PECVD silicon-rich nitride and low stress nitride films mechanical characterization using membrane point load deflection

An analysis of the mechanical properties of plasma enhanced chemical vapor (PECVD) silicon nitrides is presented, using micro fabricated silicon nitride membranes under point load deflection. The membranes are made of PECVD silicon-rich nitride and low stress nitride films. The mechanical performance of the bended membranes is examined both with analytical models and finite element simulation in order to extract the elastic modulus and residual stress values. The elastic modulus of low stress silicon nitride is calculated using stress free analytical models, while for silicon-rich silicon nitride and annealed low stress silicon nitride it is estimated with a pre-stressed model of point-load deflection. The effect of annealing both in nitrogen and hydrogen atmosphere is evaluated in terms of residual stress, refractive index and thickness variation. It is demonstrated that a hydrogen rich annealing atmosphere induces very little change in low stress silicon nitride. Nitrogen annealing effects are measured and shown to be much higher in silicon-rich nitride than in low stress silicon nitride. An estimate of PECVD silicon-rich nitride elastic modulus is obtained in the range between 240–320 GPa for deposited samples and 390 GPa for samples annealed in nitrogen atmosphere. PECVD low stress silicon nitride elastic modulus is estimated to be 88 GPa as deposited and 320 GPa after nitrogen annealing

Surface and Bulk Properties of Oxygenated FZ Silicon Wafers for Particle Detector Applications

Oxygenated FZ silicon wafers have been prepared and tested in terms of both gate oxide quality of MOS devices and leakage current of diodes and microstrip detectors. It has been observed that oxygenated wafers, with respect to virgin ones, show an improvement of the gate oxide quality while diode leakage currents remain unaffected. A negative impact on leakage currents can be described to oxygen when a long medium temperature step is present in the process flow

Investigation of oxygenation processes on FZ silicon wafers for particle detector applications

This work is focused on the evaluation of oxygenation processes based on a dedicated high temperature oxidation-diffusion step performed on high resistivity FZ wafers prior to the detector processing sequence.Measurements on detectors and test structures demonstrate that both bulk and surface leakage currents are not significantly affected by the oxygenation initial step.Experimental results also assess the enhanced radiation tolerance of the oxygenated material with respect to the non oxygenated one

Production of ALICE microstrip detectors at ITC-irst

We report on the results from the production of 600 double-sided silicon microstrip detectors for the ALICE experiment. We present the fabrication process and some selected results from the electrical characterization of detectors and test structures. The large amount of experimental data allowed a statistically relevant analysis to be performed. The main technological aspects related to production yield optimization will also be addressed

New MEMS Tweezers for the Viscoelastic Characterization of Soft Materials at the Microscale

As many studies show, there is a relation between the tissue’s mechanical characteristics and some specific diseases. Knowing this relationship would help early diagnosis or microsurgery. In this paper, a new method for measuring the viscoelastic properties of soft materials at the microscale is proposed. This approach is based on the adoption of a microsystem whose mechanical structure can be reduced to a compliant four bar linkage where the connecting rod is substituted by the tissue sample. A procedure to identify both stiffness and damping coefficients of the tissue is then applied to the developed hardware. Particularly, stiffness is calculated solving the static equations of the mechanism in a desired configuration, while the damping coefficient is inferred from the dynamic equations, which are written under the hypothesis that the sample tissue is excited by a variable compression force characterized by a suitable wave form. The whole procedure is implemented by making use of a control system

Fabrication, characterization and modeling of a silicon solar cell optimized for concentrated photovoltaic applications

Silicon is still an interesting material for developing Concentration Photovoltaic (CPV) cells working at low and medium concentration range. In this work we describe modeling, design, fabrication technology and functional characterization of a small-area silicon solar cell suitable for CPV applications up to 200 suns. Two-dimensional (2-D) numerical simulations by a state-of-the-art Technology Computer Aided Design (TCAD) tool adopting calibrated physical models have been performed for both cell design and deep understanding of its performance. Specifically, the simulations have allowed the development and optimization of front contact grid scheme and design of the cell operating under medium concentration. The cell has been tested by means of a novel indoor concentrator system up to 300 suns and a conversion efficiency higher than 22% has been measured, according to numerical simulations. The dependence of short-circuit current on concentration factor has been observed to be super-linear. An excess of short-circuit current at 300 suns of approximately 8% has been measured. The super-linear effect has been investigated by means of numerical simulations and explained in terms of enhanced carrier diffusion length under concentrated light. The dependence of the super-linear effect on the incoming photon wavelength was also observed and discussed, showing that the super-linearity is due to the spectrum portion above 600 nm only

Stiffness Characterization of Biological Tissues by Means of MEMS-Technology Based Micro Grippers Under Position Control

Abstract This paper presents a method for detecting the mechanical stiffness of micro-metric biological tissues by means of compliance tests performed with a MEMS-Technology based microgripper. Thanks to an actuating rotary comb drive working in cooperation with another sensing rotary comb drive, the system is able to recognize the tissue sample stiffness. Such characterization is possible thanks to a proper control system that is applied to the whole mechanical structure

Spectroscopy of photonic bands in two-dimensional macroporous silicon photonic crystals

The dispersion of two-dimensional photonic bands is measured by variable-angle reflectance on macroporous silicon photonic crystals. The dispersion is derived from the position of critical-point-like structures in optical spectra. A comparison between experimental and calculated reflectance shows a very good agreement. The same is found between the photonic bands obtained by plane-wave expansion and the experimental ones. A symmetry analysis yelds the selection rules for excitation of photonic modes at the Brillouin zone center and along the symmetry line