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A curved image sensor on plastic foil has been developed for cone beam computed tomography (CBCT) X-ray imaging. The image sensor of about 6 × 8 cm2 size has been built on a thin polyimide foil with an indium gallium zinc oxide (IGZO) backplane and an organic photodetectors (OPD) frontplane. A flexible cesium iodide (CsI) scintillator has been attached to the optical sensor with 480 × 640 pixels of 126 µm size. Dark current density of the OPD was low with less than 10−7 mA/cm2 at −2 V, while an external quantum efficiency (EQE) of about 50% was reached in the visible wavelength range matched to the scintillator output. The image quality of the digital X-ray detector allowed for 3D reconstruction images of a bone phantom on a rotating stage with a lab setup. The curved detector with 32 cm curvature radius opens up the path for very compact CBCT gantries with largely reduced footprint.

We review recent compact modeling solutions for Organic and Amorphous Oxide TFTs (OTFTs and AOS TFTs, respectively), which were developed, under the framework of the EU-funded project DOMINO, to address issues specifically connected to the physics of these devices. In particular, using different approaches, analytical equations were formulated to model the Density of States (DOS), different transport mechanisms, trapping/de-trapping, drain current, stress, capacitances, frequency dispersion and noise. The final TFT models were, after implementation in Verilog-A, validated by means of the design and simulation of test circuits.

Capacitive touchscreens are increasingly widespread, featuring in mobile phones and tablets, as well as everyday objects such as cars and home appliances. As a result, the interfaces are uniquely placed to provide a means of communication in the era of the Internet of Everything. Here we show that commercial touchscreens can be used as reader interfaces for capacitive coupled data transfer. The transfer of data to the touchscreen is achieved using a 12-bit thin-film capacitive radio frequency identification tag powered by a thin-film battery or a thin-film photovoltaic cell that converts light from the screen. The thin-film integrated circuit has a 0.8 cm2 on-chip monolithic antenna, employs 439 transistors, and dissipates only 31 nW of power at a supply voltage of 600 mV. The chip has an asynchronous data rate of up to 36 bps, which is limited by the touchscreen readout electronics. ispartof: NATURE ELECTRONICS vol:2 issue:12 pages:606-611 ispartof: location:England status: published

The maturity of metal–oxide thin-film transistors (TFT) highlights opportunities to develop robust and low-cost electronics on flexible and stretchable substrates over large area in an industry-compatible technology. Internet-of-Everything applications with sensor nodes are driving the development of analog-to-digital converters (ADCs). In this paper, a self-biased and self-digital-controlled successive approximation ADC with integrated references and sensor read-in circuitry together with a printed negative temperature coefficient (NTC) sensor using unipolar dual-gate metal–oxide (InGaZnO) TFTs is demonstrated. The system is operated at a clock of up to 400 Hz and a total power dissipation of 245 mW (73 $\mu \text{W}$ from analog) at a maximum power supply of 30 V is measured. The radio-frequency identification-ready ADC comprises of a total of 1394 indium–gallium–zinc oxide TFTs and 31 metal–insulator–metal capacitors. A figure of merit of 26 nJ/c.s. is achieved from the ADC driven from external microcontroller. The robustness of the various blocks of the chip is characterized and the yield is discussed.

Using flat-panel compatible processes we realized 6x8 cm, 200-ppi active-matrix imagers with solution-processed, ultrathin organic photodiodes and demonstrate its performance in a biometric palmprint detector.

We present a qHD (960 × 540 with three sub-pixels) top-emitting active-matrix organic light-emitting diode display with a 340-ppi resolution using a self-aligned IGZO thin-film transistor backplane on polyimide foil with a humidity barrier. The back plane process flow is based on a seven-layer photolithography process with a CD = 4 μm. We implement a 2T1C pixel engine and use a commercial source driver IC made for low-temperature polycrystalline silicon. By using an IGZO thin-film transistor and leveraging the extremely low off current, we can switch off the power to the source and gate driver while maintaining the image unchanged for several minutes. We demonstrate that, depending on the image content, low-refresh operation yields reduction in power consumption of up to 50% compared with normal (continuous) operation. We show that with the further increase in resolution, the power saving through state retention will be even more significant.

Three novel differential amplifier topologies using double gate a-IGZO TFTs on flexible substrate are presented in this paper. The designs exploit positive feedback and a load with self-biased top gate to achieve the highest static gain in single stage a-IGZO amplifiers reported to date. After fabrication, the three amplifiers exhibit respectively a static gain of 14 dB, 21.5 dB and 30 dB, with a bandwidth of 2 kHz, 400 Hz, and 150 Hz. Also, for each circuit the input referred noise has been measured to be $420~\mu \text {V}_{\mathrm {\mathbf {rms}}}$ , $195~\mu \text {V}_{\mathrm {\mathbf {rms}}}$ and $146~\mu \text {V}_{\mathrm {\mathbf {rms}}}$ , respectively. Based on these results, the a-IGZO amplifier providing the highest gain is suitable as front-end for heart rate measurements and, with some further optimization verified in simulation, can also be used for other bio-potential applications, like electro hysterogram and electro cardiogram.

In this paper, we propose a unified physical model of InGaZnO [amorphous indium–gallium–zinc-oxide (a-IGZO)] thin-film transistors (TFTs) accounting for both charge injection at the contact and charge transport within the channel. We extract the current-voltage characteristics of the injecting contact from the measurements of a-IGZO TFTs fabricated on plastic foil. We show that the charge injection depends on both the drain and the gate voltages. We model the charge injection in staggered a-IGZO TFTs basing on the thermionic emission–diffusion theory including the charge carrier-dependent electron velocity due to the trap states in the subgap of the a-IGZO semiconductor. Combining the charge injection model with a charge transport model, we accurately and consistently describe the measurements of staggered a-IGZO TFTs with channel-length scaling from $200~\mu m$ to $15~\mu m$ . The proposed unified model is implemented in a circuit simulator and used to design unipolar inverters. The good agreement between simulations and measurements of the inverters further confirms the effectiveness of the proposed approach.

This work presents a low power ECG interface for wearable applications, based on unipolar a-IGZO TFTs manufactured on a flexible substrate. The interface consists of a cascaded diode-connected load preamplifier followed by a reset integrator, which is used to convert the voltage signal to a pulse-width modulated (PWM) representation. The output is thus provided as a binary PWM waveform, which can be conveniently sent to a reader device using wireless communication and can be further converted to a digital representation using a simple counter. The flicker noise and the offset are eliminated using an approach similar to correlated double sampling. An input chopper is exploited to alternate the connection between the inputs of the preamplifier for each sample. The output signal is then extracted by subtracting two consecutive samples after conversion to the digital domain. In this way offset and low-frequency noise, which are correlated between the two samples, are effectively cancelled.

With the advent of the Internet of things, wearable sensing devices are gaining importance in our daily lives for applications like vital signal monitoring during sport and health diagnostics. Amorphous indium gallium zinc oxide (a-IGZO) thin film transistors (TFTs) fabricated on flexible large-area substrates are a very interesting platform to build wearable sensing devices due to their flexibility, conformability to the human body, and low cost. For this paper four different bio-signal sensing front-end circuits based on a-IGZO TFTs are designed, fabricated, measured and compared, focusing on three performance indicators which are in a trade-off: power efficiency factor (PEF), area occupation and input impedance. Considering a 200 Hz bandwidth, the measured PEF varies between 4.7 × 105 and 7.5 × 106. The area occupation spans from 4.2 to 37 mm2, while the input impedance at 1 Hz varies from 5.3 to 55.3 MΩ. The front-ends based on diode-load amplifiers are compact but have the lowest input impedance and need external capacitors; a front-end exploiting positive feedback impedance boosting has the highest input impedance and is fully integrated on foil, but occupies the largest area.

We made and characterized an X-ray detector on a 25- $\mu \text{m}$ -thick plastic substrate that is capable of medical-grade performance. As an indirect conversion flat panel detector, it combined a standard scintillator with an organic photodetector (OPD) layer and oxide thin-film transistor backplane. Using solution-processed organic bulk heterojunction photodiode rather than the usual amorphous silicon, process temperature is reduced to be compatible with plastic film substrates, and a number of costly lithography steps are eliminated, opening the door to lower production costs. With dark currents as low as 1 pA/mm $^{2}$ and sensitivity of 0.2 A/W the OPD also meets functional requirements: the proof-of-concept detector delivers high-resolution, dynamic images at 10 frames/s, and 200 pixels/in using X-ray doses as low as $3~\mu $ Gy/frame.

Thin-film transistor technologies have great potential to become the key technology for leafnode Internet of Things by utilizing the NFC protocol as a communication medium. The main requirements are manufacturability on flexible substrates at a low cost while maintaining good device performance characteristics, necessary to be compatible with the NFC specifications. Such low-cost flexible NFC tags can be attached to any object with any form factor, connecting this object to the Internet using a smartphone or tablet as an intermediate node. Among all commercial thin-film transistor technologies, metal oxide transistors is a viable technology for this application. The metal-oxide transistors in this work are based on InGaZnO as semiconductor. Since these are unipolar by nature (i.e., they exhibit only n -type transistors), different options to make logic circuits are studied from static and dynamic points of view. The different topologies are diode-load logic, dual-gate diode-load logic, and pseudo-CMOS logic. The static parameters lead to a comparison of soft yield between those circuit topologies, while the transient analysis provides insight on the power consumption and circuit speed. This is indicative for selecting the logic style matching the data rate requirements of the NFC standards. Moreover, metal-oxide NFC circuits that combine 12-bit code generators to the analog front-end of RFID tags are integrated on a PCB board to evaluate performance of a matched and optimized system. The measured data rates of these integrated NFC tags are compatible with the ISO 15693 specifications. Finally, a fully integrated, flexible NFC tag is realized, which comprises the tuning capacitor, rectifier, load modulator, and code generator.

We present a QVGA (320x240 with 3 sub-pixel) top-emitting AMOLED display with 250ppi resolution using a self-aligned (SA) IGZO TFT backplane on polyimide-foil with full barrier. The back plane process flow is based on a 7 layer photolithography process. The aperture ratio of the top-emitting OLEDs is approx. 80%. An integrated gate driver is shown that can be driven at operation speed equivalent to a 4k2k display at 100Hz

A fast, 128-b implementation of both SRAM and LPROM with integrated periphery in a thin-film amorphous indium–gallium–zinc oxide technology is reported. The SRAM block can be read in 265 $\mu \text{s}$ /byte and written in 110 $\mu \text{s}$ /byte, consumes 12.3 mW, and has an area of 11.9 mm2. Furthermore, after power down, an SRAM memory state retention time of 83 s is shown. The LPROM can be read in 40 $\mu \text{s}$ /b, consumes 4.50 mW, and has an area of 3.75 mm2. The SRAM enables fast volatile RAM memory for thin-film microprocessors, while the LPROM can be used to store the identification code for state-of-the-art thin-film RFID tags.

We present a qHD (960x540 with 3 sub-pixels) top-emitting AMOLED display with 340ppi resolution using a self-aligned (SA) IGZO TFT backplane on polyimide-foil with humidity barrier. The back plane process flow is based on a 7 layer photolithography process with a CD=4um. We implement a 2T1C pixel engine and use commercial source driver IC made for LTPS. By using IGZO TFT and leveraging the extremely low off-current, we can switch-off the power to the source and gate driver while maintaining the image un-changed for several minutes. We demonstrate that, depending on the image content, low-refresh operation yields reduction in power consumption of up to 50% compared to normal (continuous) operation. We show that with further increase in resolution, the power saving through state retention will be even more significant.

Solution type metal-oxide semiconductor was processed on mass-production ready equipment and integrated in a backplane with ESL architecture TFTs. Excellent thickness uniformity of the semiconductor layer was obtained over the complete Gen1 glass substrate (320 mm x 352 mm), resulting in homogeneous TFT performance and bias stress reliability. An 85-ppi QVGA AMOLED display is demonstrated.

This paper describes the potential of hi-res display fabrication using OLED photolithography. We demonstrate 1250 ppi multicolor arrays, pixel scaling down to 3 μm pitch, integration in active displays, and improving lifetime after patterning (200 hours T75, smOLEDs). Photolithography can enable low-cost, high resolution displays for the 8K – VR era.

In this study, the authors report high-quality amorphous Indium-Gallium-Zinc-Oxide (a-IGZO) thin film transistors (TFTs) fabricated using a new back-channel-etch (BCE) process flow on Polyethylene Naphthalate (PEN) foil. The BCE flow allows a better scalability of TFTs for high-resolution backplanes and related circuits. The maximum processing temperature was limited to less than 165oC in order to ensure good overlay accuracy (< 1µm) on foil. The presented process flow differs from to previously reported by defining the Mo S/D contacts by dry etch prior to a-IGZO patterning. The TFTs show good electrical performance, including field-effect mobilities in the range of 15.0cm2/(V.s), sub-threshold slopes of 0.3V/decade and off-currents

In this paper, we present some of the technology challenges and process temperature trade-offs when realizing AM OLED displays on thin flexible plastic films that can be mechanically bent to a roll radius of ∼1 cm. We furthermore present complementary approaches to realize low-power, high resolution OLED displays using self-aligned IGZO TFT architecture; a novel driving method using a compact 2T-1C pixel engine. cop. 2014 JSAP.

The efficiency of small-molecule OLED devices increased substantially in recent years, creating opportunities for power-efficient displays, as only light is generated proportional to the subpixel intensity. However, current active matrix OLED (AMOLED) displays on foil do not validate this power-efficient advantage, as too much power is lost in the AM backplane. AMOLED displays use the analog voltage on the gate of a drive transistor (e.g. M1 in Fig. 30.2.1) to control the pixel current and hence the pixel brightness. Accurate and uniform pixel currents can only be obtained when transistor M1 is driven is saturation. In highresolution technologies on foil, transistor parameters W, L and the mobility μ are limited by technology, imposing a minimal V GS-VT to obtain sufficient current, i.e. V GS-VT > 4V for a-IGZO on foil [1]. Subsequently, to obtain saturation, VDS > 4V, which translates in a static backplane power loss surpassing the OLED power consumption (see red stars in Fig 30.2.1). However, when the OLED pixel impedance around a specific reference current can be matched along a display column line, the accurate pixel current control can be imposed by current DACs implemented in external silicon display column drivers. In this work, we operate M1 as a switch and pixel intensity variations are obtained using Pulse Width Modulation (PWM) of a predefined pixel current, i.e. 2μA/pixel [80*80μm2] (which corresponds in our OLED technology to a light output of 2000Cd/m2). When, in a future implementation the external DACs are calibrated at 0.2μA/pixel, the full brightness would correspond to the typical display brightness of a portable PC, i.e. 200Cd/m2. This concept enables us to reduce the display power voltage at full brightness from 8.2V in a classical AMOLED display on foil configuration to 5V (measured) and for future implementations even down to 4V (see Fig. 30.2.1). As the OLED current load remains equal, a corresponding static power reduction of the display (and increased battery lifetime) is obtained. Digital driving methods of AMOLED displays have been shown before. However, ΔΣ techniques [2] still integrate charge packets on the gate of M1 and hence do not solve the power issue on foil. Other PWM techniques [3] activate only a single active line in the linedriver yielding difficulties to obtain color depths above 6 bits. When multiple independent linedrivers are implemented and their output is multiplexed to alternately drive a single select line, a higher color depth can be obtained [4]. This leads however to a bulky linedriver, which is hard to get within an e.g. 80μm pitch. The design and implementation of a compact integrated linedriver on foil enabling multiple alternating active signals through a single shift register is demonstrated here. © 2014 IEEE.

In this paper, we demonstrate a scalable and low-cost memory technology using a phase separated blend of a ferroelectric polymer and a semiconducting polymer as data storage medium on thin, flexible polyester foils of only 25μm thickness. By sandwiching this polymer blend film between rows and columns of metal electrode lines where each intersection makes up one memory cell, we obtained 1 kbit cross bar arrays with bit densities of up to 10 kbit/cm2. © 2014 The Japan Society of Applied Physics

We demonstrate organic imaging sensor arrays fabricated on flexible plastic foil with the solution processing route for both photodiodes and thin film transistors. We used the photovoltaic P3HT:PCBM blend for fabricating the photodiodes using spin coating and pentacene as semiconductor material for the TFTs. Photodiodes fabricated with P3HT:PCBM absorb in the green part of the visible spectrum which matches with the typical scintillator output wavelength. The arrays consist of 32x32 pixels with variation in pixel resolution of 200μmx200μm, 300μmx300μm and of 1mmx1mm. The accurate reproducibility of shadow images of the objects demonstrates the potential of these arrays for imaging purposes. We also demonstrate that the crosstalk is relatively insignificant despite the fact that the active photodiode forms a continuous layer in the array. Since both photodiodes and TFTs are made of organic material, they are processed at low temperatures below 150°C on foil which means that these imaging sensors can be flexible, light weight and low cost when compared to conventional amorphous silicon based imaging sensors on rigid substrates. In combination with a scintillator on top of the arrays, we show the potential of these arrays for the X-ray imaging applications. cop. 2014 Copyright SPIE. Organisations: Brussels Photonics Team (B-PHOT); Brussels-Capital Region; et al.; Fonds Wetenschappelijk Onderzoek (FWO); The Society of Photo-Optical Instrumentation Engineers (SPIE); Ville de Bruxelles

We present a QQVGA top emitting monochrome AMOLED display with 85dpi resolution using an organic TFT backplane on low temperature PEN-foil. The backplane process flow is based on a 7 layer photolithography process that yields a final mobility of the OTFT of ∼0.4 cm2/Vs. The aperture ratio of the top-emitting OLEDs is over 75%. For operation at 10 V supply voltage (VDD), the brightness of the display using red and green OLEDs exceeds 200 cd/m2.

Multiple-gate transistors featuring an ultrathin semiconductor body are widely recognized as promising candidates for future generation CMOS technology nodes. In this thesis, we have discussed the effects of reducing the channel length and the body thickness on carrier transport in ultrathin-body MOSFETs. We discussed the general features of the carrier distribution and the potential profile in long-channel Double-Gate ultrathin-body MOSFETs, including the effect of quantum confinement in the ultrathin body. In particular, we have investigated the validity of the Effective Mass Approximation by a systematic comparison of the relevant quantities with a full-band quantization approach based on the Linear Combination of Bulk Bands, for both silicon and germanium n-MOSFETs for various crystal orientations. Furthermore, we proposed a method to quantify shifts in energy band alignment due to e.g. structural quantum confinement in ultrathin-body MOSFETs, using the temperature dependence of the subthreshold current. The results were compared with the shifts in threshold voltage, which is commonly used to quantify the effect of quantum confinement. Besides reduction of the body thickness, we have also investigated the effect of decreasing the channel length to values comparable to the carrier mean-free-path, so that carrier transport becomes quasi-ballistic. We have systematically analyzed carrier back-scattering using a sophisticated Multi-Subband Monte-Carlo simulator, both in a realistic 32-nm ultrathin-body MOSFET and in a template device structure with a fixed potential and template scattering parameters. Finally, we have proposed a new model for the backscatter coefficient in nanoscale MOSFETs, assuming that carriers encounter on average just a single scattering event, so that carrier transport is nearly ballistic. Systematic comparison with results obtained from Multi-Subband Monte-Carlo simulations shows very good overall agreement, demonstrating that the proposed model provides a useful framework to help explain and predict quasi-ballistic transport phenomena in nanoscale MOSFETs.