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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.

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.

High-resolution RGB organic light-emitting diode frontplane is a key enabler for direct-view transparent augmented reality displays. In this paper, we demonstrate 1250 ppi passive displays and semi-transparent active displays. Organic light-emitting diode photolithography can provide pixel density above 1000 ppi while keeping effective emission area high because of high aperture ratio. Patterns with 2 μm line pitch were successfully transferred to emission layers, indicating possible further pixel density scaling. Lifetime after patterning, key parameter enabling industrialization, is above 150 h (T90 at 1000 nit).

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.

Thermal imagers conventionally consist of a suspended sensing element on support structure with patterned thermal detection layer to get good thermal isolation between sensor elements[1]. Large area and wearable thermal imaging applications require cost effective fabrication, robustness and a flexible form factor. We present a 16×16 active-matrix IGZO array integrated with a screen printed thermistor on a thin and flexible substrate. Screen printing of the thermistor together with a flat-panel compatible backplane technology provides a cost effective and scalable route to large area thermal imaging. Unlike conventional focal plane arrays and microbolometers, in this work no suspended structures are used. Thus, the challenge is to get sufficient thermal separation between the imager elements, in particular when the thermistor is a single, non-structured layer extending across the entire backplane. The thermal response is determined by the thermal detection layer and the substrate, limiting the thermal response time τ = C/G, with C the thermal capacitance and G the thermal conductance. We show that by integration on thin polyimide film the thermal time constant improves by a factor of 30 compared to the same thermistor array on glass. In addition, we show that the thermal response can be further improved by reducing the thickness of (mainly) the printed thermistor layer. A stretchable form factor can be achieved through the formation of thermistor islands, connected by meander-shaped interconnects, enabling large area thermal imaging on conformal surfaces down to millimeter spatial resolution.

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.

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.

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.

A process to make self-aligned top-gate amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistors (TFTs) on polyimide foil is presented. The source/drain (S/D) region's parasitic resistance reduced during the SiN interlayer deposition step. The sheet resistivity of S/D region after exposure to SiN interlayer deposition decreased to 1.5 kΩ/□. TFTs show field-effect mobility of 12.0 cm2/(V.s), sub-threshold slope of 0.5 V/decade, and current ratio (I ON/OFF) of >107. The threshold voltage shifts of the TFTs were 0.5 V in positive (+1.0 MV/cm) bias direction and 1.5 V in negative (-1.0 MV/cm) bias direction after extended stressing time of 104 s. We achieve a stage-delay of ~19.6 ns at V-DD = 20 V measured in a 41-stage ring oscillator. A top-emitting quarter-quarter-video-graphics-array active-matrix organic light-emitting diode display with 85 ppi (pixels per inch) resolution has been realized using only five lithographic mask steps. For operation at 6 V supply voltage (V-DD), the brightness of the display exceeds 150 cd/m2. A process to make self-aligned top-gate amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistors (TFTs) is presented. TFTs show field-effect mobility of 12.0 cm2/(V.s), sub-threshold slope of 0.5 V/decade, and current ratio (I ON/OFF) of over 107. In applications, a 41-stage ring oscillator with a stage-delay of ~19.6 ns (at V-DD = 20 V) and a top-emitting quarter-quarter-video-graphics-array (QQVGA) active-matrix organic light-emitting diode (AMOLED) display with 85 ppi (pixels per inch) resolution using five lithographic mask steps have been realized on a polyimide foil. Copyright 2015 Society for Information Display.

AMOLED displays using oxide TFTs and high-quality moisture barrier were fabricated on ultrathin, flexible plastic substrates to give maximum mechanical flexibility. Total display thickness is below 150μm, and repeated rollability at 1 cm roll radius has been demonstrated. Electrical/Mechanical characteristics and reliability of the flexible displays will be presented. cop. 2014 Society for Information Display.

We present a QQVGA (160times120 with 3 sub-pixel) top-emitting AMOLED display with 85ppi resolution using a self-aligned (SA) IGZO TFT backplane on polyimide-foil. The back plane process flow is based on a 5 layer photolithography process. The aperture ratio of the top-emitting OLEDs is approx. 25%. For operation at 6 V supply voltage (VDD), the brightness of the display exceeds 150cd/m2. On the same substrate a 160 stage gate-driver was measured at FHD rate. cop. 2014 Society for Information Display.

We describe the fabrication and characterization of large-area active-matrix X-ray/photodetector array of high quality using organic photodiodes and organic transistors. All layers with the exception of the electrodes are solution processed. Because it is processed on a very thin plastic substrate of 25 mu;m thickness, the photodetector is only 100 mu;m thick. When combined with an 300-μm-thick X-ray scintillator, this gives a thin, low-weight and shatterproof X-ray detector of ca. 400 mu;m thickness. We demonstrate X-ray imaging under conditions that are used in medical applications. © 2013 Elsevier B.V.

In this study, we report high-quality amorphous indiunrv-galiium-zinc-oxide (a-IGZO) thinfilm transistors (TFTs) fabricated on a polyethylene naphthalate foil using a new back-channel-etch (BCE) process flow. 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 loS'C in order to ensure good overiay accuracy (

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

We have developed a full color flexible top-emission AMOLED display with 80 ppi resolution using In-Ga-Zn-O TFT backplane on PEN foil under the maximum process temperature of 150 oC. Notwithstanding the low processing temperature, the TFTs with SiOx passivation layer show high reliability with VTH shift of less than 0.2 V at 10,000 seconds under bias-stress of -10 V. cop. 2013 Society for Information Display.

In this study, the authors report on high-quality amorphous indium-galliunv-zinc oxide thinfilm transistors (TFTs) based on a single-source dual-layer concept processed at temperatures down to ISCC. The dual-layer concept allows the precise control of local charge carrier densities by varying the 02/Ar gas ratio during sputtering for the bottom and top layers. Therefore, extensive annealing steps after the deposition can be avoided. In addition, the dual-layer concept is more robust against variation of the oxygen flow in the deposition chamber. The charge carrier density in the TFT channel is namely adjusted by varying the thickness of the two layers whereby the oxygen concentration during deposition is switched only between no oxygen for the bottom layer and very high concentration for the top layer. The dual-layer TFTs are more stable under bias conditions in comparison with single-layer TFTs processed at low temperatures. Finally, the applicability of this dual-layer concept in logic circuitry such as 19-stage ring oscillators and a TFT backplane on polyethylene naphthalate foil containing a quarter video graphics array active-matrix organic lightemitting diode display demonstrator is proven.

We demonstrate high performance X-ray imaging detectors on foil suitable for medical grade X-ray imaging applications. The detectors are based on solution-processed organic photodiodes forming bulk-heterojunctions from photovoltaic donor and acceptor blend. The organic photodiodes are deposited using an industrially compatible slot die coating technique with end of line processing temperature below 100° C. These photodiodes have extremely low dark leakage current density of 10-7 mA/cm2 at -2V bias with very high yield and have peak absorption around 550 nm wavelength. We combine these organic photodiodes with high mobility metal oxide semiconductor based thin film transistor arrays with high pixel resolution of 200ppi on thin plastic substrate. When combined with a typical CsI(TI) scintillator material on top, they are well suited for low dose X-ray imaging applications. The optical crosstalk is insignificant upto resolution of 200 ppi despite the fact that the photodiode layer is one continuous layer and is non-pixelated. Low processing temperatures are another key advantage since they can be fabricated on plastic substrate. This implies that we can make X-ray detectors on flexible foil. Those detectors can be mechanically more robust and light weight when compared to amorphous Si based detectors fabricated on glass substrate.

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.

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

Using a concept of asymmetric side gate and main gate, it is shown that it is possible to realize unipolar transport (both p-type and n-type) in a thin-film transistor with a high-performance ambipolar polymer semiconductor. In a complementary inverter, this results in higher noise margin and DC gain.

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.