A simple and highly reproducible single electron transistor (SET) has been fabricated using gated silicon nanowires. The structure is a metal-oxide-semiconductor field-effect transistor made on silicon-on-insulator thin films. The channel of the transistor is the Coulomb island at low temperature. Two silicon nitride spacers deposited on each side of the gate create a modulation of doping along the nanowire that creates tunnel barriers. Such barriers are fixed and controlled, like in metallic SETs. The period of the Coulomb oscillations is set by the gate capacitance of the transistor and therefore controlled by lithography. The source and drain capacitances have also been characterized. This design could be used to build more complex SET devices.The first and most common Coulomb blockade device is the Single Electron Transistor (SET) made with metallic leads and island, and tunnel oxide barriers 1,2 . It is used as sensitive electrometers 3 or electron pumps allowing to control the transfer of electrons one by one 4,5 . Since then very important efforts have been devoted to fabricate silicon SETs, mostly to integrate SETs together with regular transistors for building logic circuits 6,7 , and more recently for quantum logic experiments with single charge or spin in silicon quantum dots 8,9 . An important challenge is to increase the temperature of operation from the typical sub-kelvin range of original devices up to much higher temperatures. The required size of the island is of the order of the nm, and therefore out of control of current fabrication processes. Researchers took advantage of natural disorder to create such extremely small islands, mostly with constrictions in disordered thin films 10,11,12,13,14 . More recently 15 undulated thin films have been used, as well as pattern-dependent oxidation 16 .We followed another approach based on etched silicon nanowires without constrictions, as pionnered by Tilke et al. 17 and more recently Namatsu et al. 18 , and also Kim et al. 19 and Fujiwara et al. 20 . In the two first cases the formation of a Coulomb island in a nanowire underneath a very large gate was studied. In the two others two gates were defined above a nanowire, each of them acting as a tunable barrier for entering/exiting the single electron box delimited by these gates. Although this scheme allowed logic operations to be performed at 300K 15,16 , it remains a complex architecture since up to 4 gates are needed for proper operation. Our SET is much simpler since it requires a single gate to define the quantum dot, while the barriers are fixed, like in metallic SETs. Periodic Coulomb blockade is observed, with a period solely determined by the surface area of a single gate. It is therefore controlled by lithography, not by disorder. With current state of the art electron beam lithography the limit in operating temperature is of the order of 10 K. The schematics of our device is essentially similar to the original metallic SETs, the tunnel oxide barriers being re-

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Tungsten oxide is shown to be a very promising material for the fabrication of highly selective ammonia sensors. Films of WO 3 were deposited onto a silicon substrate by means of the drop-coating method. Then, the films were annealed in dry air at two different temperatures (300 and 400ЊC). X-ray photoelectron spectroscopy was used to investigate the composition of the films. Tungsten appeared both in WO 2 and WO 3 oxidation states, but the second state was clearly dominant. Scanning electron microscopy results showed that the oxide was amorphous or nanocrystalline. The WO 3 -based devices were sensitive to ammonia vapors when operated between 250 and 350ЊC. The optimal operating temperature for the highest sensitivity to ammonia was 300ЊC. Furthermore, when the devices were operated at 300ЊC, their sensitivity to other reducing species such as ethanol, methane, toluene, and water vapor was significantly lower, and this resulted in a high selectivity to ammonia. A model for the sensing mechanisms of the fabricated sensors is proposed.

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International audienc

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the latter and to achieve extremely high packing density. [9] The understanding of switching mechanisms at device level is a key factor for a technology to be viable at very large scale integration. Different types of resistive memory devices have been studied in the past years such as oxide-based memories (OxRAM) and conductive bridge random access memories (CBRAM). It should be noted that for both technologies it is very challenging to combine good cycling endurance, stable retention and high window margin (WM). Two distinct resistive states can be obtained based on a reversible filament formation (SET operation) and rupture (RESET operation) inside an insulating layer sandwiched between two electrodes; SET operation being the switching from a high resistive state (HRS) to a low resistive state (LRS) and RESET the reverse operation (HRS to LRS). In the case of CBRAM, metal ions coming from top electrode (TE) are introduced in the insulating layer. Working principle is based on a metallic filament formation and dissolution controlling performances. [10] These devices present high WM, relatively low endurance, and poor retention stability. [11,12] In the case of OxRAM, oxygen vacancies creation and annihilation inside the oxide dominates the switching mechanism. [13][14][15] This technology shows low WM combined to high endurance and stable retention. [3,16] While lots of effort have been done lately to improve switching speed and power consumption in RRAM, [17,18] several challenges need to be overcome, namely the high extrinsic (device to device) and intrinsic (cycle to cycle) variability in RRAM characteristics. [7] High WM could potentially help solving this variability by maximizing the ratio of HRS over LRS. Moreover, coupling high WM and high endurance (up to 10 8 cycles required for storage class applications [19] ) remains a critical issue. Combining CBRAM and OxRAM in one hybrid oxide-based CBRAM (hybrid-RRAM (HRRAM)) where filament can be composed of metal ions and oxygen vacancies could offer alternative performances such as high WM coupled with high endurance. Recent studies have identified materials issues in oxide and metal based RRAM. [20,21] However, material properties study is still lacking in HRRAM to guide stack choice (oxide vs electrodes) toward a given application. In a previous work, a trade-off between endurance, window margin, and retention was demonstrated. When comparing various HRRAM electrical performances and filament composition, Here, the impact of copper and oxygen vacancy balance in filament composition as a key factor for oxide-based conductive bridge random access memories (hybrid resistive random access memories (HRRAMs)) performances is investigated. To this aim, several RRAM technologies are studied using various resistive layers and top electrodes. Material analyses allow to highlight the hybrid aspect of HRRAM conductive filament. Density functional theory simulations are used to extract microscopic features and highlight differences from a material point of view. Integr...