Hagen Marien

A Fully Integrated

In this work we present a fully integrated first order continuous-time ΔΣ ADC made in a pentacene-based dual-gate organic thin-film transistor technology on flexible plastic foil. The ADC achieves a precision of 26.5 dB at a clock speed of 500 Hz and draws 100 μA from a 15 V power supply. As sub-blocks of the ADC, we also present a Vt -insensitive single-stage differential amplifier with 10 kHz GBW, a 3-stage operational amplifier, an integrator, a comparator and a level shifter. The circuits are designed following a strict Vt -insensitive design strategy and use high-pass filters for offset cancellation. The active area is 13 × 20 mm2.

\Delta \Sigma

In this work, we present the implementation and measurement results of all analog building blocks of an organic smart sensor system on foil. The presented building blocks are a 1D and a 2D 4 × 4 pixel flexible capacitive touch sensor with a sample rate of 1.5 kS/s, a DC-connected two-stage opamp with a 20 dB DC gain, a Dickson DC-DC up-converter with output bias voltages up to 60 V and down to - 40 V which are used as a bias voltage in the other building blocks, and a ΔΣ ADC with a 26.5 dB precision and a band width of 15.6 Hz. The sensors, the opamp, the DC-DC converter and the ADC respectively consume 6 μA, 15 μA, 1 μA and 100 μA from a 15 V power supply.

ADC in Organic Thin-Film Transistor Technology on Flexible Plastic Foil

In this letter, a compact model for the dc current and capacitance of organic thin-film transistors is proposed. This model is based on the variable-range hopping-transport theory, and the double-exponential density-of-state function is assumed. The presented model can accurately describe the current from subthreshold regime to linear and saturation regime via a single unified formulation. Good agreement between the theoretical calculation and measurements of pentacene field-effect transistor is found. The application of this compact model on circuit simulation is also presented.

Analog Building Blocks for Organic Smart Sensor Systems in Organic Thin-Film Transistor Technology on Flexible Plastic Foil

Organic electronics is expected to find commercial applications in flexible displays, RFID tags and smart sensor systems, e.g. for food industry or biomedical applications. Key benefits of the technology are the direct production of transistors and circuits on flexible plastic foils, the possibility to directly integrate sensors, light sources, light detectors, a.o. with the same technology, and the low processing temperatures that warrant cost-efficient production. However, organic electronics technologies suffer from important drawbacks versus silicon based technologies, such as its intrinsically lower mobility, the large parameter variation and a very low intrinsic transistor gain (typically 5). Moreover as active components almost exclusively p-type transistors are available and as passive components only capacitors exist. In place of resistors, we are limited to only linear biased transistors. Work on organic RFID [1,2] and several types of organic sensors [3] has been presented. Analog designs in organic technology are in their infancy: a first differential amplifier with differential-mode gain of 10 was presented in [4]; design considerations for analog designs were discussed in [5]; a comparator was presented in [6]; and a 6-bit D/A converter based on a C-2C chain in [7]. In the present work, we disclose the first ADC designed, fabricated and measured in an organic technology on plastic foil with a fully analog design approach.

Compact Model for Organic Thin-Film Transistor

This paper presents a comparator that is designed in an organic electronics technology on a flexible plastic substrate with p-type organic thin-film transistors (p-OTFT) only. The comparator has a gain of 12dB and works at a supply voltage of 20V consuming 9µA. At a clock frequency of 1kHz the input sensitivity is 200mV. The comparator is designed following a threshold-voltage VT insensitive strategy for analog and mixed-signal design in a way to get round VT variations of the pentacene based organic electronics technology. Measurements have been done in ambient environment. The circuits still function well after several weeks of exposure to ambient environment. This comparator can serve in organic smart sensor systems as an interface between analog sensor signals and digital circuitry or as a building block for more complex A-to-D converters.

An analog organic first-order CT ΔΣ ADC on a flexible plastic substrate with 26.5dB precision

In this work an organic dual DC-DC up-converter and an organic 2-stage operational amplifier are presented, both implemented in a thin-film organic electronics technology on foil. The converter has a conversion ratio of 2.5 and only consumes 1 μA from a 15 V power supply voltage. The converter is designed for biasing gates and backgates of transistors in a p-type only technology and enables to bias both input and output nodes of a differential amplifier to the same DC voltage. This in turn enables to directly connect consecutive differential amplifier stages together. The latter is demonstrated through the 2-stage operational amplifier that has a measured gain of 20 dB and a gain-bandwidth product of 2 kHz. This opamp consumes 15 μA from a 15 V power supply.

A mixed-signal organic 1kHz comparator with low V T sensitivity on flexible plastic substrate

In this paper a fully integrated organic DC-DC up-converter is presented in a pentacene p-type only technology. This 3-stage Dickson converter reaches a voltage conversion factor of 3 for a purely capacitive load and 2.5 for a 10 µA load current. The maximal output voltage goes up to 75 V and the Dickson core efficiency is 48 %. The clock signal is generated on-chip with a 9-stage ring oscillator, built with zero-Vgs load inverters. A tunable input voltage provides a tuning range of 30 %. The presented converter is designed for the on-chip generation of voltages for biasing a capacitive load. This converter draws 560 µA from a 20 V supply voltage. The chip area measures 2.8×2.1 mm2. This converter fulfills a direct need for bias voltages beyond the supply voltage that is uncovered in recent work on organic circuits.

DC-DC converter assisted two-stage amplifier in organic thin-film transistor technology on foil

Organic electronics are gaining attention in the electronics world, thanks to the use of organic light emitting diode (OLED) displays in TV and computer monitors and to the presented prototypes of consumer devices with flexible and rollable displays. In this tutorial, however, we take a broader outlook on the other possible applications of organic electronics technology.

An organic integrated capacitive DC-DC up-converter

In this work we present both a 1D and a 2D 4x4 capacitive touch sensor built in a dual-gate organic thin-film transistor technology on flexible foil. The maximal sample rate of the sensor read-out is 1.5kS/s, which results in a refresh rate of 93Hz for the 2D touch pad. With the given performance it is technically feasible to increase the sensor area by 4X to ~50cm2 with the same accuracy reaching a refresh rate of 23Hz. The analog sensor output can further be interpolated and an example is given that proves at least a single bit of improvement per dimension. The output of the touch sensors is given by a ratio of capacitances and consequently the sensor is insensitive to variations and is air-stable. The 1D and 2D sensors measure 1.0x4.4cm2 and 3.5x3.5cm2 respectively. The sensor chip micrographs are presented in the figure.

On the Other Applications of Organic Electronics on Foil

In this paper, we review the state of the art of digital and analog circuits that have been shown in recent years in organic thin-film transistor technology on flexible plastic foil. The transistors are developed for backplanes of displays, and therefore have the characteristics to be unipolar and to possess two gates. The dual-gate architecture is employed to increase the transistors intrinsic transconductance, and to create dual-VT logic. We highlight recent examples of digital and analog plastic thin-film circuits. Furthermore, we give an outlook into new technological evolutions, including thin-film semiconductors with high mobility, the advent of complementary thin-film circuits, and of thin-film electrically re-programmable nonvolatile memory.