Dario Della Sala

A Two-Pass Excimer Laser Annealing Process to Control Amorphous Silicon Crystallization

A new approach to control the lateral-growth mechanism of polycrystalline silicon films through appropriate spatial modulation of the absorbed laser energy and with a two-pass excimer laser annealing process is presented. In the first pass, spatial modulation of the light intensity has been achieved by irradiating the precursor amorphous silicon films through a patterned mask in contact with the sample, triggering the lateral growth of grain in excess of 1 µm. During the second pass of the process, the film is reirradiated without the mask and the laterally grown grains can be used as seeds and can be propagated to crystallize the film uniformly. With optimized mask patterns the sample area can be fully covered with laterally grown grains.

TinyNose: Developing a wireless e-nose platform for distributed air quality monitoring applications

In this work we present the development and proof of concept testing of a protoype wireless e-nose (w-nose) architecture capable of mesh shaped networking. The proposed w-nose is based on a TelosB by Crossbow Inc. and custom, power aware, TinyOS based components for data gathering and local processing. Sensor nodes are equipped with a small array of nonconductive polymer/CB based chemiresistors operating at room temperature for VOCs indoor monitoring. A properly developed conditioning stage board connects the sensor array to the microcontroller ADC. A single w-nose has been tested in a controlled test chamber for terpenes discrimination, while networked motes operation have been demonstrated in ad-hoc small testing facilities for acetic acid spill detection.

Electrical Stress Degradation of Small-Grain Polysilicon Thin-Film Transistors

This paper is focused on the stability of n-channel laser-crystallized polysilicon thin-film transistors (TFTs) submitted to a hydrogenation process during the fabrication and with small grains dimension. With the aid of numerical simulations, we investigate the effects of static stress using two types of procedures: the on stress and the hot carrier stress. Results show that the variations of trap state density into the whole polysilicon layer and not only near the drain junction are responsible for the degradation of TFTs performances in both the two types of stress and that the interface trap states play a negligible role compared to the bulk trap states

Transport properties of plasma-deposited amorphous silicon dioxide

Abstract Electronic quality a-SiO 2 have been deposited by PECVD showing high breakdown fields and low trapping probability down to thickness of 16 nm. The transport properties of this material have been analyzed. The Fowler-Nordheim mechanism has been ruled out due a marked temperature sensitivity of the current around room temperature. On the other hand thermally activated transport, such as Schottky or Frenkel-Poole mechanisms, fit reasonably well the experimental data. However a better fit of the overall data seems to support the Schottky as the main transport mechanism in our materials.

Characterization of thin amorphous silicon films with multiple internal reflectance spectroscopy

Infrared multiple internal reflection (MIR) spectroscopy has been applied here to the characterization (ex situ) of thin amorphous silicon layers on crystalline silicon substrates. The specimens are tightly clamped against a Ge prism with 45° bevel angle for the entrance and exit sides, allowing for up to 25 multiple internal reflections. This greatly enhances the thin‐film absorption, and the stretching bands of SiHn bonds in amorphous Si are detected in a range of film thickness from 3 to 600 nm. Very thin films (with thickness less than 50 nm) exhibit a different hydrogen bonding compared to the thin ones, due to hydrogenated sublayers that are not visible in IR spectra for larger film thickness. Sublayers are found both at the film/substrate interface and at the film free surface. Another transitional layer, with increased concentration of SiH2 groups and considerably less than 30 nm, is found at the film/substrate interface. MIR is also applied to study the step‐by‐step etching in CF4/O2 of a 70‐nm‐t...

Applications of thin film semiconductors

The increasing use of thin film semiconductors in device applications has forced the change to new deposition and processing technologies, compared to the familiar wafer semiconductor technologies. In spite of the lower performance, the process flexibility allowed with low temperature processing has opened the way to quite new products, based on thin film semiconductors.