Patrick Pons

Voltage and temperature effect on dielectric charging for RF-MEMS capacitive switches reliability investigation

In this paper, we study the effect of stress voltage and temperature on the dielectric charging and discharging processes of silicon nitride thin films used in RF-MEMS capacitive switches. The investigation has been performed on PECVD-SiNx dielectric materials deposited under different deposition conditions. The leakage current was found to obey the Poole–Frenkel law. The charging current decay was found to be affected by the presence of defects which are generated by electron injection at high electric fields. At high temperatures power law decay was monitored. Finally, the temperature dependence of leakage current revealed the presence of thermally activated mechanisms with similar activation energies in all materials.

Dielectric charging in silicon nitride films for MEMS capacitive switches: Effect of film thickness and deposition conditions

Abstract The paper presents a systematic investigation of the dielectric charging and discharging process in silicon nitride thin films for RF-MEMS capacitive switches. The SiN films were deposited with high frequency (HF) and low frequency (LF) PECVD method and with different thicknesses. Metal–Insulator–Metal capacitors have been chosen as test structures while the Charge/Discharge Current Transient method has been used to monitor the current transients. The investigation reveals that in LF material the stored charge increases with the film thickness while in HF one it is not affected by the film thickness. The dependence of stored charge on electric field intensity was found to follow a Poole–Frenkel like law. Finally, both the relaxation time and the stored charge were found to increase with the electric field intensity.

Charging-effects in RF capacitive switches influence of insulating layers composition

Abstract The dielectric charging is one of the major failures reducing the reliability of capacitive switches with electrostatic actuation. Then the control of the charging/discharging processes is a key factor to allow a fast recovering of the dielectric after charging. From transient current measurements on MIM capacitors it is possible to select the best material for RF-MEMS. We have studied different PECVD silicon nitride obtained under low (380 KHz), high (13.56 MHz) or mixed (380kHz/13.56MHz) frequency power supply. The conduction mechanism into the dielectrics has been deduced from current measurements on MIM capacitors. Then the film properties have been studied by infrared measurement in order to identify the chemical bond into the dielectric which can explain the charging behaviour. It was observed that low hydrogen content in the films is in good correlation with electrical quality and kinetic of the charging/discharging processes.

Dielectric charging in radio frequency microelectromechanical system capacitive switches: A study of material properties and device performance

The paper analyze the direct relation between the dielectric polarization mechanisms and the radio frequency microelectromechanical system capacitive switches performance. The dielectric polarization mechanisms are investigated in metal-insulator-metal capacitors with the aid of the thermally stimulated depolarization current method. The performance of microelectromechanical system is studied through the temperature dependence of the bias for the minimum capacitance. The simultaneous assessment allows the discrimination of dipolar and space charge polarization that allows the prediction of the shift of capacitance minimum with temperature.

On the influence of environment gases, relative humidity and gas purification on dielectric charging/discharging processes in electrostatically driven MEMS/NEMS devices

In this paper, we investigate the impact of environment gases and relative humidity on dielectric charging phenomenon in electrostatically actuated micro- and nano-electromechanical systems (MEMS and NEMS). The research is based on surface potential measurements using Kelvin probe force microscopy (KPFM). Plasma-enhanced chemical vapor deposition (PECVD) silicon nitride films were investigated in view of applications in electrostatic capacitive RF MEMS switches. Charges were injected through the atomic force microscope (AFM) tip, and the induced surface potential was measured using KPFM. Experiments have been performed in air and in nitrogen environments, both under different relative humidity levels ranging from 0.02% to 40%. The impact of oxygen gas and hydrocarbon contaminants has been studied for the first time by using different gas purifiers in both air and nitrogen lines. Voltage pulses with different bias amplitudes have been applied during the charge injection step under all investigated environmental conditions in order to investigate the effect of bias amplitude. The investigation reveals a deeper understanding of charging and discharging processes and could further lead to improved operating environment conditions in order to minimize the dielectric charging. Finally, the nanoscale KPFM results obtained in this study show a good correlation with the device level measurements for capacitive MEMS switches reported in the literature.

Kelvin probe microscopy for reliability investigation of RF-MEMS capacitive switches

In this work, we investigate the charging and reliability of interlayer dielectric materials that are used in the fabrication process of advanced RF-MEMS switches. In particular, the charge stored on the surface of a dielectric and the dynamic of this charge at nanometric scale are studied. More attention is given to the decay of the deposited charge by a variety of means: (1) surface conduction, (2) surface charge spreading due to self repulsion and (3) charge injection in the bulk of dielectric material. Kelvin force microscopy (KFM) measurements were performed for various injection time and bias voltage. These results suggest a dynamic charge and allow to predict the amount of charge injected into the dielectric.

Assessment of dielectric charging in electrostatically driven MEMS devices: A comparison of available characterization techniques

Abstract The present work investigates the results of different characterization methods for the dielectric charging phenomenon applicable to metal–insulator–metal (MIM) capacitors and electrostatically actuated micro-electro-mechanical-systems (MEMS). The discharge current transients (DCT), thermally stimulated depolarization current (TSDC) and Kelvin probe force microscopy (KPFM) assessment methods have been applied to either MIM capacitors or electrostatic capacitive MEMS switches or both. For the first time, the KPFM methodology has been used to create a link between the results obtained from the DCT and TSDC techniques applicable for MIM and the results from MEMS switches. The comparison shows that the application of KPFM method to MIM and MEMS leads to the same results on the electrical properties of the dielectric material. This provides a novel powerful tool for the assessment of dielectric charging for MEMS switches using MIM capacitors which have much simpler layer structure. On the other hand the TSDC method reveals a continuous distribution of relaxation time constants, which supports the dependence of relaxation time constant calculated for MEMS on the duration of the observation time window.

Frequency Scalable Model for MEMS Capacitive Shunt Switches at Millimeter-Wave Frequencies

This paper presents an approach to RF microelectromechanical systems (MEMS) capacitive shunt switch design from K-band up to W-band based on the scalability of the RF MEMS switch with frequency. The parameters of the switchs equivalent-circuit model also follow scaling rules. The measurement results of the fabricated switches show an excellent agreement with simulations that allow to validate the MEMS model in the entire band from 20 up to 94 GHz. This model is going to be used in the phase shifter circuit design for antenna array applications. The first 60-GHz phase shifter results are also reported here.

Radio frequency pressure transducer

A novel system is reported here for the pressure measurement at microwave and millimetre-wave frequencies. This method consists in using a radio frequency transducer based on RF resonator. Accurate determination of the pressure is expected.

A systematic reliability investigation of the dielectric charging process in electrostatically actuated MEMS based on Kelvin probe force microscopy

This paper presents a comprehensive investigation for the dielectric charging problem in electrostatically actuated microelectromechanical system (MEMS) devices. The approach is based on Kelvin probe force microscopy (KPFM) and targets, in this specific paper, thin PECVD silicon nitride films for electrostatic capacitive RF MEMS switches. KPFM has been employed in order to mimic the potential induced at the dielectric surface due to charge injection through asperities. The effect of dielectric thickness has been investigated through depositing SiNx films with different thicknesses. Then, in order to simulate the different scenarios of dielectric charging in real MEMS switches, SiNx films have been deposited over thermally grown oxide, evaporated gold and electroplated gold layers. Also, the effect of the deposition conditions has been investigated through depositing dielectric films using low and high frequency PECVD methods. The investigation reveals that thin dielectric films have larger relaxation times compared to thick ones when the same injection bias is applied, independently of the substrate nature. For the same SiNx film thickness, the decay time constant is found to be smaller in dielectric films deposited over metallic layers compared to the ones deposited over silicon substrates. Finally, the material stoichiometry is found to affect the surface potential distribution as well as the relaxation time constant.