Abstract-In this letter, we report for the first time the use of a sheet of cellulose-fiber-based paper as the dielectric layer used in oxide-based semiconductor thin-film field-effect transistors (FETs). In this new approach, we are using the cellulosefiber-based paper in an "interstrate" structure since the device is built on both sides of the cellulose sheet. Such hybrid FETs present excellent operating characteristics such as high channel saturation mobility (> 30 cm 2 /Vs), drain-source current on/off modulation ratio of approximately 10 4 , near-zero threshold voltage, enhancement n-type operation, and subthreshold gate voltage swing of 0.8 V/decade. The cellulose-fiber-based paper FETs' characteristics have been measured in air ambient conditions and present good stability, after two months of being processed. The obtained results outpace those of amorphous Si thin-film transistors (TFTs) and rival with the same oxide-based TFTs produced on either glass or crystalline silicon substrates. The compatibility of these devices with large-scale/large-area deposition techniques and lowcost substrates as well as their very low operating bias delineates this as a promising approach to attain high-performance disposable electronics like paper displays, smart labels, smart packaging, RFID, and point-of-care systems for self-analysis in bioapplications, among others.Index Terms-Cellulose fibers, oxide field-effect transistor (FET), RF magnetron sputtering, thin films.

This work analyzes the role of processing parameters on the electrical performance of GIZO (normalGa2normalO3:normalIn2normalO3:ZnO) films and thin-film transistors (TFTs). Parameters such as oxygen partial pressure, deposition pressure, target composition, thickness, and annealing temperature are studied. Generally, better devices are obtained when low oxygen partial pressure is used. This is related to the damage induced by oxygen ion bombardment and very high film’s resistivity when higher oxygen partial pressures are used. Low deposition pressures and targets with richer indium compositions led to films with high carrier concentration, resulting in transistors with field-effect mobility as high as ∼80cm2∕Vs but poor channel conductivity modulation, becoming ineffective as switching devices. Nevertheless, it is demonstrated that reducing the GIZO thickness from 40to10nm greatly enhances the switching behavior of those devices, due to the lower absolute number of free carriers and hence to their easier depletion. Annealing also proves to be crucial to control device performance, significantly modifying GIZO electrical resistivity and promoting local atomic rearrangement, being the optimal temperature determined by the as-produced films’ properties. For the best-performing transistors, even with a low annealing temperature (150°C) , remarkable properties such as μFE=73.9cm2∕Vs , on∕off ratio≈7×107 , VnormalT≈0.2V , and S=0.29V∕dec are achieved.

Copper oxide (Cu2O) thin films were used to produce bottom gate p-type transparent thin-film transistors (TFTs). Cu2O was deposited by reactive rf magnetron sputtering at room temperature and the films exhibit a polycrystalline structure with a strongest orientation along (111) plane. The TFTs exhibit improved electrical performance such as a field-effect mobility of 3.9 cm2/V s and an on/off ratio of 2×102.

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Transparent conducting oxide has been currently used as electrode [1], with conductivities approaching the metallic ones [2]. The possibility to use these oxides in active applications like TTFTs deposited on plastic substrates [3], ozone and UV sensors [4] and UV light emitting diodes [5] has become a reality. High performance TFTs for full active matrix display applications should have high electron mobility (µ), high on/off current ratio, low threshold voltage [6] and processing at low temperatures (T d ) to be compatible with polymeric substrates. These requirements cannot be fulfilled by the actual dominant crystalline/polycrystalline or amorphous silicon technologies [7]. The first one produces devices with the desired µ but uses high T d , while the second one, although using low T d , the devices exhibit low µ, not compatible with drivers' applications. The emerging organic TFT although presenting all advantages concerning low T d , they still suffer from the fact that their µ are still low (<3 cm 2 /Vs) [8]. To solve these limitations we propose the use of TTFTs based on amorphous oxide semiconductors produced at room temperature and composed of heavy-metal cations [9]. Contrary to amorphous covalent semiconductors where the carrier transport is limited by bulk defects, in these oxides the degenerated band conduction is not band tail limited, but dependent on channel conduction governed by metal cations and vacancies (source of free carriers) that lead to films with high electron mobilities, independent of their structure [10]. To produce films with a high electronic activity, it is preferable to use very thin films (up to 100 nm) based either on amorphous or nanostructured layers, highly compact and dense, with high smooth surfaces, to reduce the role of interface and surface states on carrier transport, as needed in TFTs.In this study we present a fully transparent TFT in which the channel and drain/source regions are based on the same material, binary amorphous In 2 O 3 -ZnO oxides, where the electronic performances can be in-situ tailored through the oxygen partial pressure (PO 2 ) used during the deposition [10]. The a-IZO for the active channel was deposited at room temperature onto borosilicate glass substrate (1 mm thickness) with 100 × 100 mm 2 surface area, coated with a 200 nm sputtered ITO film and a 220 nm atomic layer deposition ATO film, supplied by Planar Systems [11]. The ITO presents an average transmittance of 85%, a resistivity (ρ) of 2.3 × 10 -4 Ω cm, and carrier concentration (n) of 7.7 × 10 20 cm -3 and µ ≥ 36 cm 2 /Vs. The a-IZO films were deposited by rf (13.56 MHz) magnetron sputtering at room temperature, using a ceramic oxide target In 2 O 3 -ZnO (9:1), with a purity of 99.99%.X-ray diffraction measurements were performed at RT in air, using the Cu K α line. The optical transmittance measurements were performed with a double beam spectrophotometer in the wavelength range from 200 nm to 2500 nm.In this paper we demonstrate the use of amorphous binary In 2 O 3 -ZnO oxides simul...

High mobility bottom gate thin film transistors (TFTs) with an amorphous gallium tin zinc oxide (a-GSZO) channel layer have been produced by rf magnetron cosputtering using a gallium zinc oxide (GZO) and tin (Sn) targets. The effect of postannealing temperatures (200, 250, and 300°C) was evaluated and compared with two series of TFTs produced at room temperature (S1) and 150°C (S2) during the channel deposition. From the results, it was observed that the effect of postannealing is crucial for both series of TFTs either for stability as well as for improving the electrical characteristics. The a-GSZO TFTs (W∕L=50∕50μm) operate in the enhancement mode (n-type), present a high saturation mobility of 24.6cm2∕Vs, a subthreshold gate swing voltage of 0.38V/decade, a turn-on voltage of −0.5V, a threshold voltage of 4.6V, and an Ion∕Ioff ratio of 8×107, satisfying all the requirements to be used as active-matrix backplane.

We report the architecture and the performances of a memory based on a single field-effect transistor built on paper able to write-erase and read. The device is composed of natural multilayer cellulose fibers that simultaneously act as structural support and gate dielectric; active and passive multicomponent amorphous oxides that work as the channel and gate electrode layers, respectively, complemented by the use of patterned metal layers as source/drain electrodes. The devices exhibit a large counterclockwise hysteresis associated with the memory effect, with a turn-on voltage shift between 1 and −14.5 V, on/off ratio and saturation mobilities of about 10 4 and 40 cm 2 V −1 s −1 , respectively, and estimated charge retention times above 14 000 h. © 2008 American Institute of Physics. ͓DOI: 10.1063/1.3030873͔Nowadays the microelectronics industry is demanding for inexpensive, lightweight, and disposable memory devices. This has been pushing research toward the use of low cost materials and devices whose structures are easily fabricated at low temperatures and with low energy consumption. This demand is mainly fulfilled by organic devices and several attempts have been made to use them as memories: to write and read information, 1 for random access memory circuits for storing and retrieving information, 2 and nonvolatile memories. 3 Nevertheless, all these organic memory devices still suffer from a low carrier mobility ͑below 3-7 cm 2 V −1 s −1 ͒ that limits the device switching time and exhibit low charge retention times ͑4500 s͒ 3 that restricts their field of applications. Up to now, paper has been mainly used either as substrate in organic thin-film transistors ͑TFTs͒ 4 , logic circuits, 5 and electrochromic displays, 6 or in thin-film flexible Li batteries. 7 Here we show the possibility to use multilayer mechanically compact natural cellulose fibers ͑paper͒ simultaneously as structural support and dielectric in n-type memory field-effect transistors able to writeerase and read ͑WERM-FETs͒. The channel and gate electrode layers are respectively based on active and passive multicomponent amorphous oxides such as gallium indium zinc oxide ͑GIZO͒ 8 and indium zinc oxide ͑IZO͒. 9 The WERM-FETs were fabricated at room temperature in a three step process described elsewhere, 10 using paper from Renova 11 composed by long pine fibers mixed with polyester fibers, embedded in a matrix of an ionic resin and adhesive glue to give the need mechanical stiffness. The paper surface was treated with an amylaceous solution to make it hydrophobic. On one side of the paper sheet ͑55 m thick͒, a 40 nm thick amorphous GIZO ͑Ga 2 O 3 -In 2 O 3 -ZnO; 1:2:1 mol %͒ deposited by rf magnetron sputtering coats the surface of the fibers ͑acting as the channel layer͒. This was followed by e-beam assisted evaporation of the Al or Au source/drain thick electrodes that connect all fibers over the edges of the patterned channel region, using shadow masks with a width-to-length ratio of 2165/ 216 m, see Fig. 1͑a͒. After, the paper is turned u...

The role of order and disorder on the electronic performances of n-type ionic oxides such as zinc oxide, gallium zinc oxide, and indium zinc oxide used as active (channel) or passive (drain/source) layers in thin film transistors (TFTs) processed at room temperature are discussed, taking as reference the known behavior observed in conventional covalent semiconductors such as silicon. The work performed shows that while in the oxide semiconductors the Fermi level can be pinned up within the conduction band, independent of the state of order, the same does not happen with silicon. Besides, in the oxide semiconductors the carrier mobility is not bandtail limited and so disorder does not affect so strongly the mobility as it happens in covalent semiconductors. The electrical properties of the oxide films (resistivity, carrier concentration, and mobility) are highly dependent on the oxygen vacancies (source of free carriers), which can be controlled by changing the oxygen partial pressure during the deposition process and/or by adding other metal ions to the matrix. In this case, we make the oxide matrix less sensitive to the presence of oxygen, widening the range of oxygen partial pressures that can be used and thus improving the process control of the film resistivity. The results obtained in fully transparent TFT using polycrystalline ZnO or amorphous indium zinc oxide (IZO) as channel layers and highly conductive poly/nanocrystalline ZGO films or amorphous IZO as drain/source layers show that both devices work in the enhancement mode, but the TFT with the highest electronic saturation mobility and on/off ratio 49.9cm2∕Vs and 4.3×108, respectively, are the ones in which the active and passive layers are amorphous. The ZnO TFT whose channel is based on polycrystalline ZnO, the mobility and on/off ratio are, respectively, 26cm2∕Vs and 3×106. This behavior is attributed to the fact that the electronic transport is governed by the s-like metal cation conduction bands, not significantly affected by any type of angular disorder promoted by the 2p O states related to the valence band, or small amounts of incorporated metal impurities that lead to a better control of vacancies and of the TFT off current.