Low-temperature and low-voltage, solution-processed metal oxide n-TFTs and flexible circuitry on large-area polyimide foil

In this article, we report on high-performance solution-based n-type metal oxide TFTs processed directly on polyimide foil and annealed at 250 °C. Saturation mobilities exceeding 2 cm²/(Vs) and Ion/Ioff ratios beyond 108 have been achieved. Using these oxide n-TFTs, fast and low-voltage flexible circuitry is presented. Furthermore, a complete 8-bit RFID transponder chip, containing 294 oxide n-TFTs has been fabricated. Both high-speed and low-voltage operation makes the presented oxide n-TFT technology suited for both the pixel driving and embedded line-drive circuitry at the borders of flexible AMOLED displays

Hybrid Oxide-Organic Complementary Thin-Film Semiconductor Technology on Foil (Hybride oxide-organische complementaire dunne-film halfgeleidertechnologie op folie)

The realization of fast, robust and low-power integrated circuits on plastic foil are hard to achieve with today's unipolar (p-type only) organic thin-film technology. Only a technology of complementary logic at low temperatures can result in a further breakthrough.Owing to the electronic structure and ionic bonding nature, n-type metal-oxides (such as ZnO, In2O3, and InGaZnO) have unique properties such as large bandgaps, wide controllability of carrier concentration, and great flexibility in impurity doping while still retaining reasonably high carrier mobility.Compared to organic n-type semiconductors, higher mobilities and better stability are achieved with metal-oxide semiconductors. Therefore, the most realistic approach for complementary logic is the integration of organic p-type and metal-oxide n-type thin-film transistors. Combining both types of transistors on plastic foil with reasonable performance and high density in one single technology was the main goal of this Ph.D. Two generations hybrid oxide-organic complementary technologies have been developed, respectively on PI and PEN foil, based on solution-processed oxide n-type and organic p-type transistors. The process temperature was limited to 150 - 250C and finally resulted in a few complex digital circuit demonstrators such as a 96-bit RFID transponder chip on PEN foil, operating at 13.56 MHz with bi-directional communication, and a 8-bit thin-film microprocessor with print-programmable read-only memory, comprising of 4356 transistors. To date, only a limited amount of candidate p-type oxide semiconductors have been identified. In this work, we showed that high performance p-type tin monoxide (SnO) TFTs could be obtained by thermal vacuum evaporation. This broadens the view on complementary thin-film logic towards fully oxide-oxide integration schemes.The understanding of charge tranport in metal-oxide TFTs is of primary importance in the evolution towards more stable and higher performance devices. The temperature dependence of transistor mobility was therefore studied for both n- and p-type oxide TFTs. We obtained a better insight in the conduction mechanisms and found one single measure to judge the quality of disordered solution-based n-type oxides, being the Meyer-Neldel temperature. In addition we derived the density of localized tail states distribution in p-type SnO, based on an analytical model for hopping transport and Hall effect measurements.status: publishe

Solution-processed and low-temperature metal oxide n-channel thin-film transistors and low-voltage complementary circuitry on large-area flexible polyimide foil

High-performance solution-based n-type metal oxide thin-film transistors (TFTs), fabricated directly on polyimide foil at a post-annealing temperature of only 250 °C, are realized and reported. Saturation mobilities exceeding 2 cm²/(Vs) and on-to-off current ratios up to 108 are achieved. The usage of these oxide n-type TFTs as the pixel drive and select transistors in future flexible active-matrix organic light-emitting diode (AMOLED) displays is proposed. With these oxide n-type TFTs, fast and low-voltage n-type only flexible circuitry is demonstrated. Furthermore, a complete 8-bit radio-frequency identification transponder chip on foil has been fabricated and measured, to prove that these oxide n-type TFTs have reached already a high level of yield and reliability. The integration of the same solution-based oxide n-type TFTs with organic p-type TFTs into hybrid complementary circuitry on polyimide foil is demonstrated. A comparison between both the n-type only and complementary elementary circuitry shows the high potential of this hybrid complementary technology for future line-drive circuitry embedded at the borders of flexible AMOLED displays

Bi-directional communication in an HF hybrid organic/solution-processed metal-oxide RFID tag

A bidirectional communication protocol allows radio-frequency identification (RFID) tags to have readout of multiple tags in the RF field without collision of data. In this paper, we realized bidirectional communication between a reader system and thin-film RFID tag by introducing a novel protocol for the uplink communication. Amplitude modulation on the 13.56-MHz base carrier is used to transmit the uplink clock, whereas the data is modulated by varying pulsewidths on this clock. The technology for the thin-film RFID tags combines metal-oxide n-type transistors with organic p-type transistors resulting in a hybrid complementary technology flow. The design of the RFID tag comprises of two metal-oxide transistor rectifiers and a comparator to decode the data transmitted by the reader and different code generators that send 8 bits or 96 bits to the reader.status: publishe

Solution-processed and low-temperature metal oxide n-channel thin-film transistors and low-voltage complementary circuitry on large-area flexible polyimide foil

High-performance solution-based n-type metal oxide thin-film transistors (TFTs), fabricated directly on polyimide foil at a post-annealing temperature of only 250 °C, are realized and reported. Saturation mobilities exceeding 2 cm²/(Vs) and on-to-off current ratios up to 108 are achieved. The usage of these oxide n-type TFTs as the pixel drive and select transistors in future flexible active-matrix organic light-emitting diode (AMOLED) displays is proposed. With these oxide n-type TFTs, fast and low-voltage n-type only flexible circuitry is demonstrated. Furthermore, a complete 8-bit radio-frequency identification transponder chip on foil has been fabricated and measured, to prove that these oxide n-type TFTs have reached already a high level of yield and reliability. The integration of the same solution-based oxide n-type TFTs with organic p-type TFTs into hybrid complementary circuitry on polyimide foil is demonstrated. A comparison between both the n-type only and complementary elementary circuitry shows the high potential of this hybrid complementary technology for future line-drive circuitry embedded at the borders of flexible AMOLED displays

Bidirectional Communication in an HF Hybrid Organic/Solution-Processed Metal-Oxide RFID Tag

The ambition of printing item-level RFID tags is one of the driving forces behind printed electronics research. Organic RFID tags have been shown, initially using p-type organic semiconductors [1-4]. The introduction of n-type organic semiconductors with reasonable performance made organic CMOS conceivable [5] and organic CMOS RFID tags were shown [6]. However, all currently reported organic RFID tags are based on a tag-talks-first principle: as soon as the tag gets powered from the RF field, its code is transmitted at a data rate determined by an internal ring oscillator. Practical RFID systems will need to be able to read multiple RFID tags within the reach of the reader antenna. Existing anti-collision protocols implemented in organic RFID tags [2,4] are limited to about maximum 4 tags and come at the cost of a slow reading time. In this paper, we for the first time realize a reader-talks-first low-temperature thin-film transistor (TFT) RFID circuit. We use a complementary hybrid organic/oxide technology. As organic transistors with reasonable channel lengths ( >2 um) have a cut-off frequency below 13.56MHz, the base carrier frequency of HF communication, present technologies on foil do not yet allow to extract the circuit clock as a fraction of the base carrier. We solve this by introducing an original uplink (reader-to-tag) scheme, in which a slow clock (compatible with our transistors' speed) is transmitted as amplitude-modulation on the base carrier while data is encoded on this clock by pulse width modulation (PWM).status: publishe