(I ) vs. drain-source voltage (VDS) at various gate voltages (VGS)]
for such an OTFT (with a channel width of 20 cm and a channel
length of 10 mm) is shown in Fig. 5(a). The OTFT operates in the
p-type enhancement mode and exhibits a hard saturation. Fig. 5(b)
1
0 R. Ruiz, A. C. Mayer, G. G. Malliaras, B. Nickel, G. Scoles,
A. Kazimirov, H. Kim, R. L. Headrick and Z. Islam, Appl. Phys. Lett.,
004, 85, 4926.
1 K. P. Weidkamp, C. A. Hacker, M. P. Schwartz, X. Cao, R. M. Tromp
2
1
shows the corresponding transfer characteristics [log(I
for VDS = 260 V, !I vs. VGS in the saturation mode]. The OTFT
exhibits an on/off current ratio of about 1.2 6 10 . From !I
GS in the saturation mode, the apparent field-effect mobility m is
D
) vs. VGS
and R. J. Hamers, J. Phys. Chem. B, 2003, 107, 11142; S. Lukas,
S. S o¨ hnchen, G. Witte and C. W o¨ ll, ChemPhysChem, 2004, 5, 266.
12 W. S. Hu, Y. T. Tao, Y. J. Hsu, D. H. Wei and Y. S. Wu, Langmuir,
D
5
D
vs.
2
005, 21, 2260.
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996, 80, 2501.
4 R. B. Campbell, J. M. Robertson and J. Trotter, Acta Crystallogr., 1961,
14, 705.
V
23
2
21 21
estimated to be 8.8 6 10 cm V
s . Since the pentacene did
1
not cover the whole area between the source and the drain, the
actual mobility is actually higher. Efforts to improve the quality of
1
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