Daniele Raiteri

Fast ambipolar integrated circuits with poly(diketopyrrolopyrrole-terthiophene)

Ambipolar integrated circuits were prepared with poly(diketopyrrolopyrrole-terthiophene) as the semiconductor. The field-effect mobility of around 0.02 cm2/V s for both electrons and holes allowed for fabrication of functional integrated complementary metal-oxide semiconductor (CMOS)-like inverters and ring oscillators. The oscillation frequency was found to have a near quadratic dependence on the supply bias. The maximum oscillation frequency was determined to be 42 kHz, which makes this ring oscillator the fastest CMOS-like organic circuit reported to date.

Ultra-high gain diffusion-driven organic transistor

Emerging large-area technologies based on organic transistors are enabling the fabrication of low-cost flexible circuits, smart sensors and biomedical devices. High-gain transistors are essential for the development of large-scale circuit integration, high-sensitivity sensors and signal amplification in sensing systems. Unfortunately, organic field-effect transistors show limited gain, usually of the order of tens, because of the large contact resistance and channel-length modulation. Here we show a new organic field-effect transistor architecture with a gain larger than 700. This is the highest gain ever reported for organic field-effect transistors. In the proposed organic field-effect transistor, the charge injection and extraction at the metal–semiconductor contacts are driven by the charge diffusion. The ideal conditions of ohmic contacts with negligible contact resistance and flat current saturation are demonstrated. The approach is general and can be extended to any thin-film technology opening unprecedented opportunities for the development of high-performance flexible electronics.

An organic VCO-based ADC for quasi-static signals achieving 1LSB INL at 6b resolution

Smart sensors embedded in packaging films for food or pharmaceuticals, and read out using RFID protocols, are an important future application of large-area organic electronics. The first steps towards flexible organic electronics were code generators for RFID tags [1]. To realize flexible smart sensors it is also essential to develop analog sensor interfaces and ADCs, which will enable the integration of sensors, data processing and RF communication (Fig. 6.6.1) on the same plastic foil [2]. This paper focuses on the design of an organic ADC for quasi-static signals, like the ones provided by chemical and temperature sensors. Only a few ADCs made with organic TFTs (OTFTs) have been reported [3,4] so far. Their linearity is limited by the poor matching typical of organic technologies and reached an INL of 2.6LSB at 6b resolution before calibration. This paper addresses an ADC whose linearity is not related to the matching of OTFTs or capacitances, but relies on the electrical properties of a transconductor. Even without calibration, the INL is 1LSB and the DNL is 0.6LSB at 6b resolution. The converter is manufactured in a double-gate p-type OTFT technology [5], which provides two gates to control the semiconductor channel, G and TG (Fig. 6.6.1): a voltage applied to the top gate TG produces a linearly proportional shift of the threshold voltage.

A 6b 10MS/s current-steering DAC manufactured with amorphous Gallium-Indium-Zinc-Oxide TFTs achieving SFDR > 30dB up to 300kHz

Amorphous Gallium-lndium-Zinc-Oxide (GIZO or IGZO) has been recently pro- posed [1] as an interesting semiconductor for manufacturing TFTs because of its mobility (μ~20cm7Vs), superior to other common materials for large-area elec- tronics like organic semiconductors and a-Si (μ~1cm7Vs). The amorphous nature of GIZO grants also a good uniformity, contrary to Low Temperature Polycrystalline Silicon (LTPS), which still offers the best mobility among large- area TFT technologies (μ~100cm2Λ/s). The optical transparency and the relative- ly low fabrication temperature (<;150°C) make this technology especially suitable for display backplanes and relative driving electronics [2], as well as for any kind of large-area applications on plastic foils, e.g. biomedical sensors, non-volatile memories [3], RFIDs [4], etc.

A tunable transconductor for analog amplification and filtering based on double-gate organic TFTs

This paper presents a transconductor designed using a physical model of double-gate p-type organic thin film transistors (OTFTs). A control voltage can be used to vary the output resistance and the transconductance over one order of magnitude. The voltage gain does not depend on process parameters and therefore is insensitive to shelf and operational degradation. This circuit can be used as a tunable resistor, in voltage amplifiers or in GmC filters.

A synchronous rail-to-rail latched comparator based on double-gate organic thin-film-transistors

This paper presents a latched comparator designed in a double-gate p-type-only organic thin film transistors (OTFTs) technology. The circuit is tailored to take the maximum advantage of the features of the double-gate technology, which allows an input capacitance of only ~35fF. The measured single stage-latch reaches rail-to-rail logic levels with less than 100mV differential input signal and about 10V input common mode range for VDD=20V. The DC small-signal gain is larger than 46dB and the static power dissipation is ~30nW. All measurements were taken in air and in daylight.

A discrete-time amplifier based on Thin-Film Trans-Capacitors for sensor systems on foil

Organic materials can be used to fabricate sensors for physical and chemical quantities, and also to make electronics. The integration of these two elements holds the promise to enable novel smart-sensors on foil. In this paper, we deal with the design of the first stage of a signal conditioning chain on foil: the amplifier. The poor electrical performance of organic TFTs hampers the design of complex circuits, and negatively affects the characteristics of continuous-time amplifiers. In order to improve small-signal gain and speed, a mixed discrete-time and continuous-time approach is presented in this paper for the sensor frontend. A new device, the Thin-Film Trans-Capacitor, is presented and used to build the discrete-time amplifier, while the continuous time amplifier exploits a simple traditional architecture to improve yield. Simulations of the circuit proposed show that the total gain of the sensor frontend increases of about one decade without any detrimental effect on the speed. CAD (Computer-Aided Design) simulations confirm the results of the simple mathematical model we present.

Analog to digital converters on plastic foils

Circuits based on transistors which are manufactured at near-to-ambient temperatures on plastic foils are suited for mechanically flexible and large-area applications. Examples include bendable displays, large-area sensor surfaces for man-machine interfaces, and sensors-augmented RFIDs embedded in packaging material for food monitoring. This paper discusses circuit and system-level techniques that, minimizing the impact of the poor matching of organic transistors, enable analog to digital converters manufactured using unipolar and complementary organic technologies.

A discrete-time amplifier based on Thin-Film Trans-Capacitors for organic sensor frontends

The high sensitivity of organic materials to many different physical quantities makes smart sensors one of the most appealing applications for organic electronics. In this paper we deal with the design of a new device, a Thin-Film Trans-Capacitor, that can be employed to design discrete-time amplifiers for sensor frontends. Simulations of the circuit proposed show that the gain of the sensor frontend increases of about one decade without any detrimental effect on the speed. CAD (Computer-Aided Design) simulations confirm the results of the simple mathematical model we present.

Circuit design on plastic foils

This book illustrates a variety of circuit designs on plastic foils and provides all the information needed to undertake successful designs in large-area electronics. The authors demonstrate architectural, circuit, layout, and device solutions and explain the reasons and the creative process behind each. Readers will learn how to keep under control large-area technologies and achieve robust, reliable circuit designs that can face the challenges imposed by low-cost low-temperature high-throughput manufacturing. ? Discusses implications of problems associated with large-area electronics and compares them to standard silicon; ? Provides the basis for understanding physics and modeling of disordered material; ? Includes guidelines to quickly setup the basic CAD tools enabling efficient and reliable designs; ? Illustrates practical solutions to cope with hard/soft faults, variability, mismatch, aging and bias stress at architecture, circuit, layout, and device levels.?