DART-SSPFM multi-imaging of ferroelectric and electrostatic properties of KNN thin film at nanoscale

International audienc

Cartographies DFRT-SSPFM des propriétés ferroélectriques et électrostatiques d'un film mince de KNN

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Electrical induced cracking of PZT films and its effect on electrical properties of piezoelectric capacitors

International audienceLead zirconate titanate, Pb(Zr$_{0.52}$Ti$_{0.48}$)O$_3$ (PZT), offers a high piezoelectric coefficient and is used in many fields of MEMS actuator devices: optics (varifocal lens, micro-mirror), acoustics (micro-speaker), ultrasonics (PMUT), fluidics (inkjet head, micro-pump), and haptics (tactile feedback). In actuator mode, during operation, the piezoelectric film is subjected to an electrical signal resulting in a mechanical displacement. The piezoelectric layer must then show large electrical breakdown strength to prevent electrical failure. Mechanical failure may also occur, but it has been much less studied. In very recent papers, cracking of PZT films, either under mechanical or electrical stresses, has been reported [1]. Despite the appearance of cracks, PZT capacitors remain most often functional, with changed properties though. However, the modified properties are rarely, not to say never, detailed and quantified. In the present study, PZT based capacitors (2 μm thick) were operated under electric field, either bipolar or unipolar with various amplitudes, until cracking. The density of cracks varies as a function of the applied signal conditions. The effect of the cracks on the PZT properties has been evaluated by conducting various electrical tests, before and after cracking: ferroelectric polarization loops, dielectric capacitance curves, leakage currents and piezoelectric measurements. Remnant polarization and maximum polarization tend to increase by almost 100% and 40%, respectively (Figure 1), whereas permittivity and piezoelectric coefficient d$_{33,f}$ decrease down to 20% and 30%, respectively. In addition, XRD measurements show a clear modification of the PZT crystallographic pattern, suggesting that the observed evolution of electrical properties results from a change in domain structure associated with stress relaxation

Electrical induced cracking of PZT films and its effect on electrical properties of piezoelectric capacitors

International audienceLead zirconate titanate, Pb(Zr$_{0.52}$Ti$_{0.48}$)O$_3$ (PZT), offers a high piezoelectric coefficient and is used in many fields of MEMS actuator devices: optics (varifocal lens, micro-mirror), acoustics (micro-speaker), ultrasonics (PMUT), fluidics (inkjet head, micro-pump), and haptics (tactile feedback). In actuator mode, during operation, the piezoelectric film is subjected to an electrical signal resulting in a mechanical displacement. The piezoelectric layer must then show large electrical breakdown strength to prevent electrical failure. Mechanical failure may also occur, but it has been much less studied. In very recent papers, cracking of PZT films, either under mechanical or electrical stresses, has been reported [1]. Despite the appearance of cracks, PZT capacitors remain most often functional, with changed properties though. However, the modified properties are rarely, not to say never, detailed and quantified. In the present study, PZT based capacitors (2 μm thick) were operated under electric field, either bipolar or unipolar with various amplitudes, until cracking. The density of cracks varies as a function of the applied signal conditions. The effect of the cracks on the PZT properties has been evaluated by conducting various electrical tests, before and after cracking: ferroelectric polarization loops, dielectric capacitance curves, leakage currents and piezoelectric measurements. Remnant polarization and maximum polarization tend to increase by almost 100% and 40%, respectively (Figure 1), whereas permittivity and piezoelectric coefficient d$_{33,f}$ decrease down to 20% and 30%, respectively. In addition, XRD measurements show a clear modification of the PZT crystallographic pattern, suggesting that the observed evolution of electrical properties results from a change in domain structure associated with stress relaxation

Total Harmonic Distortion of a Piezoelectric MEMS Loudspeaker in an IEC 60318-4 Coupler Estimation Using Static Measurements and a Nonlinear State Space Model

We propose a method to evaluate the Total Harmonic Distortion generated by a cantilever-based PZT loudspeaker inside an IEC 60318-4 coupler. The model is validated using experimental data of a commercial loudspeaker. Using the time domain equations of the equivalent electrical circuit of the loudspeaker inside the coupler and a state space formulation, the acoustic pressure response is calculated and compared to the measurement of the manufacturer. Next, the stiffness, transduction and capacitance nonlinear functions are evaluated with a Double-Beam Laser Interferometer (DBLI) and a nanoindenter on test devices and on the commercial loudspeaker. By introducing the nonlinear functions into the model as amplitude-dependent parameters, the THD generated by the loudspeaker is calculated and compared to the value provided by the manufacturer. The good agreement between the measurement and the simulation could allow for a rather quick simulation of the performance of similarly designed loudspeakers at the early stage of the design, by only estimating the static linearity of the main nonlinearity sources

KNN lead-free technology on 200 mm Si wafer for piezoelectric actuator applications

International audienceState-of-the-art (K,Na)NbO3 (KNN) films were integrated into MEMS actuator devices in a 200 mm silicon wafer technology environment following industry compatible process. The ferroelectric, dielectric and piezoelectric properties of KNN films with a thickness of 1 µm and 1.9 µm integrated into capacitors were assessed throughout the whole 200 mm wafers. The actuator behavior was highlighted through electromechanical measurements on KNN based devices such as cantilever beams and membranes. KNN was eventually used to actuate micro-mirrors, one of the main piezoMEMS components that may drive the market in the near future. The results demonstrate that KNN technology is promising for replacing lead content PZT technology in piezoelectric MEMS industry

The risk of COVID-19 death is much greater and age dependent with type I IFN autoantibodies

International audienceSignificance There is growing evidence that preexisting autoantibodies neutralizing type I interferons (IFNs) are strong determinants of life-threatening COVID-19 pneumonia. It is important to estimate their quantitative impact on COVID-19 mortality upon SARS-CoV-2 infection, by age and sex, as both the prevalence of these autoantibodies and the risk of COVID-19 death increase with age and are higher in men. Using an unvaccinated sample of 1,261 deceased patients and 34,159 individuals from the general population, we found that autoantibodies against type I IFNs strongly increased the SARS-CoV-2 infection fatality rate at all ages, in both men and women. Autoantibodies against type I IFNs are strong and common predictors of life-threatening COVID-19. Testing for these autoantibodies should be considered in the general population

The risk of COVID-19 death is much greater and age dependent with type I IFN autoantibodies

International audienceSignificance There is growing evidence that preexisting autoantibodies neutralizing type I interferons (IFNs) are strong determinants of life-threatening COVID-19 pneumonia. It is important to estimate their quantitative impact on COVID-19 mortality upon SARS-CoV-2 infection, by age and sex, as both the prevalence of these autoantibodies and the risk of COVID-19 death increase with age and are higher in men. Using an unvaccinated sample of 1,261 deceased patients and 34,159 individuals from the general population, we found that autoantibodies against type I IFNs strongly increased the SARS-CoV-2 infection fatality rate at all ages, in both men and women. Autoantibodies against type I IFNs are strong and common predictors of life-threatening COVID-19. Testing for these autoantibodies should be considered in the general population