Laurent Ventura

Leakage current evolution versus dielectric thickness in lead zirconate titanate thin film capacitors

In this paper, the evolution of lead zirconate titanate (PZT) capacitor leakage current mechanism as a function of dielectric thickness has been investigated. It has been pointed out that PZT leakage current switches from Schottky to Poole–Frenkel conduction mechanisms as PZT thickness decreases. The leakage current evolution seems to be dependant on the presence of a dead layer at metal/PZT interface. The dead layer thickness is estimated at about 40 nm. The switch from an interface limited conduction mode to a bulk limited mode can be attributed to the presence of a higher defect concentration in the dead layer in comparison with PZT bulk.

Lateral gettering of iron by cavities induced by helium implantation in silicon

Lateral gettering has been studied by introducing cavities in the periphery of large active devices. Cavities were induced by helium implantation followed by a thermal treatment on samples previously contaminated by iron. Those cavities are known to be efficient to trap metallic impurities in silicon by chemisorption. The iron distribution in samples of 6×6 mm2 area has been monitored by measuring current versus voltage characteristics and interstitial iron concentrations by deep level transient spectroscopy on Schottky diodes uniformly distributed. A symmetrical iron distribution has been observed with a decreasing concentration close to the gettering region. This lateral gettering is enhanced with increasing thermal budget. Extensions of several millimeters can be obtained allowing applications in power device technology.

Modeling of a New SOI Bidirectional Bipolar Junction Transistor for Low-Loss Household Appliances

In this paper, a new monolithic bidirectional bipolar junction transistor with full turn-off control is studied due to technology computer-aided tools. The structure is built on a symmetrical transistor using silicon-on-insulator technology, which functionality relies on reduced surface field and base shielding effects. These concepts allow high drift doping concentrations and a thin and/or lowly doped base. Such a structure is suitable for bidirectional household appliances within a confined environment where power dissipation is a critical parameter.

Percolation theory applied to PZT thin films capacitors breakdown mechanisms.

Abstract Time-Dependent Dielectric Breakdown (TDDB) mechanisms remain the key issue to understand in order to enhance the reliability of new capacitors technologies. In this work we tried to model capacitors failure mechanism according to percolation theory, in agreement with the statistical behavior of PZT capacitors times to breakdown ( t bd ). The role of microstructural defects such as interlayers and cavities in failure mechanism has been emphasized.

Impact of Lanthanum on PZT Resistance Degradation

This work presents the impact of lanthanum doping on PZT leakage current behavior by comparing the amplitude of the maximum Schottky barrier lowering between PZT and lanthanum doped PZT (PLZT). PZT and PLZT films have been also estimated in terms of capacitors reliability. The time to breakdown distribution obtained with PLZT capacitors drifts by a factor 2.5, which tends to demonstrate also the benefits of lanthanum doping on improving reliability.

Deep trench etching combining aluminum thermomigration and electrochemical silicon dissolution

A micromachining technique for silicon deep anisotropic etching and isolating porous silicon structures is developed. This original method combines aluminum thermomigration and silicon electrochemical etching. In this way, we have generated high aspect ratio trenches and porous silicon isolating regions as well, through the entire thickness of the wafer. In order to evaluate our method, we performed etching rate measurements varying the current density. A maximum value of 22μm∕min has been already measured. The interest of the method in terms of cost and structures diversity is also justified.

Gettering on Cavities Induced by Helium Implantation in Si: The Case of Boron

In this paper, we shed light on the strong interaction between the cavity layer induced by helium implantation and boron. First, we present the impact of the He gettering step on a boron-diffused profile. In order to study the boron-cavity interaction, we used uniformly boron-doped wafers implanted with a high dose of helium and annealed using conventional furnace annealing as well as rapid thermal annealing. Then, to avoid any precipitation phenomena, conditions were chosen such that the boron solid solubility value was not exceeded. Our experimental results indicate a large trapping of boron within the cavity layer that occurs at the early stage of the annealing. A quantitative study of the gettered dopant fraction has been performed. These results enable us to have a better understanding of this interaction of the He-gettering step with boron atoms, which are of great interest for device applications.

Macroporous Silicon Electrochemical Etching for Gas Diffusion Layers Applications: Effect of Processing Temperature

MEMS technology requires low cost techniques to permit large scale fabrication for production. Porous silicon (PS) can be used in different manner to replace standard expensive etching techniques like DRIE (Deep Reactive Ion Etching). To perform same process quality as the latter, one need to understand how different parameters can influence porous silicon properties. We investigate here local formation of macroporous silicon on 2D and 3D silicon substrates. The blank substrate is a low doped (26–33 Ω cm) n type 6 inches silicon wafer. Then, an in situ phosphorus-doped polycrystalline silicon (N+ Poly-Si) is deposited on a thermal oxide layer to delimit the regions to be etched. Porous silicon is obtained afterwards using electrochemical anodization in a hydrofluoric acid (HF) solution. The effect of the temperature process on Si-HF electrochemical system voltamperometric curves, macropores morphology and electrochemical etch rates is more specifically studied. Moreover, permeation of porous substrates to hydrogen is studied after various anodization post-treatments such as KOH and HF wet etching or after a thin gold layer deposition used as current collector in micro fuel cells.

Improvement of a bidirectional field effect transistor (FET) switch with less loss

In this paper, we suggest a new behaviour for a MOSFET bidirectional switch for AC mains application. We use two transistors of high voltage Power MOSFETs new technology based on the CoolMOS, one to control the forward current, and the second one to short-circuit the complementary diode, thus, for the first time, significantly decrease its power dissipation. For that, we must improve the power transistors with the low switching losses (RDS(on)).

Cavity origin and influence on reliability in lead zirconate titanate thin film capacitors

This paper deals with the origin of void defects in lead zirconale titanate (PZT) microstructure, appearing after top electrode postdeposition heat treatment. The process conditions of void apparition are especially investigated, as well as the consequences of these defects on capacitor’s electrical properties. We point out that structures presenting the biggest cavities exhibit the shortest time to breakdown (tbd). This result indicates that cavities might play an important role in PZT capacitor degradation mechanisms.