C. Malhaire

Modified free vibrating beam method for characterization of effective e31 coefficient and leakage resistance of piezoelectric thin films

A modified free vibrating beam method has been developed in order to characterize the effective e31 piezoelectric transversal coefficient and the leakage resistance of piezoelectric thin films deposited onto a silicon beam. The main advantage of this method is that it requires no extra electrical measurements. Experiment was realized on lead zirconate titanate thin films.

Effect of clamping conditions and built-in stresses on the thermopneumatic deflection of SiO2/Si membranes with various geometries

Abstract Built-in stresses are known to induce deflections in microstructures such as composite membranes. The thermoelastic behaviour of large square SiO 2 /Si membranes with a side length from 3 to 7.5 mm, a Si thickness in the [7.7–50] μm range and a SiO 2 thickness up to 1.5 μm, was studied by optical profilometry. A very satisfactory agreement within 10% has been found between the experimental and the simulated deflections of prestressed SiO 2 /Si membranes. However, clamping conditions have been found to play a major role in built-in stress relaxation. This tendency was confirmed by Finite Element Modelling. Oxidized (up to 1.5 μm) and bare Si membranes with thicknesses from 7.7 to 50 μm were studied under pressure in the [0–1] bar range. We observed that the membrane stiffness is affected by the oxide depending on SiO 2 /Si thickness ratio. Finally, F.E.M. results are in good agreement for various membrane geometries, and the interest of this tool for the design of packaging structures is shown.

Micro Tensile Tests on Aluminium Thin Films: Tensile Device and In Situ Observations

The results of micromechanical tensile experiments performed on thin aluminum samples are presented and discussed. The micro tensile test system and the design of the samples, based on finite element modeling (FEM), and their production by micromachining are briefly described. Some examples of the stress strain curves are presented. The Youngs modulus and critical parameters (flow and rupture stress and strains) are reported. The micro structural changes induced by the tensile experiment were observed during and after the testing by scanning electron microscopy (SEM) and transmission electron microscopy (TEM).The results of micromechanical tensile experiments performed on thin aluminum samples are presented and discussed. The micro tensile test system and the design of the samples, based on finite element modeling (FEM), and their production by micromachining are briefly described. Some examples of the stress strain curves are presented. The Youngs modulus and critical parameters (flow and rupture stress and strains) are reported. The micro structural changes induced by the tensile experiment were observed during and after the testing by scanning electron microscopy (SEM) and transmission electron microscopy (TEM).

Effect of Thermoelastic Stress on the Pressure Response of a Composite SiO 2 /Si Membrane

The layout design of membrane-based sensors such as Silicon On Insulator micromachined pressure sensors requires the knowledge of the mechanical behavior of the complete structure as a function of pressure and temperature. Unfortunately, as a result of thermal mismatch, large stresses usually exist in composite SiO 2 /Si membranes that significantly affect the pressure response of such sensors, We present here an original study on the 3D-FEM modeling (ANSYS) of pre-stressed SiO 2 /Si membranes submitted to pressure. The model of thermoelastic stress (without any applied pressure) has been first validated by optical profilometry deflection measurements. 2.94 mm width membranes with Si thickness varying from 10.7 to 19.3 μm, as measured by FT-IR, and covered with 1.46 μm thick thermal oxide grown at 1130°C, have been studied. Thermoelastic deflections from I to 25 μm have been measured for decreasing Si thickness in agreement with the simulation. The simulated longitudinal stress relaxation over the oxide varies from 5 to 40 MPa between the membrane center and the frame when decreasing membrane thickness. Under pressure (10 and 100 mbar) and for a 19.3 μm thick composite membrane (0.5 )μm thick oxide), the calculated strains can exceed by 20% that of a bare Si one, due to a lower overall stiffness produced by the oxide compressive stress.

Comparison of Bulge Test and Point Deflection Methods for the Mechanical Characterisation of Submicron Thick Composite Membranes

The aim of this work is to compare two methods for the determination of thin films Youngs modulus and stress state: the bulge test and the point-deflection methods. The tested structures are silicon nitride and bilayers silicon nitride/silicon oxide membranes with thicknesses down to 100 nm. We report new experimental results for different shapes (square or rectangular) and dimensions.

Stress and Stress Relaxation Study of Sputtered PZT Thin Films for Microsystems Applications

Residual stresses in thin films play an important role in the mechanical behaviour of MEMS. In this paper we present a study of the stress and its relaxation for the PZT films, and associated electrodes, deposited on oxidized silicon substrates. The stresses were calculated from the bending plate method and the Stoneys equation. The radius of curvature were measured by optical profilometry before and after films deposition. The substrates (180 μm Si + 0.66 μm thermal SiO 2 ) were coated with sputtered Ti (20 nm) and Pt (200 nm) used as bottom electrode. The global stress in the Ti/Pt layer was found compressive (−1.29 GPa) after deposition and tensile (465 MPa) after annealing (400°C, 30s, Ar). A 0.55 μm thick PZT layer was RF-magnetron sputtered and crystallized by a RTA (700°, 30s, Air). The as-deposited PZT films exhibited a little tensile stress of 43 MPa. After annealing, a tensile stress value of 363 MPa was found. Finally, we observed that the stress of the whole multilayer showed a decrease as a function of time. In order to explain this phenomenon, depth profile of each component of the PZT layer were obtained by Secondary Ion Mass Spectrometry (SIMS). This time-dependent stress relaxation was then correlated to a lead and oxygen migration across the PZT layer.