This paper studies the effect of atomic layer deposition (ALD) temperature on the performance of top-down ZnO nanowire transistors. Electrical characteristics are presented for 10-μm ZnO nanowire field-effect transistors (FETs) and for deposition temperatures in the range 120°C to 210°C. Well-behaved transistor output characteristics are obtained for all deposition temperatures. It is shown that the maximum field-effect mobility occurs for an ALD temperature of 190°C. This maximum field-effect mobility corresponds with a maximum Hall effect bulk mobility and with a ZnO film that is stoichiometric. The optimized transistors have a field-effect mobility of 10 cm2/V.s, which is approximately ten times higher than can typically be achieved in thin-film amorphous silicon transistors. Furthermore, simulations indicate that the drain current and field-effect mobility extraction are limited by the contact resistance. When the effects of contact resistance are de-embedded, a field-effect mobility of 129 cm2/V.s is obtained. This excellent result demonstrates the promise of top-down ZnO nanowire technology for a wide variety of applications such as high-performance thin-film electronics, flexible electronics, and biosensing.

Abstract-Top-down fabrication is used to produce ZnO nanowires by remote plasma atomic layer deposition over a SiO 2 pillar and anisotropic dry etching. Nanowire field-effect transistors (FETs), with channel lengths in the range of 1.3-18.6 µm, are then fabricated using these 80 nm × 40 nm nanowires. Measured electrical results show n-type enhancement behavior and a breakdown voltage ≥75 V at all channel lengths. This is the first report of high-voltage operation for ZnO nanowire FETs. Reproducible well-behaved electrical characteristics are obtained, and the drain current scales with 1/L, as expected for long-channel FETs. A respectable I ON /I OFF ratio of 2 × 10 6 is obtained.Index Terms-Atomic layer deposition (ALD), field-effect transistor (FET), nanowire, remote plasma, top-down fabrication, ZnO.

a b s t r a c tThis paper describes a systematic approach to analyze the simultaneous impact of various reactant plasma parameters of remote plasma enhanced ALD (PEALD) on the ZnO thin film properties. Particular emphasis is placed on the film stoichiometry which affects the electrical properties of the thin film. Design of Experiment (DOE) is used to study the impact of the oxygen plasma parameters such as the RF power, pressure and plasma time to realize semiconductor quality of ZnO thin film. Based on the optimized plasma condition, staggered bottom-gate TFTs were fabricated and its electrical characteristics were measured.

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Many micro electromechanical systems (MEMS) require a vacuum or controlled atmosphere encapsulation in order to ensure either a good performance or an acceptable lifetime of operation. Two approaches for wafer-scale zero-level packaging exist. The most popular approach is based on wafer bonding. Alternatively, encapsulation can be done by the fabrication and sealing of perforated surface micromachined membranes.In this paper, a sealing method is proposed for zerolevel packaging using a thin film reflow technique. This sealing method can be done at arbitrary ambient and pressure. Also, it is self-aligned and it can be used for sealing openings diectly above the MEMS device. It thus allows for a smaller die area for the sealing ring reducing in this way the device dimensions and costs.The sealing method has been demonstrated with reflowed aluminium, germanium, and boron phosphorous silica glass. This allows for conducting as well as nonconducting sealing layers and for a variety of allowable thermal budgets. The proposed technique is therefore very versatile.