Enhancement of Field-Effect Mobility Due to Surface-Mediated Molecular Ordering in Regioregular Polythiophene Thin Film Transistors

Kim, D. H.,Park, Y. D.,Jang, Y.,Yang, H.,Kim, Y. H.,Han, J. I.,Moon, D. G.,Park, S.,Chang, T.,Chang, C.,Joo, M.,Ryu, C. Y.,Cho, K. WILEY-VCH Verlag 2005 Advanced functional materials Vol.15 No.1

<P>With the aim of enhancing the field-effect mobility by promoting surface-mediated two-dimensional molecular ordering in self-aligned regioregular poly(3-hexylthiophene) (P3HT) we have controlled the intermolecular interaction at the interface between P3HT and the insulator substrate by using self-assembled monolayers (SAMs) functionalized with various groups (–NH<SUB>2</SUB>, –OH, and –CH<SUB>3</SUB>). We have found that, depending on the properties of the substrate surface, the P3HT nanocrystals adopt two different orientations—parallel and perpendicular to the insulator substrate—which have field-effect mobilities that differ by more than a factor of 4, and that are as high as 0.28 cm<SUP>2</SUP> V<SUP>–1</SUP> s<SUP>–1</SUP>. This surprising increase in field-effect mobility arises in particular for the perpendicular orientation of the nanocrystals with respect to the insulator substrate. Further, the perpendicular orientation of P3HT nanocrystals can be explained by the following factors: the unshared electron pairs of the SAM end groups, the &pgr;–H interactions between the thienyl-backbone bearing &pgr;-systems and the H (hydrogen) atoms of the SAM end groups, and interdigitation between the alkyl chains of P3HT and the alkyl chains of the SAMs.</P> <B>Graphic Abstract</B> <P>Surface-mediated molecular ordering (see Figure) has a substantial effect on the preferential orientations of the P3HT chains, and this effect is used to enhance the field-effect mobility. Depending on the surface properties, the P3HT nanocrystals can adopt two different orientations – parallel and perpendicular to the insulator substrate – the field-effect mobilities of which differ by more than a factor of 4 and can reach 0.28 cm<SUP>2</SUP> V<SUP>–1</SUP> s<SUP>–1</SUP>. <img src='wiley_img/1616301X-2005-15-1-ADFM200400054-content.gif' alt='wiley_img/1616301X-2005-15-1-ADFM200400054-content'> </P>

Field-effect transistors based on PPV derivatives as a semiconducting layer

Lee, Woo-Hyung,Kong, Hoyoul,Oh, Se-Young,Shim, Hong-Ku,Kang, In-Nam Wiley Subscription Services, Inc., A Wiley Company 2009 Journal of polymer science Part A, Polymer chemist Vol.47 No.1

<P>A series of modified thiophene groups containing PPV-based semiconducting materials, poly[(2,5-bis(octyloxy)-1,4-phenylenevinylene)-alt-(2,2′bithienylenevinylene)] (PPBT), poly[(2,5-bis(octyloxy)-1,4-phenylenevinylene)-alt-(5,5-thiostilylenevinylene)] (PPTVT), have been synthesized through a Horner coupling reaction. From the FTIR and <SUP>1</SUP>H NMR spectroscopy, the configuration of the vinylene groups in the polymers was all trans (E) geometry. The weight-average molecular weights (M<SUB>w</SUB>) of PPBT and PPTVT were found to be 11,700 and 11,800, with polydispersity indices of 2.51 and 2.53, respectively. PPBT and PPTVT thin films exhibit UV–visible absorption maxima at 538 and 558 nm, respectively, and the strong absorption shoulder peaks at 578 and 602 nm, respectively. Solution processed field-effect transistors (FET) fabricated using all the polymers showed p-type OTFT characteristics. The field-effect mobility of the PPTVT was obtained up to 2.3 × 10<SUP>−3</SUP> cm<SUP>2</SUP> V<SUP>−1</SUP> s<SUP>−1</SUP>, an on/off ratio of 1.0 × 10<SUP>5</SUP> with ambient air stability. Studies of the atomic force microscopy (AFM) and X-ray diffraction (XRD) analysis of the polymer thin films revealed that all the polymers were amorphous structure. The greater planarity and rigidity of PPTVT compared to PPBT results in elongation of conjugation length and better π–π stacking of polymer chains in amorphous region, which leads to improved FET performance. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 111–120, 2009</P> <B>Graphic Abstract</B> <P>A series of modified thiophene groups containing PPV-based polymers has been synthesized through a Horner coupling reaction. The polymers were designed to possess different rigid thiophene groups in polymer backbones. The physical and optical properties of the polymers were carefully characterized. Studies of the atomic force microscopy (AFM) and X-ray diffraction (XRD) analysis of the polymer thin films revealed that all the polymers were amorphous structure. Field-effect transistors (FET) exhibit that the relatively rigid polymer, PPTVT gave better FET device performance, which depend on the elongation of conjugation length and better π–π stacking of polymer chains in amorphous region. [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com.] <img src='wiley_img/0887624X-2009-47-1-POLA23126-gra001.gif' alt='wiley_img/0887624X-2009-47-1-POLA23126-gra001'> </P>

Effect of the Si Nanowire’s Diameter and Doping Profile on the Electrical Characteristics of Gate-all-around Twin Si-nanowire Field-effect Transistors

김동훈,김태환 한국물리학회 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.67 No.3

The effect of the Si nanowire’s diameter and doping profile on the electrical characteristics of gate-all-around twin Si-nanowire field-effect transistors (TSNWFETs) was simulated by using the three-dimensional technology computer-aided design simulation tools of Sentaurus and taking into account quantum effects. While the switching and the short-channel immunity characteristics were improved with decreasing nanowire diameter, the threshold voltage and the total on-current for the TSNWFETs decreased, resulting in a deterioration of device performances. The swing characteristics for the TSNWFETs maintained almost the same behaviors regardless of the boron concentration variation in the nanowire. Gate-induced drain leakage (GIDL) of the TSNWFETs appeared at a high drain voltage, and the GIDL current increased with increasing boron concentration in the Si nanowires. The electrical characteristics of the TSNWFETs were improved by optimizing the diameter and the doping concentration of the Si nanowire to lower the GIDL and the off-state leakage current.

Effective Channel Mobility of AlGaN/GaN-on-Si Recessed-MOS-HFETs

Kim, Hyun-Seop,Heo, Seoweon,Cha, Ho-Young The Institute of Electronics and Information Engin 2016 Journal of semiconductor technology and science Vol.16 No.6

We have investigated the channel mobility of AlGaN/GaN-on-Si recessed-metal-oxide-semiconductor-heterojunction field-effect transistors (recessed-MOS-HFET) with $SiO_2$ gate oxide. Both field-effect mobility and effective mobility for the recessed-MOS channel region were extracted as a function of the effective transverse electric field. The maximum field effect mobility was $380cm^2/V{\cdot}s$ near the threshold voltage. The effective channel mobility at the on-state bias condition was $115cm^2/V{\cdot}s$ at which the effective transverse electric field was 340 kV/cm. The influence of the recessed-MOS region on the overall channel mobility of AlGaN/GaN recessed-MOS-HFETs was also investigated.

Effective Threshold Voltage Control in GaN Nanowire Field-effect Transistors with a Dual-gate Structure

김효석,J.-R. Kim,김주진,이정오 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.61 No.12

To control the gate threshold voltages of nano-devices, we fabricated a GaN nanowire field effect transistor with a sandwich-type dual-gate structure in which the top- and bottom-gate electrodes could independently apply a gate voltage bias to the nanowire conducting channel. The fabricated device showed a clear <I>n</I>-type gate response. The gate threshold voltage of the nanowire field effect transistor could be effectively tuned over a wide range, from -13 V to +1 V, by scanning the top- or bottom-gate voltage between -10 and +10 V, respectively. As the top-gate voltage was varied from -10 V to +10 V, the carrier mobility increased from 16 to 56 cm<SUP>2</SUP>/Vs and the channel conductance increased. The turn-on position of the channel conductance could be tuned precisely by varying the voltage at one of the gates.

Influence of Dielectric Layers on Charge Transport through Diketopyrrolopyrrole-Containing Polymer Films: Dielectric Polarizability vs Capacitance

Lee, Jiyoul,Chung, Jong Won,Yoon, Gyu Bok,Lee, Moo Hyung,Kim, Do Hwan,Park, Jozeph,Lee, Jin-Kyun,Kang, Moon Sung American Chemical Society 2016 ACS APPLIED MATERIALS & INTERFACES Vol.8 No.44

<P>Field-effect mobility of a polymer semiconductor film is known to be enhanced when the gate dielectric interfacing with the film is weakly polarizable. Accordingly, gate dielectrics with lower dielectric constant (k) are preferred for attaining polymer field-effect transistors (PFETs) with larger mobilities. At the same time, it is also known that inducing more charge carriers into the polymer semiconductor films helps in enhancing their field-effect mobility, because the large number of traps presented in such a disorder system can be compensated substantially: In this sense, it may seem that employing higher k dielectrics is rather beneficial because capacitance is proportional to the dielectric constant. This, however, contradicts with the statement above. In this study, we compare the impact of the two, i.e., the polarizability and the capacitance of the gate dielectric, on the transport properties of poly[(diketopyrrolopyrrole)-alt-(2,2'-(1,4-phenylene)bisthiophene)] (PDPPTPT) semiconductor layers in an FET architecture. For the study, three different dielectric layers were employed: fluorinated organic CYTOP (k = similar to 2) poly(methyl methacrylate) (k = similar to 4) and relaxor ferroelectric poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethykne) (k = similar to 60). The beneficial influence of attaining more carriers in the PDPPTPT films on their charge transport properties was consistently observed from all three systems. However, the more dominant factor determining the large carrier mobility was the low polarizability of the gate dielectric rather than its large capacitance; field-effect mobilities of PDPPTPT films were always larger when lower k dielectric was employed than when higher k dielectric was used. The higher mobilities obtained when using lower k dielectrics could be attributed to the suppressed distribution of the density of localized states (DOS) near the transport level and to the resulting enhanced electronic coupling between the macromolecules.</P>

Effect of pre-aggregation in conjugated polymer solution on performance of diketopyrrolopyrrole-based organic field-effect transistors

Dereje, Mamo Melaku,Ji, Dongseob,Kang, So-Huei,Yang, Changduk,Noh, Yong-Young Applied Science Publishers 2017 Dyes and pigments Vol.145 No.-

<P><B>Abstract</B></P> <P>In this work, we investigate the effect of pre-aggregated solutions of diketopyrrolopyrrole (DPP)-based conjugated polymers to achieve highly-aligned polymer films for high-performance organic field-effect transistors (OFETs). A suitable marginal solvent is selected for 5-octyl-pentadecyl branched DPP and selenophene-based semiconducting polymer (PDPP(SE)-ε-C<SUB>8</SUB>C<SUB>15</SUB>) by utilizing the Hansen solubility parameter calculation. The anisotropic one-dimensional aligned PDPP(SE)-ε-C<SUB>8</SUB>C<SUB>15</SUB> film was off-center spin-coated from the pre-aggregated solution is studied by atomic force microscopy and polarized UV-Vis absorption spectroscopy. A significantly high hole mobility of 4.16 cm<SUP>2</SUP>V<SUP>−1</SUP>s<SUP>−1</SUP> was achieved from the OFETs with a unidirectionally-aligned PDPP(SE)-ε-C<SUB>8</SUB>C<SUB>15</SUB> film to the transistor channel direction.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Selection of suitable solvent for preparing pre-aggregated solutions of polymers. </LI> <LI> Formation of anisotropic thin films from the pre-aggregated polymer solutions. </LI> <LI> Directionally aligned polymer films differ in property and their FET performances. </LI> <LI> Thin films aligned parallel to the transistor channel direction show high mobility. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Effect of pre-aggregation in solution state on the performance of organic field-effect transistors with indacenodithiophene-co-benzothiadiazole

Shin, Eun-Sol,Noh, Yong-Young Elsevier 2018 ORGANIC ELECTRONICS Vol.53 No.-

<P><B>Abstract</B></P> <P>We study the effect of solvent and pre-aggregated solution formed in a binary solvent system to achieve high performance organic field-effect transistors (OFETs) with indacenodithiophene-co-benzothiadiazole (IDT-BT) polymer. To quantify the degree of pre-aggregation, we selected a binary solvent system consisting of a mixture of good (chloronaphthanlene (CN), bp = 259 °C) and bad (2-methoxyl ethanol (2-ME), bp = 124 °C) solvents with various mixing ratios from 0 to 30 v% with the help of a Hansen solubility parameters program. The formation of pre-aggregated IDT-BT polymer was identified in an 8:2 CN:2-ME solvent ratio via a red-shift in a UV–vis absorption spectrum. The off-center spin coated IDT-BT OFETs from 8:2 ratio (CN:2-ME) solution exhibited more than double the improvement in field effect mobility (<SUP>μFET</SUP> = 1.38 ± 0.19 cm<SUP>2</SUP>/Vs) due to efficient charge injection through the smooth semiconducting film surface fabricated by the off-center spin-coating process from the polymer pre-aggregate in the binary solvent system with an appropriate mixing ratio.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Effect of binary solvent for performance in IDT-BT based OFETs is investigated. </LI> <LI> Twice improved field effect mobility of <SUP>μFET</SUP> = 1.38 ± 0.19 cm<SUP>2</SUP>/Vs is achieved. </LI> <LI> This improvement is due to efficient charge injection through the smooth IDT-BT film surface. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Enhancement of Interconnectivity in the Channels of Pentacene Thin-Film Transistors and Its Effect on Field-Effect Mobility

Lee, H. S.,Kim, D. H.,Cho, J. H.,Park, Y. D.,Kim, J. S.,Cho, K. WILEY-VCH Verlag 2006 Advanced Functional Materials Vol.16 No.14

<P>With the aim of improving the field-effect mobility of transistors by promoting the interconnectivity of the grains in pentacene thin films, deposition conditions of the pentacene molecules using one-step (total thickness of layer 50 nm: 0.1 Å s<SUP>–1</SUP>) and two-step (first layer 10 nm: 0.1 Å s<SUP>–1</SUP>, second layer 40 nm: 4.0 Å s<SUP>–1</SUP>) depositions are controlled. Significantly, it is found that the continuities of the pentacene thin films vary with the deposition conditions of the pentacene molecules. Specifically, a smaller number of voids is observed at the interface for the two-step deposition, which results in field-effect mobilities as high as 1.2 cm<SUP>2</SUP> V<SUP>–1</SUP> s<SUP>–1</SUP>; these are higher by more than a factor of two than those of the pentacene films deposited in one step. This remarkable increase in field-effect mobility is due in particular to the interconnectivity of the pentacene grains near the insulator substrate.</P> <B>Graphic Abstract</B> <P>Interconnectivity in the channels of pentacene TFTs can be enhanced by two-step deposition (1st layer 10 nm: 0.1 Å s<SUP>–1</SUP>, 2nd layer 40 nm: 4.0 Å s<SUP>–1</SUP>) (see figure). A smaller number of voids is observed at the interface between the pentacene film and insulator, which results in field-effect mobilities as high as 1.2 cm<SUP>2</SUP> V<SUP>–1</SUP> s<SUP>–1</SUP>. This approach to improving the quality of small-molecule active layers will be beneficial to TFT production. <img src='wiley_img/1616301X-2006-16-14-ADFM200500854-content.gif' alt='wiley_img/1616301X-2006-16-14-ADFM200500854-content'> </P>

Effective Channel Mobility of AlGaN/GaN-on-Si Recessed-MOS-HFETs

Hyun-Seop Kim,Seoweon Heo,Ho-Young Cha 대한전자공학회 2016 Journal of semiconductor technology and science Vol.16 No.6

We have investigated the channel mobility of AlGaN/GaN-on-Si recessed-metal-oxide-semiconductor-heterojunction field-effect transistors (recessed-MOS-HFET) with SiO2 gate oxide. Both field-effect mobility and effective mobility for the recessed-MOS channel region were extracted as a function of the effective transverse electric field. The maximum field effect mobility was 380 cm<SUP>2</SUP>/V·s near the threshold voltage. The effective channel mobility at the on-state bias condition was 115 cm<SUP>2</SUP>/V·s at which the effective transverse electric field was 340 kV/cm. The influence of the recessed-MOS region on the overall channel mobility of AlGaN/GaN recessed-MOS-HFETs was also investigated.