Bottom Gate Top Contact Research Articles

Structure engineering of naphthalene diimides for improved charge carrier mobility: self-assembly by hydrogen bonding, good or bad?

Two families of naphthalene diimide (NDI) derivatives were compared and contrasted for the effect of self-assembly on charge carrier transport. One series of NDI derivatives had a terminal phenyl ring attached to a hexyl spacer substituted naphthalene core either through an ester or an amide linkage (NDI-E and NDI-A, respectively), while the other series had a 3,4,5-tridodecyloxy phenyl unit (NDI-E3, NDI-A3) instead of the terminal phenyl unit. Solution processed thin films of these molecules exhibited n-type charge transport characteristics in a bottom gate top contact organic field effect transistor (OFET) geometry. The amide derivatives showed evidence of self-organization with observation of red shifted aggregate emission in solution as well as solid state. Variable temperature FTIR studies in the solid state confirmed the existence of strong hydrogen bonding which could be broken only at very high temperature. However, contrary to expectations, the NDI ester derivatives showed better device efficiency with electron mobilities in the range 8.5 × 10−3 to 2 × 10−2 cm2 V−1 s−1 and on/off ratio ∼104. The thin film crystallinity and morphology of NDI-E and NDI-A were examined through X-ray diffraction and atomic force microscopy (AFM). The correlation of crystallinity, hydrogen bonding and charge carrier mobility was studied using energy minimized structures from density functional theory (DFT). The higher electron mobility of ester linked NDI derivatives over the amide linked ones was attributed to the freedom in charge transport pathways offered by a three dimensional crystalline organization in the ester compared to the restricted directional hydrogen bonding interaction in the amide derivatives.

FET performance and substitution effect on 2,6-dithienylanthracene devices prepared by photoirradiation of their diketone precursors

Hole mobility was evaluated by top-contact bottom gate field effect transistor and time resolved microwave conductivity measurements in 2,6-dithienylanthracene and hexyl-substituted 2,6-dithienylanthracene films prepared by spin-coating of their α-diketone precursors followed by photoirradiation, revealing enough high potentials for semiconducting films with charge carrier mobilities of 0.8-0.9 cm(2) V(-1) s(-1) in the photo-irradiated films.

Highly Soluble Poly(thienylenevinylene) Derivatives with Charge-Carrier Mobility Exceeding 1 cm2V–1s–1

We report synthesis and characterization of high performance p-type conjugated polymers containing alkyl-substituted thienylenevinylene (PC6TV12T and PC12TV12T) as an active layer for organic thin film transistors (OTFTs). Maximum mobility of annealed PC6TV12T and PC12TV12T films measured in OTFTs showed 0.47 and 1.05 cm2V−1s−1, respectively, in the top-gate/bottom-contact (TG/BC) configuration.

One-step micropatterning of highly-ordered semi-crystalline poly(vinylidene fluoride- co-trifluoroethylene) films by a selective shear and detachment process

We present a one-step route for micropatterning a thin ferroelectric poly(vinylidene fluoride- co-trifluoroethylene) (PVDF-TrFE) film with both molecular and microstructural crystal control over a large area. The method is based on the static mechanical shearing and subsequent detachment of a film spin coated on pre-patterned Al which has been lithographically prepared on a SiO 2 substrate under appropriate thermal conditions. Selective detachment of the film in contact with the SiO 2 substrate gave rise to micropatterns of PVDF-TrFE film positioned only on the Al regions. Further, the PVDF-TrFE film showed 25-nm-thick crystalline lamellae aligned perpendicular to the shear direction, wherein the c axis of the crystals was globally ordered parallel to the shear direction. The sheared and patterned PVDF-TrFE thin films are readily incorporated into non-volatile memory units of metal/ferroelectric/metal capacitors and bottom gate-top contact field effect transistors, leading to arrays of memory devices with enhanced performance.

High speeds complementary integrated circuits fabricated with all‐printed polymeric semiconductors

AbstractInkjet‐printed high speed polymeric complementary circuits are fabricated using an n‐type ([poly{[N,N′‐bis(2‐octyldodecyl)‐naphthalene‐1,4,5,8‐bis(dicarboximide)‐2,6‐diyl]‐alt‐5,5′‐(2,2′‐dithiophene)} [P(NDI2OD‐T2), Polyera ActivInk N2200] and two p‐type polymers [poly(3‐hexylthiophene) (P3HT) and a dithiophene‐based polymer (Polyera ActivInk P2100)]. The top‐gate/bottom‐contact (TG/BC) organic field‐effect transistors (OFETs) exhibit well‐balanced and very‐high hole and electron mobilities (μFET) of 0.2–0.5 cm2/Vs, which were enabled by optimization of the inkjet‐printed active features, small contact resistance both of electron and hole injections, and effective control over gate dielectrics and its orthogonal solvent effect (selection of poly(methyl methacrylate) and 2‐ethoxyethanol). Our first demonstrated inkjet‐printed polymeric complementary devices have been integrated to high‐performance complementary inverters (gain >30) and ring oscillators (oscillation frequency ∼50 kHz). We believe that the operating frequency of printable organic circuits can be further improved more than 10 MHz by fine‐tuning of the device architecture and optimization of the p‐ and n‐channel semiconductor processing. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010

Highly end-doped silicon nanowires for field-effect transistors on flexible substrates

We report on the VLS (vapour-liquid-solid) fabrication and characterization of in situ axially doped silicon nanowires (SiNWs) at both ends, and on their integration into a bottom gate-top contact geometry on both rigid and flexible substrates to realize field-effect transistors (FETs). To improve contact resistance between SiNWs and source/drain electrodes, we axially tuned the level of doping at both ends of the SiNWs by sequential in situ addition of PH(3). Characterisation of SiNWs by scanning spreading resistance microscopy in the device configuration allowed us to determine precisely the different sections of the SiNWs. The transfer to flexible substrates still allowed for workable FET structures. Transistors with electron mobilities exceeding 120 cm(2) V(-1) s(-1), I(on)/I(off) ratios greater than 10(7) and ambipolar behaviour were achieved.

Composition influence of SiN x gate insulator fabricated by radio frequency (RF) Magnetron sputtering on characteristics of organic thin-film transistors

To investigate the effect of composition of SiN x on the properties of organic thin-film transistors (OTFTs), we fabricated bottom gate top contact OTFTs devices with different composition SiN x gate insulator. Pentacene based OTFTs with SiN x insulator, prepared using an interface modification process of UV-ozone treatment, exhibited effective mobility of 0.63 cm2/Vs and on/off current ratio of 10 5. Overall improvement in field-effect mobility, threshold voltage was observed as silicon content in SiN x increases. The results demonstrate that the viability of using SiN x for OTFTs and of UV-ozone treatment could be used to improve the properties of organic thin-film transistors. The dependence of the contact angle on the SiN x film composition is evident for the untreated samples, the contact angle increases as the silicon content in the untreated nitride film increases. In contrast, the rise in contact angle across all samples after surface treatment signifies effective surface modification to promote hydrophobicity of the nitride surface. The hydrophobic surface is needed for the organic semiconductor.