Vincenzo Pecunia

Two-Dimensional Carrier Distribution in Top-Gate Polymer Field-Effect Transistors: Correlation between Width of Density of Localized States and Urbach Energy

A general semiconductor-independent two-dimensional character of the carrier distribution in top-gate polymer field-effect transistors is revealed by analysing temperature-dependent transfer characteristics and the sub-bandgap absorption tails of the polymer semiconductors. A correlation between the extracted width of the density of states and the Urbach energy is presented, corroborating the 2D accumulation layer and demonstrating an intricate connection between optical measurements concerning disorder and charge transport in transistors.

Scanning Kelvin Probe Microscopy Investigation of the Role of Minority Carriers on the Switching Characteristics of Organic Field-Effect Transistors.

A method based on scanning Kelvin probe microscopy is developed to probe the effects of minority carriers on the switching characteristics of organic field-effect transistors. The mobility of the minority carriers is extracted and the role they play in screening of the gate potential in the OFF state and in recombination of trapped majority carriers trapped after an ON state is understood.

Squaraine-based organic photodetector coupled to a scintillating crystal for X-ray sensing applications

To the aim of developing an X-ray imager based on a scintillator coupled to an organic photodetector, we fabricated and tested a detector pixel whose active material is a blend of squaraine dyes and Phenyl-C61-Butyric-Acid-Methyl-Ester (PCBM), processed to obtain a detector thickness of 2μm and a leakage current, at the operating voltage, below 10nA/cm2. The detector was coupled to a CsI(Tl) scintillator crystal obtaining, upon collimated 30keV x-ray beam, clear current signals of few hundreds of pA for a dose less than 5μGray/s, both in QCW and under 500μs long pulses. In addition, the development of the pixel on a flexible and transparent substrate leads to a better scintillator light collection.

Trap Healing for High-Performance Low-Voltage Polymer Transistors and Solution-Based Analog Amplifiers on Foil

Solution-processed semiconductors such as conjugated polymers have great potential in large-area electronics. While extremely appealing due to their low-temperature and high-throughput deposition methods, their integration in high-performance circuits has been difficult. An important remaining challenge is the achievement of low-voltage circuit operation. The present study focuses on state-of-the-art polymer thin-film transistors based on poly(indacenodithiophene-benzothiadiazole) and shows that the general paradigm for low-voltage operation via an enhanced gate-to-channel capacitive coupling is unable to deliver high-performance device behavior. The order-of-magnitude longitudinal-field reduction demanded by low-voltage operation plays a fundamental role, enabling bulk trapping and leading to compromised contact properties. A trap-reduction technique based on small molecule additives, however, is capable of overcoming this effect, allowing low-voltage high-mobility operation. This approach is readily applicable to low-voltage circuit integration, as this work exemplifies by demonstrating high-performance analog differential amplifiers operating at a battery-compatible power supply voltage of 5 V with power dissipation of 11 µW, and attaining a voltage gain above 60 dB at a power supply voltage below 8 V. These findings constitute an important milestone in realizing low-voltage polymer transistors for solution-based analog electronics that meets performance and power-dissipation requirements for a range of battery-powered smart-sensing applications.

Selective Conversion from p-Type to n-Type of Printed Bottom-Gate Carbon Nanotube Thin-Film Transistors and Application in Complementary Metal–Oxide–Semiconductor Inverters

The fabrication of printed high-performance and environmentally stable n-type single-walled carbon nanotube (SWCNT) transistors and their integration into complementary (i.e., complementary metal-oxide-semiconductor, CMOS) circuits are widely recognized as key to achieving the full potential of carbon nanotube electronics. Here, we report a simple, efficient, and robust method to convert the polarity of SWCNT thin-film transistors (TFTs) using cheap and readily available ethanolamine as an electron doping agent. Printed p-type bottom-gate SWCNT TFTs can be selectively converted into n-type by deposition of ethanolamine inks on the transistor active region via aerosol jet printing. Resulted n-type TFTs show excellent electrical properties with an on/off ratio of 106, effective mobility up to 30 cm2 V-1 s-1, small hysteresis, and small subthreshold swing (90-140 mV dec-1), which are superior compared to the original p-type SWCNT devices. The n-type SWCNT TFTs also show good stability in air, and any deterioration of performance due to shelf storage can be fully recovered by a short low-temperature annealing. The easy polarity conversion process allows construction of CMOS circuitry. As an example, CMOS inverters were fabricated using printed p-type and n-type TFTs and exhibited a large noise margin (50 and 103% of 1/2 Vdd = 1 V) and a voltage gain as high as 30 (at Vdd = 1 V). Additionally, the CMOS inverters show full rail-to-rail output voltage swing and low power dissipation (0.1 μW at Vdd = 1 V). The new method paves the way to construct fully functional complex CMOS circuitry by printed TFTs.

Inkjet-Printed Nanocavities on a Photonic Crystal Template

The possibility to create high Q cavities by the deposition of a thin film of a low refractive index material on the surface of a photonic crystal (PhC) template [1] has been rarely explored. The few experimental demonstrations to date have involved material-specific e-beam or UV exposure techniques. In this work we use a commercially available inkjet printer with fL droplet delivery to create nanocavities on-demand with structurally tunable resonance on the surface of a PhC template. We show that this fabrication method is particularly suited to the creation of 1 μm-wide strips with sub-100 nm film thicknesses on the PhC surface, resulting in high Q cavity modes with mode volume approaching a cubic wavelength. A new paradigm for a direct-written nanophotonics is thus established, allowing the efficient coupling of any solution-processable material [2] to optical modes by a simple, non-contaminating and local deposition method.

High-Resolution Inkjet-Printed Oxide Thin-Film Transistors with a Self-Aligned Fine Channel Bank Structure

A self-aligned inkjet printing process has been developed to construct small channel metal oxide (a-IGZO) thin-film transistors (TFTs) with independent bottom gates on transparent glass substrates. Poly(methylsilsesquioxane) was used to pattern hydrophobic banks on the transparent substrate instead of commonly used self-assembled octadecyltrichlorosilane. Photolithographic exposure from backside using bottom-gate electrodes as mask formed hydrophilic channel areas for the TFTs. IGZO ink was selectively deposited by an inkjet printer in the hydrophilic channel region and confined by the hydrophobic bank structure, resulting in the precise deposition of semiconductor layers just above the gate electrodes. Inkjet-printed IGZO TFTs with independent gate electrodes of 10 μm width have been demonstrated, avoiding completely printed channel beyond the broad of the gate electrodes. The TFTs showed on/off ratios of 108, maximum mobility of 3.3 cm2 V-1 s-1, negligible hysteresis, and good uniformity. This method is conductive to minimizing the area of printed TFTs so as to the development of high-resolution printing displays.

Inkjet printed nanocavities on a photonic crystal template

The possibility to create high Q cavities by the deposition of a thin film of a low refractive index material on the surface of a photonic crystal (PhC) template [1] has been rarely explored. The few experimental demonstrations to date have involved material-specific e-beam or UV exposure techniques. In this work we use a commercially available inkjet printer with fL droplet delivery to create nanocavities on-demand with structurally tunable resonance on the surface of a PhC template. We show that this fabrication method is particularly suited to the creation of 1 μm-wide strips with sub-100 nm film thicknesses on the PhC surface, resulting in high Q cavity modes with mode volume approaching a cubic wavelength. A new paradigm for a direct-written nanophotonics is thus established, allowing the efficient coupling of any solution-processable material [2] to optical modes by a simple, non-contaminating and local deposition method.