Piotr Czarnecki

Evidences of oxygen-mediated resistive-switching mechanism in TiN\HfO2\Pt cells

In this letter, we study the influence of the Pt top-electrode thickness and of the chamber atmosphere during cell operation on the resistive switching of TiN\HfO2\Pt cells. The oxygen permeability of the Pt electrode directly in contact with the atmosphere significantly affects the resistive switching and the resistance states of the cell. The results provide strong experimental indications that the electroforming operation leads to oxygen-vacancy formation and that the subsequent reset operation relies on the available oxygen species in the filament neighborhood. Significant implications with respect to endurance and retention assessment of resistive-switching memory devices are discussed.

An electrostatic fringing-field actuator (EFFA): application towards a low-complexity thin-film RF-MEMS technology

This paper presents a novel electrostatic actuator using fringing fields as the actuation mechanism, i.e. an electrostatic fringing-field actuator or EFFA. The novel device is produced on an insulating substrate in a simple two-mask process involving only one sacrificial layer and one metallization. To demonstrate the EFFA capabilities, we produced and characterized EFFAs in various technological implementations of remarkable simplicity. This simplicity allows a vast flexibility for the processing and as a result strongly eases the integration of the EFFAs into existing technologies. For the basic device, we report a non-de-embedded measured capacitance ratio of 1:3 and a lifetime of more than 107 cycles with 40 V bipolar actuation at 100 Hz in N2 atmosphere. Both the capacitance ratio and the C–V profile were tuned by modifying the technology, e.g. coating the substrate before processing the EFFAs and the design, e.g. switching from clamped-free to clamped–clamped devices. We finally report a complete RF-MEMS technology using the EFFAs as single actuators. Switchable and tunable LC tanks, phase shifters, series and shunt parallel-plate capacitors actuated as relays and capacitive relays are presented to demonstrate the possibilities of this technology.

Influence of the substrate on the lifetime of capacitive RF MEMS switches

We show for the first time that the substrate can influence the lifetime of capacitive RF MEMS switches. We demonstrate that the influence of the substrate should not be ignored. The influence of the environment on the lifetime of a switch is different when it is fabricated on two different substrates. We also present that a switch actuated with a DC voltage lower than the pull-in voltage can pull-in after some time. The goal of the performed experiment was to emphasize the charging of the substrate. The presented results help to understand the substrate charging problem.

New insights into charging in capacitive RF MEMS switches

This paper discusses dielectric charging in electrostatic RF-MEMS switches. We show that more than one charging mechanism can be present and impacts their lifetime. These different mechanisms can cancel, mitigate or enhance each otherpsilas influence on the lifetime, depending on the materials used and on the test conditions. Contrarily to the common understanding of the dielectric charging, we show that charge trapping in the dielectric interposer is not always the dominant charging mechanism leading to the failure. We finally show that bipolar actuation is not a general remedy for charging in electrostatic RF MEMS switches.

Effect of Gas Pressure on the Lifetime of Capacitive RF MEMS Switches

For the first time it is shown that the lifetime of capacitive RF MEMS switches depends on the ambient gas pressure. A change of the pressure causes a change of the electric strength of the gas and as a result electric discharging during the operation can occur. This indicates that insulator charging, the main failure mode in these switches, probably not only occurs upon contact between the top electrode and the insulator, but also without contact, due to electron emission or electrode-gap breakdown.

The influence of the package environment on the functioning and reliability of RF-MEMS switches

This paper discusses the influence of pressure and gas inside a package on the functioning and lifetime of capacitive RF-MEMS switches. It is shown that decreasing the pressure strongly influences the switching speed of a switch, but if it becomes too low it causes anomalous vibration effects. When testing at the same pressure, it is shown that the lifetime of the capacitive switches is higher in a nitrogen environment than in ambient air (lab) environment. These effects are attributed to the humidity of the air and its influence on charge trapping in the insulator, resulting in stiction of the switch bridge. It is also shown that this charge is not stable and that the switch recovers when it is not actuated.

Poly-SiGe-based CMUT array with high acoustical pressure

Capacitive micromachined ultrasound transducers (CMUT) have the potential to enable 3-D ultrasound imaging. This paper reports a novel manufacturable buildup of a CMUT device which is CMOS compatible. The approach allows high density integration and independent optimization of the CMUT device and the integrated electronics. The CMUT device makes use of polycrystalline silicon-germanium (poly-SiGe) as the structural material, in combination with silicon carbide (SiC) as the dielectric layer to allow high electrical field in the transduction gap. Breakdown voltage of above 500V is demonstrated. Transmit pressure normalized to the surface of the transducer is as high as 580kPa for DC and AC voltages of 340 and 75V, respectively. Initial characterization of pulse-echo measurement is also reported.

RF-MEMS technology platform for agile mobile and satellite communications

In the past years, the RF-MEMS activities have focused on the development of generic technology platforms integrating switches as well as tunable and fixed passives components. This is in strict opposition to a former device-centered development of the RF-MEMS technologies. Fruitful efforts were put at IMEC in the reliability analysis and modeling of the devices, the exploration of various packaging scenario and finally the process optimization to allow the handling of the devices throughout the full packaging chain. In this paper, we present several results of these developments. Various architectures of functional narrowband and wideband RF-MEMS capacitive switches are demonstrated, all processed on a single wafer, in the same process flow. The demonstrated working frequencies are 40GHz, 35GHz, 18GHz and 6GHz with measured lifetimes in excess of 107 cycles at 100Hz switching frequency in N2 atmosphere. Representative insertion loss and isolation are respectively better than 0.4dB and 20dB. Finally, we report the realization of a hybrid MEMS/MCM-D filter for GPS-GALILEO band-switching

Optimisation of PECVD poly-SiGe layers for MEMS post-processing on top of CMOS

Poly-SiGe offers an attractive alternative for low temperature MEMS postprocessing above CMOS. This paper illustrates this fact through several investigations made to obtain a material with excellent mechanical properties (low stress, low stress gradient), and electrical properties (low resistivity) for different structural layer thicknesses and deposition techniques. It was also established that these layers are stable with time and temperature variation, thus ensuring long-term stability in the performance of poly-SiGe based MEMS devices.

Metal-bonded, hermetic 0-level package for MEMS

This paper presents a zero-level packaging technology for hermetic encapsulation of MEMS. The technology relies on the “chip capping” of the MEMS using a metallic bond made by means of diffusion soldering of a Cu-Sn system at a temperature of around 250°C. For this, on a “capping wafer” a sealing ring (or bond frame), composed of a double layer of Cu/Sn, is grown, and on the MEMS wafer a matching ring of a single Cu layer is made. Next, the “capping chip” is assembled onto the “MEMS die”, either in a die-to-wafer (D2W) or a wafer-to-wafer (W2W) fashion. The thicknesses of the layers (Cu/Sn and Cu) and the bonding process parameters (temperature and force profile) have been optimized so as to achieve a strong, hermetic package, that remains stable up to temperatures as high as ∼415°C. Leak testing, based on the “membrane deflection method”, revealed that the packages are air tight and He leak tight. No noticeable change of the deflection of the cap (thinned down to 20–50 µm) was observed as a result of pressurizing the packages for 11 days under He at 30 MPa.