Thin-film getter integration is one of the key technologies enabling the development of a wide class of MEMS devices,
such as IR microbolometers and inertial sensors, where stringent vacuum requirements must be satisfied to achieve the
desired performances and preserve them for the entire lifetime. Despite its importance, the question about lifetime
prediction is still very difficult to answer in a reliable way. Here we present an experimental approach to the evaluation
of lifetime, based on an accelerated life test performed varying both the storage conditions and the getter area. A test
vehicle based on a resonator device was used. The hermeticity was evaluated by means of specific leak testing, while
MEMS behavior during the ageing test was studied monitoring device functional parameters and by residual gas analysis
(RGA). Unexpected results were observed leading to the discovery that methane is pumped by the getter below 100°C.
These results served as the inputs of a suitable model allowing extrapolating the device lifetime in operating? conditions,
and pointed out that RGA is an essential tool to correctly interpret the aging tests.
Several optical methods have been developed for the measurement of in-plane vibration of microscopic objects. However most of them need a scattering surface or a specific surface structuring. A low cost method which has not these limitations is optical stroboscopic microscopy combined with image processing by optical flow techniques. Previous works have shown that a nanometric sensitivity can be obtained. In this paper, we investigated several subpixel image processing methods for in-plane vibration measurements of MEMS by this technique. Emphasis was put on whole displacement field measurements and on fast algorithms able to process a large sequence of images without the need of a multi-resolution approach to get local vibration amplitudes. It is notably shown that use of spatiotemporal regularity between images is an efficient way to reduce noise and that a resolution in the 0.01 - 0.03 pixel range can be achieved. Results are applied to in-plane vibration local measurements in two perpendicular directions at video rate as well as to full-field mapping of in-plane vibration mode of electrostatically actuated MEMS devices in SOI technology.
This paper is dedicated to a global study of large amplitude effects of electrostatically driven microresonators. Special attention is given to the electrostatic soft spring effect. A theoretical description of the amplitude-induced soft spring effect is given to an electrostatically driven parallel-plate type resonator. A coefficient representing the beam mode shape is introduced, for a clamped-clamped beam resonator. Electrostatic soft spring effect is combined with hard spring effect to highlight the possibility of obtaining a design criteria for compensating the two effects. Hysterisis due to nonlinear forces are addressed, and a critical amplitude is given. A numeric simulator based on MATLAB/Simulink is developed to highlight the electrostatic soft spring effect. Three prototypes with different geometries, which represent each a typical case, are fabricated on an SOI wafer. The design criteria has been compared with measurements obtained with prototypes and experimental results showed good agreements with theory and simulations.
This paper is dedicated to an electronic oscillator designed to control a MEMS (Micro-Electro-Mechanical System) sensor based on a clamped-clamped silicon micro-beam resonator. Due to the high-temperature environment (200°C) and the MEMS specificities, a specific architecture (MRC transimpedance) was implemented in a standard CMOS technology to improve the robustness and to enable the compensation of drifts due to the technologies used for both the sensor and the ASIC. Particular attention is given to the transimpedance first stage of the oscillator. In this paper and after a brief description of the entire oscillator, experimental results are given to demonstrate the capability of the designed ASIC.
This paper is dedicated to the fabrication and technological aspect of a silicon microresonator sensor. The entire project includes the fabrication processes, the system modelling/simulation, and the electronic interface. The mechanical model of such resonator is presented including description of frequency stability and Hysterises behaviour of the electrostatically driven resonator. Numeric model and FEM simulations are used to simulate the system dynamic
behaviour. The complete fabrication process is based on standard microelectronics technology with specific MEMS technological steps. The key steps are described: micromachining on SOI by Deep Reactive Ion Etching (DRIE), specific release processes to prevent sticking (resist and HF-vapour release process) and collective vacuum encapsulation by Silicon Direct Bonding (SDB). The complete process has been validated and prototypes have been fabricated. The ASIC was designed to interface the sensor and to control the vibration amplitude. This electronic was simulated and designed to work up to 200°C and implemented in a standard 0.6μ CMOS technology. Characterizations of sensor prototypes are done both mechanically and electrostatically. These measurements showed good agreements with theory and FEM simulations.
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